package static

import (
	"bytes"
	"compress/gzip"
	"crypto/md5"
	"fmt"
	"mime"
	"net/http"
	"path"
	"strings"
)

type StaticContent struct {
	Content     string
	ContentType string
	ETag        string
	GZIPContent []byte
	GZIPETag    string
	DisableGZIP bool
}

func (ctx *StaticContent) Init() error {
	// Do we have a content type? If not, initialize it
	if ctx.ContentType == "" {
		ext := path.Ext(ctx.Content)
		ctx.ContentType = mime.TypeByExtension(ext)
		// Fallback to default mime type
		if ctx.ContentType == "" {
			ctx.ContentType = "application/octet-stream"
		}
	}

	// Do we have an etag? If not, generate one
	if ctx.ETag == "" {
		ctx.ETag = fmt.Sprintf("%x", md5.Sum(Assets[ctx.Content]))
	}

	// If gzip is allowed and we have no gzip etag, generate
	// gzip content and etag
	if !ctx.DisableGZIP && ctx.GZIPETag == "" {
		var buf bytes.Buffer
		gz, _ := gzip.NewWriterLevel(&buf, gzip.BestCompression)
		defer gz.Close()

		if _, err := gz.Write(Assets[ctx.Content]); err != nil {
			return err
		}

		if err := gz.Flush(); err != nil {
			return err
		}

		// Check if GZIP actually resulted in a smaller file
		if buf.Len() < len(Assets[ctx.Content]) {
			ctx.GZIPContent = buf.Bytes()
			ctx.GZIPETag = fmt.Sprintf("%x", md5.Sum(Assets[ctx.Content]))
		} else {
			// If gzip turns out to be ineffective, disable it
			ctx.DisableGZIP = true
		}
	}

	return nil
}

func (ctx *StaticContent) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// By default, don't use gzip
	useGZIP := false

	// If gzip isn't explicitly disabled, test for it
	if !ctx.DisableGZIP {
		useGZIP = strings.Contains(r.Header.Get("Accept-Encoding"), "gzip")
	}

	// Use the correct etag
	var localETag string
	if useGZIP {
		localETag = ctx.GZIPETag
	} else {
		localETag = ctx.ETag
	}

	// Check the etag, maybe we don't need to send content
	remoteETag := r.Header.Get("If-None-Match")
	if localETag == remoteETag {
		w.WriteHeader(http.StatusNotModified)
		return
	}
	w.Header().Set("ETag", localETag)

	w.Header().Set("Content-Type", ctx.ContentType)

	// Finally, write our content
	if useGZIP {
		w.Header().Set("Content-Encoding", "gzip")
		w.Header().Set("Content-Length", fmt.Sprintf("%d", len(ctx.GZIPContent)))
		w.Write(ctx.GZIPContent)
	} else {
		w.Header().Set("Content-Length", fmt.Sprintf("%d", len(Assets[ctx.Content])))
		w.Write(Assets[ctx.Content])
	}
}