package terminal

// stepAfterEscape decides what kind of sequence an ESC begins.
func (p *Parser) stepAfterEscape(b byte) {
	switch b {
	case '[':
		p.state = inCSI
	case ']':
		p.state = inOSC
		p.osc = p.osc[:0]
	case 'P', 'X', '^', '_':
		// A device control, privacy message or application command. None is
		// implemented, and all of them run to a string terminator.
		p.state = inOSC
		p.osc = p.osc[:0]
	case '(', ')', '*', '+', '%', '#', ' ':
		// A character-set or size selector: one more byte follows, and this
		// emulator works in UTF-8 regardless.
		p.state = ignoring
	default:
		p.simpleEscape(b)
		p.state = ground
	}
}

// simpleEscape runs the escape sequences that are one byte long.
func (p *Parser) simpleEscape(b byte) {
	switch b {
	case 'D': // IND, index: down one line, scrolling if need be.
		p.screen.LineFeed()
	case 'M': // RI, reverse index: up one line, scrolling if need be.
		p.screen.ReverseLineFeed()
	case 'E': // NEL, next line.
		p.screen.CarriageReturn()
		p.screen.LineFeed()
	case '7': // DECSC, save the cursor and the style.
		p.screen.SaveCursor()
	case '8': // DECRC, restore them.
		p.screen.RestoreCursor()
	case 'c': // RIS, reset to the initial state.
		p.screen.Reset()
	}
	// Anything else — keypad modes, character sets — changes nothing this
	// emulator models, and is dropped rather than printed.
}

// stepIgnoring skips the one byte that completes a sequence being ignored.
func (p *Parser) stepIgnoring(byte) {
	p.state = ground
}

// stepOSC collects an operating-system command until its terminator.
func (p *Parser) stepOSC(b byte) {
	switch {
	case b == bell:
		p.endOSC()
	case b == escape:
		p.state = inOSCEscape
	case len(p.osc) >= maxOSC:
		// A program that has sent this much without a terminator is not going
		// to send one.
		p.state = ground
	default:
		p.osc = append(p.osc, b)
	}
}

// stepOSCEscape decides whether the ESC inside an OSC ended it.
func (p *Parser) stepOSCEscape(b byte) {
	if b == '\\' { // ST, the string terminator.
		p.endOSC()
		return
	}

	// It was not a terminator, so the OSC is abandoned and this byte starts
	// whatever the ESC really began.
	p.state = ground
	p.step(escape)
	p.step(b)
}

// endOSC acts on a completed operating-system command.
//
// Only the window title is kept. The rest — colour palettes, clipboard
// requests, working-directory hints — is dropped, which is what a terminal
// that does not implement them is expected to do.
func (p *Parser) endOSC() {
	p.state = ground

	command := string(p.osc)
	p.osc = p.osc[:0]

	// "0;title" sets both the icon name and the title; "2;title" the title.
	for _, prefix := range []string{"0;", "2;"} {
		if len(command) >= len(prefix) && command[:len(prefix)] == prefix {
			p.title = command[len(prefix):]
			return
		}
	}
}