Add diff inputs command (#204)

This command introduces the command "baur diff inputs".
It prints a diff of the inputs of the current files of task in the filesystem or a recorded task-run.

Co-authored-by: Fabian Holler <[email protected]>

diff.go

@@ -0,0 +1,82 @@
+package baur
+
+import (
+	"fmt"
+	"sort"
+)
+
+type DiffType int
+
+const (
+	DigestMismatch DiffType = iota
+	Removed
+	Added
+)
+
+var diffTypeStrings = [...]string{"D", "-", "+"}
+
+func (d DiffType) String() string {
+	return diffTypeStrings[d]
+}
+
+type InputDiff struct {
+	State   DiffType
+	Path    string
+	Digest1 string
+	Digest2 string
+}
+
+// DiffInputs returns the differences between two sets of Inputs.
+// The Input.String() is used as the key to identify each Input.
+func DiffInputs(a, b *Inputs) ([]*InputDiff, error) {
+	aMap, err := inputsToStrMap(a.Inputs())
+	if err != nil {
+		return nil, err
+	}
+
+	bMap, err := inputsToStrMap(b.Inputs())
+	if err != nil {
+		return nil, err
+	}
+
+	var diffs []*InputDiff
+
+	for aPath, aDigest := range aMap {
+		bDigest, exists := bMap[aPath]
+		if !exists {
+			diffs = append(diffs, &InputDiff{State: Removed, Path: aPath, Digest1: aDigest})
+			continue
+		}
+
+		if aDigest != bDigest {
+			diffs = append(diffs, &InputDiff{State: DigestMismatch, Path: aPath, Digest1: aDigest, Digest2: bDigest})
+		}
+	}
+
+	for bPath, bDigest := range bMap {
+		if _, exists := aMap[bPath]; !exists {
+			diffs = append(diffs, &InputDiff{State: Added, Path: bPath, Digest2: bDigest})
+		}
+	}
+
+	sort.Slice(diffs, func(i, j int) bool {
+		return diffs[i].Path < diffs[j].Path
+	})
+
+	return diffs, nil
+}
+
+func inputsToStrMap(inputs []Input) (map[string]string, error) {
+	inputsMap := make(map[string]string, len(inputs))
+
+	for _, input := range inputs {
+		digest, err := input.Digest()
+		if err != nil {
+			return nil, fmt.Errorf("%s: calculating digest failed: %w", input, err)
+		}
+
+		inputsMap[input.String()] = digest.String()
+	}
+
+	return inputsMap, nil
+}

internal/command/diff.go

@@ -0,0 +1,14 @@
+package command
+
+import (
+	"github.com/spf13/cobra"
+)
+
+var diffCmd = &cobra.Command{
+	Use:   "diff",
+	Short: "list inputs that differ between two task-runs",
+}
+
+func init() {
+	rootCmd.AddCommand(diffCmd)
+}