1 files changed, 139 insertions, 0 deletions
diff --git a/licensediff/licensediff.go b/licensediff/licensediff.go
new file mode 100644
index 0000000..ba8cd84
--- /dev/null
+++ b/licensediff/licensediff.go
@@ -0,0 +1,139 @@
+// Package licensediff is used to generate a "diff" between the concluded
+// licenses in two SPDX Packages, using the filename as the match point.
+// SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+package licensediff
+
+import (
+	"github.com/spdx/tools-golang/spdx/v2_1"
+	"github.com/spdx/tools-golang/spdx/v2_2"
+	"github.com/spdx/tools-golang/spdx/v2_3"
+)
+
+// LicensePair is a result set where we are talking about two license strings,
+// potentially differing, for a single filename between two SPDX Packages.
+type LicensePair struct {
+	First  string
+	Second string
+}
+
+// MakePairs2_1 essentially just consolidates all files and LicenseConcluded
+// strings into a single data structure.
+func MakePairs2_1(p1 *v2_1.Package, p2 *v2_1.Package) (map[string]LicensePair, error) {
+	pairs := map[string]LicensePair{}
+
+	// first, go through and add all files/licenses from p1
+	for _, f := range p1.Files {
+		pair := LicensePair{First: f.LicenseConcluded, Second: ""}
+		pairs[f.FileName] = pair
+	}
+
+	// now, go through all files/licenses from p2. If already
+	// present, add as .second; if not, create new pair
+	for _, f := range p2.Files {
+		firstLic := ""
+		existingPair, ok := pairs[f.FileName]
+		if ok {
+			// already present; update it
+			firstLic = existingPair.First
+		}
+		// now, update what's there, either way
+		pair := LicensePair{First: firstLic, Second: f.LicenseConcluded}
+		pairs[f.FileName] = pair
+	}
+
+	return pairs, nil
+}
+
+// MakePairs2_2 essentially just consolidates all files and LicenseConcluded
+// strings into a single data structure.
+func MakePairs2_2(p1 *v2_2.Package, p2 *v2_2.Package) (map[string]LicensePair, error) {
+	pairs := map[string]LicensePair{}
+
+	// first, go through and add all files/licenses from p1
+	for _, f := range p1.Files {
+		pair := LicensePair{First: f.LicenseConcluded, Second: ""}
+		pairs[f.FileName] = pair
+	}
+
+	// now, go through all files/licenses from p2. If already
+	// present, add as .second; if not, create new pair
+	for _, f := range p2.Files {
+		firstLic := ""
+		existingPair, ok := pairs[f.FileName]
+		if ok {
+			// already present; update it
+			firstLic = existingPair.First
+		}
+		// now, update what's there, either way
+		pair := LicensePair{First: firstLic, Second: f.LicenseConcluded}
+		pairs[f.FileName] = pair
+	}
+
+	return pairs, nil
+}
+
+// MakePairs2_3 essentially just consolidates all files and LicenseConcluded
+// strings into a single data structure.
+func MakePairs2_3(p1 *v2_3.Package, p2 *v2_3.Package) (map[string]LicensePair, error) {
+	pairs := map[string]LicensePair{}
+
+	// first, go through and add all files/licenses from p1
+	for _, f := range p1.Files {
+		pair := LicensePair{First: f.LicenseConcluded, Second: ""}
+		pairs[f.FileName] = pair
+	}
+
+	// now, go through all files/licenses from p2. If already
+	// present, add as .second; if not, create new pair
+	for _, f := range p2.Files {
+		firstLic := ""
+		existingPair, ok := pairs[f.FileName]
+		if ok {
+			// already present; update it
+			firstLic = existingPair.First
+		}
+		// now, update what's there, either way
+		pair := LicensePair{First: firstLic, Second: f.LicenseConcluded}
+		pairs[f.FileName] = pair
+	}
+
+	return pairs, nil
+}
+
+// LicenseDiff is a structured version of the output of MakePairs. It is
+// meant to make it easier to find and report on, e.g., just the files that
+// have different licenses, or those that are in just one scan.
+type LicenseDiff struct {
+	InBothChanged map[string]LicensePair
+	InBothSame    map[string]string
+	InFirstOnly   map[string]string
+	InSecondOnly  map[string]string
+}
+
+// MakeResults creates a more structured set of results from the output
+// of MakePairs.
+func MakeResults(pairs map[string]LicensePair) (*LicenseDiff, error) {
+	diff := &LicenseDiff{
+		InBothChanged: map[string]LicensePair{},
+		InBothSame:    map[string]string{},
+		InFirstOnly:   map[string]string{},
+		InSecondOnly:  map[string]string{},
+	}
+
+	// walk through pairs and allocate them where they belong
+	for filename, pair := range pairs {
+		if pair.First == pair.Second {
+			diff.InBothSame[filename] = pair.First
+		} else {
+			if pair.First == "" {
+				diff.InSecondOnly[filename] = pair.Second
+			} else if pair.Second == "" {
+				diff.InFirstOnly[filename] = pair.First
+			} else {
+				diff.InBothChanged[filename] = pair
+			}
+		}
+	}
+
+	return diff, nil
+}