//! Validation utilities for checkpoint integrity
//!
//! Provides checksum validation and corruption detection for checkpoints.

use std::collections::HashMap;
use std::path::Path;

use sha2::{Digest, Sha256};
use tracing::{debug, error, warn};

use super::{CheckpointMetadata, ModelType};
use crate::MLError;

/// Write SHA-256 checksum sidecar file alongside a safetensors checkpoint.
/// Creates `{path}.sha256` containing the hex digest.
pub fn write_checksum(safetensors_path: &Path) -> Result<(), MLError> {
    let bytes = std::fs::read(safetensors_path).map_err(|e| {
        MLError::CheckpointError(format!("Failed to read file for checksum: {}", e))
    })?;
    let hash = Sha256::digest(&bytes);
    let hex = format!("{:x}", hash);
    let checksum_path = safetensors_path.with_extension("sha256");
    std::fs::write(&checksum_path, hex.as_bytes()).map_err(|e| {
        MLError::CheckpointError(format!("Failed to write checksum: {}", e))
    })?;
    Ok(())
}

/// Verify SHA-256 checksum of a safetensors file against its `.sha256` sidecar.
/// Returns `Ok(true)` if valid, `Ok(false)` if mismatch.
/// Returns `Ok(true)` if no sidecar exists (backwards compatible).
pub fn verify_checksum(safetensors_path: &Path) -> Result<bool, MLError> {
    let checksum_path = safetensors_path.with_extension("sha256");
    if !checksum_path.exists() {
        warn!(
            "No checksum file for {}, skipping integrity check",
            safetensors_path.display()
        );
        return Ok(true);
    }
    let expected = std::fs::read_to_string(&checksum_path).map_err(|e| {
        MLError::CheckpointError(format!("Failed to read checksum: {}", e))
    })?;
    let bytes = std::fs::read(safetensors_path).map_err(|e| {
        MLError::CheckpointError(format!("Failed to read file for verification: {}", e))
    })?;
    let actual = format!("{:x}", Sha256::digest(&bytes));
    Ok(actual.trim() == expected.trim())
}

/// Validation manager for checkpoint integrity
#[derive(Debug)]
pub struct ValidationManager {
    /// Validation statistics
    stats: ValidationStats,
}

impl ValidationManager {
    /// Create a new validation manager
    pub fn new() -> Self {
        Self {
            stats: ValidationStats::default(),
        }
    }

    /// Calculate SHA-256 checksum of data
    pub fn calculate_checksum(&self, data: &[u8]) -> String {
        let mut hasher = Sha256::new();
        hasher.update(data);
        format!("{:x}", hasher.finalize())
    }

    /// Validate checksum of data
    pub fn validate_checksum(&self, data: &[u8], expected_checksum: &str) -> Result<(), MLError> {
        let calculated_checksum = self.calculate_checksum(data);

        if calculated_checksum != expected_checksum {
            error!(
                "Checksum mismatch: expected {}, got {}",
                expected_checksum, calculated_checksum
            );
            return Err(MLError::ModelError(format!(
                "Checkpoint corruption detected: checksum mismatch (expected: {}, got: {})",
                expected_checksum, calculated_checksum
            )));
        }

        debug!("Checksum validation passed: {}", calculated_checksum);
        Ok(())
    }

    /// Validate metadata consistency
    pub fn validate_metadata(&self, metadata: &CheckpointMetadata) -> Result<(), MLError> {
        // Check required fields
        if metadata.checkpoint_id.is_empty() {
            return Err(MLError::ModelError(
                "Checkpoint ID cannot be empty".to_owned(),
            ));
        }

        if metadata.model_name.is_empty() {
            return Err(MLError::ModelError(
                "Model name cannot be empty".to_owned(),
            ));
        }

        if metadata.version.is_empty() {
            return Err(MLError::ModelError(
                "Model version cannot be empty".to_owned(),
            ));
        }

        // Validate version format (basic semantic versioning)
        if !self.is_valid_version(&metadata.version) {
            return Err(MLError::ModelError(format!(
                "Invalid version format: {}",
                metadata.version
            )));
        }

        // Check file size consistency
        if metadata.file_size == 0 {
            warn!("Checkpoint has zero file size: {}", metadata.checkpoint_id);
        }

        if let Some(compressed_size) = metadata.compressed_size {
            if compressed_size > metadata.file_size {
                return Err(MLError::ModelError(
                    "Compressed size cannot be larger than original size".to_owned(),
                ));
            }
        }

        // Validate metrics ranges
        if let Some(accuracy) = metadata.accuracy {
            if !(0.0..=1.0).contains(&accuracy) {
                return Err(MLError::ModelError(format!(
                    "Accuracy must be between 0 and 1, got: {}",
                    accuracy
                )));
            }
        }

        debug!(
            "Metadata validation passed for checkpoint: {}",
            metadata.checkpoint_id
        );
        Ok(())
    }

    /// Validate model type compatibility
    pub fn validate_model_compatibility(
        &self,
        expected_type: ModelType,
        metadata: &CheckpointMetadata,
    ) -> Result<(), MLError> {
        if metadata.model_type != expected_type {
            return Err(MLError::ModelError(format!(
                "Model type mismatch: expected {:?}, got {:?}",
                expected_type, metadata.model_type
            )));
        }

        debug!("Model compatibility validation passed");
        Ok(())
    }

    /// Validate version compatibility
    pub fn validate_version_compatibility(
        &self,
        current_version: &str,
        checkpoint_version: &str,
    ) -> Result<(), MLError> {
        let current_parts = self.parse_version(current_version)?;
        let checkpoint_parts = self.parse_version(checkpoint_version)?;

        // Check major version compatibility
        if current_parts.0 != checkpoint_parts.0 {
            return Err(MLError::ModelError(format!(
                "Major version incompatibility: current {}, checkpoint {}",
                current_version, checkpoint_version
            )));
        }

        // Warn about minor version differences
        if current_parts.1 != checkpoint_parts.1 {
            warn!(
                "Minor version difference: current {}, checkpoint {}",
                current_version, checkpoint_version
            );
        }

        debug!("Version compatibility validation passed");
        Ok(())
    }

    /// Check if version string is valid
    fn is_valid_version(&self, version: &str) -> bool {
        self.parse_version(version).is_ok()
    }

    /// Parse semantic version string
    fn parse_version(&self, version: &str) -> Result<(u32, u32, u32), MLError> {
        let parts: Vec<&str> = version.split('.').collect();
        if parts.len() != 3 {
            return Err(MLError::ModelError(format!(
                "Invalid version format: {} (expected major.minor.patch)",
                version
            )));
        }

        let major = parts[0]
            .parse::<u32>()
            .map_err(|e| MLError::ModelError(format!("Invalid major version '{}': {e}", parts[0])))?;

        let minor = parts[1]
            .parse::<u32>()
            .map_err(|e| MLError::ModelError(format!("Invalid minor version '{}': {e}", parts[1])))?;

        let patch = parts[2]
            .parse::<u32>()
            .map_err(|e| MLError::ModelError(format!("Invalid patch version '{}': {e}", parts[2])))?;

        Ok((major, minor, patch))
    }

    /// Perform comprehensive validation
    pub fn comprehensive_validation(
        &self,
        data: &[u8],
        metadata: &CheckpointMetadata,
        expected_model_type: ModelType,
        current_version: &str,
    ) -> Result<ValidationReport, MLError> {
        let mut report = ValidationReport::new();

        // Checksum validation
        if let Err(e) = self.validate_checksum(data, &metadata.checksum) {
            report.add_error("checksum".to_owned(), e.to_string());
        } else {
            report.add_success("checksum".to_owned());
        }

        // Metadata validation
        if let Err(e) = self.validate_metadata(metadata) {
            report.add_error("metadata".to_owned(), e.to_string());
        } else {
            report.add_success("metadata".to_owned());
        }

        // Model compatibility validation
        if let Err(e) = self.validate_model_compatibility(expected_model_type, metadata) {
            report.add_error("model_compatibility".to_owned(), e.to_string());
        } else {
            report.add_success("model_compatibility".to_owned());
        }

        // Version compatibility validation
        if let Err(e) = self.validate_version_compatibility(current_version, &metadata.version) {
            report.add_warning("version_compatibility".to_owned(), e.to_string());
        } else {
            report.add_success("version_compatibility".to_owned());
        }

        // Data size validation
        if data.len() as u64 != metadata.file_size {
            report.add_error(
                "data_size".to_owned(),
                format!(
                    "Data size mismatch: expected {}, got {}",
                    metadata.file_size,
                    data.len()
                ),
            );
        } else {
            report.add_success("data_size".to_owned());
        }

        debug!(
            "Comprehensive validation completed with {} errors, {} warnings",
            report.errors.len(),
            report.warnings.len()
        );

        Ok(report)
    }

    /// Get validation statistics
    pub const fn get_stats(&self) -> &ValidationStats {
        &self.stats
    }
}

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

/// Validation statistics
#[derive(Debug, Clone, Default)]
pub struct ValidationStats {
    /// Total validations performed
    pub total_validations: u64,

    /// Successful validations
    pub successful_validations: u64,

    /// Failed validations
    pub failed_validations: u64,

    /// Checksum mismatches detected
    pub checksum_failures: u64,

    /// Metadata validation failures
    pub metadata_failures: u64,

    /// Version compatibility issues
    pub version_issues: u64,
}

impl ValidationStats {
    /// Calculate success rate
    pub fn success_rate(&self) -> f64 {
        if self.total_validations > 0 {
            self.successful_validations as f64 / self.total_validations as f64
        } else {
            0.0
        }
    }
}

/// Validation report containing results of comprehensive validation
#[derive(Debug, Clone)]
pub struct ValidationReport {
    /// Successful validation checks
    pub successes: Vec<String>,

    /// Validation warnings (non-critical issues)
    pub warnings: HashMap<String, String>,

    /// Validation errors (critical issues)
    pub errors: HashMap<String, String>,
}

impl ValidationReport {
    /// Create a new validation report
    pub fn new() -> Self {
        Self {
            successes: Vec::new(),
            warnings: HashMap::new(),
            errors: HashMap::new(),
        }
    }

    /// Add a successful check
    pub fn add_success(&mut self, check: String) {
        self.successes.push(check);
    }

    /// Add a warning
    pub fn add_warning(&mut self, check: String, message: String) {
        self.warnings.insert(check, message);
    }

    /// Add an error
    pub fn add_error(&mut self, check: String, message: String) {
        self.errors.insert(check, message);
    }

    /// Check if validation passed (no errors)
    pub fn is_valid(&self) -> bool {
        self.errors.is_empty()
    }

    /// Check if there are warnings
    pub fn has_warnings(&self) -> bool {
        !self.warnings.is_empty()
    }

    /// Get summary of validation results
    pub fn summary(&self) -> String {
        if self.is_valid() {
            if self.has_warnings() {
                format!(
                    "Validation passed with {} warnings ({} successful checks)",
                    self.warnings.len(),
                    self.successes.len()
                )
            } else {
                format!(
                    "Validation passed successfully ({} checks)",
                    self.successes.len()
                )
            }
        } else {
            format!(
                "Validation failed with {} errors and {} warnings",
                self.errors.len(),
                self.warnings.len()
            )
        }
    }
}

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

#[cfg(test)]
#[allow(
    clippy::assertions_on_result_states,
    clippy::len_zero,
    clippy::redundant_clone
)]
mod tests {
    use super::*;
    use chrono::Utc;


    #[test]
    fn test_checksum_validation() {
        let validator = ValidationManager::new();
        let data = b"test data for checksum";

        let checksum = validator.calculate_checksum(data);
        assert!(validator.validate_checksum(data, &checksum).is_ok());

        // Test with wrong checksum
        let wrong_checksum = "wrong_checksum";
        assert!(validator.validate_checksum(data, wrong_checksum).is_err());
    }

    #[test]
    fn test_metadata_validation() {
        let validator = ValidationManager::new();

        // Valid metadata
        let valid_metadata = CheckpointMetadata {
            checkpoint_id: "test_id".to_owned(),
            model_type: ModelType::DQN,
            model_name: "test_model".to_owned(),
            version: "1.2.3".to_owned(),
            created_at: Utc::now(),
            file_size: 1000,
            compressed_size: Some(800),
            accuracy: Some(0.95),
            ..Default::default()
        };

        assert!(validator.validate_metadata(&valid_metadata).is_ok());

        // Invalid metadata - empty model name
        let mut invalid_metadata = valid_metadata.clone();
        invalid_metadata.model_name = "".to_owned();
        assert!(validator.validate_metadata(&invalid_metadata).is_err());

        // Invalid metadata - invalid version
        let mut invalid_version = valid_metadata.clone();
        invalid_version.version = "invalid_version".to_owned();
        assert!(validator.validate_metadata(&invalid_version).is_err());

        // Invalid metadata - accuracy out of range
        let mut invalid_accuracy = valid_metadata.clone();
        invalid_accuracy.accuracy = Some(1.5);
        assert!(validator.validate_metadata(&invalid_accuracy).is_err());
    }

    #[test]
    fn test_version_parsing() -> Result<(), MLError> {
        let validator = ValidationManager::new();

        assert_eq!(validator.parse_version("1.2.3")?, (1, 2, 3));
        assert_eq!(validator.parse_version("0.1.0")?, (0, 1, 0));

        assert!(validator.parse_version("1.2").is_err());
        assert!(validator.parse_version("1.2.3.4").is_err());
        assert!(validator.parse_version("a.b.c").is_err());
        Ok(())
    }

    #[test]
    fn test_version_compatibility() {
        let validator = ValidationManager::new();

        // Same major version should be compatible
        assert!(validator
            .validate_version_compatibility("1.2.3", "1.3.0")
            .is_ok());

        // Different major version should be incompatible
        assert!(validator
            .validate_version_compatibility("1.0.0", "2.0.0")
            .is_err());

        // Invalid versions should return error
        assert!(validator
            .validate_version_compatibility("invalid", "1.0.0")
            .is_err());
    }

    #[test]
    fn test_model_compatibility() {
        let validator = ValidationManager::new();

        let metadata = CheckpointMetadata {
            model_type: ModelType::DQN,
            ..Default::default()
        };

        // Same model type should be compatible
        assert!(validator
            .validate_model_compatibility(ModelType::DQN, &metadata)
            .is_ok());

        // Different model type should be incompatible
        assert!(validator
            .validate_model_compatibility(ModelType::MAMBA, &metadata)
            .is_err());
    }

    #[test]
    fn test_comprehensive_validation() -> Result<(), MLError> {
        let validator = ValidationManager::new();
        let data = b"test checkpoint data";

        let metadata = CheckpointMetadata {
            checkpoint_id: "test_id".to_owned(),
            model_type: ModelType::TFT,
            model_name: "test_model".to_owned(),
            version: "1.0.0".to_owned(),
            created_at: Utc::now(),
            file_size: data.len() as u64,
            checksum: validator.calculate_checksum(data),
            ..Default::default()
        };

        let report =
            validator.comprehensive_validation(data, &metadata, ModelType::TFT, "1.0.0")?;

        assert!(report.is_valid());
        assert!(!report.has_warnings());
        assert!(report.successes.len() > 0);
        Ok(())
    }

    #[test]
    fn test_validation_report() {
        let mut report = ValidationReport::new();

        report.add_success("checksum".to_owned());
        report.add_warning("version".to_owned(), "Minor version mismatch".to_owned());
        report.add_error("metadata".to_owned(), "Invalid field".to_owned());

        assert!(!report.is_valid());
        assert!(report.has_warnings());
        assert_eq!(report.successes.len(), 1);
        assert_eq!(report.warnings.len(), 1);
        assert_eq!(report.errors.len(), 1);

        let summary = report.summary();
        assert!(summary.contains("failed"));
        assert!(summary.contains("1 errors"));
        assert!(summary.contains("1 warnings"));
    }

    #[test]
    fn test_sidecar_checksum_roundtrip() -> Result<(), Box<dyn std::error::Error>> {
        let dir = tempfile::TempDir::new()?;
        let path = dir.path().join("test_model.safetensors");
        std::fs::write(&path, b"fake model data")?;

        write_checksum(&path)?;

        let checksum_path = path.with_extension("sha256");
        assert!(checksum_path.exists());

        assert!(verify_checksum(&path)?);
        Ok(())
    }

    #[test]
    fn test_sidecar_checksum_detects_corruption() -> Result<(), Box<dyn std::error::Error>> {
        let dir = tempfile::TempDir::new()?;
        let path = dir.path().join("test_model.safetensors");
        std::fs::write(&path, b"original data")?;

        write_checksum(&path)?;

        // Corrupt the file
        std::fs::write(&path, b"corrupted data")?;
        assert!(!verify_checksum(&path)?);
        Ok(())
    }

    #[test]
    fn test_verify_without_sidecar_returns_true() -> Result<(), Box<dyn std::error::Error>> {
        let dir = tempfile::TempDir::new()?;
        let path = dir.path().join("test_model.safetensors");
        std::fs::write(&path, b"no checksum file")?;

        // No .sha256 file exists -- should return true (backwards compatible)
        assert!(verify_checksum(&path)?);
        Ok(())
    }
}