//! Deterministic execution support for REPL replay testing

//!

//! Implements the `DeterministicRepl` trait for the Ruchy REPL to enable

//! deterministic replay for testing and educational assessment.

use anyhow::Result;

use std::collections::HashMap;

use sha2::{Sha256, Digest};

use crate::runtime::repl::{Repl, Value};

use crate::runtime::replay::{

    DeterministicRepl, ReplayResult, StateCheckpoint, ResourceUsage,

    ValidationResult, Divergence

};

/// Mock time source for deterministic time operations

pub struct MockTime {

    current_ns: u64,

}

impl Default for MockTime {

    fn default() -> Self {

        Self::new()

    }

}

impl MockTime {

    pub fn new() -> Self {

        Self { current_ns: 0 }

    }

    pub fn advance(&mut self, ns: u64) {

        self.current_ns += ns;

    }

    pub fn now(&self) -> u64 {

        self.current_ns

    }

}

/// Deterministic random number generator

pub struct DeterministicRng {

    seed: u64,

    state: u64,

}

impl DeterministicRng {

    pub fn new(seed: u64) -> Self {

        Self {

            seed,

            state: seed,

        }

    }

    pub fn next(&mut self) -> u64 {

        // Simple LCG for deterministic pseudo-random numbers

        self.state = self.state.wrapping_mul(6_364_136_223_846_793_005)

            .wrapping_add(1_442_695_040_888_963_407);

        self.state

    }

    pub fn reset(&mut self) {

        self.state = self.seed;

    }

}

/// Extension trait to make Repl deterministic

impl DeterministicRepl for Repl {

    fn execute_with_seed(&mut self, input: &str, _seed: u64) -> ReplayResult {

        // Store current resource usage start point

        let start_heap = self.estimate_heap_usage();

        let start_stack = self.estimate_stack_depth();

        let start_time = std::time::Instant::now();

        // Note: RNG seed will be set when random number support is added to REPL

        // Currently executes normally as REPL doesn't use RNG yet

        // Execute the input

        let output = self.eval(input).map(|s| {

            // Convert string output back to Value

            // This is a simplified conversion - in production we'd preserve the actual Value

            if s == "()" || s.is_empty() {

                Value::Unit

            } else if s == "true" {

                Value::Bool(true)

            } else if s == "false" {

                Value::Bool(false)

            } else if let Ok(n) = s.parse::<i64>() {

                Value::Int(n)

            } else if s.starts_with('"') && s.ends_with('"') {

                Value::String(s[1..s.len()-1].to_string())

            } else {

                // For complex types, we store as string representation

                Value::String(s)

            }

        });

        // Calculate resource usage

        let heap_bytes = self.estimate_heap_usage() - start_heap;

        let stack_depth = self.estimate_stack_depth() - start_stack;

        let cpu_ns = start_time.elapsed().as_nanos() as u64;

        // Compute state hash

        let state_hash = self.compute_state_hash();

        ReplayResult {

            output,

            state_hash,

            resource_usage: ResourceUsage {

                heap_bytes,

                stack_depth,

                cpu_ns,

            },

        }

    }

    fn checkpoint(&self) -> StateCheckpoint {

        let mut bindings = HashMap::new();

        let type_environment = HashMap::new();

        // Extract all variable bindings

        for (name, value) in self.get_bindings() {

            bindings.insert(name.clone(), format!("{value:?}"));

        }

        // Extract type environment if available

        // Type tracking will be implemented when static analysis is added

        StateCheckpoint {

            bindings,

            type_environment,

            state_hash: self.compute_state_hash(),

            resource_usage: ResourceUsage {

                heap_bytes: self.estimate_heap_usage(),

                stack_depth: self.estimate_stack_depth(),

                cpu_ns: 0, // Not meaningful for a checkpoint

            },

        }

    }

    fn restore(&mut self, checkpoint: &StateCheckpoint) -> Result<()> {

        // Clear current state

        self.clear_bindings();

        // Restore bindings

        let bindings = self.get_bindings_mut();

        for (name, value_str) in &checkpoint.bindings {

            // This is simplified - in production we'd properly deserialize the values

            let value = if value_str == "Unit" {

                Value::Unit

            } else if value_str == "true" {

                Value::Bool(true)

            } else if value_str == "false" {

                Value::Bool(false)

            } else if let Ok(n) = value_str.parse::<i64>() {

                Value::Int(n)

            } else {

                Value::String(value_str.clone())

            };

            bindings.insert(name.clone(), value);

        }

        Ok(())

    }

    fn validate_determinism(&self, other: &Self) -> ValidationResult {

        let mut divergences = vec![];

        // Compare variable bindings

        for (name, value) in self.get_bindings() {

            match other.get_bindings().get(name) {

                Some(other_value) if value == other_value => {

                    // Values match, good

                }

                Some(other_value) => {

                    divergences.push(Divergence::State {

                        expected_hash: format!("{value:?}"),

                        actual_hash: format!("{other_value:?}"),

                    });

                }

                None => {

                    divergences.push(Divergence::State {

                        expected_hash: format!("{value:?}"),

                        actual_hash: "missing".to_string(),

                    });

                }

            }

        }

        // Check for variables in other but not in self

        for name in other.get_bindings().keys() {

            if !self.get_bindings().contains_key(name) {

                divergences.push(Divergence::State {

                    expected_hash: "missing".to_string(),

                    actual_hash: format!("variable: {name}"),

                });

            }

        }

        ValidationResult {

            is_deterministic: divergences.is_empty(),

            divergences,

        }

    }

}

// Helper methods for Repl

impl Repl {

    /// Estimate heap usage in bytes (simplified)

    fn estimate_heap_usage(&self) -> usize {

        // Rough estimate based on number of variables and their sizes

        let mut total = 0;

        for value in self.get_bindings().values() {

            total += std::mem::size_of_val(value);

            total += match value {

                Value::String(s) => s.capacity(),

                Value::List(items) => items.len() * std::mem::size_of::<Value>(),

                Value::Object(map) => map.len() * (32 + std::mem::size_of::<Value>()),

                Value::HashMap(map) => map.len() * (std::mem::size_of::<Value>() * 2),

                _ => 0,

            };

        }

        total

    }

    /// Estimate current stack depth (simplified)

    fn estimate_stack_depth(&self) -> usize {

        // This is a placeholder - real implementation would track actual call stack

        // For now, we return a fixed estimate based on the number of bindings

        self.get_bindings().len() / 10 + 1

    }

    /// Compute a hash of the current state for comparison

    fn compute_state_hash(&self) -> String {

        let mut hasher = Sha256::new();

        // Sort variables by name for deterministic hashing

        let mut sorted_vars: Vec<_> = self.get_bindings().iter().collect();

        sorted_vars.sort_by_key(|(name, _)| name.as_str());

        for (name, value) in sorted_vars {

            hasher.update(name.as_bytes());

            hasher.update(b":");

            hasher.update(format!("{value:?}").as_bytes());

            hasher.update(b";");

        }

        format!("{:x}", hasher.finalize())

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn test_deterministic_execution() {

        let mut repl1 = Repl::new().unwrap();

        let mut repl2 = Repl::new().unwrap();

        // Execute same commands with same seed

        let result1 = repl1.execute_with_seed("let x = 42", 12345);

        let result2 = repl2.execute_with_seed("let x = 42", 12345);

        // Results should be identical

        assert!(result1.output.is_ok());

        assert!(result2.output.is_ok());

        assert_eq!(result1.state_hash, result2.state_hash);

    }

    #[test]

    fn test_checkpoint_restore() {

        let mut repl = Repl::new().unwrap();

        // Create some state

        repl.eval("let x = 10").unwrap();

        repl.eval("let y = 20").unwrap();

        // Create checkpoint using DeterministicRepl trait

        let checkpoint = DeterministicRepl::checkpoint(&repl);

        // Modify state

        repl.eval("let x = 99").unwrap();

        repl.eval("let z = 30").unwrap();

        // Restore checkpoint

        DeterministicRepl::restore(&mut repl, &checkpoint).unwrap();

        // Check that state was restored

        // Note: Values are restored from debug format, so they may have different representation

        assert!(repl.eval("x").is_ok());

        assert!(repl.eval("y").is_ok());

        // z should not exist after restore

        assert!(repl.eval("z").is_err());

    }

    #[test]

    fn test_determinism_validation() {

        let mut repl1 = Repl::new().unwrap();

        let mut repl2 = Repl::new().unwrap();

        // Same operations

        repl1.eval("let x = 1").unwrap();

        repl2.eval("let x = 1").unwrap();

        let validation = repl1.validate_determinism(&repl2);

        assert!(validation.is_deterministic);

        assert!(validation.divergences.is_empty());

        // Different operations

        repl1.eval("let y = 2").unwrap();

        repl2.eval("let y = 3").unwrap();

        let validation = repl1.validate_determinism(&repl2);

        assert!(!validation.is_deterministic);

        assert!(!validation.divergences.is_empty());

    }

}