//! Pattern 4: Loop with Continue - STUB
//!
//! Target: Loops with continue statements
//! Status: Deferred to Phase 195+
//!
//! # Transformation
//!
//! ```text
//! fn loop_step(i, sum):
//!   exit_cond = !(i < 10)
//!   Jump(k_exit, [sum], cond=exit_cond)      // Natural exit
//!   i_next = i + 1
//!   continue_cond = (i_next % 2 == 0)
//!   Jump(loop_step, [i_next, sum], cond=continue_cond)  // Continue jumps to loop start
//!   sum_next = sum + i_next
//!   Call(loop_step, [i_next, sum_next])      // Normal iteration
//! ```

use crate::mir::join_ir::lowering::loop_to_join::LoopToJoinLowerer;
use crate::mir::join_ir::JoinInst;
use crate::mir::loop_form::LoopForm;

/// Lowering for Pattern 4: Loop with Continue
///
/// # Transformation (Pseudocode)
///
/// ```text
/// fn loop_step(i, sum):
///   exit_cond = !(i < 10)
///   Jump(k_exit, [sum], cond=exit_cond)      // Natural exit
///   i_next = i + 1
///   continue_cond = (i_next % 2 == 0)
///   Jump(loop_step, [i_next, sum], cond=continue_cond)  // Continue jumps to loop start
///   sum_next = sum + i_next
///   Call(loop_step, [i_next, sum_next])      // Normal iteration
/// ```
///
/// # Steps (Pattern 4 Transformation)
///
/// 1. **Extract Loop Variables** (multiple carriers: i + sum)
/// 2. **Create loop_step Function** (params: i, sum, k_exit)
/// 3. **Create k_exit with Exit PHI** (receives sum exit value)
/// 4. **Generate Exit Condition Check** (same as Pattern 1)
/// 5. **Generate Continue Check**
///    - Extract continue condition (if exists)
///    - Add conditional Jump back to loop_step: `Jump(loop_step, [i_next, sum], cond=continue_cond)`
/// 6. **Translate Loop Body** (remaining instructions after continue)
/// 7. **Generate Tail Recursion** (with multiple carriers: i_next, sum_next)
///
/// # Key Difference from Pattern 1/2/3
///
/// - **Continue Jump**: Continue jumps back to loop_step with current carrier values
/// - **Dual Path**: Continue path + normal path (both recursive)
/// - **PHI at Loop Start**: Loop header receives values from both continue and normal paths
///
/// # Arguments
///
/// * `loop_form` - The loop structure to lower (must have continue_targets)
/// * `lowerer` - The LoopToJoinLowerer builder
///
/// # Returns
///
/// * `Some(JoinInst)` - Lowering succeeded, returns generated JoinIR instruction
/// * `None` - Lowering failed (pattern not matched or unsupported)
///
/// # Errors
///
/// Returns `None` if:
/// - Loop has no continues (use Pattern 1 instead)
/// - Loop has break statements (not yet supported)
/// - Continue is not in an if statement
///
/// # Reference
///
/// See design.md § Pattern 4 for complete transformation details and pseudocode.
///
/// # Example Usage
///
/// ```rust,ignore
/// use crate::mir::loop_pattern_detection::is_loop_with_continue_pattern;
///
/// if is_loop_with_continue_pattern(&loop_form) {
///     lower_loop_with_continue_to_joinir(&loop_form, &mut lowerer)?;
/// }
/// ```
pub fn lower_loop_with_continue_to_joinir(
    _loop_form: &LoopForm,
    _lowerer: &mut LoopToJoinLowerer,
) -> Option<JoinInst> {
    // Phase 188-Impl-4: Pattern 4 implementation placeholder
    // TODO: Implement Pattern 4 lowering
    //
    // Step 1: Extract Loop Variables (Carriers)
    // ==========================================
    // From header PHI: %i = phi [%0, preheader], [%i_next, body]
    //                  %sum = phi [%0, preheader], [%sum_next, body]
    // Extract: (var_name: "i", init_value: 0, next_value: i_next)
    //          (var_name: "sum", init_value: 0, next_value: sum_next)
    //
    // Step 2: Create loop_step Function Signature
    // ============================================
    // Signature: fn loop_step(i: ValueId, sum: ValueId, k_exit: JoinContId) -> ...
    //
    // Step 3: Create k_exit Continuation
    // ===================================
    // fn k_exit(sum_exit) -> ValueId  // Returns final sum value
    //
    // Step 4: Generate Exit Condition Check
    // ======================================
    // exit_cond = !(i < 10)
    // Jump(k_exit, [sum], cond=exit_cond)
    //
    // Step 5: Generate Continue Check
    // ================================
    // i_next = i + 1
    // continue_cond = (i_next % 2 == 0)
    // Jump(loop_step, [i_next, sum], cond=continue_cond)  // Continue to loop start
    //
    // Step 6: Translate Loop Body (after continue)
    // =============================================
    // sum_next = sum + i_next
    //
    // Step 7: Generate Tail Recursion
    // ================================
    // Call(loop_step, [i_next, sum_next], k_next: None)

    eprintln!("[loop_patterns] Pattern 4: Continue lowering not yet implemented");
    None
}
