msmsg/message.go

package msmsg

import (
	"errors"
	"fmt"
	"strings"
)

type Message struct {
	Dialect       string
	ID            string
	Parameters    map[string]string
	Body          string
	ClosesChannel bool
}

func (m Message) String() string {
	switch {
	case m.Chatter():
		return m.Body
	}
	var builder strings.Builder

	return builder.String()
}

func ByteIsSpace(b byte) bool {
	return b == ' ' ||
		b == '\t' ||
		b == '\r' ||
		b == '\n'
}

// Lines that are not encapsulated in XML tags or
// are not recognized as part of a known dialect
// are called chatter.
func (m *Message) Chatter() bool {
	return len(m.Dialect) == 0 && len(m.ID) == 0 && len(m.Parameters) == 0
}

// Lines that have no associated ChannelID are
// called anonymous messages.
func (m *Message) Anonymous() bool {
	return !m.Chatter() && len(m.ID) == 0
}

type token struct {
	dialect       string
	id            string
	parameters    map[string]string
	body          string
	closesMessage bool
	closesChannel bool
}

var (
	errTokenMalformed = errors.New("token is malformed")
)

func parseToken(s string) (token, error) {
	var results token

	if !strings.HasPrefix(s, "<") || !strings.HasSuffix(s, ">") {
		return token{body: s}, fmt.Errorf("%w: missing opening and/or closing angle bracket", errTokenMalformed)
	}

	buffer := strings.TrimSpace(s[1 : len(s)-1])
	if strings.HasPrefix(buffer, "/") {
		results.closesMessage = true
		buffer = strings.TrimSpace(buffer[1:])
	}
	if strings.HasSuffix(buffer, "/") {
		results.closesMessage = true
		results.closesChannel = true
		buffer = strings.TrimSpace(buffer[:len(buffer)-1])
	}

	// try to grab the first word off the front, this should be the dialect
	i := strings.IndexAny(buffer, " \t\r\n")
	if i == -1 {
		results.dialect = buffer
		return results, nil
	} else if i < len(buffer) {
		// is the next non-whitespace char an '='?
		for j := i + 1; j < len(buffer); j++ {
			if ByteIsSpace(buffer[j]) {
				i = j
				break
			} else if buffer[j] == '=' {
				i = 0
				break
			} else {
				break
			}
		}
		if i > 0 {
			results.dialect = buffer[:i]
			buffer = strings.TrimSpace(buffer[i:])
		}
	}

	// everything else is presumed to be key=value pairs
	type STATE int8
	const (
		KEY STATE = iota
		VALUE
	)
	var key, value strings.Builder
	var quote byte
	var state STATE
	for i = 0; i < len(buffer); i++ {
		theChar := buffer[i]
		switch state {
		case KEY:
			// parse the key and prepare to parse the value by finding the '=' and the quotation mark
			if ByteIsSpace(theChar) {
				continue
			} else if theChar == '=' {
				// find the next quotation mark
				for i = i + 1; i < len(buffer); i++ {
					theChar = buffer[i]
					if ByteIsSpace(theChar) {
						continue
					} else if theChar == '\'' || theChar == '"' {
						quote = theChar
						state = VALUE
						break
					} else {
						return token{body: s}, fmt.Errorf("%w: parameter value missing quotation mark", errTokenMalformed)
					}
				}
			} else {
				key.WriteByte(theChar)
			}
		case VALUE:
			// if quote == \0 something bad has happened - we don't know what we're looking for
			if quote == '\x00' {
				return token{body: s}, fmt.Errorf("%w: missing quotation mark in VALUE state...", errTokenMalformed)
			} else if theChar == quote {
				// we have a key and a value - add them to the parameters
				if results.parameters == nil {
					results.parameters = make(map[string]string, 1)
				}
				results.parameters[key.String()] = value.String()
				key.Reset()
				value.Reset()
				quote = '\x00'
				state = KEY
				continue
			} else {
				value.WriteByte(theChar)
			}
		}
	}
	return results, nil
}

// <dialect ch='0'>This message is opening this channel.</dialect>

func ParseMessage(s string) Message {
	var message Message
	if !strings.HasPrefix(s, "<") || !strings.HasSuffix(s, ">") {
		message.Body = s
	}
	headerEnd := strings.IndexByte(s, '>')
	headerString := s[:headerEnd+1]
	header, err := parseToken(headerString)
	if err != nil {
		return Message{Body: s}
	}
	message.Dialect = strings.Clone(header.dialect)
	for k, v := range header.parameters {
		switch strings.ToLower(k) {
		case "ch":
			message.ID = strings.Clone(v)
		default:
			if message.Parameters == nil {
				message.Parameters = make(map[string]string, len(header.parameters))
			}
			message.Parameters[strings.Clone(k)] = strings.Clone(v)
		}
	}
	// is there a footer?
	if headerEnd == len(s)-1 {
		if header.closesChannel {
			message.ClosesChannel = true
		}
		return message
	}
	footerStart := strings.LastIndexByte(s, '<')
	if footerStart <= 0 {
		// malformed
		return Message{Body: s}
	}
	footer, err := parseToken(s[footerStart:])
	if err != nil {
		return Message{Body: s}
	}
	if want, got := header.dialect, footer.dialect; want != got {
		return Message{Body: s}
	} else if !footer.closesMessage {
		return Message{Body: s}
	}
	// the stuff between is the body
	message.Body = strings.TrimSpace(s[headerEnd+1 : footerStart])
	return message
}