package notify

import "encoding/binary"

const (
	streamFastPathVersionV1      = 1
	streamFastPathVersionV2      = 2
	streamFastPathVersionCurrent = streamFastPathVersionV2
)

const (
	streamFastBatchMagic         = "NSB1"
	streamFastBatchVersion       = 1
	streamFastBatchHeaderLen     = 12
	streamFastBatchItemHeaderLen = 24
	streamFastBatchMaxItems      = 64
	streamFastBatchMaxPlainBytes = 8 * 1024 * 1024
)

func normalizeStreamFastPathVersion(version uint8) uint8 {
	if version < streamFastPathVersionV1 {
		return streamFastPathVersionV1
	}
	if version > streamFastPathVersionCurrent {
		return streamFastPathVersionCurrent
	}
	return version
}

func negotiateStreamFastPathVersion(version uint8) uint8 {
	return normalizeStreamFastPathVersion(version)
}

func streamFastPathSupportsBatch(version uint8) bool {
	return normalizeStreamFastPathVersion(version) >= streamFastPathVersionV2
}

func streamFastBatchFrameLen(frame streamFastDataFrame) int {
	return streamFastBatchItemHeaderLen + len(frame.Payload)
}

func streamFastBatchPlainLen(frames []streamFastDataFrame) int {
	total := streamFastBatchHeaderLen
	for _, frame := range frames {
		total += streamFastBatchFrameLen(frame)
	}
	return total
}

func encodeStreamFastBatchPlain(frames []streamFastDataFrame) ([]byte, error) {
	if len(frames) == 0 {
		return nil, errStreamFastPayloadInvalid
	}
	buf := make([]byte, streamFastBatchPlainLen(frames))
	if err := writeStreamFastBatchPlain(buf, frames); err != nil {
		return nil, err
	}
	return buf, nil
}

func encodeStreamFastBatchPayloadFast(encode transportFastPlainEncoder, secretKey []byte, frames []streamFastDataFrame) ([]byte, error) {
	if encode == nil {
		return nil, errTransportPayloadEncryptFailed
	}
	plainLen := streamFastBatchPlainLen(frames)
	return encode(secretKey, plainLen, func(dst []byte) error {
		return writeStreamFastBatchPlain(dst, frames)
	})
}

func writeStreamFastBatchPlain(dst []byte, frames []streamFastDataFrame) error {
	if len(frames) == 0 || len(dst) != streamFastBatchPlainLen(frames) {
		return errStreamFastPayloadInvalid
	}
	copy(dst[:4], streamFastBatchMagic)
	dst[4] = streamFastBatchVersion
	binary.BigEndian.PutUint32(dst[8:12], uint32(len(frames)))
	offset := streamFastBatchHeaderLen
	for _, frame := range frames {
		if frame.DataID == 0 {
			return errStreamFastPayloadInvalid
		}
		dst[offset] = frame.Flags
		binary.BigEndian.PutUint64(dst[offset+4:offset+12], frame.DataID)
		binary.BigEndian.PutUint64(dst[offset+12:offset+20], frame.Seq)
		binary.BigEndian.PutUint32(dst[offset+20:offset+24], uint32(len(frame.Payload)))
		offset += streamFastBatchItemHeaderLen
		copy(dst[offset:offset+len(frame.Payload)], frame.Payload)
		offset += len(frame.Payload)
	}
	return nil
}

func walkStreamFastBatchPlain(payload []byte, fn func(streamFastDataFrame) error) (bool, error) {
	if len(payload) < 4 || string(payload[:4]) != streamFastBatchMagic {
		return false, nil
	}
	if len(payload) < streamFastBatchHeaderLen {
		return true, errStreamFastPayloadInvalid
	}
	if payload[4] != streamFastBatchVersion {
		return true, errStreamFastPayloadInvalid
	}
	count := int(binary.BigEndian.Uint32(payload[8:12]))
	if count <= 0 {
		return true, errStreamFastPayloadInvalid
	}
	offset := streamFastBatchHeaderLen
	for index := 0; index < count; index++ {
		if len(payload)-offset < streamFastBatchItemHeaderLen {
			return true, errStreamFastPayloadInvalid
		}
		flags := payload[offset]
		dataID := binary.BigEndian.Uint64(payload[offset+4 : offset+12])
		seq := binary.BigEndian.Uint64(payload[offset+12 : offset+20])
		payloadLen := int(binary.BigEndian.Uint32(payload[offset+20 : offset+24]))
		offset += streamFastBatchItemHeaderLen
		if dataID == 0 || payloadLen < 0 || len(payload)-offset < payloadLen {
			return true, errStreamFastPayloadInvalid
		}
		if fn != nil {
			if err := fn(streamFastDataFrame{
				Flags:   flags,
				DataID:  dataID,
				Seq:     seq,
				Payload: payload[offset : offset+payloadLen],
			}); err != nil {
				return true, err
			}
		}
		offset += payloadLen
	}
	if offset != len(payload) {
		return true, errStreamFastPayloadInvalid
	}
	return true, nil
}

func decodeStreamFastBatchPlain(payload []byte) ([]streamFastDataFrame, bool, error) {
	frames := make([]streamFastDataFrame, 0, 1)
	matched, err := walkStreamFastBatchPlain(payload, func(frame streamFastDataFrame) error {
		frames = append(frames, frame)
		return nil
	})
	if !matched || err != nil {
		return nil, matched, err
	}
	return frames, true, nil
}

func walkStreamFastFrames(payload []byte, fn func(streamFastDataFrame) error) (bool, error) {
	if matched, err := walkStreamFastBatchPlain(payload, fn); matched {
		return true, err
	}
	frame, matched, err := decodeStreamFastDataFrame(payload)
	if !matched || err != nil {
		return matched, err
	}
	if fn != nil {
		if err := fn(frame); err != nil {
			return true, err
		}
	}
	return true, nil
}

func decodeStreamFastDataFrames(payload []byte) ([]streamFastDataFrame, bool, error) {
	frames := make([]streamFastDataFrame, 0, 1)
	matched, err := walkStreamFastFrames(payload, func(frame streamFastDataFrame) error {
		frames = append(frames, frame)
		return nil
	})
	if !matched || err != nil {
		return nil, matched, err
	}
	return frames, true, nil
}