LargeHadronCollider/api/ws/commands.go

package ws

import (
	"errors"
	"io"
	"strings"
)

type Command struct {
	Command string
	Args []string
}

type parser struct {
	cmd *Command
	r *strings.Reader
	arg string
	args []string
}

type parserQuote rune
const (
	parserQuoteSingle parserQuote = '\''
	parserQuoteDouble parserQuote = '"'
)

type parserBracket rune
const (
	parserBracketCurly parserBracket = '{'
	parserBracketSquare parserBracket = '['
	parserBracketTriangle parserBracket = '<'
)
var parserClosingBracket = map[parserBracket]rune{
	parserBracketCurly: '}',
	parserBracketSquare: ']',
	parserBracketTriangle: '>',
}

func parseCommand(msg string) (*Command, error) {
	cmd := &Command{}
	r := strings.NewReader(msg)
	parser := &parser{cmd: cmd, r: r}
	return cmd, parser.parse()
}

func (p *parser) parse() error {
	err := p.stateBase()
	if err != nil {
		return err
	}

	p.args = append(p.args, p.arg)

	filteredArgs := []string{}
	for _, arg := range p.args {
		if arg != "" {
			filteredArgs = append(filteredArgs, arg)
		}
	}
	
	if len(p.args) >= 1 {
		p.cmd.Command = p.args[0]
	}
	
	if len(p.args) >= 2 {
		p.cmd.Args = p.args[1:]
	}

	return nil
}

func (p *parser) consume() (rune, bool, error) {
	b := make([]byte, 1)
	_, err := p.r.Read(b)
	if err == io.EOF {
		return 0, true, nil 
	}
	if err != nil {
		return 0, false, err
	}
	return rune(b[0]), false, nil
}

func (p *parser) push(r rune) {
	p.arg += string(r)
}

func (p *parser) flush() {
	p.args = append(p.args, p.arg)
	p.arg = ""
}

func (p *parser) stateBase() error {
	for {
		ch, eof, err := p.consume()
		if err != nil {
			return err
		}
		if eof {
			return nil
		}

		switch ch {
		case '\\':
			err := p.stateEscape()
			if err != nil {
				return err
			}
		
		case rune(parserQuoteDouble): fallthrough
		case rune(parserQuoteSingle):
			err := p.stateQuote(parserQuote(ch))
			if err != nil {
				return err
			}
		
		// special case, if the arg starts with a { then parse it with rough object mode
		case rune(parserBracketCurly): fallthrough
		case rune(parserBracketSquare): fallthrough
		case rune(parserBracketTriangle):
			if p.arg != "" {
				p.push(ch)
			} else {
				err := p.stateBracket(parserBracket(ch))
				if err != nil {
					return err
				}
			}

		case '\n': fallthrough
		case '\t': fallthrough
		case ' ':
			p.flush()

		default:
			p.push(ch)
		}

	}
}

func (p *parser) stateQuote(quote parserQuote) error {
	for {
		ch, eof, err := p.consume()
		if err != nil {
			return err
		}
		if eof {
			return errors.New("missing closing quote")
		}

		switch ch {
		case '\\':
			err := p.stateEscape()
			if err != nil {
				return err
			}
		
		case rune(quote):
			return nil
		
		default:
			p.push(ch)
		}
	}
}

func (p *parser) stateBracket(bracket parserBracket) error {
	p.push(rune(bracket))
	for {
		ch, eof, err := p.consume()
		if err != nil {
			return err
		}
		if eof {
			return errors.New("missing closing bracket")
		}

		switch ch {
		case '\\':
			err := p.stateEscape()
			if err != nil {
				return err
			}
		
		case rune(parserQuoteDouble): fallthrough
		case rune(parserQuoteSingle):
			p.push(ch)
			err := p.stateQuote(parserQuote(ch))
			if err != nil {
				return err
			}
			p.push(ch)

		case rune(parserBracketCurly): fallthrough
		case rune(parserBracketSquare): fallthrough
		case rune(parserBracketTriangle):
			err := p.stateBracket(parserBracket(ch))
			if err != nil {
				return err
			}

		case parserClosingBracket[bracket]:
			p.push(ch)
			return nil

		default:
			p.push(ch)
		}
	}
}

func (p *parser) stateEscape() error {
	ch, eof, err := p.consume()
	if err != nil {
		return err
	}
	if eof {
		return errors.New("invalid escape sequence before end of file")
	}
	
	switch ch {
	case 'n':
		p.arg += "\n"
	
	case 't':
		p.arg += "\t"
	
	default:
		p.push(ch)
	}

	return nil
}