//! Model loading and caching infrastructure
//!
//! Provides ML model loading from S3 with LRU caching and version management.
//! Supports historical model retrieval for backtesting scenarios.

#![deny(clippy::unwrap_used, clippy::expect_used)]

use anyhow::{Context, Result};
use async_trait::async_trait;
use lru::LruCache;
use parking_lot::Mutex;
use semver::Version;
use serde::{Deserialize, Serialize};
use std::num::NonZeroUsize;
use std::sync::Arc;
use std::time::SystemTime;
use storage::{ObjectStoreBackend, Storage};
use tracing::{debug, info, warn};

// Re-export canonical ModelType from common crate
pub use common::model_types::ModelType;

/// Model metadata for version tracking
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LoadedModelInfo {
    /// Model name
    pub name: String,
    /// Semantic version
    pub version: Version,
    /// Model type
    pub model_type: ModelType,
    /// Timestamp when model was created
    pub created_at: SystemTime,
    /// File size in bytes
    pub size_bytes: usize,
    /// Checksum for integrity validation
    pub checksum: String,
}

/// Cache key for model lookups
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct CacheKey {
    model_name: String,
    version: Version,
}

/// Configuration for model loader
#[derive(Debug, Clone)]
pub struct ModelLoaderConfig {
    /// S3 prefix for model files
    pub prefix: String,
    /// Maximum number of models to cache
    pub cache_size: usize,
}

impl Default for ModelLoaderConfig {
    fn default() -> Self {
        Self {
            prefix: "models/".to_owned(),
            cache_size: 1000,
        }
    }
}

/// Trait for model loading operations
#[async_trait]
pub trait ModelLoader: Send + Sync {
    /// Load a model by name and version
    async fn load_model(&self, model_name: &str, version: &Version) -> Result<Vec<u8>>;

    /// Get model metadata
    async fn get_metadata(&self, model_name: &str, version: &Version) -> Result<LoadedModelInfo>;

    /// List all available versions of a model
    async fn list_versions(&self, model_name: &str) -> Result<Vec<Version>>;

    /// Get the most recent model version for a time period
    async fn get_model_for_period(
        &self,
        model_name: &str,
        start: SystemTime,
        end: SystemTime,
    ) -> Result<(Version, Vec<u8>)>;
}

/// S3-based model loader with LRU caching
pub struct S3ModelLoader {
    storage: Arc<ObjectStoreBackend>,
    config: ModelLoaderConfig,
    cache: Arc<Mutex<LruCache<CacheKey, Vec<u8>>>>,
}

impl S3ModelLoader {
    /// Create a new S3 model loader
    pub fn new(storage: ObjectStoreBackend, config: ModelLoaderConfig) -> Self {
        let cache_size = if config.cache_size == 0 {
            warn!("Cache size cannot be 0, using default value of 1000");
            // SAFETY: This is a compile-time constant that is guaranteed to be non-zero
            #[allow(clippy::expect_used)]
            NonZeroUsize::new(1000).expect("1000 is non-zero")
        } else {
            // SAFETY: We just checked that cache_size is non-zero
            #[allow(clippy::expect_used)]
            NonZeroUsize::new(config.cache_size).expect("cache_size is non-zero after check")
        };

        Self {
            storage: Arc::new(storage),
            config,
            cache: Arc::new(Mutex::new(LruCache::new(cache_size))),
        }
    }

    /// Build S3 key for model file
    fn build_model_key(&self, model_name: &str, version: &Version) -> String {
        format!("{}{}/{}/model.bin", self.config.prefix, model_name, version)
    }

    /// Build S3 key for metadata file
    fn build_metadata_key(&self, model_name: &str, version: &Version) -> String {
        format!(
            "{}{}/{}/metadata.json",
            self.config.prefix, model_name, version
        )
    }

    /// Build S3 prefix for listing versions
    fn build_version_prefix(&self, model_name: &str) -> String {
        format!("{}{}/", self.config.prefix, model_name)
    }

    /// Get from cache or load from S3
    async fn get_cached_or_load(&self, model_name: &str, version: &Version) -> Result<Vec<u8>> {
        let cache_key = CacheKey {
            model_name: model_name.to_owned(),
            version: version.clone(),
        };

        // Check cache first
        {
            let mut cache = self.cache.lock();
            if let Some(data) = cache.get(&cache_key) {
                debug!("Cache hit for model {}/{}", model_name, version);
                return Ok(data.clone());
            }
        }

        // Cache miss - load from S3
        debug!(
            "Cache miss for model {}/{}, loading from S3",
            model_name, version
        );
        let key = self.build_model_key(model_name, version);
        let data =
            self.storage.retrieve(&key).await.with_context(|| {
                format!("Failed to load model {}/{} from S3", model_name, version)
            })?;

        // Store in cache
        {
            let mut cache = self.cache.lock();
            cache.put(cache_key, data.clone());
        }

        info!(
            "Loaded model {}/{} from S3 ({} bytes)",
            model_name,
            version,
            data.len()
        );
        Ok(data)
    }
}

#[async_trait]
impl ModelLoader for S3ModelLoader {
    async fn load_model(&self, model_name: &str, version: &Version) -> Result<Vec<u8>> {
        self.get_cached_or_load(model_name, version).await
    }

    async fn get_metadata(&self, model_name: &str, version: &Version) -> Result<LoadedModelInfo> {
        let key = self.build_metadata_key(model_name, version);
        let data =
            self.storage.retrieve(&key).await.with_context(|| {
                format!("Failed to load metadata for {}/{}", model_name, version)
            })?;

        let metadata: LoadedModelInfo = serde_json::from_slice(&data)
            .with_context(|| "Failed to deserialize model metadata")?;

        Ok(metadata)
    }

    async fn list_versions(&self, model_name: &str) -> Result<Vec<Version>> {
        let prefix = self.build_version_prefix(model_name);
        let objects = self
            .storage
            .list(&prefix)
            .await
            .with_context(|| format!("Failed to list versions for model {}", model_name))?;

        let mut versions = Vec::new();
        for key in objects {
            // Extract version from key: models/model_name/VERSION/...
            if let Some(version_str) = key.strip_prefix(&prefix).and_then(|s| s.split('/').next()) {
                if let Ok(version) = Version::parse(version_str) {
                    versions.push(version);
                }
            }
        }

        versions.sort();
        versions.reverse(); // Most recent first
        Ok(versions)
    }

    async fn get_model_for_period(
        &self,
        model_name: &str,
        start: SystemTime,
        _end: SystemTime,
    ) -> Result<(Version, Vec<u8>)> {
        // List all versions
        let versions = self.list_versions(model_name).await?;

        // Find the most recent version that was created before the period start
        for version in &versions {
            let metadata = self.get_metadata(model_name, version).await?;

            if metadata.created_at <= start {
                let data = self.load_model(model_name, version).await?;
                info!(
                    "Found model {}/{} for period (created at {:?})",
                    model_name, version, metadata.created_at
                );
                return Ok((version.clone(), data));
            }
        }

        // If no version found before start, use the oldest version
        if let Some(oldest) = versions.last() {
            warn!(
                "No model version found before period start, using oldest version {}",
                oldest
            );
            let data = self.load_model(model_name, oldest).await?;
            return Ok((oldest.clone(), data));
        }

        anyhow::bail!("No versions found for model {}", model_name)
    }
}

/// Backtesting model cache module for historical model loading
pub mod backtesting_cache {
    use super::{
        Arc, ModelLoader, ModelLoaderConfig, ObjectStoreBackend, Result, S3ModelLoader, SystemTime,
        Version,
    };
    use anyhow::Context;
    use std::path::PathBuf;

    /// Configuration for backtesting model cache
    #[derive(Debug, Clone)]
    pub struct BacktestCacheConfig {
        /// Directory for caching model files
        pub cache_dir: PathBuf,
        /// S3 configuration for model storage
        pub model_loader_config: ModelLoaderConfig,
    }

    impl Default for BacktestCacheConfig {
        fn default() -> Self {
            Self {
                cache_dir: PathBuf::from("/tmp/foxhunt/model_cache"),
                model_loader_config: ModelLoaderConfig::default(),
            }
        }
    }

    /// Backtesting model cache
    ///
    /// Provides access to historical model versions for backtesting scenarios.
    pub struct BacktestingModelCache {
        loader: Arc<dyn ModelLoader>,
        _config: BacktestCacheConfig,
    }

    impl BacktestingModelCache {
        /// Create a new backtesting model cache
        ///
        /// # Errors
        /// Returns error if the operation fails
        ///
        /// # Errors
        /// Returns error if cache initialization fails
        pub async fn new(storage: ObjectStoreBackend, config: BacktestCacheConfig) -> Result<Self> {
            let loader = S3ModelLoader::new(storage, config.model_loader_config.clone());

            Ok(Self {
                loader: Arc::new(loader),
                _config: config,
            })
        }

        /// Initialize the model cache
        ///
        /// # Errors
        /// Returns error if initialization fails
        pub async fn initialize(&mut self) -> Result<()> {
            // Cache is ready immediately with LRU
            Ok(())
        }

        /// Get a model by name and version
        ///
        ///
        /// # Errors
        /// Returns error if the operation fails
        /// # Errors
        /// Returns error if the version string is invalid or model cannot be loaded
        pub async fn get_model(&self, model_name: &str, version_str: &str) -> Result<Vec<u8>> {
            let version = Version::parse(version_str)
                .with_context(|| format!("Invalid version string: {}", version_str))?;
            self.loader.load_model(model_name, &version).await
        }

        /// Get a specific model version
        ///
        /// # Errors
        /// Returns error if the model cannot be loaded
        pub async fn get_model_version(
            &self,
            model_name: &str,
            version: &Version,
        ) -> Result<Vec<u8>> {
            self.loader.load_model(model_name, version).await
        }

        /// Get a model for a specific time period
        ///
        /// # Errors
        /// Returns error if the operation fails
        ///
        /// This is used for backtesting to load historically accurate model versions
        ///
        /// # Errors
        /// Returns error if no suitable model version is found or model cannot be loaded
        pub async fn get_model_for_period(
            &self,
            model_name: &str,
            start: SystemTime,
            end: SystemTime,
        ) -> Result<(Version, Vec<u8>)> {
            self.loader
                .get_model_for_period(model_name, start, end)
                .await
        }

        /// List all available versions of a model
        ///
        /// # Errors
        /// Returns error if listing model versions fails
        pub async fn list_model_versions(&self, model_name: &str) -> Result<Vec<Version>> {
            self.loader.list_versions(model_name).await
        }
    }
}

#[cfg(test)]
#[allow(clippy::unwrap_used, clippy::expect_used)]
mod tests {
    use super::*;

    #[test]
    fn test_model_type_s3_prefix() {
        assert_eq!(ModelType::TLOB.s3_prefix(), "tlob_transformer");
        assert_eq!(ModelType::DQN.s3_prefix(), "dqn");
        assert_eq!(ModelType::MAMBA.s3_prefix(), "mamba2");
    }

    #[test]
    fn test_model_type_as_str() {
        assert_eq!(ModelType::TLOB.as_str(), "tlob");
        assert_eq!(ModelType::DQN.as_str(), "dqn");
        assert_eq!(ModelType::MAMBA.as_str(), "mamba");
    }

    #[test]
    fn test_cache_key_equality() {
        let key1 = CacheKey {
            model_name: "test_model".to_owned(),
            version: Version::new(1, 0, 0),
        };
        let key2 = CacheKey {
            model_name: "test_model".to_owned(),
            version: Version::new(1, 0, 0),
        };
        assert_eq!(key1, key2);
    }

    #[test]
    fn test_model_loader_config_default() {
        let config = ModelLoaderConfig::default();
        assert_eq!(config.prefix, "models/");
        assert_eq!(config.cache_size, 1000);
    }
}