From 2887d66a939b3b8d7e84d9c71c0a86d5132b5e54 Mon Sep 17 00:00:00 2001
From: n-peugnet <n.peugnet@free.fr>
Date: Tue, 21 Sep 2021 16:29:44 +0200
Subject: change recipe into a generic slice patch/diff package

---
 slice/slice.go      | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 slice/slice_test.go | 21 +++++++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 slice/slice.go
 create mode 100644 slice/slice_test.go

(limited to 'slice')

diff --git a/slice/slice.go b/slice/slice.go
new file mode 100644
index 0000000..15be5dd
--- /dev/null
+++ b/slice/slice.go
@@ -0,0 +1,74 @@
+package slice
+
+import "reflect"
+
+type Slice []interface{}
+
+type SliceDel int
+
+type SliceIns struct {
+	Idx   int
+	Value []interface{}
+}
+
+type SlicePatch struct {
+	Del []SliceDel
+	Ins []SliceIns
+}
+
+func PatchSlice(source Slice, patch SlicePatch) (target Slice) {
+	// apply Del part from patch to source into temp
+	size := len(source) - len(patch.Del)
+	temp := make(Slice, size)
+	fill := 0
+	prev := 0
+	for _, del := range patch.Del {
+		di := int(del)
+		copy(temp[fill:], source[prev:di])
+		fill += di - prev
+		prev = di + 1
+	}
+	copy(temp[fill:], source[prev:])
+	// apply Ins part from patch to temp into target
+	for _, ins := range patch.Ins {
+		size += len(ins.Value)
+	}
+	target = make(Slice, size)
+	fill = 0
+	prev = 0
+	tpos := 0
+	for _, ins := range patch.Ins {
+		offset := ins.Idx - prev
+		copy(target[fill:], temp[tpos:tpos+offset])
+		fill += offset
+		tpos += offset
+		copy(target[fill:], ins.Value)
+		fill += len(ins.Value)
+		prev = ins.Idx + len(ins.Value)
+	}
+	return
+}
+
+func DiffSlice(source Slice, target Slice) (patch SlicePatch) {
+	var si, ti int
+	var found bool
+	for ; si < len(source); si++ {
+		for i := ti; i < len(target); i++ {
+			found = reflect.DeepEqual(target[i], source[si])
+			if found {
+				if i != ti {
+					patch.Ins = append(patch.Ins, SliceIns{ti, target[ti:i]})
+				}
+				ti = i + 1
+				break
+			}
+		}
+		if !found {
+			patch.Del = append(patch.Del, SliceDel(si))
+		}
+	}
+	if ti < len(target) {
+		patch.Ins = append(patch.Ins, SliceIns{ti, target[ti:]})
+	}
+	return
+}
diff --git a/slice/slice_test.go b/slice/slice_test.go
new file mode 100644
index 0000000..b73946e
--- /dev/null
+++ b/slice/slice_test.go
@@ -0,0 +1,21 @@
+package slice
+
+import (
+	"testing"
+
+	"github.com/n-peugnet/dna-backup/testutils"
+)
+
+func TestPatch(t *testing.T) {
+	source := Slice{1, 2, 3, 4}
+	target := Slice{2, 5, 3, 6, 4, 7, 8}
+	patch := DiffSlice(source, target)
+	testutils.AssertSame(t, []SliceDel{0}, patch.Del, "Patch del part")
+	testutils.AssertSame(t, []SliceIns{
+		{1, Slice{5}},
+		{3, Slice{6}},
+		{5, Slice{7, 8}},
+	}, patch.Ins, "Patch ins part")
+	actual := PatchSlice(source, patch)
+	testutils.AssertSame(t, target, actual, "Target obtained from patch application")
+}
-- 
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