Merging two snapshots into one.

debian/list.go

@@ -473,3 +473,66 @@ func (l *PackageRefList) Diff(r *PackageRefList, packageCollection *PackageColle
 
 	return
 }
+
+// Merge merges reflist r into current reflist. Merge replaces matching packages (by architecture/name)
+// with reference from r.
+func (l *PackageRefList) Merge(r *PackageRefList) (result *PackageRefList) {
+	// pointer to left and right reflists
+	il, ir := 0, 0
+	// length of reflists
+	ll, lr := l.Len(), r.Len()
+
+	result = &PackageRefList{}
+	result.Refs = make([][]byte, 0, ll+lr)
+
+	// until we reached end of both lists
+	for il < ll || ir < lr {
+		// if we've exhausted left list, pull the rest from the right
+		if il == ll {
+			result.Refs = append(result.Refs, r.Refs[ir:]...)
+			break
+		}
+		// if we've exhausted right list, pull the rest from the left
+		if ir == lr {
+			result.Refs = append(result.Refs, l.Refs[il:]...)
+			break
+		}
+
+		// refs on both sides are present, load them
+		rl, rr := l.Refs[il], r.Refs[ir]
+		// compare refs
+		rel := bytes.Compare(rl, rr)
+
+		if rel == 0 {
+			// refs are identical, so are packages, advance pointer
+			result.Refs = append(result.Refs, l.Refs[il])
+			il++
+			ir++
+		} else {
+			partsL := bytes.Split(rl, []byte(" "))
+			archL, nameL := partsL[0][1:], partsL[1]
+
+			partsR := bytes.Split(rr, []byte(" "))
+			archR, nameR := partsR[0][1:], partsR[1]
+
+			if bytes.Compare(archL, archR) == 0 && bytes.Compare(nameL, nameR) == 0 {
+				// override with package from the right
+				result.Refs = append(result.Refs, r.Refs[ir])
+				il++
+				ir++
+			} else {
+				// otherwise append smallest of two
+				if rel < 0 {
+					result.Refs = append(result.Refs, l.Refs[il])
+					il++
+				} else {
+					result.Refs = append(result.Refs, r.Refs[ir])
+					ir++
+				}
+			}
+
+		}
+	}
+
+	return
+}

debian/list_test.go

@@ -394,3 +394,56 @@ func (s *PackageListSuite) TestDiff(c *C) {
 	c.Check(diffBA[3].Left, IsNil)
 
 }
+
+func (s *PackageListSuite) TestMerge(c *C) {
+	db, _ := database.OpenDB(c.MkDir())
+	coll := NewPackageCollection(db)
+
+	packages := []*Package{
+		&Package{Name: "lib", Version: "1.0", Architecture: "i386"},      //0
+		&Package{Name: "dpkg", Version: "1.7", Architecture: "i386"},     //1
+		&Package{Name: "data", Version: "1.1~bp1", Architecture: "all"},  //2
+		&Package{Name: "app", Version: "1.1~bp1", Architecture: "i386"},  //3
+		&Package{Name: "app", Version: "1.1~bp2", Architecture: "i386"},  //4
+		&Package{Name: "app", Version: "1.1~bp2", Architecture: "amd64"}, //5
+		&Package{Name: "dpkg", Version: "1.0", Architecture: "i386"},     //6
+		&Package{Name: "xyz", Version: "1.0", Architecture: "sparc"},     //7
+	}
+
+	for _, p := range packages {
+		coll.Update(p)
+	}
+
+	listA := NewPackageList()
+	listA.Add(packages[0])
+	listA.Add(packages[1])
+	listA.Add(packages[2])
+	listA.Add(packages[3])
+	listA.Add(packages[7])
+
+	listB := NewPackageList()
+	listB.Add(packages[0])
+	listB.Add(packages[2])
+	listB.Add(packages[4])
+	listB.Add(packages[5])
+	listB.Add(packages[6])
+
+	reflistA := NewPackageRefListFromPackageList(listA)
+	reflistB := NewPackageRefListFromPackageList(listB)
+
+	mergeAB := reflistA.Merge(reflistB)
+	mergeBA := reflistB.Merge(reflistA)
+
+	toStrSlice := func(reflist *PackageRefList) (result []string) {
+		result = make([]string, reflist.Len())
+		for i, r := range reflist.Refs {
+			result[i] = string(r)
+		}
+		return
+	}
+
+	c.Check(toStrSlice(mergeAB), DeepEquals,
+		[]string{"Pall data 1.1~bp1", "Pamd64 app 1.1~bp2", "Pi386 app 1.1~bp2", "Pi386 dpkg 1.0", "Pi386 lib 1.0", "Psparc xyz 1.0"})
+	c.Check(toStrSlice(mergeBA), DeepEquals,
+		[]string{"Pall data 1.1~bp1", "Pamd64 app 1.1~bp2", "Pi386 app 1.1~bp1", "Pi386 dpkg 1.7", "Pi386 lib 1.0", "Psparc xyz 1.0"})
+}