commit 1c029d98566ce670f79b77334b2977f986bcdd9d
Author: Stephen Searles <stephen.searles@gmail.com>
Date:   Mon Jun 12 01:30:51 2017 -0700

    initial

diff --git a/acedoc.go b/acedoc.go
new file mode 100644
index 0000000..b0f0802
--- /dev/null
+++ b/acedoc.go
@@ -0,0 +1,196 @@
+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
+}
diff --git a/acedoc_test.go b/acedoc_test.go
new file mode 100644
index 0000000..15f8f8f
--- /dev/null
+++ b/acedoc_test.go
@@ -0,0 +1,42 @@
+package acedoc
+
+import "testing"
+
+func TestDelta(t *testing.T) {
+	type c struct {
+		name   string
+		start  string
+		expect string
+		delta  Delta
+	}
+
+	cases := []c{
+		{"empty", "", "", Delta{}},
+		{"empty with content", "a", "a", Delta{}},
+		{"insert with no content", "a", "a", Insert(0, 1, "")},
+		{"insert", "a", "ab", Insert(0, 1, "b")},
+		{"insert across line", "a", "a\nb", Insert(0, 1, "\nb")},
+		{"insert new line", "ab", "a\nb", Insert(0, 1, "\n")},
+		{"insert lines at beginning", "ab", "\n\nab", Insert(0, 0, "\n\n")},
+		{"insert lines at end", "ab", "ab\n\n", Insert(0, 2, "\n\n")},
+		{"insert more lines", "a\nb", "a\n\n\nb", Insert(0, 1, "\n\n")},
+
+		{"remove", "a", "", Remove(0, 0, "a")},
+		{"remove across line", "a\nb", "a", Remove(0, 1, "\nb")},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			doc := NewString(c.start)
+			err := doc.Apply(c.delta)
+			if err != nil {
+				t.Error(err)
+				return
+			}
+
+			if doc.Contents() != c.expect {
+				t.Errorf("unexpected output: %q, expected: %q", doc.Contents(), c.expect)
+			}
+		})
+	}
+}
diff --git a/delta.go b/delta.go
new file mode 100644
index 0000000..b74f9a0
--- /dev/null
+++ b/delta.go
@@ -0,0 +1,31 @@
+package acedoc
+
+/* ***** BEGIN LICENSE BLOCK *****
+* Distributed under the BSD license:
+*
+* Copyright (c) 2010, Ajax.org B.V.
+* All rights reserved.
+*
+* Redistribution and use in source and binary forms, with or without
+* modification, are permitted provided that the following conditions are met:
+*     * Redistributions of source code must retain the above copyright
+*       notice, this list of conditions and the following disclaimer.
+*     * Redistributions in binary form must reproduce the above copyright
+*       notice, this list of conditions and the following disclaimer in the
+*       documentation and/or other materials provided with the distribution.
+*     * Neither the name of Ajax.org B.V. nor the
+*       names of its contributors may be used to endorse or promote products
+*       derived from this software without specific prior written permission.
+*
+* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+* DISCLAIMED. IN NO EVENT SHALL AJAX.ORG B.V. BE LIABLE FOR ANY
+* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*
+* ***** END LICENSE BLOCK ***** */