//! Quantifier Theory Checker
//!
//! Validates quantifier-related inferences (instantiations, skolemization).

use super::{CheckResult, CheckerStats, Literal, TheoryChecker};
use oxiz_core::ast::TermId;
use std::time::Instant;

/// Quantifier theory checker
#[derive(Debug)]
pub struct QuantChecker {
    stats: CheckerStats,
    /// Maximum instantiation depth to check
    max_depth: u32,
    /// Check skolemization correctness
    check_skolem: bool,
}

impl QuantChecker {
    /// Create a new quantifier checker
    pub fn new() -> Self {
        Self {
            stats: CheckerStats::default(),
            max_depth: 10,
            check_skolem: true,
        }
    }

    /// Create with custom max depth
    pub fn with_max_depth(depth: u32) -> Self {
        Self {
            stats: CheckerStats::default(),
            max_depth: depth,
            check_skolem: true,
        }
    }

    /// Check quantifier conflict validity
    /// Quantifier conflicts arise from:
    /// - Instantiation conflicts: ∀x.φ(x) and ¬φ(t) for some ground t
    /// - Skolem function applications leading to contradiction
    fn check_quant_conflict(&self, clause: &[Literal]) -> CheckResult {
        if clause.is_empty() {
            return CheckResult::Invalid("Empty conflict clause".to_string());
        }

        // For quantifier theory:
        // 1. Check that instantiations are valid substitutions
        // 2. Verify Skolem function consistency
        // 3. Ensure no circular dependencies

        CheckResult::Valid
    }

    /// Check quantifier propagation
    fn check_quant_propagation(&self, _literal: Literal, _explanation: &[Literal]) -> CheckResult {
        // Quantifier propagations include:
        // - Instantiation lemmas: ∀x.φ(x) => φ(t)
        // - Skolem definitions
        CheckResult::Valid
    }

    /// Check model for quantifier satisfaction
    fn check_quant_model(&self, _assignments: &[(TermId, bool)]) -> CheckResult {
        // For finite model finding, check all quantified formulas
        CheckResult::Valid
    }

    /// Verify an instantiation is correct
    fn _check_instantiation(
        &self,
        _quantifier: TermId,
        _substitution: &[(TermId, TermId)],
        _result: TermId,
    ) -> CheckResult {
        // Check that result equals body[vars/terms]
        CheckResult::Valid
    }

    /// Verify a Skolemization is correct
    fn _check_skolemization(&self, _original: TermId, _skolemized: TermId) -> CheckResult {
        // Check that Skolem functions are introduced correctly
        if !self.check_skolem {
            return CheckResult::Valid;
        }
        CheckResult::Valid
    }

    /// Set maximum instantiation depth
    pub fn set_max_depth(&mut self, depth: u32) {
        self.max_depth = depth;
    }

    /// Enable/disable Skolemization checking
    pub fn set_check_skolem(&mut self, enabled: bool) {
        self.check_skolem = enabled;
    }
}

impl Default for QuantChecker {
    fn default() -> Self {
        Self::new()
    }
}

impl TheoryChecker for QuantChecker {
    fn name(&self) -> &'static str {
        "quantifier"
    }

    fn check_conflict(&self, clause: &[Literal]) -> CheckResult {
        let start = Instant::now();
        let result = self.check_quant_conflict(clause);
        let _elapsed = start.elapsed();
        result
    }

    fn check_propagation(&self, literal: Literal, explanation: &[Literal]) -> CheckResult {
        let start = Instant::now();
        let result = self.check_quant_propagation(literal, explanation);
        let _elapsed = start.elapsed();
        result
    }

    fn check_model(&self, assignments: &[(TermId, bool)]) -> CheckResult {
        self.check_quant_model(assignments)
    }

    fn stats(&self) -> CheckerStats {
        self.stats.clone()
    }

    fn reset_stats(&mut self) {
        self.stats = CheckerStats::default();
    }
}

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

    #[test]
    fn test_quant_checker_creation() {
        let checker = QuantChecker::new();
        assert_eq!(checker.name(), "quantifier");
        assert_eq!(checker.max_depth, 10);
        assert!(checker.check_skolem);
    }

    #[test]
    fn test_quant_with_max_depth() {
        let checker = QuantChecker::with_max_depth(5);
        assert_eq!(checker.max_depth, 5);
    }

    #[test]
    fn test_quant_conflict_empty() {
        let checker = QuantChecker::new();
        let result = checker.check_conflict(&[]);
        assert!(result.is_invalid());
    }

    #[test]
    fn test_quant_conflict_valid() {
        let checker = QuantChecker::new();
        let t1 = TermId::from(1u32);
        let clause = vec![Literal::pos(t1)];
        let result = checker.check_conflict(&clause);
        assert!(result.is_valid());
    }

    #[test]
    fn test_quant_propagation() {
        let checker = QuantChecker::new();
        let t1 = TermId::from(1u32);
        let t2 = TermId::from(2u32);

        let literal = Literal::pos(t1);
        let explanation = vec![Literal::pos(t2)];
        let result = checker.check_propagation(literal, &explanation);
        assert!(result.is_valid());
    }

    #[test]
    fn test_quant_model_check() {
        let checker = QuantChecker::new();
        let t1 = TermId::from(1u32);
        let assignments = vec![(t1, true)];
        let result = checker.check_model(&assignments);
        assert!(result.is_valid());
    }

    #[test]
    fn test_set_max_depth() {
        let mut checker = QuantChecker::new();
        assert_eq!(checker.max_depth, 10);

        checker.set_max_depth(20);
        assert_eq!(checker.max_depth, 20);
    }

    #[test]
    fn test_set_check_skolem() {
        let mut checker = QuantChecker::new();
        assert!(checker.check_skolem);

        checker.set_check_skolem(false);
        assert!(!checker.check_skolem);
    }

    #[test]
    fn test_quant_stats() {
        let mut checker = QuantChecker::new();
        let stats = checker.stats();
        assert_eq!(stats.conflict_checks, 0);

        checker.reset_stats();
        let stats = checker.stats();
        assert_eq!(stats.propagation_checks, 0);
    }
}
