use std::{
    collections::{HashMap, VecDeque},
    fs,
    hash::Hash,
    path::{Path, PathBuf},
    sync::Mutex,
};

use serde::{Deserialize, Serialize};

#[derive(thiserror::Error, Debug)]
pub enum StorageError {
    #[error("io error: {0}")]
    Io(String),
    #[error("serialization error")]
    Serde,
    #[error("database error: {0}")]
    Db(String),
}

fn lock<T>(m: &Mutex<T>) -> Result<std::sync::MutexGuard<'_, T>, StorageError> {
    m.lock()
        .map_err(|e| StorageError::Io(format!("lock poisoned: {e}")))
}

// ── Store trait ──────────────────────────────────────────────────────────────

/// Abstraction over storage backends (file-backed, SQLCipher, etc.).
pub trait Store: Send + Sync {
    fn upload_key_package(&self, identity_key: &[u8], package: Vec<u8>)
        -> Result<(), StorageError>;

    fn fetch_key_package(&self, identity_key: &[u8]) -> Result<Option<Vec<u8>>, StorageError>;

    /// Enqueue a payload and return the monotonically increasing per-inbox sequence number
    /// assigned to this message. Clients sort by seq before MLS processing.
    fn enqueue(
        &self,
        recipient_key: &[u8],
        channel_id: &[u8],
        payload: Vec<u8>,
    ) -> Result<u64, StorageError>;

    /// Fetch and drain all queued messages, returning `(seq, payload)` pairs ordered by seq.
    fn fetch(
        &self,
        recipient_key: &[u8],
        channel_id: &[u8],
    ) -> Result<Vec<(u64, Vec<u8>)>, StorageError>;

    /// Fetch up to `limit` messages without draining the entire queue (Fix 8).
    /// Returns `(seq, payload)` pairs ordered by seq.
    fn fetch_limited(
        &self,
        recipient_key: &[u8],
        channel_id: &[u8],
        limit: usize,
    ) -> Result<Vec<(u64, Vec<u8>)>, StorageError>;

    /// Return the number of queued messages for (recipient, channel) (Fix 7).
    fn queue_depth(&self, recipient_key: &[u8], channel_id: &[u8]) -> Result<usize, StorageError>;

    /// Delete messages older than `max_age_secs`. Returns count deleted (Fix 7).
    fn gc_expired_messages(&self, max_age_secs: u64) -> Result<usize, StorageError>;

    fn upload_hybrid_key(
        &self,
        identity_key: &[u8],
        hybrid_pk: Vec<u8>,
    ) -> Result<(), StorageError>;

    fn fetch_hybrid_key(&self, identity_key: &[u8]) -> Result<Option<Vec<u8>>, StorageError>;

    /// Store the OPAQUE `ServerSetup` (generated once, loaded on restart).
    fn store_server_setup(&self, setup: Vec<u8>) -> Result<(), StorageError>;

    /// Load the persisted `ServerSetup`, if any.
    fn get_server_setup(&self) -> Result<Option<Vec<u8>>, StorageError>;

    /// Store an OPAQUE user record (serialized `ServerRegistration`).
    fn store_user_record(&self, username: &str, record: Vec<u8>) -> Result<(), StorageError>;

    /// Retrieve an OPAQUE user record by username.
    fn get_user_record(&self, username: &str) -> Result<Option<Vec<u8>>, StorageError>;

    /// Check if a user record already exists (Fix 5).
    fn has_user_record(&self, username: &str) -> Result<bool, StorageError>;

    /// Store identity key for a user (Fix 2).
    fn store_user_identity_key(
        &self,
        username: &str,
        identity_key: Vec<u8>,
    ) -> Result<(), StorageError>;

    /// Retrieve identity key for a user (Fix 2).
    fn get_user_identity_key(&self, username: &str) -> Result<Option<Vec<u8>>, StorageError>;

    /// Publish a P2P endpoint address for an identity key.
    fn publish_endpoint(&self, identity_key: &[u8], node_addr: Vec<u8>)
        -> Result<(), StorageError>;

    /// Resolve a peer's P2P endpoint address.
    fn resolve_endpoint(&self, identity_key: &[u8]) -> Result<Option<Vec<u8>>, StorageError>;
}

// ── ChannelKey ───────────────────────────────────────────────────────────────

#[derive(Serialize, Deserialize, Clone, Eq, PartialEq, Debug)]
pub struct ChannelKey {
    pub channel_id: Vec<u8>,
    pub recipient_key: Vec<u8>,
}

impl Hash for ChannelKey {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.channel_id.hash(state);
        self.recipient_key.hash(state);
    }
}

// ── FileBackedStore ──────────────────────────────────────────────────────────

#[derive(Serialize, Deserialize, Default)]
struct QueueMapV1 {
    map: HashMap<Vec<u8>, VecDeque<Vec<u8>>>,
}

#[derive(Serialize, Deserialize, Default)]
struct QueueMapV2 {
    map: HashMap<ChannelKey, VecDeque<Vec<u8>>>,
}

#[derive(Serialize, Deserialize, Default, Clone)]
struct SeqEntry {
    seq: u64,
    data: Vec<u8>,
}

/// V3 delivery store: each queue entry carries a monotonic per-inbox sequence number.
#[derive(Serialize, Deserialize, Default)]
struct QueueMapV3 {
    map: HashMap<ChannelKey, VecDeque<SeqEntry>>,
    next_seq: HashMap<ChannelKey, u64>,
}

/// File-backed storage for KeyPackages and delivery queues.
///
/// Each mutation flushes the entire map to disk. Suitable for MVP-scale loads.
pub struct FileBackedStore {
    kp_path: PathBuf,
    ds_path: PathBuf,
    hk_path: PathBuf,
    setup_path: PathBuf,
    users_path: PathBuf,
    identity_keys_path: PathBuf,
    key_packages: Mutex<HashMap<Vec<u8>, VecDeque<Vec<u8>>>>,
    deliveries: Mutex<QueueMapV3>,
    hybrid_keys: Mutex<HashMap<Vec<u8>, Vec<u8>>>,
    users: Mutex<HashMap<String, Vec<u8>>>,
    identity_keys: Mutex<HashMap<String, Vec<u8>>>,
    endpoints: Mutex<HashMap<Vec<u8>, Vec<u8>>>,
}

impl FileBackedStore {
    pub fn open(dir: impl AsRef<Path>) -> Result<Self, StorageError> {
        let dir = dir.as_ref();
        if !dir.exists() {
            fs::create_dir_all(dir).map_err(|e| StorageError::Io(e.to_string()))?;
        }
        let kp_path = dir.join("keypackages.bin");
        let ds_path = dir.join("deliveries.bin");
        let hk_path = dir.join("hybridkeys.bin");
        let setup_path = dir.join("server_setup.bin");
        let users_path = dir.join("users.bin");
        let identity_keys_path = dir.join("identity_keys.bin");

        let key_packages = Mutex::new(Self::load_kp_map(&kp_path)?);
        let deliveries = Mutex::new(Self::load_delivery_map_v3(&ds_path)?);
        let hybrid_keys = Mutex::new(Self::load_hybrid_keys(&hk_path)?);
        let users = Mutex::new(Self::load_users(&users_path)?);
        let identity_keys = Mutex::new(Self::load_map_string_bytes(&identity_keys_path)?);

        Ok(Self {
            kp_path,
            ds_path,
            hk_path,
            setup_path,
            users_path,
            identity_keys_path,
            key_packages,
            deliveries,
            hybrid_keys,
            users,
            identity_keys,
            endpoints: Mutex::new(HashMap::new()),
        })
    }

    fn load_kp_map(path: &Path) -> Result<HashMap<Vec<u8>, VecDeque<Vec<u8>>>, StorageError> {
        if !path.exists() {
            return Ok(HashMap::new());
        }
        let bytes = fs::read(path).map_err(|e| StorageError::Io(e.to_string()))?;
        if bytes.is_empty() {
            return Ok(HashMap::new());
        }
        let map: QueueMapV1 = bincode::deserialize(&bytes).map_err(|_| StorageError::Serde)?;
        Ok(map.map)
    }

    fn flush_kp_map(
        &self,
        path: &Path,
        map: &HashMap<Vec<u8>, VecDeque<Vec<u8>>>,
    ) -> Result<(), StorageError> {
        let payload = QueueMapV1 { map: map.clone() };
        let bytes = bincode::serialize(&payload).map_err(|_| StorageError::Serde)?;
        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent).map_err(|e| StorageError::Io(e.to_string()))?;
        }
        fs::write(path, bytes).map_err(|e| StorageError::Io(e.to_string()))
    }

    /// Load deliveries as V3. Falls back to V2 format (assigns seqs starting at 0).
    fn load_delivery_map_v3(path: &Path) -> Result<QueueMapV3, StorageError> {
        if !path.exists() {
            return Ok(QueueMapV3::default());
        }
        let bytes = fs::read(path).map_err(|e| StorageError::Io(e.to_string()))?;
        if bytes.is_empty() {
            return Ok(QueueMapV3::default());
        }
        // Try V3 first.
        if let Ok(v3) = bincode::deserialize::<QueueMapV3>(&bytes) {
            return Ok(v3);
        }
        // Fall back to V2: assign ascending seqs starting at 0 per channel.
        let v2 = bincode::deserialize::<QueueMapV2>(&bytes)
            .map_err(|_| StorageError::Io("deliveries file: unrecognised format".into()))?;
        let mut v3 = QueueMapV3::default();
        for (key, queue) in v2.map {
            let entries: VecDeque<SeqEntry> = queue
                .into_iter()
                .enumerate()
                .map(|(i, data)| SeqEntry { seq: i as u64, data })
                .collect();
            let next = entries.len() as u64;
            v3.next_seq.insert(key.clone(), next);
            v3.map.insert(key, entries);
        }
        Ok(v3)
    }

    fn flush_delivery_map(&self, path: &Path, map: &QueueMapV3) -> Result<(), StorageError> {
        let bytes = bincode::serialize(map).map_err(|_| StorageError::Serde)?;
        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent).map_err(|e| StorageError::Io(e.to_string()))?;
        }
        fs::write(path, bytes).map_err(|e| StorageError::Io(e.to_string()))
    }

    fn load_hybrid_keys(path: &Path) -> Result<HashMap<Vec<u8>, Vec<u8>>, StorageError> {
        if !path.exists() {
            return Ok(HashMap::new());
        }
        let bytes = fs::read(path).map_err(|e| StorageError::Io(e.to_string()))?;
        if bytes.is_empty() {
            return Ok(HashMap::new());
        }
        bincode::deserialize(&bytes).map_err(|_| StorageError::Serde)
    }

    fn flush_hybrid_keys(
        &self,
        path: &Path,
        map: &HashMap<Vec<u8>, Vec<u8>>,
    ) -> Result<(), StorageError> {
        let bytes = bincode::serialize(map).map_err(|_| StorageError::Serde)?;
        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent).map_err(|e| StorageError::Io(e.to_string()))?;
        }
        fs::write(path, bytes).map_err(|e| StorageError::Io(e.to_string()))
    }

    fn load_users(path: &Path) -> Result<HashMap<String, Vec<u8>>, StorageError> {
        if !path.exists() {
            return Ok(HashMap::new());
        }
        let bytes = fs::read(path).map_err(|e| StorageError::Io(e.to_string()))?;
        if bytes.is_empty() {
            return Ok(HashMap::new());
        }
        bincode::deserialize(&bytes).map_err(|_| StorageError::Serde)
    }

    fn flush_users(&self, path: &Path, map: &HashMap<String, Vec<u8>>) -> Result<(), StorageError> {
        let bytes = bincode::serialize(map).map_err(|_| StorageError::Serde)?;
        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent).map_err(|e| StorageError::Io(e.to_string()))?;
        }
        fs::write(path, bytes).map_err(|e| StorageError::Io(e.to_string()))
    }

    fn load_map_string_bytes(path: &Path) -> Result<HashMap<String, Vec<u8>>, StorageError> {
        Self::load_users(path)
    }

    fn flush_map_string_bytes(
        &self,
        path: &Path,
        map: &HashMap<String, Vec<u8>>,
    ) -> Result<(), StorageError> {
        self.flush_users(path, map)
    }
}

impl Store for FileBackedStore {
    fn upload_key_package(
        &self,
        identity_key: &[u8],
        package: Vec<u8>,
    ) -> Result<(), StorageError> {
        let mut map = lock(&self.key_packages)?;
        map.entry(identity_key.to_vec())
            .or_default()
            .push_back(package);
        self.flush_kp_map(&self.kp_path, &*map)
    }

    fn fetch_key_package(&self, identity_key: &[u8]) -> Result<Option<Vec<u8>>, StorageError> {
        let mut map = lock(&self.key_packages)?;
        let package = map.get_mut(identity_key).and_then(|q| q.pop_front());
        self.flush_kp_map(&self.kp_path, &*map)?;
        Ok(package)
    }

    fn enqueue(
        &self,
        recipient_key: &[u8],
        channel_id: &[u8],
        payload: Vec<u8>,
    ) -> Result<u64, StorageError> {
        let mut inner = lock(&self.deliveries)?;
        let key = ChannelKey {
            channel_id: channel_id.to_vec(),
            recipient_key: recipient_key.to_vec(),
        };
        let seq = {
            let entry = inner.next_seq.entry(key.clone()).or_insert(0);
            let s = *entry;
            *entry = s + 1;
            s
        };
        inner.map.entry(key).or_default().push_back(SeqEntry { seq, data: payload });
        self.flush_delivery_map(&self.ds_path, &*inner)?;
        Ok(seq)
    }

    fn fetch(
        &self,
        recipient_key: &[u8],
        channel_id: &[u8],
    ) -> Result<Vec<(u64, Vec<u8>)>, StorageError> {
        let mut inner = lock(&self.deliveries)?;
        let key = ChannelKey {
            channel_id: channel_id.to_vec(),
            recipient_key: recipient_key.to_vec(),
        };
        let messages: Vec<(u64, Vec<u8>)> = inner
            .map
            .get_mut(&key)
            .map(|q| q.drain(..).map(|e| (e.seq, e.data)).collect())
            .unwrap_or_default();
        self.flush_delivery_map(&self.ds_path, &*inner)?;
        Ok(messages)
    }

    fn fetch_limited(
        &self,
        recipient_key: &[u8],
        channel_id: &[u8],
        limit: usize,
    ) -> Result<Vec<(u64, Vec<u8>)>, StorageError> {
        let mut inner = lock(&self.deliveries)?;
        let key = ChannelKey {
            channel_id: channel_id.to_vec(),
            recipient_key: recipient_key.to_vec(),
        };
        let messages: Vec<(u64, Vec<u8>)> = inner
            .map
            .get_mut(&key)
            .map(|q| {
                let count = limit.min(q.len());
                q.drain(..count).map(|e| (e.seq, e.data)).collect()
            })
            .unwrap_or_default();
        self.flush_delivery_map(&self.ds_path, &*inner)?;
        Ok(messages)
    }

    fn queue_depth(&self, recipient_key: &[u8], channel_id: &[u8]) -> Result<usize, StorageError> {
        let inner = lock(&self.deliveries)?;
        let key = ChannelKey {
            channel_id: channel_id.to_vec(),
            recipient_key: recipient_key.to_vec(),
        };
        Ok(inner.map.get(&key).map(|q| q.len()).unwrap_or(0))
    }

    fn gc_expired_messages(&self, _max_age_secs: u64) -> Result<usize, StorageError> {
        // FileBackedStore does not track timestamps per message — no-op.
        Ok(0)
    }

    fn upload_hybrid_key(
        &self,
        identity_key: &[u8],
        hybrid_pk: Vec<u8>,
    ) -> Result<(), StorageError> {
        let mut map = lock(&self.hybrid_keys)?;
        map.insert(identity_key.to_vec(), hybrid_pk);
        self.flush_hybrid_keys(&self.hk_path, &*map)
    }

    fn fetch_hybrid_key(&self, identity_key: &[u8]) -> Result<Option<Vec<u8>>, StorageError> {
        let map = lock(&self.hybrid_keys)?;
        Ok(map.get(identity_key).cloned())
    }

    fn store_server_setup(&self, setup: Vec<u8>) -> Result<(), StorageError> {
        if let Some(parent) = self.setup_path.parent() {
            fs::create_dir_all(parent).map_err(|e| StorageError::Io(e.to_string()))?;
        }
        fs::write(&self.setup_path, setup).map_err(|e| StorageError::Io(e.to_string()))
    }

    fn get_server_setup(&self) -> Result<Option<Vec<u8>>, StorageError> {
        if !self.setup_path.exists() {
            return Ok(None);
        }
        let bytes = fs::read(&self.setup_path).map_err(|e| StorageError::Io(e.to_string()))?;
        if bytes.is_empty() {
            return Ok(None);
        }
        Ok(Some(bytes))
    }

    fn store_user_record(&self, username: &str, record: Vec<u8>) -> Result<(), StorageError> {
        let mut map = lock(&self.users)?;
        map.insert(username.to_string(), record);
        self.flush_users(&self.users_path, &*map)
    }

    fn get_user_record(&self, username: &str) -> Result<Option<Vec<u8>>, StorageError> {
        let map = lock(&self.users)?;
        Ok(map.get(username).cloned())
    }

    fn has_user_record(&self, username: &str) -> Result<bool, StorageError> {
        let map = lock(&self.users)?;
        Ok(map.contains_key(username))
    }

    fn store_user_identity_key(
        &self,
        username: &str,
        identity_key: Vec<u8>,
    ) -> Result<(), StorageError> {
        let mut map = lock(&self.identity_keys)?;
        map.insert(username.to_string(), identity_key);
        self.flush_map_string_bytes(&self.identity_keys_path, &*map)
    }

    fn get_user_identity_key(&self, username: &str) -> Result<Option<Vec<u8>>, StorageError> {
        let map = lock(&self.identity_keys)?;
        Ok(map.get(username).cloned())
    }

    fn publish_endpoint(
        &self,
        identity_key: &[u8],
        node_addr: Vec<u8>,
    ) -> Result<(), StorageError> {
        let mut map = lock(&self.endpoints)?;
        map.insert(identity_key.to_vec(), node_addr);
        Ok(())
    }

    fn resolve_endpoint(&self, identity_key: &[u8]) -> Result<Option<Vec<u8>>, StorageError> {
        let map = lock(&self.endpoints)?;
        Ok(map.get(identity_key).cloned())
    }
}