ryo-source 0.1.0

//! Pure AST types - Span-free, thread-safe.
//!
//! All types support optional serde serialization via the `serde` feature.

use std::sync::Arc;

/// A complete Rust source file (pure, no spans).
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureFile {
    /// Attributes on the file (e.g., `#![allow(...)]`).
    pub attrs: Vec<PureAttribute>,
    /// Items in the file.
    pub items: Vec<PureItem>,
}

// SAFETY: PureFile contains no raw pointers or non-Send types
unsafe impl Send for PureFile {}
unsafe impl Sync for PureFile {}

impl PureFile {
    /// Create a new empty file.
    pub fn new() -> Self {
        Self {
            attrs: Vec::new(),
            items: Vec::new(),
        }
    }

    /// Get all functions.
    pub fn functions(&self) -> Vec<&PureFn> {
        self.items
            .iter()
            .filter_map(|item| {
                if let PureItem::Fn(f) = item {
                    Some(f)
                } else {
                    None
                }
            })
            .collect()
    }

    /// Get all structs.
    pub fn structs(&self) -> Vec<&PureStruct> {
        self.items
            .iter()
            .filter_map(|item| {
                if let PureItem::Struct(s) = item {
                    Some(s)
                } else {
                    None
                }
            })
            .collect()
    }

    /// Get all use statements.
    pub fn uses(&self) -> Vec<&PureUse> {
        self.items
            .iter()
            .filter_map(|item| {
                if let PureItem::Use(u) = item {
                    Some(u)
                } else {
                    None
                }
            })
            .collect()
    }

    /// Find a function by name.
    pub fn find_fn(&self, name: &str) -> Option<&PureFn> {
        self.functions().into_iter().find(|f| f.name == name)
    }

    /// Get all traits.
    pub fn traits(&self) -> Vec<&PureTrait> {
        self.items
            .iter()
            .filter_map(|item| {
                if let PureItem::Trait(t) = item {
                    Some(t)
                } else {
                    None
                }
            })
            .collect()
    }

    /// Get all impl blocks.
    pub fn impls(&self) -> Vec<&PureImpl> {
        self.items
            .iter()
            .filter_map(|item| {
                if let PureItem::Impl(i) = item {
                    Some(i)
                } else {
                    None
                }
            })
            .collect()
    }

    /// Wrap in Arc for thread-safe sharing.
    pub fn into_arc(self) -> Arc<Self> {
        Arc::new(self)
    }
}

impl Default for PureFile {
    fn default() -> Self {
        Self::new()
    }
}

/// An item in a file or module.
///
/// # Future: PureAnyItem
///
/// If unified handling across PureItem, PureImplItem, and PureTraitItem
/// is needed, consider adding a `PureAnyItem` enum that wraps all item types.
/// This would be separate from PureItem to maintain context-specific type safety.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureItem {
    /// Use statement.
    Use(PureUse),
    /// Function definition.
    Fn(PureFn),
    /// Struct definition.
    Struct(PureStruct),
    /// Enum definition.
    Enum(PureEnum),
    /// Impl block.
    Impl(PureImpl),
    /// Const item.
    Const(PureConst),
    /// Static item.
    Static(PureStatic),
    /// Type alias.
    Type(PureTypeAlias),
    /// Module.
    Mod(PureMod),
    /// Trait definition.
    Trait(PureTrait),
    /// Macro invocation.
    Macro(PureMacro),
    /// Other/unsupported item (stored as string).
    Other(String),
}

/// The meta content of an attribute.
///
/// Follows the structure of `syn::Meta`:
/// - `Path`: Simple path attribute like `#[test]`
/// - `List`: List attribute like `#[derive(Debug, Clone)]`
/// - `NameValue`: Name-value attribute like `#[doc = "comment"]`
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureAttrMeta {
    /// Path only (e.g., `#[test]`, `#[inline]`)
    Path,
    /// List with arguments (e.g., `#[derive(Debug, Clone)]` → args = "Debug, Clone")
    List(String),
    /// Name-value pair (e.g., `#[doc = "comment"]` → value = "\"comment\"")
    NameValue(String),
}

/// An attribute (e.g., `#[derive(Debug)]`).
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureAttribute {
    /// The attribute path (e.g., "derive", "cfg").
    pub path: String,
    /// The meta content.
    pub meta: PureAttrMeta,
    /// Is this an inner attribute (`#![...]`)?
    pub is_inner: bool,
}

/// A use statement.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureUse {
    /// Visibility.
    pub vis: PureVis,
    /// The use tree.
    pub tree: PureUseTree,
}

/// A use tree.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureUseTree {
    /// Simple path: `use std::io;`
    Path {
        /// Path segment (e.g. `std`).
        path: String,
        /// Continuation of the use tree after this segment.
        tree: Box<PureUseTree>,
    },
    /// Name: `use std::io;` (the `io` part)
    Name(String),
    /// Rename: `use std::io as stdio;`
    Rename {
        /// Original name (`io`).
        name: String,
        /// Alias (`stdio`).
        rename: String,
    },
    /// Glob: `use std::io::*;`
    Glob,
    /// Group: `use std::{io, fs};`
    Group(Vec<PureUseTree>),
}

/// Visibility.
#[derive(Debug, Clone, PartialEq, Eq, Default)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureVis {
    /// Private (default).
    #[default]
    Private,
    /// `pub`
    Public,
    /// `pub(crate)`
    Crate,
    /// `pub(super)`
    Super,
    /// `pub(in path)`
    In(String),
}

/// A function definition.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureFn {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Is async (explicit `async fn`)?
    pub is_async: bool,
    /// Is async inferred from return type (`Pin<Box<dyn Future<...>>>`)?
    /// This is typically set when `#[async_trait]` or similar macros are used.
    #[cfg_attr(feature = "serde", serde(default))]
    pub is_async_inferred: bool,
    /// Is const?
    pub is_const: bool,
    /// Is unsafe?
    pub is_unsafe: bool,
    /// ABI (e.g., `"C"`, `"Rust"`, `"system"`). None means default Rust ABI.
    #[cfg_attr(feature = "serde", serde(default))]
    pub abi: Option<String>,
    /// Function name.
    pub name: String,
    /// Generic parameters.
    pub generics: PureGenerics,
    /// Parameters.
    pub params: Vec<PureParam>,
    /// Return type (None = unit).
    pub ret: Option<PureType>,
    /// Function body.
    pub body: PureBlock,
}

impl PureFn {
    /// Returns true if the function is async (either explicit or inferred).
    ///
    /// This includes:
    /// - Explicit `async fn` declarations
    /// - Functions with `Pin<Box<dyn Future<...>>>` return type (e.g., from `#[async_trait]`)
    pub fn is_effectively_async(&self) -> bool {
        self.is_async || self.is_async_inferred
    }
}

/// Function parameter.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureParam {
    /// `self`
    SelfValue {
        /// `&self` / `&mut self` (i.e. taken by reference).
        is_ref: bool,
        /// `mut self` / `&mut self`.
        is_mut: bool,
    },
    /// Named parameter.
    Typed {
        /// Parameter binding name.
        name: String,
        /// Parameter type.
        ty: PureType,
    },
}

/// Closure parameter with optional type annotation.
///
/// Unlike function parameters (`PureParam`), closure parameters:
/// - Use patterns (destructuring, wildcards, etc.) not just names
/// - Type annotations are optional (often inferred)
///
/// # Examples
/// - `|x|` → `PureClosureParam { pattern: Ident("x"), ty: None }`
/// - `|x: Foo|` → `PureClosureParam { pattern: Ident("x"), ty: Some(Path("Foo")) }`
/// - `|(a, b): (Foo, Bar)|` → `PureClosureParam { pattern: Tuple(..), ty: Some(Tuple(..)) }`
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureClosureParam {
    /// The parameter pattern.
    pub pattern: PurePattern,
    /// Optional type annotation.
    pub ty: Option<PureType>,
}

impl PureClosureParam {
    /// Create an untyped closure parameter (type will be inferred).
    pub fn untyped(pattern: PurePattern) -> Self {
        Self { pattern, ty: None }
    }

    /// Create a typed closure parameter.
    pub fn typed(pattern: PurePattern, ty: PureType) -> Self {
        Self {
            pattern,
            ty: Some(ty),
        }
    }
}

/// A block of statements.
#[derive(Debug, Clone, PartialEq, Eq, Default)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureBlock {
    /// Statements in the block.
    pub stmts: Vec<PureStmt>,
}

impl PureBlock {
    /// Get statement at index.
    #[inline]
    pub fn get_stmt(&self, index: usize) -> Option<&PureStmt> {
        self.stmts.get(index)
    }

    /// Get mutable statement at index.
    #[inline]
    pub fn get_stmt_mut(&mut self, index: usize) -> Option<&mut PureStmt> {
        self.stmts.get_mut(index)
    }

    /// Number of statements.
    #[inline]
    pub fn len(&self) -> usize {
        self.stmts.len()
    }

    /// Is block empty?
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.stmts.is_empty()
    }
}

/// A statement.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureStmt {
    /// Local variable: `let x = 1;`
    Local {
        /// Binding pattern (LHS of `let`).
        pattern: PurePattern,
        /// Optional explicit type annotation.
        ty: Option<PureType>,
        /// Optional initializer expression.
        init: Option<PureExpr>,
    },
    /// Expression with semicolon.
    Semi(PureExpr),
    /// Expression without semicolon (tail expression).
    Expr(PureExpr),
    /// Item statement (function inside function, etc.).
    Item(Box<PureItem>),
}

impl PureStmt {
    /// Get the expression contained in this statement.
    ///
    /// Returns `Some` for `Local` (init expr), `Semi`, and `Expr` variants.
    /// Returns `None` for `Item` or if `Local` has no initializer.
    pub fn get_expr(&self) -> Option<&PureExpr> {
        match self {
            PureStmt::Local { init, .. } => init.as_ref(),
            PureStmt::Semi(e) | PureStmt::Expr(e) => Some(e),
            PureStmt::Item(_) => None,
        }
    }

    /// Get mutable expression contained in this statement.
    pub fn get_expr_mut(&mut self) -> Option<&mut PureExpr> {
        match self {
            PureStmt::Local { init, .. } => init.as_mut(),
            PureStmt::Semi(e) | PureStmt::Expr(e) => Some(e),
            PureStmt::Item(_) => None,
        }
    }

    /// Check if this statement contains an expression.
    pub fn has_expr(&self) -> bool {
        match self {
            PureStmt::Local { init, .. } => init.is_some(),
            PureStmt::Semi(_) | PureStmt::Expr(_) => true,
            PureStmt::Item(_) => false,
        }
    }
}

/// A pattern.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PurePattern {
    /// Identifier: `x`, `mut x`
    Ident {
        /// Binding name.
        name: String,
        /// `mut` qualifier.
        is_mut: bool,
    },
    /// Wildcard: `_`
    Wild,
    /// Tuple: `(a, b)`
    Tuple(Vec<PurePattern>),
    /// Struct: `Point { x, y }` or `Point { x, .. }`
    Struct {
        /// Struct path (e.g. `Point`).
        path: String,
        /// Field bindings (name, sub-pattern).
        fields: Vec<(String, PurePattern)>,
        /// Whether the pattern has a rest (`..`) at the end
        rest: bool,
    },
    /// Reference: `&x`, `&mut x`
    Ref {
        /// `mut` qualifier (`&mut`).
        is_mut: bool,
        /// Inner pattern after `&` / `&mut`.
        pattern: Box<PurePattern>,
    },
    /// Literal (for matching).
    Lit(String),
    /// Or pattern: `A | B`
    Or(Vec<PurePattern>),
    /// Path pattern: `Some`, `None`, `Enum::Variant`
    Path(String),
    /// Range pattern: `1..=5`, `'a'..='z'`
    Range {
        /// Start literal (None = unbounded below).
        start: Option<String>,
        /// End literal (None = unbounded above).
        end: Option<String>,
        /// `..=` (inclusive) vs `..` (exclusive).
        inclusive: bool,
    },
    /// Slice pattern: `[a, b, ..]`
    Slice(Vec<PurePattern>),
    /// Rest pattern: `..`
    Rest,
    /// Other (as string) - unsupported patterns with error guidance.
    Other(String),
}

/// An expression.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureExpr {
    /// Literal: `1`, `"hello"`, `true`
    Lit(String),
    /// Path: `x`, `std::io::stdin`
    Path(String),
    /// Binary operation: `a + b`
    Binary {
        /// Operator token (e.g. `+`, `==`).
        op: String,
        /// Left operand.
        left: Box<PureExpr>,
        /// Right operand.
        right: Box<PureExpr>,
    },
    /// Unary operation: `-x`, `!x`, `*x`, `&x`
    Unary {
        /// Operator token (`-` / `!` / `*` / `&`).
        op: String,
        /// Operand expression.
        expr: Box<PureExpr>,
    },
    /// Function call: `foo(a, b)`
    Call {
        /// Callee expression.
        func: Box<PureExpr>,
        /// Argument expressions.
        args: Vec<PureExpr>,
    },
    /// Method call: `x.foo(a, b)` or `x.foo::<T>(a, b)`
    MethodCall {
        /// Receiver expression (LHS of `.`).
        receiver: Box<PureExpr>,
        /// Method name.
        method: String,
        /// Turbofish type arguments: `::<T, U>` → `"< T , U >"`
        turbofish: Option<String>,
        /// Argument expressions.
        args: Vec<PureExpr>,
    },
    /// Field access: `x.field`
    Field {
        /// Base expression.
        expr: Box<PureExpr>,
        /// Field name (or tuple index as string).
        field: String,
    },
    /// Index: `x[i]`
    Index {
        /// Base expression (`x`).
        expr: Box<PureExpr>,
        /// Index expression (`i`).
        index: Box<PureExpr>,
    },
    /// Block: `{ ... }` or `'label: { ... }`
    Block {
        /// Optional label (e.g., `'block`)
        label: Option<String>,
        /// Inner block.
        block: PureBlock,
    },
    /// If: `if cond { ... } else { ... }`
    If {
        /// Condition expression.
        cond: Box<PureExpr>,
        /// `then` branch block.
        then_branch: PureBlock,
        /// Optional `else` branch (another expression).
        else_branch: Option<Box<PureExpr>>,
    },
    /// Match: `match x { ... }`
    Match {
        /// Scrutinee expression.
        expr: Box<PureExpr>,
        /// Match arms.
        arms: Vec<PureMatchArm>,
    },
    /// Loop: `loop { ... }` or `'label: loop { ... }`
    Loop {
        /// Optional label (e.g., `'outer`)
        label: Option<String>,
        /// Loop body block.
        body: PureBlock,
    },
    /// While: `while cond { ... }` or `'label: while cond { ... }`
    While {
        /// Optional label (e.g., `'outer`)
        label: Option<String>,
        /// Loop condition.
        cond: Box<PureExpr>,
        /// Loop body block.
        body: PureBlock,
    },
    /// For: `for pat in expr { ... }` or `'label: for pat in expr { ... }`
    For {
        /// Optional label (e.g., `'outer`)
        label: Option<String>,
        /// Iteration binding pattern.
        pat: PurePattern,
        /// Iterator expression.
        expr: Box<PureExpr>,
        /// Loop body block.
        body: PureBlock,
    },
    /// Return: `return x`
    Return(Option<Box<PureExpr>>),
    /// Break: `break x` or `break 'label x`
    Break {
        /// Optional label to break to (e.g., `'outer`)
        label: Option<String>,
        /// Optional value carried out of the loop.
        expr: Option<Box<PureExpr>>,
    },
    /// Continue: `continue` or `continue 'label`
    Continue {
        /// Optional label to continue to (e.g., `'outer`)
        label: Option<String>,
    },
    /// Closure: `|x| x + 1`, `|x: Foo| -> Bar { x }`, `move |x| x`
    Closure {
        /// Is async closure?
        is_async: bool,
        /// Is move closure?
        is_move: bool,
        /// Parameters with optional type annotations.
        params: Vec<PureClosureParam>,
        /// Optional return type annotation.
        ret: Option<PureType>,
        /// Closure body expression.
        body: Box<PureExpr>,
    },
    /// Struct literal: `Point { x: 1, y: 2 }`
    Struct {
        /// Struct path (e.g. `Point`).
        path: String,
        /// Field initializers (name, expr).
        fields: Vec<(String, PureExpr)>,
    },
    /// Tuple: `(a, b, c)`
    Tuple(Vec<PureExpr>),
    /// Array: `[1, 2, 3]`
    Array(Vec<PureExpr>),
    /// Reference: `&x`, `&mut x`
    Ref {
        /// `mut` qualifier (`&mut`).
        is_mut: bool,
        /// Referent expression.
        expr: Box<PureExpr>,
    },
    /// Macro invocation: `println!(...)`
    Macro {
        /// Macro name (without `!`).
        name: String,
        /// Delimiter style around tokens.
        delimiter: MacroDelimiter,
        /// Raw token stream as a string.
        tokens: String,
    },
    /// Await: `x.await`
    Await(Box<PureExpr>),
    /// Try: `x?`
    Try(Box<PureExpr>),
    /// Range: `a..b`, `..b`, `a..`, `..`, `a..=b`
    Range {
        /// Start bound expression (None = unbounded).
        start: Option<Box<PureExpr>>,
        /// End bound expression (None = unbounded).
        end: Option<Box<PureExpr>>,
        /// true for `..=`, false for `..`
        inclusive: bool,
    },
    /// Cast: `x as T`
    Cast {
        /// Source expression.
        expr: Box<PureExpr>,
        /// Target type.
        ty: PureType,
    },
    /// Let expression (in conditions): `let Some(x) = y`
    Let {
        /// Pattern on the LHS of `let`.
        pattern: PurePattern,
        /// Scrutinee expression on the RHS.
        expr: Box<PureExpr>,
    },
    /// Async block: `async { ... }` or `async move { ... }`
    Async {
        /// `move` qualifier.
        is_move: bool,
        /// Async block body.
        body: PureBlock,
    },
    /// Unsafe block: `unsafe { ... }`
    Unsafe(PureBlock),
    /// Array repeat: `[expr; N]`
    Repeat {
        /// Element expression to repeat.
        expr: Box<PureExpr>,
        /// Repeat count expression.
        len: Box<PureExpr>,
    },
    /// Other (as string).
    Other(String),
}

impl PureExpr {
    /// Create a MethodCall with default turbofish (None)
    pub fn method_call(receiver: Box<PureExpr>, method: String, args: Vec<PureExpr>) -> Self {
        PureExpr::MethodCall {
            receiver,
            method,
            turbofish: None,
            args,
        }
    }

    /// Create a Closure with untyped params and no return type annotation.
    pub fn closure(params: Vec<PureClosureParam>, body: Box<PureExpr>) -> Self {
        PureExpr::Closure {
            is_async: false,
            is_move: false,
            params,
            ret: None,
            body,
        }
    }

    // ========== AST Navigation ==========

    /// Get child expression at index.
    ///
    /// Index mapping varies by variant:
    /// - `Binary`: 0=left, 1=right
    /// - `Unary`, `Field`, `Ref`, `Await`, `Try`, `Cast`, `Let`: 0=expr
    /// - `Call`: 0=func, 1..=args
    /// - `MethodCall`: 0=receiver, 1..=args
    /// - `Index`, `Repeat`: 0=expr, 1=index/len
    /// - `Range`: 0=start, 1=end (if present)
    /// - `If`: 0=cond, 1=else_branch (if present)
    /// - `While`, `For`: 0=cond/expr
    /// - `Match`: 0=expr
    /// - `Return`, `Break`: 0=inner (if present)
    /// - `Closure`: 0=body
    /// - `Tuple`, `Array`: 0..n=elements
    /// - `Struct`: 0..n=field values
    /// - Others: None
    pub fn get_child(&self, index: usize) -> Option<&PureExpr> {
        match self {
            // Single child at index 0
            PureExpr::Unary { expr, .. }
            | PureExpr::Field { expr, .. }
            | PureExpr::Ref { expr, .. }
            | PureExpr::Await(expr)
            | PureExpr::Try(expr)
            | PureExpr::Cast { expr, .. }
            | PureExpr::Let { expr, .. } => {
                if index == 0 {
                    Some(expr)
                } else {
                    None
                }
            }

            // Two children
            PureExpr::Binary { left, right, .. } => match index {
                0 => Some(left),
                1 => Some(right),
                _ => None,
            },
            PureExpr::Index { expr, index: idx } => match index {
                0 => Some(expr),
                1 => Some(idx),
                _ => None,
            },
            PureExpr::Repeat { expr, len } => match index {
                0 => Some(expr),
                1 => Some(len),
                _ => None,
            },

            // func/receiver + args
            PureExpr::Call { func, args } => {
                if index == 0 {
                    Some(func)
                } else {
                    args.get(index - 1)
                }
            }
            PureExpr::MethodCall { receiver, args, .. } => {
                if index == 0 {
                    Some(receiver)
                } else {
                    args.get(index - 1)
                }
            }

            // Optional children
            PureExpr::Range { start, end, .. } => match index {
                0 => start.as_deref(),
                1 => end.as_deref(),
                _ => None,
            },
            PureExpr::If {
                cond, else_branch, ..
            } => match index {
                0 => Some(cond),
                1 => else_branch.as_deref(),
                _ => None,
            },
            PureExpr::Return(opt) => {
                if index == 0 {
                    opt.as_deref()
                } else {
                    None
                }
            }
            PureExpr::Break { expr: opt, .. } => {
                if index == 0 {
                    opt.as_deref()
                } else {
                    None
                }
            }

            // Control flow with expr
            PureExpr::While { cond, .. } => {
                if index == 0 {
                    Some(cond)
                } else {
                    None
                }
            }
            PureExpr::For { expr, .. } => {
                if index == 0 {
                    Some(expr)
                } else {
                    None
                }
            }
            PureExpr::Match { expr, .. } => {
                if index == 0 {
                    Some(expr)
                } else {
                    None
                }
            }

            // Closure body
            PureExpr::Closure { body, .. } => {
                if index == 0 {
                    Some(body)
                } else {
                    None
                }
            }

            // Collections
            PureExpr::Tuple(exprs) | PureExpr::Array(exprs) => exprs.get(index),
            PureExpr::Struct { fields, .. } => fields.get(index).map(|(_, e)| e),

            // No direct children (use get_block for Block, Loop, Async, Unsafe)
            PureExpr::Lit(_)
            | PureExpr::Path(_)
            | PureExpr::Block { .. }
            | PureExpr::Loop { .. }
            | PureExpr::Async { .. }
            | PureExpr::Unsafe(_)
            | PureExpr::Continue { .. }
            | PureExpr::Macro { .. }
            | PureExpr::Other(_) => None,
        }
    }

    /// Get mutable child expression at index.
    pub fn get_child_mut(&mut self, index: usize) -> Option<&mut PureExpr> {
        match self {
            PureExpr::Unary { expr, .. }
            | PureExpr::Field { expr, .. }
            | PureExpr::Ref { expr, .. }
            | PureExpr::Await(expr)
            | PureExpr::Try(expr)
            | PureExpr::Cast { expr, .. }
            | PureExpr::Let { expr, .. } => {
                if index == 0 {
                    Some(expr)
                } else {
                    None
                }
            }

            PureExpr::Binary { left, right, .. } => match index {
                0 => Some(left),
                1 => Some(right),
                _ => None,
            },
            PureExpr::Index { expr, index: idx } => match index {
                0 => Some(expr),
                1 => Some(idx),
                _ => None,
            },
            PureExpr::Repeat { expr, len } => match index {
                0 => Some(expr),
                1 => Some(len),
                _ => None,
            },

            PureExpr::Call { func, args } => {
                if index == 0 {
                    Some(func)
                } else {
                    args.get_mut(index - 1)
                }
            }
            PureExpr::MethodCall { receiver, args, .. } => {
                if index == 0 {
                    Some(receiver)
                } else {
                    args.get_mut(index - 1)
                }
            }

            PureExpr::Range { start, end, .. } => match index {
                0 => start.as_deref_mut(),
                1 => end.as_deref_mut(),
                _ => None,
            },
            PureExpr::If {
                cond, else_branch, ..
            } => match index {
                0 => Some(cond.as_mut()),
                1 => else_branch.as_deref_mut(),
                _ => None,
            },
            PureExpr::Return(opt) => {
                if index == 0 {
                    opt.as_deref_mut()
                } else {
                    None
                }
            }
            PureExpr::Break { expr: opt, .. } => {
                if index == 0 {
                    opt.as_deref_mut()
                } else {
                    None
                }
            }

            PureExpr::While { cond, .. } => {
                if index == 0 {
                    Some(cond)
                } else {
                    None
                }
            }
            PureExpr::For { expr, .. } => {
                if index == 0 {
                    Some(expr)
                } else {
                    None
                }
            }
            PureExpr::Match { expr, .. } => {
                if index == 0 {
                    Some(expr)
                } else {
                    None
                }
            }

            PureExpr::Closure { body, .. } => {
                if index == 0 {
                    Some(body)
                } else {
                    None
                }
            }

            PureExpr::Tuple(exprs) | PureExpr::Array(exprs) => exprs.get_mut(index),
            PureExpr::Struct { fields, .. } => fields.get_mut(index).map(|(_, e)| e),

            PureExpr::Lit(_)
            | PureExpr::Path(_)
            | PureExpr::Block { .. }
            | PureExpr::Loop { .. }
            | PureExpr::Async { .. }
            | PureExpr::Unsafe(_)
            | PureExpr::Continue { .. }
            | PureExpr::Macro { .. }
            | PureExpr::Other(_) => None,
        }
    }

    /// Get the contained block (for Block, Loop, Async, Unsafe, If, While, For).
    pub fn get_block(&self) -> Option<&PureBlock> {
        match self {
            PureExpr::Block { block: b, .. }
            | PureExpr::Loop { body: b, .. }
            | PureExpr::Unsafe(b) => Some(b),
            PureExpr::Async { body, .. } => Some(body),
            PureExpr::If { then_branch, .. } => Some(then_branch),
            PureExpr::While { body, .. } | PureExpr::For { body, .. } => Some(body),
            _ => None,
        }
    }

    /// Get mutable contained block.
    pub fn get_block_mut(&mut self) -> Option<&mut PureBlock> {
        match self {
            PureExpr::Block { block: b, .. }
            | PureExpr::Loop { body: b, .. }
            | PureExpr::Unsafe(b) => Some(b),
            PureExpr::Async { body, .. } => Some(body),
            PureExpr::If { then_branch, .. } => Some(then_branch),
            PureExpr::While { body, .. } | PureExpr::For { body, .. } => Some(body),
            _ => None,
        }
    }

    /// Number of direct child expressions.
    pub fn child_count(&self) -> usize {
        match self {
            PureExpr::Lit(_)
            | PureExpr::Path(_)
            | PureExpr::Continue { .. }
            | PureExpr::Macro { .. }
            | PureExpr::Other(_)
            | PureExpr::Block { .. }
            | PureExpr::Loop { .. }
            | PureExpr::Async { .. }
            | PureExpr::Unsafe(_) => 0,

            PureExpr::Unary { .. }
            | PureExpr::Field { .. }
            | PureExpr::Ref { .. }
            | PureExpr::Await(_)
            | PureExpr::Try(_)
            | PureExpr::Cast { .. }
            | PureExpr::Let { .. }
            | PureExpr::Closure { .. }
            | PureExpr::While { .. }
            | PureExpr::For { .. }
            | PureExpr::Match { .. } => 1,

            PureExpr::Binary { .. } | PureExpr::Index { .. } | PureExpr::Repeat { .. } => 2,

            PureExpr::Range { start, end, .. } => start.is_some() as usize + end.is_some() as usize,
            PureExpr::If { else_branch, .. } => 1 + else_branch.is_some() as usize,
            PureExpr::Return(opt) => opt.is_some() as usize,
            PureExpr::Break { expr: opt, .. } => opt.is_some() as usize,

            PureExpr::Call { args, .. } => 1 + args.len(),
            PureExpr::MethodCall { args, .. } => 1 + args.len(),
            PureExpr::Tuple(v) | PureExpr::Array(v) => v.len(),
            PureExpr::Struct { fields, .. } => fields.len(),
        }
    }

    /// Navigate to a nested expression by path (slice of indices).
    ///
    /// # Example
    /// ```ignore
    /// // For: x.foo(a + b, c)
    /// // Path [1, 0] navigates to: args[0].left = `a`
    /// expr.navigate(&[1, 0])
    /// ```
    pub fn navigate(&self, path: &[usize]) -> Option<&PureExpr> {
        let mut current = self;
        for &idx in path {
            current = current.get_child(idx)?;
        }
        Some(current)
    }

    /// Navigate to a nested expression mutably.
    pub fn navigate_mut(&mut self, path: &[usize]) -> Option<&mut PureExpr> {
        let mut current = self;
        for &idx in path {
            current = current.get_child_mut(idx)?;
        }
        Some(current)
    }
}

/// Match arm.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureMatchArm {
    /// Pattern.
    pub pattern: PurePattern,
    /// Guard: `if cond`
    pub guard: Option<PureExpr>,
    /// Body.
    pub body: PureExpr,
}

/// A type.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureType {
    /// Path type: `String`, `std::io::Result<T>`
    Path(String),
    /// Reference: `&T`, `&mut T`, `&'a T`
    Ref {
        /// Optional explicit lifetime (`'a`).
        lifetime: Option<String>,
        /// `mut` qualifier (`&mut`).
        is_mut: bool,
        /// Referent type.
        ty: Box<PureType>,
    },
    /// Tuple: `(A, B, C)`
    Tuple(Vec<PureType>),
    /// Array: `[T; N]`
    Array {
        /// Element type.
        ty: Box<PureType>,
        /// Length expression as a raw string.
        len: String,
    },
    /// Slice: `[T]`
    Slice(Box<PureType>),
    /// Function pointer: `fn(A) -> B`
    Fn {
        /// Parameter types.
        params: Vec<PureType>,
        /// Optional return type (None = unit).
        ret: Option<Box<PureType>>,
    },
    /// Impl trait: `impl Trait`
    ImplTrait(Vec<String>),
    /// Dyn trait: `dyn Trait`
    TraitObject(Vec<String>),
    /// Inferred: `_`
    Infer,
    /// Never: `!`
    Never,
    /// Other (as string).
    Other(String),
}

/// Generic parameters.
#[derive(Debug, Clone, PartialEq, Eq, Default)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureGenerics {
    /// Type parameters.
    pub params: Vec<PureGenericParam>,
    /// Where clause.
    pub where_clause: Vec<String>,
}

/// A generic parameter.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureGenericParam {
    /// Type parameter: `T`, `T: Clone`
    Type {
        /// Parameter name (`T`).
        name: String,
        /// Trait bounds (`Clone + Send`).
        bounds: Vec<String>,
    },
    /// Lifetime: `'a`, `'a: 'b`
    Lifetime {
        /// Lifetime name (`'a`).
        name: String,
        /// Lifetime bounds (`'b`).
        bounds: Vec<String>,
    },
    /// Const: `const N: usize`
    Const {
        /// Const parameter name (`N`).
        name: String,
        /// Const parameter type as a raw string (`usize`).
        ty: String,
    },
}

/// A struct definition.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureStruct {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Name.
    pub name: String,
    /// Generics.
    pub generics: PureGenerics,
    /// Fields.
    pub fields: PureFields,
}

/// Struct fields.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureFields {
    /// Named fields: `{ x: i32, y: i32 }`
    Named(Vec<PureField>),
    /// Tuple fields: `(i32, i32)`
    Tuple(Vec<PureType>),
    /// Unit struct: no fields.
    Unit,
}

/// A struct field.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureField {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Name.
    pub name: String,
    /// Type.
    pub ty: PureType,
}

/// An enum definition.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureEnum {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Name.
    pub name: String,
    /// Generics.
    pub generics: PureGenerics,
    /// Variants.
    pub variants: Vec<PureVariant>,
}

/// An enum variant.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureVariant {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Name.
    pub name: String,
    /// Fields.
    pub fields: PureFields,
    /// Discriminant: `= 1`
    pub discriminant: Option<String>,
}

/// An impl block.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureImpl {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Generics.
    pub generics: PureGenerics,
    /// Whether this is an unsafe impl.
    pub is_unsafe: bool,
    /// Trait being implemented (if any).
    pub trait_: Option<String>,
    /// Type being implemented for.
    pub self_ty: String,
    /// Items in the impl.
    pub items: Vec<PureImplItem>,
}

/// An item in an impl block.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureImplItem {
    /// Method.
    Fn(PureFn),
    /// Const.
    Const(PureConst),
    /// Type alias.
    Type(PureTypeAlias),
    /// Other.
    Other(String),
}

/// A const item.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureConst {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Name.
    pub name: String,
    /// Type.
    pub ty: PureType,
    /// Value expression (None for trait consts without default).
    pub value: Option<PureExpr>,
}

/// A static item.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureStatic {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Is mutable?
    pub is_mut: bool,
    /// Name.
    pub name: String,
    /// Type.
    pub ty: PureType,
    /// Value expression.
    pub value: PureExpr,
}

/// A type alias.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureTypeAlias {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Name.
    pub name: String,
    /// Generics.
    pub generics: PureGenerics,
    /// The aliased type.
    pub ty: PureType,
}

/// A module definition.
///
/// Contains all items belonging to this module.
/// File vs inline distinction is handled at the file system layer,
/// not in the AST representation.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureMod {
    /// Attributes (both outer `#[...]` and inner `#![...]`).
    /// Use `PureAttribute::is_inner` to distinguish.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Module name.
    pub name: String,
    /// Module items.
    pub items: Vec<PureItem>,
}

/// A trait definition.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureTrait {
    /// Attributes.
    pub attrs: Vec<PureAttribute>,
    /// Visibility.
    pub vis: PureVis,
    /// Is unsafe?
    pub is_unsafe: bool,
    /// Is auto?
    pub is_auto: bool,
    /// Name.
    pub name: String,
    /// Generics.
    pub generics: PureGenerics,
    /// Supertraits.
    pub supertraits: Vec<String>,
    /// Items in the trait.
    pub items: Vec<PureTraitItem>,
}

/// An item in a trait.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum PureTraitItem {
    /// Method (with optional default impl).
    Fn(PureFn),
    /// Const.
    Const(PureConst),
    /// Type.
    Type {
        /// Associated type name.
        name: String,
        /// Trait bounds on the associated type.
        bounds: Vec<String>,
        /// Optional default type.
        default: Option<PureType>,
    },
    /// Other.
    Other(String),
}

/// A macro invocation at item level.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct PureMacro {
    /// Macro path.
    pub path: String,
    /// Delimiter used.
    pub delimiter: MacroDelimiter,
    /// Tokens inside (as string).
    pub tokens: String,
}

/// Macro delimiter.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum MacroDelimiter {
    /// `( ... )`
    Paren,
    /// `{ ... }`
    Brace,
    /// `[ ... ]`
    Bracket,
}

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

    #[test]
    fn test_pure_file_send_sync() {
        fn assert_send_sync<T: Send + Sync>() {}
        assert_send_sync::<PureFile>();
    }

    #[test]
    #[cfg(feature = "serde")]
    fn test_serde_json_roundtrip() {
        let file = PureFile::from_source(
            r#"
            use std::io;

            fn hello(name: &str) -> String {
                format!("Hello, {}!", name)
            }

            struct Point {
                x: i32,
                y: i32,
            }
            "#,
        )
        .unwrap();

        // Serialize to JSON
        let json = serde_json::to_string_pretty(&file).unwrap();
        assert!(json.contains("hello"));
        assert!(json.contains("Point"));

        // Deserialize back
        let restored: PureFile = serde_json::from_str(&json).unwrap();
        assert_eq!(file, restored);
    }

    #[test]
    #[cfg(feature = "serde")]
    fn test_serde_compact() {
        let file = PureFile::from_source("fn main() {}").unwrap();

        // Compact JSON
        let json = serde_json::to_string(&file).unwrap();

        // Should be relatively compact
        assert!(json.len() < 500);

        // Roundtrip
        let restored: PureFile = serde_json::from_str(&json).unwrap();
        assert_eq!(file, restored);
    }

    #[test]
    #[cfg(feature = "serde")]
    fn test_serde_complex_ast() {
        let file = PureFile::from_source(
            r#"
            pub struct Config<T: Clone> {
                pub name: String,
                pub value: T,
            }

            impl<T: Clone> Config<T> {
                pub fn new(name: String, value: T) -> Self {
                    Self { name, value }
                }
            }

            pub trait Configurable {
                fn config(&self) -> &str;
            }
            "#,
        )
        .unwrap();

        let json = serde_json::to_string(&file).unwrap();
        let restored: PureFile = serde_json::from_str(&json).unwrap();
        assert_eq!(file, restored);

        // Verify structure preserved
        assert_eq!(restored.structs().len(), 1);
        assert_eq!(restored.structs()[0].name, "Config");
    }

    // ========== Navigation Tests ==========

    #[test]
    fn test_pure_block_navigation() {
        let block = PureBlock {
            stmts: vec![
                PureStmt::Semi(PureExpr::Lit("1".into())),
                PureStmt::Semi(PureExpr::Lit("2".into())),
                PureStmt::Expr(PureExpr::Lit("3".into())),
            ],
        };

        assert_eq!(block.len(), 3);
        assert!(!block.is_empty());

        let stmt0 = block.get_stmt(0).unwrap();
        assert!(matches!(stmt0, PureStmt::Semi(PureExpr::Lit(s)) if s == "1"));

        let stmt2 = block.get_stmt(2).unwrap();
        assert!(matches!(stmt2, PureStmt::Expr(PureExpr::Lit(s)) if s == "3"));

        assert!(block.get_stmt(3).is_none());
    }

    #[test]
    fn test_pure_stmt_get_expr() {
        let semi = PureStmt::Semi(PureExpr::Lit("x".into()));
        assert!(semi.has_expr());
        assert!(matches!(semi.get_expr(), Some(PureExpr::Lit(_))));

        let local_with_init = PureStmt::Local {
            pattern: PurePattern::Ident {
                name: "x".into(),
                is_mut: false,
            },
            ty: None,
            init: Some(PureExpr::Lit("42".into())),
        };
        assert!(local_with_init.has_expr());
        assert!(matches!(local_with_init.get_expr(), Some(PureExpr::Lit(_))));

        let local_no_init = PureStmt::Local {
            pattern: PurePattern::Ident {
                name: "x".into(),
                is_mut: false,
            },
            ty: None,
            init: None,
        };
        assert!(!local_no_init.has_expr());
        assert!(local_no_init.get_expr().is_none());
    }

    #[test]
    fn test_pure_expr_get_child_binary() {
        // a + b
        let expr = PureExpr::Binary {
            op: "+".into(),
            left: Box::new(PureExpr::Path("a".into())),
            right: Box::new(PureExpr::Path("b".into())),
        };

        assert_eq!(expr.child_count(), 2);

        let left = expr.get_child(0).unwrap();
        assert!(matches!(left, PureExpr::Path(s) if s == "a"));

        let right = expr.get_child(1).unwrap();
        assert!(matches!(right, PureExpr::Path(s) if s == "b"));

        assert!(expr.get_child(2).is_none());
    }

    #[test]
    fn test_pure_expr_get_child_method_call() {
        // x.foo(a, b)
        let expr = PureExpr::MethodCall {
            receiver: Box::new(PureExpr::Path("x".into())),
            method: "foo".into(),
            turbofish: None,
            args: vec![PureExpr::Path("a".into()), PureExpr::Path("b".into())],
        };

        assert_eq!(expr.child_count(), 3); // receiver + 2 args

        let receiver = expr.get_child(0).unwrap();
        assert!(matches!(receiver, PureExpr::Path(s) if s == "x"));

        let arg0 = expr.get_child(1).unwrap();
        assert!(matches!(arg0, PureExpr::Path(s) if s == "a"));

        let arg1 = expr.get_child(2).unwrap();
        assert!(matches!(arg1, PureExpr::Path(s) if s == "b"));

        assert!(expr.get_child(3).is_none());
    }

    #[test]
    fn test_pure_expr_navigate() {
        // x.foo(a + b, c)
        let expr = PureExpr::MethodCall {
            receiver: Box::new(PureExpr::Path("x".into())),
            method: "foo".into(),
            turbofish: None,
            args: vec![
                PureExpr::Binary {
                    op: "+".into(),
                    left: Box::new(PureExpr::Path("a".into())),
                    right: Box::new(PureExpr::Path("b".into())),
                },
                PureExpr::Path("c".into()),
            ],
        };

        // Navigate to receiver
        let r = expr.navigate(&[0]).unwrap();
        assert!(matches!(r, PureExpr::Path(s) if s == "x"));

        // Navigate to first arg (a + b)
        let arg0 = expr.navigate(&[1]).unwrap();
        assert!(matches!(arg0, PureExpr::Binary { .. }));

        // Navigate to left of first arg (a)
        let a = expr.navigate(&[1, 0]).unwrap();
        assert!(matches!(a, PureExpr::Path(s) if s == "a"));

        // Navigate to right of first arg (b)
        let b = expr.navigate(&[1, 1]).unwrap();
        assert!(matches!(b, PureExpr::Path(s) if s == "b"));

        // Invalid path
        assert!(expr.navigate(&[1, 2]).is_none());
        assert!(expr.navigate(&[5]).is_none());
    }

    #[test]
    fn test_pure_expr_get_block() {
        let block_expr = PureExpr::Block {
            label: None,
            block: PureBlock {
                stmts: vec![PureStmt::Expr(PureExpr::Lit("1".into()))],
            },
        };
        assert!(block_expr.get_block().is_some());
        assert_eq!(block_expr.get_block().unwrap().len(), 1);

        let lit = PureExpr::Lit("x".into());
        assert!(lit.get_block().is_none());
    }
}