varpulis_parser/

pest_parser.rs

//! Pest-based parser for VPL
//!
//! This module provides parsing using the pest PEG parser generator.
//!
//! The `Rule` enum and its variants are auto-generated by `pest_derive`
//! from the grammar file and cannot carry doc comments.

use pest::Parser;
use pest_derive::Parser;
use varpulis_core::ast::*;
use varpulis_core::span::{Span, Spanned};
use varpulis_core::types::Type;

use crate::error::{ParseError, ParseResult};
use crate::helpers::{parse_duration, parse_timestamp};
use crate::indent::preprocess_indentation;

/// Extension trait for safer iterator extraction
trait IteratorExt<'a> {
    /// Get the next element or return an error with the expected rule description
    fn expect_next(&mut self, expected: &str) -> ParseResult<pest::iterators::Pair<'a, Rule>>;
}

impl<'a> IteratorExt<'a> for pest::iterators::Pairs<'a, Rule> {
    fn expect_next(&mut self, expected: &str) -> ParseResult<pest::iterators::Pair<'a, Rule>> {
        self.next().ok_or_else(|| ParseError::Located {
            line: 0,
            column: 0,
            position: 0,
            message: format!("Expected {expected}"),
            hint: None,
        })
    }
}

/// Pest-based VPL parser.
///
/// The grammar rules are auto-generated from `varpulis.pest` by the
/// `pest_derive` macro. Use [`parse`] instead of calling this directly.
#[derive(Debug, Parser)]
#[grammar = "varpulis.pest"]
pub struct VarpulisParser;

/// Maximum wall-clock time the parser is allowed to run before being aborted.
///
/// PEG recursive-descent parsers can exhibit exponential backtracking on
/// adversarial inputs even after bracket-depth and unmatched-bracket pre-scans.
/// A hard timeout protects callers (CLI, LSP, fuzz targets) from hangs.
/// 10 seconds is orders of magnitude more than any real VPL program needs
/// (typical parse time is <5 ms for a 1000-line file).
const PARSE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);

/// Parse a VPL source string into a Program AST.
///
/// On native targets: runs pest parsing in a dedicated thread with a 16 MB
/// stack and a wall-clock timeout to guard against stack overflow and
/// exponential backtracking on adversarial inputs.
///
/// On WASM: calls the parser directly (no threads, no timeout).
#[cfg(not(target_arch = "wasm32"))]
pub fn parse(source: &str) -> ParseResult<Program> {
    let source = source.to_string();
    let handle = std::thread::Builder::new()
        .stack_size(16 * 1024 * 1024)
        .spawn(move || parse_inner(&source))
        .map_err(|e| ParseError::InvalidToken {
            position: 0,
            message: format!("Failed to spawn parser thread: {e}"),
        })?;

    // Park the current thread until the parser finishes or the timeout fires.
    let deadline = std::time::Instant::now() + PARSE_TIMEOUT;
    loop {
        if handle.is_finished() {
            return handle.join().unwrap_or_else(|_| {
                Err(ParseError::InvalidToken {
                    position: 0,
                    message: "Parser stack overflow on deeply nested input".to_string(),
                })
            });
        }
        let remaining = deadline.saturating_duration_since(std::time::Instant::now());
        if remaining.is_zero() {
            return Err(ParseError::InvalidToken {
                position: 0,
                message: format!(
                    "Parser timed out after {}s on pathological input",
                    PARSE_TIMEOUT.as_secs()
                ),
            });
        }
        std::thread::sleep(std::time::Duration::from_millis(5).min(remaining));
    }
}

/// WASM fallback: parse directly without thread spawning or timeout.
#[cfg(target_arch = "wasm32")]
pub fn parse(source: &str) -> ParseResult<Program> {
    parse_inner(source)
}

/// Maximum bracket nesting depth allowed before pest parsing.
///
/// PEG recursive descent can cause exponential backtracking when unmatched
/// brackets create ambiguity between array_literal, index_access, and
/// slice_access rules.  Measured scaling is O(2.35^depth): depth 20 takes
/// 1200s+, depth 16 takes 39s, depth 10 takes under 0.3s.  10 levels is
/// generous for real VPL programs (typical nesting is 3-6 levels, extreme
/// real-world is about 8) while keeping worst-case parse time under 1 second.
const MAX_NESTING_DEPTH: usize = 10;

/// Maximum number of unmatched open brackets allowed.
///
/// Even when nesting depth stays within limits, many unmatched open brackets
/// at different positions (e.g. `a[b[c[d[` with no closing `]`) cause
/// combinatorial explosion as pest tries each `[` as a potential array_literal,
/// index_access, or slice_access start. 6 is generous for real VPL programs
/// (unmatched brackets are always parse errors anyway).
const MAX_UNMATCHED_OPEN_BRACKETS: usize = 6;

/// O(n) pre-scan that rejects inputs with bracket nesting deeper than
/// `MAX_NESTING_DEPTH` or too many unmatched open brackets. Respects string
/// literals and comments so that brackets inside `"..."`, `# ...`, or
/// `/* ... */` are ignored.
fn check_nesting_depth(source: &str) -> ParseResult<()> {
    let mut depth: usize = 0;
    let mut max_depth: usize = 0;
    let mut max_depth_pos: usize = 0;
    let bytes = source.as_bytes();
    let len = bytes.len();
    let mut i = 0;

    // Per-bracket-type counters for unmatched detection
    let mut paren_open: usize = 0;
    let mut paren_close: usize = 0;
    let mut square_open: usize = 0;
    let mut square_close: usize = 0;
    let mut curly_open: usize = 0;
    let mut curly_close: usize = 0;

    while i < len {
        let b = bytes[i];

        // Skip double-quoted strings
        if b == b'"' {
            i += 1;
            while i < len {
                if bytes[i] == b'\\' {
                    i += 2; // skip escaped char
                    continue;
                }
                if bytes[i] == b'"' {
                    i += 1;
                    break;
                }
                i += 1;
            }
            continue;
        }

        // Skip VPL line comments (# to end of line)
        if b == b'#' {
            i += 1;
            while i < len && bytes[i] != b'\n' {
                i += 1;
            }
            continue;
        }

        // Skip block comments
        if b == b'/' && i + 1 < len && bytes[i + 1] == b'*' {
            i += 2;
            while i + 1 < len {
                if bytes[i] == b'*' && bytes[i + 1] == b'/' {
                    i += 2;
                    break;
                }
                i += 1;
            }
            continue;
        }

        // Track bracket depth
        match b {
            b'(' => {
                depth += 1;
                paren_open += 1;
            }
            b'[' => {
                depth += 1;
                square_open += 1;
            }
            b'{' => {
                depth += 1;
                curly_open += 1;
            }
            b')' => {
                depth = depth.saturating_sub(1);
                paren_close += 1;
            }
            b']' => {
                depth = depth.saturating_sub(1);
                square_close += 1;
            }
            b'}' => {
                depth = depth.saturating_sub(1);
                curly_close += 1;
            }
            _ => {}
        }

        if depth > max_depth {
            max_depth = depth;
            max_depth_pos = i;
        }

        if max_depth > MAX_NESTING_DEPTH {
            return Err(ParseError::InvalidToken {
                position: max_depth_pos,
                message: format!("Nesting depth exceeds maximum of {MAX_NESTING_DEPTH} levels"),
            });
        }

        i += 1;
    }

    // Reject inputs with too many unmatched open brackets.
    // Unmatched brackets are always parse errors, but they cause exponential
    // backtracking in pest before it can report the error.
    let unmatched = paren_open.saturating_sub(paren_close)
        + square_open.saturating_sub(square_close)
        + curly_open.saturating_sub(curly_close);
    if unmatched > MAX_UNMATCHED_OPEN_BRACKETS {
        return Err(ParseError::InvalidToken {
            position: max_depth_pos,
            message: format!(
                "Too many unmatched open brackets ({unmatched}); maximum is {MAX_UNMATCHED_OPEN_BRACKETS}"
            ),
        });
    }

    Ok(())
}

fn parse_inner(source: &str) -> ParseResult<Program> {
    // Expand compile-time declaration loops (top-level for with {var} interpolation)
    let expanded =
        crate::expand::expand_declaration_loops(source).map_err(|e| ParseError::InvalidToken {
            position: 0,
            message: e,
        })?;
    // Preprocess to add INDENT/DEDENT markers
    let preprocessed = preprocess_indentation(&expanded);

    // Reject deeply nested input before pest parsing to prevent stack overflow
    check_nesting_depth(&preprocessed)?;

    let pairs = VarpulisParser::parse(Rule::program, &preprocessed).map_err(convert_pest_error)?;

    let mut statements = Vec::new();

    for pair in pairs {
        if pair.as_rule() == Rule::program {
            for inner in pair.into_inner() {
                if inner.as_rule() == Rule::statement {
                    statements.push(parse_statement(inner)?);
                }
            }
        }
    }

    Ok(crate::optimize::fold_program(Program { statements }))
}

fn convert_pest_error(e: pest::error::Error<Rule>) -> ParseError {
    let position = match e.location {
        pest::error::InputLocation::Pos(p) => p,
        pest::error::InputLocation::Span((s, _)) => s,
    };

    // Extract line/column from pest error
    let (line, column) = match e.line_col {
        pest::error::LineColLocation::Pos((l, c)) => (l, c),
        pest::error::LineColLocation::Span((l, c), _) => (l, c),
    };

    // Create a human-readable message based on what was expected
    let (message, hint) = match &e.variant {
        pest::error::ErrorVariant::ParsingError {
            positives,
            negatives: _,
        } => {
            if positives.is_empty() {
                ("Unexpected token".to_string(), None)
            } else if is_stream_op_error(positives) {
                // All positives are stream operations — produce a concise error
                (
                    "unknown stream operation".to_string(),
                    Some(
                        "valid operations: .where(), .select(), .emit(), .window(), .aggregate(), \
                         .partition_by(), .within(), .having(), .to(), .context(), .log(), .print(), \
                         .enrich(), .forecast(), .trend_aggregate(), .watermark(), .tap()"
                            .to_string(),
                    ),
                )
            } else {
                let expected: Vec<String> = positives.iter().map(format_rule_name).collect();
                if expected.len() == 1 {
                    (format!("Expected {}", expected[0]), None)
                } else {
                    (format!("Expected one of: {}", expected.join(", ")), None)
                }
            }
        }
        pest::error::ErrorVariant::CustomError { message } => (message.clone(), None),
    };

    ParseError::Located {
        line,
        column,
        position,
        message,
        hint,
    }
}

/// Convert pest Rule names to human-readable format
fn format_rule_name(rule: &Rule) -> String {
    match rule {
        Rule::identifier => "identifier".to_string(),
        Rule::integer => "number".to_string(),
        Rule::float => "number".to_string(),
        Rule::string => "string".to_string(),
        Rule::primitive_type => "type (int, float, bool, str, timestamp, duration)".to_string(),
        Rule::type_expr => "type".to_string(),
        Rule::expr => "expression".to_string(),
        Rule::statement => "statement".to_string(),
        Rule::context_decl => "context declaration".to_string(),
        Rule::stream_decl => "stream declaration".to_string(),
        Rule::pattern_decl => "pattern declaration".to_string(),
        Rule::event_decl => "event declaration".to_string(),
        Rule::fn_decl => "function declaration".to_string(),
        Rule::INDENT => "indented block".to_string(),
        Rule::DEDENT => "end of block".to_string(),
        Rule::field => "field declaration (name: type)".to_string(),
        Rule::comparison_op => "comparison operator (==, !=, <, >, <=, >=)".to_string(),
        Rule::additive_op => "operator (+, -)".to_string(),
        Rule::multiplicative_op => "operator (*, /, %)".to_string(),
        Rule::postfix_suffix => "method call or member access".to_string(),
        Rule::sase_pattern_expr => "SASE pattern expression".to_string(),
        Rule::sase_seq_expr => "SEQ expression".to_string(),
        Rule::kleene_op => "Kleene operator (+, *, ?)".to_string(),
        _ => format!("{rule:?}").to_lowercase().replace('_', " "),
    }
}

/// Returns true when all positives look like stream operation rules.
/// This is used to produce a concise "unknown stream operation" error
/// instead of listing 30+ individual operation names.
fn is_stream_op_error(positives: &[Rule]) -> bool {
    const STREAM_OP_RULES: &[Rule] = &[
        Rule::context_op,
        Rule::where_op,
        Rule::select_op,
        Rule::window_op,
        Rule::aggregate_op,
        Rule::having_op,
        Rule::partition_by_op,
        Rule::order_by_op,
        Rule::limit_op,
        Rule::distinct_op,
        Rule::map_op,
        Rule::filter_op,
        Rule::tap_op,
        Rule::print_op,
        Rule::log_op,
        Rule::emit_op,
        Rule::to_op,
        Rule::pattern_op,
        Rule::concurrent_op,
        Rule::process_op,
        Rule::on_error_op,
        Rule::collect_op,
        Rule::on_op,
        Rule::within_op,
        Rule::not_op,
        Rule::fork_op,
        Rule::any_op,
        Rule::all_op,
        Rule::first_op,
        Rule::watermark_op,
        Rule::allowed_lateness_op,
        Rule::trend_aggregate_op,
        Rule::score_op,
        Rule::forecast_op,
        Rule::enrich_op,
        Rule::alert_op,
    ];
    positives.len() >= 10 && positives.iter().all(|r| STREAM_OP_RULES.contains(r))
}

fn parse_statement(pair: pest::iterators::Pair<Rule>) -> ParseResult<Spanned<Stmt>> {
    let span = Span::new(pair.as_span().start(), pair.as_span().end());
    let inner = pair.into_inner().expect_next("statement body")?;

    let stmt = match inner.as_rule() {
        Rule::context_decl => parse_context_decl(inner)?,
        Rule::connector_decl => parse_connector_decl(inner)?,
        Rule::stream_decl => parse_stream_decl(inner)?,
        Rule::pattern_decl => parse_pattern_decl(inner)?,
        Rule::event_decl => parse_event_decl(inner)?,
        Rule::type_decl => parse_type_decl(inner)?,
        Rule::var_decl => parse_var_decl(inner)?,
        Rule::const_decl => parse_const_decl(inner)?,
        Rule::fn_decl => parse_fn_decl(inner)?,
        Rule::config_block => parse_config_block(inner)?,
        Rule::import_stmt => parse_import_stmt(inner)?,
        Rule::if_stmt => parse_if_stmt(inner)?,
        Rule::for_stmt => parse_for_stmt(inner)?,
        Rule::while_stmt => parse_while_stmt(inner)?,
        Rule::return_stmt => parse_return_stmt(inner)?,
        Rule::break_stmt => Stmt::Break,
        Rule::continue_stmt => Stmt::Continue,
        Rule::emit_stmt => parse_emit_stmt(inner)?,
        Rule::assignment_stmt => {
            let mut inner = inner.into_inner();
            let name = inner.expect_next("variable name")?.as_str().to_string();
            let value = parse_expr(inner.expect_next("assignment value")?)?;
            Stmt::Assignment { name, value }
        }
        Rule::expr_stmt => Stmt::Expr(parse_expr(inner.into_inner().expect_next("expression")?)?),
        _ => {
            return Err(ParseError::UnexpectedToken {
                position: span.start,
                expected: "statement".to_string(),
                found: format!("{:?}", inner.as_rule()),
            })
        }
    };

    Ok(Spanned::new(stmt, span))
}

// ============================================================================
// Context Declaration Parsing
// ============================================================================

fn parse_context_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("context name")?.as_str().to_string();
    let mut cores = None;

    for p in inner {
        if p.as_rule() == Rule::context_params {
            for param in p.into_inner() {
                if param.as_rule() == Rule::context_param {
                    // Parse cores: [0, 1, 2]
                    let core_ids: Vec<usize> = param
                        .into_inner()
                        .filter(|p| p.as_rule() == Rule::integer)
                        .map(|p| p.as_str().parse::<usize>().unwrap_or(0))
                        .collect();
                    cores = Some(core_ids);
                }
            }
        }
    }

    Ok(Stmt::ContextDecl { name, cores })
}

// ============================================================================
// Connector Parsing
// ============================================================================

fn parse_connector_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("connector name")?.as_str().to_string();
    let connector_type = inner.expect_next("connector type")?.as_str().to_string();
    let mut params = Vec::new();

    for p in inner {
        if p.as_rule() == Rule::connector_params {
            params = parse_connector_params(p)?;
        }
    }

    Ok(Stmt::ConnectorDecl {
        name,
        connector_type,
        params,
    })
}

fn parse_connector_params(pair: pest::iterators::Pair<Rule>) -> ParseResult<Vec<ConnectorParam>> {
    let mut params = Vec::new();
    for p in pair.into_inner() {
        if p.as_rule() == Rule::connector_param {
            let mut inner = p.into_inner();
            let name = inner.expect_next("param name")?.as_str().to_string();
            let value_pair = inner.expect_next("param value")?;
            let value = parse_config_value(value_pair)?;
            params.push(ConnectorParam { name, value });
        }
    }
    Ok(params)
}

fn parse_stream_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("stream name")?.as_str().to_string();

    let mut type_annotation = None;
    let mut source = StreamSource::Ident(String::new());
    let mut ops = Vec::new();
    let mut op_spans = Vec::new();

    for p in inner {
        match p.as_rule() {
            Rule::type_annotation => {
                type_annotation = Some(parse_type(p.into_inner().expect_next("type")?)?);
            }
            Rule::stream_expr => {
                let (s, o, spans) = parse_stream_expr(p)?;
                source = s;
                ops = o;
                op_spans = spans;
            }
            _ => {}
        }
    }

    Ok(Stmt::StreamDecl {
        name,
        type_annotation,
        source,
        ops,
        op_spans,
    })
}

fn parse_stream_expr(
    pair: pest::iterators::Pair<Rule>,
) -> ParseResult<(StreamSource, Vec<StreamOp>, Vec<varpulis_core::span::Span>)> {
    let mut inner = pair.into_inner();
    let source = parse_stream_source(inner.expect_next("stream source")?)?;
    let mut ops = Vec::new();
    let mut op_spans = Vec::new();

    for p in inner {
        if p.as_rule() == Rule::stream_op {
            let pest_span = p.as_span();
            let span = varpulis_core::span::Span::new(pest_span.start(), pest_span.end());
            ops.push(parse_stream_op(p)?);
            op_spans.push(span);
        }
    }

    Ok((source, ops, op_spans))
}

// ============================================================================
// SASE+ Pattern Declaration Parsing
// ============================================================================

fn parse_pattern_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("pattern name")?.as_str().to_string();

    let mut expr = SasePatternExpr::Event(String::new());
    let mut within = None;
    let mut partition_by = None;

    for p in inner {
        match p.as_rule() {
            Rule::sase_pattern_expr => {
                expr = parse_sase_pattern_expr(p)?;
            }
            Rule::pattern_within_clause => {
                let dur_pair = p.into_inner().expect_next("within duration")?;
                within = Some(Expr::Duration(
                    parse_duration(dur_pair.as_str()).map_err(ParseError::InvalidDuration)?,
                ));
            }
            Rule::pattern_partition_clause => {
                let key = p
                    .into_inner()
                    .expect_next("partition key")?
                    .as_str()
                    .to_string();
                partition_by = Some(Expr::Ident(key));
            }
            _ => {}
        }
    }

    Ok(Stmt::PatternDecl {
        name,
        expr,
        within,
        partition_by,
    })
}

fn parse_sase_pattern_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternExpr> {
    let inner = pair.into_inner().expect_next("SASE pattern expression")?;
    parse_sase_or_expr(inner)
}

fn parse_sase_or_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternExpr> {
    let mut inner = pair.into_inner();
    let mut left = parse_sase_and_expr(inner.expect_next("OR expression operand")?)?;

    for right_pair in inner {
        let right = parse_sase_and_expr(right_pair)?;
        left = SasePatternExpr::Or(Box::new(left), Box::new(right));
    }

    Ok(left)
}

fn parse_sase_and_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternExpr> {
    let mut inner = pair.into_inner();
    let mut left = parse_sase_not_expr(inner.expect_next("AND expression operand")?)?;

    for right_pair in inner {
        let right = parse_sase_not_expr(right_pair)?;
        left = SasePatternExpr::And(Box::new(left), Box::new(right));
    }

    Ok(left)
}

fn parse_sase_not_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternExpr> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("NOT or primary expression")?;

    if first.as_rule() == Rule::sase_not_keyword {
        let expr = parse_sase_primary_expr(inner.expect_next("expression after NOT")?)?;
        Ok(SasePatternExpr::Not(Box::new(expr)))
    } else {
        parse_sase_primary_expr(first)
    }
}

fn parse_sase_primary_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternExpr> {
    let inner = pair.into_inner().expect_next("SASE primary expression")?;

    match inner.as_rule() {
        Rule::sase_seq_expr => parse_sase_seq_expr(inner),
        Rule::sase_grouped_expr => {
            let nested = inner.into_inner().expect_next("grouped expression")?;
            let expr = parse_sase_pattern_expr(nested)?;
            Ok(SasePatternExpr::Group(Box::new(expr)))
        }
        Rule::sase_event_ref => parse_sase_event_ref(inner),
        _ => Ok(SasePatternExpr::Event(inner.as_str().to_string())),
    }
}

fn parse_sase_seq_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternExpr> {
    let mut items = Vec::new();

    for p in pair.into_inner() {
        if p.as_rule() == Rule::sase_seq_items {
            for item in p.into_inner() {
                if item.as_rule() == Rule::sase_seq_item {
                    items.push(parse_sase_seq_item(item)?);
                }
            }
        }
    }

    Ok(SasePatternExpr::Seq(items))
}

fn parse_sase_seq_item(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternItem> {
    let inner = pair.into_inner().expect_next("sequence item")?;

    match inner.as_rule() {
        Rule::sase_negated_item => parse_sase_item_inner(inner, true),
        Rule::sase_positive_item => parse_sase_item_inner(inner, false),
        _ => parse_sase_item_inner(inner, false),
    }
}

fn parse_sase_item_inner(
    pair: pest::iterators::Pair<Rule>,
    _negated: bool,
) -> ParseResult<SasePatternItem> {
    let mut inner = pair.into_inner();
    let event_type = inner.expect_next("event type")?.as_str().to_string();

    let mut kleene = None;
    let mut filter = None;
    let mut alias = None;

    for p in inner {
        match p.as_rule() {
            Rule::kleene_op => {
                kleene = Some(match p.as_str() {
                    "+" => KleeneOp::Plus,
                    "*" => KleeneOp::Star,
                    "?" => KleeneOp::Optional,
                    _ => KleeneOp::Plus,
                });
            }
            Rule::sase_where_clause => {
                filter = Some(parse_expr(
                    p.into_inner().expect_next("filter expression")?,
                )?);
            }
            Rule::sase_alias_clause => {
                alias = Some(p.into_inner().expect_next("alias")?.as_str().to_string());
            }
            _ => {}
        }
    }

    // For negated items, we prefix with "!" to indicate negation
    // The runtime will interpret this
    let event_type = if _negated {
        format!("!{event_type}")
    } else {
        event_type
    };

    Ok(SasePatternItem {
        event_type,
        alias,
        kleene,
        filter,
    })
}

fn parse_sase_event_ref(pair: pest::iterators::Pair<Rule>) -> ParseResult<SasePatternExpr> {
    // Single event reference with optional kleene, where, alias
    let item = parse_sase_item_inner(pair, false)?;

    // If it's a simple event with no modifiers, return Event variant
    if item.alias.is_none() && item.kleene.is_none() && item.filter.is_none() {
        Ok(SasePatternExpr::Event(item.event_type))
    } else {
        // Otherwise wrap in a single-item Seq
        Ok(SasePatternExpr::Seq(vec![item]))
    }
}

fn parse_stream_source(pair: pest::iterators::Pair<Rule>) -> ParseResult<StreamSource> {
    let inner = pair.into_inner().expect_next("stream source type")?;

    match inner.as_rule() {
        Rule::from_connector_source => {
            let mut inner_iter = inner.into_inner();
            let event_type = inner_iter.expect_next("event type")?.as_str().to_string();
            let connector_name = inner_iter
                .expect_next("connector name")?
                .as_str()
                .to_string();
            let mut params = Vec::new();
            for p in inner_iter {
                if p.as_rule() == Rule::connector_params {
                    params = parse_connector_params(p)?;
                }
            }
            Ok(StreamSource::FromConnector {
                event_type,
                connector_name,
                params,
            })
        }
        Rule::merge_source => {
            let mut streams = Vec::new();
            for p in inner.into_inner() {
                if p.as_rule() == Rule::inline_stream_list {
                    for is in p.into_inner() {
                        streams.push(parse_inline_stream(is)?);
                    }
                }
            }
            Ok(StreamSource::Merge(streams))
        }
        Rule::join_source
        | Rule::left_join_source
        | Rule::right_join_source
        | Rule::full_join_source => {
            let join_type = match inner.as_rule() {
                Rule::left_join_source => varpulis_core::ast::JoinType::Left,
                Rule::right_join_source => varpulis_core::ast::JoinType::Right,
                Rule::full_join_source => varpulis_core::ast::JoinType::Full,
                _ => varpulis_core::ast::JoinType::Inner,
            };
            let mut clauses = Vec::new();
            for p in inner.into_inner() {
                if p.as_rule() == Rule::join_clause_list {
                    for jc in p.into_inner() {
                        clauses.push(parse_join_clause(jc, join_type)?);
                    }
                }
            }
            Ok(StreamSource::Join(clauses))
        }
        Rule::sequence_source => {
            let decl =
                parse_sequence_decl(inner.into_inner().expect_next("sequence declaration")?)?;
            Ok(StreamSource::Sequence(decl))
        }
        Rule::timer_source => {
            let timer_args = inner.into_inner().expect_next("timer arguments")?;
            let decl = parse_timer_decl(timer_args)?;
            Ok(StreamSource::Timer(decl))
        }
        Rule::all_source => {
            let mut inner_iter = inner.into_inner();
            let name = inner_iter.expect_next("event name")?.as_str().to_string();
            let alias = inner_iter.next().map(|p| p.as_str().to_string());
            Ok(StreamSource::AllWithAlias { name, alias })
        }
        Rule::filtered_source => {
            let mut inner_iter = inner.into_inner();
            let name = inner_iter.expect_next("event type")?.as_str().to_string();
            let filter_pair = inner_iter.expect_next("filter expression")?;
            let filter = parse_filter_expr(filter_pair)?;
            let alias = inner_iter.next().map(|p| p.as_str().to_string());
            Ok(StreamSource::IdentWithFilterAndAlias {
                name,
                filter,
                alias,
            })
        }
        Rule::aliased_source => {
            let mut inner_iter = inner.into_inner();
            let name = inner_iter.expect_next("event name")?.as_str().to_string();
            let alias = inner_iter.expect_next("alias")?.as_str().to_string();
            Ok(StreamSource::IdentWithAlias { name, alias })
        }
        Rule::identifier => Ok(StreamSource::Ident(inner.as_str().to_string())),
        _ => Err(ParseError::UnexpectedToken {
            position: 0,
            expected: "stream source".to_string(),
            found: format!("{:?}", inner.as_rule()),
        }),
    }
}

fn parse_inline_stream(pair: pest::iterators::Pair<Rule>) -> ParseResult<InlineStreamDecl> {
    let mut inner = pair.into_inner();

    // Check if it's a simple identifier or full declaration
    let first = inner.expect_next("stream identifier")?;
    if first.as_rule() == Rule::identifier && inner.clone().next().is_none() {
        let name = first.as_str().to_string();
        return Ok(InlineStreamDecl {
            name: name.clone(),
            source: name,
            filter: None,
        });
    }

    let name = first.as_str().to_string();
    let source = inner.expect_next("stream source")?.as_str().to_string();
    let filter = inner.next().map(|p| parse_expr(p)).transpose()?;

    Ok(InlineStreamDecl {
        name,
        source,
        filter,
    })
}

fn parse_join_clause(
    pair: pest::iterators::Pair<Rule>,
    join_type: varpulis_core::ast::JoinType,
) -> ParseResult<JoinClause> {
    let mut inner = pair.into_inner();

    let first = inner.expect_next("join clause identifier")?;
    if first.as_rule() == Rule::identifier && inner.clone().next().is_none() {
        let name = first.as_str().to_string();
        return Ok(JoinClause {
            name: name.clone(),
            source: name,
            on: None,
            join_type,
        });
    }

    let name = first.as_str().to_string();
    let source = inner.expect_next("join source")?.as_str().to_string();
    let on = inner.next().map(|p| parse_expr(p)).transpose()?;

    Ok(JoinClause {
        name,
        source,
        on,
        join_type,
    })
}

fn parse_sequence_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<SequenceDecl> {
    let mut steps = Vec::new();

    for p in pair.into_inner() {
        if p.as_rule() == Rule::sequence_step {
            steps.push(parse_sequence_step(p)?);
        }
    }

    Ok(SequenceDecl {
        match_all: false,
        timeout: None,
        steps,
    })
}

fn parse_sequence_step(pair: pest::iterators::Pair<Rule>) -> ParseResult<SequenceStepDecl> {
    let mut inner = pair.into_inner();
    let alias = inner.expect_next("step alias")?.as_str().to_string();
    let event_type = inner.expect_next("event type")?.as_str().to_string();

    let mut filter = None;
    let mut timeout = None;

    for p in inner {
        match p.as_rule() {
            Rule::or_expr => filter = Some(parse_expr(p)?),
            Rule::within_suffix => {
                let expr = p.into_inner().expect_next("within duration")?;
                timeout = Some(Box::new(parse_expr(expr)?));
            }
            _ => {}
        }
    }

    Ok(SequenceStepDecl {
        alias,
        event_type,
        filter,
        timeout,
    })
}

fn parse_timer_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<TimerDecl> {
    let mut inner = pair.into_inner();

    // First argument is the interval (duration expression)
    let interval = parse_expr(inner.expect_next("timer interval")?)?;

    // Optional second argument is initial_delay (named argument)
    let mut initial_delay = None;
    for p in inner {
        if p.as_rule() == Rule::named_arg {
            let arg = parse_named_arg(p)?;
            if arg.name == "initial_delay" {
                initial_delay = Some(Box::new(arg.value));
            }
        }
    }

    Ok(TimerDecl {
        interval,
        initial_delay,
    })
}

fn parse_stream_op(pair: pest::iterators::Pair<Rule>) -> ParseResult<StreamOp> {
    let inner = pair.into_inner().expect_next("stream operation")?;

    match inner.as_rule() {
        Rule::dot_op => {
            let op_inner = inner.into_inner().expect_next("dot operation")?;
            parse_dot_op(op_inner)
        }
        Rule::followed_by_op => parse_followed_by_op(inner),
        _ => Err(ParseError::UnexpectedToken {
            position: 0,
            expected: "stream operation".to_string(),
            found: format!("{:?}", inner.as_rule()),
        }),
    }
}

fn parse_dot_op(pair: pest::iterators::Pair<Rule>) -> ParseResult<StreamOp> {
    match pair.as_rule() {
        Rule::context_op => {
            let name = pair
                .into_inner()
                .expect_next("context name")?
                .as_str()
                .to_string();
            Ok(StreamOp::Context(name))
        }
        Rule::where_op => {
            let expr = parse_expr(pair.into_inner().expect_next("where expression")?)?;
            Ok(StreamOp::Where(expr))
        }
        Rule::select_op => {
            let mut items = Vec::new();
            for p in pair.into_inner() {
                if p.as_rule() == Rule::select_list {
                    for si in p.into_inner() {
                        items.push(parse_select_item(si)?);
                    }
                }
            }
            Ok(StreamOp::Select(items))
        }
        Rule::window_op => {
            let args = parse_window_args(pair.into_inner().expect_next("window arguments")?)?;
            Ok(StreamOp::Window(args))
        }
        Rule::aggregate_op => {
            let mut items = Vec::new();
            for p in pair.into_inner() {
                if p.as_rule() == Rule::agg_list {
                    for ai in p.into_inner() {
                        items.push(parse_agg_item(ai)?);
                    }
                }
            }
            Ok(StreamOp::Aggregate(items))
        }
        Rule::having_op => {
            let expr = parse_expr(pair.into_inner().expect_next("having expression")?)?;
            Ok(StreamOp::Having(expr))
        }
        Rule::map_op => {
            let expr = parse_expr(pair.into_inner().expect_next("map expression")?)?;
            Ok(StreamOp::Map(expr))
        }
        Rule::filter_op => {
            let expr = parse_expr(pair.into_inner().expect_next("filter expression")?)?;
            Ok(StreamOp::Filter(expr))
        }
        Rule::within_op => {
            let expr = parse_expr(pair.into_inner().expect_next("within duration")?)?;
            Ok(StreamOp::Within(expr))
        }
        Rule::emit_op => {
            let mut output_type = None;
            let mut fields = Vec::new();
            let mut target_context = None;
            for p in pair.into_inner() {
                match p.as_rule() {
                    Rule::emit_type_cast => {
                        output_type = Some(
                            p.into_inner()
                                .expect_next("type name")?
                                .as_str()
                                .to_string(),
                        );
                    }
                    Rule::named_arg_list => {
                        for arg in p.into_inner() {
                            let parsed = parse_named_arg(arg)?;
                            // Extract `context: ctx_name` as target_context
                            if parsed.name == "context" {
                                if let Expr::Ident(ctx_name) = &parsed.value {
                                    target_context = Some(ctx_name.clone());
                                    continue;
                                }
                            }
                            fields.push(parsed);
                        }
                    }
                    _ => {}
                }
            }
            Ok(StreamOp::Emit {
                output_type,
                fields,
                target_context,
            })
        }
        Rule::print_op => {
            let exprs = pair
                .into_inner()
                .filter(|p| p.as_rule() == Rule::expr_list)
                .flat_map(|p| p.into_inner())
                .map(parse_expr)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(StreamOp::Print(exprs))
        }
        Rule::collect_op => Ok(StreamOp::Collect),
        Rule::pattern_op => {
            let def_pair = pair.into_inner().expect_next("pattern definition")?;
            let mut inner = def_pair.into_inner();
            let name = inner.expect_next("pattern name")?.as_str().to_string();
            let body_pair = inner.expect_next("pattern body")?;

            // pattern_body can be lambda_expr or pattern_or_expr
            let body_inner = body_pair.into_inner().expect_next("pattern expression")?;
            let matcher = match body_inner.as_rule() {
                Rule::lambda_expr => parse_lambda_expr(body_inner)?,
                Rule::pattern_or_expr => parse_pattern_expr_as_expr(body_inner)?,
                _ => parse_expr_inner(body_inner)?,
            };
            Ok(StreamOp::Pattern(PatternDef { name, matcher }))
        }
        Rule::partition_by_op => {
            let expr = parse_expr(pair.into_inner().expect_next("partition expression")?)?;
            Ok(StreamOp::PartitionBy(expr))
        }
        Rule::order_by_op => {
            let mut items = Vec::new();
            for p in pair.into_inner() {
                if p.as_rule() == Rule::order_list {
                    for oi in p.into_inner() {
                        items.push(parse_order_item(oi)?);
                    }
                }
            }
            Ok(StreamOp::OrderBy(items))
        }
        Rule::limit_op => {
            let expr = parse_expr(pair.into_inner().expect_next("limit expression")?)?;
            Ok(StreamOp::Limit(expr))
        }
        Rule::distinct_op => {
            let expr = pair.into_inner().next().map(parse_expr).transpose()?;
            Ok(StreamOp::Distinct(expr))
        }
        Rule::tap_op => {
            let args = pair
                .into_inner()
                .filter(|p| p.as_rule() == Rule::named_arg_list)
                .flat_map(|p| p.into_inner())
                .map(parse_named_arg)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(StreamOp::Tap(args))
        }
        Rule::log_op => {
            let args = pair
                .into_inner()
                .filter(|p| p.as_rule() == Rule::named_arg_list)
                .flat_map(|p| p.into_inner())
                .map(parse_named_arg)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(StreamOp::Log(args))
        }
        Rule::to_op => {
            let mut inner = pair.into_inner();
            let connector_name = inner.expect_next("connector name")?.as_str().to_string();
            let mut params = Vec::new();
            for p in inner {
                if p.as_rule() == Rule::connector_params {
                    params = parse_connector_params(p)?;
                }
            }
            Ok(StreamOp::To {
                connector_name,
                params,
            })
        }
        Rule::process_op => {
            let expr = parse_expr(pair.into_inner().expect_next("process expression")?)?;
            Ok(StreamOp::Process(expr))
        }
        Rule::on_error_op => {
            let expr = parse_expr(pair.into_inner().expect_next("on_error handler")?)?;
            Ok(StreamOp::OnError(expr))
        }
        Rule::on_op => {
            let expr = parse_expr(pair.into_inner().expect_next("on handler")?)?;
            Ok(StreamOp::On(expr))
        }
        Rule::not_op => {
            let mut inner = pair.into_inner();
            let event_type = inner.expect_next("event type")?.as_str().to_string();
            let filter = inner.next().map(parse_expr).transpose()?;
            Ok(StreamOp::Not(FollowedByClause {
                event_type,
                filter,
                alias: None,
                match_all: false,
            }))
        }
        Rule::fork_op => {
            let mut paths = Vec::new();
            for p in pair.into_inner() {
                if p.as_rule() == Rule::fork_path_list {
                    for fp in p.into_inner() {
                        paths.push(parse_fork_path(fp)?);
                    }
                }
            }
            Ok(StreamOp::Fork(paths))
        }
        Rule::any_op => {
            let count = pair
                .into_inner()
                .next()
                .map(|p| p.as_str().parse().unwrap_or(1));
            Ok(StreamOp::Any(count))
        }
        Rule::all_op => Ok(StreamOp::All),
        Rule::first_op => Ok(StreamOp::First),
        Rule::concurrent_op => {
            let args = pair
                .into_inner()
                .filter(|p| p.as_rule() == Rule::named_arg_list)
                .flat_map(|p| p.into_inner())
                .map(parse_named_arg)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(StreamOp::Concurrent(args))
        }
        Rule::watermark_op => {
            let args = pair
                .into_inner()
                .filter(|p| p.as_rule() == Rule::named_arg_list)
                .flat_map(|p| p.into_inner())
                .map(parse_named_arg)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(StreamOp::Watermark(args))
        }
        Rule::allowed_lateness_op => {
            let expr = parse_expr(pair.into_inner().expect_next("allowed lateness duration")?)?;
            Ok(StreamOp::AllowedLateness(expr))
        }
        Rule::trend_aggregate_op => {
            let mut items = Vec::new();
            for p in pair.into_inner() {
                if p.as_rule() == Rule::trend_agg_list {
                    for item_pair in p.into_inner() {
                        if item_pair.as_rule() == Rule::trend_agg_item {
                            let mut inner = item_pair.into_inner();
                            let alias = inner.expect_next("trend agg alias")?.as_str().to_string();
                            let func_pair = inner.expect_next("trend agg function")?;
                            let mut func_inner = func_pair.into_inner();
                            let func_name = func_inner
                                .expect_next("function name")?
                                .as_str()
                                .to_string();
                            let arg = func_inner.next().map(parse_expr).transpose()?;
                            items.push(TrendAggItem {
                                alias,
                                func: func_name,
                                arg,
                            });
                        }
                    }
                }
            }
            Ok(StreamOp::TrendAggregate(items))
        }
        Rule::forecast_op => {
            let mut confidence = None;
            let mut horizon = None;
            let mut warmup = None;
            let mut max_depth = None;
            let mut hawkes = None;
            let mut conformal = None;
            let mut mode = None;
            for p in pair.into_inner() {
                if p.as_rule() == Rule::forecast_params {
                    for param_pair in p.into_inner() {
                        if param_pair.as_rule() == Rule::forecast_param {
                            let mut inner = param_pair.into_inner();
                            let name = inner.expect_next("forecast param name")?.as_str();
                            let value_pair = inner.expect_next("forecast param value")?;
                            let expr = parse_expr(value_pair)?;
                            match name {
                                "confidence" => confidence = Some(expr),
                                "horizon" => horizon = Some(expr),
                                "warmup" => warmup = Some(expr),
                                "max_depth" => max_depth = Some(expr),
                                "hawkes" => hawkes = Some(expr),
                                "conformal" => conformal = Some(expr),
                                "mode" => mode = Some(expr),
                                _ => {}
                            }
                        }
                    }
                }
            }
            Ok(StreamOp::Forecast(ForecastSpec {
                confidence,
                horizon,
                warmup,
                max_depth,
                hawkes,
                conformal,
                mode,
            }))
        }
        Rule::enrich_op => {
            let mut inner = pair.into_inner();
            let connector_name = inner.expect_next("connector name")?.as_str().to_string();
            let mut key_expr = None;
            let mut fields = Vec::new();
            let mut cache_ttl = None;
            let mut timeout = None;
            let mut fallback = None;
            for p in inner {
                if p.as_rule() == Rule::enrich_params {
                    for param_pair in p.into_inner() {
                        if param_pair.as_rule() == Rule::enrich_param {
                            let param_inner =
                                param_pair.into_inner().expect_next("enrich param")?;
                            match param_inner.as_rule() {
                                Rule::enrich_key_param => {
                                    let expr_pair =
                                        param_inner.into_inner().expect_next("key expression")?;
                                    key_expr = Some(parse_expr(expr_pair)?);
                                }
                                Rule::enrich_fields_param => {
                                    for field in param_inner.into_inner() {
                                        if field.as_rule() == Rule::identifier {
                                            fields.push(field.as_str().to_string());
                                        }
                                    }
                                }
                                Rule::enrich_cache_ttl_param => {
                                    let expr_pair = param_inner
                                        .into_inner()
                                        .expect_next("cache_ttl expression")?;
                                    cache_ttl = Some(parse_expr(expr_pair)?);
                                }
                                Rule::enrich_timeout_param => {
                                    let expr_pair = param_inner
                                        .into_inner()
                                        .expect_next("timeout expression")?;
                                    timeout = Some(parse_expr(expr_pair)?);
                                }
                                Rule::enrich_fallback_param => {
                                    let literal_pair =
                                        param_inner.into_inner().expect_next("fallback literal")?;
                                    fallback = Some(parse_expr(literal_pair)?);
                                }
                                _ => {}
                            }
                        }
                    }
                }
            }
            let key = key_expr.ok_or_else(|| ParseError::Located {
                line: 0,
                column: 0,
                position: 0,
                message: ".enrich() requires a key: parameter".to_string(),
                hint: Some("add key: <expression> to .enrich()".to_string()),
            })?;
            Ok(StreamOp::Enrich(EnrichSpec {
                connector_name,
                key_expr: Box::new(key),
                fields,
                cache_ttl,
                timeout,
                fallback,
            }))
        }
        Rule::score_op => {
            let mut model_path = String::new();
            let mut inputs = Vec::new();
            let mut outputs = Vec::new();
            let mut gpu = false;
            let mut batch_size: usize = 1;
            let mut device_id: i32 = 0;
            for p in pair.into_inner() {
                if p.as_rule() == Rule::score_params {
                    for param_pair in p.into_inner() {
                        if param_pair.as_rule() == Rule::score_param {
                            let mut inner = param_pair.into_inner();
                            let name = inner.expect_next("score param name")?.as_str();
                            let value_pair = inner.expect_next("score param value")?;
                            match name {
                                "model" => {
                                    let raw = value_pair.as_str();
                                    model_path = raw.trim_matches('"').to_string();
                                }
                                "inputs" => {
                                    if value_pair.as_rule() == Rule::score_field_list {
                                        for field in value_pair.into_inner() {
                                            if field.as_rule() == Rule::identifier {
                                                inputs.push(field.as_str().to_string());
                                            }
                                        }
                                    }
                                }
                                "outputs" => {
                                    if value_pair.as_rule() == Rule::score_field_list {
                                        for field in value_pair.into_inner() {
                                            if field.as_rule() == Rule::identifier {
                                                outputs.push(field.as_str().to_string());
                                            }
                                        }
                                    }
                                }
                                "gpu" => {
                                    gpu = value_pair.as_str() == "true";
                                }
                                "batch_size" => {
                                    batch_size = value_pair.as_str().parse().unwrap_or(1);
                                }
                                "device" | "device_id" => {
                                    device_id = value_pair.as_str().parse().unwrap_or(0);
                                }
                                _ => {}
                            }
                        }
                    }
                }
            }
            Ok(StreamOp::Score(ScoreSpec {
                model_path,
                inputs,
                outputs,
                gpu,
                batch_size,
                device_id,
            }))
        }
        Rule::alert_op => {
            let args = pair
                .into_inner()
                .filter(|p| p.as_rule() == Rule::named_arg_list)
                .flat_map(|p| p.into_inner())
                .map(parse_named_arg)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(StreamOp::Alert(args))
        }
        _ => Err(ParseError::UnexpectedToken {
            position: 0,
            expected: "stream operation".to_string(),
            found: format!("{:?}", pair.as_rule()),
        }),
    }
}

fn parse_order_item(pair: pest::iterators::Pair<Rule>) -> ParseResult<OrderItem> {
    let mut inner = pair.into_inner();
    let expr = parse_expr(inner.expect_next("order expression")?)?;
    let desc = inner.next().is_some_and(|p| p.as_str() == "desc");
    Ok(OrderItem {
        expr,
        descending: desc,
    })
}

fn parse_fork_path(pair: pest::iterators::Pair<Rule>) -> ParseResult<ForkPath> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("fork path name")?.as_str().to_string();
    let mut ops = Vec::new();
    for p in inner {
        if p.as_rule() == Rule::stream_op {
            ops.push(parse_stream_op(p)?);
        }
    }
    Ok(ForkPath { name, ops })
}

fn parse_followed_by_op(pair: pest::iterators::Pair<Rule>) -> ParseResult<StreamOp> {
    let mut inner = pair.into_inner();
    let mut match_all = false;

    let first = inner.expect_next("event type or match_all")?;
    let event_type = if first.as_rule() == Rule::match_all_keyword {
        match_all = true;
        inner.expect_next("event type")?.as_str().to_string()
    } else {
        first.as_str().to_string()
    };

    let mut filter = None;
    let mut alias = None;

    for p in inner {
        match p.as_rule() {
            Rule::or_expr => filter = Some(parse_or_expr(p)?),
            Rule::filter_expr => filter = Some(parse_filter_expr(p)?),
            Rule::identifier => alias = Some(p.as_str().to_string()),
            _ => {}
        }
    }

    Ok(StreamOp::FollowedBy(FollowedByClause {
        event_type,
        filter,
        alias,
        match_all,
    }))
}

fn parse_select_item(pair: pest::iterators::Pair<Rule>) -> ParseResult<SelectItem> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("select field or alias")?;

    if let Some(second) = inner.next() {
        Ok(SelectItem::Alias(
            first.as_str().to_string(),
            parse_expr(second)?,
        ))
    } else {
        Ok(SelectItem::Field(first.as_str().to_string()))
    }
}

fn parse_window_args(pair: pest::iterators::Pair<Rule>) -> ParseResult<WindowArgs> {
    let raw = pair.as_str().trim();
    let is_session = raw.starts_with("session");

    let mut inner = pair.into_inner();

    if is_session {
        // session: <gap_expr>
        let gap_expr = parse_expr(inner.expect_next("session gap duration")?)?;
        return Ok(WindowArgs {
            duration: gap_expr.clone(),
            sliding: None,
            policy: None,
            session_gap: Some(gap_expr),
        });
    }

    let duration = parse_expr(inner.expect_next("window duration")?)?;

    let mut sliding = None;
    let mut policy = None;

    for p in inner {
        if p.as_rule() == Rule::expr {
            // Need to determine if it's sliding or policy based on context
            if sliding.is_none() {
                sliding = Some(parse_expr(p)?);
            } else {
                policy = Some(parse_expr(p)?);
            }
        }
    }

    Ok(WindowArgs {
        duration,
        sliding,
        policy,
        session_gap: None,
    })
}

fn parse_agg_item(pair: pest::iterators::Pair<Rule>) -> ParseResult<AggItem> {
    let mut inner = pair.into_inner();
    let alias = inner.expect_next("aggregate alias")?.as_str().to_string();
    let expr = parse_expr(inner.expect_next("aggregate expression")?)?;
    Ok(AggItem { alias, expr })
}

fn parse_named_arg(pair: pest::iterators::Pair<Rule>) -> ParseResult<NamedArg> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("argument name")?.as_str().to_string();
    let value = parse_expr(inner.expect_next("argument value")?)?;
    Ok(NamedArg { name, value })
}

fn parse_event_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("event name")?.as_str().to_string();

    let mut extends = None;
    let mut fields = Vec::new();

    for p in inner {
        match p.as_rule() {
            Rule::identifier => extends = Some(p.as_str().to_string()),
            Rule::field => fields.push(parse_field(p)?),
            _ => {}
        }
    }

    Ok(Stmt::EventDecl {
        name,
        extends,
        fields,
    })
}

fn parse_field(pair: pest::iterators::Pair<Rule>) -> ParseResult<Field> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("field name")?.as_str().to_string();
    let ty = parse_type(inner.expect_next("field type")?)?;
    let optional = inner.next().is_some();
    Ok(Field { name, ty, optional })
}

fn parse_type_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("type name")?.as_str().to_string();
    let next = inner.expect_next("type body")?;
    match next.as_rule() {
        Rule::field => {
            let mut fields = vec![parse_field(next)?];
            for p in inner {
                if p.as_rule() == Rule::field {
                    fields.push(parse_field(p)?);
                }
            }
            Ok(Stmt::TypeDecl {
                name,
                ty: None,
                fields,
            })
        }
        _ => Ok(Stmt::TypeDecl {
            name,
            ty: Some(parse_type(next)?),
            fields: vec![],
        }),
    }
}

fn parse_type(pair: pest::iterators::Pair<Rule>) -> ParseResult<Type> {
    let cloned = pair.clone();
    let inner = pair.into_inner().next().unwrap_or(cloned);

    match inner.as_rule() {
        Rule::primitive_type => match inner.as_str() {
            "int" => Ok(Type::Int),
            "float" => Ok(Type::Float),
            "bool" => Ok(Type::Bool),
            "str" => Ok(Type::Str),
            "timestamp" => Ok(Type::Timestamp),
            "duration" => Ok(Type::Duration),
            _ => Ok(Type::Named(inner.as_str().to_string())),
        },
        Rule::array_type => {
            let inner_type = parse_type(inner.into_inner().expect_next("array element type")?)?;
            Ok(Type::Array(Box::new(inner_type)))
        }
        Rule::map_type => {
            let mut inner_pairs = inner.into_inner();
            let key_type = parse_type(inner_pairs.expect_next("map key type")?)?;
            let val_type = parse_type(inner_pairs.expect_next("map value type")?)?;
            Ok(Type::Map(Box::new(key_type), Box::new(val_type)))
        }
        Rule::tuple_type => {
            let types: Vec<Type> = inner
                .into_inner()
                .map(parse_type)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(Type::Tuple(types))
        }
        Rule::stream_type => {
            let inner_type = parse_type(inner.into_inner().expect_next("stream element type")?)?;
            Ok(Type::Stream(Box::new(inner_type)))
        }
        Rule::optional_type => {
            let inner_type = parse_type(inner.into_inner().expect_next("optional inner type")?)?;
            Ok(Type::Optional(Box::new(inner_type)))
        }
        Rule::named_type | Rule::identifier => Ok(Type::Named(inner.as_str().to_string())),
        _ => Ok(Type::Named(inner.as_str().to_string())),
    }
}

fn parse_var_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let keyword = inner.expect_next("var_keyword")?.as_str();
    let mutable = keyword == "var";
    let name = inner.expect_next("variable name")?.as_str().to_string();

    let mut ty = None;
    let mut value = Expr::Null;

    for p in inner {
        match p.as_rule() {
            Rule::type_annotation => ty = Some(parse_type(p.into_inner().expect_next("type")?)?),
            _ => value = parse_expr(p)?,
        }
    }

    Ok(Stmt::VarDecl {
        mutable,
        name,
        ty,
        value,
    })
}

fn parse_const_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("constant name")?.as_str().to_string();

    let mut ty = None;
    let mut value = Expr::Null;

    for p in inner {
        match p.as_rule() {
            Rule::type_annotation => ty = Some(parse_type(p.into_inner().expect_next("type")?)?),
            _ => value = parse_expr(p)?,
        }
    }

    Ok(Stmt::ConstDecl { name, ty, value })
}

fn parse_fn_decl(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("function name")?.as_str().to_string();

    let mut params = Vec::new();
    let mut ret = None;
    let mut body = Vec::new();

    for p in inner {
        match p.as_rule() {
            Rule::param_list => {
                for param in p.into_inner() {
                    params.push(parse_param(param)?);
                }
            }
            Rule::type_expr => ret = Some(parse_type(p)?),
            Rule::block => body = parse_block(p)?,
            Rule::statement => body.push(parse_statement(p)?),
            _ => {}
        }
    }

    Ok(Stmt::FnDecl {
        name,
        params,
        ret,
        body,
    })
}

fn parse_block(pair: pest::iterators::Pair<Rule>) -> ParseResult<Vec<Spanned<Stmt>>> {
    let mut statements = Vec::new();
    for p in pair.into_inner() {
        if p.as_rule() == Rule::statement {
            statements.push(parse_statement(p)?);
        }
    }
    Ok(statements)
}

fn parse_param(pair: pest::iterators::Pair<Rule>) -> ParseResult<Param> {
    let mut inner = pair.into_inner();
    let name = inner.expect_next("parameter name")?.as_str().to_string();
    let ty = parse_type(inner.expect_next("parameter type")?)?;
    Ok(Param { name, ty })
}

fn parse_config_block(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("config name or item")?;

    // Check if first token is identifier (new syntax) or config_item (old syntax)
    let (name, items_start) = if first.as_rule() == Rule::identifier {
        (first.as_str().to_string(), None)
    } else {
        // Old syntax: config: with indentation - use "default" as name
        ("default".to_string(), Some(first))
    };

    let mut items = Vec::new();

    // If we have a config_item from old syntax, parse it first
    if let Some(first_item) = items_start {
        if first_item.as_rule() == Rule::config_item {
            items.push(parse_config_item(first_item)?);
        }
    }

    for p in inner {
        if p.as_rule() == Rule::config_item {
            items.push(parse_config_item(p)?);
        }
    }
    Ok(Stmt::Config { name, items })
}

fn parse_config_item(pair: pest::iterators::Pair<Rule>) -> ParseResult<ConfigItem> {
    let mut inner = pair.into_inner();
    let key = inner.expect_next("config key")?.as_str().to_string();
    let value = parse_config_value(inner.expect_next("config value")?)?;
    Ok(ConfigItem::Value(key, value))
}

fn parse_config_value(pair: pest::iterators::Pair<Rule>) -> ParseResult<ConfigValue> {
    let cloned = pair.clone();
    let inner = pair.into_inner().next().unwrap_or(cloned);

    match inner.as_rule() {
        Rule::config_concat => {
            let parts: Vec<ConfigValue> = inner
                .into_inner()
                .map(|atom| {
                    // Each atom is a config_atom containing either string or identifier
                    let inner_atom = atom.into_inner().next().expect("config_atom child");
                    match inner_atom.as_rule() {
                        Rule::string => {
                            let s = inner_atom.as_str();
                            Ok(ConfigValue::Str(s[1..s.len() - 1].to_string()))
                        }
                        Rule::identifier => Ok(ConfigValue::Ident(inner_atom.as_str().to_string())),
                        _ => Ok(ConfigValue::Ident(inner_atom.as_str().to_string())),
                    }
                })
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(ConfigValue::Concat(parts))
        }
        Rule::config_array => {
            let values: Vec<ConfigValue> = inner
                .into_inner()
                .map(parse_config_value)
                .collect::<ParseResult<Vec<_>>>()?;
            Ok(ConfigValue::Array(values))
        }
        Rule::integer => Ok(ConfigValue::Int(inner.as_str().parse().unwrap_or(0))),
        Rule::float => Ok(ConfigValue::Float(inner.as_str().parse().unwrap_or(0.0))),
        Rule::string => {
            let s = inner.as_str();
            Ok(ConfigValue::Str(s[1..s.len() - 1].to_string()))
        }
        Rule::duration => Ok(ConfigValue::Duration(
            parse_duration(inner.as_str()).map_err(ParseError::InvalidDuration)?,
        )),
        Rule::boolean => Ok(ConfigValue::Bool(inner.as_str() == "true")),
        Rule::identifier => Ok(ConfigValue::Ident(inner.as_str().to_string())),
        _ => Ok(ConfigValue::Ident(inner.as_str().to_string())),
    }
}

fn parse_import_stmt(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let path_pair = inner.expect_next("import path")?;
    let path = path_pair.as_str();
    let path = path[1..path.len() - 1].to_string();
    let alias = inner.next().map(|p| p.as_str().to_string());
    Ok(Stmt::Import { path, alias })
}

fn parse_if_stmt(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let cond = parse_expr(inner.expect_next("if condition")?)?;

    let mut then_branch = Vec::new();
    let mut elif_branches = Vec::new();
    let mut else_branch = None;

    for p in inner {
        match p.as_rule() {
            Rule::block => then_branch = parse_block(p)?,
            Rule::statement => then_branch.push(parse_statement(p)?),
            Rule::elif_clause => {
                let mut elif_inner = p.into_inner();
                let elif_cond = parse_expr(elif_inner.expect_next("elif condition")?)?;
                let mut elif_body = Vec::new();
                for ep in elif_inner {
                    match ep.as_rule() {
                        Rule::block => elif_body = parse_block(ep)?,
                        Rule::statement => elif_body.push(parse_statement(ep)?),
                        _ => {}
                    }
                }
                elif_branches.push((elif_cond, elif_body));
            }
            Rule::else_clause => {
                let mut else_body = Vec::new();
                for ep in p.into_inner() {
                    match ep.as_rule() {
                        Rule::block => else_body = parse_block(ep)?,
                        Rule::statement => else_body.push(parse_statement(ep)?),
                        _ => {}
                    }
                }
                else_branch = Some(else_body);
            }
            _ => {}
        }
    }

    Ok(Stmt::If {
        cond,
        then_branch,
        elif_branches,
        else_branch,
    })
}

fn parse_for_stmt(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let var = inner.expect_next("loop variable")?.as_str().to_string();
    let iter = parse_expr(inner.expect_next("iterable expression")?)?;
    let mut body = Vec::new();
    for p in inner {
        match p.as_rule() {
            Rule::block => body = parse_block(p)?,
            Rule::statement => body.push(parse_statement(p)?),
            _ => {}
        }
    }
    Ok(Stmt::For { var, iter, body })
}

fn parse_while_stmt(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let cond = parse_expr(inner.expect_next("while condition")?)?;
    let mut body = Vec::new();
    for p in inner {
        match p.as_rule() {
            Rule::block => body = parse_block(p)?,
            Rule::statement => body.push(parse_statement(p)?),
            _ => {}
        }
    }
    Ok(Stmt::While { cond, body })
}

fn parse_return_stmt(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let expr = pair.into_inner().next().map(parse_expr).transpose()?;
    Ok(Stmt::Return(expr))
}

fn parse_emit_stmt(pair: pest::iterators::Pair<Rule>) -> ParseResult<Stmt> {
    let mut inner = pair.into_inner();
    let event_type = inner.expect_next("event type name")?.as_str().to_string();
    let mut fields = Vec::new();
    for p in inner {
        if p.as_rule() == Rule::named_arg_list {
            for arg in p.into_inner() {
                fields.push(parse_named_arg(arg)?);
            }
        }
    }
    Ok(Stmt::Emit { event_type, fields })
}

// ============================================================================
// Expression Parsing
// ============================================================================

fn parse_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let inner = pair.into_inner().next();

    match inner {
        Some(p) => parse_expr_inner(p),
        None => Ok(Expr::Null),
    }
}

fn parse_expr_inner(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    match pair.as_rule() {
        Rule::expr => parse_expr(pair),
        Rule::lambda_expr => parse_lambda_expr(pair),
        Rule::range_expr => parse_range_expr(pair),
        Rule::or_expr => parse_or_expr(pair),
        Rule::and_expr => parse_and_expr(pair),
        Rule::not_expr => parse_not_expr(pair),
        Rule::comparison_expr => parse_comparison_expr(pair),
        Rule::bitwise_or_expr => parse_bitwise_or_expr(pair),
        Rule::bitwise_xor_expr => parse_bitwise_xor_expr(pair),
        Rule::bitwise_and_expr => parse_bitwise_and_expr(pair),
        Rule::shift_expr => parse_shift_expr(pair),
        Rule::additive_expr => parse_additive_expr(pair),
        Rule::multiplicative_expr => parse_multiplicative_expr(pair),
        Rule::power_expr => parse_power_expr(pair),
        Rule::unary_expr => parse_unary_expr(pair),
        Rule::postfix_expr => parse_postfix_expr(pair),
        Rule::primary_expr => parse_primary_expr(pair),
        Rule::literal => parse_literal(pair),
        Rule::identifier => Ok(Expr::Ident(pair.as_str().to_string())),
        Rule::if_expr => parse_if_expr(pair),
        _ => Ok(Expr::Ident(pair.as_str().to_string())),
    }
}

fn parse_lambda_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut params = Vec::new();

    // Parse parameters
    let first = inner.expect_next("lambda parameters")?;
    match first.as_rule() {
        Rule::identifier_list => {
            for p in first.into_inner() {
                params.push(p.as_str().to_string());
            }
        }
        Rule::identifier => {
            params.push(first.as_str().to_string());
        }
        _ => {}
    }

    // Parse body - could be expression or block
    let body_pair = inner.expect_next("lambda body")?;
    let body = match body_pair.as_rule() {
        Rule::lambda_block => parse_lambda_block(body_pair)?,
        _ => parse_expr_inner(body_pair)?,
    };

    Ok(Expr::Lambda {
        params,
        body: Box::new(body),
    })
}

fn parse_lambda_block(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut stmts = Vec::new();
    let mut final_expr = None;

    for p in pair.into_inner() {
        match p.as_rule() {
            Rule::statement => {
                // Check if it's a var_decl to extract for Block
                let stmt = parse_statement(p)?;
                match &stmt.node {
                    Stmt::VarDecl {
                        mutable,
                        name,
                        ty,
                        value,
                    } => {
                        stmts.push((name.clone(), ty.clone(), value.clone(), *mutable));
                    }
                    Stmt::Expr(e) => {
                        // Last expression becomes result
                        final_expr = Some(e.clone());
                    }
                    _ => {
                        // Other statements - treat as expression if possible
                    }
                }
            }
            _ => {
                // Expression at end of block
                final_expr = Some(parse_expr_inner(p)?);
            }
        }
    }

    // If we have variable declarations, wrap in a Block expression
    if stmts.is_empty() {
        Ok(final_expr.unwrap_or(Expr::Null))
    } else {
        Ok(Expr::Block {
            stmts,
            result: Box::new(final_expr.unwrap_or(Expr::Null)),
        })
    }
}

fn parse_pattern_expr_as_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    // Convert pattern_or_expr to an Expr representation
    // pattern_or_expr = pattern_and_expr ~ ("or" ~ pattern_and_expr)*
    let mut inner = pair.into_inner();
    let mut left = parse_pattern_and_as_expr(inner.expect_next("pattern expression")?)?;

    for right_pair in inner {
        let right = parse_pattern_and_as_expr(right_pair)?;
        left = Expr::Binary {
            op: BinOp::Or,
            left: Box::new(left),
            right: Box::new(right),
        };
    }
    Ok(left)
}

fn parse_pattern_and_as_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_pattern_xor_as_expr(inner.expect_next("and expression")?)?;

    for right_pair in inner {
        let right = parse_pattern_xor_as_expr(right_pair)?;
        left = Expr::Binary {
            op: BinOp::And,
            left: Box::new(left),
            right: Box::new(right),
        };
    }
    Ok(left)
}

fn parse_pattern_xor_as_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_pattern_unary_as_expr(inner.expect_next("xor expression")?)?;

    for right_pair in inner {
        let right = parse_pattern_unary_as_expr(right_pair)?;
        left = Expr::Binary {
            op: BinOp::Xor,
            left: Box::new(left),
            right: Box::new(right),
        };
    }
    Ok(left)
}

fn parse_pattern_unary_as_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("unary expression or operand")?;

    if first.as_rule() == Rule::not_keyword {
        let expr = parse_pattern_primary_as_expr(inner.expect_next("pattern expression")?)?;
        Ok(Expr::Unary {
            op: UnaryOp::Not,
            expr: Box::new(expr),
        })
    } else {
        parse_pattern_primary_as_expr(first)
    }
}

fn parse_pattern_primary_as_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let inner = pair
        .into_inner()
        .expect_next("pattern primary expression")?;

    match inner.as_rule() {
        Rule::pattern_or_expr => parse_pattern_expr_as_expr(inner),
        Rule::pattern_sequence => parse_pattern_sequence_as_expr(inner),
        _ => Ok(Expr::Ident(inner.as_str().to_string())),
    }
}

fn parse_pattern_sequence_as_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    // pattern_sequence = identifier ~ ("->" ~ identifier)*
    // Convert to a chain of FollowedBy binary operations
    let mut inner = pair.into_inner();
    let mut left = Expr::Ident(inner.expect_next("sequence start")?.as_str().to_string());

    for right_pair in inner {
        let right = Expr::Ident(right_pair.as_str().to_string());
        left = Expr::Binary {
            op: BinOp::FollowedBy,
            left: Box::new(left),
            right: Box::new(right),
        };
    }
    Ok(left)
}

fn parse_filter_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let inner = pair.into_inner().expect_next("filter expression")?;
    parse_filter_or_expr(inner)
}

fn parse_filter_or_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_filter_and_expr(inner.expect_next("or expression operand")?)?;

    for right_pair in inner {
        let right = parse_filter_and_expr(right_pair)?;
        left = Expr::Binary {
            op: BinOp::Or,
            left: Box::new(left),
            right: Box::new(right),
        };
    }
    Ok(left)
}

fn parse_filter_and_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_filter_not_expr(inner.expect_next("and expression operand")?)?;

    for right_pair in inner {
        let right = parse_filter_not_expr(right_pair)?;
        left = Expr::Binary {
            op: BinOp::And,
            left: Box::new(left),
            right: Box::new(right),
        };
    }
    Ok(left)
}

fn parse_filter_not_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("not or expression")?;

    if first.as_rule() == Rule::not_keyword {
        let expr = parse_filter_comparison_expr(inner.expect_next("expression after not")?)?;
        Ok(Expr::Unary {
            op: UnaryOp::Not,
            expr: Box::new(expr),
        })
    } else {
        parse_filter_comparison_expr(first)
    }
}

fn parse_filter_comparison_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let left = parse_filter_additive_expr(inner.expect_next("comparison left operand")?)?;

    if let Some(op_pair) = inner.next() {
        let op = match op_pair.as_str() {
            "==" => BinOp::Eq,
            "!=" => BinOp::NotEq,
            "<" => BinOp::Lt,
            "<=" => BinOp::Le,
            ">" => BinOp::Gt,
            ">=" => BinOp::Ge,
            "in" => BinOp::In,
            "is" => BinOp::Is,
            s if s.contains("not") && s.contains("in") => BinOp::NotIn,
            _ => BinOp::Eq,
        };
        let right = parse_filter_additive_expr(inner.expect_next("comparison right operand")?)?;
        Ok(Expr::Binary {
            op,
            left: Box::new(left),
            right: Box::new(right),
        })
    } else {
        Ok(left)
    }
}

fn parse_filter_additive_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left =
        parse_filter_multiplicative_expr(inner.expect_next("additive expression operand")?)?;

    while let Some(op_pair) = inner.next() {
        let op = if op_pair.as_str() == "-" {
            BinOp::Sub
        } else {
            BinOp::Add
        };
        if let Some(right_pair) = inner.next() {
            let right = parse_filter_multiplicative_expr(right_pair)?;
            left = Expr::Binary {
                op,
                left: Box::new(left),
                right: Box::new(right),
            };
        }
    }
    Ok(left)
}

fn parse_filter_multiplicative_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left =
        parse_filter_unary_expr(inner.expect_next("multiplicative expression operand")?)?;

    while let Some(op_pair) = inner.next() {
        let op = match op_pair.as_str() {
            "*" => BinOp::Mul,
            "/" => BinOp::Div,
            "%" => BinOp::Mod,
            _ => BinOp::Mul,
        };
        if let Some(right_pair) = inner.next() {
            let right = parse_filter_unary_expr(right_pair)?;
            left = Expr::Binary {
                op,
                left: Box::new(left),
                right: Box::new(right),
            };
        }
    }
    Ok(left)
}

fn parse_filter_unary_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("unary operator or expression")?;

    // Check if first is a unary operator or the expression itself
    if first.as_rule() == Rule::filter_unary_op {
        let op_str = first.as_str();
        let expr =
            parse_filter_postfix_expr(inner.expect_next("expression after unary operator")?)?;
        let op = match op_str {
            "-" => UnaryOp::Neg,
            "~" => UnaryOp::BitNot,
            _ => unreachable!("Grammar only allows - or ~"),
        };
        Ok(Expr::Unary {
            op,
            expr: Box::new(expr),
        })
    } else {
        parse_filter_postfix_expr(first)
    }
}

fn parse_filter_postfix_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut expr = parse_filter_primary_expr(inner.expect_next("postfix expression base")?)?;

    for suffix in inner {
        expr = parse_filter_postfix_suffix(expr, suffix)?;
    }
    Ok(expr)
}

fn parse_filter_postfix_suffix(expr: Expr, pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();

    if let Some(first) = inner.next() {
        match first.as_rule() {
            Rule::identifier => {
                // Member access: .identifier
                Ok(Expr::Member {
                    expr: Box::new(expr),
                    member: first.as_str().to_string(),
                })
            }
            Rule::optional_member_access => {
                let member = first
                    .into_inner()
                    .expect_next("member name")?
                    .as_str()
                    .to_string();
                Ok(Expr::OptionalMember {
                    expr: Box::new(expr),
                    member,
                })
            }
            Rule::index_access => {
                let index = parse_expr(first.into_inner().expect_next("index expression")?)?;
                Ok(Expr::Index {
                    expr: Box::new(expr),
                    index: Box::new(index),
                })
            }
            Rule::call_args => {
                let args = first
                    .into_inner()
                    .filter(|p| p.as_rule() == Rule::arg_list)
                    .flat_map(|p| p.into_inner())
                    .map(parse_arg)
                    .collect::<ParseResult<Vec<_>>>()?;
                Ok(Expr::Call {
                    func: Box::new(expr),
                    args,
                })
            }
            _ => Ok(expr),
        }
    } else {
        Ok(expr)
    }
}

fn parse_filter_primary_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let inner = pair.into_inner().expect_next("filter primary expression")?;

    match inner.as_rule() {
        Rule::literal => parse_literal(inner),
        Rule::identifier => Ok(Expr::Ident(inner.as_str().to_string())),
        Rule::filter_expr => parse_filter_expr(inner),
        _ => Ok(Expr::Ident(inner.as_str().to_string())),
    }
}

fn parse_range_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let left = parse_expr_inner(inner.expect_next("range start")?)?;

    if let Some(op_pair) = inner.next() {
        let inclusive = op_pair.as_str() == "..=";
        let right = parse_expr_inner(inner.expect_next("range end")?)?;
        Ok(Expr::Range {
            start: Box::new(left),
            end: Box::new(right),
            inclusive,
        })
    } else {
        Ok(left)
    }
}

fn parse_or_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_expr_inner(inner.expect_next("or expression operand")?)?;

    for right_pair in inner {
        let right = parse_expr_inner(right_pair)?;
        left = Expr::Binary {
            op: BinOp::Or,
            left: Box::new(left),
            right: Box::new(right),
        };
    }

    Ok(left)
}

fn parse_and_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_expr_inner(inner.expect_next("and expression operand")?)?;

    for right_pair in inner {
        let right = parse_expr_inner(right_pair)?;
        left = Expr::Binary {
            op: BinOp::And,
            left: Box::new(left),
            right: Box::new(right),
        };
    }

    Ok(left)
}

fn parse_not_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("not keyword or expression")?;

    if first.as_rule() == Rule::not_keyword {
        let expr = parse_expr_inner(inner.expect_next("expression after not")?)?;
        Ok(Expr::Unary {
            op: UnaryOp::Not,
            expr: Box::new(expr),
        })
    } else {
        parse_expr_inner(first)
    }
}

fn parse_comparison_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let left = parse_expr_inner(inner.expect_next("comparison left operand")?)?;

    if let Some(op_pair) = inner.next() {
        let op_str = op_pair.as_str();
        let op = match op_str {
            "==" => BinOp::Eq,
            "!=" => BinOp::NotEq,
            "<" => BinOp::Lt,
            "<=" => BinOp::Le,
            ">" => BinOp::Gt,
            ">=" => BinOp::Ge,
            "in" => BinOp::In,
            "is" => BinOp::Is,
            s if s.contains("not") && s.contains("in") => BinOp::NotIn,
            _ => BinOp::Eq,
        };
        let right = parse_expr_inner(inner.expect_next("comparison right operand")?)?;
        Ok(Expr::Binary {
            op,
            left: Box::new(left),
            right: Box::new(right),
        })
    } else {
        Ok(left)
    }
}

fn parse_bitwise_or_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    parse_binary_chain(pair, BinOp::BitOr)
}

fn parse_bitwise_xor_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    parse_binary_chain(pair, BinOp::BitXor)
}

fn parse_bitwise_and_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    parse_binary_chain(pair, BinOp::BitAnd)
}

fn parse_shift_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_expr_inner(inner.expect_next("shift expression operand")?)?;

    while let Some(op_or_expr) = inner.next() {
        let op = match op_or_expr.as_str() {
            "<<" => BinOp::Shl,
            ">>" => BinOp::Shr,
            _ => {
                let right = parse_expr_inner(op_or_expr)?;
                left = Expr::Binary {
                    op: BinOp::Shl,
                    left: Box::new(left),
                    right: Box::new(right),
                };
                continue;
            }
        };
        if let Some(right_pair) = inner.next() {
            let right = parse_expr_inner(right_pair)?;
            left = Expr::Binary {
                op,
                left: Box::new(left),
                right: Box::new(right),
            };
        }
    }

    Ok(left)
}

fn parse_additive_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_expr_inner(inner.expect_next("additive expression operand")?)?;

    while let Some(op_pair) = inner.next() {
        let op_text = op_pair.as_str();
        let op = if op_text == "-" {
            BinOp::Sub
        } else {
            BinOp::Add
        };

        if let Some(right_pair) = inner.next() {
            let right = parse_expr_inner(right_pair)?;
            left = Expr::Binary {
                op,
                left: Box::new(left),
                right: Box::new(right),
            };
        }
    }

    Ok(left)
}

fn parse_multiplicative_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_expr_inner(inner.expect_next("multiplicative expression operand")?)?;

    while let Some(op_pair) = inner.next() {
        let op_text = op_pair.as_str();
        let op = match op_text {
            "*" => BinOp::Mul,
            "/" => BinOp::Div,
            "%" => BinOp::Mod,
            _ => BinOp::Mul,
        };

        if let Some(right_pair) = inner.next() {
            let right = parse_expr_inner(right_pair)?;
            left = Expr::Binary {
                op,
                left: Box::new(left),
                right: Box::new(right),
            };
        }
    }

    Ok(left)
}

fn parse_power_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let base = parse_expr_inner(inner.expect_next("power expression base")?)?;

    if let Some(exp_pair) = inner.next() {
        let exp = parse_expr_inner(exp_pair)?;
        Ok(Expr::Binary {
            op: BinOp::Pow,
            left: Box::new(base),
            right: Box::new(exp),
        })
    } else {
        Ok(base)
    }
}

fn parse_unary_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("unary operator or expression")?;

    // Check if first is a unary operator or the expression itself
    match first.as_rule() {
        Rule::unary_op => {
            let op_str = first.as_str();
            let expr = parse_expr_inner(inner.expect_next("expression after unary operator")?)?;
            let op = match op_str {
                "-" => UnaryOp::Neg,
                "~" => UnaryOp::BitNot,
                _ => unreachable!("Grammar only allows - or ~"),
            };
            Ok(Expr::Unary {
                op,
                expr: Box::new(expr),
            })
        }
        _ => parse_expr_inner(first),
    }
}

fn parse_postfix_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut expr = parse_expr_inner(inner.expect_next("postfix expression base")?)?;

    for suffix in inner {
        expr = parse_postfix_suffix(expr, suffix)?;
    }

    Ok(expr)
}

fn parse_postfix_suffix(expr: Expr, pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let inner = pair.into_inner().expect_next("postfix suffix")?;

    match inner.as_rule() {
        Rule::member_access => {
            let member = inner
                .into_inner()
                .expect_next("member name")?
                .as_str()
                .to_string();
            Ok(Expr::Member {
                expr: Box::new(expr),
                member,
            })
        }
        Rule::optional_member_access => {
            let member = inner
                .into_inner()
                .expect_next("member name")?
                .as_str()
                .to_string();
            Ok(Expr::OptionalMember {
                expr: Box::new(expr),
                member,
            })
        }
        Rule::slice_access => {
            // Parse slice: [start:end], [:end], [start:], [:]
            let slice_range = inner.into_inner().expect_next("slice range")?;
            let slice_inner = slice_range.into_inner();

            let mut start = None;
            let mut end = None;

            for p in slice_inner {
                match p.as_rule() {
                    Rule::slice_start => {
                        start = Some(Box::new(parse_expr_inner(
                            p.into_inner().expect_next("slice start expression")?,
                        )?));
                    }
                    Rule::slice_end => {
                        end = Some(Box::new(parse_expr_inner(
                            p.into_inner().expect_next("slice end expression")?,
                        )?));
                    }
                    _ => {}
                }
            }

            Ok(Expr::Slice {
                expr: Box::new(expr),
                start,
                end,
            })
        }
        Rule::index_access => {
            let index = parse_expr(inner.into_inner().expect_next("index expression")?)?;
            Ok(Expr::Index {
                expr: Box::new(expr),
                index: Box::new(index),
            })
        }
        Rule::call_args => {
            let mut args = Vec::new();
            for p in inner.into_inner() {
                if p.as_rule() == Rule::arg_list {
                    for arg in p.into_inner() {
                        args.push(parse_arg(arg)?);
                    }
                }
            }
            Ok(Expr::Call {
                func: Box::new(expr),
                args,
            })
        }
        _ => Ok(expr),
    }
}

fn parse_arg(pair: pest::iterators::Pair<Rule>) -> ParseResult<Arg> {
    let mut inner = pair.into_inner();
    let first = inner.expect_next("argument")?;

    if let Some(second) = inner.next() {
        Ok(Arg::Named(
            first.as_str().to_string(),
            parse_expr_inner(second)?,
        ))
    } else {
        Ok(Arg::Positional(parse_expr_inner(first)?))
    }
}

fn parse_primary_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let inner = pair.into_inner().expect_next("primary expression")?;

    match inner.as_rule() {
        Rule::if_expr => parse_if_expr(inner),
        Rule::literal => parse_literal(inner),
        Rule::identifier => Ok(Expr::Ident(inner.as_str().to_string())),
        Rule::array_literal => parse_array_literal(inner),
        Rule::map_literal => parse_map_literal(inner),
        Rule::expr => parse_expr(inner),
        _ => Ok(Expr::Ident(inner.as_str().to_string())),
    }
}

fn parse_if_expr(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let cond = parse_expr_inner(inner.expect_next("if condition")?)?;
    let then_branch = parse_expr_inner(inner.expect_next("then branch")?)?;
    let else_branch = parse_expr_inner(inner.expect_next("else branch")?)?;

    Ok(Expr::If {
        cond: Box::new(cond),
        then_branch: Box::new(then_branch),
        else_branch: Box::new(else_branch),
    })
}

fn parse_literal(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let inner = pair.into_inner().expect_next("literal value")?;

    match inner.as_rule() {
        Rule::integer => inner
            .as_str()
            .parse::<i64>()
            .map(Expr::Int)
            .map_err(|e| ParseError::InvalidNumber(format!("'{}': {}", inner.as_str(), e))),
        Rule::float => inner
            .as_str()
            .parse::<f64>()
            .map(Expr::Float)
            .map_err(|e| ParseError::InvalidNumber(format!("'{}': {}", inner.as_str(), e))),
        Rule::string => {
            let s = inner.as_str();
            Ok(Expr::Str(s[1..s.len() - 1].to_string()))
        }
        Rule::duration => Ok(Expr::Duration(
            parse_duration(inner.as_str()).map_err(ParseError::InvalidDuration)?,
        )),
        Rule::timestamp => Ok(Expr::Timestamp(parse_timestamp(inner.as_str()))),
        Rule::boolean => Ok(Expr::Bool(inner.as_str() == "true")),
        Rule::null => Ok(Expr::Null),
        _ => Ok(Expr::Null),
    }
}

fn parse_array_literal(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut items = Vec::new();
    for p in pair.into_inner() {
        if p.as_rule() == Rule::expr_list {
            for expr in p.into_inner() {
                items.push(parse_expr(expr)?);
            }
        }
    }
    Ok(Expr::Array(items))
}

fn parse_map_literal(pair: pest::iterators::Pair<Rule>) -> ParseResult<Expr> {
    let mut entries = Vec::new();
    for p in pair.into_inner() {
        if p.as_rule() == Rule::map_entry_list {
            for entry in p.into_inner() {
                let mut inner = entry.into_inner();
                let key = inner.expect_next("map key")?.as_str().to_string();
                let key = if key.starts_with('"') {
                    key[1..key.len() - 1].to_string()
                } else {
                    key
                };
                let value = parse_expr(inner.expect_next("map value")?)?;
                entries.push((key, value));
            }
        }
    }
    Ok(Expr::Map(entries))
}

fn parse_binary_chain(pair: pest::iterators::Pair<Rule>, op: BinOp) -> ParseResult<Expr> {
    let mut inner = pair.into_inner();
    let mut left = parse_expr_inner(inner.expect_next("binary chain operand")?)?;

    for right_pair in inner {
        let right = parse_expr_inner(right_pair)?;
        left = Expr::Binary {
            op,
            left: Box::new(left),
            right: Box::new(right),
        };
    }

    Ok(left)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_parse_simple_stream() {
        let result = parse("stream output = input");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_stream_with_filter() {
        let result = parse("stream output = input.where(value > 100)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_stream_with_map() {
        let result = parse("stream output = input.map(x * 2)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_event_declaration() {
        let result = parse("event SensorReading:\n  sensor_id: str\n  value: float");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_variable() {
        let result = parse("let x = 42");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_function() {
        let result = parse("fn add(a: int, b: int) -> int:\n  return a + b");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_lambda() {
        let result = parse("let f = (x) => x * 2");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_if_expression() {
        let result = parse("let x = if a > b then a else b");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_followed_by() {
        let result = parse("stream alerts = orders.where(amount > 1000) -> Payment where payment.order_id == orders.id");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_window() {
        let result = parse("stream windowed = input.window(5s)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_aggregate() {
        let result =
            parse("stream stats = input.window(1m).aggregate(count: count(), avg: avg(value))");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_merge() {
        let result = parse("stream combined = merge(stream1, stream2)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sequence() {
        let result = parse("stream seq = sequence(a: EventA, b: EventB where b.id == a.id)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_config() {
        let result = parse("config:\n  window_size: 5s\n  batch_size: 100");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_complex_expression() {
        let result = parse("let x = (a + b) * c / d - e");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sliding_window() {
        let result = parse("stream output = input.window(5m, sliding: 1m)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_fork_construct() {
        let result =
            parse("stream forked = input.fork(branch1: .where(x > 0), branch2: .where(x < 0))");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_aggregate_functions() {
        let result = parse(
            "stream stats = input.window(1h).aggregate(total: sum(value), average: avg(value))",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_complex_parentheses() {
        let result = parse("let x = ((a + b) * (c - d)) / e");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sequence_with_alias() {
        let result = parse(
            r#"
            stream TwoTicks = StockTick as first
                -> StockTick as second
                .emit(result: "two_ticks")
        "#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_followed_by_with_alias() {
        let result = parse("stream alerts = Order as a -> Payment as b");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_followed_by_with_filter_and_alias() {
        // This is the problematic case: 'as b' should be the alias, not part of the expression
        let result = parse(
            r#"
            stream Test = A as a
                -> B where value == a.base + 10 as b
                .emit(status: "matched")
        "#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_pattern_with_lambda() {
        let result =
            parse("stream Test = Trade.window(1m).pattern(p: x => x.len() > 3).emit(alert: true)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_simple() {
        let result = parse("pattern SimpleAlert = SEQ(Login, Transaction)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_with_kleene() {
        let result = parse("pattern MultiTx = SEQ(Login, Transaction+ where amount > 1000)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_with_alias() {
        let result = parse("pattern AliasedPattern = SEQ(Login as login, Transaction as tx)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_with_within() {
        let result = parse("pattern TimedPattern = SEQ(A, B) within 10m");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_with_partition() {
        let result = parse("pattern PartitionedPattern = SEQ(A, B) partition by user_id");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_full() {
        // Note: In SASE+ syntax, 'where' comes before 'as' (filter then alias)
        let result = parse(
            "pattern SuspiciousActivity = SEQ(Transaction+ where amount > 1000 as txs) within 10m partition by user_id"
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_or() {
        let result = parse("pattern AlertOrWarn = Login OR Logout");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_and() {
        let result = parse("pattern BothEvents = Login AND Transaction");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_sase_pattern_decl_not() {
        let result = parse("pattern NoLogout = SEQ(Login, NOT Logout, Transaction)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_having() {
        let result = parse(
            "stream filtered = input.window(1m).aggregate(count: count(), total: sum(value)).having(count > 10)",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_having_with_partition() {
        let result = parse(
            "stream grouped = input.partition_by(category).window(5m).aggregate(avg_price: avg(price)).having(avg_price > 100.0)",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_timer_source() {
        let result = parse("stream heartbeat = timer(5s).emit(type: \"heartbeat\")");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_timer_source_with_initial_delay() {
        let result =
            parse("stream delayed_timer = timer(1m, initial_delay: 10s).emit(type: \"periodic\")");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_var_decl() {
        let result = parse("var threshold: float = 10.0");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_let_decl() {
        let result = parse("let max_count: int = 100");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_assignment() {
        let result = parse("threshold := threshold + 10.0");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_assignment_with_expression() {
        let result = parse("count := count * 2 + offset");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_nested_stream_reference() {
        let result = parse("stream Base = Event\nstream Derived = Base.where(x > 0)");
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_multi_stage_pipeline() {
        let result = parse(
            "stream L1 = Raw\nstream L2 = L1.where(a > 1)\nstream L3 = L2.window(5).aggregate(cnt: count())",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_stream_with_operations_chain() {
        let result = parse(
            "stream Processed = Source.where(valid).window(10).aggregate(sum: sum(value)).having(sum > 100)",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    // =========================================================================
    // Connectivity Architecture Tests
    // =========================================================================

    #[test]
    fn test_parse_connector_mqtt() {
        let result = parse(
            r#"connector MqttBroker = mqtt (
                host: "localhost",
                port: 1883,
                client_id: "varpulis"
            )"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_connector_kafka() {
        let result = parse(
            r#"connector KafkaCluster = kafka (
                brokers: ["kafka1:9092", "kafka2:9092"],
                group_id: "my-group"
            )"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_connector_http() {
        let result = parse(
            r#"connector ApiEndpoint = http (
                base_url: "https://api.example.com"
            )"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_stream_with_from_connector() {
        let result = parse(
            r#"stream Temperatures = TemperatureReading.from(MqttSensors, topic: "sensors/temp/#")"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_stream_with_from_and_operations() {
        let result = parse(
            r#"stream HighTemp = TemperatureReading
                .from(MqttSensors, topic: "sensors/#")
                .where(value > 30)
                .emit(alert: "high_temp")"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_full_connectivity_pipeline() {
        let result = parse(
            r#"
            connector MqttSensors = mqtt (host: "localhost", port: 1883)
            connector KafkaAlerts = kafka (brokers: ["kafka:9092"])

            event TemperatureReading:
                sensor_id: str
                value: float
                ts: timestamp

            stream Temperatures = TemperatureReading.from(MqttSensors, topic: "sensors/#")

            stream HighTempAlert = Temperatures
                .where(value > 30)
                .emit(alert_type: "HIGH_TEMP", temperature: value)

            "#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_emit_as_type() {
        let result = parse(
            r#"stream Alerts = Temperatures
                .where(value > 30)
                .emit as AlertEvent(severity: "high", temp: value)"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_stream_with_to_connector() {
        let result = parse(
            r#"stream Output = Input
                .where(x > 0)
                .emit(y: x * 2)
                .to(KafkaOutput, topic: "output")"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_emit_stmt_parses() {
        let result = parse(
            r"fn test():
    emit Pixel(x: 1, y: 2)",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
        let program = result.unwrap();
        // Find the fn_decl
        if let Stmt::FnDecl { body, .. } = &program.statements[0].node {
            match &body[0].node {
                Stmt::Emit { event_type, fields } => {
                    assert_eq!(event_type, "Pixel");
                    assert_eq!(fields.len(), 2);
                    assert_eq!(fields[0].name, "x");
                    assert_eq!(fields[1].name, "y");
                }
                other => panic!("Expected Stmt::Emit, got {other:?}"),
            }
        } else {
            panic!("Expected FnDecl");
        }
    }

    #[test]
    fn test_emit_stmt_no_args() {
        let result = parse(
            r"fn test():
    emit Done()",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
        let program = result.unwrap();
        if let Stmt::FnDecl { body, .. } = &program.statements[0].node {
            match &body[0].node {
                Stmt::Emit { event_type, fields } => {
                    assert_eq!(event_type, "Done");
                    assert!(fields.is_empty());
                }
                other => panic!("Expected Stmt::Emit, got {other:?}"),
            }
        } else {
            panic!("Expected FnDecl");
        }
    }

    #[test]
    fn test_emit_in_function_with_for_loop() {
        let result = parse(
            r"fn generate(n: int):
    for i in 0..n:
        emit Item(index: i, value: i * 2)",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_process_op() {
        let result = parse(
            r"fn do_work():
    emit Result(v: 42)

stream S = timer(1s).process(do_work())",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
    }

    #[test]
    fn test_parse_trend_aggregate_count_trends() {
        let result = parse(
            r#"stream S = StockTick as first
    -> all StockTick where price > first.price as rising
    -> StockTick where price < rising.price as drop
    .within(60s)
    .trend_aggregate(count: count_trends())
    .emit(event_type: "TrendStats", trends: count)"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
        let program = result.unwrap();
        // Find the stream declaration and check for TrendAggregate op
        for stmt in &program.statements {
            if let Stmt::StreamDecl { ops, .. } = &stmt.node {
                let has_trend_agg = ops
                    .iter()
                    .any(|op| matches!(op, StreamOp::TrendAggregate(_)));
                assert!(has_trend_agg, "Expected TrendAggregate op in stream ops");
                // Check that TrendAggregate has the right item
                for op in ops {
                    if let StreamOp::TrendAggregate(items) = op {
                        assert_eq!(items.len(), 1);
                        assert_eq!(items[0].alias, "count");
                        assert_eq!(items[0].func, "count_trends");
                        assert!(items[0].arg.is_none());
                    }
                }
                return;
            }
        }
        panic!("No stream declaration found");
    }

    #[test]
    fn test_parse_trend_aggregate_multiple_items() {
        let result = parse(
            r"stream S = StockTick as first
    -> all StockTick as rising
    .within(60s)
    .trend_aggregate(
        trend_count: count_trends(),
        event_count: count_events(rising)
    )
    .emit(trends: trend_count, events: event_count)",
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
        let program = result.unwrap();
        for stmt in &program.statements {
            if let Stmt::StreamDecl { ops, .. } = &stmt.node {
                for op in ops {
                    if let StreamOp::TrendAggregate(items) = op {
                        assert_eq!(items.len(), 2);
                        assert_eq!(items[0].alias, "trend_count");
                        assert_eq!(items[0].func, "count_trends");
                        assert_eq!(items[1].alias, "event_count");
                        assert_eq!(items[1].func, "count_events");
                        assert!(items[1].arg.is_some());
                        return;
                    }
                }
            }
        }
        panic!("No TrendAggregate found");
    }

    #[test]
    fn test_parse_score_basic() {
        let result = parse(
            r#"stream S = TradeEvent
    .score(model: "models/fraud.onnx", inputs: [amount, risk_score], outputs: [fraud_prob, category])"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
        let program = result.unwrap();
        for stmt in &program.statements {
            if let Stmt::StreamDecl { ops, .. } = &stmt.node {
                for op in ops {
                    if let StreamOp::Score(spec) = op {
                        assert_eq!(spec.model_path, "models/fraud.onnx");
                        assert_eq!(spec.inputs, vec!["amount", "risk_score"]);
                        assert_eq!(spec.outputs, vec!["fraud_prob", "category"]);
                        return;
                    }
                }
            }
        }
        panic!("No Score op found");
    }

    #[test]
    fn test_parse_score_single_field() {
        let result = parse(
            r#"stream S = Event
    .score(model: "model.onnx", inputs: [value], outputs: [prediction])"#,
        );
        assert!(result.is_ok(), "Failed: {:?}", result.err());
        let program = result.unwrap();
        for stmt in &program.statements {
            if let Stmt::StreamDecl { ops, .. } = &stmt.node {
                for op in ops {
                    if let StreamOp::Score(spec) = op {
                        assert_eq!(spec.model_path, "model.onnx");
                        assert_eq!(spec.inputs, vec!["value"]);
                        assert_eq!(spec.outputs, vec!["prediction"]);
                        return;
                    }
                }
            }
        }
        panic!("No Score op found");
    }

    // Regression tests for fuzz-discovered parser hangs (2026-02-21).
    // Unmatched `[` brackets cause exponential backtracking in pest's PEG
    // recursive descent through array_literal / index_access / slice_access.

    #[test]
    fn fuzz_regression_unmatched_brackets_timeout() {
        // Simplified version of the fuzzer-discovered timeout input (28 unmatched '[')
        let input = "c2222222s[s[22s[U2s[U6[U6[22222222s[s[22s[U2s[U6[U6[222*2222s[U6[U6[222*2222s[22s[U6[U6[22*2222s[U6[U6[222*2222s[22s[U6[U6[222*26[U6[222*2";
        let start = std::time::Instant::now();
        let result = parse(input);
        let elapsed = start.elapsed();
        assert!(
            result.is_err(),
            "Should reject deeply nested unmatched brackets"
        );
        assert!(
            elapsed.as_millis() < 100,
            "Parser should reject fast, took {elapsed:?}"
        );
    }

    #[test]
    fn fuzz_regression_deeply_nested_brackets_slow_unit() {
        // 30 unmatched '[' — must be rejected by nesting depth check
        let input = "stream x[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[";
        let start = std::time::Instant::now();
        let result = parse(input);
        let elapsed = start.elapsed();
        assert!(result.is_err(), "Should reject deeply nested brackets");
        assert!(
            elapsed.as_millis() < 100,
            "Parser should reject fast, took {elapsed:?}"
        );
    }

    #[test]
    fn nesting_depth_allows_reasonable_programs() {
        // 10 levels of nesting — well within the limit
        let input = "let x = foo(bar(baz(qux(a, [1, [2, [3, [4]]]]))))";
        let result = parse(input);
        // May fail for other reasons (not a valid program) but should NOT
        // fail with "Nesting depth exceeds maximum"
        if let Err(ref e) = result {
            let msg = format!("{e}");
            assert!(
                !msg.contains("Nesting depth"),
                "Should allow 10 levels of nesting: {msg}"
            );
        }
    }

    #[test]
    fn nesting_depth_ignores_brackets_in_comments() {
        // Brackets inside # comments should not count
        let input = "# [[[[[[[[[[[[[[[[[[[[[[[[[[\nstream x = y";
        let result = parse(input);
        assert!(
            result.is_ok(),
            "Brackets in comments should be ignored: {:?}",
            result.err()
        );
    }

    #[test]
    fn nesting_depth_ignores_brackets_in_strings() {
        // Brackets inside strings should not count
        let input = r#"let x = "[[[[[[[[[[[[[[[[[[[[[[[[[[""#;
        let result = parse(input);
        if let Err(ref e) = result {
            let msg = format!("{e}");
            assert!(
                !msg.contains("Nesting depth"),
                "Brackets in strings should be ignored: {msg}"
            );
        }
    }
}