// Copyright 2014 Manu Martinez-Almeida.  All rights reserved.
// Use of this source code is governed by a MIT style
// license that can be found in the LICENSE file.

package sse

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"reflect"
	"strings"
)

// Server-Sent Events
// W3C Working Draft 29 October 2009
// http://www.w3.org/TR/2009/WD-eventsource-20091029/

const ContentType = "text/event-stream"

type Event struct {
	Event string
	Id    string
	Retry uint
	Data  interface{}
}

func Encode(w io.Writer, event Event) error {
	writeId(w, event.Id)
	writeEvent(w, event.Event)
	writeRetry(w, event.Retry)
	return writeData(w, event.Data)
}

func writeId(w io.Writer, id string) {
	if len(id) > 0 {
		w.Write([]byte("id: "))
		w.Write([]byte(escape(id)))
		w.Write([]byte("\n"))
	}
}

func writeEvent(w io.Writer, event string) {
	if len(event) > 0 {
		w.Write([]byte("event: "))
		w.Write([]byte(escape(event)))
		w.Write([]byte("\n"))
	}
}

func writeRetry(w io.Writer, retry uint) {
	if retry > 0 {
		fmt.Fprintf(w, "retry: %d\n", retry)
	}
}

func writeData(w io.Writer, data interface{}) error {
	w.Write([]byte("data: "))
	switch typeOfData(data) {
	case reflect.Struct, reflect.Slice, reflect.Map:
		err := json.NewEncoder(w).Encode(data)
		if err != nil {
			return err
		}
		w.Write([]byte("\n"))
	default:
		text := fmt.Sprint(data)
		w.Write([]byte(escape(text)))
		w.Write([]byte("\n\n"))
	}
	return nil
}

func (r Event) Write(w http.ResponseWriter) error {
	header := w.Header()
	header.Set("Content-Type", ContentType)

	if _, exist := header["Cache-Control"]; !exist {
		header.Set("Cache-Control", "no-cache")
	}
	return Encode(w, r)
}

func typeOfData(data interface{}) reflect.Kind {
	value := reflect.ValueOf(data)
	valueType := value.Kind()
	if valueType == reflect.Ptr {
		valueType = value.Elem().Kind()
	}
	return valueType
}

func escape(str string) string {
	// any-char		= %x0000-0009 / %x000B-000C / %x000E-10FFFF
	// ; a Unicode character other than U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR)
	str = strings.Replace(str, "\n", "\\n", -1)
	str = strings.Replace(str, "\r", "\\r", -1)
	return str
}