package rtsp

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"net/http"
	"net/url"
	"strconv"
	"strings"
)

// rtsp protocol described by:
// https://tools.ietf.org/html/rfc7826

// RTSP methods.
const (
	describe = "DESCRIBE"
	options  = "OPTIONS"
	play     = "PLAY"
	setup    = "SETUP"
)

type Session struct {
	cSeq    int
	conn    net.Conn
	session string
}

func NewSession() *Session {
	return &Session{}
}

func (s *Session) Describe(urlStr string) (*Response, error) {
	return s.writeRequest(describe, urlStr, func(req *Request) { req.Header.Add("Accept", "application/sdp") }, nil)
}

func (s *Session) Options(urlStr string) (*Response, error) {
	return s.writeRequest(options, urlStr, nil, nil)
}

func (s *Session) Setup(urlStr, transport string) (*Response, error) {
	return s.writeRequest(
		setup,
		urlStr,
		func(req *Request) {
			req.Header.Add("Transport", transport)
		},
		func(resp *Response) {
			s.session = resp.Header.Get("Session")
		},
	)
}

func (s *Session) Play(urlStr string) (*Response, error) {
	return s.writeRequest(play, urlStr, func(req *Request) { req.Header.Add("Session", s.session) }, nil)
}

func (s *Session) writeRequest(method, urlStr string, headerOp func(*Request), respOp func(*Response)) (*Response, error) {
	req, err := NewRequest(method, urlStr, s.nextCSeq(), nil)
	if err != nil {
		return nil, err
	}

	if headerOp != nil {
		headerOp(req)
	}

	if s.conn == nil {
		s.conn, err = net.Dial("tcp", req.URL.Host)
		if err != nil {
			return nil, err
		}
	}

	_, err = io.WriteString(s.conn, (*Request)(req).String())
	if err != nil {
		return nil, err
	}

	res, err := ReadResponse(s.conn)
	if err != nil {
		return nil, err
	}

	if respOp != nil {
		respOp(res)
	}
	return res, nil
}

func (s *Session) nextCSeq() string {
	s.cSeq++
	return strconv.Itoa(s.cSeq)
}

type Request struct {
	Method        string
	URL           *url.URL
	Proto         string
	ProtoMajor    int
	ProtoMinor    int
	Header        http.Header
	ContentLength int
	Body          io.ReadCloser
}

func (r Request) String() string {
	s := fmt.Sprintf("%s %s %s/%d.%d\r\n", r.Method, r.URL, r.Proto, r.ProtoMajor, r.ProtoMinor)
	for k, v := range r.Header {
		for _, v := range v {
			s += fmt.Sprintf("%s: %s\r\n", k, v)
		}
	}
	s += "\r\n"
	if r.Body != nil {
		str, _ := ioutil.ReadAll(r.Body)
		s += string(str)
	}
	return s
}

func NewRequest(method, urlStr, cSeq string, body io.ReadCloser) (*Request, error) {
	u, err := url.Parse(urlStr)
	if err != nil {
		return nil, err
	}

	req := &Request{
		Method:     method,
		URL:        u,
		Proto:      "RTSP",
		ProtoMajor: 1,
		ProtoMinor: 0,
		Header:     map[string][]string{"CSeq": []string{cSeq}},
		Body:       body,
	}
	return req, nil
}

type Response struct {
	Proto      string
	ProtoMajor int
	ProtoMinor int

	StatusCode int
	Status     string

	ContentLength int64

	Header http.Header
	Body   io.ReadCloser
}

func (res Response) String() string {
	s := fmt.Sprintf("%s/%d.%d %d %s\n", res.Proto, res.ProtoMajor, res.ProtoMinor, res.StatusCode, res.Status)
	for k, v := range res.Header {
		for _, v := range v {
			s += fmt.Sprintf("%s: %s\n", k, v)
		}
	}
	return s
}

func ReadResponse(r io.Reader) (res *Response, err error) {
	res = new(Response)
	res.Header = make(map[string][]string)

	b := bufio.NewReader(r)
	var s string

	// TODO: allow CR, LF, or CRLF
	if s, err = b.ReadString('\n'); err != nil {
		return
	}

	parts := strings.SplitN(s, " ", 3)
	res.Proto, res.ProtoMajor, res.ProtoMinor, err = ParseRTSPVersion(parts[0])
	if err != nil {
		return
	}

	if res.StatusCode, err = strconv.Atoi(parts[1]); err != nil {
		return
	}

	res.Status = strings.TrimSpace(parts[2])

	// read headers
	for {
		if s, err = b.ReadString('\n'); err != nil {
			return
		} else if s = strings.TrimRight(s, "\r\n"); s == "" {
			break
		}

		parts := strings.SplitN(s, ":", 2)
		res.Header.Add(strings.TrimSpace(parts[0]), strings.TrimSpace(parts[1]))
	}

	res.ContentLength, _ = strconv.ParseInt(res.Header.Get("Content-Length"), 10, 64)

	res.Body = closer{b, r}
	return
}

type closer struct {
	*bufio.Reader
	r io.Reader
}

func (c closer) Close() error {
	if c.Reader == nil {
		return nil
	}
	defer func() {
		c.Reader = nil
		c.r = nil
	}()
	if r, ok := c.r.(io.ReadCloser); ok {
		return r.Close()
	}
	return nil
}

func ParseRTSPVersion(s string) (proto string, major int, minor int, err error) {
	parts := strings.SplitN(s, "/", 2)
	proto = parts[0]
	parts = strings.SplitN(parts[1], ".", 2)
	if major, err = strconv.Atoi(parts[0]); err != nil {
		return
	}
	if minor, err = strconv.Atoi(parts[0]); err != nil {
		return
	}
	return
}