package http

import (
	"bytes"
	"errors"
	"strings"

	"v2ray.com/core"
)

type version byte

const (
	HTTP1 version = iota
	HTTP2
)

type SniffHeader struct {
	version version
	host    string
}

func (h *SniffHeader) Protocol() string {
	switch h.version {
	case HTTP1:
		return "http1"
	case HTTP2:
		return "http2"
	default:
		return "unknown"
	}
}

func (h *SniffHeader) Domain() string {
	return h.host
}

var (
	methods = [...]string{"get", "post", "head", "put", "delete", "options", "connect"}

	errNotHTTPMethod = errors.New("not an HTTP method")
)

func beginWithHTTPMethod(b []byte) error {
	for _, m := range methods {
		if len(b) >= len(m) && strings.ToLower(string(b[:len(m)])) == m {
			return nil
		}

		if len(b) < len(m) {
			return core.ErrNoClue
		}
	}

	return errNotHTTPMethod
}

func SniffHTTP(b []byte) (*SniffHeader, error) {
	if err := beginWithHTTPMethod(b); err != nil {
		return nil, err
	}

	sh := &SniffHeader{
		version: HTTP1,
	}

	headers := bytes.Split(b, []byte{'\n'})
	for i := 1; i < len(headers); i++ {
		header := headers[i]
		if len(header) == 0 {
			return nil, core.ErrNoClue
		}
		parts := bytes.SplitN(header, []byte{':'}, 2)
		if len(parts) != 2 {
			continue
		}
		key := strings.ToLower(string(parts[0]))
		value := strings.ToLower(string(bytes.Trim(parts[1], " ")))
		if key == "host" {
			domain := strings.Split(value, ":")
			sh.host = strings.TrimSpace(domain[0])
		}
	}

	if len(sh.host) > 0 {
		return sh, nil
	}

	return nil, core.ErrNoClue
}