Source file src/cmd/internal/edit/edit.go

     1	// Copyright 2017 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	// Package edit implements buffered position-based editing of byte slices.
     6	package edit
     7	
     8	import (
     9		"fmt"
    10		"sort"
    11	)
    12	
    13	// A Buffer is a queue of edits to apply to a given byte slice.
    14	type Buffer struct {
    15		old []byte
    16		q   edits
    17	}
    18	
    19	// An edit records a single text modification: change the bytes in [start,end) to new.
    20	type edit struct {
    21		start int
    22		end   int
    23		new   string
    24	}
    25	
    26	// An edits is a list of edits that is sortable by start offset, breaking ties by end offset.
    27	type edits []edit
    28	
    29	func (x edits) Len() int      { return len(x) }
    30	func (x edits) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
    31	func (x edits) Less(i, j int) bool {
    32		if x[i].start != x[j].start {
    33			return x[i].start < x[j].start
    34		}
    35		return x[i].end < x[j].end
    36	}
    37	
    38	// NewBuffer returns a new buffer to accumulate changes to an initial data slice.
    39	// The returned buffer maintains a reference to the data, so the caller must ensure
    40	// the data is not modified until after the Buffer is done being used.
    41	func NewBuffer(data []byte) *Buffer {
    42		return &Buffer{old: data}
    43	}
    44	
    45	func (b *Buffer) Insert(pos int, new string) {
    46		if pos < 0 || pos > len(b.old) {
    47			panic("invalid edit position")
    48		}
    49		b.q = append(b.q, edit{pos, pos, new})
    50	}
    51	
    52	func (b *Buffer) Delete(start, end int) {
    53		if end < start || start < 0 || end > len(b.old) {
    54			panic("invalid edit position")
    55		}
    56		b.q = append(b.q, edit{start, end, ""})
    57	}
    58	
    59	func (b *Buffer) Replace(start, end int, new string) {
    60		if end < start || start < 0 || end > len(b.old) {
    61			panic("invalid edit position")
    62		}
    63		b.q = append(b.q, edit{start, end, new})
    64	}
    65	
    66	// Bytes returns a new byte slice containing the original data
    67	// with the queued edits applied.
    68	func (b *Buffer) Bytes() []byte {
    69		// Sort edits by starting position and then by ending position.
    70		// Breaking ties by ending position allows insertions at point x
    71		// to be applied before a replacement of the text at [x, y).
    72		sort.Stable(b.q)
    73	
    74		var new []byte
    75		offset := 0
    76		for i, e := range b.q {
    77			if e.start < offset {
    78				e0 := b.q[i-1]
    79				panic(fmt.Sprintf("overlapping edits: [%d,%d)->%q, [%d,%d)->%q", e0.start, e0.end, e0.new, e.start, e.end, e.new))
    80			}
    81			new = append(new, b.old[offset:e.start]...)
    82			offset = e.end
    83			new = append(new, e.new...)
    84		}
    85		new = append(new, b.old[offset:]...)
    86		return new
    87	}
    88	
    89	// String returns a string containing the original data
    90	// with the queued edits applied.
    91	func (b *Buffer) String() string {
    92		return string(b.Bytes())
    93	}
    94	

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