/**
 * Standalone signaling server for the Nextcloud Spreed app.
 * Copyright (C) 2017 struktur AG
 *
 * @author Joachim Bauch <bauch@struktur.de>
 *
 * @license GNU AGPL version 3 or any later version
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package container

import (
	"container/list"
	"sync"
)

type cacheEntry[T any] struct {
	key   string
	value T
}

type LruCache[T any] struct {
	size int // +checklocksignore: Only written to from constructor.
	mu   sync.Mutex
	// +checklocks:mu
	entries *list.List
	// +checklocks:mu
	data map[string]*list.Element
}

func NewLruCache[T any](size int) *LruCache[T] {
	return &LruCache[T]{
		size:    size,
		entries: list.New(),
		data:    make(map[string]*list.Element),
	}
}

func (c *LruCache[T]) Set(key string, value T) {
	c.mu.Lock()
	if v, found := c.data[key]; found {
		c.entries.MoveToFront(v)
		v.Value.(*cacheEntry[T]).value = value
		c.mu.Unlock()
		return
	}

	v := c.entries.PushFront(&cacheEntry[T]{
		key:   key,
		value: value,
	})
	c.data[key] = v
	if c.size > 0 && c.entries.Len() > c.size {
		c.removeOldestLocked()
	}
	c.mu.Unlock()
}

func (c *LruCache[T]) Get(key string) T {
	c.mu.Lock()
	if v, found := c.data[key]; found {
		c.entries.MoveToFront(v)
		value := v.Value.(*cacheEntry[T]).value
		c.mu.Unlock()
		return value
	}

	c.mu.Unlock()
	var defaultValue T
	return defaultValue
}

func (c *LruCache[T]) Remove(key string) {
	c.mu.Lock()
	if v, found := c.data[key]; found {
		c.removeElement(v)
	}
	c.mu.Unlock()
}

// +checklocks:c.mu
func (c *LruCache[T]) removeOldestLocked() {
	v := c.entries.Back()
	if v != nil {
		c.removeElement(v)
	}
}

func (c *LruCache[T]) RemoveOldest() {
	c.mu.Lock()
	c.removeOldestLocked()
	c.mu.Unlock()
}

// +checklocks:c.mu
func (c *LruCache[T]) removeElement(e *list.Element) {
	c.entries.Remove(e)
	entry := e.Value.(*cacheEntry[T])
	delete(c.data, entry.key)
}

func (c *LruCache[T]) Len() int {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.entries.Len()
}