/*
Copyright IBM Corp. 2017 All Rights Reserved.

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.
*/

package lib

import (
	"encoding/json"
	"net/http"

	"github.com/cloudflare/cfssl/api"
	"github.com/cloudflare/cfssl/log"
)

// serverEndpoint represents a particular endpoint (e.g. to "/api/v1/enroll")
type serverEndpoint struct {
	// The HTTP methods ("GET", "POST", etc) which the function will handle
	Methods []string
	// The HTTP status code for a successful response
	successRC int
	// Handler is the handler function for this endpoint
	Handler func(ctx *serverRequestContextImpl) (interface{}, error)
	// Server which hosts this endpoint
	Server *Server
}

// ServeHTTP encapsulates the call to underlying Handlers to handle the request
// and return the response with a proper HTTP status code
func (se *serverEndpoint) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	var resp interface{}
	url := r.URL.String()
	log.Debugf("Received request for %s", url)
	w = newHTTPResponseWriter(r, w, se)
	err := se.validateMethod(r)
	if err == nil {
		// Call the endpoint handler to handle the request.  The handler may
		// a) return the response in the 'resp' variable below, or
		// b) write the response one chunk at a time, which is appropriate if the response may be large
		//    and we don't want the server to buffer the entire response in memory.
		resp, err = se.Handler(newServerRequestContext(r, w, se))
	}
	he := getHTTPErr(err)
	if he != nil {
		// An error occurred
		w.WriteHeader(he.scode)
		log.Infof(`%s %s %s %d %d "%s"`, r.RemoteAddr, r.Method, r.URL, he.scode, he.lcode, he.lmsg)
	} else {
		// No error occurred
		scode := se.getSuccessRC()
		w.WriteHeader(scode)
		log.Infof(`%s %s %s %d 0 "OK"`, r.RemoteAddr, r.Method, r.URL, scode)
	}
	// If a response was returned by the handler, write it now.
	if resp != nil {
		writeJSON(resp, w)
	}
	// If nothing has been written, write an empty string for the response
	if !w.(*httpResponseWriter).writeCalled {
		w.Write([]byte(`""`))
	}
	// If an error was returned by the handler, write it now.
	w.Write([]byte(`,"errors":[`))
	if he != nil {
		rm := &api.ResponseMessage{Code: he.rcode, Message: he.rmsg}
		writeJSON(rm, w)
	}
	// Write true or false for success
	w.Write([]byte(`],"messages":[],"success":`))
	if he != nil {
		w.Write([]byte(`false}`))
	} else {
		w.Write([]byte(`true}`))
	}
	w.(http.Flusher).Flush()
}

func (se *serverEndpoint) getSuccessRC() int {
	if se.successRC == 0 {
		return 200
	}
	return se.successRC
}

// Validate that the HTTP method is supported for this endpoint
func (se *serverEndpoint) validateMethod(r *http.Request) error {
	for _, m := range se.Methods {
		if m == r.Method {
			return nil
		}
	}
	return newHTTPErr(405, ErrMethodNotAllowed, "Method %s is not allowed", r.Method)
}

// Get the top-most HTTP error from the cause stack.
// If not found, create one with an unknown error code.
func getHTTPErr(err error) *httpErr {
	if err == nil {
		return nil
	}
	type causer interface {
		Cause() error
	}
	curErr := err
	for curErr != nil {
		switch curErr.(type) {
		case *httpErr:
			return curErr.(*httpErr)
		case causer:
			curErr = curErr.(causer).Cause()
		default:
			return createHTTPErr(500, ErrUnknown, err.Error())
		}
	}
	return createHTTPErr(500, ErrUnknown, "nil error")
}

func writeJSON(obj interface{}, w http.ResponseWriter) {
	enc := json.NewEncoder(w)
	err := enc.Encode(obj)
	if err != nil {
		log.Errorf("Failed encoding response to JSON: %s", err)
	}
}

func newHTTPResponseWriter(r *http.Request, w http.ResponseWriter, se *serverEndpoint) *httpResponseWriter {
	return &httpResponseWriter{r: r, w: w, se: se}
}

type httpResponseWriter struct {
	r                 *http.Request
	w                 http.ResponseWriter
	se                *serverEndpoint
	writeHeaderCalled bool
	writeCalled       bool
}

// Header returns the header map that will be sent by WriteHeader.
func (hrw *httpResponseWriter) Header() http.Header {
	return hrw.w.Header()
}

// WriteHeader sends an HTTP response header with status code.
func (hrw *httpResponseWriter) WriteHeader(scode int) {
	if !hrw.writeHeaderCalled {
		w := hrw.w
		w.Header().Set("Connection", "Keep-Alive")
		if hrw.isHead() {
			w.Header().Set("Content-Length", "0")
		} else {
			w.Header().Set("Transfer-Encoding", "chunked")
			w.Header().Set("Content-Type", "application/json")
		}
		// Write the appropriate successful status code for this endpoint
		if scode == http.StatusOK {
			scode = hrw.se.getSuccessRC()
		}
		w.WriteHeader(scode)
		hrw.writeHeaderCalled = true
	}
}

// Write writes the data to the connection as part of an HTTP reply.
func (hrw *httpResponseWriter) Write(buf []byte) (int, error) {
	if hrw.isHead() {
		return 0, nil
	}
	w := hrw.w
	hrw.WriteHeader(http.StatusOK)
	if !hrw.writeCalled {
		// Write the header of the body of the result
		b, err := w.Write([]byte(`{"result":`))
		if err != nil {
			return b, err
		}
		hrw.writeCalled = true
	}
	if buf == nil {
		return 0, nil
	}
	return w.Write(buf)
}

func (hrw *httpResponseWriter) Flush() {
	hrw.w.(http.Flusher).Flush()
}

func (hrw *httpResponseWriter) isHead() bool {
	return hrw.r.Method == "HEAD"
}