textedit/indent.go

package textedit

import "unicode"

const nonbreakSpace = '\u00a0'

type wrapIndentState struct {
	currentWord       []rune
	currentLineLength int
	multipleLines     bool
}

func indentLength(i []rune) int {
	var l int
	for _, ii := range i {
		if ii == '\t' {
			l += 8
			continue
		}

		l++
	}

	return l
}

func wrapIndentEdit(first, rest []rune, firstWidth, restWidth int) func(rune, wrapIndentState) ([]rune, wrapIndentState) {
	firstIndentLength := indentLength(first)
	restIndentLength := indentLength(rest)
	return func(r rune, state wrapIndentState) ([]rune, wrapIndentState) {
		var ret []rune
		indent := first
		il := firstIndentLength
		width := firstWidth
		if state.multipleLines {
			indent = rest
			il = restIndentLength
			width = restWidth
		}

		nw := width <= 0
		cl := state.currentLineLength
		wl := len(state.currentWord)
		nl := r == '\n'
		ws := unicode.IsSpace(r) && r != nonbreakSpace
		if nw && nl && wl > 0 {
			if cl == 0 {
				ret = append(ret, indent...)
			}

			if cl > 0 {
				ret = append(ret, ' ')
			}

			ret = append(ret, state.currentWord...)
			ret = append(ret, '\n')
			state.currentWord = nil
			state.currentLineLength = 0
			state.multipleLines = true
			return ret, state
		}

		if nw && nl {
			ret = append(ret, '\n')
			state.currentLineLength = 0
			state.multipleLines = true
			return ret, state
		}

		if nw && ws && wl > 0 {
			if cl == 0 {
				ret = append(ret, indent...)
			}

			if cl > 0 {
				ret = append(ret, ' ')
				state.currentLineLength++
			}

			ret = append(ret, state.currentWord...)
			state.currentLineLength += wl
			state.currentWord = nil
			return ret, state
		}

		if nw && ws {
			return nil, state
		}

		if nw {
			state.currentWord = append(state.currentWord, r)
			return nil, state
		}

		if ws && cl > 0 && cl+wl+il+1 > width && wl > 0 {
			ret = append(ret, '\n')
			ret = append(ret, rest...)
			ret = append(ret, state.currentWord...)
			state.currentLineLength = wl
			state.multipleLines = true
			state.currentWord = nil
			return ret, state
		}

		if ws && cl > 0 && cl+wl+il+1 > width {
			ret = append(ret, '\n')
			state.currentLineLength = 0
			state.multipleLines = true
			return ret, state
		}

		if ws && cl > 0 && wl > 0 {
			ret = append(ret, ' ')
			ret = append(ret, state.currentWord...)
			state.currentLineLength++
			state.currentLineLength += wl
			state.currentWord = nil
			return ret, state
		}

		if ws && wl > 0 {
			ret = append(ret, indent...)
			ret = append(ret, state.currentWord...)
			state.currentLineLength += wl
			state.currentWord = nil
			return ret, state
		}

		if ws {
			return nil, state
		}

		state.currentWord = append(state.currentWord, r)
		return nil, state
	}
}

func wrapIndentRelease(first, rest []rune) func(wrapIndentState) []rune {
	return func(state wrapIndentState) []rune {
		if len(state.currentWord) == 0 {
			return nil
		}

		var ret []rune
		indent := first
		if state.multipleLines {
			indent = rest
		}

		if state.currentLineLength == 0 {
			ret = append(ret, indent...)
		}

		if state.currentLineLength > 0 {
			ret = append(ret, ' ')
		}

		ret = append(ret, state.currentWord...)
		return ret
	}
}

func wrapIndent(first, rest []rune, firstWidth, restWidth int) Editor {
	return Func(
		wrapIndentEdit(first, rest, firstWidth, restWidth),
		wrapIndentRelease(first, rest),
	)
}