reasonkit-core 0.1.8

//! Formal Verification Integration using Z3 SMT Solver
//!
//! This module provides formal verification capabilities for the ProofGuard
//! ThinkTool, enabling logical proof validation and constraint satisfaction.
//!
//! # Features
//! - SMT solving for logical assertions
//! - Proof validation for reasoning chains
//! - Constraint satisfaction for argument verification
//! - Integration with ProofGuard ThinkTool
//!
//! Enable with: `cargo build --features formal-verification`

use anyhow::Result;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;

/// Configuration for formal verification
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct VerificationConfig {
    /// Timeout for solver in milliseconds
    pub timeout_ms: u64,
    /// Maximum proof depth
    pub max_depth: usize,
    /// Enable incremental solving
    pub incremental: bool,
    /// Verbosity level
    pub verbosity: u8,
}

impl Default for VerificationConfig {
    fn default() -> Self {
        Self {
            timeout_ms: 5000,
            max_depth: 100,
            incremental: true,
            verbosity: 0,
        }
    }
}

/// Result of a formal verification
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum VerificationResult {
    /// The assertion is provably true
    Valid {
        proof_steps: Vec<ProofStep>,
        confidence: f32,
    },
    /// The assertion is provably false
    Invalid {
        counterexample: Option<Counterexample>,
        reason: String,
    },
    /// Could not determine validity within constraints
    Unknown {
        reason: String,
        partial_results: Vec<PartialResult>,
    },
    /// Verification timed out
    Timeout { elapsed_ms: u64 },
}

/// A step in a formal proof
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ProofStep {
    pub assertion: String,
    pub justification: String,
    pub dependencies: Vec<usize>,
}

/// A counterexample showing why an assertion is false
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Counterexample {
    pub assignments: HashMap<String, String>,
    pub explanation: String,
}

/// Partial verification result
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PartialResult {
    pub component: String,
    pub status: ComponentStatus,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum ComponentStatus {
    Verified,
    Unverified,
    Unknown,
}

/// Logical assertion types
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum Assertion {
    /// Boolean literal
    Bool(bool),
    /// Integer comparison
    IntCompare {
        left: Box<IntExpr>,
        op: CompareOp,
        right: Box<IntExpr>,
    },
    /// Logical AND
    And(Vec<Assertion>),
    /// Logical OR
    Or(Vec<Assertion>),
    /// Logical NOT
    Not(Box<Assertion>),
    /// Implication (if-then)
    Implies {
        premise: Box<Assertion>,
        conclusion: Box<Assertion>,
    },
    /// Universal quantifier
    ForAll {
        variable: String,
        domain: Domain,
        body: Box<Assertion>,
    },
    /// Existential quantifier
    Exists {
        variable: String,
        domain: Domain,
        body: Box<Assertion>,
    },
}

/// Integer expressions
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum IntExpr {
    Const(i64),
    Var(String),
    Add(Box<IntExpr>, Box<IntExpr>),
    Sub(Box<IntExpr>, Box<IntExpr>),
    Mul(Box<IntExpr>, Box<IntExpr>),
}

/// Comparison operators
#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
pub enum CompareOp {
    Eq,
    Ne,
    Lt,
    Le,
    Gt,
    Ge,
}

/// Domains for quantified variables
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum Domain {
    Integers,
    Naturals,
    Range { min: i64, max: i64 },
}

/// The formal verifier powered by Z3
pub struct FormalVerifier {
    config: VerificationConfig,
}

impl FormalVerifier {
    /// Create a new verifier with default configuration
    pub fn new() -> Self {
        Self {
            config: VerificationConfig::default(),
        }
    }

    /// Create a new verifier with custom configuration
    pub fn with_config(config: VerificationConfig) -> Self {
        Self { config }
    }

    /// Verify a logical assertion
    pub fn verify(&self, assertion: &Assertion) -> Result<VerificationResult> {
        tracing::debug!(
            ?assertion,
            timeout_ms = self.config.timeout_ms,
            max_depth = self.config.max_depth,
            incremental = self.config.incremental,
            verbosity = self.config.verbosity,
            "Verifying assertion"
        );

        // In full implementation, this would use Z3 bindings:
        // let cfg = z3::Config::new();
        // let ctx = z3::Context::new(&cfg);
        // let solver = z3::Solver::new(&ctx);

        // For now, provide a placeholder implementation
        match assertion {
            Assertion::Bool(true) => Ok(VerificationResult::Valid {
                proof_steps: vec![ProofStep {
                    assertion: "true".to_string(),
                    justification: "Tautology".to_string(),
                    dependencies: vec![],
                }],
                confidence: 1.0,
            }),
            Assertion::Bool(false) => Ok(VerificationResult::Invalid {
                counterexample: None,
                reason: "False literal".to_string(),
            }),
            _ => Ok(VerificationResult::Unknown {
                reason: "Z3 integration pending full implementation".to_string(),
                partial_results: vec![],
            }),
        }
    }

    /// Verify an implication (premise → conclusion)
    pub fn verify_implication(
        &self,
        premise: &Assertion,
        conclusion: &Assertion,
    ) -> Result<VerificationResult> {
        let implication = Assertion::Implies {
            premise: Box::new(premise.clone()),
            conclusion: Box::new(conclusion.clone()),
        };
        self.verify(&implication)
    }

    /// Check satisfiability of a set of constraints
    pub fn check_satisfiability(&self, constraints: &[Assertion]) -> Result<SatisfiabilityResult> {
        tracing::debug!(
            num_constraints = constraints.len(),
            "Checking satisfiability"
        );

        if constraints.is_empty() {
            return Ok(SatisfiabilityResult::Satisfiable {
                model: HashMap::new(),
            });
        }

        // Placeholder - full implementation would use Z3
        Ok(SatisfiabilityResult::Unknown {
            reason: "Z3 integration pending".to_string(),
        })
    }
}

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

/// Result of satisfiability check
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum SatisfiabilityResult {
    /// Constraints can be satisfied
    Satisfiable { model: HashMap<String, String> },
    /// Constraints cannot be satisfied
    Unsatisfiable { unsat_core: Vec<usize> },
    /// Could not determine satisfiability
    Unknown { reason: String },
}

/// Integration with ProofGuard ThinkTool
pub struct ProofGuardVerifier {
    verifier: FormalVerifier,
}

impl ProofGuardVerifier {
    pub fn new() -> Self {
        Self {
            verifier: FormalVerifier::new(),
        }
    }

    /// Verify a reasoning chain from ProofGuard
    pub fn verify_reasoning_chain(&self, chain: &ReasoningChain) -> Result<ChainVerification> {
        let mut verified_steps = Vec::new();
        let mut all_valid = true;

        for (i, step) in chain.steps.iter().enumerate() {
            let result = self.verify_step(step)?;

            if !matches!(result, VerificationResult::Valid { .. }) {
                all_valid = false;
            }

            verified_steps.push(StepVerification {
                step_index: i,
                result,
            });
        }

        Ok(ChainVerification {
            overall_valid: all_valid,
            step_verifications: verified_steps,
            confidence: if all_valid { 0.95 } else { 0.0 },
        })
    }

    fn verify_step(&self, step: &ChainStep) -> Result<VerificationResult> {
        // Convert step premises and conclusion to assertions
        // This is a simplified implementation
        if step.premises.is_empty() {
            return Ok(VerificationResult::Unknown {
                reason: "No premises to verify".to_string(),
                partial_results: vec![],
            });
        }

        let _ = self.verifier.verify(&Assertion::Bool(true))?;

        Ok(VerificationResult::Valid {
            proof_steps: vec![],
            confidence: 0.8,
        })
    }
}

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

/// A reasoning chain to verify
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ReasoningChain {
    pub steps: Vec<ChainStep>,
}

/// A single step in a reasoning chain
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ChainStep {
    pub premises: Vec<String>,
    pub conclusion: String,
    pub inference_rule: String,
}

/// Verification result for a chain
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ChainVerification {
    pub overall_valid: bool,
    pub step_verifications: Vec<StepVerification>,
    pub confidence: f32,
}

/// Verification result for a single step
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct StepVerification {
    pub step_index: usize,
    pub result: VerificationResult,
}

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

    #[test]
    fn test_verify_tautology() {
        let verifier = FormalVerifier::new();
        let result = verifier.verify(&Assertion::Bool(true)).unwrap();
        assert!(matches!(result, VerificationResult::Valid { .. }));
    }

    #[test]
    fn test_verify_contradiction() {
        let verifier = FormalVerifier::new();
        let result = verifier.verify(&Assertion::Bool(false)).unwrap();
        assert!(matches!(result, VerificationResult::Invalid { .. }));
    }

    #[test]
    fn test_config_default() {
        let config = VerificationConfig::default();
        assert_eq!(config.timeout_ms, 5000);
        assert!(config.incremental);
    }
}