hakorune/src/mir/loop_pattern_detection.rs

//! Loop Pattern Detection Module
//!
//! Phase 188 Task 188-4: Pattern detection helpers for JoinIR loop lowering.
//!
//! This module provides detection functions for 4 loop patterns:
//! - Pattern 1: Simple While Loop (foundational)
//! - Pattern 2: Loop with Conditional Break (early exit)
//! - Pattern 3: Loop with If-Else PHI (variable mutation)
//! - Pattern 4: Loop with Continue (skip iteration)
//!
//! Phase 194+: Structure-based detection using LoopFeatures.
//! Patterns are classified based on CFG structure, not function names.
//!
//! # Architecture
//!
//! ```
//! LoopForm → extract_features() → LoopFeatures → classify() → LoopPatternKind
//! ```
//!
//! Reference: docs/private/roadmap2/phases/phase-188-joinir-loop-pattern-expansion/design.md

use crate::mir::loop_form::LoopForm;
use crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape;

// ============================================================================
// Pattern Classification System (Phase 194+)
// ============================================================================

/// Loop pattern classification based on structure.
///
/// This enum represents the 4 main loop patterns we support.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum LoopPatternKind {
    /// Pattern 1: Simple While Loop
    /// - No break, no continue
    /// - Single backedge
    Pattern1SimpleWhile,

    /// Pattern 2: Loop with Conditional Break
    /// - Has break statement(s)
    /// - No continue statements
    Pattern2Break,

    /// Pattern 3: Loop with If-Else PHI
    /// - Has if-else statement with PHI
    /// - No break, no continue
    /// - Multiple carrier variables
    Pattern3IfPhi,

    /// Pattern 4: Loop with Continue
    /// - Has continue statement(s)
    /// - No break statements (for simplicity)
    Pattern4Continue,

    /// Pattern not recognized
    Unknown,
}

impl LoopPatternKind {
    /// Phase 193-3: Get human-readable pattern name
    ///
    /// Returns the friendly name for this pattern (e.g., "Pattern 1: Simple While")
    pub fn name(&self) -> &'static str {
        match self {
            LoopPatternKind::Pattern1SimpleWhile => "Pattern 1: Simple While Loop",
            LoopPatternKind::Pattern2Break => "Pattern 2: Loop with Conditional Break",
            LoopPatternKind::Pattern3IfPhi => "Pattern 3: Loop with If-Else PHI",
            LoopPatternKind::Pattern4Continue => "Pattern 4: Loop with Continue",
            LoopPatternKind::Unknown => "Unknown Pattern",
        }
    }

    /// Phase 193-3: Get numeric pattern ID
    ///
    /// Returns the pattern number (1-4) or 0 for unknown.
    /// Useful for priority sorting.
    pub fn pattern_id(&self) -> u8 {
        match self {
            LoopPatternKind::Pattern1SimpleWhile => 1,
            LoopPatternKind::Pattern2Break => 2,
            LoopPatternKind::Pattern3IfPhi => 3,
            LoopPatternKind::Pattern4Continue => 4,
            LoopPatternKind::Unknown => 0,
        }
    }

    /// Phase 193-3: Check if this is a recognized pattern
    ///
    /// Returns false only for Unknown.
    pub fn is_recognized(&self) -> bool {
        !matches!(self, LoopPatternKind::Unknown)
    }

    /// Phase 193-3: Check if pattern has special control flow
    ///
    /// Returns true if pattern involves break or continue.
    pub fn has_special_control_flow(&self) -> bool {
        matches!(
            self,
            LoopPatternKind::Pattern2Break | LoopPatternKind::Pattern4Continue
        )
    }

    /// Phase 193-3: Check if pattern involves PHI merging
    ///
    /// Returns true if pattern has if-else PHI merge.
    pub fn has_phi_merge(&self) -> bool {
        matches!(self, LoopPatternKind::Pattern3IfPhi)
    }
}

/// Feature vector extracted from loop structure.
///
/// This structure captures all relevant properties needed for pattern classification.
/// It is name-agnostic and purely structure-based.
#[derive(Debug, Clone)]
pub struct LoopFeatures {
    /// Has break statement(s)?
    pub has_break: bool,

    /// Has continue statement(s)?
    pub has_continue: bool,

    /// Has if statement(s) in body?
    pub has_if: bool,

    /// Has if-else statement with PHI nodes?
    /// (detected via multiple carriers or specific CFG patterns)
    pub has_if_else_phi: bool,

    /// Number of carrier variables (loop variables that are updated)
    pub carrier_count: usize,

    /// Number of break targets
    pub break_count: usize,

    /// Number of continue targets
    pub continue_count: usize,

    /// Phase 170-C-2b: Carrier update pattern summary
    ///
    /// Contains UpdateKind (CounterLike/AccumulationLike/Other) for each carrier.
    /// Used by CaseALoweringShape for more precise shape detection.
    /// None if carrier names are not available.
    pub update_summary: Option<crate::mir::join_ir::lowering::loop_update_summary::LoopUpdateSummary>,
}

impl LoopFeatures {
    /// Phase 193-3: Get debug statistics string
    ///
    /// Returns a formatted string showing all feature values for debugging.
    pub fn debug_stats(&self) -> String {
        format!(
            "LoopFeatures {{ break: {}, continue: {}, if: {}, if_else_phi: {}, carriers: {}, break_count: {}, continue_count: {} }}",
            self.has_break,
            self.has_continue,
            self.has_if,
            self.has_if_else_phi,
            self.carrier_count,
            self.break_count,
            self.continue_count
        )
    }

    /// Phase 193-3: Count total control flow divergences
    ///
    /// Returns the total number of break + continue targets.
    /// Useful for determining loop complexity.
    pub fn total_divergences(&self) -> usize {
        self.break_count + self.continue_count
    }

    /// Phase 193-3: Check if loop has complex control flow
    ///
    /// Returns true if loop has multiple divergences or multiple carriers.
    pub fn is_complex(&self) -> bool {
        self.total_divergences() > 1 || self.carrier_count > 1
    }

    /// Phase 193-3: Check if loop is simple (no special features)
    ///
    /// Returns true if loop is purely sequential.
    pub fn is_simple(&self) -> bool {
        !self.has_break && !self.has_continue && !self.has_if_else_phi && self.carrier_count <= 1
    }
}

/// Extract features from LoopForm for pattern classification.
///
/// This function is the entry point for structure-based pattern detection.
/// It analyzes the CFG structure without relying on variable names.
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
/// * `scope` - Optional LoopScopeShape for carrier analysis
///
/// # Returns
/// * `LoopFeatures` - Feature vector for pattern classification
pub fn extract_features(loop_form: &LoopForm, scope: Option<&LoopScopeShape>) -> LoopFeatures {
    // Phase 194: Basic feature extraction from LoopForm
    let has_break = !loop_form.break_targets.is_empty();
    let has_continue = !loop_form.continue_targets.is_empty();
    let break_count = loop_form.break_targets.len();
    let continue_count = loop_form.continue_targets.len();

    // Phase 194+: Extract carrier_count from LoopScopeShape if available
    let carrier_count = scope.map(|s| s.carriers.len()).unwrap_or(0);

    // Pattern 3 heuristic: has_if_else_phi if carrier_count > 1
    // This is a conservative heuristic - multiple carriers typically
    // indicate if-else statements with PHI nodes.
    let has_if_else_phi = carrier_count > 1;

    // TODO: Implement has_if detection via CFG analysis
    // For now, we infer it from carrier_count > 1 (Pattern 3 heuristic)
    let has_if = has_if_else_phi;

    // Phase 170-C-2b: Build update_summary from carrier names
    // Note: carriers is BTreeSet<String>, so each item is already a String
    let update_summary = scope.map(|s| {
        let carrier_names: Vec<String> = s.carriers.iter().cloned().collect();
        crate::mir::join_ir::lowering::loop_update_summary::analyze_loop_updates(&carrier_names)
    });

    LoopFeatures {
        has_break,
        has_continue,
        has_if,
        has_if_else_phi,
        carrier_count,
        break_count,
        continue_count,
        update_summary,
    }
}

/// Classify loop pattern based on feature vector.
///
/// This function implements the pattern classification logic using
/// structure-based rules. It does NOT depend on function names or
/// variable names like "sum".
///
/// # Pattern Classification Rules
///
/// 1. **Pattern 4 (Continue)**: `has_continue == true`
///    - Priority: Check first (most specific)
///
/// 2. **Pattern 3 (If-Else PHI)**: `has_if_else_phi && !has_break && !has_continue`
///    - Multiple carriers indicate if-else with PHI
///
/// 3. **Pattern 2 (Break)**: `has_break && !has_continue`
///    - Has break but no continue
///
/// 4. **Pattern 1 (Simple While)**: `!has_break && !has_continue && !has_if_else_phi`
///    - No control flow alterations
///
/// # Arguments
/// * `features` - Feature vector from extract_features()
///
/// # Returns
/// * `LoopPatternKind` - Classified pattern
pub fn classify(features: &LoopFeatures) -> LoopPatternKind {
    // Pattern 4: Continue (highest priority)
    if features.has_continue {
        return LoopPatternKind::Pattern4Continue;
    }

    // Pattern 3: If-Else PHI (check before Pattern 1)
    if features.has_if_else_phi && !features.has_break && !features.has_continue {
        return LoopPatternKind::Pattern3IfPhi;
    }

    // Pattern 2: Break
    if features.has_break && !features.has_continue {
        return LoopPatternKind::Pattern2Break;
    }

    // Pattern 1: Simple While
    if !features.has_break && !features.has_continue && !features.has_if_else_phi {
        return LoopPatternKind::Pattern1SimpleWhile;
    }

    // Unknown pattern
    LoopPatternKind::Unknown
}

/// Phase 193-3: Diagnose pattern classification with details
///
/// This function performs classification AND generates diagnostic information.
/// Useful for debugging and logging.
///
/// # Returns
/// * `(LoopPatternKind, String)` - The classified pattern and a diagnostic message
pub fn classify_with_diagnosis(features: &LoopFeatures) -> (LoopPatternKind, String) {
    let pattern = classify(features);
    let reason = match pattern {
        LoopPatternKind::Pattern4Continue => {
            format!(
                "Has continue statement (continue_count={})",
                features.continue_count
            )
        }
        LoopPatternKind::Pattern3IfPhi => {
            format!(
                "Has if-else PHI with {} carriers, no break/continue",
                features.carrier_count
            )
        }
        LoopPatternKind::Pattern2Break => {
            format!(
                "Has break statement (break_count={}), no continue",
                features.break_count
            )
        }
        LoopPatternKind::Pattern1SimpleWhile => {
            "Simple while loop with no special control flow".to_string()
        }
        LoopPatternKind::Unknown => {
            format!(
                "Unknown pattern: {}",
                features.debug_stats()
            )
        }
    };

    (pattern, reason)
}

// ============================================================================
// Legacy Detection Functions (Phase 188)
// ============================================================================

// ============================================================================
// Pattern 1: Simple While Loop
// ============================================================================

/// Detect Pattern 1: Simple While Loop
///
/// Returns true ONLY if:
/// - Loop condition is simple comparison (no &&, ||)
/// - Loop body contains only assignments + prints (no nested loops, no breaks)
/// - Loop has single increment/decrement
/// - NO break statements (break_targets is empty)
/// - NO continue statements (continue_targets is empty)
/// - Single backedge (latches.len() == 1)
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
///
/// # Returns
/// * `true` if the loop matches Pattern 1 (Simple While), `false` otherwise
///
/// # Reference
/// See design.md § Pattern 1 → LoopScopeShape Recognition
///
/// # Example
/// ```rust,ignore
/// let loop_form = /* ... */;
/// if is_simple_while_pattern(&loop_form) {
///     // Lower to simple while pattern
/// }
/// ```
pub fn is_simple_while_pattern(loop_form: &LoopForm) -> bool {
    // Pattern 1 Recognition Criteria (from design.md § Pattern 1):
    // 1. break_targets: EMPTY (no break statements)
    // 2. continue_targets: EMPTY (no continue statements)
    // 3. Single backedge (single latch - LoopShape has singular latch field)
    //
    // Note: LoopShape has a singular `latch` field, not `latches`, so we don't
    // need to check length. The existence of a LoopShape implies a valid latch.

    // Check 1: No break statements
    if !loop_form.break_targets.is_empty() {
        return false;
    }

    // Check 2: No continue statements
    if !loop_form.continue_targets.is_empty() {
        return false;
    }

    // Check 3: All other checks passed
    // The LoopShape structure guarantees:
    // - Single preheader, header, body, latch, exit
    // - Valid loop structure
    //
    // Pattern 1 ONLY requires:
    // - No breaks, no continues
    // - Natural loop structure (which LoopShape guarantees)
    //
    // Advanced checks (nested loops, complex conditions) are deferred to
    // lowering phase where we can fail gracefully if needed.

    true
}

// ============================================================================
// Pattern 2: Loop with Conditional Break
// ============================================================================

/// Detect Pattern 2: Loop with Conditional Break
///
/// Returns true ONLY if:
/// - Loop condition exists
/// - Loop body contains exactly ONE if statement with break
/// - Break is in then-branch
/// - NO nested loops
/// - break_targets is NON-EMPTY (has at least one break)
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
///
/// # Returns
/// * `true` if the loop matches Pattern 2 (Break), `false` otherwise
///
/// # Reference
/// See design.md § Pattern 2 → LoopScopeShape Recognition
///
/// # Example
/// ```rust,ignore
/// let loop_form = /* ... */;
/// if is_loop_with_break_pattern(&loop_form) {
///     // Lower to loop with break pattern
/// }
/// ```
pub fn is_loop_with_break_pattern(loop_form: &LoopForm) -> bool {
    // Pattern 2 Recognition Criteria (from design.md § Pattern 2):
    // 1. break_targets: NON-EMPTY (at least 1 break)
    // 2. continue_targets: EMPTY (for simplicity)
    // 3. Exactly ONE break target
    //
    // Phase 188-Impl-2: Minimal implementation
    // Advanced checks (nested loops, if-statement structure) are deferred to
    // lowering phase where we can fail gracefully if needed.

    // Check 1: break_targets is NON-EMPTY (has at least 1 break)
    if loop_form.break_targets.is_empty() {
        return false;
    }

    // Check 2: Exactly ONE break target (pattern assumes single break)
    if loop_form.break_targets.len() != 1 {
        return false;
    }

    // Check 3: No continue statements (for simplicity in Pattern 2)
    if !loop_form.continue_targets.is_empty() {
        return false;
    }

    // Pattern 2 matched
    // The LoopForm structure guarantees:
    // - Valid loop structure
    // - Single break target
    // - No continues
    //
    // Advanced checks (break is in if-statement, etc.) are deferred to
    // lowering phase for graceful failure.

    true
}

// ============================================================================
// Pattern 3: Loop with If-Else PHI
// ============================================================================

/// Detect Pattern 3: Loop with If-Else PHI
///
/// Returns true ONLY if:
/// - Loop has if-else statement assigning to variable(s)
/// - Both branches assign to same variable
/// - NO nested loops
/// - NO break or continue statements
/// - Loop has multiple carrier variables (e.g., i + sum)
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
///
/// # Returns
/// * `true` if the loop matches Pattern 3 (If-Else PHI), `false` otherwise
///
/// # Reference
/// See design.md § Pattern 3 → LoopScopeShape Recognition
///
/// # Example
/// ```rust,ignore
/// let loop_form = /* ... */;
/// if is_loop_with_conditional_phi_pattern(&loop_form) {
///     // Lower to loop with if-else phi pattern
/// }
/// ```
pub fn is_loop_with_conditional_phi_pattern(loop_form: &LoopForm) -> bool {
    // Phase 188-Impl-3: Minimal implementation
    // Pattern 3 Recognition Criteria (from design.md § Pattern 3):
    // 1. break_targets: EMPTY (no break statements)
    // 2. continue_targets: EMPTY (no continue statements)
    // 3. All Pattern 3 loops are valid Pattern 1 loops with extra PHI nodes
    //
    // For now: return true as fallback for Pattern 1 loops
    // Advanced checks (if-else detection, multiple carriers) are deferred to
    // lowering phase where we can fail gracefully if needed.

    // Check 1: No break statements
    if !loop_form.break_targets.is_empty() {
        return false;
    }

    // Check 2: No continue statements
    if !loop_form.continue_targets.is_empty() {
        return false;
    }

    // Pattern 3 matched (fallback for now)
    // Since all Pattern 3 loops are also Pattern 1 loops, we can safely return true
    // The lowering phase will determine if the specific pattern is supported
    true
}

// ============================================================================
// Pattern 4: Loop with Continue
// ============================================================================

/// Detect Pattern 4: Loop with Continue
///
/// Returns true ONLY if:
/// - Loop has continue statement(s)
/// - Continue is typically in an if statement
/// - NO break statements (for simplicity)
/// - Loop has multiple carrier variables
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
///
/// # Returns
/// * `true` if the loop matches Pattern 4 (Continue), `false` otherwise
///
/// # Reference
/// See design.md § Pattern 4 → LoopScopeShape Recognition
///
/// # Example
/// ```rust,ignore
/// let loop_form = /* ... */;
/// if is_loop_with_continue_pattern(&loop_form) {
///     // Lower to loop with continue pattern
/// }
/// ```
pub fn is_loop_with_continue_pattern(loop_form: &LoopForm) -> bool {
    // Pattern 4 Recognition Criteria:
    // 1. continue_targets: NON-EMPTY (at least 1 continue)
    // 2. break_targets: EMPTY (for simplicity in Pattern 4)
    // 3. At least ONE continue target
    //
    // Phase 188-Impl-4: Minimal implementation
    // Advanced checks (nested loops, if-statement structure) are deferred to
    // lowering phase where we can fail gracefully if needed.

    // Check 1: continue_targets is NON-EMPTY (has at least 1 continue)
    if loop_form.continue_targets.is_empty() {
        return false;
    }

    // Check 2: At least ONE continue target (pattern assumes single continue for now)
    if loop_form.continue_targets.len() < 1 {
        return false;
    }

    // Check 3: No break statements (for simplicity in Pattern 4)
    if !loop_form.break_targets.is_empty() {
        return false;
    }

    // Pattern 4 matched
    // The LoopForm structure guarantees:
    // - Valid loop structure
    // - At least one continue target
    // - No breaks
    //
    // Advanced checks (continue is in if-statement, etc.) are deferred to
    // lowering phase for graceful failure.

    true
}

// ============================================================================
// Helper Functions (Future Use)
// ============================================================================

/// Count the number of carrier variables in a loop
///
/// Carrier variables are loop variables that are updated in the loop body
/// and carried through PHI nodes in the header.
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
///
/// # Returns
/// * Number of carrier variables
///
/// # TODO
/// Implement by analyzing header PHI nodes
#[allow(dead_code)]
fn count_carrier_variables(loop_form: &LoopForm) -> usize {
    // TODO: Implement carrier variable counting
    // Step 1: Access loop_form.header block
    // Step 2: Count PHI instructions in header
    // Step 3: Return count
    0
}

/// Check if loop body contains nested loops
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
///
/// # Returns
/// * `true` if nested loops found, `false` otherwise
///
/// # TODO
/// Implement by checking for LoopForm within body blocks
#[allow(dead_code)]
fn has_nested_loops(loop_form: &LoopForm) -> bool {
    // TODO: Implement nested loop detection
    // Step 1: Traverse body blocks
    // Step 2: Check for loop headers in body
    // Step 3: Return true if any found
    false
}

/// Check if loop condition is simple (single comparison, no && or ||)
///
/// # Arguments
/// * `loop_form` - The loop structure to analyze
///
/// # Returns
/// * `true` if condition is simple, `false` otherwise
///
/// # TODO
/// Implement by checking header condition complexity
#[allow(dead_code)]
fn has_simple_condition(loop_form: &LoopForm) -> bool {
    // TODO: Implement condition complexity check
    // Step 1: Access loop_form.header block
    // Step 2: Find condition instruction
    // Step 3: Check for && or || operators
    // Step 4: Return true if no complex operators
    true // Assume simple for now
}

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

    // ========================================================================
    // Pattern 1: Simple While Loop Tests
    // ========================================================================

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern1_simple_while_detection() {
        // TODO: Add unit test for simple while pattern detection
        // Step 1: Create mock LoopForm with:
        //   - Empty break_targets
        //   - Empty continue_targets
        //   - Single latch
        // Step 2: Call is_simple_while_pattern()
        // Step 3: Assert returns true
    }

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern1_rejects_break() {
        // TODO: Add test that rejects loop with break
        // Step 1: Create mock LoopForm with non-empty break_targets
        // Step 2: Call is_simple_while_pattern()
        // Step 3: Assert returns false
    }

    // ========================================================================
    // Pattern 2: Loop with Break Tests
    // ========================================================================

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern2_break_detection() {
        // TODO: Add unit test for break pattern detection
        // Step 1: Create mock LoopForm with:
        //   - Non-empty break_targets (exactly 1)
        //   - Empty continue_targets
        //   - If statement with break
        // Step 2: Call is_loop_with_break_pattern()
        // Step 3: Assert returns true
    }

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern2_rejects_no_break() {
        // TODO: Add test that rejects loop without break
        // Step 1: Create mock LoopForm with empty break_targets
        // Step 2: Call is_loop_with_break_pattern()
        // Step 3: Assert returns false
    }

    // ========================================================================
    // Pattern 3: Loop with If-Else PHI Tests
    // ========================================================================

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern3_if_else_phi_detection() {
        // TODO: Add unit test for if-else phi pattern detection
        // Step 1: Create mock LoopForm with:
        //   - Empty break_targets
        //   - Empty continue_targets
        //   - If-else statement in body
        //   - Multiple carrier variables
        // Step 2: Call is_loop_with_conditional_phi_pattern()
        // Step 3: Assert returns true
    }

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern3_rejects_break() {
        // TODO: Add test that rejects loop with break
        // Step 1: Create mock LoopForm with non-empty break_targets
        // Step 2: Call is_loop_with_conditional_phi_pattern()
        // Step 3: Assert returns false
    }

    // ========================================================================
    // Pattern 4: Loop with Continue Tests
    // ========================================================================

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern4_continue_detection() {
        // TODO: Add unit test for continue pattern detection
        // Step 1: Create mock LoopForm with:
        //   - Non-empty continue_targets (at least 1)
        //   - Empty break_targets
        //   - If statement with continue
        // Step 2: Call is_loop_with_continue_pattern()
        // Step 3: Assert returns true
    }

    #[test]
    #[ignore] // TODO: Implement test after detection logic is complete
    fn test_pattern4_rejects_no_continue() {
        // TODO: Add test that rejects loop without continue
        // Step 1: Create mock LoopForm with empty continue_targets
        // Step 2: Call is_loop_with_continue_pattern()
        // Step 3: Assert returns false
    }
}