//! Semantic equivalence oracle (beyond I/O)
//!
//! Provides advanced verification methods that go beyond simple I/O comparison:
//! - AST-based semantic similarity
//! - Memory layout equivalence
//! - Performance profile matching
//! - Formal verification integration (bounded model checking)
//!
//! See VERIFICAR-091.

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

/// Semantic equivalence verdict
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub enum SemanticVerdict {
    /// Semantically equivalent
    Equivalent,
    /// Semantically different with explanation
    Different {
        /// Reason for the difference
        reason: String,
        /// Detailed difference information
        details: DifferenceDetails,
    },
    /// Cannot determine equivalence
    Unknown {
        /// Reason equivalence could not be determined
        reason: String,
    },
}

/// Details about semantic differences
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct DifferenceDetails {
    /// AST similarity score (0.0 to 1.0)
    pub ast_similarity: f64,
    /// Memory layout match
    pub memory_match: bool,
    /// Performance ratio (target/source)
    pub performance_ratio: Option<f64>,
    /// Specific differences found
    pub differences: Vec<SemanticDifference>,
}

/// A specific semantic difference
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct SemanticDifference {
    /// Category of difference
    pub category: DifferenceCategory,
    /// Location in source (line, column)
    pub source_location: Option<(usize, usize)>,
    /// Location in target (line, column)
    pub target_location: Option<(usize, usize)>,
    /// Description of the difference
    pub description: String,
}

/// Categories of semantic differences
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum DifferenceCategory {
    /// Control flow difference
    ControlFlow,
    /// Data flow difference
    DataFlow,
    /// Type system difference
    TypeSystem,
    /// Memory model difference
    MemoryModel,
    /// Concurrency semantics difference
    Concurrency,
    /// Numeric precision difference
    NumericPrecision,
    /// Exception/error handling difference
    ErrorHandling,
    /// Other semantic difference
    Other,
}

/// AST node for semantic analysis
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct SemanticNode {
    /// Node type
    pub node_type: String,
    /// Node value (if any)
    pub value: Option<String>,
    /// Child nodes
    pub children: Vec<SemanticNode>,
    /// Semantic annotations
    pub annotations: HashMap<String, String>,
}

impl SemanticNode {
    /// Create a new semantic node
    #[must_use]
    pub fn new(node_type: impl Into<String>) -> Self {
        Self {
            node_type: node_type.into(),
            value: None,
            children: Vec::new(),
            annotations: HashMap::new(),
        }
    }

    /// Add a child node
    #[must_use]
    pub fn with_child(mut self, child: SemanticNode) -> Self {
        self.children.push(child);
        self
    }

    /// Set node value
    #[must_use]
    pub fn with_value(mut self, value: impl Into<String>) -> Self {
        self.value = Some(value.into());
        self
    }

    /// Add annotation
    #[must_use]
    pub fn with_annotation(mut self, key: impl Into<String>, value: impl Into<String>) -> Self {
        self.annotations.insert(key.into(), value.into());
        self
    }

    /// Count total nodes in tree
    #[must_use]
    pub fn node_count(&self) -> usize {
        1 + self
            .children
            .iter()
            .map(SemanticNode::node_count)
            .sum::<usize>()
    }

    /// Calculate tree depth
    #[must_use]
    pub fn depth(&self) -> usize {
        1 + self
            .children
            .iter()
            .map(SemanticNode::depth)
            .max()
            .unwrap_or(0)
    }
}

/// Memory layout information
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct MemoryLayout {
    /// Stack allocations
    pub stack_size: usize,
    /// Heap allocations
    pub heap_allocations: Vec<HeapAllocation>,
    /// Static/global data
    pub static_size: usize,
}

/// A heap allocation
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct HeapAllocation {
    /// Allocation size in bytes
    pub size: usize,
    /// Type being allocated
    pub type_name: String,
    /// Allocation site (function name)
    pub site: String,
}

/// Performance profile
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct PerformanceProfile {
    /// Estimated time complexity
    pub time_complexity: Complexity,
    /// Estimated space complexity
    pub space_complexity: Complexity,
    /// Number of loop iterations (estimated)
    pub loop_iterations: Option<usize>,
    /// Number of function calls
    pub function_calls: usize,
    /// Number of allocations
    pub allocations: usize,
}

/// Complexity class
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum Complexity {
    /// O(1)
    Constant,
    /// O(log n)
    Logarithmic,
    /// O(n)
    Linear,
    /// O(n log n)
    Linearithmic,
    /// O(n^2)
    Quadratic,
    /// O(n^3)
    Cubic,
    /// O(2^n)
    Exponential,
    /// Unknown complexity
    Unknown,
}

/// Semantic oracle trait
pub trait SemanticOracle: Send + Sync {
    /// Check semantic equivalence between source and target
    fn check_equivalence(&self, source: &str, target: &str) -> SemanticVerdict;

    /// Calculate AST similarity score
    fn ast_similarity(&self, source: &str, target: &str) -> f64;

    /// Compare memory layouts
    fn compare_memory(&self, source: &str, target: &str) -> bool;

    /// Compare performance profiles
    fn compare_performance(&self, source: &str, target: &str) -> Option<f64>;
}

/// Basic semantic oracle using AST comparison
#[derive(Debug, Default)]
pub struct AstSemanticOracle {
    /// Similarity threshold for equivalence
    pub similarity_threshold: f64,
}

impl AstSemanticOracle {
    /// Create a new AST semantic oracle
    #[must_use]
    pub fn new(similarity_threshold: f64) -> Self {
        Self {
            similarity_threshold,
        }
    }

    /// Parse code into semantic AST (placeholder)
    fn parse_semantic_ast(&self, _code: &str) -> Option<SemanticNode> {
        // Placeholder: actual implementation would use tree-sitter
        None
    }

    /// Calculate tree edit distance similarity
    fn tree_similarity(&self, _source: &SemanticNode, _target: &SemanticNode) -> f64 {
        // Placeholder: would implement Zhang-Shasha or similar algorithm
        0.0
    }
}

impl SemanticOracle for AstSemanticOracle {
    fn check_equivalence(&self, source: &str, target: &str) -> SemanticVerdict {
        let similarity = self.ast_similarity(source, target);

        if similarity >= self.similarity_threshold {
            SemanticVerdict::Equivalent
        } else {
            SemanticVerdict::Different {
                reason: format!(
                    "AST similarity {:.2} below threshold {:.2}",
                    similarity, self.similarity_threshold
                ),
                details: DifferenceDetails {
                    ast_similarity: similarity,
                    memory_match: self.compare_memory(source, target),
                    performance_ratio: self.compare_performance(source, target),
                    differences: vec![],
                },
            }
        }
    }

    fn ast_similarity(&self, source: &str, target: &str) -> f64 {
        let source_ast = self.parse_semantic_ast(source);
        let target_ast = self.parse_semantic_ast(target);

        if let (Some(s), Some(t)) = (source_ast, target_ast) {
            self.tree_similarity(&s, &t)
        } else {
            // Fallback: simple text similarity
            let source_tokens: Vec<&str> = source.split_whitespace().collect();
            let target_tokens: Vec<&str> = target.split_whitespace().collect();

            if source_tokens.is_empty() && target_tokens.is_empty() {
                return 1.0;
            }

            let common = source_tokens
                .iter()
                .filter(|t| target_tokens.contains(t))
                .count();
            let total = source_tokens.len().max(target_tokens.len());

            common as f64 / total as f64
        }
    }

    fn compare_memory(&self, _source: &str, _target: &str) -> bool {
        // Placeholder: would analyze memory patterns
        true
    }

    fn compare_performance(&self, _source: &str, _target: &str) -> Option<f64> {
        // Placeholder: would estimate performance ratio
        Some(1.0)
    }
}

/// Formal verification oracle (bounded model checking)
#[derive(Debug, Default)]
pub struct FormalVerificationOracle {
    /// Maximum bound for model checking
    pub max_bound: usize,
    /// Timeout in milliseconds
    pub timeout_ms: u64,
}

impl FormalVerificationOracle {
    /// Create a new formal verification oracle
    #[must_use]
    pub fn new(max_bound: usize, timeout_ms: u64) -> Self {
        Self {
            max_bound,
            timeout_ms,
        }
    }

    /// Encode program as SMT formula (placeholder)
    fn encode_smt(&self, _code: &str) -> Option<String> {
        // Placeholder: would generate SMT-LIB format
        None
    }

    /// Check satisfiability (placeholder)
    fn check_sat(&self, _formula: &str) -> Option<bool> {
        // Placeholder: would call Z3 or similar
        None
    }
}

impl SemanticOracle for FormalVerificationOracle {
    fn check_equivalence(&self, source: &str, target: &str) -> SemanticVerdict {
        let source_smt = self.encode_smt(source);
        let target_smt = self.encode_smt(target);

        match (source_smt, target_smt) {
            (Some(s), Some(t)) => {
                // Check if source != target is satisfiable
                let diff_formula = format!("(assert (not (= {s} {t})))");
                match self.check_sat(&diff_formula) {
                    Some(false) => SemanticVerdict::Equivalent,
                    Some(true) => SemanticVerdict::Different {
                        reason: "Counterexample found".to_string(),
                        details: DifferenceDetails {
                            ast_similarity: 0.0,
                            memory_match: false,
                            performance_ratio: None,
                            differences: vec![],
                        },
                    },
                    None => SemanticVerdict::Unknown {
                        reason: "SMT solver timeout or error".to_string(),
                    },
                }
            }
            _ => SemanticVerdict::Unknown {
                reason: "Failed to encode programs as SMT".to_string(),
            },
        }
    }

    fn ast_similarity(&self, _source: &str, _target: &str) -> f64 {
        // Formal verification doesn't use AST similarity
        0.0
    }

    fn compare_memory(&self, _source: &str, _target: &str) -> bool {
        // Would need memory model encoding
        false
    }

    fn compare_performance(&self, _source: &str, _target: &str) -> Option<f64> {
        // Formal verification doesn't estimate performance
        None
    }
}

/// Combined semantic oracle
#[derive(Debug)]
pub struct CombinedSemanticOracle {
    /// AST-based oracle
    pub ast_oracle: AstSemanticOracle,
    /// Formal verification oracle (optional)
    pub formal_oracle: Option<FormalVerificationOracle>,
    /// Minimum AST similarity to consider formal verification
    pub formal_threshold: f64,
}

impl Default for CombinedSemanticOracle {
    fn default() -> Self {
        Self {
            ast_oracle: AstSemanticOracle::new(0.8),
            formal_oracle: None,
            formal_threshold: 0.5,
        }
    }
}

impl CombinedSemanticOracle {
    /// Create with formal verification enabled
    #[must_use]
    pub fn with_formal_verification(max_bound: usize, timeout_ms: u64) -> Self {
        Self {
            ast_oracle: AstSemanticOracle::new(0.8),
            formal_oracle: Some(FormalVerificationOracle::new(max_bound, timeout_ms)),
            formal_threshold: 0.5,
        }
    }
}

impl SemanticOracle for CombinedSemanticOracle {
    fn check_equivalence(&self, source: &str, target: &str) -> SemanticVerdict {
        // First, quick AST check
        let ast_similarity = self.ast_oracle.ast_similarity(source, target);

        if ast_similarity >= self.ast_oracle.similarity_threshold {
            return SemanticVerdict::Equivalent;
        }

        // If similarity is above threshold, try formal verification
        if ast_similarity >= self.formal_threshold {
            if let Some(ref formal) = self.formal_oracle {
                return formal.check_equivalence(source, target);
            }
        }

        SemanticVerdict::Different {
            reason: format!("AST similarity {ast_similarity:.2} below threshold"),
            details: DifferenceDetails {
                ast_similarity,
                memory_match: self.ast_oracle.compare_memory(source, target),
                performance_ratio: self.ast_oracle.compare_performance(source, target),
                differences: vec![],
            },
        }
    }

    fn ast_similarity(&self, source: &str, target: &str) -> f64 {
        self.ast_oracle.ast_similarity(source, target)
    }

    fn compare_memory(&self, source: &str, target: &str) -> bool {
        self.ast_oracle.compare_memory(source, target)
    }

    fn compare_performance(&self, source: &str, target: &str) -> Option<f64> {
        self.ast_oracle.compare_performance(source, target)
    }
}

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

    #[test]
    fn test_semantic_node_new() {
        let node = SemanticNode::new("function");
        assert_eq!(node.node_type, "function");
        assert!(node.value.is_none());
        assert!(node.children.is_empty());
    }

    #[test]
    fn test_semantic_node_builder() {
        let node = SemanticNode::new("function")
            .with_value("add")
            .with_child(SemanticNode::new("param").with_value("a"))
            .with_child(SemanticNode::new("param").with_value("b"))
            .with_annotation("return_type", "int");

        assert_eq!(node.node_type, "function");
        assert_eq!(node.value, Some("add".to_string()));
        assert_eq!(node.children.len(), 2);
        assert_eq!(
            node.annotations.get("return_type"),
            Some(&"int".to_string())
        );
    }

    #[test]
    fn test_semantic_node_count() {
        let node = SemanticNode::new("root")
            .with_child(SemanticNode::new("child1"))
            .with_child(SemanticNode::new("child2").with_child(SemanticNode::new("grandchild")));

        assert_eq!(node.node_count(), 4);
    }

    #[test]
    fn test_semantic_node_depth() {
        let node = SemanticNode::new("root")
            .with_child(SemanticNode::new("child1"))
            .with_child(SemanticNode::new("child2").with_child(SemanticNode::new("grandchild")));

        assert_eq!(node.depth(), 3);
    }

    #[test]
    fn test_ast_oracle_identical_code() {
        let oracle = AstSemanticOracle::new(0.8);
        let code = "def add(a, b): return a + b";

        let similarity = oracle.ast_similarity(code, code);
        assert!((similarity - 1.0).abs() < f64::EPSILON);
    }

    #[test]
    fn test_ast_oracle_similar_code() {
        let oracle = AstSemanticOracle::new(0.5);
        let source = "def add(a, b): return a + b";
        let target = "fn add(a: i32, b: i32) -> i32 { a + b }";

        let similarity = oracle.ast_similarity(source, target);
        assert!(similarity > 0.0);
        assert!(similarity < 1.0);
    }

    #[test]
    fn test_ast_oracle_empty_code() {
        let oracle = AstSemanticOracle::new(0.8);
        let similarity = oracle.ast_similarity("", "");
        assert!((similarity - 1.0).abs() < f64::EPSILON);
    }

    #[test]
    fn test_ast_oracle_check_equivalence() {
        let oracle = AstSemanticOracle::new(0.99);
        let code = "x = 1";

        let verdict = oracle.check_equivalence(code, code);
        assert_eq!(verdict, SemanticVerdict::Equivalent);
    }

    #[test]
    fn test_ast_oracle_check_different() {
        let oracle = AstSemanticOracle::new(0.99);
        let source = "def foo(): pass";
        let target = "fn bar() {}";

        let verdict = oracle.check_equivalence(source, target);
        assert!(matches!(verdict, SemanticVerdict::Different { .. }));
    }

    #[test]
    fn test_difference_category_serialization() {
        let category = DifferenceCategory::ControlFlow;
        let json = serde_json::to_string(&category).unwrap();
        assert!(json.contains("ControlFlow"));

        let parsed: DifferenceCategory = serde_json::from_str(&json).unwrap();
        assert_eq!(parsed, category);
    }

    #[test]
    fn test_complexity_ordering() {
        // Just verify these compile and are distinct
        let complexities = vec![
            Complexity::Constant,
            Complexity::Logarithmic,
            Complexity::Linear,
            Complexity::Linearithmic,
            Complexity::Quadratic,
            Complexity::Cubic,
            Complexity::Exponential,
            Complexity::Unknown,
        ];
        assert_eq!(complexities.len(), 8);
    }

    #[test]
    fn test_memory_layout_default() {
        let layout = MemoryLayout {
            stack_size: 1024,
            heap_allocations: vec![],
            static_size: 0,
        };
        assert_eq!(layout.stack_size, 1024);
        assert!(layout.heap_allocations.is_empty());
    }

    #[test]
    fn test_performance_profile() {
        let profile = PerformanceProfile {
            time_complexity: Complexity::Linear,
            space_complexity: Complexity::Constant,
            loop_iterations: Some(100),
            function_calls: 5,
            allocations: 2,
        };
        assert_eq!(profile.time_complexity, Complexity::Linear);
        assert_eq!(profile.loop_iterations, Some(100));
    }

    #[test]
    fn test_combined_oracle_default() {
        let oracle = CombinedSemanticOracle::default();
        assert!(oracle.formal_oracle.is_none());
        assert!((oracle.formal_threshold - 0.5).abs() < f64::EPSILON);
    }

    #[test]
    fn test_combined_oracle_with_formal() {
        let oracle = CombinedSemanticOracle::with_formal_verification(10, 5000);
        assert!(oracle.formal_oracle.is_some());
    }

    #[test]
    fn test_semantic_verdict_serialization() {
        let verdict = SemanticVerdict::Equivalent;
        let json = serde_json::to_string(&verdict).unwrap();
        let parsed: SemanticVerdict = serde_json::from_str(&json).unwrap();
        assert_eq!(parsed, verdict);
    }

    #[test]
    fn test_semantic_difference() {
        let diff = SemanticDifference {
            category: DifferenceCategory::NumericPrecision,
            source_location: Some((10, 5)),
            target_location: Some((12, 8)),
            description: "Float precision loss".to_string(),
        };
        assert_eq!(diff.category, DifferenceCategory::NumericPrecision);
        assert_eq!(diff.source_location, Some((10, 5)));
    }

    // RED PHASE: Tests that require full implementation

    #[test]
    #[ignore = "requires tree-sitter AST parsing"]
    fn test_ast_oracle_real_parsing() {
        // TODO: Implement with tree-sitter
        // let oracle = AstSemanticOracle::new(0.8);
        // let source = "def add(a: int, b: int) -> int:\n    return a + b";
        // let ast = oracle.parse_semantic_ast(source);
        // assert!(ast.is_some());
        // let ast = ast.unwrap();
        // assert_eq!(ast.node_type, "function_definition");
        unimplemented!("Real AST parsing not yet implemented")
    }

    #[test]
    #[ignore = "requires tree edit distance algorithm"]
    fn test_tree_edit_distance() {
        // TODO: Implement Zhang-Shasha algorithm
        // let oracle = AstSemanticOracle::new(0.8);
        // let source = SemanticNode::new("add")
        //     .with_child(SemanticNode::new("param").with_value("a"))
        //     .with_child(SemanticNode::new("param").with_value("b"));
        // let target = SemanticNode::new("add")
        //     .with_child(SemanticNode::new("param").with_value("x"))
        //     .with_child(SemanticNode::new("param").with_value("y"));
        // let similarity = oracle.tree_similarity(&source, &target);
        // assert!(similarity > 0.8); // Same structure, different names
        unimplemented!("Tree edit distance not yet implemented")
    }

    #[test]
    #[ignore = "requires Z3 SMT solver integration"]
    fn test_formal_verification_basic() {
        // TODO: Implement Z3 integration
        // let oracle = FormalVerificationOracle::new(10, 5000);
        // let source = "x = a + b";
        // let target = "let x = a + b;";
        // let verdict = oracle.check_equivalence(source, target);
        // assert_eq!(verdict, SemanticVerdict::Equivalent);
        unimplemented!("Z3 integration not yet implemented")
    }

    #[test]
    #[ignore = "requires Z3 SMT solver integration"]
    fn test_formal_verification_counterexample() {
        // TODO: Find counterexample via SMT
        // let oracle = FormalVerificationOracle::new(10, 5000);
        // let source = "x = a + b";  // Python: wraps on overflow
        // let target = "let x: i32 = a + b;";  // Rust: panics on overflow
        // let verdict = oracle.check_equivalence(source, target);
        // assert!(matches!(verdict, SemanticVerdict::Different { .. }));
        unimplemented!("Z3 counterexample generation not yet implemented")
    }

    #[test]
    #[ignore = "requires memory analysis"]
    fn test_memory_layout_analysis() {
        // TODO: Implement memory layout extraction
        // let oracle = AstSemanticOracle::new(0.8);
        // let source = "xs = [1, 2, 3]";  // Python list (heap)
        // let target = "let xs = vec![1, 2, 3];";  // Rust Vec (heap)
        // assert!(oracle.compare_memory(source, target));
        unimplemented!("Memory layout analysis not yet implemented")
    }

    #[test]
    #[ignore = "requires performance estimation"]
    fn test_performance_estimation() {
        // TODO: Implement performance profiling
        // let oracle = AstSemanticOracle::new(0.8);
        // let source = "for i in range(n): sum += i";  // O(n)
        // let target = "let sum: i32 = (0..n).sum();";  // O(n)
        // let ratio = oracle.compare_performance(source, target);
        // assert!(ratio.is_some());
        // assert!((ratio.unwrap() - 1.0).abs() < 0.5);  // Within 50%
        unimplemented!("Performance estimation not yet implemented")
    }

    #[test]
    #[ignore = "requires bounded model checking"]
    fn test_bounded_model_checking() {
        // TODO: Implement BMC
        // let oracle = FormalVerificationOracle::new(100, 10000);
        // let source = "def loop(n):\n    for i in range(n): pass";
        // let target = "fn loop(n: usize) { for _ in 0..n {} }";
        // let verdict = oracle.check_equivalence(source, target);
        // assert_eq!(verdict, SemanticVerdict::Equivalent);
        unimplemented!("Bounded model checking not yet implemented")
    }
}
