Added text manipulation

text/text.go

@@ -0,0 +1,248 @@
+package text
+
+import "unicode"
+
+// Dot represents a cursor or text selection. It has a start and end position,
+// referring to where the user began and ended the selection respectively.
+type Dot struct { Start, End int }
+
+// EmptyDot returns a zero-width dot at the specified position.
+func EmptyDot (position int) Dot {
+	return Dot { position, position }
+}
+
+// Canon places the lesser value at the start, and the greater value at the end.
+// Note that a canonized dot does not in all cases correspond directly to the
+// original, because there is a semantic value to the start and end positions.
+func (dot Dot) Canon () Dot {
+	if dot.Start > dot.End {
+		return Dot { dot.End, dot.Start }
+	} else {
+		return dot
+	}
+}
+
+// Empty returns whether or not the 
+func (dot Dot) Empty () bool {
+	return dot.Start == dot.End
+}
+
+// Add shifts the dot to the right by the specified amount.
+func (dot Dot) Add (delta int) Dot {
+	return Dot {
+		dot.Start + delta,
+		dot.End   + delta,
+	}
+}
+
+// Sub shifts the dot to the left by the specified amount.
+func (dot Dot) Sub (delta int) Dot {
+	return Dot {
+		dot.Start - delta,
+		dot.End   - delta,
+	}
+}
+
+// Constrain constrains the dot's start and end from zero to length (inclusive).
+func (dot Dot) Constrain (length int) Dot {
+	if dot.Start < 0      { dot.Start = 0      }
+	if dot.Start > length { dot.Start = length }
+	if dot.End   < 0      { dot.End   = 0      }
+	if dot.End   > length { dot.End   = length }
+	return dot
+}
+
+// Width returns how many runes the dot spans.
+func (dot Dot) Width () int {
+	dot = dot.Canon()
+	return dot.End - dot.Start
+}
+
+// Slice returns the subset of text that the dot covers.
+func (dot Dot) Slice (text []rune) []rune {
+	dot = dot.Canon().Constrain(len(text))
+	return text[dot.Start:dot.End]
+}
+
+// WordToLeft returns how far away to the left the next word boundary is from a
+// given position.
+func WordToLeft (text []rune, position int) (length int) {
+	if position < 1 { return }
+	if position > len(text) { position = len(text) }
+
+	index := position - 1
+	for index >= 0 && unicode.IsSpace(text[index]) {
+		length ++
+		index --
+	}
+	for index >= 0 && !unicode.IsSpace(text[index]) {
+		length ++
+		index --
+	}
+	return
+}
+
+// WordToRight returns how far away to the right the next word boundary is from
+// a given position.
+func WordToRight (text []rune, position int) (length int) {
+	if position < 0 { return }
+	if position > len(text) { position = len(text) }
+
+	index := position
+	for index < len(text) && unicode.IsSpace(text[index]) {
+		length ++
+		index ++
+	}
+	for index < len(text) && !unicode.IsSpace(text[index]) {
+		length ++
+		index ++
+	}
+	return
+}
+
+// WordAround returns a dot that surrounds the word at the specified position.
+func WordAround (text []rune, position int) (around Dot) {
+	return Dot {
+		position - WordToLeft(text, position),
+		position + WordToRight(text, position),
+	}
+}
+
+// Backspace deletes the rune to the left of the dot. If word is true, it
+// deletes up until the next word boundary on the left. If the dot is non-empty,
+// it deletes the text inside of the dot.
+func Backspace (text []rune, dot Dot, word bool) (result []rune, moved Dot) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		distance := 1
+		if word {
+			distance = WordToLeft(text, dot.End)
+		}
+		result = append (
+			result,
+			text[:dot.Sub(distance).Constrain(len(text)).End]...)
+		result = append(result, text[dot.End:]...)
+		moved = EmptyDot(dot.Sub(distance).Start)
+		return
+	} else {
+		return Delete(text, dot, word)
+	}
+}
+
+// Delete deletes the rune to the right of the dot. If word is true, it deletes
+// up until the next word boundary on the right. If the dot is non-empty, it
+// deletes the text inside of the dot.
+func Delete (text []rune, dot Dot, word bool) (result []rune, moved Dot) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		distance := 1
+		if word {
+			distance = WordToRight(text, dot.End)
+		}
+		result = append(result, text[:dot.End]...)
+		result = append (
+			result,
+			text[dot.Add(distance).Constrain(len(text)).End:]...)
+		moved = dot
+		return	
+	} else {
+		dot = dot.Canon()
+		result = append(result, text[:dot.Start]...)
+		result = append(result, text[dot.End:]...)
+		moved = EmptyDot(dot.Start)
+		return
+	}
+}
+
+// Lift removes the section of text inside of the dot, and returns a copy of it.
+func Lift (text []rune, dot Dot) (result []rune, moved Dot, lifted []rune) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		moved = dot
+		return
+	}
+
+	dot = dot.Canon()
+	lifted = make([]rune, dot.Width())
+	copy(lifted, dot.Slice(text))
+	result = append(result, text[:dot.Start]...)
+	result = append(result, text[dot.End:]...)
+	moved = EmptyDot(dot.Start)
+	return
+}
+
+// Type inserts one of more runes into the text at the dot position. If the dot
+// is non-empty, it replaces the text inside of the dot with the new runes.
+func Type (text []rune, dot Dot, characters ...rune) (result []rune, moved Dot) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		result = append(result, text[:dot.End]...)
+		result = append(result, characters...)
+		if dot.End < len(text) {
+			result = append(result, text[dot.End:]...)
+		}
+		moved = EmptyDot(dot.Add(len(characters)).End)
+		return
+	} else {
+		dot = dot.Canon()
+		result = append(result, text[:dot.Start]...)
+		result = append(result, characters...)
+		result = append(result, text[dot.End:]...)
+		moved = EmptyDot(dot.Add(len(characters)).Start)
+		return
+	}
+}
+
+// MoveLeft moves the dot left one rune. If word is true, it moves the dot to
+// the next word boundary on the left.
+func MoveLeft (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Canon().Constrain(len(text))
+	distance := 0
+	if dot.Empty() {
+		distance = 1
+	}
+	if word {
+		distance = WordToLeft(text, dot.Start)
+	}
+	moved = EmptyDot(dot.Sub(distance).Start)
+	return
+}
+
+// MoveRight moves the dot right one rune. If word is true, it moves the dot to
+// the next word boundary on the right.
+func MoveRight (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Canon().Constrain(len(text))
+	distance := 0
+	if dot.Empty() {
+		distance = 1
+	}
+	if word {
+		distance = WordToRight(text, dot.End)
+	}
+	moved = EmptyDot(dot.Add(distance).End)
+	return
+}
+
+// SelectLeft moves the end of the dot left one rune. If word is true, it moves
+// the end of the dot to the next word boundary on the left.
+func SelectLeft (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Constrain(len(text))
+	distance := 1
+	if word {
+		distance = WordToLeft(text, dot.End)
+	}
+	dot.End -= distance
+	return dot
+}
+
+// SelectRight moves the end of the dot right one rune. If word is true, it
+// moves the end of the dot to the next word boundary on the right.
+func SelectRight (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Constrain(len(text))
+	distance := 1
+	if word {
+		distance = WordToRight(text, dot.End)
+	}
+	dot.End += distance
+	return dot
+}