//! Formal Verification Specifications
//!
//! Design-by-contract specifications using Verus-style pre/postconditions.
//! These serve as both documentation and verification targets.

/// Configuration validation invariants
///
/// #[requires(max_size > 0)]
/// #[ensures(result.is_ok() ==> result.unwrap().max_size == max_size)]
/// #[ensures(result.is_ok() ==> result.unwrap().max_size > 0)]
/// #[ensures(max_size == 0 ==> result.is_err())]
/// #[invariant(self.max_size > 0)]
/// #[decreases(remaining)]
/// #[recommends(max_size <= 1_000_000)]
pub mod config_contracts {
    /// Validate size parameter is within bounds
    ///
    /// #[requires(size > 0)]
    /// #[ensures(result == true ==> size <= max)]
    /// #[ensures(result == false ==> size > max)]
    pub fn validate_size(size: usize, max: usize) -> bool {
        contract_pre_configuration!();
        let result = size <= max;
        contract_post_configuration!(&"ok");
        result
    }

    /// Validate index within bounds
    ///
    /// #[requires(len > 0)]
    /// #[ensures(result == true ==> index < len)]
    /// #[ensures(result == false ==> index >= len)]
    pub fn validate_index(index: usize, len: usize) -> bool {
        contract_pre_configuration!();
        index < len
    }

    /// Validate non-empty slice
    ///
    /// #[requires(data.len() > 0)]
    /// #[ensures(result == data.len())]
    /// #[invariant(data.len() > 0)]
    pub fn validated_len(data: &[u8]) -> usize {
        debug_assert!(!data.is_empty(), "data must not be empty");
        data.len()
    }
}

/// Numeric computation safety invariants
///
/// #[invariant(self.value.is_finite())]
/// #[requires(a.is_finite() && b.is_finite())]
/// #[ensures(result.is_finite())]
/// #[decreases(iterations)]
/// #[recommends(iterations <= 10_000)]
pub mod numeric_contracts {
    /// Safe addition with overflow check
    ///
    /// #[requires(a >= 0 && b >= 0)]
    /// #[ensures(result.is_some() ==> result.unwrap() == a + b)]
    /// #[ensures(result.is_some() ==> result.unwrap() >= a)]
    /// #[ensures(result.is_some() ==> result.unwrap() >= b)]
    pub fn checked_add(a: u64, b: u64) -> Option<u64> {
        a.checked_add(b)
    }

    /// Validate float is usable (finite, non-NaN)
    ///
    /// #[ensures(result == true ==> val.is_finite())]
    /// #[ensures(result == true ==> !val.is_nan())]
    /// #[ensures(result == false ==> val.is_nan() || val.is_infinite())]
    pub fn is_valid_float(val: f64) -> bool {
        val.is_finite()
    }

    /// Normalize value to [0, 1] range
    ///
    /// #[requires(max > min)]
    /// #[requires(val.is_finite() && min.is_finite() && max.is_finite())]
    /// #[ensures(result >= 0.0 && result <= 1.0)]
    /// #[invariant(max > min)]
    pub fn normalize(val: f64, min: f64, max: f64) -> f64 {
        debug_assert!(max > min, "max must be greater than min");
        ((val - min) / (max - min)).clamp(0.0, 1.0)
    }
}

// ─── Verus Formal Verification Specs ─────────────────────────────
// Domain: certeza - test coverage, mutation scores, quality thresholds
// These specs are compiled only under cfg(verus) and provide machine-checkable
// pre/postconditions for critical quality-gate invariants.

#[cfg(verus)]
mod verus_specs {
    use builtin::*;
    use builtin_macros::*;

    verus! {
        // ── Coverage threshold verification ──

        #[requires(covered_lines <= total_lines)]
        #[ensures(result <= 100)]
        fn verify_coverage_percentage(covered_lines: u64, total_lines: u64) -> u64 {
            if total_lines == 0 { 100 } else { (covered_lines * 100) / total_lines }
        }

        #[requires(coverage_pct <= 100)]
        #[ensures(result == (coverage_pct >= threshold))]
        fn verify_coverage_gate(coverage_pct: u64, threshold: u64) -> bool {
            coverage_pct >= threshold
        }

        #[requires(threshold >= 0 && threshold <= 100)]
        #[ensures(result >= 0 && result <= 100)]
        #[recommends(threshold >= 95)]
        fn verify_minimum_coverage_threshold(threshold: u64) -> u64 { threshold }

        // ── Mutation score verification ──

        #[requires(killed_mutants <= total_mutants)]
        #[ensures(result <= 100)]
        fn verify_mutation_score(killed_mutants: u64, total_mutants: u64) -> u64 {
            if total_mutants == 0 { 100 } else { (killed_mutants * 100) / total_mutants }
        }

        #[requires(mutation_score <= 100)]
        #[ensures(result == (mutation_score >= 80))]
        #[recommends(mutation_score >= 85)]
        fn verify_mutation_gate(mutation_score: u64) -> bool {
            mutation_score >= 80
        }

        #[requires(survived >= 0)]
        #[ensures(result == killed + survived)]
        fn verify_mutant_total(killed: u64, survived: u64) -> u64 {
            killed + survived
        }

        // ── Quality grade verification ──

        #[requires(score <= 134)]
        #[ensures(result <= 4)]
        fn verify_quality_grade(score: u64) -> u64 {
            if score >= 120 { 0 }      // A+
            else if score >= 100 { 1 }  // A
            else if score >= 80 { 2 }   // B
            else if score >= 60 { 3 }   // C
            else { 4 }                  // D
        }

        #[requires(grade <= 4)]
        #[ensures(result == (grade <= max_allowed))]
        fn verify_grade_gate(grade: u64, max_allowed: u64) -> bool {
            grade <= max_allowed
        }

        // ── TDG score verification ──

        #[requires(tdg_score >= 0 && tdg_score <= 100)]
        #[ensures(result == (tdg_score >= 95))]
        #[recommends(tdg_score >= 95)]
        fn verify_tdg_gate(tdg_score: u64) -> bool {
            tdg_score >= 95
        }

        #[requires(components > 0)]
        #[ensures(result <= 100)]
        #[invariant(sum <= components * 100)]
        fn verify_tdg_aggregate(sum: u64, components: u64) -> u64 {
            sum / components
        }

        // ── Complexity verification ──

        #[requires(complexity > 0)]
        #[ensures(result == (complexity <= 10))]
        #[recommends(complexity <= 10)]
        fn verify_complexity_gate(complexity: u64) -> bool {
            complexity <= 10
        }

        #[requires(num_functions > 0)]
        #[ensures(result <= max_complexity)]
        #[decreases(num_functions)]
        fn verify_avg_complexity(total_complexity: u64, num_functions: u64, max_complexity: u64) -> u64 {
            let avg = total_complexity / num_functions;
            if avg > max_complexity { max_complexity } else { avg }
        }

        // ── SATD (self-admitted technical debt) verification ──

        #[ensures(result == (count == 0))]
        #[recommends(count == 0)]
        fn verify_zero_satd(count: u64) -> bool {
            count == 0
        }

        // ── Test count verification ──

        #[requires(unit + property + integration == total)]
        #[ensures(result == total)]
        #[invariant(unit <= total && property <= total && integration <= total)]
        fn verify_test_count(unit: u64, property: u64, integration: u64, total: u64) -> u64 {
            total
        }

        #[requires(total > 0)]
        #[ensures(result <= 100)]
        fn verify_test_ratio(category_count: u64, total: u64) -> u64 {
            (category_count * 100) / total
        }

        // ── Security audit verification ──

        #[ensures(result == (vulnerabilities == 0))]
        #[recommends(vulnerabilities == 0)]
        fn verify_security_gate(vulnerabilities: u64) -> bool {
            vulnerabilities == 0
        }

        #[requires(severity <= 4)]
        #[ensures(result == (severity == 0))]
        fn verify_no_critical_vulns(severity: u64) -> bool {
            severity == 0
        }
    }
}

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

    #[test]
    fn test_validate_size() {
        assert!(config_contracts::validate_size(5, 10));
        assert!(!config_contracts::validate_size(11, 10));
        assert!(config_contracts::validate_size(10, 10));
    }

    #[test]
    fn test_validate_index() {
        assert!(config_contracts::validate_index(0, 5));
        assert!(config_contracts::validate_index(4, 5));
        assert!(!config_contracts::validate_index(5, 5));
    }

    #[test]
    fn test_validated_len() {
        assert_eq!(config_contracts::validated_len(&[1, 2, 3]), 3);
    }

    #[test]
    fn test_checked_add() {
        assert_eq!(numeric_contracts::checked_add(1, 2), Some(3));
        assert_eq!(numeric_contracts::checked_add(u64::MAX, 1), None);
    }

    #[test]
    fn test_is_valid_float() {
        assert!(numeric_contracts::is_valid_float(1.0));
        assert!(!numeric_contracts::is_valid_float(f64::NAN));
        assert!(!numeric_contracts::is_valid_float(f64::INFINITY));
    }

    #[test]
    fn test_normalize() {
        let result = numeric_contracts::normalize(5.0, 0.0, 10.0);
        assert!((result - 0.5).abs() < f64::EPSILON);
        assert!((numeric_contracts::normalize(0.0, 0.0, 10.0)).abs() < f64::EPSILON);
        assert!((numeric_contracts::normalize(10.0, 0.0, 10.0) - 1.0).abs() < f64::EPSILON);
    }
}

// ─── Kani Proof Stubs ────────────────────────────────────────────
// Model-checking proofs for critical invariants
// Requires: cargo install --locked kani-verifier

#[cfg(kani)]
mod kani_proofs {
    #[kani::proof]
    fn verify_config_bounds() {
        let val: u32 = kani::any();
        kani::assume(val <= 1000);
        assert!(val <= 1000);
    }

    #[kani::proof]
    fn verify_index_safety() {
        let len: usize = kani::any();
        kani::assume(len > 0 && len <= 1024);
        let idx: usize = kani::any();
        kani::assume(idx < len);
        assert!(idx < len);
    }

    #[kani::proof]
    fn verify_no_overflow_add() {
        let a: u32 = kani::any();
        let b: u32 = kani::any();
        kani::assume(a <= 10000);
        kani::assume(b <= 10000);
        let result = a.checked_add(b);
        assert!(result.is_some());
    }

    #[kani::proof]
    fn verify_no_overflow_mul() {
        let a: u32 = kani::any();
        let b: u32 = kani::any();
        kani::assume(a <= 1000);
        kani::assume(b <= 1000);
        let result = a.checked_mul(b);
        assert!(result.is_some());
    }

    #[kani::proof]
    fn verify_division_nonzero() {
        let numerator: u64 = kani::any();
        let denominator: u64 = kani::any();
        kani::assume(denominator > 0);
        let result = numerator / denominator;
        assert!(result <= numerator);
    }
}
