package cache

import (
	"container/list"
	"context"
	"sync"
	"time"

	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
)

type lruEntry struct {
	key       string
	response  *CachedResponse
	expiresAt time.Time
}

type memoryResponseCache struct {
	cfg      config.ResponseCacheConfig
	mu       sync.RWMutex
	items    map[string]*list.Element
	eviction *list.List
	stats    responseCacheStats
}

func newMemoryResponseCache(cfg config.ResponseCacheConfig) *memoryResponseCache {
	maxEntries := cfg.MaxMemoryEntries
	if maxEntries <= 0 {
		maxEntries = 1000
	}
	return &memoryResponseCache{
		cfg:      cfg,
		items:    make(map[string]*list.Element, maxEntries),
		eviction: list.New(),
	}
}

func (m *memoryResponseCache) Get(_ context.Context, key string) (*CachedResponse, bool) {
	m.mu.RLock()
	elem, ok := m.items[key]
	m.mu.RUnlock()
	if !ok {
		m.stats.recordMiss()
		return nil, false
	}

	entry := elem.Value.(*lruEntry)
	if time.Now().After(entry.expiresAt) {
		// Lazy expiry
		m.mu.Lock()
		m.removeElement(elem)
		m.mu.Unlock()
		m.stats.recordMiss()
		return nil, false
	}

	// Move to front (most recently used)
	m.mu.Lock()
	m.eviction.MoveToFront(elem)
	m.mu.Unlock()

	m.stats.recordHit()
	return entry.response, true
}

func (m *memoryResponseCache) Set(_ context.Context, key string, resp *CachedResponse, ttl time.Duration) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	// Update existing
	if elem, ok := m.items[key]; ok {
		entry := elem.Value.(*lruEntry)
		entry.response = resp
		entry.expiresAt = time.Now().Add(ttl)
		m.eviction.MoveToFront(elem)
		return nil
	}

	maxEntries := m.cfg.MaxMemoryEntries
	if maxEntries <= 0 {
		maxEntries = 1000
	}

	// Evict if at capacity
	for len(m.items) >= maxEntries && m.eviction.Len() > 0 {
		back := m.eviction.Back()
		if back != nil {
			m.removeElement(back)
		}
	}

	// Add new
	entry := &lruEntry{
		key:       key,
		response:  resp,
		expiresAt: time.Now().Add(ttl),
	}
	elem := m.eviction.PushFront(entry)
	m.items[key] = elem
	return nil
}

func (m *memoryResponseCache) Delete(_ context.Context, _ string) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.items = make(map[string]*list.Element)
	m.eviction.Init()
	return nil
}

func (m *memoryResponseCache) Stats() CacheStats {
	m.mu.RLock()
	size := int64(len(m.items))
	m.mu.RUnlock()
	return CacheStats{
		Hits:   m.stats.hits.Load(),
		Misses: m.stats.misses.Load(),
		Size:   size,
	}
}

func (m *memoryResponseCache) Close() error {
	return nil
}

func (m *memoryResponseCache) removeElement(elem *list.Element) {
	entry := elem.Value.(*lruEntry)
	delete(m.items, entry.key)
	m.eviction.Remove(elem)
}