// Copyright 2013 The Gorilla Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// copied from https://github.com/gorilla/handlers/blob/master/compress.go

package http_api

import (
    "compress/flate"
    "compress/gzip"
    "io"
    "net/http"
    "strings"
)

type compressResponseWriter struct {
    io.Writer
    http.ResponseWriter
    http.Hijacker
}

func (w *compressResponseWriter) Header() http.Header {
    return w.ResponseWriter.Header()
}

func (w *compressResponseWriter) WriteHeader(c int) {
    w.ResponseWriter.Header().Del("Content-Length")
    w.ResponseWriter.WriteHeader(c)
}

func (w *compressResponseWriter) Write(b []byte) (int, error) {
    h := w.ResponseWriter.Header()
    if h.Get("Content-Type") == "" {
        h.Set("Content-Type", http.DetectContentType(b))
    }
    h.Del("Content-Length")
    return w.Writer.Write(b)
}

// CompressHandler gzip compresses HTTP responses for clients that support it
// via the 'Accept-Encoding' header.
func CompressHandler(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    L:
        for _, enc := range strings.Split(r.Header.Get("Accept-Encoding"), ",") {
            switch strings.TrimSpace(enc) {
            case "gzip":
                w.Header().Set("Content-Encoding", "gzip")
                w.Header().Add("Vary", "Accept-Encoding")

                gw := gzip.NewWriter(w)
                defer gw.Close()

                h, hok := w.(http.Hijacker)
                if !hok { /* w is not Hijacker... oh well... */
                    h = nil
                }

                w = &compressResponseWriter{
                    Writer:         gw,
                    ResponseWriter: w,
                    Hijacker:       h,
                }

                break L
            case "deflate":
                w.Header().Set("Content-Encoding", "deflate")
                w.Header().Add("Vary", "Accept-Encoding")

                fw, _ := flate.NewWriter(w, flate.DefaultCompression)
                defer fw.Close()

                h, hok := w.(http.Hijacker)
                if !hok { /* w is not Hijacker... oh well... */
                    h = nil
                }

                w = &compressResponseWriter{
                    Writer:         fw,
                    ResponseWriter: w,
                    Hijacker:       h,
                }

                break L
            }
        }

        h.ServeHTTP(w, r)
    })
}