1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216

package terminal

// stepCSI collects the parameters of a control sequence and runs it when its
// final byte arrives.
//
// The shape is ESC [ [private] [params] [intermediate] final, where the
// parameters are decimal numbers separated by semicolons.
func (p *Parser) stepCSI(b byte) {
	switch {
	case b >= '0' && b <= '9':
		p.digit(b)
	case b == ';':
		p.nextParam()
	case b == '?' || b == '<' || b == '=' || b == '>':
		p.private = b
	case b >= ' ' && b <= '/':
		p.intermediate = b
	case b >= '@' && b <= '~':
		p.runCSI(b)
		p.state = ground
	default:
		// A control character inside a sequence is acted on where it stands,
		// which is what a real terminal does with, say, a carriage return
		// arriving mid-sequence.
		p.stepGround(b)
	}
}

// digit adds a decimal digit to the parameter being collected.
func (p *Parser) digit(b byte) {
	if len(p.params) == 0 {
		p.params = append(p.params, 0)
	}
	last := len(p.params) - 1
	p.params[last] = p.params[last]*10 + int(b-'0')
}

// nextParam starts the next parameter of the sequence.
func (p *Parser) nextParam() {
	if len(p.params) == 0 {
		p.params = append(p.params, 0)
	}
	if len(p.params) < maxParams {
		p.params = append(p.params, 0)
	}
}

// param returns parameter i, or a default when it was not given. An omitted
// parameter is zero in the protocol, and nearly every sequence reads zero as
// "the default", which is what makes this one helper enough.
func (p *Parser) param(i, fallback int) int {
	if i >= len(p.params) || p.params[i] == 0 {
		return fallback
	}
	return p.params[i]
}

// runCSI performs the sequence its final byte names.
func (p *Parser) runCSI(final byte) {
	if p.private == '?' {
		p.runPrivateMode(final)
		return
	}

	switch final {
	case 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'f', 'd':
		p.runMovement(final)
	case 'J':
		p.screen.EraseDisplay(eraseMode(p.param(0, 0)))
	case 'K':
		p.screen.EraseLine(eraseMode(p.param(0, 0)))
	case 'L':
		p.screen.InsertLines(p.param(0, 1))
	case 'M':
		p.screen.DeleteLines(p.param(0, 1))
	case '@':
		p.screen.InsertChars(p.param(0, 1))
	case 'P':
		p.screen.DeleteChars(p.param(0, 1))
	case 'X':
		p.screen.EraseChars(p.param(0, 1))
	case 'S':
		p.screen.ScrollUp(p.param(0, 1))
	case 'T':
		p.screen.ScrollDown(p.param(0, 1))
	case 'r':
		p.runSetScrollRegion()
	case 'm':
		p.runSGR()
	case 's':
		p.screen.SaveCursor()
	case 'u':
		p.screen.RestoreCursor()
	}
	// Everything else is dropped: device reports, tab-stop management, window
	// manipulation, and the non-private modes — of which only insert mode would
	// mean anything here, and programs that want to push text along use ICH,
	// which is implemented. A terminal that does not implement a sequence must
	// swallow it rather than print it.
}

// runMovement performs the sequences that only move the cursor.
func (p *Parser) runMovement(final byte) {
	switch final {
	case 'A': // CUU, up
		p.screen.MoveBy(-p.param(0, 1), 0)
	case 'B': // CUD, down
		p.screen.MoveBy(p.param(0, 1), 0)
	case 'C': // CUF, forward
		p.screen.MoveBy(0, p.param(0, 1))
	case 'D': // CUB, back
		p.screen.MoveBy(0, -p.param(0, 1))
	case 'E': // CNL, down and to the first column
		p.screen.MoveBy(p.param(0, 1), 0)
		p.screen.CarriageReturn()
	case 'F': // CPL, up and to the first column
		p.screen.MoveBy(-p.param(0, 1), 0)
		p.screen.CarriageReturn()
	case 'G': // CHA, to a column
		p.screen.MoveTo(p.screen.Cursor().Row, p.param(0, 1)-1)
	case 'd': // VPA, to a row
		p.screen.MoveTo(p.param(0, 1)-1, p.screen.Cursor().Col)
	case 'H', 'f': // CUP, HVP, to a row and column
		p.screen.MoveTo(p.param(0, 1)-1, p.param(1, 1)-1)
	}
}

// runSetScrollRegion performs DECSTBM. With no parameters it opens the region
// back up to the whole screen.
func (p *Parser) runSetScrollRegion() {
	_, height := p.screen.Size()

	top := p.param(0, 1) - 1
	bottom := p.param(1, height) - 1
	if bottom <= top {
		bottom = height - 1
	}

	p.screen.SetScrollRegion(top, bottom)
}

// eraseMode turns the number in an erase sequence into a mode, treating
// anything unexpected as "from the cursor onwards".
func eraseMode(n int) EraseMode {
	switch n {
	case 1:
		return EraseToStart
	case 2, 3:
		return EraseAll
	default:
		return EraseToEnd
	}
}

// runPrivateMode performs the DEC private set and reset sequences, ESC [ ? … h
// and ESC [ ? … l.
func (p *Parser) runPrivateMode(final byte) {
	if final != 'h' && final != 'l' {
		return
	}
	set := final == 'h'

	for i := range max(len(p.params), 1) {
		p.setPrivateMode(p.param(i, 0), set)
	}
}

// The DEC private modes this emulator implements.
const (
	modeApplicationCursor = 1    // DECCKM
	modeAutoWrap          = 7    // DECAWM
	modeCursorVisible     = 25   // DECTCEM
	modeAlternate47       = 47   // the oldest alternate-screen switch
	modeAlternate1047     = 1047 // alternate screen
	modeSaveCursor1048    = 1048 // save and restore the cursor
	modeAlternate1049     = 1049 // save the cursor, then the alternate screen
)

// setPrivateMode turns one DEC private mode on or off.
func (p *Parser) setPrivateMode(mode int, set bool) {
	switch mode {
	case modeApplicationCursor:
		p.screen.SetApplicationCursor(set)
	case modeAutoWrap:
		p.screen.SetAutoWrap(set)
	case modeCursorVisible:
		p.screen.SetCursorVisible(set)
	case modeAlternate47, modeAlternate1047:
		p.screen.UseAlternate(set)
	case modeSaveCursor1048:
		p.saveOrRestore(set)
	case modeAlternate1049:
		// The one programs actually use: save the cursor on the way in and put
		// it back on the way out, around the alternate screen.
		if set {
			p.screen.SaveCursor()
			p.screen.UseAlternate(true)
			return
		}
		p.screen.UseAlternate(false)
		p.screen.RestoreCursor()
	}
	// Every other private mode — mouse reporting, bracketed paste, focus
	// events — is accepted and ignored. The program is told nothing, which is
	// exactly what a terminal without those features looks like.
}

// saveOrRestore saves the cursor when setting a mode and restores it when
// resetting one.
func (p *Parser) saveOrRestore(set bool) {
	if set {
		p.screen.SaveCursor()
		return
	}
	p.screen.RestoreCursor()
}