package cache

/*
   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

import (
	"errors"
	"net/http"
	"net/url"
	"time"

	"github.com/apache/trafficcontrol/grove/cacheobj"
	"github.com/apache/trafficcontrol/grove/icache"
	"github.com/apache/trafficcontrol/grove/remap"
	"github.com/apache/trafficcontrol/grove/thread"
	"github.com/apache/trafficcontrol/grove/web"

	"github.com/apache/trafficcontrol/lib/go-log"
	"github.com/apache/trafficcontrol/lib/go-rfc"
)

const CodeConnectFailure = http.StatusBadGateway

type Retrier struct {
	H                 *Handler
	ReqHdr            http.Header
	ReqTime           time.Time
	ReqCacheControl   rfc.CacheControlMap
	RemappingProducer *remap.RemappingProducer
	ReqID             uint64
}

func NewRetrier(h *Handler, reqHdr http.Header, reqTime time.Time, reqCacheControl rfc.CacheControlMap, remappingProducer *remap.RemappingProducer, reqID uint64) *Retrier {
	return &Retrier{
		H:                 h,
		ReqHdr:            reqHdr,
		ReqCacheControl:   reqCacheControl,
		RemappingProducer: remappingProducer,
		ReqID:             reqID,
	}
}

// Get takes the HTTP request and the cached object if there is one, and makes a new request, retrying according to its RemappingProducer. If no cached object exists, pass a nil obj.
// Along with the cacheobj.CacheObj, a string pointer to the request hostname used to fetch the cacheobj.CacheObj is returned.
func (r *Retrier) Get(req *http.Request, obj *cacheobj.CacheObj) (*cacheobj.CacheObj, *string, error) {
	retryGetFunc := func(remapping remap.Remapping, retryFailures bool, obj *cacheobj.CacheObj) *cacheobj.CacheObj {
		// return true for Revalidate, and issue revalidate requests separately.
		canReuse := func(cacheObj *cacheobj.CacheObj) bool {
			return cacheobj.CanReuse(r.ReqHdr, r.ReqCacheControl, cacheObj, r.H.strictRFC, true)
		}
		getAndCache := func() *cacheobj.CacheObj {
			return GetAndCache(remapping.Request, remapping.ProxyURL, remapping.CacheKey, remapping.Name, remapping.Request.Header, r.ReqTime, r.H.strictRFC, remapping.Cache, r.H.ruleThrottlers[remapping.Name], obj, remapping.Timeout, retryFailures, remapping.RetryNum, remapping.RetryCodes, remapping.Transport, r.ReqID)
		}
		gotObj, getReqID := r.H.getter.Get(remapping.CacheKey, getAndCache, canReuse, r.ReqID)

		req := remapping.Request
		log.Debugf("Retrier.Get Y URI %v %v %v remapping.CacheKey %v rule %v parent %v code %v headers %+v len(body) %v getterid %v (reqid %v)\n", req.URL.Scheme, req.URL.Host, req.URL.EscapedPath(), remapping.CacheKey, remapping.Name, remapping.ProxyURL, gotObj.Code, gotObj.RespHeaders, len(gotObj.Body), getReqID, r.ReqID)

		return gotObj
	}

	return retryingGet(retryGetFunc, req, r.RemappingProducer, obj)
}

// retryingGet takes a function, and retries failures up to the RemappingProducer RetryNum limit. On failure, it creates a new remapping. The func f should use `remapping` to make its request. If it hits failures up to the limit, it returns the last received cacheobj.CacheObj
// Along with the cacheobj.CacheObj, a string pointer to the request hostname used to fetch the cacheobj.CacheObj is returned.
// TODO refactor to not close variables - it's awkward and confusing.
func retryingGet(getCacheObj func(remapping remap.Remapping, retryFailures bool, obj *cacheobj.CacheObj) *cacheobj.CacheObj, request *http.Request, remappingProducer *remap.RemappingProducer, cachedObj *cacheobj.CacheObj) (*cacheobj.CacheObj, *string, error) {
	obj := (*cacheobj.CacheObj)(nil)
	for {
		remapping, retryAllowed, err := remappingProducer.GetNext(request)
		if err == remap.ErrNoMoreRetries {
			if obj == nil {
				return nil, nil, errors.New("remapping producer allows no requests") // should never happen
			}
			return obj, nil, nil
		} else if err != nil {
			return nil, nil, err
		}
		obj = getCacheObj(remapping, retryAllowed, cachedObj)
		if !isFailure(obj, remapping.RetryCodes) {
			return obj, &remapping.Request.URL.Host, nil
		}
	}
}

func isFailure(o *cacheobj.CacheObj, retryCodes map[int]struct{}) bool {
	_, failureCode := retryCodes[o.Code]
	return failureCode || o.Code == CodeConnectFailure
}

const ModifiedSinceHdr = "If-Modified-Since"

// GetAndCache makes a client request for the given `http.Request` and caches it if `CanCache`.
// THe `ruleThrottler` may be nil, in which case the request will be unthrottled.
func GetAndCache(
	req *http.Request,
	proxyURL *url.URL,
	cacheKey string,
	remapName string,
	reqHeader http.Header,
	reqTime time.Time,
	strictRFC bool,
	cache icache.Cache,
	ruleThrottler thread.Throttler,
	revalidateObj *cacheobj.CacheObj,
	timeout time.Duration,
	cacheFailure bool,
	retryNum int,
	retryCodes map[int]struct{},
	transport *http.Transport,
	reqID uint64,
) *cacheobj.CacheObj {
	// TODO this is awkward, with 'revalidateObj' indicating whether the request is a Revalidate. Should Getting and Caching be split up? How?
	get := func() *cacheobj.CacheObj {
		// TODO figure out why respReqTime isn't used by rules
		log.Debugf("GetAndCache calling request %v %v %v %v %v (reqid %v)\n", req.Method, req.URL.Scheme, req.URL.Host, req.URL.EscapedPath(), req.Header, reqID)
		// TODO Verify overriding the passed reqTime is the right thing to do
		proxyURLStr := ""
		if proxyURL != nil {
			proxyURLStr = proxyURL.Host
		}
		if revalidateObj != nil {
			req.Header.Set(ModifiedSinceHdr, revalidateObj.LastModified.Format(time.RFC1123))
		} else {
			req.Header.Del(ModifiedSinceHdr)
		}
		respCode, respHeader, respBody, reqTime, reqRespTime, err := web.Request(transport, req)
		log.Debugf("GetAndCache web.Request URI %v %v %v cacheKey %v rule %v parent %v error %v reval %v code %v len(body) %v (reqid %v)\n", req.URL.Scheme, req.URL.Host, req.URL.EscapedPath(), cacheKey, remapName, proxyURLStr, err, revalidateObj != nil, respCode, len(respBody), reqID)

		if err != nil {
			log.Errorf("Parent error for URI %v %v %v cacheKey %v rule %v parent %v error %v (reqid %v)\n", req.URL.Scheme, req.URL.Host, req.URL.EscapedPath(), cacheKey, remapName, proxyURLStr, err, reqID)
			code := CodeConnectFailure
			body := []byte(http.StatusText(code))
			return cacheobj.New(reqHeader, body, code, code, proxyURLStr, respHeader, reqTime, reqRespTime, reqRespTime, time.Time{})
		}
		if _, ok := retryCodes[respCode]; ok && !cacheFailure {
			return cacheobj.New(reqHeader, respBody, respCode, respCode, proxyURLStr, respHeader, reqTime, reqRespTime, reqRespTime, time.Time{})
		}

		log.Debugf("GetAndCache request returned %v headers %+v (reqid %v)\n", respCode, respHeader, reqID)
		respRespTime, ok := rfc.GetHTTPDate(respHeader, "Date")
		if !ok {
			log.Errorf("request %v returned no Date header - RFC Violation! Using local response timestamp (reqid %v)\n", req.RequestURI, reqID)
			respRespTime = reqRespTime // if no Date was returned using the client response time simulates latency 0
		}

		lastModified, ok := rfc.GetHTTPDate(respHeader, "Last-Modified")
		if !ok {
			lastModified = respRespTime
		}

		obj := (*cacheobj.CacheObj)(nil)
		log.Debugf("h.cache.Add %v (reqid %v)\n", cacheKey, reqID)
		log.Debugf("GetAndCache respCode %v (reqid %v)\n", respCode, reqID)
		if revalidateObj == nil || respCode != http.StatusNotModified {
			log.Debugf("GetAndCache new %v (reqid %v)\n", cacheKey, reqID)
			obj = cacheobj.New(reqHeader, respBody, respCode, respCode, proxyURLStr, respHeader, reqTime, reqRespTime, respRespTime, lastModified)
			if !rfc.CanCache(req.Method, reqHeader, respCode, respHeader, strictRFC) {
				return obj // return without caching
			}
		} else {
			log.Debugf("GetAndCache revalidating %v len(revalidateObj.Body) %v (reqid %v)\n", cacheKey, len(revalidateObj.Body), reqID)
			// must copy, because this cache object may be concurrently read by other goroutines
			newRespHeader := web.CopyHeader(revalidateObj.RespHeaders)
			newRespHeader.Set("Date", respHeader.Get("Date"))
			obj = &cacheobj.CacheObj{
				Body:             revalidateObj.Body,
				ReqHeaders:       revalidateObj.ReqHeaders,
				RespHeaders:      newRespHeader,
				RespCacheControl: revalidateObj.RespCacheControl,
				Code:             revalidateObj.Code,
				OriginCode:       respCode,
				ProxyURL:         proxyURLStr,
				ReqTime:          reqTime,
				ReqRespTime:      reqRespTime,
				RespRespTime:     respRespTime,
				LastModified:     revalidateObj.LastModified,
				Size:             revalidateObj.Size,
				HitCount:         revalidateObj.HitCount, // no need to +1 here, the cache Get did that
			}
		}
		cache.Add(cacheKey, obj) // TODO store pointer?
		return obj
	}

	c := (*cacheobj.CacheObj)(nil)
	if ruleThrottler == nil {
		log.Errorf("rule %v not in ruleThrottlers map. Requesting with no origin limit! (reqid %v)\n", remapName, reqID)
		ruleThrottler = thread.NewNoThrottler()
	}
	ruleThrottler.Throttle(func() { c = get() })
	return c
}