Add destination state comparison

internal/state/compare.go

@@ -0,0 +1,89 @@
+package state
+
+import (
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/distributor/internal/bundle"
+)
+
+type Outcome string
+
+const (
+	OutcomeDestinationAbsent       Outcome = "destination_absent"
+	OutcomeDestinationUnmanaged    Outcome = "destination_unmanaged"
+	OutcomeInvalidState            Outcome = "invalid_destination_state"
+	OutcomeIdentityMismatch        Outcome = "destination_identity_mismatch"
+	OutcomeSameSource              Outcome = "same_source_manifest"
+	OutcomeDestinationOlder        Outcome = "destination_older"
+	OutcomeDestinationNewer        Outcome = "destination_newer"
+	OutcomeSameCreatedConflict     Outcome = "same_created_digest_conflict"
+	OutcomeDifferentSourceConflict Outcome = "different_source_conflict"
+)
+
+type DestinationStatus struct {
+	State       *DistributorState
+	StateErr    error
+	HasContents bool
+}
+
+type Comparison struct {
+	Outcome Outcome
+	Reason  string
+}
+
+func Compare(source bundle.Manifest, pipelineID, destinationID string, status DestinationStatus) Comparison {
+	if status.StateErr != nil {
+		return Comparison{Outcome: OutcomeInvalidState, Reason: status.StateErr.Error()}
+	}
+	if status.State == nil {
+		if status.HasContents {
+			return Comparison{Outcome: OutcomeDestinationUnmanaged, Reason: "destination has content but no distributor state"}
+		}
+		return Comparison{Outcome: OutcomeDestinationAbsent, Reason: "destination state is absent"}
+	}
+
+	destinationState := *status.State
+	if err := Validate(destinationState); err != nil {
+		return Comparison{Outcome: OutcomeInvalidState, Reason: err.Error()}
+	}
+	if destinationState.PipelineID != pipelineID {
+		return Comparison{Outcome: OutcomeIdentityMismatch, Reason: fmt.Sprintf("pipeline id %q does not match %q", destinationState.PipelineID, pipelineID)}
+	}
+	if destinationState.DestinationID != destinationID {
+		return Comparison{Outcome: OutcomeIdentityMismatch, Reason: fmt.Sprintf("destination id %q does not match %q", destinationState.DestinationID, destinationID)}
+	}
+
+	destinationManifest := destinationState.Source.Manifest
+	if manifestsEqual(source, destinationManifest) {
+		return Comparison{Outcome: OutcomeSameSource, Reason: "destination source manifest matches source"}
+	}
+	if destinationManifest.ID != source.ID {
+		return Comparison{Outcome: OutcomeDifferentSourceConflict, Reason: "destination source id differs from source"}
+	}
+	if destinationManifest.Created.Before(source.Created) {
+		return Comparison{Outcome: OutcomeDestinationOlder, Reason: "destination source is older than source"}
+	}
+	if destinationManifest.Created.After(source.Created) {
+		return Comparison{Outcome: OutcomeDestinationNewer, Reason: "destination source is newer than source"}
+	}
+	if destinationManifest.Digest != source.Digest {
+		return Comparison{Outcome: OutcomeSameCreatedConflict, Reason: "destination source has same id and created time but different digest"}
+	}
+	return Comparison{Outcome: OutcomeInvalidState, Reason: "destination source differs from source without a supported comparison outcome"}
+}
+
+func manifestsEqual(a, b bundle.Manifest) bool {
+	if a.SchemaVersion != b.SchemaVersion ||
+		a.ID != b.ID ||
+		a.Digest != b.Digest ||
+		!a.Created.Equal(b.Created) ||
+		len(a.Files) != len(b.Files) {
+		return false
+	}
+	for index := range a.Files {
+		if a.Files[index] != b.Files[index] {
+			return false
+		}
+	}
+	return true
+}