acedoc/acedoc.go

package acedoc

import (
	"fmt"
	"strings"
	"sync"
)

type DeltaAction bool

const (
	DeltaInsert DeltaAction = true
	DeltaRemove DeltaAction = false
)

type Delta struct {
	Action     DeltaAction
	Lines      []string
	Start, End Position
}

func Remove(row, col uint, str string) Delta {
	lines := strings.Split(str, "\n")
	return Delta{
		Action: DeltaRemove,
		Lines:  lines,
		Start:  Position{row, col},
		End:    Position{row + uint(len(lines)-1), uint(len(lines[len(lines)-1]))},
	}

}

func Insert(row, col uint, str string) Delta {
	lines := strings.Split(str, "\n")
	return Delta{
		Action: DeltaInsert,
		Lines:  lines,
		Start:  Position{row, col},
		End:    Position{row + uint(len(lines)-1), uint(len(lines[len(lines)-1]))},
	}

}

type Document struct {
	mtx   sync.RWMutex
	Lines []string
}

func NewString(str string) *Document {
	d := &Document{
		Lines: strings.Split(str, "\n"),
	}
	return d
}

func (d *Document) NLines() uint {
	n := uint(len(d.Lines))
	if n == 0 {
		n = 1
	}
	return n
}

func (d Delta) NLines() uint {
	n := uint(len(d.Lines))
	if n == 0 {
		n = 1
	}
	return n
}

func (d *Document) Apply(dl Delta) error {
	d.mtx.Lock()
	defer d.mtx.Unlock()

	err := d.validate(dl)
	if err != nil {
		return fmt.Errorf("delta does not apply to document: %v", err)
	}

	row := dl.Start.Row
	col := dl.Start.Column
	line := d.Lines[row]

	switch dl.Action {
	case DeltaInsert:

		if dl.NLines() == 1 {
			d.Lines[row] = line[:col] + dl.Line(0) + line[col:]
		} else {
			newlines := []string{}
			if row != 0 {
				newlines = append(newlines, d.Lines[:row-1]...) // old content
			}
			newlines = append(newlines, d.Lines[row][:col]+dl.Lines[0])
			newlines = append(newlines, dl.Lines[1:]...) // new content
			newlines[len(newlines)-1] += d.Lines[row][col:]
			if uint(len(d.Lines)) > row {
				newlines = append(newlines, d.Lines[row+1:]...) // old content
			}
			d.Lines = newlines
		}

	case DeltaRemove:
		endCol := dl.End.Column
		endRow := dl.End.Row

		if row == endRow {
			d.Lines[row] = line[:col] + line[endCol:]
		} else {
			newlines := []string{}
			newlines = append(newlines, d.Lines[:row]...)
			newlines = append(newlines, d.Lines[endRow:]...)
			newlines[endRow] = newlines[endRow][endCol:]
			d.Lines = newlines
		}
	}

	return nil
}

func (d *Document) validate(dl Delta) error {
	if !d.InDocument(dl.Start) {
		return fmt.Errorf("start is not in document")
	}

	if dl.Action == DeltaRemove && !d.InDocument(dl.End) {
		return fmt.Errorf("end is not in document for remove")
	}

	if dl.NLines() != dl.NRows() {
		return fmt.Errorf("delta has %d lines, but positions show range of %d lines", dl.NLines(), dl.NRows())
	}

	lastDlLine := dl.Line(dl.NRows() - 1)

	if uint(len(lastDlLine)) != dl.Cols() {
		return fmt.Errorf("delta has %d chars on the final line, but positions show range of %d chars", len(lastDlLine), dl.Cols())
	}

	return nil
}

func (d Document) Line(i uint) string {
	if i >= uint(len(d.Lines)) {
		return ""
	}
	return d.Lines[i]
}
func (d Delta) Line(i uint) string {
	if i >= uint(len(d.Lines)) {
		return ""
	}
	return d.Lines[i]
}

func (d Delta) NRows() uint {
	r := d.End.Row - d.Start.Row
	if r == 0 {
		return 1
	}
	return r
}

func (d Delta) Rows() uint {
	r := d.End.Row - d.Start.Row
	return r
}

func (d Delta) Cols() uint {
	r := d.End.Column
	return r
}

func (d *Document) Contents() string {
	d.mtx.RLock()
	defer d.mtx.RUnlock()

	return strings.Join(d.Lines, "\n")
}

type Position struct {
	Row, Column uint
}

func (d *Document) InDocument(pos Position) bool {
	if pos.Row > d.NLines() {
		return false
	}

	line := d.Line(pos.Row)
	if pos.Column > uint(len(line)) {
		return false
	}
	return true
}