package util

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

// Gzip is a HTTP middleware to transparently compress responses using gzip.
// Original code from https://gist.github.com/CJEnright/bc2d8b8dc0c1389a9feeddb110f822d7 (MIT)
func Gzip(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
			next.ServeHTTP(w, r)
			return
		}
		w.Header().Set("Content-Encoding", "gzip")

		gz := gzPool.Get().(*gzip.Writer)
		defer gzPool.Put(gz)

		gz.Reset(w)
		defer gz.Close()

		r.Header.Del("Accept-Encoding") // prevent double-gzipping
		next.ServeHTTP(&gzipResponseWriter{ResponseWriter: w, Writer: gz}, r)
	})
}

var gzPool = sync.Pool{
	New: func() interface{} {
		w := gzip.NewWriter(io.Discard)
		return w
	},
}

type gzipResponseWriter struct {
	io.Writer
	http.ResponseWriter
}

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

func (w *gzipResponseWriter) Write(b []byte) (int, error) {
	return w.Writer.Write(b)
}