package main

import (
	"encoding/json"
	"io"
	"time"

	"github.com/peterbourgon/diskv"
)

// An AlbumCoverCache is used to fetch and cache Album Cover image from www.bedetheque.com
type AlbumCoverCache struct {
	dv     *diskv.Diskv
	getter HTTPGetter
	// time to live of the cache, data which is older than this TTL will be automatically removed
	TTL time.Duration
}

// NewAlbumCoverCache is creating a new cache at specified location on the fs
func NewAlbumCoverCache(basepath string, maxRequest uint, window time.Duration) *AlbumCoverCache {
	res := &AlbumCoverCache{
		dv: diskv.New(diskv.Options{
			BasePath:     basepath,
			CacheSizeMax: 100 * 1024 * 1024, // 100 Mb
		}),
		getter: NewRateLimitedGetter(maxRequest, window),
		TTL:    3 * 31 * 24 * time.Hour, // 3 Months
	}
	return res
}

func (c *AlbumCoverCache) fetch(a *Album) (io.ReadCloser, error) {
	resp, err := c.getter.Get(a.CoverURL)
	if err != nil {
		return nil, err
	}
	defer closeOrPanic(resp.Body, "GET "+a.CoverURL)

	err = c.dv.WriteStream(c.dataKey(a), resp.Body, false)
	if err != nil {
		return nil, err
	}
	md := coverMetadata{
		Age: time.Now(),
	}
	mdbyte, err := json.Marshal(&md)
	if err == nil {
		err = c.dv.Write(c.metadataKey(a), mdbyte)
		if err != nil {
			return nil, err
		}
	}

	return c.dv.ReadStream(c.dataKey(a), false)
}

type coverMetadata struct {
	Age time.Time
}

func (c *AlbumCoverCache) metadataKey(a *Album) string {
	return AlbumIDString(a.ID) + ".metadata"
}

func (c *AlbumCoverCache) dataKey(a *Album) string {
	return AlbumIDString(a.ID) + ".data"
}

// GetCover retrieves from the cache or either from www.bedetheque.com the Cover of an album
func (c *AlbumCoverCache) GetCover(a *Album) (io.ReadCloser, error) {
	//
	if c.dv.Has(c.metadataKey(a)) == false {
		return c.fetch(a)
	}

	mdbytes, err := c.dv.Read(c.metadataKey(a))
	if err != nil {
		return c.fetch(a)
	}
	var md coverMetadata
	err = json.Unmarshal(mdbytes, &md)
	if err != nil {
		return c.fetch(a)
	}

	// check TTL
	if time.Now().Add(-c.TTL).After(md.Age) == true {
		return c.fetch(a)
	}

	return c.dv.ReadStream(c.dataKey(a), false)
}