package codec

import "errors"

type VP8FrameTag struct {
	FrameType     uint32 //0: I frame , 1: P frame
	Version       uint32
	Display       uint32
	FirstPartSize uint32
}

type VP8KeyFrameHead struct {
	Width      int
	Height     int
	HorizScale int
	VertScale  int
}

func DecodeFrameTag(frame []byte) (*VP8FrameTag, error) {
	if len(frame) < 3 {
		return nil, errors.New("frame bytes < 3")
	}
	var tmp uint32 = (uint32(frame[2]) << 16) | (uint32(frame[1]) << 8) | uint32(frame[0])
	tag := &VP8FrameTag{}
	tag.FrameType = tmp & 0x01
	tag.Version = (tmp >> 1) & 0x07
	tag.Display = (tmp >> 4) & 0x01
	tag.FirstPartSize = (tmp >> 5) & 0x7FFFF
	return tag, nil
}

func DecodeKeyFrameHead(frame []byte) (*VP8KeyFrameHead, error) {
	if len(frame) < 7 {
		return nil, errors.New("frame bytes < 3")
	}

	if frame[0] != 0x9d || frame[1] != 0x01 || frame[2] != 0x2a {
		return nil, errors.New("not find Start code")
	}

	head := &VP8KeyFrameHead{}
	head.Width = int(uint16(frame[4]&0x3f)<<8 | uint16(frame[3]))
	head.HorizScale = int(frame[4] >> 6)
	head.Height = int(uint16(frame[6]&0x3f)<<8 | uint16(frame[5]))
	head.VertScale = int(frame[6] >> 6)
	return head, nil
}

func IsKeyFrame(frame []byte) bool {
	tag, err := DecodeFrameTag(frame)
	if err != nil {
		return false
	}

	if tag.FrameType == 0 {
		return true
	} else {
		return false
	}
}

func GetResloution(frame []byte) (width int, height int, err error) {
	if !IsKeyFrame(frame) {
		return 0, 0, errors.New("the frame is not Key frame")
	}

	head, err := DecodeKeyFrameHead(frame[3:])
	if err != nil {
		return 0, 0, err
	}
	return head.Width, head.Height, nil
}