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// Package diffbytes provides routines to perform line-based diffs.
package diffbytes
import "bytes"
// DiffBytes performs a line-based diff.
// Lines are bytes up to and including '\n' (final line may lack '\n').
func DiffBytes(oldB, newB []byte) ([]BytesDiffChunk, error) {
type lineRef struct {
base []byte
start int
end int
}
split := func(b []byte) []lineRef {
if len(b) == 0 {
return nil
}
var res []lineRef
start := 0
for i := range b {
if b[i] == '\n' {
res = append(res, lineRef{base: b, start: start, end: i + 1})
start = i + 1
}
}
if start < len(b) {
res = append(res, lineRef{base: b, start: start, end: len(b)})
}
return res
}
oldLines := split(oldB)
newLines := split(newB)
n := len(oldLines)
m := len(newLines)
if n == 0 && m == 0 {
return nil, nil
}
idOf := make(map[string]int)
nextID := 0
oldIDs := make([]int, n)
for i, ln := range oldLines {
key := bytesToString(ln.base[ln.start:ln.end])
id, ok := idOf[key]
if !ok {
id = nextID
idOf[key] = id
nextID++
}
oldIDs[i] = id
}
newIDs := make([]int, m)
for i, ln := range newLines {
key := bytesToString(ln.base[ln.start:ln.end])
id, ok := idOf[key]
if !ok {
id = nextID
idOf[key] = id
nextID++
}
newIDs[i] = id
}
max := n + m
offset := max
trace := make([][]int, 0, max+1)
Vprev := make([]int, 2*max+1)
for i := range Vprev {
Vprev[i] = -1
}
x0 := 0
y0 := 0
for x0 < n && y0 < m && oldIDs[x0] == newIDs[y0] {
x0++
y0++
}
Vprev[offset+0] = x0
trace = append(trace, append([]int(nil), Vprev...))
found := x0 >= n && y0 >= m
for D := 1; D <= max && !found; D++ {
V := make([]int, 2*max+1)
for i := range V {
V[i] = -1
}
for k := -D; k <= D; k += 2 {
var x int
if k == -D || (k != D && Vprev[offset+(k-1)] < Vprev[offset+(k+1)]) {
x = Vprev[offset+(k+1)]
} else {
x = Vprev[offset+(k-1)] + 1
}
y := x - k
for x < n && y < m && oldIDs[x] == newIDs[y] {
x++
y++
}
V[offset+k] = x
if x >= n && y >= m {
trace = append(trace, V)
found = true
break
}
}
if !found {
trace = append(trace, V)
Vprev = V
}
}
type edit struct {
kind BytesDiffChunkKind
lineref lineRef
}
revEdits := make([]edit, 0, n+m)
x := n
y := m
for D := len(trace) - 1; D >= 0; D-- {
k := x - y
var (
prevK int
prevX int
prevY int
)
if D > 0 {
prevV := trace[D-1]
if k == -D || (k != D && prevV[offset+(k-1)] < prevV[offset+(k+1)]) {
prevK = k + 1
} else {
prevK = k - 1
}
prevX = prevV[offset+prevK]
prevY = prevX - prevK
}
for x > prevX && y > prevY {
x--
y--
revEdits = append(revEdits, edit{kind: BytesDiffChunkKindUnchanged, lineref: oldLines[x]})
}
if D == 0 {
break
}
if x == prevX {
y--
revEdits = append(revEdits, edit{kind: BytesDiffChunkKindAdded, lineref: newLines[y]})
} else {
x--
revEdits = append(revEdits, edit{kind: BytesDiffChunkKindDeleted, lineref: oldLines[x]})
}
}
for i, j := 0, len(revEdits)-1; i < j; i, j = i+1, j-1 {
revEdits[i], revEdits[j] = revEdits[j], revEdits[i]
}
var out []BytesDiffChunk
type meta struct {
base []byte
start int
end int
}
var metas []meta
for _, e := range revEdits {
curBase := e.lineref.base
curStart := e.lineref.start
curEnd := e.lineref.end
if len(out) == 0 || out[len(out)-1].Kind != e.kind {
out = append(out, BytesDiffChunk{Kind: e.kind, Data: curBase[curStart:curEnd]})
metas = append(metas, meta{base: curBase, start: curStart, end: curEnd})
continue
}
lastIdx := len(out) - 1
lastMeta := metas[lastIdx]
if bytes.Equal(lastMeta.base, curBase) && lastMeta.end == curStart {
metas[lastIdx].end = curEnd
out[lastIdx].Data = curBase[metas[lastIdx].start:metas[lastIdx].end]
continue
}
out[lastIdx].Data = append(out[lastIdx].Data, curBase[curStart:curEnd]...)
metas[lastIdx] = meta{base: nil, start: 0, end: 0}
}
return out, nil
}
// BytesDiffChunk represents a contiguous region of bytes categorized
// as unchanged, deleted, or added.
type BytesDiffChunk struct {
Kind BytesDiffChunkKind
Data []byte
}
// BytesDiffChunkKind enumerates the type of diff chunk.
type BytesDiffChunkKind int
const (
// BytesDiffChunkKindUnchanged represents an unchanged diff chunk.
BytesDiffChunkKindUnchanged BytesDiffChunkKind = iota
// BytesDiffChunkKindDeleted represents a deleted diff chunk.
BytesDiffChunkKindDeleted
// BytesDiffChunkKindAdded represents an added diff chunk.
BytesDiffChunkKindAdded
)
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