edit.go

Documentation: cmd/internal/edit

     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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