package iris

import (
	"github.com/valyala/fasthttp"
	"net/url"
	"strconv"
	"sync"
	"time"
)

type (
	// CacheServiceAPI describes the cache service which caches the whole response body
	CacheServiceAPI interface {
		// Cache accepts a route's handler which will cache its response and a time.Duration(int64) which is the expiration duration
		Cache(HandlerFunc, time.Duration) HandlerFunc
		// ServeRemoteCache creates & returns a new handler which saves cache by POST method and serves a cache entry by GET method to clients
		// usually set it with iris.Any,
		// but developer is able to set different paths for save or get cache entries: using the iris.Post/.Get(...,iris.ServeRemote())
		// CacheRemote IS not ready for production yet and that's why it is not in docs or history yet.
		// propably this method will go to another package which will be ready at the next 24 hours,
		// because it can work both on iris and raw net/http, lets no limit it:)
		ServeRemoteCache(time.Duration) HandlerFunc
		// Invalidate accepts a cache key (which can be retrieved by 'GetCacheKey') and remove its cache response body
		InvalidateCache(string)
	}

	cacheService struct {
		cache map[string]*cacheEntry
		mu    sync.RWMutex
		// keep track of the minimum cache duration of all cache entries, this will be used when gcDuration inside .start() is <=time.Second
		gcDuration time.Duration
	}

	cacheEntry struct {
		statusCode  int
		contentType string
		body        []byte
		// we could have a new Timer foreach cache entry in order to be persise on the expiration but this will cost us a lot of performance,
		// (the ticker should be stopped if delete or key ovveride and so on...)
		// but I chosen to just have a generic timer with its tick on the lowest 'expires' of all cache entries that cache keeps
		expires time.Time
	}
)

func (e *cacheEntry) serve(ctx *Context) {
	ctx.SetContentType(e.contentType)
	ctx.SetStatusCode(e.statusCode)
	ctx.RequestCtx.Write(e.body)
}

var _ CacheServiceAPI = &cacheService{}

func newCacheService() *cacheService {
	cs := &cacheService{
		cache:      make(map[string]*cacheEntry),
		mu:         sync.RWMutex{},
		gcDuration: -1, // will set as the lowest of the cache entries, if not set then the cache doesn't starts its garbage collector
	}

	return cs
}

// start called last (after the lowest cache gc duration has been setted by the Cache funcs)
func (cs *cacheService) start() {
	if cs.gcDuration > 0 {
		// start the timer to check for expirated cache entries
		tick := time.Tick(cs.gcDuration)
		go func() {
			for range tick {
				cs.mu.Lock()
				now := time.Now()
				for k, v := range cs.cache {
					if now.After(v.expires) {
						delete(cs.cache, k)
					}
				}
				cs.mu.Unlock()
			}
		}()
	}

}

func (cs *cacheService) get(key string) *cacheEntry {
	cs.mu.RLock()
	if v, ok := cs.cache[key]; ok && time.Now().Before(v.expires) { // we check for expiration, the gc clears the cache but gc maybe late
		cs.mu.RUnlock()
		return v
	}
	cs.mu.RUnlock()
	return nil
}

var minimumAllowedCacheDuration = 2 * time.Second

func validateCacheDuration(expiration time.Duration) time.Duration {
	if expiration <= minimumAllowedCacheDuration {
		expiration = minimumAllowedCacheDuration * 2
	}
	return expiration
}

func validateStatusCode(statusCode int) int {
	if statusCode <= 0 {
		statusCode = StatusOK
	}
	return statusCode
}

func validateContentType(cType string) string {
	if cType == "" {
		cType = contentText
	}
	return cType
}

func (cs *cacheService) set(key string, statusCode int, cType string, body []byte, expiration time.Duration) {
	entry := &cacheEntry{
		statusCode:  validateStatusCode(statusCode),
		contentType: validateContentType(cType),
		expires:     time.Now().Add(validateCacheDuration(expiration)),
		body:        body,
	}

	cs.mu.Lock()
	cs.cache[key] = entry
	cs.mu.Unlock()
}

func (cs *cacheService) remove(key string) {
	cs.mu.Lock()
	delete(cs.cache, key)
	cs.mu.Unlock()
}

// GetCacheKey returns the cache key(string) from a context
// it's just the RequestURI
func GetCacheKey(ctx *Context) string {
	return string(ctx.Request.URI().RequestURI())
}

// InvalidateCache clears the cache body for a specific key(request uri, can be retrieved by GetCacheKey(ctx))
//
// Note that it depends on a station instance's cache service.
// Do not try to call it from default' station if you use the form of app := iris.New(),
// use the app.InvalidateCache instead of iris.InvalidateCache
//
// Example: https://github.com/iris-contrib/examples/tree/master/cache_body
func InvalidateCache(key string) {
	Default.InvalidateCache(key)
}

// InvalidateCache clears the cache body for a specific key(request uri, can be retrieved by GetCacheKey(ctx))
//
// Note that it depends on a station instance's cache service.
// Do not try to call it from default' station if you use the form of app := iris.New(),
// use the app.Cache instead of iris.Cache
//
// Example: https://github.com/iris-contrib/examples/tree/master/cache_body
func (cs *cacheService) InvalidateCache(key string) {
	cs.remove(key)
}

// Cache is just a wrapper for a route's handler which you want to enable body caching
// Usage: iris.Get("/", iris.Cache(func(ctx *iris.Context){
//    ctx.WriteString("Hello, world!") // or a template or anything else
// }, time.Duration(10*time.Second))) // duration of expiration
// if <=time.Second then it tries to find it though request header's "cache-control" maxage value
//
// Note that it depends on a station instance's cache service.
// Do not try to call it from default' station if you use the form of app := iris.New(),
// use the app.Cache instead of iris.Cache
//
// Example: https://github.com/iris-contrib/examples/tree/master/cache_body
func Cache(bodyHandler HandlerFunc, expiration time.Duration) HandlerFunc {
	return Default.Cache(bodyHandler, expiration)
}

func getResponseContentType(ctx *Context) string {
	return validateContentType(string(ctx.Response.Header.ContentType()))
}

func getResponseStatusCode(ctx *Context) int {
	return validateStatusCode(ctx.Response.StatusCode())
}

// Cache is just a wrapper for a route's handler which you want to enable body caching
// Usage: iris.Get("/", iris.Cache(func(ctx *iris.Context){
//    ctx.WriteString("Hello, world!") // or a template or anything else
// }, time.Duration(10*time.Second))) // duration of expiration
// if <=time.Second then it tries to find it though request header's "cache-control" maxage value
//
// Note that it depends on a station instance's cache service.
// Do not try to call it from default' station if you use the form of app := iris.New(),
// use the app.Cache instead of iris.Cache
//
// Example: https://github.com/iris-contrib/examples/tree/master/cache_body
func (cs *cacheService) Cache(bodyHandler HandlerFunc, expiration time.Duration) HandlerFunc {
	expiration = validateCacheDuration(expiration)

	if cs.gcDuration == -1 || expiration < cs.gcDuration {
		cs.gcDuration = expiration // the first time the  gcDuration should be > minimumAllowedCacheDuration so:
	}

	h := func(ctx *Context) {
		key := GetCacheKey(ctx)
		if v := cs.get(key); v != nil {
			v.serve(ctx)
			return
		}

		// if not found then serve the handler and collect its results after
		bodyHandler.Serve(ctx)

		if expiration <= minimumAllowedCacheDuration {
			// try to set the expiraion from header
			expiration = time.Duration(ctx.MaxAge()) * time.Second
		}

		cType := getResponseContentType(ctx)
		statusCode := getResponseStatusCode(ctx)
		body := ctx.Response.Body()
		// and set the cache value as its response body in a goroutine, because we want to exit from the route's handler as soon as possible
		go cs.set(key, statusCode, cType, body, expiration)
	}

	return h
}

// GetRemoteCacheKey returns the context's cache key,
// differs from GetCacheKey is that this method parses the query arguments
// because this key must be sent to an external server
func GetRemoteCacheKey(ctx *Context) string {
	return url.QueryEscape(ctx.Request.URI().String())
}

const (
	queryCacheKey         = "cache_key"
	queryCacheDuration    = "cache_duration"
	queryCacheStatusCode  = "cache_status_code"
	queryCacheContentType = "cache_content_type"
	requestCacheTimeout   = 5 * time.Second
	statusCacheSucceed    = StatusOK
	statusCacheFailed     = StatusBadRequest
)

// RemoteCache accepts the remote server address and path of the external cache service, the body handler and optional an expiration
// the last 2 receivers works like .Cache(...) function
//
// Note: Remotecache is a global function, usage:
// app.Get("/", iris.RemoteCache("http://127.0.0.1:8888/cache", bodyHandler, time.Duration(15)*time.Second))
//
// IT IS NOT READY FOR PRODUCTION YET, READ THE HISTORY.md for the available working cache methods
func RemoteCache(cacheServerAddr string, bodyHandler HandlerFunc, expiration time.Duration) HandlerFunc {
	client := fasthttp.Client{}
	//	buf := utils.NewBufferPool(10)
	cacheDurationStr := strconv.Itoa(int(expiration.Seconds()))
	h := func(ctx *Context) {
		req := fasthttp.AcquireRequest()
		req.SetRequestURI(cacheServerAddr)
		req.Header.SetMethodBytes(MethodGetBytes)
		req.URI().QueryArgs().Add(queryCacheKey, GetRemoteCacheKey(ctx))

		res := fasthttp.AcquireResponse()
		err := client.DoTimeout(req, res, requestCacheTimeout)
		if err != nil || res.StatusCode() == statusCacheFailed {
			// if not found on cache, then execute the handler and save the cache to the remote server
			bodyHandler.Serve(ctx)
			// save to the remote cache
			req.Header.SetMethodBytes(MethodPostBytes)
			args := req.URI().QueryArgs()
			args.Add(queryCacheDuration, cacheDurationStr)
			statusCode := strconv.Itoa(ctx.Response.StatusCode())
			args.Add(queryCacheStatusCode, statusCode)
			cType := string(ctx.Response.Header.Peek(contentType))
			args.Add(queryCacheContentType, cType)

			req.SetBody(ctx.Response.Body())
			go func() {
				client.DoTimeout(req, res, requestCacheTimeout)
				fasthttp.ReleaseRequest(req)
				fasthttp.ReleaseResponse(res)
			}()

		} else {
			// get the status code , content type and the write the response body
			statusCode := res.StatusCode()
			cType := res.Header.ContentType()
			ctx.SetStatusCode(statusCode)
			ctx.Response.Header.SetContentTypeBytes(cType)

			ctx.RequestCtx.Write(res.Body())

			fasthttp.ReleaseRequest(req)
			fasthttp.ReleaseResponse(res)
		}

	}
	return h
}

// ServeRemoteCache usage: iris.Any("/cacheservice", iris.ServeRemote())
// client does an http request to retrieve cached body from the external/remote server which keeps the cache service.
//
// if is GET method request then gets from cache
// if it's POST method request then its saves to the cache
// if it's DELETE method request then its invalidates/removes from cache manually
// the content type and the status are setted inside the caller's handler
// this is not like cs.Cache, it's useful only when you separate your servers to achieve horizontal scaling
//
// Note that it depends on a station instance's cache service.
// Do not try to call it from default' station if you use the form of app := iris.New(),
// use the app.ServeRemoteCache instead of iris.ServeRemoteCache
func ServeRemoteCache(gcDuration time.Duration) HandlerFunc {
	return Default.ServeRemoteCache(gcDuration)
}

// ServeRemoteCache usage: iris.Any("/cacheservice", iris.ServeRemoteCache())
// client does an http request to retrieve cached body from the external/remote server which keeps the cache service.
//
// if is GET method request then gets from cache
// if it's POST method request then its saves to the cache
// if it's DELETE method request then its invalidates/removes from cache manually
// the content type and the status are setted inside the caller's handler
// this is not like cs.Cache, it's useful only when you separate your servers to achieve horizontal scaling
//
// Note that it depends on a station instance's cache service.
// Do not try to call it from default' station if you use the form of app := iris.New(),
// use the app.ServeRemoteCache instead of iris.ServeRemoteCache
func (cs *cacheService) ServeRemoteCache(gcDuration time.Duration) HandlerFunc {
	cs.gcDuration = validateCacheDuration(gcDuration)
	// the service started at pre-listen state(on .Build) if gcDuration > 0
	h := func(ctx *Context) {
		key := ctx.URLParam(queryCacheKey)
		if key == "" {
			ctx.SetStatusCode(statusCacheFailed)
			return
		}

		if ctx.IsGet() {
			if v := cs.get(key); v != nil {
				v.serve(ctx)
				return
			}
		} else if ctx.IsPost() {
			// get the cache expiration via url param
			expirationSeconds, err := ctx.URLParamInt64(queryCacheDuration)
			// get the body from the requested body
			body := ctx.Request.Body()
			if len(body) == 0 {
				ctx.SetStatusCode(statusCacheFailed)
				return

			}
			// get the expiration from the "cache-control's maxage" if no url param is setted
			if expirationSeconds <= 0 || err != nil {
				expirationSeconds = ctx.MaxAge()
			}

			// if not setted then try to get it via
			if expirationSeconds <= 0 {
				expirationSeconds = int64(minimumAllowedCacheDuration.Seconds())
			}

			cacheDuration := validateCacheDuration(time.Duration(expirationSeconds) * time.Second)
			statusCode, _ := ctx.URLParamInt(queryCacheDuration)
			statusCode = validateStatusCode(statusCode)
			cType := validateContentType(ctx.URLParam(queryCacheContentType))

			cs.set(key, statusCode, cType, body, cacheDuration)

			ctx.SetStatusCode(statusCacheSucceed)
			return
		} else if ctx.IsDelete() {
			cs.remove(key)
			ctx.SetStatusCode(statusCacheSucceed)
			return
		}

		ctx.SetStatusCode(statusCacheFailed)
	}

	return h
}