initial

README.md

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+# Diff3
+
+A diff3 text merge implementation in Go based on the awesome paper below.
+
+["A Formal Investigation of Diff3" by Sanjeev Khanna, Keshav Kunal, and Benjamin C. Pierce](https://www.cis.upenn.edu/~bcpierce/papers/diff3-short.pdf)
+
+## Usage
+
+```go
+import "github.com/nasdf/diff3"
+textO := "original"
+textA := "changesA"
+textB := "changesB"
+merge := diff3.Merge(textO, textA, textB)
+```
+
+### Customize seperators
+
+```go
+diff3.Sep1 = "$$$$$$$"
+diff3.Sep2 = "@@@@@@@"
+diff3.Sep3 = "*******"
+```
+
+### Customize DiffMatchPatch settings
+
+```go
+diff3.DiffMatchPatch.DiffTimeout = time.Second
+diff3.DiffMatchPatch.DiffEditCost = 4
+diff3.DiffMatchPatch.MatchThreshold = 0.5
+diff3.DiffMatchPatch.MatchDistance = 1000
+diff3.DiffMatchPatch.PatchDeleteThreshold = 0.5
+diff3.DiffMatchPatch.PatchMargin = 4
+diff3.DiffMatchPatch.MatchMaxBits = 32
+```
+
+## License
+
+MIT

diff3.go

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+package diff3
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/sergi/go-diff/diffmatchpatch"
+)
+
+const (
+	// Sep1 signifies the start of a conflict.
+	Sep1 = "<<<<<<<"
+	// Sep2 signifies the middle of a conflict.
+	Sep2 = "======="
+	// Sep3 signifies the end of a conflict.
+	Sep3 = ">>>>>>>"
+)
+
+// DiffMatchPatch contains the diff algorithm settings.
+var DiffMatchPatch = diffmatchpatch.New()
+
+// Merge implements the diff3 algorithm to merge two texts into a common base.
+func Merge(textO, textA, textB string) string {
+	runesO, runesA, linesA := DiffMatchPatch.DiffLinesToRunes(textO, textA)
+	_, runesB, linesB := DiffMatchPatch.DiffLinesToRunes(textO, textB)
+
+	diffsA := DiffMatchPatch.DiffMainRunes(runesO, runesA, false)
+	diffsB := DiffMatchPatch.DiffMainRunes(runesO, runesB, false)
+
+	matchesA := matches(diffsA, runesA)
+	matchesB := matches(diffsB, runesB)
+
+	var result strings.Builder
+	indexO, indexA, indexB := 0, 0, 0
+	for {
+		i := nextMismatch(indexO, indexA, indexB, runesA, runesB, matchesA, matchesB)
+
+		o, a, b := 0, 0, 0
+		if i == 1 {
+			o, a, b = nextMatch(indexO, runesO, matchesA, matchesB)
+		} else if i > 1 {
+			o, a, b = indexO+i, indexA+i, indexB+i
+		}
+
+		if o == 0 || a == 0 || b == 0 {
+			break
+		}
+
+		chunk(indexO, indexA, indexB, o-1, a-1, b-1, runesO, runesA, runesB, linesA, linesB, &result)
+		indexO, indexA, indexB = o-1, a-1, b-1
+	}
+
+	chunk(indexO, indexA, indexB, len(runesO), len(runesA), len(runesB), runesO, runesA, runesB, linesA, linesB, &result)
+	return result.String()
+}
+
+// matches returns a map of the non-crossing matches.
+func matches(diffs []diffmatchpatch.Diff, runes []rune) map[int]int {
+	matches := make(map[int]int)
+	for _, d := range diffs {
+		if d.Type != diffmatchpatch.DiffEqual {
+			continue
+		}
+
+		for _, r := range d.Text {
+			matches[int(r)] = indexOf(runes, r) + 1
+		}
+	}
+	return matches
+}
+
+// nextMismatch searches for the next index where a or b is not equal to o.
+func nextMismatch(indexO, indexA, indexB int, runesA, runesB []rune, matchesA, matchesB map[int]int) int {
+	for i := 1; i <= len(runesA) && i <= len(runesB); i++ {
+		a, okA := matchesA[indexO+i]
+		b, okB := matchesB[indexO+i]
+
+		if !okA || a != indexA+i || !okB || b != indexB+i {
+			return i
+		}
+	}
+	return 0
+}
+
+// nextMatch searches for the next index where a and b are equal to o.
+func nextMatch(indexO int, runesO []rune, matchesA, matchesB map[int]int) (int, int, int) {
+	for o := indexO + 1; o <= len(runesO); o++ {
+		a, okA := matchesA[o]
+		b, okB := matchesB[o]
+
+		if okA && okB {
+			return o, a, b
+		}
+	}
+	return 0, 0, 0
+}
+
+// chunk merges the lines from o, a, and b into a single text.
+func chunk(indexO, indexA, indexB, o, a, b int, runesO, runesA, runesB []rune, linesA, linesB []string, result *strings.Builder) {
+	chunkO := buildChunk(linesA, runesO[indexO:o])
+	chunkA := buildChunk(linesA, runesA[indexA:a])
+	chunkB := buildChunk(linesB, runesB[indexB:b])
+
+	switch {
+	case chunkA == chunkB:
+		fmt.Fprint(result, chunkO)
+	case chunkO == chunkA:
+		fmt.Fprint(result, chunkB)
+	case chunkO == chunkB:
+		fmt.Fprint(result, chunkA)
+	default:
+		fmt.Fprintf(result, "%s\n%s%s\n%s%s\n", Sep1, chunkA, Sep2, chunkB, Sep3)
+	}
+}
+
+// indexOf returns the index of the first occurance of the given value.
+func indexOf(runes []rune, value rune) int {
+	for i, r := range runes {
+		if r == value {
+			return i
+		}
+	}
+	return -1
+}
+
+// buildChunk assembles the lines of the chunk into a string.
+func buildChunk(lines []string, runes []rune) string {
+	var chunk strings.Builder
+	for _, r := range runes {
+		fmt.Fprint(&chunk, lines[int(r)])
+	}
+	return chunk.String()
+}

diff3_test.go

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+package diff3
+
+import (
+	"testing"
+)
+
+const textO = `celery
+garlic
+onions
+salmon
+tomatoes
+wine
+`
+
+const textA = `celery
+salmon
+tomatoes
+garlic
+onions
+wine
+`
+
+const textB = `celery
+garlic
+salmon
+tomatoes
+onions
+wine
+`
+
+const expect = `celery
+salmon
+tomatoes
+garlic
+<<<<<<<
+onions
+=======
+salmon
+tomatoes
+onions
+>>>>>>>
+wine
+`
+
+func TestMerge(t *testing.T) {
+	if Merge(textO, textA, textB) != expect {
+		t.Errorf("unexpected merge result")
+	}
+}

go.mod

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+module github.com/nasdf/diff3
+
+go 1.14
+
+require github.com/sergi/go-diff v1.1.0

go.sum

@@ -0,0 +1,14 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sergi/go-diff v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
+github.com/sergi/go-diff v1.1.0/go.mod h1:STckp+ISIX8hZLjrqAeVduY0gWCT9IjLuqbuNXdaHfM=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=