lambdust 0.1.1

//! Main macro expander implementation.
//!
//! This module contains the core macro expansion logic that coordinates
//! pattern matching, template expansion, and hygiene preservation.

use super::{MacroEnvironment, Pattern, Template, HygieneContext, PatternBindings};
use crate::ast::Expr;
use crate::diagnostics::{Error, Result, Span, Spanned};
// use std::collections::HashMap;

/// Configuration for macro expansion behavior.
#[derive(Debug, Clone)]
pub struct ExpansionConfig {
    /// Maximum depth for macro expansion
    pub max_depth: usize,
    /// Whether to enable hygiene preservation
    pub hygiene_enabled: bool,
    /// Whether to collect expansion statistics
    pub collect_stats: bool,
}

impl Default for ExpansionConfig {
    fn default() -> Self {
        Self {
            max_depth: 100,
            hygiene_enabled: true,
            collect_stats: false,
        }
    }
}

/// Statistics collected during macro expansion.
#[derive(Debug, Clone, Default)]
pub struct ExpansionStats {
    /// Number of macro expansions performed
    pub expansions: usize,
    /// Maximum expansion depth reached
    pub max_depth_reached: usize,
    /// Number of hygiene renamings performed
    pub hygiene_renamings: usize,
}

/// Core macro expander that handles pattern matching and template expansion.
pub struct ConfigurableExpander {
    /// Macro environment for looking up macro definitions
    pub macro_env: MacroEnvironment,
    /// Current expansion depth
    pub expansion_depth: usize,
    /// Maximum allowed expansion depth
    pub max_expansion_depth: usize,
    /// Hygiene context for identifier management
    pub hygiene_context: HygieneContext,
    /// Configuration for expansion behavior
    pub config: ExpansionConfig,
    /// Statistics collected during expansion
    pub stats: ExpansionStats,
}

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

impl ConfigurableExpander {
    /// Creates a new macro expander with default settings.
    pub fn new() -> Self {
        Self {
            macro_env: MacroEnvironment::new(),
            expansion_depth: 0,
            max_expansion_depth: 100,
            hygiene_context: HygieneContext::new(),
            config: ExpansionConfig::default(),
            stats: ExpansionStats::default(),
        }
    }

    /// Creates a new macro expander with custom configuration.
    pub fn with_config(config: ExpansionConfig) -> Self {
        Self {
            macro_env: MacroEnvironment::new(),
            expansion_depth: 0,
            max_expansion_depth: config.max_depth,
            hygiene_context: HygieneContext::new(),
            config,
            stats: ExpansionStats::default(),
        }
    }

    /// Expands a macro by matching patterns and expanding templates.
    pub fn expand_macro(
        &mut self,
        transformer: &SyntaxTransformer,
        args: &[Spanned<Expr>],
        span: Span,
    ) -> Result<Spanned<Expr>> {
        // Try each rule in the syntax transformer
        for rule in &transformer.rules {
            // For now, do a simple pattern match - this will need to be improved
            // for full macro support
            let mut bindings = crate::macro_system::PatternBindings::new();
            if self.try_match_simple_pattern(&rule.pattern, args, &mut bindings).is_ok() {
                // Pattern matched, expand the template
                let expanded = rule.template.expand(&bindings, span)?;
                
                // Apply hygiene if enabled
                if self.config.hygiene_enabled {
                    // Create a dummy environment for hygiene context
                    use crate::eval::Environment;
                    let env = Environment::new(None, 0);
                    let renamed_expr = self.hygiene_context.rename_identifiers(
                        expanded.clone(),
                        &env
                    )?;
                    if self.config.collect_stats {
                        self.stats.hygiene_renamings += 1;
                    }
                    return Ok(renamed_expr);
                }
                
                return Ok(expanded);
            }
        }
        
        Err(Box::new(Error::macro_error(
            "No matching pattern for macro".to_string(),
            span,
        )))
    }

    /// Resets the expander state for a new expansion session.
    pub fn reset(&mut self) {
        self.expansion_depth = 0;
        self.stats = ExpansionStats::default();
    }

    /// Returns the current expansion statistics.
    pub fn stats(&self) -> &ExpansionStats {
        &self.stats
    }

    /// Simple pattern matching helper (to be replaced with full pattern matching)
    fn try_match_simple_pattern(
        &self,
        _pattern: &Pattern,
        _args: &[Spanned<Expr>],
        _bindings: &mut PatternBindings,
    ) -> Result<()> {
        // For now, just return Ok to allow compilation
        // This needs to be implemented properly for full macro support
        Ok(())
    }
}

/// A syntax transformer that contains pattern-template rules.
#[derive(Debug, Clone)]
pub struct SyntaxTransformer {
    /// The rules for this transformer
    pub rules: Vec<SyntaxRule>,
    /// Optional name for debugging
    pub name: Option<String>,
}

/// A single syntax rule with a pattern and template.
#[derive(Debug, Clone)]
pub struct SyntaxRule {
    /// Pattern to match against
    pub pattern: Pattern,
    /// Template to expand with
    pub template: Template,
}

impl SyntaxTransformer {
    /// Creates a new syntax transformer with the given rules.
    pub fn new(rules: Vec<SyntaxRule>) -> Self {
        Self {
            rules,
            name: None,
        }
    }

    /// Creates a new syntax transformer with a name.
    pub fn with_name(rules: Vec<SyntaxRule>, name: String) -> Self {
        Self {
            rules,
            name: Some(name),
        }
    }
}

impl SyntaxRule {
    /// Creates a new syntax rule with the given pattern and template.
    pub fn new(pattern: Pattern, template: Template) -> Self {
        Self { pattern, template }
    }
}