hakorune/src/mir/join_ir/lowering/loop_update_summary.rs

//! Phase 170-C-2: LoopUpdateSummary - ループ更新パターン解析
//!
//! キャリア変数の更新パターン（CounterLike / AccumulationLike）を判定し、
//! CaseALoweringShape の検出精度を向上させる。
//!
//! ## 設計思想
//!
//! - 責務: AST のループ body から「各キャリアがどう更新されているか」を判定
//! - 差し替え可能: 名前ヒューリスティック → AST 解析 → MIR 解析と段階的に精度向上
//! - LoopFeatures / CaseALoweringShape から独立したモジュール
//!
//! ## 使用例
//!
//! ```ignore
//! let summary = analyze_loop_updates(&carrier_names);
//! if summary.has_single_counter() {
//!     // StringExamination パターン
//! }
//! ```

/// キャリア変数の更新パターン
///
/// Phase 170-C-2: 3種類のパターンを区別
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum UpdateKind {
    /// カウンタ系: i = i + 1, i = i - 1, i += 1
    ///
    /// 典型的な skip/trim パターン。進捗変数として使われる。
    CounterLike,

    /// 蓄積系: result = result + x, arr.push(x), list.append(x)
    ///
    /// 典型的な collect/filter パターン。結果を蓄積する変数。
    AccumulationLike,

    /// 判定不能
    ///
    /// 複雑な更新パターン、または解析できなかった場合。
    Other,
}

impl UpdateKind {
    /// デバッグ用の名前を返す
    pub fn name(&self) -> &'static str {
        match self {
            UpdateKind::CounterLike => "CounterLike",
            UpdateKind::AccumulationLike => "AccumulationLike",
            UpdateKind::Other => "Other",
        }
    }
}

/// 単一キャリアの更新情報
#[derive(Debug, Clone)]
pub struct CarrierUpdateInfo {
    /// キャリア変数名
    pub name: String,

    /// 更新パターン
    pub kind: UpdateKind,

    /// Phase 213: Then branch update expression (for Pattern 3 if-sum)
    /// e.g., for "if (cond) { sum = sum + 1 }", then_expr is "sum + 1"
    #[allow(dead_code)]
    pub then_expr: Option<crate::ast::ASTNode>,

    /// Phase 213: Else branch update expression (for Pattern 3 if-sum)
    /// e.g., for "else { sum = sum + 0 }", else_expr is "sum + 0"
    /// If no else branch, this can be the identity update (e.g., "sum")
    #[allow(dead_code)]
    pub else_expr: Option<crate::ast::ASTNode>,
}

/// ループ全体の更新サマリ
///
/// Phase 170-C-2: CaseALoweringShape の判定入力として使用
#[derive(Debug, Clone, Default)]
pub struct LoopUpdateSummary {
    /// 各キャリアの更新情報
    pub carriers: Vec<CarrierUpdateInfo>,
}

impl LoopUpdateSummary {
    /// 空のサマリを作成
    pub fn empty() -> Self {
        Self { carriers: vec![] }
    }

    /// 単一 CounterLike キャリアを持つか
    ///
    /// StringExamination パターンの判定に使用
    pub fn has_single_counter(&self) -> bool {
        self.carriers.len() == 1 && self.carriers[0].kind == UpdateKind::CounterLike
    }

    /// AccumulationLike キャリアを含むか
    ///
    /// ArrayAccumulation パターンの判定に使用
    pub fn has_accumulation(&self) -> bool {
        self.carriers
            .iter()
            .any(|c| c.kind == UpdateKind::AccumulationLike)
    }

    /// CounterLike キャリアの数
    pub fn counter_count(&self) -> usize {
        self.carriers
            .iter()
            .filter(|c| c.kind == UpdateKind::CounterLike)
            .count()
    }

    /// AccumulationLike キャリアの数
    pub fn accumulation_count(&self) -> usize {
        self.carriers
            .iter()
            .filter(|c| c.kind == UpdateKind::AccumulationLike)
            .count()
    }

    /// Phase 213: Check if this is a simple if-sum pattern
    ///
    /// Simple if-sum pattern:
    /// - Has exactly 1 CounterLike carrier (loop index, e.g., "i")
    /// - Has exactly 1 AccumulationLike carrier (accumulator, e.g., "sum")
    /// - Optionally has additional accumulators (e.g., "count")
    ///
    /// Examples:
    /// - `loop(i < len) { if cond { sum = sum + 1 } i = i + 1 }` ✅
    /// - `loop(i < len) { if cond { sum = sum + 1; count = count + 1 } i = i + 1 }` ✅
    /// - `loop(i < len) { result = result + data[i]; i = i + 1 }` ❌ (no if statement)
    pub fn is_simple_if_sum_pattern(&self) -> bool {
        let counter_count = self.counter_count();
        let accumulation_count = self.accumulation_count();

        // Must have exactly 1 counter (loop index)
        if counter_count != 1 {
            return false;
        }
        // Must have at least 1 accumulator (sum)
        if accumulation_count < 1 {
            return false;
        }
        // For now, only support up to 2 accumulators (sum, count)
        // This matches the Phase 212 if-sum minimal test case
        if accumulation_count > 2 {
            return false;
        }

        true
    }
}

/// Phase 219: Extract all assigned variable names from loop body AST
///
/// Returns a set of variable names that are assigned (LHS) in the loop body.
/// This prevents phantom carriers from non-assigned variables.
fn extract_assigned_variables(loop_body: &[crate::ast::ASTNode]) -> std::collections::HashSet<String> {
    use crate::ast::ASTNode;
    let mut assigned = std::collections::HashSet::new();

    fn visit_node(node: &ASTNode, assigned: &mut std::collections::HashSet<String>) {
        match node {
            // Direct assignment: target = value
            ASTNode::Assignment { target, value, .. } => {
                if let ASTNode::Variable { name, .. } = target.as_ref() {
                    assigned.insert(name.clone());
                }
                // Recurse into value (for nested assignments)
                visit_node(value, assigned);
            }
            // If statement: recurse into then/else branches
            ASTNode::If { then_body, else_body, .. } => {
                for stmt in then_body {
                    visit_node(stmt, assigned);
                }
                if let Some(else_stmts) = else_body {
                    for stmt in else_stmts {
                        visit_node(stmt, assigned);
                    }
                }
            }
            // Loop statement: recurse into body (for nested loops)
            ASTNode::Loop { body, .. } => {
                for stmt in body {
                    visit_node(stmt, assigned);
                }
            }
            // Other nodes: no assignment tracking needed
            _ => {}
        }
    }

    for stmt in loop_body {
        visit_node(stmt, &mut assigned);
    }

    assigned
}

/// Phase 219: Classify update kind from RHS expression structure
///
/// Returns UpdateKind based on RHS pattern, NOT variable name.
fn classify_update_kind_from_rhs(rhs: &crate::ast::ASTNode) -> UpdateKind {
    use crate::ast::{ASTNode, BinaryOperator, LiteralValue};

    match rhs {
        // x = x + 1 → CounterLike
        // x = x + n → AccumulationLike (where n is not 1)
        ASTNode::BinaryOp { operator, left, right, .. } => {
            if matches!(operator, BinaryOperator::Add) {
                // Check if left is self-reference (will be validated by caller)
                if matches!(left.as_ref(), ASTNode::Variable { .. }) {
                    // Check right operand
                    if let ASTNode::Literal { value, .. } = right.as_ref() {
                        if let LiteralValue::Integer(n) = value {
                            if *n == 1 {
                                return UpdateKind::CounterLike;  // x = x + 1
                            } else {
                                return UpdateKind::AccumulationLike;  // x = x + n
                            }
                        }
                    } else {
                        // x = x + expr (variable accumulation)
                        return UpdateKind::AccumulationLike;
                    }
                }
            }
            UpdateKind::Other
        }
        _ => UpdateKind::Other,
    }
}

/// Phase 219: Analyze loop updates from loop body AST (assignment-based)
///
/// # New Design (Phase 219)
///
/// - Takes loop body AST as input (not just carrier names)
/// - Only analyzes variables that are ASSIGNED in loop body
/// - Uses RHS structure analysis (NOT name heuristics)
///
/// # Arguments
///
/// * `carrier_names` - Candidate carrier variable names from scope
/// * `loop_body` - Loop body AST for assignment detection
///
/// # Returns
///
/// LoopUpdateSummary with only actually-assigned carriers
/// Phase 219: Extract assignment RHS for a given variable
///
/// Returns the RHS expression of the first assignment to `var_name` in loop body.
fn find_assignment_rhs<'a>(var_name: &str, loop_body: &'a [crate::ast::ASTNode]) -> Option<&'a crate::ast::ASTNode> {
    use crate::ast::ASTNode;

    fn visit_node<'a>(var_name: &str, node: &'a ASTNode) -> Option<&'a ASTNode> {
        match node {
            ASTNode::Assignment { target, value, .. } => {
                if let ASTNode::Variable { name, .. } = target.as_ref() {
                    if name == var_name {
                        return Some(value.as_ref());
                    }
                }
                // Recurse into value
                visit_node(var_name, value)
            }
            ASTNode::If { then_body, else_body, .. } => {
                for stmt in then_body {
                    if let Some(rhs) = visit_node(var_name, stmt) {
                        return Some(rhs);
                    }
                }
                if let Some(else_stmts) = else_body {
                    for stmt in else_stmts {
                        if let Some(rhs) = visit_node(var_name, stmt) {
                            return Some(rhs);
                        }
                    }
                }
                None
            }
            ASTNode::Loop { body, .. } => {
                for stmt in body {
                    if let Some(rhs) = visit_node(var_name, stmt) {
                        return Some(rhs);
                    }
                }
                None
            }
            _ => None,
        }
    }

    for stmt in loop_body {
        if let Some(rhs) = visit_node(var_name, stmt) {
            return Some(rhs);
        }
    }
    None
}

/// Phase 219: Check if variable name looks like loop index
///
/// Simple heuristic: single-letter names (i, j, k, e) or "index"/"idx"
fn is_likely_loop_index(name: &str) -> bool {
    matches!(name, "i" | "j" | "k" | "e" | "idx" | "index" | "pos" | "n")
}

pub fn analyze_loop_updates_from_ast(
    carrier_names: &[String],
    loop_body: &[crate::ast::ASTNode],
) -> LoopUpdateSummary {
    // Phase 219-1: Extract assigned variables from loop body
    let assigned_vars = extract_assigned_variables(loop_body);

    // Phase 219-2: Filter carriers to only assigned ones and classify by RHS
    let mut carriers = Vec::new();
    for name in carrier_names {
        if assigned_vars.contains(name) {
            // Phase 219-3: Classify by variable name + RHS structure
            // - Loop index-like names (i, j, k) with `x = x + 1` → CounterLike
            // - Other names with `x = x + 1` or `x = x + expr` → AccumulationLike
            let kind = if is_likely_loop_index(name) {
                UpdateKind::CounterLike
            } else if let Some(rhs) = find_assignment_rhs(name, loop_body) {
                let classified = classify_update_kind_from_rhs(rhs);
                match classified {
                    UpdateKind::CounterLike => UpdateKind::AccumulationLike, // Override: non-index + `x=x+1` → accumulation
                    other => other,
                }
            } else {
                UpdateKind::Other
            };

            carriers.push(CarrierUpdateInfo {
                name: name.clone(),
                kind,
                then_expr: None,
                else_expr: None,
            });
        }
    }

    LoopUpdateSummary { carriers }
}

/// Phase 219: Legacy wrapper for backward compatibility
///
/// # Deprecated (Phase 219)
///
/// This function uses name-based heuristics and is deprecated.
/// Use `analyze_loop_updates_from_ast()` instead.
///
/// # Arguments
///
/// * `carrier_names` - キャリア変数名のリスト
///
/// # Returns
///
/// 各キャリアの更新パターンをまとめた LoopUpdateSummary
#[deprecated(since = "Phase 219", note = "Use analyze_loop_updates_from_ast() instead")]
pub fn analyze_loop_updates(carrier_names: &[String]) -> LoopUpdateSummary {
    // Phase 219: Fallback to simple heuristic (for legacy call sites)
    // This will be removed once all call sites are migrated
    let carriers = carrier_names
        .iter()
        .map(|name| CarrierUpdateInfo {
            name: name.clone(),
            kind: UpdateKind::AccumulationLike,  // Default to accumulation
            then_expr: None,
            else_expr: None,
        })
        .collect();

    LoopUpdateSummary { carriers }
}

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

    #[test]
    fn test_update_kind_name() {
        assert_eq!(UpdateKind::CounterLike.name(), "CounterLike");
        assert_eq!(UpdateKind::AccumulationLike.name(), "AccumulationLike");
        assert_eq!(UpdateKind::Other.name(), "Other");
    }

    #[test]
    fn test_typical_index_names() {
        assert!(is_typical_index_name("i"));
        assert!(is_typical_index_name("idx"));
        assert!(is_typical_index_name("pos"));
        assert!(!is_typical_index_name("result"));
        assert!(!is_typical_index_name("sum"));
    }

    #[test]
    fn test_analyze_single_counter() {
        let names = vec!["i".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(summary.has_single_counter());
        assert!(!summary.has_accumulation());
        assert_eq!(summary.counter_count(), 1);
    }

    #[test]
    fn test_analyze_accumulation() {
        let names = vec!["result".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(!summary.has_single_counter());
        assert!(summary.has_accumulation());
        assert_eq!(summary.accumulation_count(), 1);
    }

    #[test]
    fn test_analyze_mixed() {
        let names = vec!["i".to_string(), "sum".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(!summary.has_single_counter()); // 2つあるので false
        assert!(summary.has_accumulation());
        assert_eq!(summary.counter_count(), 1);
        assert_eq!(summary.accumulation_count(), 1);
    }

    // Phase 213 tests for is_simple_if_sum_pattern
    #[test]
    fn test_is_simple_if_sum_pattern_basic() {
        // phase212_if_sum_min.hako pattern: i (counter) + sum (accumulator)
        let names = vec!["i".to_string(), "sum".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(summary.is_simple_if_sum_pattern());
    }

    #[test]
    fn test_is_simple_if_sum_pattern_with_count() {
        // Phase 195 pattern: i (counter) + sum + count (2 accumulators)
        let names = vec!["i".to_string(), "sum".to_string(), "count".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(summary.is_simple_if_sum_pattern());
    }

    #[test]
    fn test_is_simple_if_sum_pattern_no_accumulator() {
        // Only counter, no accumulator
        let names = vec!["i".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(!summary.is_simple_if_sum_pattern()); // No accumulator
    }

    #[test]
    fn test_is_simple_if_sum_pattern_no_counter() {
        // Only accumulator, no counter
        let names = vec!["sum".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(!summary.is_simple_if_sum_pattern()); // No counter
    }

    #[test]
    fn test_is_simple_if_sum_pattern_multiple_counters() {
        // Multiple counters (not supported)
        let names = vec!["i".to_string(), "j".to_string(), "sum".to_string()];
        let summary = analyze_loop_updates(&names);

        assert!(!summary.is_simple_if_sum_pattern()); // 2 counters
    }
}