theory_core 0.1.0

//! SMT Solver Backend Integration
//!
//! Provides integration with SMT solvers (Z3, CVC5, etc.) for formal
//! constraint satisfaction and verification.

use crate::ir::{ConstraintIR, TheoryTag};
use crate::surrogate::SolutionResult;
use anyhow::{Context, Result};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::time::{Duration, Instant};
// use z3::{ast, Config, Context as Z3Context, Solver};  // Commented out for now

/// SMT solver backend configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SmtBackendConfig {
    /// Timeout for solver calls in milliseconds
    pub timeout_ms: u64,
    /// Maximum number of solver instances to pool
    pub max_solver_pool: usize,
    /// Enable incremental solving
    pub incremental: bool,
    /// Z3 specific options
    pub z3_options: HashMap<String, String>,
}

impl Default for SmtBackendConfig {
    fn default() -> Self {
        let mut z3_options = HashMap::new();
        z3_options.insert("model".to_string(), "true".to_string());
        z3_options.insert("proof".to_string(), "false".to_string());

        Self {
            timeout_ms: 5000,
            max_solver_pool: 4,
            incremental: true,
            z3_options,
        }
    }
}

/// SMT solver backend (Z3 integration placeholder)
pub struct SmtBackend {
    config: SmtBackendConfig,
    // z3_context: Z3Context,  // Commented out for now
}

impl SmtBackend {
    pub fn new(config: SmtBackendConfig) -> Result<Self> {
        // TODO: Initialize Z3 when available
        Ok(Self {
            config,
            // z3_context,
        })
    }

    /// Solve constraints using appropriate SMT solver
    pub async fn solve(&self, constraints: &ConstraintIR) -> Result<SolutionResult> {
        let start_time = Instant::now();

        // Route to appropriate solver based on theory tags
        let solver_type = self.select_solver(&constraints.theory_tags);

        let result = match solver_type {
            SolverType::Z3 => self.solve_with_z3(constraints).await?,
            SolverType::CVC5 => {
                // TODO: Implement CVC5 integration
                return Err(anyhow::anyhow!("CVC5 not yet implemented"));
            }
        };

        let solve_time = start_time.elapsed();

        // Update result with actual solving time
        let mut final_result = result;
        final_result.estimated_time_ms = solve_time.as_millis() as f64;

        Ok(final_result)
    }

    /// Select appropriate solver based on theory tags
    fn select_solver(&self, theory_tags: &[TheoryTag]) -> SolverType {
        // For now, always use Z3 as it's the most general-purpose
        // TODO: Implement more sophisticated solver selection

        for tag in theory_tags {
            match tag {
                TheoryTag::BV => return SolverType::Z3, // Could route to Boolector
                TheoryTag::String => return SolverType::Z3, // Could route to CVC5
                _ => {}
            }
        }

        SolverType::Z3
    }

    /// Solve using Z3 SMT solver
    async fn solve_with_z3(&self, constraints: &ConstraintIR) -> Result<SolutionResult> {
        let solver = Solver::new(&self.z3_context);

        // Set timeout
        solver.set_timeout(Duration::from_millis(self.config.timeout_ms));

        // Convert constraint IR to Z3 AST
        let (z3_vars, z3_constraints) = self.constraints_to_z3(constraints)?;

        // Add constraints to solver
        for constraint in z3_constraints {
            solver.assert(&constraint);
        }

        // Check satisfiability
        let satisfiable = match solver.check() {
            z3::SatResult::Sat => true,
            z3::SatResult::Unsat => false,
            z3::SatResult::Unknown => {
                return Err(anyhow::anyhow!(
                    "Solver returned unknown (possibly timeout)"
                ));
            }
        };

        let mut assignment = HashMap::new();

        if satisfiable {
            if let Some(model) = solver.get_model() {
                // Extract variable assignments from model
                for (var_name, z3_var) in z3_vars {
                    if let Some(value) = model.eval(&z3_var, true) {
                        let solution_value = self.z3_value_to_solution_value(&value)?;
                        assignment.insert(var_name, solution_value);
                    }
                }
            }
        }

        Ok(SolutionResult {
            satisfiable,
            assignment,
            confidence: 1.0,        // SMT solver results are definitive
            estimated_time_ms: 0.0, // Will be updated by caller
            method: "Z3-Direct".to_string(),
            winning_branch_id: Some("Z3".to_string()),
            winning_strategy: Some("SMT".to_string()),
            winning_backend: Some("Z3".to_string()),
            variable_ranges: None,
        })
    }

    /// Convert constraint IR to Z3 AST
    fn constraints_to_z3(
        &self,
        constraints: &ConstraintIR,
    ) -> Result<(HashMap<String, ast::Dynamic>, Vec<ast::Bool>)> {
        let mut z3_vars = HashMap::new();
        let mut z3_constraints = Vec::new();

        // Create Z3 variables
        for (var_id, variable) in &constraints.variables {
            let var_name = format!("v{}", var_id.0);

            let z3_var = match &variable.domain {
                crate::ir::Domain::Boolean => {
                    ast::Bool::new_const(&self.z3_context, &var_name).into()
                }
                crate::ir::Domain::Integer { min: _, max: _ } => {
                    ast::Int::new_const(&self.z3_context, &var_name).into()
                }
                crate::ir::Domain::Real { min: _, max: _ } => {
                    ast::Real::new_const(&self.z3_context, &var_name).into()
                }
                crate::ir::Domain::BitVector { width } => {
                    ast::BV::new_const(&self.z3_context, &var_name, *width).into()
                }
                _ => {
                    return Err(anyhow::anyhow!(
                        "Unsupported domain type for variable {}",
                        var_name
                    ));
                }
            };

            z3_vars.insert(var_name, z3_var);
        }

        // Convert constraints (simplified for now)
        for constraint in &constraints.constraints {
            if let Some(z3_constraint) = self.constraint_to_z3(constraint, &z3_vars)? {
                z3_constraints.push(z3_constraint);
            }
        }

        Ok((z3_vars, z3_constraints))
    }

    /// Convert single constraint to Z3 (simplified implementation)
    fn constraint_to_z3(
        &self,
        constraint: &crate::ir::Constraint,
        _z3_vars: &HashMap<String, ast::Dynamic>,
    ) -> Result<Option<ast::Bool>> {
        // TODO: Implement full constraint translation
        // For now, return a trivial constraint
        match constraint {
            crate::ir::Constraint::Equal { lhs: _, rhs: _ } => {
                // Create a simple true constraint as placeholder
                Ok(Some(ast::Bool::from_bool(&self.z3_context, true)))
            }
            _ => {
                // Skip other constraint types for now
                Ok(None)
            }
        }
    }

    /// Convert Z3 value to solution value
    fn z3_value_to_solution_value(
        &self,
        z3_value: &ast::Dynamic,
    ) -> Result<crate::surrogate::SolutionValue> {
        // TODO: Implement proper Z3 value extraction
        // For now, return a default value
        Ok(crate::surrogate::SolutionValue::Integer(0))
    }
}

/// Supported SMT solver types
#[derive(Debug, Clone, Copy)]
enum SolverType {
    Z3,
    CVC5,
}