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// Copyright 2013 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package diff implements a linewise diff algorithm.
package diff
import (
"bytes"
"fmt"
"strings"
)
// Chunk represents a piece of the diff. A chunk will not have both added and
// deleted lines. Equal lines are always after any added or deleted lines.
// A Chunk may or may not have any lines in it, especially for the first or last
// chunk in a computation.
type Chunk struct {
Added []string
Deleted []string
Equal []string
}
// Diff returns a string containing a line-by-line unified diff of the linewise
// changes required to make A into B. Each line is prefixed with '+', '-', or
// ' ' to indicate if it should be added, removed, or is correct respectively.
func Diff(A, B string) string {
aLines := strings.Split(A, "\n")
bLines := strings.Split(B, "\n")
chunks := DiffChunks(aLines, bLines)
buf := new(bytes.Buffer)
for _, c := range chunks {
for _, line := range c.Added {
fmt.Fprintf(buf, "+%s\n", line)
}
for _, line := range c.Deleted {
fmt.Fprintf(buf, "-%s\n", line)
}
for _, line := range c.Equal {
fmt.Fprintf(buf, " %s\n", line)
}
}
return strings.TrimRight(buf.String(), "\n")
}
// DiffChunks uses an O(D(N+M)) shortest-edit-script algorithm
// to compute the edits required from A to B and returns the
// edit chunks.
func DiffChunks(A, B []string) []Chunk {
// algorithm: http://www.xmailserver.org/diff2.pdf
N, M := len(A), len(B)
MAX := N + M
V := make([]int, 2*MAX+1)
Vs := make([][]int, 0, 8)
var D int
dLoop:
for D = 0; D <= MAX; D++ {
for k := -D; k <= D; k += 2 {
var x int
if k == -D || (k != D && V[MAX+k-1] < V[MAX+k+1]) {
x = V[MAX+k+1]
} else {
x = V[MAX+k-1] + 1
}
y := x - k
for x < N && y < M && A[x] == B[y] {
x++
y++
}
V[MAX+k] = x
if x >= N && y >= M {
Vs = append(Vs, append(make([]int, 0, len(V)), V...))
break dLoop
}
}
Vs = append(Vs, append(make([]int, 0, len(V)), V...))
}
if D == 0 {
return nil
}
chunks := make([]Chunk, D+1)
x, y := N, M
for d := D; d > 0; d-- {
V := Vs[d]
k := x - y
insert := k == -d || (k != d && V[MAX+k-1] < V[MAX+k+1])
x1 := V[MAX+k]
var x0, xM, kk int
if insert {
kk = k + 1
x0 = V[MAX+kk]
xM = x0
} else {
kk = k - 1
x0 = V[MAX+kk]
xM = x0 + 1
}
y0 := x0 - kk
var c Chunk
if insert {
c.Added = B[y0:][:1]
} else {
c.Deleted = A[x0:][:1]
}
if xM < x1 {
c.Equal = A[xM:][:x1-xM]
}
x, y = x0, y0
chunks[d] = c
}
if x > 0 {
chunks[0].Equal = A[:x]
}
return chunks
}
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