//! Phase 121: StepTree → JoinModule shadow lowering (if-only)
//!
//! ## Responsibility
//!
//! - Convert StepTree to JoinModule (Normalized dialect)
//! - Only for if-only patterns (no loops)
//! - Returns None for out-of-scope patterns
//! - Returns Err for patterns that should be supported but conversion failed
//!
//! ## Design
//!
//! - Input: `&StepTree` with pre-computed contract
//! - No AST re-analysis (contract-only decisions)
//! - Single responsibility: structure → JoinIR conversion

use crate::mir::control_tree::step_tree::StepTree;
use crate::mir::join_ir::lowering::carrier_info::{ExitMeta, JoinFragmentMeta};
use crate::mir::join_ir::JoinModule;

use super::contracts::{check_if_only, CapabilityCheckResult};

/// Box-First: StepTree → Normalized shadow lowering
pub struct StepTreeNormalizedShadowLowererBox;

impl StepTreeNormalizedShadowLowererBox {
    /// Try to lower an if-only StepTree to normalized form
    ///
    /// ## Returns
    ///
    /// - `Ok(None)`: Out of scope (e.g., contains loops)
    /// - `Ok(Some(...))`: Shadow generation succeeded
    /// - `Err(...)`: Should be supported but conversion failed (internal error)
    ///
    /// ## Contract
    ///
    /// - Only processes if-only patterns (no loops/breaks/continues)
    /// - Uses contract information only (no AST re-analysis)
    /// - Dev-only: caller must check `joinir_dev_enabled()` before calling
    pub fn try_lower_if_only(
        step_tree: &StepTree,
    ) -> Result<Option<(JoinModule, JoinFragmentMeta)>, String> {
        // Phase 121 P1: Capability check (if-only scope)
        let capability = check_if_only(step_tree);
        match capability {
            CapabilityCheckResult::Supported => {
                // Phase 121 P1: For now, return empty module + empty meta
                // Full lowering implementation in future phases
                let module = JoinModule::new();
                let meta = JoinFragmentMeta::empty();
                Ok(Some((module, meta)))
            }
            CapabilityCheckResult::Unsupported(_reason) => {
                // Out of scope for Phase 121
                Ok(None)
            }
        }
    }

    /// Get shadow lowering status string for dev logging
    ///
    /// ## Contract
    ///
    /// - Returns 1-line summary: "shadow_lowered=true/false reason=..."
    /// - Does not perform actual lowering (use `try_lower_if_only` for that)
    pub fn get_status_string(step_tree: &StepTree) -> String {
        let capability = check_if_only(step_tree);
        match capability {
            CapabilityCheckResult::Supported => {
                format!(
                    "shadow_lowered=true step_tree_sig={} exits={:?} writes={:?}",
                    step_tree.signature_basis_string(),
                    step_tree.contract.exits,
                    step_tree.contract.writes
                )
            }
            CapabilityCheckResult::Unsupported(reason) => {
                format!(
                    "shadow_lowered=false reason=\"{}\" step_tree_sig={}",
                    reason.reason(),
                    step_tree.signature_basis_string()
                )
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::mir::control_tree::step_tree::{StepNode, StepTreeFeatures, StepTreeSignature};
    use crate::mir::control_tree::step_tree_contract_box::StepTreeContract;

    fn make_if_only_tree() -> StepTree {
        StepTree {
            root: StepNode::Block(vec![]),
            features: StepTreeFeatures {
                has_if: true,
                has_loop: false,
                has_break: false,
                has_continue: false,
                has_return: false,
                max_if_depth: 1,
                max_loop_depth: 0,
            },
            contract: StepTreeContract {
                exits: Default::default(),
                writes: Default::default(),
                required_caps: Default::default(),
                cond_sig: Default::default(),
            },
            signature: StepTreeSignature(0),
        }
    }

    fn make_loop_tree() -> StepTree {
        StepTree {
            root: StepNode::Block(vec![]),
            features: StepTreeFeatures {
                has_if: false,
                has_loop: true,
                has_break: false,
                has_continue: false,
                has_return: false,
                max_if_depth: 0,
                max_loop_depth: 1,
            },
            contract: StepTreeContract {
                exits: Default::default(),
                writes: Default::default(),
                required_caps: Default::default(),
                cond_sig: Default::default(),
            },
            signature: StepTreeSignature(0),
        }
    }

    #[test]
    fn test_if_only_supported() {
        let tree = make_if_only_tree();
        let result = StepTreeNormalizedShadowLowererBox::try_lower_if_only(&tree);
        assert!(result.is_ok());
        assert!(result.unwrap().is_some());
    }

    #[test]
    fn test_loop_rejected() {
        let tree = make_loop_tree();
        let result = StepTreeNormalizedShadowLowererBox::try_lower_if_only(&tree);
        assert!(result.is_ok());
        assert!(result.unwrap().is_none());
    }

    #[test]
    fn test_status_string_if_only() {
        let tree = make_if_only_tree();
        let status = StepTreeNormalizedShadowLowererBox::get_status_string(&tree);
        assert!(status.contains("shadow_lowered=true"));
        assert!(status.contains("step_tree_sig="));
    }

    #[test]
    fn test_status_string_loop() {
        let tree = make_loop_tree();
        let status = StepTreeNormalizedShadowLowererBox::get_status_string(&tree);
        assert!(status.contains("shadow_lowered=false"));
        assert!(status.contains("reason=\"contains loop"));
    }
}