1// Modified from rsc.io/edit
2
3// Copyright 2017 The Go Authors. All rights reserved.
4// Use of this source code is governed by a BSD-style
5// license that can be found in the LICENSE file.
6
7// Package edit implements buffered position-based editing of byte slices.
8package editbuf
9
10import (
11 "fmt"
12 "sort"
13)
14
15// A Buffer is a queue of edits to apply to a given byte slice.
16type Buffer struct {
17 old []byte
18 q edits
19}
20
21// An edit records a single text modification: change the bytes in [start,end) to new.
22type edit struct {
23 start int
24 end int
25 new string
26}
27
28// An edits is a list of edits that is sortable by start offset, breaking ties by end offset.
29type edits []edit
30
31func (x edits) Len() int { return len(x) }
32func (x edits) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
33func (x edits) Less(i, j int) bool {
34 if x[i].start != x[j].start {
35 return x[i].start < x[j].start
36 }
37 return x[i].end < x[j].end
38}
39
40// NewBuffer returns a new buffer to accumulate changes to an initial data slice.
41// The returned buffer maintains a reference to the data, so the caller must ensure
42// the data is not modified until after the Buffer is done being used.
43func NewBuffer(old []byte) *Buffer {
44 return &Buffer{old: old}
45}
46
47// Insert inserts the new string at old[pos:pos].
48func (b *Buffer) Insert(pos int, new string) {
49 if pos < 0 || pos > len(b.old) {
50 panic("invalid edit position")
51 }
52 b.q = append(b.q, edit{pos, pos, new})
53}
54
55// Delete deletes the text old[start:end].
56func (b *Buffer) Delete(start, end int) {
57 if end < start || start < 0 || end > len(b.old) {
58 panic("invalid edit position")
59 }
60 b.q = append(b.q, edit{start, end, ""})
61}
62
63// Replace replaces old[start:end] with new.
64func (b *Buffer) Replace(start, end int, new string) {
65 if end < start || start < 0 || end > len(b.old) {
66 panic("invalid edit position")
67 }
68 b.q = append(b.q, edit{start, end, new})
69}
70
71// Bytes returns a new byte slice containing the original data
72// with the queued edits applied.
73func (b *Buffer) Bytes() ([]byte, error) {
74 // Sort edits by starting position and then by ending position.
75 // Breaking ties by ending position allows insertions at point x
76 // to be applied before a replacement of the text at [x, y).
77 sort.Stable(b.q)
78
79 var new []byte
80 offset := 0
81 for i, e := range b.q {
82 if e.start < offset {
83 e0 := b.q[i-1]
84 return nil, fmt.Errorf("overlapping edits: [%d,%d)->%q, [%d,%d)->%q", e0.start, e0.end, e0.new, e.start, e.end, e.new)
85 }
86 new = append(new, b.old[offset:e.start]...)
87 offset = e.end
88 new = append(new, e.new...)
89 }
90 new = append(new, b.old[offset:]...)
91 return new, nil
92}