package stario

import (
	"bytes"
	"fmt"
	"reflect"
)

// ParseMessage 用于解析收到的msg信息。
func (q *StarQueue) ParseMessage(msg []byte, conn interface{}) error {
	return q.parseMessage(msg, conn, false, func(payload []byte) error {
		return q.push2list(MsgQueue{
			Msg:  payload,
			Conn: conn,
		})
	})
}

// ParseMessageView parses frames and exposes each payload to fn without
// forcing StarQueue to clone it first.
//
// The provided payload is only valid during the callback. If q uses the legacy
// DecodeFunc path, StarQueue still has to allocate a decoded payload first.
func (q *StarQueue) ParseMessageView(msg []byte, conn interface{}, fn func(FrameView) error) error {
	if fn == nil {
		return ErrQueueFrameHandlerNil
	}
	return q.parseMessage(msg, conn, true, func(payload []byte) error {
		return fn(FrameView{
			Payload: payload,
			Conn:    conn,
		})
	})
}

// ParseMessageOwned parses frames and emits owned payload copies to fn without
// routing them through RestoreChan.
//
// Compared with ParseMessage, this keeps StarQueue state handling the same but
// lets callers decide how to dispatch parsed messages themselves.
func (q *StarQueue) ParseMessageOwned(msg []byte, conn interface{}, fn func(MsgQueue) error) error {
	if fn == nil {
		return ErrQueueFrameHandlerNil
	}
	frames := make([]MsgQueue, 0, 1)
	parseErr := q.parseMessage(msg, conn, false, func(payload []byte) error {
		frames = append(frames, MsgQueue{
			Msg:  payload,
			Conn: conn,
		})
		return nil
	})
	for _, frame := range frames {
		if err := fn(frame); err != nil {
			if parseErr != nil {
				return fmt.Errorf("%v: %w", parseErr, err)
			}
			return err
		}
	}
	return parseErr
}

func (q *StarQueue) parseMessage(msg []byte, conn interface{}, borrowPayload bool, emit func([]byte) error) error {
	state, err := q.connState(conn)
	if err != nil {
		return err
	}
	var firstErr error
	for {
		payload, ok, err := q.nextPayload(state, conn, msg, borrowPayload)
		msg = nil
		if err != nil && firstErr == nil {
			firstErr = err
		}
		if !ok {
			break
		}
		if err := emit(payload); err != nil {
			if firstErr != nil {
				return fmt.Errorf("%v: %w", firstErr, err)
			}
			return err
		}
	}
	return firstErr
}

func (q *StarQueue) nextPayload(state *queConnState, conn interface{}, msg []byte, borrowPayload bool) ([]byte, bool, error) {
	state.mu.Lock()
	defer state.mu.Unlock()

	if len(msg) != 0 {
		state.buf = append(state.buf, msg...)
	}

	var firstErr error
	for {
		synced, err := syncFrameStart(&state.buf)
		if err != nil && firstErr == nil {
			firstErr = err
		}
		if !synced {
			if len(state.buf) == 0 {
				q.states.Delete(conn)
			}
			return nil, false, firstErr
		}
		if len(state.buf) < queHeaderSize {
			return nil, false, firstErr
		}

		header, err := parseHeaderBytes(state.buf[:queHeaderSize], q.maxLength)
		if err != nil {
			if firstErr == nil {
				firstErr = err
			}
			state.buf = shrinkBuffer(state.buf[1:])
			continue
		}

		frameLen := queHeaderSize + int(header.Length)
		if len(state.buf) < frameLen {
			return nil, false, firstErr
		}

		payload, rest := extractPayload(state.buf, frameLen, borrowPayload && !(q.Encode && q.DecodeFunc != nil))
		state.buf = rest
		if q.Encode && q.DecodeFunc != nil {
			payload = q.DecodeFunc(payload)
		}
		if len(state.buf) == 0 {
			q.states.Delete(conn)
		}
		return payload, true, firstErr
	}
}

func extractPayload(buf []byte, frameLen int, borrowPayload bool) ([]byte, []byte) {
	payload := buf[queHeaderSize:frameLen]
	if !borrowPayload {
		return cloneBytes(payload), shrinkBuffer(buf[frameLen:])
	}
	if frameLen == len(buf) {
		return payload, nil
	}
	return payload, cloneBytes(buf[frameLen:])
}

func (q *StarQueue) push2list(msg MsgQueue) error {
	select {
	case <-q.ctx.Done():
		return q.ctx.Err()
	default:
	}
	q.sendMu.RLock()
	defer q.sendMu.RUnlock()
	select {
	case <-q.ctx.Done():
		return q.ctx.Err()
	case q.msgPool <- msg:
		return nil
	}
}

func validateConnKey(conn interface{}) error {
	if conn == nil {
		return ErrQueueConnKeyNil
	}
	typ := reflect.TypeOf(conn)
	if typ != nil && !typ.Comparable() {
		return ErrQueueConnKeyInvalid
	}
	return nil
}

func (q *StarQueue) connState(conn interface{}) (*queConnState, error) {
	if err := validateConnKey(conn); err != nil {
		return nil, err
	}
	state, _ := q.states.LoadOrStore(conn, &queConnState{})
	return state.(*queConnState), nil
}

func syncFrameStart(buf *[]byte) (bool, error) {
	if len(*buf) == 0 {
		return false, nil
	}

	if len(*buf) >= queMagicSize && equalMagic((*buf)[:queMagicSize]) {
		return true, nil
	}

	idx := bytes.Index(*buf, queMagic)
	if idx == 0 {
		return true, nil
	}
	if idx > 0 {
		*buf = cloneBytes((*buf)[idx:])
		return true, ErrQueueDataFormat
	}

	keep := trailingMagicPrefixLen(*buf)
	if keep == len(*buf) {
		return false, nil
	}
	if keep > 0 {
		*buf = cloneBytes((*buf)[len(*buf)-keep:])
		return false, ErrQueueDataFormat
	}

	*buf = (*buf)[:0]
	return false, ErrQueueDataFormat
}

func trailingMagicPrefixLen(buf []byte) int {
	max := len(buf)
	if max > queMagicSize-1 {
		max = queMagicSize - 1
	}
	for keep := max; keep > 0; keep-- {
		if bytes.Equal(buf[len(buf)-keep:], queMagic[:keep]) {
			return keep
		}
	}
	return 0
}

func shrinkBuffer(buf []byte) []byte {
	if len(buf) == 0 {
		return nil
	}
	if cap(buf) > len(buf)*4 {
		return cloneBytes(buf)
	}
	return buf
}