// Copyright (C) 2019-2025, Lux Industries Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package cache

import (
	"sync"

	"github.com/luxfi/container/linked"
	"github.com/luxfi/utils"
)

var _ Cacher[struct{}, struct{}] = (*LRU[struct{}, struct{}])(nil)

// NewLRU creates a new LRU cache with the specified size
func NewLRU[K comparable, V any](size int) *LRU[K, V] {
	return &LRU[K, V]{
		Size: size,
	}
}

// LRU is a key value store with bounded size. If the size is attempted to be
// exceeded, then an element is removed from the cache before the insertion is
// done, based on evicting the least recently used value.
type LRU[K comparable, V any] struct {
	lock     sync.Mutex
	elements *linked.Hashmap[K, V]
	// If set to <= 0, will be set internally to 1.
	Size int
}

func (c *LRU[K, V]) Put(key K, value V) {
	c.lock.Lock()
	defer c.lock.Unlock()

	c.put(key, value)
}

func (c *LRU[K, V]) Get(key K) (V, bool) {
	c.lock.Lock()
	defer c.lock.Unlock()

	return c.get(key)
}

func (c *LRU[K, _]) Evict(key K) {
	c.lock.Lock()
	defer c.lock.Unlock()

	c.evict(key)
}

func (c *LRU[_, _]) Flush() {
	c.lock.Lock()
	defer c.lock.Unlock()

	c.flush()
}

func (c *LRU[_, _]) Len() int {
	c.lock.Lock()
	defer c.lock.Unlock()

	return c.len()
}

func (c *LRU[_, _]) PortionFilled() float64 {
	c.lock.Lock()
	defer c.lock.Unlock()

	return c.portionFilled()
}

func (c *LRU[K, V]) put(key K, value V) {
	c.resize()

	if c.elements.Len() == c.Size {
		oldestKey, _, _ := c.elements.Oldest()
		c.elements.Delete(oldestKey)
	}
	c.elements.Put(key, value)
}

func (c *LRU[K, V]) get(key K) (V, bool) {
	c.resize()

	val, ok := c.elements.Get(key)
	if !ok {
		return utils.Zero[V](), false
	}
	c.elements.Put(key, val) // Mark [k] as MRU.
	return val, true
}

func (c *LRU[K, _]) evict(key K) {
	c.resize()

	c.elements.Delete(key)
}

func (c *LRU[K, V]) flush() {
	if c.elements != nil {
		c.elements.Clear()
	}
}

func (c *LRU[_, _]) len() int {
	if c.elements == nil {
		return 0
	}
	return c.elements.Len()
}

func (c *LRU[_, _]) portionFilled() float64 {
	return float64(c.len()) / float64(c.Size)
}

// Initializes [c.elements] if it's nil.
// Sets [c.size] to 1 if it's <= 0.
// Removes oldest elements to make number of elements
// in the cache == [c.size] if necessary.
func (c *LRU[K, V]) resize() {
	if c.elements == nil {
		c.elements = linked.NewHashmap[K, V]()
	}
	if c.Size <= 0 {
		c.Size = 1
	}
	for c.elements.Len() > c.Size {
		oldestKey, _, _ := c.elements.Oldest()
		c.elements.Delete(oldestKey)
	}
}