use std::time::{SystemTime, UNIX_EPOCH};

use async_trait::async_trait;
use fred::prelude::*;

use crate::socket::message_bus::redis::RedisMessageBus;
use crate::socket::session_store::{SessionError, SessionInfo, SessionStoreTrait};

fn now_millis() -> u64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_millis() as u64
}

const DEFAULT_TTL_SECS: u64 = 60;
const KEY_PREFIX: &str = "socket.io:session";

pub struct RedisSessionStore {
    client: Client,
    ttl_secs: u64,
}

impl RedisSessionStore {
    pub fn new(bus: &RedisMessageBus, ttl_secs: Option<u64>) -> Self {
        Self {
            client: bus.client().clone(),
            ttl_secs: ttl_secs.unwrap_or(DEFAULT_TTL_SECS),
        }
    }

    fn key(&self, sid: &str) -> String {
        format!("{}:{}", KEY_PREFIX, sid)
    }
}

#[async_trait]
impl SessionStoreTrait for RedisSessionStore {
    async fn create(&self, sid: &str, transport: &str, server_id: &str) -> Result<(), SessionError> {
        let key = self.key(sid);
        let now = now_millis();

        // Batch all fields in a single HSET call for efficiency
        let fields: Vec<(&str, String)> = vec![
            ("sid", sid.to_string()),
            ("transport", transport.to_string()),
            ("state", "connecting".to_string()),
            ("server_id", server_id.to_string()),
            ("created_at", now.to_string()),
            ("last_ping", now.to_string()),
        ];
        self.client
            .hset::<(), _, _>(&key, fields)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        self.client
            .expire::<(), _>(&key, self.ttl_secs as i64, None)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        Ok(())
    }

    async fn get(&self, sid: &str) -> Result<Option<SessionInfo>, SessionError> {
        let key = self.key(sid);

        // Use hgetall directly — if the key doesn't exist Redis returns an empty map.
        // This avoids the TOCTOU race between EXISTS and HGETALL.
        let values: std::collections::HashMap<String, String> = self.client
            .hgetall::<std::collections::HashMap<String, String>, _>(&key)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        if values.is_empty() {
            return Ok(None);
        }

        let info = SessionInfo {
            sid: values.get("sid").cloned().unwrap_or_default(),
            transport: values.get("transport").cloned().unwrap_or_default(),
            state: values.get("state").cloned().unwrap_or_default(),
            server_id: values.get("server_id").cloned().unwrap_or_default(),
            created_at: values.get("created_at").and_then(|v| v.parse::<u64>().ok()).unwrap_or(0),
            last_ping: values.get("last_ping").and_then(|v| v.parse::<u64>().ok()).unwrap_or(0),
        };

        Ok(Some(info))
    }

    async fn set_state(&self, sid: &str, state: &str) -> Result<(), SessionError> {
        let key = self.key(sid);

        // Use HSET (not HSETNX) to overwrite existing fields
        self.client
            .hset::<(), _, _>(&key, ("state", state))
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        self.client
            .expire::<(), _>(&key, self.ttl_secs as i64, None)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        Ok(())
    }

    async fn set_transport(&self, sid: &str, transport: &str) -> Result<(), SessionError> {
        let key = self.key(sid);

        // Use HSET (not HSETNX) to overwrite existing fields
        self.client
            .hset::<(), _, _>(&key, ("transport", transport))
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        self.client
            .expire::<(), _>(&key, self.ttl_secs as i64, None)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        Ok(())
    }

    async fn update_ping(&self, sid: &str) -> Result<(), SessionError> {
        let key = self.key(sid);
        let now = now_millis();

        // Use HSET (not HSETNX) to overwrite existing fields
        self.client
            .hset::<(), _, _>(&key, ("last_ping", now.to_string()))
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        self.client
            .expire::<(), _>(&key, self.ttl_secs as i64, None)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        Ok(())
    }

    async fn remove(&self, sid: &str) -> Result<(), SessionError> {
        let key = self.key(sid);

        self.client
            .del::<(), _>(&key)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        Ok(())
    }

    async fn exists(&self, sid: &str) -> Result<bool, SessionError> {
        let key = self.key(sid);

        let exists: bool = self.client
            .exists::<bool, _>(&key)
            .await
            .map_err(|e| SessionError::Redis(e.to_string()))?;

        Ok(exists)
    }
}