package gziphandler

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

type gw struct {
	http.ResponseWriter
	w *gzip.Writer
}

func (w *gw) Write(d []byte) (int, error) {
	return w.w.Write(d)
}

func (w *gw) Close() error {
	return w.w.Close()
}

func acceptsGzip(r *http.Request) bool {
	ae := r.Header.Get("Accept-Encoding")
	for _, e := range strings.Split(ae, ",") {
		vals := strings.Split(e, ";")
		if len(vals) < 1 {
			continue
		}
		if strings.TrimSpace(vals[0]) == "gzip" {
			return true
		}
	}
	return false
}

// Handler returns an http.Handler that compresses the response data written
// by an existing handler h, using the compress/gzip.Writer with default
// compression level.
func Handler(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !acceptsGzip(r) {
			h.ServeHTTP(w, r)
			return
		}
		w.Header().Set("Content-Encoding", "gzip")
		gw := &gw{
			ResponseWriter: w,
			w:              gzip.NewWriter(w),
		}
		h.ServeHTTP(gw, r)
		gw.Close()
	})
}