// Copyright 2024 RustFS Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::collections::HashMap;
use std::hash::{Hash, Hasher};
use std::sync::Arc;
use std::time::{Duration, SystemTime};
use tokio::sync::RwLock;

use crate::{
    FastLockGuard, GlobalLockManager, LockClient, LockId, LockInfo, LockManager, LockMetadata, LockPriority, LockRequest,
    LockResponse, LockStats, LockStatus, LockType, Result,
};

/// Default shard count for guard storage (must be power of 2)
const DEFAULT_GUARD_SHARD_COUNT: usize = 64;

/// Local lock client using FastLock with sharded guard storage for better concurrency
#[derive(Debug)]
pub struct LocalClient {
    /// Sharded guard storage to reduce lock contention
    guard_storage: Vec<Arc<RwLock<HashMap<LockId, LocalGuardEntry>>>>,
    /// Mask for fast shard index calculation (shard_count - 1)
    shard_mask: usize,
    /// Optional lock manager (if None, uses global singleton)
    manager: Option<Arc<GlobalLockManager>>,
}

#[derive(Debug)]
struct LocalGuardEntry {
    guard: FastLockGuard,
    expires_at: SystemTime,
    ttl: Duration,
}

impl LocalGuardEntry {
    fn new(guard: FastLockGuard, ttl: Duration) -> Self {
        let now = SystemTime::now();
        Self {
            guard,
            expires_at: now + ttl,
            ttl,
        }
    }

    fn is_expired(&self) -> bool {
        self.expires_at <= SystemTime::now()
    }

    fn refresh(&mut self) {
        self.expires_at = SystemTime::now() + self.ttl;
    }
}

impl LocalClient {
    /// Create new local client with default shard count
    pub fn new() -> Self {
        Self::with_shard_count(DEFAULT_GUARD_SHARD_COUNT)
    }

    /// Create new local client with custom shard count
    /// Shard count must be a power of 2 for efficient masking
    pub fn with_shard_count(shard_count: usize) -> Self {
        assert!(shard_count.is_power_of_two(), "Shard count must be power of 2");

        let guard_storage: Vec<Arc<RwLock<HashMap<LockId, LocalGuardEntry>>>> =
            (0..shard_count).map(|_| Arc::new(RwLock::new(HashMap::new()))).collect();

        Self {
            guard_storage,
            shard_mask: shard_count - 1,
            manager: None,
        }
    }

    /// Create new local client with a specific lock manager
    /// This allows simulating multi-node environments where each node has its own lock backend
    pub fn with_manager(manager: Arc<GlobalLockManager>) -> Self {
        Self {
            guard_storage: (0..DEFAULT_GUARD_SHARD_COUNT)
                .map(|_| Arc::new(RwLock::new(HashMap::new())))
                .collect(),
            shard_mask: DEFAULT_GUARD_SHARD_COUNT - 1,
            manager: Some(manager),
        }
    }

    /// Get the lock manager (injected manager if available, otherwise global singleton)
    pub fn get_lock_manager(&self) -> Arc<GlobalLockManager> {
        self.manager.clone().unwrap_or_else(crate::get_global_lock_manager)
    }

    /// Get the shard index for a given lock ID
    fn get_shard_index(&self, lock_id: &LockId) -> usize {
        let mut hasher = std::collections::hash_map::DefaultHasher::new();
        lock_id.hash(&mut hasher);
        (hasher.finish() as usize) & self.shard_mask
    }

    /// Get the shard for a given lock ID
    fn get_shard(&self, lock_id: &LockId) -> &Arc<RwLock<HashMap<LockId, LocalGuardEntry>>> {
        let index = self.get_shard_index(lock_id);
        &self.guard_storage[index]
    }

    async fn reclaim_expired_guards_for_resource(&self, resource: &crate::ObjectKey) -> usize {
        let mut reclaimed = 0usize;

        for shard in &self.guard_storage {
            let expired_entries = {
                let mut guards = shard.write().await;
                let mut retained = HashMap::with_capacity(guards.len());
                let mut expired_entries = Vec::new();

                for (lock_id, entry) in std::mem::take(&mut *guards) {
                    if &lock_id.resource == resource && entry.is_expired() {
                        expired_entries.push(entry);
                    } else {
                        retained.insert(lock_id, entry);
                    }
                }

                *guards = retained;
                expired_entries
            };

            for mut entry in expired_entries {
                let _ = entry.guard.release();
                reclaimed = reclaimed.saturating_add(1);
            }
        }

        reclaimed
    }
}

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

#[async_trait::async_trait]
impl LockClient for LocalClient {
    async fn acquire_lock(&self, request: &LockRequest) -> Result<LockResponse> {
        let lock_manager = self.get_lock_manager();
        let reclaimed_before_acquire = self.reclaim_expired_guards_for_resource(&request.resource).await;

        let build_lock_request = || match request.lock_type {
            LockType::Exclusive => crate::ObjectLockRequest::new_write(request.resource.clone(), request.owner.clone())
                .with_acquire_timeout(request.acquire_timeout),
            LockType::Shared => crate::ObjectLockRequest::new_read(request.resource.clone(), request.owner.clone())
                .with_acquire_timeout(request.acquire_timeout),
        };

        let mut retried_after_reclaim = reclaimed_before_acquire > 0;
        loop {
            match lock_manager.acquire_lock(build_lock_request()).await {
                Ok(guard) => {
                    let lock_id = request.lock_id.clone();
                    let acquired_at = SystemTime::now();
                    let expires_at = acquired_at + request.ttl;

                    {
                        let shard = self.get_shard(&lock_id);
                        let mut guards = shard.write().await;
                        guards.insert(lock_id.clone(), LocalGuardEntry::new(guard, request.ttl));
                    }

                    let lock_info = LockInfo {
                        id: lock_id,
                        resource: request.resource.clone(),
                        lock_type: request.lock_type,
                        status: crate::types::LockStatus::Acquired,
                        owner: request.owner.clone(),
                        acquired_at,
                        expires_at,
                        last_refreshed: acquired_at,
                        metadata: request.metadata.clone(),
                        priority: request.priority,
                        wait_start_time: None,
                    };
                    return Ok(LockResponse::success(lock_info, Duration::ZERO));
                }
                Err(crate::fast_lock::LockResult::Timeout) => {
                    if !retried_after_reclaim && self.reclaim_expired_guards_for_resource(&request.resource).await > 0 {
                        retried_after_reclaim = true;
                        continue;
                    }
                    return Ok(LockResponse::failure("Lock acquisition timeout", request.acquire_timeout));
                }
                Err(crate::fast_lock::LockResult::Conflict {
                    current_owner,
                    current_mode,
                }) => {
                    if !retried_after_reclaim && self.reclaim_expired_guards_for_resource(&request.resource).await > 0 {
                        retried_after_reclaim = true;
                        continue;
                    }
                    return Ok(LockResponse::failure(
                        format!("Lock conflict: resource held by {current_owner} in {current_mode:?} mode"),
                        Duration::ZERO,
                    ));
                }
                Err(crate::fast_lock::LockResult::Acquired) => {
                    unreachable!("Acquired should not be an error")
                }
            }
        }
    }

    async fn release(&self, lock_id: &LockId) -> Result<bool> {
        let shard = self.get_shard(lock_id);
        let mut guards = shard.write().await;
        if let Some(guard) = guards.remove(lock_id) {
            // Guard automatically releases the lock when dropped
            drop(guard.guard);
            Ok(true)
        } else {
            // Lock not found or already released
            Ok(false)
        }
    }

    async fn refresh(&self, lock_id: &LockId) -> Result<bool> {
        let shard = self.get_shard(lock_id);
        let mut guards = shard.write().await;
        if let Some(entry) = guards.get_mut(lock_id) {
            entry.refresh();
            Ok(true)
        } else {
            Ok(false)
        }
    }

    async fn force_release(&self, lock_id: &LockId) -> Result<bool> {
        self.release(lock_id).await
    }

    async fn check_status(&self, lock_id: &LockId) -> Result<Option<LockInfo>> {
        let shard = self.get_shard(lock_id);
        let guards = shard.read().await;
        if let Some(entry) = guards.get(lock_id) {
            // We have an active guard for this lock
            let lock_type = match entry.guard.mode() {
                crate::LockMode::Shared => LockType::Shared,
                crate::LockMode::Exclusive => LockType::Exclusive,
            };
            let status = if entry.is_expired() {
                LockStatus::Expired
            } else {
                LockStatus::Acquired
            };
            Ok(Some(LockInfo {
                id: lock_id.clone(),
                resource: lock_id.resource.clone(),
                lock_type,
                status,
                owner: entry.guard.owner().to_string(),
                acquired_at: SystemTime::now(),
                expires_at: entry.expires_at,
                last_refreshed: SystemTime::now(),
                metadata: LockMetadata::default(),
                priority: LockPriority::Normal,
                wait_start_time: None,
            }))
        } else {
            Ok(None)
        }
    }

    async fn get_stats(&self) -> Result<LockStats> {
        Ok(LockStats::default())
    }

    async fn close(&self) -> Result<()> {
        Ok(())
    }

    async fn is_online(&self) -> bool {
        true
    }

    async fn is_local(&self) -> bool {
        true
    }
}