// Author: simon (ynwdlxm@163.com)
// Date: 2025/7/11 15:58
// Desc: Parser for Redis protocol
//
// The parser is used to parse the byte stream of the Redis protocol into abstract response objects

package parser

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"runtime/debug"
	"strconv"
	"strings"

	"github.com/runningwater/go-redis/interface/resp"
	"github.com/runningwater/go-redis/lib/logger"
	"github.com/runningwater/go-redis/resp/reply"
)

// Payload is the payload of the parser
// Used to store the state information of the parser
type Payload struct {
	Data resp.Reply // Parsed response object, consistent with the return data structure
	Err  error      // Errors that occurred during parsing
}

func (p *Payload) String() string {
	return fmt.Sprintf("payload: %s, err: %v", p.Data, p.Err)
}

type currentState struct {
	readingMultiLine  bool     // Whether multi-line data is being read
	expectedArgsCount int      // Expected number of arguments
	msgType           byte     // Message type
	args              [][]byte // Argument list
	bulkLen           int64    // Length of bulk data
}

func (s *currentState) finished() bool {
	return s.expectedArgsCount > 0 && len(s.args) == s.expectedArgsCount
}

// ParseStream parses data in the input stream
// The parser parses the data in the input stream according to the rules of the Redis protocol
// The parsed results will be sent to the caller through the channel
// Parameters:
//
//	reader io.Reader - Input stream reader
//
// Return value:
//
//	<-chan *Payload - Parse result channel, each element is a parsed Payload object
func ParseStream(reader io.Reader) <-chan *Payload {
	logger.Debug("parse stream...")
	ch := make(chan *Payload)
	go parse0(reader, ch)
	return ch
}

func parse0(reader io.Reader, ch chan<- *Payload) {
	defer func() {
		if err := recover(); err != nil {
			logger.Error(string(debug.Stack()))
		}
	}()
	logger.Debug("parse0 ...")
	bufReader := bufio.NewReader(reader)
	var state currentState
	var err error
	var line []byte // A line of data
	for {           // Infinite loop
		var ioErr bool
		line, ioErr, err = readLine(bufReader, &state)
		if err != nil {
			ch <- &Payload{
				Err: err,
			}
			if ioErr {
				close(ch)
				return
			}
			state = currentState{} // Reset state
			continue
		}

		// Check if it is multi-line mode
		if !state.readingMultiLine {
			if line[0] == '*' { // *3/r/n
				err = parseMultiBulkHeader(line, &state)
				if err != nil {
					ch <- &Payload{
						Err: errors.New("protocol error: " + string(line)),
					}
					state = currentState{} // Reset state
					continue
				}
				if state.expectedArgsCount == 0 {
					ch <- &Payload{
						Data: reply.NewEmptyMultiBulkReply(),
					}
					state = currentState{} // Reset state
					continue
				}
			} else if line[0] == '$' { // $3/r/n
				err = parseBulkHeader(line, &state)
				if err != nil {
					ch <- &Payload{
						Err: errors.New("protocol error: " + string(line)),
					}
					state = currentState{} // Reset state
					continue
				}
				// $-1\r\n
				if state.bulkLen == -1 {
					ch <- &Payload{
						Data: reply.NewNullBulkReply(),
					}
					state = currentState{} // Reset state
					continue
				}
			} else {
				var result resp.Reply
				result, err = parseSingleLineReply(line)
				ch <- &Payload{
					Data: result,
					Err:  err,
				}
				state = currentState{}
				continue
			}
		} else {
			// Parse multi-line mode
			err = readBody(line, &state)
			if err != nil {
				ch <- &Payload{
					Err: errors.New("protocol error: " + string(line)),
				}
				state = currentState{}
				continue
			}
			if state.finished() {
				var result resp.Reply
				switch state.msgType {
				case '*':
					result = reply.NewMultiBulkReply(state.args)
				case '$':
					result = reply.NewBulkReply(state.args[0])
				}
				ch <- &Payload{
					Data: result,
				}
				state = currentState{} // Reset state
			}
		}
	} // End for true
}

// Read a line of data
// The read data may be a complete line or an incomplete line
//
// Return values:
// 1. Data read
// 2. Whether an incomplete line was read
// 3. Error message
// For example: *3\r\n$3\r\nSET\r\n$3\r\nkey\r\n$5\r\nvalue\r\n
// The data read may be: *3\r\n, $3\r\nSET\r\n, $3\r\nkey\r\n, $5\r\nvalue\r\n
// The data read may be: *3\r\n$3\r\nSET\r\n$3\r\nkey\r\n$5\r\nvalue\r\n
func readLine(reader *bufio.Reader, state *currentState) ([]byte, bool, error) {
	var msg []byte
	var err error
	if state.bulkLen == 0 { // \r\n split
		// Read a line of data
		msg, err = reader.ReadBytes('\n')
		logger.Debug("\r\n***readLine: ", string(msg))
		if err != nil {
			return nil, true, err
		}
		// Data that does not end with \r\n
		if len(msg) == 0 || msg[len(msg)-2] != '\r' {
			return nil, false, errors.New("readLine-protocol error: " + string(msg))
		}

	} else {
		// ELSE previously read $number, strictly read number of bytes
		msg = make([]byte, state.bulkLen+2)
		_, err := io.ReadFull(reader, msg)
		if err != nil {
			return nil, true, err
		}
		// Data that does not end with \r\n
		if len(msg) == 0 || msg[len(msg)-2] != '\r' || msg[len(msg)-1] != '\n' {
			return nil, false, errors.New("readLine-protocol error: " + string(msg))
		}

		// Reset bulkLen
		state.bulkLen = 0
	}
	return msg, false, nil
}

// Parse the header information of the string
//
// For example: *3\r\n$3\r\nSET\r\n$3\r\nkey\r\n$5\r\nvalue\r\n
// Parsed as: *3\r\n
func parseMultiBulkHeader(msg []byte, state *currentState) error {
	var err error
	var expectedLine uint64
	expectedLine, err = strconv.ParseUint(string(msg[1:len(msg)-2]), 10, 32)
	if err != nil {
		return errors.New("protocol error: " + string(msg))
	}
	if expectedLine == 0 {
		state.expectedArgsCount = 0
		return nil
	} else if expectedLine > 0 {
		state.msgType = msg[0]
		state.readingMultiLine = true
		state.expectedArgsCount = int(expectedLine)
		state.args = make([][]byte, 0, expectedLine)
		return nil
	} else {
		return errors.New("protocol error: " + string(msg))
	}
}

// Single line string
//
// $4\r\nPING\r\n
func parseBulkHeader(msg []byte, state *currentState) error {
	var err error
	// $ Start line, read bulkLen
	state.bulkLen, err = strconv.ParseInt(string(msg[1:len(msg)-2]), 10, 64)
	if err != nil {
		return errors.New("protocol error: " + string(msg))
	}

	if state.bulkLen == -1 {
		return nil
	} else if state.bulkLen > 0 {
		state.msgType = msg[0] // $
		state.readingMultiLine = true
		state.expectedArgsCount = 1
		state.args = make([][]byte, 0, 1)
		return nil
	} else {
		return errors.New("protocol error: " + string(msg))
	}
}

// Parse single line reply
//
// For example：
// +OK\r\n
// -err\r\n
// :1\r\n
func parseSingleLineReply(msg []byte) (resp.Reply, error) {
	str := strings.TrimSuffix(string(msg), "\r\n") // Remove \r\n

	var result resp.Reply
	switch msg[0] {
	case '+':
		result = reply.NewStatusReply(str[1:])
	case '-':
		result = reply.NewErrReply(str[1:])
	case ':':
		val, err := strconv.ParseInt(str[1:], 10, 64)
		if err != nil {
			return nil, errors.New("protocol error: " + string(msg))
		}
		result = reply.NewIntReply(val)
	default:
		return nil, errors.New("protocol error: " + string(msg))
	}
	return result, nil
}

// readBody parses the message body part in the Redis protocol, handling bulk strings starting with $ or ordinary strings
//
// For example：
// PING\r\n
// SET\r\n$3\r\nkey\r\n$5\r\nvalue\r\n
//
// Parameters:
//
//	msg: Complete message byte slice, including \r\n ending
//	state: Pointer to current parsing state, used to store parsing results
//
// Return value:
//
//	error: Errors that occurred during parsing, such as protocol format errors, etc.
func readBody(msg []byte, state *currentState) error {
	line := msg[0 : len(msg)-2] // Remove \r\n

	var err error

	// Handle bulk string format starting with $
	if line[0] == '$' {
		state.bulkLen, err = strconv.ParseInt(string(line[1:]), 10, 64)
		if err != nil {
			return errors.New("protocol error: " + string(msg))
		}
		// Handle empty string case, $0\r\n represents empty string
		if state.bulkLen <= 0 {
			state.args = append(state.args, []byte{})
			state.bulkLen = 0
		}
	} else {
		// Handle ordinary strings, directly add to argument list
		state.args = append(state.args, line)
	}
	return nil
}