edit.go

Documentation: golang.org/x/tools/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(old []byte) *Buffer {
    42  	return &Buffer{old: old}
    43  }
    44  
    45  // Insert inserts the new string at old[pos:pos].
    46  func (b *Buffer) Insert(pos int, new string) {
    47  	if pos < 0 || pos > len(b.old) {
    48  		panic("invalid edit position")
    49  	}
    50  	b.q = append(b.q, edit{pos, pos, new})
    51  }
    52  
    53  // Delete deletes the text old[start:end].
    54  func (b *Buffer) Delete(start, end int) {
    55  	if end < start || start < 0 || end > len(b.old) {
    56  		panic("invalid edit position")
    57  	}
    58  	b.q = append(b.q, edit{start, end, ""})
    59  }
    60  
    61  // Replace replaces old[start:end] with new.
    62  func (b *Buffer) Replace(start, end int, new string) {
    63  	if end < start || start < 0 || end > len(b.old) {
    64  		panic("invalid edit position")
    65  	}
    66  	b.q = append(b.q, edit{start, end, new})
    67  }
    68  
    69  // Bytes returns a new byte slice containing the original data
    70  // with the queued edits applied.
    71  func (b *Buffer) Bytes() []byte {
    72  	// Sort edits by starting position and then by ending position.
    73  	// Breaking ties by ending position allows insertions at point x
    74  	// to be applied before a replacement of the text at [x, y).
    75  	sort.Stable(b.q)
    76  
    77  	var new []byte
    78  	offset := 0
    79  	for i, e := range b.q {
    80  		if e.start < offset {
    81  			e0 := b.q[i-1]
    82  			panic(fmt.Sprintf("overlapping edits: [%d,%d)->%q, [%d,%d)->%q", e0.start, e0.end, e0.new, e.start, e.end, e.new))
    83  		}
    84  		new = append(new, b.old[offset:e.start]...)
    85  		offset = e.end
    86  		new = append(new, e.new...)
    87  	}
    88  	new = append(new, b.old[offset:]...)
    89  	return new
    90  }
    91  
    92  // String returns a string containing the original data
    93  // with the queued edits applied.
    94  func (b *Buffer) String() string {
    95  	return string(b.Bytes())
    96  }
    97
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