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

//! Pattern 1: Simple While Loop → JoinIR Lowering
//!
//! Phase 188 Task 188-4: Implementation of simple while loop pattern.
//!
//! ## Pattern Characteristics
//!
//! - Single loop variable (carrier)
//! - Simple condition
//! - NO control flow statements (no break, no continue, no nested if)
//! - Natural exit only (condition becomes false)
//!
//! ## Example
//!
//! ```nyash
//! local i = 0
//! loop(i < 3) {
//!   print(i)
//!   i = i + 1
//! }
//! return 0
//! ```
//!
//! ## JoinIR Transformation
//!
//! ```text
//! fn main():
//!   i_init = 0
//!   return loop_step(i_init)
//!
//! fn loop_step(i):
//!   exit_cond = !(i < 3)
//!   Jump(k_exit, [], cond=exit_cond)  // early return
//!   print(i)
//!   i_next = i + 1
//!   Call(loop_step, [i_next])  // tail recursion
//!
//! fn k_exit():
//!   return 0
//! ```

use crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape;
use crate::mir::join_ir::{
    ConstValue, JoinContId, JoinFuncId, JoinFunction, JoinInst, JoinModule, MirLikeInst, UnaryOp,
};
use crate::mir::ValueId;

/// Pattern detection: Simple While Loop
///
/// Criteria:
/// - No break statements (break_targets.is_empty())
/// - No continue statements (continue_targets.is_empty())
/// - Has at least one carrier variable
///
/// # Returns
///
/// - `true`: Pattern matches (safe to call lower_simple_while_pattern)
/// - `false`: Pattern does not match (try other patterns)
pub fn is_simple_while_pattern(_scope: &LoopScopeShape) -> bool {
    // Phase 188: Pattern detection logic will be implemented after understanding
    // LoopScopeShape structure better. For now, return false to avoid breaking existing code.
    // TODO: Implement proper detection based on break_targets, continue_targets, and carriers.
    false
}

/// Lower simple while loop to JoinIR
///
/// Transforms a simple while loop (Pattern 1) into JoinIR representation:
/// - Loop → tail-recursive function (loop_step)
/// - Exit condition → conditional Jump to k_exit
/// - Loop body → sequential Compute instructions
/// - Backedge → tail Call to loop_step
///
/// # Arguments
///
/// - `scope`: LoopScopeShape containing loop structure and variable classification
///
/// # Returns
///
/// - `Some(JoinModule)`: Successfully lowered to JoinIR
/// - `None`: Lowering failed (try other patterns or fallback)
pub fn lower_simple_while_pattern(_scope: LoopScopeShape) -> Option<JoinModule> {
    // Phase 188: Lowering implementation
    // This is a skeleton that will be filled in after examining LoopScopeShape structure
    // and understanding how to extract loop header, body, latch, and exit information.

    // TODO Phase 188-4:
    // 1. Extract carrier variables from scope.carriers
    // 2. Create JoinModule with 3 functions: main/entry, loop_step, k_exit
    // 3. Generate exit condition check (negate loop condition)
    // 4. Generate conditional Jump to k_exit
    // 5. Generate loop body instructions
    // 6. Generate tail Call to loop_step with updated carriers
    // 7. Wire k_exit to return appropriate value

    None // Placeholder
}

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

    #[test]
    fn test_pattern_detection_placeholder() {
        // Placeholder test - will be implemented with actual LoopScopeShape instances
        // after understanding the structure better
    }
}