package caching

import (
	"fmt"

	lru "github.com/hashicorp/golang-lru"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
)

func NewInMemoryLRUCache() (*Caches, error) {
	roomVersions, err := NewInMemoryLRUCachePartition(
		RoomVersionCacheName,
		RoomVersionCacheMutable,
		RoomVersionCacheMaxEntries,
	)
	if err != nil {
		return nil, err
	}
	serverKeys, err := NewInMemoryLRUCachePartition(
		ServerKeyCacheName,
		ServerKeyCacheMutable,
		ServerKeyCacheMaxEntries,
	)
	if err != nil {
		return nil, err
	}
	return &Caches{
		RoomVersions: roomVersions,
		ServerKeys:   serverKeys,
	}, nil
}

type InMemoryLRUCachePartition struct {
	name       string
	mutable    bool
	maxEntries int
	lru        *lru.Cache
}

func NewInMemoryLRUCachePartition(name string, mutable bool, maxEntries int) (*InMemoryLRUCachePartition, error) {
	var err error
	cache := InMemoryLRUCachePartition{
		name:       name,
		mutable:    mutable,
		maxEntries: maxEntries,
	}
	cache.lru, err = lru.New(maxEntries)
	if err != nil {
		return nil, err
	}
	promauto.NewGaugeFunc(prometheus.GaugeOpts{
		Namespace: "dendrite",
		Subsystem: "caching_in_memory_lru",
		Name:      name,
	}, func() float64 {
		return float64(cache.lru.Len())
	})
	return &cache, nil
}

func (c *InMemoryLRUCachePartition) Set(key string, value interface{}) {
	if !c.mutable {
		if peek, ok := c.lru.Peek(key); ok && peek != value {
			panic(fmt.Sprintf("invalid use of immutable cache tries to mutate existing value of %q", key))
		}
	}
	c.lru.Add(key, value)
}

func (c *InMemoryLRUCachePartition) Get(key string) (value interface{}, ok bool) {
	return c.lru.Get(key)
}