package gzip

import (
	"compress/gzip"
	"fmt"
	"io/ioutil"
	"net/http"
	"path/filepath"
	"strings"
	"sync"

	"github.com/gin-gonic/gin"
)

type gzipHandler struct {
	gzPool sync.Pool
}

func newGzipHandler(level int) *gzipHandler {
	var gzPool sync.Pool
	gzPool.New = func() interface{} {
		gz, err := gzip.NewWriterLevel(ioutil.Discard, level)
		if err != nil {
			panic(err)
		}
		return gz
	}
	handler := &gzipHandler{
		gzPool: gzPool,
	}
	return handler
}

func (g *gzipHandler) Handle(c *gin.Context) {
	if !g.shouldCompress(c.Request) {
		return
	}

	gz := g.gzPool.Get().(*gzip.Writer)
	defer g.gzPool.Put(gz)
	defer gz.Reset(ioutil.Discard)
	gz.Reset(c.Writer)

	c.Header("Content-Encoding", "gzip")
	c.Header("Vary", "Accept-Encoding")
	c.Writer = &gzipWriter{c.Writer, gz}
	defer func() {
		gz.Close()
		c.Header("Content-Length", fmt.Sprint(c.Writer.Size()))
	}()
	c.Next()
}

func (g *gzipHandler) shouldCompress(req *http.Request) bool {
	if !strings.Contains(req.Header.Get("Accept-Encoding"), "gzip") ||
		strings.Contains(req.Header.Get("Connection"), "Upgrade") ||
		strings.Contains(req.Header.Get("Content-Type"), "text/event-stream") {

		return false
	}

	extension := filepath.Ext(req.URL.Path)
	if len(extension) < 4 { // fast path
		return true
	}

	switch extension {
	case ".png", ".gif", ".jpeg", ".jpg":
		return false
	default:
		return true
	}
}