rmpca 0.1.0

//! Lean 4 FFI Bridge
//!
//! This module provides the boundary between Rust and Lean 4 for verified optimization.
//!
//! THE PROBLEM:
//! Passing complex Rust data structures (petgraph, HashMap, HashSet) to Lean 4
//! via C FFI is notoriously difficult due to:
//! - Different memory layouts (Rust's struct packing vs C's ABI)
//! - Ownership semantics (Rust's RAII vs manual C memory management)
//! - Iterators and complex types don't have C equivalents
//!
//! THE SOLUTION:
//! Flatten data structures before crossing the FFI boundary. We extract minimal
//! information needed for the Eulerian path problem and pass it as simple
//! C-compatible arrays (contiguous memory + length).
//!
//! Data flow:
//!   Rust Graph → FlatArrays → Lean 4 → VerifiedResult → Rust
//!
//! Benefits:
//! - Safe C ABI compatibility
//! - Zero-copy when possible
//! - Clear ownership boundaries
//! - Easier to verify in Lean 4 (simple arrays vs complex graphs)

use anyhow::Result;
use std::os::raw::{c_double, c_int, c_uint};

/// Flattened graph representation for FFI
///
/// This structure contains only primitive C-compatible types
/// that can be safely passed to Lean 4 via C FFI.
#[repr(C)]
pub struct FlatGraph {
    /// Contiguous array of node coordinates: [lat1, lon1, lat2, lon2, ...]
    pub nodes: *mut c_double,

    /// Number of nodes (array length / 2)
    pub node_count: c_uint,

    /// Contiguous array of edges: [from_idx, to_idx, from_idx, to_idx, ...]
    pub edges: *mut c_uint,

    /// Number of edges (array length / 2)
    pub edge_count: c_uint,

    /// Starting node index for circuit
    pub start_node: c_uint,
}

unsafe impl Send for FlatGraph {}
unsafe impl Sync for FlatGraph {}

/// Verified result from Lean 4
#[repr(C)]
pub struct VerifiedResult {
    /// Ordered node indices forming the circuit
    pub circuit: *mut c_uint,

    /// Length of circuit array
    pub circuit_length: c_uint,

    /// Total distance in meters
    pub total_distance: c_double,

    /// Success flag (0 = error, 1 = success)
    pub success: c_int,
}

unsafe impl Send for VerifiedResult {}
unsafe impl Sync for VerifiedResult {}

/// Lean 4 optimizer bridge
///
/// This struct manages the Lean 4 runtime when compiled with the lean4 feature.
pub struct Lean4Bridge {}

impl Lean4Bridge {
    /// Create a new Lean 4 bridge
    ///
    /// Note: This is a placeholder for future Lean 4 integration.
    /// When Lean 4 proofs are ready, this will initialize
    /// the Lean 4 runtime.
    pub fn new() -> Result<Self> {
        Ok(Self {})
    }

    /// Call Lean 4 optimizer via FFI
    ///
    /// SAFETY: This function is unsafe because:
    /// 1. It dereferences raw pointers from FlatGraph
    /// 2. The caller must ensure pointers are valid and memory is owned
    /// 3. The Lean 4 runtime must be initialized
    #[cfg(feature = "lean4")]
    pub unsafe fn optimize_lean4(
        &self,
        nodes: *const c_double,
        node_count: c_uint,
        edges: *const c_uint,
        edge_count: c_uint,
        start_node: c_uint,
    ) -> Result<VerifiedResult> {
        // Call Lean 4 function via C FFI
        // This assumes Lean 4 is compiled with a compatible C ABI
        let result = self.call_optimize_eulerian(
            nodes,
            node_count,
            edges,
            edge_count,
            start_node,
        );

        if result.success == 0 {
            return Err(anyhow::anyhow!("Lean 4 optimization failed"));
        }

        Ok(result)
    }

    /// Internal method to call Lean 4 optimization
    #[cfg(feature = "lean4")]
    unsafe fn call_optimize_eulerian(
        &self,
        _nodes: *const c_double,
        _node_count: c_uint,
        _edges: *const c_uint,
        _edge_count: c_uint,
        _start_node: c_uint,
    ) -> VerifiedResult {
        // TODO: Replace with actual Lean 4 FFI call
        // let result = lean4_sys::optimize_eulerian(
        //     nodes,
        //     node_count,
        //     edges,
        //     edge_count,
        //     start_node,
        // );

        // Placeholder result for testing
        VerifiedResult {
            circuit: std::ptr::null_mut(),
            circuit_length: 0,
            total_distance: 0.0,
            success: 0,
        }
    }
}

impl Drop for Lean4Bridge {
    fn drop(&mut self) {
        #[cfg(feature = "lean4")]
        if let Some(_runtime) = self._runtime.take() {
            // TODO: Shutdown Lean 4 runtime when available
            // lean4_sys::shutdown_runtime(runtime);
        }
    }
}

/// Extension trait for RouteOptimizer to flatten for FFI
///
/// This trait provides methods to convert complex Rust graph structures
/// into simple C-compatible arrays for Lean 4 FFI integration.
pub trait FlattenForFFI {
    /// Convert graph to flat C-compatible arrays
    ///
    /// This method extracts the minimal information needed for the
    /// Eulerian path problem and represents it as flat arrays
    /// that can be safely passed to Lean 4 via C FFI.
    fn flatten_for_ffi(&self) -> FlatGraph;

    /// Reconstruct optimization result from Lean 4 result
    ///
    /// This method converts the flat result from Lean 4 back into
    /// the Rust optimization result format.
    fn from_verified_result(&self, result: VerifiedResult) -> Result<super::types::OptimizationResult>;
}

/// Placeholder implementation for testing
///
/// This will be implemented when the RouteOptimizer is fully developed.
impl FlattenForFFI for super::types::Node {
    fn flatten_for_ffi(&self) -> FlatGraph {
        // Placeholder implementation
        let node_coords: Vec<c_double> = vec![self.lat, self.lon];
        let node_count = (node_coords.len() / 2) as c_uint;
        
        let edge_indices: Vec<c_uint> = Vec::new();
        let edge_count = (edge_indices.len() / 2) as c_uint;

        FlatGraph {
            nodes: Box::into_raw(node_coords.into_boxed_slice()) as *mut c_double,
            node_count,
            edges: Box::into_raw(edge_indices.into_boxed_slice()) as *mut c_uint,
            edge_count,
            start_node: 0,
        }
    }

    fn from_verified_result(&self, _result: VerifiedResult) -> Result<super::types::OptimizationResult> {
        // Placeholder implementation
        Ok(super::types::OptimizationResult {
            route: vec![super::types::RoutePoint::new(self.lat, self.lon)],
            total_distance: 0.0,
            message: "Verified by Lean 4 (placeholder)".to_string(),
            stats: None,
        })
    }
}

impl Drop for FlatGraph {
    fn drop(&mut self) {
        // Free memory allocated for flat arrays
        unsafe {
            if !self.nodes.is_null() {
                let _ = Vec::from_raw_parts(
                    self.nodes as *mut c_double,
                    (self.node_count * 2) as usize,
                    (self.node_count * 2) as usize,
                );
            }
            if !self.edges.is_null() {
                let _ = Vec::from_raw_parts(
                    self.edges as *mut c_uint,
                    (self.edge_count * 2) as usize,
                    (self.edge_count * 2) as usize,
                );
            }
        }
    }
}

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

    #[test]
    fn test_flat_graph_creation() {
        let node = super::super::types::Node::new("", 45.5, -73.6);
        let flat = node.flatten_for_ffi();

        assert_eq!(flat.node_count, 1);
        assert!(!flat.nodes.is_null());
        assert_eq!(flat.edge_count, 0);

        // Verify node coordinates
        unsafe {
            assert_eq!(*flat.nodes, 45.5);
            assert_eq!(*flat.nodes.add(1), -73.6);
        }
    }

    #[test]
    fn test_lean4_bridge_creation() {
        let bridge = Lean4Bridge::new();
        assert!(bridge.is_ok());
    }

    #[test]
    fn test_verified_result_structure() {
        let result = VerifiedResult {
            circuit: std::ptr::null_mut(),
            circuit_length: 0,
            total_distance: 1000.0,
            success: 1,
        };

        assert_eq!(result.total_distance, 1000.0);
        assert_eq!(result.success, 1);
    }
}