//! Phase 27.10: Common utilities for JoinIR lowering
//!
//! CFG sanity checks and dispatcher helpers for MIR-based lowering.

use crate::mir::{BasicBlockId, BinaryOp, ConstValue, MirInstruction};
use crate::mir::query::{MirQuery, MirQueryBox};

/// Check if entry block has at least one successor
///
/// Returns `true` if the entry block has at least one successor, `false` otherwise.
/// This is a basic sanity check to ensure the MIR CFG is well-formed.
pub fn ensure_entry_has_succs(query: &MirQueryBox, entry: BasicBlockId) -> bool {
    !query.succs(entry).is_empty()
}

/// Check if a basic block contains `Const { value: Integer(value) }`
///
/// Returns `true` if the block contains a constant integer instruction with the specified value.
///
/// # Example
/// ```ignore
/// // Check if entry block contains Const(0)
/// if has_const_int(&query, entry_id, 0) {
///     // ...
/// }
/// ```
pub fn has_const_int(query: &MirQueryBox, bb: BasicBlockId, value: i64) -> bool {
    query.insts_in_block(bb).iter().any(|inst| {
        matches!(
            inst,
            MirInstruction::Const {
                value: ConstValue::Integer(v),
                ..
            } if *v == value
        )
    })
}

/// Check if a basic block contains `Const { value: String(value) }`
///
/// Returns `true` if the block contains a constant string instruction with the specified value.
///
/// # Example
/// ```ignore
/// // Check if entry block contains Const("")
/// if has_const_string(&query, entry_id, "") {
///     // ...
/// }
/// ```
pub fn has_const_string(query: &MirQueryBox, bb: BasicBlockId, value: &str) -> bool {
    query.insts_in_block(bb).iter().any(|inst| {
        matches!(
            inst,
            MirInstruction::Const {
                value: ConstValue::String(s),
                ..
            } if s == value
        )
    })
}

/// Check if a basic block contains `BoxCall { method: method_name }`
///
/// Returns `true` if the block contains a BoxCall instruction with the specified method name.
///
/// # Example
/// ```ignore
/// // Check if entry block contains String.length()
/// if has_string_method(&query, entry_id, "length") {
///     // ...
/// }
/// ```
pub fn has_string_method(query: &MirQueryBox, bb: BasicBlockId, method: &str) -> bool {
    query.insts_in_block(bb).iter().any(|inst| {
        matches!(
            inst,
            MirInstruction::BoxCall { method: m, .. } if m == method
        )
    })
}

/// Check if a basic block contains `BinOp { op: operation }`
///
/// Returns `true` if the block contains a binary operation instruction with the specified operation.
///
/// # Example
/// ```ignore
/// // Check if entry block contains BinOp(Add)
/// if has_binop(&query, entry_id, BinaryOp::Add) {
///     // ...
/// }
/// ```
pub fn has_binop(query: &MirQueryBox, bb: BasicBlockId, op: BinaryOp) -> bool {
    query.insts_in_block(bb).iter().any(|inst| {
        matches!(
            inst,
            MirInstruction::BinOp { op: o, .. } if *o == op
        )
    })
}

/// Log fallback to handwritten lowering with reason
///
/// Prints a diagnostic message when MIR-based lowering falls back to handwritten version.
///
/// # Example
/// ```ignore
/// log_fallback("skip_ws", "entry has no successors");
/// // Output: [joinir/skip_ws/mir] unexpected MIR shape: entry has no successors, falling back to handwritten
/// ```
pub fn log_fallback(tag: &str, reason: &str) {
    eprintln!(
        "[joinir/{}/mir] unexpected MIR shape: {}, falling back to handwritten",
        tag, reason
    );
}

/// Dispatch between MIR-based and handwritten lowering based on environment variable
///
/// Checks `NYASH_JOINIR_LOWER_FROM_MIR` and dispatches to the appropriate lowering function.
/// This consolidates the toggle pattern used across all JoinIR lowering implementations.
///
/// # Arguments
/// - `tag`: Identifier for logging (e.g., "skip_ws", "trim")
/// - `module`: MIR module to lower
/// - `mir_based`: Closure for MIR-based lowering (returns `Option<JoinModule>`)
/// - `handwritten`: Closure for handwritten lowering (returns `Option<JoinModule>`)
///
/// # Returns
/// `Option<JoinModule>` - Both implementations may return None on errors
///
/// # Example
/// ```ignore
/// pub fn lower_skip_ws_to_joinir(module: &MirModule) -> Option<JoinModule> {
///     dispatch_lowering(
///         "skip_ws",
///         module,
///         lower_skip_ws_from_mir,
///         lower_skip_ws_handwritten,
///     )
/// }
/// ```
pub fn dispatch_lowering<F1, F2>(
    tag: &str,
    module: &crate::mir::MirModule,
    mir_based: F1,
    handwritten: F2,
) -> Option<crate::mir::join_ir::JoinModule>
where
    F1: FnOnce(&crate::mir::MirModule) -> Option<crate::mir::join_ir::JoinModule>,
    F2: FnOnce(&crate::mir::MirModule) -> Option<crate::mir::join_ir::JoinModule>,
{
    use crate::mir::join_ir::env_flag_is_1;

    if env_flag_is_1("NYASH_JOINIR_LOWER_FROM_MIR") {
        eprintln!("[joinir/{}] Using MIR-based lowering (NYASH_JOINIR_LOWER_FROM_MIR=1)", tag);
        mir_based(module)
    } else {
        eprintln!("[joinir/{}] Using handwritten lowering (default)", tag);
        handwritten(module)
    }
}