package stario

import (
	"encoding/binary"
	"fmt"
	"io"
	"net"
)

// BuildMessage builds one full frame and panics if the payload is too large to
// fit in the framing format.
//
// New code should prefer BuildMessageErr when it needs an explicit error path.
func (q *StarQueue) BuildMessage(src []byte) []byte {
	frame, err := q.BuildMessageErr(src)
	if err != nil {
		panic(err)
	}
	return frame
}

// BuildMessageErr builds one full frame and returns an explicit error when the
// payload exceeds the 32-bit frame length.
func (q *StarQueue) BuildMessageErr(src []byte) ([]byte, error) {
	payload := src
	if q.Encode && q.EncodeFunc != nil {
		payload = q.EncodeFunc(payload)
	}
	length, err := payloadSizeToUint32(uint64(len(payload)))
	if err != nil {
		return nil, err
	}
	header := q.BuildHeader(length)
	frame := make([]byte, 0, len(header)+len(payload))
	frame = append(frame, header...)
	frame = append(frame, payload...)
	return frame, nil
}

// WriteFrame writes one framed payload directly to w without building an
// intermediate full-frame slice first.
func (q *StarQueue) WriteFrame(w io.Writer, src []byte) error {
	if w == nil {
		return io.ErrClosedPipe
	}
	payload := src
	if q.Encode && q.EncodeFunc != nil {
		payload = q.EncodeFunc(payload)
	}
	length, err := payloadSizeToUint32(uint64(len(payload)))
	if err != nil {
		return err
	}
	var header [queHeaderSize]byte
	writeHeaderBytes(header[:], queHeader{
		Length:  length,
		Version: queVersionV1,
		Flags:   queSupportedFlags,
	})
	if err := writeFull(w, header[:]); err != nil {
		return err
	}
	return writeFull(w, payload)
}

// WriteFrameBuffers writes one framed payload using net.Buffers so callers can
// opt into gather writes when the underlying writer supports it well.
func (q *StarQueue) WriteFrameBuffers(w io.Writer, src []byte) error {
	if w == nil {
		return io.ErrClosedPipe
	}
	payload := src
	if q.Encode && q.EncodeFunc != nil {
		payload = q.EncodeFunc(payload)
	}
	length, err := payloadSizeToUint32(uint64(len(payload)))
	if err != nil {
		return err
	}
	var header [queHeaderSize]byte
	writeHeaderBytes(header[:], queHeader{
		Length:  length,
		Version: queVersionV1,
		Flags:   queSupportedFlags,
	})
	buffers := net.Buffers{header[:], payload}
	_, err = buffers.WriteTo(w)
	return err
}

// WriteFramesBuffers writes multiple framed payloads using one net.Buffers
// batch so callers can reduce write calls on stream transports.
func (q *StarQueue) WriteFramesBuffers(w io.Writer, payloads ...[]byte) error {
	if w == nil {
		return io.ErrClosedPipe
	}
	if len(payloads) == 0 {
		return nil
	}
	buffers := make(net.Buffers, 0, len(payloads)*2)
	headers := make([][queHeaderSize]byte, len(payloads))
	for i, src := range payloads {
		payload := src
		if q.Encode && q.EncodeFunc != nil {
			payload = q.EncodeFunc(payload)
		}
		length, err := payloadSizeToUint32(uint64(len(payload)))
		if err != nil {
			return err
		}
		writeHeaderBytes(headers[i][:], queHeader{
			Length:  length,
			Version: queVersionV1,
			Flags:   queSupportedFlags,
		})
		buffers = append(buffers, headers[i][:], payload)
	}
	_, err := buffers.WriteTo(w)
	return err
}

// BuildHeader 生成编码后的Header用于发送。
func (q *StarQueue) BuildHeader(length uint32) []byte {
	return buildHeaderBytes(queHeader{
		Length:  length,
		Version: queVersionV1,
		Flags:   queSupportedFlags,
	})
}

func buildHeaderBytes(header queHeader) []byte {
	buf := make([]byte, queHeaderSize)
	writeHeaderBytes(buf, header)
	return buf
}

func writeHeaderBytes(dst []byte, header queHeader) {
	if len(dst) < queHeaderSize {
		return
	}
	copy(dst[:queMagicSize], queMagic)
	binary.BigEndian.PutUint32(dst[queMagicSize:queMagicSize+4], header.Length)
	dst[12] = header.Version
	dst[13] = header.Flags
}

func payloadSizeToUint32(size uint64) (uint32, error) {
	const maxFramePayload = ^uint32(0)
	if size > uint64(maxFramePayload) {
		return 0, fmt.Errorf("%w: %d > %d", ErrQueueMessageTooLarge, size, uint64(maxFramePayload))
	}
	return uint32(size), nil
}

func writeFull(w io.Writer, data []byte) error {
	for len(data) > 0 {
		n, err := w.Write(data)
		if n > 0 {
			data = data[n:]
		}
		if err != nil {
			return err
		}
		if n == 0 {
			return io.ErrNoProgress
		}
	}
	return nil
}

func parseHeaderBytes(src []byte, maxLength uint32) (queHeader, error) {
	if len(src) < queHeaderSize {
		return queHeader{}, ErrQueueDataFormat
	}
	if !equalMagic(src[:queMagicSize]) {
		return queHeader{}, ErrQueueDataFormat
	}

	header := queHeader{
		Length:  ByteToUint32(src[queMagicSize : queMagicSize+4]),
		Version: src[12],
		Flags:   src[13],
	}

	if header.Version != queVersionV1 {
		return queHeader{}, fmt.Errorf("%w: %d", ErrQueueUnsupportedVersion, header.Version)
	}
	if header.Flags != queSupportedFlags {
		return queHeader{}, fmt.Errorf("%w: %d", ErrQueueUnsupportedFlags, header.Flags)
	}
	if maxLength != 0 && header.Length > maxLength {
		return queHeader{}, fmt.Errorf("%w: %d > %d", ErrQueueMessageTooLarge, header.Length, maxLength)
	}

	return header, nil
}

func equalMagic(src []byte) bool {
	if len(src) != queMagicSize {
		return false
	}
	for i, b := range src {
		if b != queMagic[i] {
			return false
		}
	}
	return true
}