//! Session persistence and storage management backed by SQLite

use crate::types::Conversation;
use crate::{Error, Result};
use aes_gcm::aead::{Aead, KeyInit};
use aes_gcm::{Aes256Gcm, Nonce};
use ring::rand::{SecureRandom, SystemRandom};
use serde::{Deserialize, Serialize};
use sqlx::sqlite::{SqliteConnectOptions, SqliteJournalMode, SqlitePoolOptions, SqliteSynchronous};
use sqlx::{Pool, Row, Sqlite};
use std::fs;
use std::io::IsTerminal;
use std::io::{self, Write};
use std::path::{Path, PathBuf};
use std::str::FromStr;
use std::time::{Duration, SystemTime, UNIX_EPOCH};
use uuid::Uuid;

/// Metadata about a saved session
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SessionMeta {
    /// Conversation ID
    pub id: Uuid,
    /// Optional session name
    pub name: Option<String>,
    /// Optional AI-generated description
    pub description: Option<String>,
    /// Number of messages in the conversation
    pub message_count: usize,
    /// Model used
    pub model: String,
    /// When the session was created
    pub created_at: SystemTime,
    /// When the session was last updated
    pub updated_at: SystemTime,
}

/// Storage manager for persisting conversations in SQLite
pub struct StorageManager {
    pool: Pool<Sqlite>,
    database_path: PathBuf,
}

impl StorageManager {
    /// Create a new storage manager using the default database path
    pub async fn new() -> Result<Self> {
        let db_path = Self::default_database_path()?;
        Self::with_database_path(db_path).await
    }

    /// Create a storage manager using the provided database path
    pub async fn with_database_path(database_path: PathBuf) -> Result<Self> {
        if let Some(parent) = database_path.parent() {
            if !parent.exists() {
                std::fs::create_dir_all(parent).map_err(|e| {
                    Error::Storage(format!(
                        "Failed to create database directory {parent:?}: {e}"
                    ))
                })?;
            }
        }

        let options = SqliteConnectOptions::from_str(&format!(
            "sqlite://{}",
            database_path
                .to_str()
                .ok_or_else(|| Error::Storage("Invalid database path".to_string()))?
        ))
        .map_err(|e| Error::Storage(format!("Invalid database URL: {e}")))?
        .create_if_missing(true)
        .journal_mode(SqliteJournalMode::Wal)
        .synchronous(SqliteSynchronous::Normal);

        let pool = SqlitePoolOptions::new()
            .max_connections(5)
            .connect_with(options)
            .await
            .map_err(|e| Error::Storage(format!("Failed to connect to database: {e}")))?;

        sqlx::migrate!("./migrations")
            .run(&pool)
            .await
            .map_err(|e| Error::Storage(format!("Failed to run database migrations: {e}")))?;

        let storage = Self {
            pool,
            database_path,
        };

        storage.try_migrate_legacy_sessions().await?;

        Ok(storage)
    }

    /// Save a conversation. Existing entries are updated in-place.
    pub async fn save_conversation(
        &self,
        conversation: &Conversation,
        name: Option<String>,
    ) -> Result<()> {
        self.save_conversation_with_description(conversation, name, None)
            .await
    }

    /// Save a conversation with an optional description override
    pub async fn save_conversation_with_description(
        &self,
        conversation: &Conversation,
        name: Option<String>,
        description: Option<String>,
    ) -> Result<()> {
        let mut serialized = conversation.clone();
        if name.is_some() {
            serialized.name = name.clone();
        }
        if description.is_some() {
            serialized.description = description.clone();
        }

        let data = serde_json::to_string(&serialized)
            .map_err(|e| Error::Storage(format!("Failed to serialize conversation: {e}")))?;

        let created_at = to_epoch_seconds(serialized.created_at);
        let updated_at = to_epoch_seconds(serialized.updated_at);
        let message_count = serialized.messages.len() as i64;

        sqlx::query(
            r#"
            INSERT INTO conversations (
                id,
                name,
                description,
                model,
                message_count,
                created_at,
                updated_at,
                data
            ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8)
            ON CONFLICT(id) DO UPDATE SET
                name = excluded.name,
                description = excluded.description,
                model = excluded.model,
                message_count = excluded.message_count,
                created_at = excluded.created_at,
                updated_at = excluded.updated_at,
                data = excluded.data
        "#,
        )
        .bind(serialized.id.to_string())
        .bind(name.or(serialized.name.clone()))
        .bind(description.or(serialized.description.clone()))
        .bind(&serialized.model)
        .bind(message_count)
        .bind(created_at)
        .bind(updated_at)
        .bind(data)
        .execute(&self.pool)
        .await
        .map_err(|e| Error::Storage(format!("Failed to save conversation: {e}")))?;

        Ok(())
    }

    /// Load a conversation by ID
    pub async fn load_conversation(&self, id: Uuid) -> Result<Conversation> {
        let record = sqlx::query(r#"SELECT data FROM conversations WHERE id = ?1"#)
            .bind(id.to_string())
            .fetch_optional(&self.pool)
            .await
            .map_err(|e| Error::Storage(format!("Failed to load conversation: {e}")))?;

        let row =
            record.ok_or_else(|| Error::Storage(format!("No conversation found with id {id}")))?;

        let data: String = row
            .try_get("data")
            .map_err(|e| Error::Storage(format!("Failed to read conversation payload: {e}")))?;

        serde_json::from_str(&data)
            .map_err(|e| Error::Storage(format!("Failed to deserialize conversation: {e}")))
    }

    /// List metadata for all saved conversations ordered by most recent update
    pub async fn list_sessions(&self) -> Result<Vec<SessionMeta>> {
        let rows = sqlx::query(
            r#"
            SELECT id, name, description, model, message_count, created_at, updated_at
            FROM conversations
            ORDER BY updated_at DESC
        "#,
        )
        .fetch_all(&self.pool)
        .await
        .map_err(|e| Error::Storage(format!("Failed to list sessions: {e}")))?;

        let mut sessions = Vec::with_capacity(rows.len());
        for row in rows {
            let id_text: String = row
                .try_get("id")
                .map_err(|e| Error::Storage(format!("Failed to read id column: {e}")))?;
            let id = Uuid::parse_str(&id_text)
                .map_err(|e| Error::Storage(format!("Invalid UUID in storage: {e}")))?;

            let message_count: i64 = row
                .try_get("message_count")
                .map_err(|e| Error::Storage(format!("Failed to read message count: {e}")))?;

            let created_at: i64 = row
                .try_get("created_at")
                .map_err(|e| Error::Storage(format!("Failed to read created_at: {e}")))?;
            let updated_at: i64 = row
                .try_get("updated_at")
                .map_err(|e| Error::Storage(format!("Failed to read updated_at: {e}")))?;

            sessions.push(SessionMeta {
                id,
                name: row
                    .try_get("name")
                    .map_err(|e| Error::Storage(format!("Failed to read name: {e}")))?,
                description: row
                    .try_get("description")
                    .map_err(|e| Error::Storage(format!("Failed to read description: {e}")))?,
                model: row
                    .try_get("model")
                    .map_err(|e| Error::Storage(format!("Failed to read model: {e}")))?,
                message_count: message_count as usize,
                created_at: from_epoch_seconds(created_at),
                updated_at: from_epoch_seconds(updated_at),
            });
        }

        Ok(sessions)
    }

    /// Delete a conversation by ID
    pub async fn delete_session(&self, id: Uuid) -> Result<()> {
        sqlx::query("DELETE FROM conversations WHERE id = ?1")
            .bind(id.to_string())
            .execute(&self.pool)
            .await
            .map_err(|e| Error::Storage(format!("Failed to delete conversation: {e}")))?;
        Ok(())
    }

    pub async fn store_secure_item(
        &self,
        key: &str,
        plaintext: &[u8],
        master_key: &[u8],
    ) -> Result<()> {
        let cipher = create_cipher(master_key)?;
        let nonce_bytes = generate_nonce()?;
        let nonce = Nonce::from_slice(&nonce_bytes);
        let ciphertext = cipher
            .encrypt(nonce, plaintext)
            .map_err(|e| Error::Storage(format!("Failed to encrypt secure item: {e}")))?;

        let now = to_epoch_seconds(SystemTime::now());

        sqlx::query(
            r#"
            INSERT INTO secure_items (key, nonce, ciphertext, created_at, updated_at)
            VALUES (?1, ?2, ?3, ?4, ?5)
            ON CONFLICT(key) DO UPDATE SET
                nonce = excluded.nonce,
                ciphertext = excluded.ciphertext,
                updated_at = excluded.updated_at
        "#,
        )
        .bind(key)
        .bind(&nonce_bytes[..])
        .bind(&ciphertext[..])
        .bind(now)
        .bind(now)
        .execute(&self.pool)
        .await
        .map_err(|e| Error::Storage(format!("Failed to store secure item: {e}")))?;

        Ok(())
    }

    pub async fn load_secure_item(&self, key: &str, master_key: &[u8]) -> Result<Option<Vec<u8>>> {
        let record = sqlx::query("SELECT nonce, ciphertext FROM secure_items WHERE key = ?1")
            .bind(key)
            .fetch_optional(&self.pool)
            .await
            .map_err(|e| Error::Storage(format!("Failed to load secure item: {e}")))?;

        let Some(row) = record else {
            return Ok(None);
        };

        let nonce_bytes: Vec<u8> = row
            .try_get("nonce")
            .map_err(|e| Error::Storage(format!("Failed to read secure item nonce: {e}")))?;
        let ciphertext: Vec<u8> = row
            .try_get("ciphertext")
            .map_err(|e| Error::Storage(format!("Failed to read secure item ciphertext: {e}")))?;

        if nonce_bytes.len() != 12 {
            return Err(Error::Storage(
                "Invalid nonce length for secure item".to_string(),
            ));
        }

        let cipher = create_cipher(master_key)?;
        let nonce = Nonce::from_slice(&nonce_bytes);
        let plaintext = cipher
            .decrypt(nonce, ciphertext.as_ref())
            .map_err(|e| Error::Storage(format!("Failed to decrypt secure item: {e}")))?;

        Ok(Some(plaintext))
    }

    pub async fn delete_secure_item(&self, key: &str) -> Result<()> {
        sqlx::query("DELETE FROM secure_items WHERE key = ?1")
            .bind(key)
            .execute(&self.pool)
            .await
            .map_err(|e| Error::Storage(format!("Failed to delete secure item: {e}")))?;
        Ok(())
    }

    pub async fn clear_secure_items(&self) -> Result<()> {
        sqlx::query("DELETE FROM secure_items")
            .execute(&self.pool)
            .await
            .map_err(|e| Error::Storage(format!("Failed to clear secure items: {e}")))?;
        Ok(())
    }

    /// Database location used by this storage manager
    pub fn database_path(&self) -> &Path {
        &self.database_path
    }

    /// Determine default database path (platform specific)
    pub fn default_database_path() -> Result<PathBuf> {
        let data_dir = dirs::data_local_dir()
            .ok_or_else(|| Error::Storage("Could not determine data directory".to_string()))?;
        Ok(data_dir.join("owlen").join("owlen.db"))
    }

    fn legacy_sessions_dir() -> Result<PathBuf> {
        let data_dir = dirs::data_local_dir()
            .ok_or_else(|| Error::Storage("Could not determine data directory".to_string()))?;
        Ok(data_dir.join("owlen").join("sessions"))
    }

    async fn database_has_records(&self) -> Result<bool> {
        let (count,): (i64,) = sqlx::query_as("SELECT COUNT(*) FROM conversations")
            .fetch_one(&self.pool)
            .await
            .map_err(|e| Error::Storage(format!("Failed to inspect database: {e}")))?;
        Ok(count > 0)
    }

    async fn try_migrate_legacy_sessions(&self) -> Result<()> {
        if self.database_has_records().await? {
            return Ok(());
        }

        let legacy_dir = match Self::legacy_sessions_dir() {
            Ok(dir) => dir,
            Err(_) => return Ok(()),
        };

        if !legacy_dir.exists() {
            return Ok(());
        }

        let entries = fs::read_dir(&legacy_dir).map_err(|e| {
            Error::Storage(format!("Failed to read legacy sessions directory: {e}"))
        })?;

        let mut json_files = Vec::new();
        for entry in entries.flatten() {
            let path = entry.path();
            if path.extension().and_then(|s| s.to_str()) == Some("json") {
                json_files.push(path);
            }
        }

        if json_files.is_empty() {
            return Ok(());
        }

        if !io::stdin().is_terminal() {
            return Ok(());
        }

        println!(
            "Legacy OWLEN session files were found in {}.",
            legacy_dir.display()
        );
        if !prompt_yes_no("Migrate them to the new SQLite storage? (y/N) ")? {
            println!("Skipping legacy session migration.");
            return Ok(());
        }

        println!("Migrating legacy sessions...");
        let mut migrated = 0usize;
        for path in &json_files {
            match fs::read_to_string(path) {
                Ok(content) => match serde_json::from_str::<Conversation>(&content) {
                    Ok(conversation) => {
                        if let Err(err) = self
                            .save_conversation_with_description(
                                &conversation,
                                conversation.name.clone(),
                                conversation.description.clone(),
                            )
                            .await
                        {
                            println!("  • Failed to migrate {}: {}", path.display(), err);
                        } else {
                            migrated += 1;
                        }
                    }
                    Err(err) => {
                        println!(
                            "  • Failed to parse conversation {}: {}",
                            path.display(),
                            err
                        );
                    }
                },
                Err(err) => {
                    println!("  • Failed to read {}: {}", path.display(), err);
                }
            }
        }

        if migrated > 0 {
            if let Err(err) = archive_legacy_directory(&legacy_dir) {
                println!(
                    "Warning: migrated sessions but failed to archive legacy directory: {}",
                    err
                );
            }
        }

        println!("Migrated {} legacy sessions.", migrated);
        Ok(())
    }
}

fn to_epoch_seconds(time: SystemTime) -> i64 {
    match time.duration_since(UNIX_EPOCH) {
        Ok(duration) => duration.as_secs() as i64,
        Err(_) => 0,
    }
}

fn from_epoch_seconds(seconds: i64) -> SystemTime {
    UNIX_EPOCH + Duration::from_secs(seconds.max(0) as u64)
}

fn prompt_yes_no(prompt: &str) -> Result<bool> {
    print!("{}", prompt);
    io::stdout()
        .flush()
        .map_err(|e| Error::Storage(format!("Failed to flush stdout: {e}")))?;

    let mut input = String::new();
    io::stdin()
        .read_line(&mut input)
        .map_err(|e| Error::Storage(format!("Failed to read input: {e}")))?;
    let trimmed = input.trim().to_lowercase();
    Ok(matches!(trimmed.as_str(), "y" | "yes"))
}

fn archive_legacy_directory(legacy_dir: &Path) -> Result<()> {
    let mut backup_dir = legacy_dir.with_file_name("sessions_legacy_backup");
    let mut counter = 1;
    while backup_dir.exists() {
        backup_dir = legacy_dir.with_file_name(format!("sessions_legacy_backup_{}", counter));
        counter += 1;
    }

    fs::rename(legacy_dir, &backup_dir).map_err(|e| {
        Error::Storage(format!(
            "Failed to archive legacy sessions directory {}: {}",
            legacy_dir.display(),
            e
        ))
    })?;

    println!("Legacy session files archived to {}", backup_dir.display());
    Ok(())
}

fn create_cipher(master_key: &[u8]) -> Result<Aes256Gcm> {
    if master_key.len() != 32 {
        return Err(Error::Storage(
            "Master key must be 32 bytes for AES-256-GCM".to_string(),
        ));
    }
    Aes256Gcm::new_from_slice(master_key).map_err(|_| {
        Error::Storage("Failed to initialize cipher with provided master key".to_string())
    })
}

fn generate_nonce() -> Result<[u8; 12]> {
    let mut nonce = [0u8; 12];
    SystemRandom::new()
        .fill(&mut nonce)
        .map_err(|_| Error::Storage("Failed to generate nonce".to_string()))?;
    Ok(nonce)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::types::{Conversation, Message};
    use tempfile::tempdir;

    fn sample_conversation() -> Conversation {
        Conversation {
            id: Uuid::new_v4(),
            name: Some("Test conversation".to_string()),
            description: Some("A sample conversation".to_string()),
            messages: vec![
                Message::user("Hello".to_string()),
                Message::assistant("Hi".to_string()),
            ],
            model: "test-model".to_string(),
            created_at: SystemTime::now(),
            updated_at: SystemTime::now(),
        }
    }

    #[tokio::test]
    async fn test_storage_lifecycle() {
        let temp_dir = tempdir().expect("failed to create temp dir");
        let db_path = temp_dir.path().join("owlen.db");
        let storage = StorageManager::with_database_path(db_path).await.unwrap();

        let conversation = sample_conversation();
        storage
            .save_conversation(&conversation, None)
            .await
            .expect("failed to save conversation");

        let sessions = storage.list_sessions().await.unwrap();
        assert_eq!(sessions.len(), 1);
        assert_eq!(sessions[0].id, conversation.id);

        let loaded = storage.load_conversation(conversation.id).await.unwrap();
        assert_eq!(loaded.messages.len(), 2);

        storage
            .delete_session(conversation.id)
            .await
            .expect("failed to delete conversation");
        let sessions = storage.list_sessions().await.unwrap();
        assert!(sessions.is_empty());
    }
}