package parser

import "asciigoat.org/core/lexer"

// Run parses the source
func (p *Parser) Run() error {
	p.setDefaults()
	p.pos.Reset()

	return lexer.Run(p.lexStart)
}

func (p *Parser) lexStart() (lexer.StateFn, error) {
	for {
		r, _, err := p.src.ReadRune()
		switch {
		case err != nil:
			return p.emitError("", err)
		case IsNewLine(r):
			// new line
			p.lexMoreNewLine(r)
			p.stepLine()
		case IsSpace(r):
			// whitespace
			p.stepRune()
		case IsCommentStart(r):
			// switch to comment lexer
			p.src.UnreadRune()
			return p.lexComment, nil
		case IsSectionStart(r):
			// section
			return p.lexSectionStart, nil
		default:
			// entry
			p.src.UnreadRune()
			return p.lexEntryStart, nil
		}
	}
}

func (p *Parser) lexMoreNewLine(r1 rune) {
	// r1 is warrantied to be either '\r' or '\n'
	r2, _, err := p.src.ReadRune()
	switch r1 {
	case '\n':
		switch {
		case r2 == '\r':
			// LN CR
		case err == nil:
			// LN
			p.src.UnreadRune()
		default:
			// LN EOF
		}
	case '\r':
		switch {
		case r2 == '\n':
			// CR LN
		case err == nil:
			// CR
			p.src.UnreadRune()
		default:
			// CR EOF
		}
	default:
		panic("unreachable")
	}
}

func (p *Parser) lexComment() (lexer.StateFn, error) {
	// until the end of the line
	p.src.AcceptAll(IsNotNewLine)

	err := p.emitString(TokenComment)
	return p.lexStart, err
}

func (p *Parser) lexSectionStart() (lexer.StateFn, error) {
	if err := p.emitString(TokenSectionStart); err != nil {
		return nil, err
	}

	// remove whitespace between `[` and the name
	if p.src.AcceptAll(IsSpaceNotNewLine) {
		p.stepString()
	}

	if !p.src.AcceptAll(IsName) {
		// no name
		return p.emitError("section name missing", lexer.ErrUnacceptableRune)
	}

	if err := p.emitString(TokenSectionName); err != nil {
		return nil, err
	}

	// remove whitespace between the name andthe closing `]`
	if p.src.AcceptAll(IsSpaceNotNewLine) {
		p.stepString()
	}

	r, _, err := p.src.ReadRune()
	switch {
	case err != nil:
		return p.emitError("", err)
	case IsSectionEnd(r):
		err := p.emitString(TokenSectionEnd)
		return p.lexStart, err
	default:
		return p.emitInvalidRune(r)
	}
}

func (p *Parser) lexEntryStart() (lexer.StateFn, error) {
	p.src.AcceptAll(IsName)
	if err := p.emitString(TokenFieldKey); err != nil {
		return nil, err
	}

	// ignore whitespace between key and the '=' sign
	if p.src.AcceptAll(IsSpaceNotNewLine) {
		p.stepString()
	}

	r, _, err := p.src.ReadRune()
	switch {
	case err != nil:
		return p.emitError("", err)
	case r != RuneFieldEqual:
		return p.emitInvalidRune(r)
	}

	// ignore whitespace between the '=' and the value
	if p.src.AcceptAll(IsSpaceNotNewLine) {
		p.stepString()
	}

	p.src.AcceptAll(IsNotNewLine)
	if err := p.emitString(TokenFieldValue); err != nil {
		return nil, err
	}

	return p.lexStart, err
}