package engine

import (
	"bytes"
	"reflect"
	"strings"
	"testing"

	"go.maximumdirect.net/configkit/internal/document"
)

func TestSequenceHistoryReplaysAppendAtAssignedIndexes(t *testing.T) {
	policy := mustCompileSequenceIdentityPolicy(t, []sequenceIdentityRegistration{
		{selector: sequenceIdentitySelector{
			literalSequenceSelector("collections"), anyMappingSequenceSelector(), literalSequenceSelector("records"),
		}, identityFields: []string{"id"}},
	})
	first := parseCompositionDocument(t, "source-1", "collections: {north: {records: [{id: a, value: first}]}, south: {records: [{id: x}]}}\n")
	second := parseCompositionDocument(t, "source-2", "collections: {north: {records: [{id: b, value: second}]}, south: {records: [{id: y}]}}\n")
	composed, diagnostics := composeDocumentsWithPolicy(policy, first, second)
	if len(diagnostics) != 0 {
		t.Fatalf("compose diagnostics = %#v", diagnostics)
	}
	for applicationIndex, application := range composed.applications {
		for path, want := range map[string]int{"/collections/north/records": 1, "/collections/south/records": 1} {
			sequence, present := documentAtPath(application.value, mustParsePath(t, path))
			if !present || sequence.Kind != document.Sequence || len(sequence.Sequence) != want {
				t.Errorf("application %d retained %s = %#v, %v; want one source fragment item", applicationIndex, path, sequence, present)
			}
		}
	}

	working := parseCompositionDocument(t, "defaults", "collections: {north: {records: [{id: default}]}, south: {records: [{id: default}]}}\n")
	index := new(mappingIndex)
	for _, application := range composed.applications {
		applyHistoryApplication(&working, application, index)
	}
	for path, want := range map[string][]string{
		"/collections/north/records": {"a", "b"},
		"/collections/south/records": {"x", "y"},
	} {
		sequence, present := documentAtPath(working, mustParsePath(t, path))
		if !present || sequence.Kind != document.Sequence || len(sequence.Sequence) != len(want) {
			t.Fatalf("replayed %s = %#v", path, sequence)
		}
		for itemIndex, id := range want {
			field := sequence.Sequence[itemIndex].Mapping[0].Value.Text
			if field != id {
				t.Errorf("replayed %s[%d].id = %q, want %q", path, itemIndex, field, id)
			}
		}
	}

	application := composed.applications[1]
	cloned := cloneHistoryApplications(composed.applications)
	cloned[1].sequences[0].path.segments[0].key = "mutated"
	if composed.applications[1].sequences[0].path.String() != "/collections/north/records" {
		t.Fatal("cloned sequence history path aliases its source")
	}
	addedPath := Keys("collections", "north", "records").Index(1).Key("value")
	if operation, relevant := applicationOperationPath(application, addedPath, nil); !relevant || operation.String() != addedPath.String() {
		t.Fatalf("appended value operation = %s, %v", operation.String(), relevant)
	}
	if _, relevant := applicationOperationPath(application, Keys("collections", "north", "records").Index(0).Key("value"), nil); relevant {
		t.Fatal("later contribution was reported as changing an earlier record")
	}
	origin := historyApplicationOrigin(application, addedPath, nil)
	if len(origin.Locations) != 1 || origin.Locations[0].SourceID != "source-2" {
		t.Fatalf("appended value origin = %#v", origin)
	}
	overlay := historyApplication{
		layer: LayerOverlay,
		value: parseCompositionDocument(t, "overlay", "collections: {north: {records: []}}\n"),
	}
	applyHistoryApplication(&working, overlay, index)
	replaced, present := documentAtPath(working, Keys("collections", "north", "records"))
	if !present || replaced.Kind != document.Sequence || len(replaced.Sequence) != 0 {
		t.Fatalf("ordinary later list replacement = %#v, %v", replaced, present)
	}
}

func TestTierSequenceHistoryReplaysSelectedOperation(t *testing.T) {
	t.Parallel()
	policy := mustCompileSequenceIdentityPolicy(t, []sequenceIdentityRegistration{{
		selector: sequenceIdentitySelector{literalSequenceSelector("records")}, identityFields: []string{"id"},
	}})
	for _, test := range []struct {
		name string
		mode sequenceMode
	}{{"append", sequenceModeAppend}, {"upsert", sequenceModeUpsert}, {"replace", sequenceModeReplace}} {
		t.Run(test.name, func(t *testing.T) {
			mode := test.mode
			lower, diagnostics := composeDocumentsWithPolicy(policy, parseCompositionDocument(t, "lower", "records: [{id: a, removed: old}, {id: b, value: old, removed: old}]\n"))
			if len(diagnostics) != 0 {
				t.Fatal(diagnostics)
			}
			secondID := "d"
			if mode == sequenceModeUpsert {
				secondID = "b"
			}
			declarations := []sequenceDeclarationSpec{{destination: Keys("records"), modePresent: true, mode: mode}}
			higher, diagnostics := composeDocumentsWithCollectionPolicy(policy, lower.collectionPolicies, declarations,
				parseCompositionDocument(t, "first-peer", "records: [{id: c, value: first}]\n"),
				parseCompositionDocument(t, "second-peer", "records: [{id: "+secondID+", value: second}]\n"),
			)
			if len(diagnostics) != 0 {
				t.Fatal(diagnostics)
			}
			assembly := newAssemblyAccumulator(lower)
			if diagnostics := assembly.applyOverlayWithCollectionPolicy(higher.root, higher.origins, higher.collectionPolicies, higher.applications, LayerMain, policy, declarations); len(diagnostics) != 0 {
				t.Fatal(diagnostics)
			}
			if len(assembly.current.applications) != 3 {
				t.Fatalf("source applications = %d, want all three sources", len(assembly.current.applications))
			}
			if mode == sequenceModeUpsert {
				query := Keys("records").Index(1).Key("value")
				if _, relevant := applicationOperationPath(assembly.current.applications[1], query, nil); relevant {
					t.Fatal("first peer was attributed to another peer's upserted record")
				}
				origin := historyApplicationOrigin(assembly.current.applications[2], query, nil)
				if len(origin.Locations) != 1 || origin.Locations[0].SourceID != "second-peer" {
					t.Fatalf("upsert history source = %#v", origin)
				}
			}
			working := parseCompositionDocument(t, "initial", "{}\n")
			index := new(mappingIndex)
			for _, application := range assembly.current.applications {
				applyHistoryApplication(&working, application, index)
			}
			if !configurationValuesEqual(working, assembly.current.root) {
				t.Fatal("tier history differs from structural assembly before decoding")
			}
			overlay := parseCompositionDocument(t, "overlay", "records: [{id: c, value: overlay}]\n")
			declarations[0].mode = sequenceModeUpsert
			if diagnostics := assembly.applyOverlayWithCollectionPolicy(overlay, nil, collectionPolicyScope{}, nil, LayerOverlay, policy, declarations); len(diagnostics) != 0 {
				t.Fatal(diagnostics)
			}
			applyHistoryApplication(&working, assembly.current.applications[3], index)
			if !configurationValuesEqual(working, assembly.current.root) {
				t.Fatal("subsequent overlay history differs from structural assembly")
			}
		})
	}
}

func TestSequenceHistoryPreservesTierReplacementAndEmptyLists(t *testing.T) {
	policy := mustCompileSequenceIdentityPolicy(t, []sequenceIdentityRegistration{
		{selector: sequenceIdentitySelector{literalSequenceSelector("records")}, identityFields: []string{"id"}},
		{selector: sequenceIdentitySelector{literalSequenceSelector("independent")}, identityFields: []string{"id"}},
	})
	first, diagnostics := composeDocumentsWithPolicy(policy,
		parseCompositionDocument(t, "underlay-1a", "records: [{id: shared}]\nindependent: [{id: x}]\n"),
		parseCompositionDocument(t, "underlay-1b", "records: [{id: lower}]\n"),
	)
	if len(diagnostics) != 0 {
		t.Fatalf("first tier diagnostics = %#v", diagnostics)
	}
	for index := range first.applications {
		first.applications[index].layer = LayerUnderlay
	}
	second, diagnostics := composeDocumentsWithPolicy(policy,
		parseCompositionDocument(t, "underlay-2", "records: [{id: shared}]\nindependent: []\n"),
	)
	if len(diagnostics) != 0 {
		t.Fatalf("second tier diagnostics = %#v", diagnostics)
	}
	main, diagnostics := composeDocumentsWithPolicy(policy,
		parseCompositionDocument(t, "main", "records: []\n"),
	)
	if len(diagnostics) != 0 {
		t.Fatalf("main diagnostics = %#v", diagnostics)
	}

	assembly := newAssemblyAccumulator(first)
	if diagnostics := assembly.applyOverlay(second.root, second.origins, second.applications, LayerUnderlay); len(diagnostics) != 0 {
		t.Fatalf("second tier handoff diagnostics = %#v", diagnostics)
	}
	if diagnostics := assembly.applyOverlay(main.root, main.origins, main.applications, LayerMain); len(diagnostics) != 0 {
		t.Fatalf("main handoff diagnostics = %#v", diagnostics)
	}
	if len(assembly.current.applications) != 4 {
		t.Fatalf("retained source applications = %d, want 4", len(assembly.current.applications))
	}

	working := parseCompositionDocument(t, "defaults", "records: [{id: default}]\nindependent: [{id: default}]\n")
	index := new(mappingIndex)
	for _, application := range assembly.current.applications {
		applyHistoryApplication(&working, application, index)
	}
	for path, want := range map[string][]string{
		"/records":     nil,
		"/independent": nil,
	} {
		sequence, present := documentAtPath(working, mustParsePath(t, path))
		if !present || sequence.Kind != document.Sequence || len(sequence.Sequence) != len(want) {
			t.Errorf("replayed replacement %s = %#v, want an explicit empty sequence", path, sequence)
		}
	}

	// The same identity may appear in separate tiers, while each tier still
	// retains its individual source applications for explanation replay.
	if got := []Layer{assembly.current.applications[0].layer, assembly.current.applications[1].layer,
		assembly.current.applications[2].layer, assembly.current.applications[3].layer}; !reflect.DeepEqual(got, []Layer{LayerUnderlay, LayerUnderlay, LayerUnderlay, LayerMain}) {
		t.Fatalf("application layers = %#v", got)
	}
}

func TestHistoryMergeSupportsSemanticIndexedPrefixes(t *testing.T) {
	root := parseCompositionDocument(t, "base", "records: [{id: one, helper: {value: old}}]\n")
	application := historyApplication{
		path:  Keys("records").Index(0).Key("helper"),
		value: parseCompositionDocument(t, "helper", "value: new\n"),
	}
	applyHistoryApplication(&root, application, new(mappingIndex))
	value, present := documentAtPath(root, Keys("records").Index(0).Key("helper").Key("value"))
	if !present || value.Text != "new" {
		t.Fatalf("indexed helper replay = %#v, %v", value, present)
	}

	root = parseCompositionDocument(t, "base", "records: [{id: one, helper: {items: [{id: a}]}}]\n")
	application.value = parseCompositionDocument(t, "helper", "items: [{id: b}]\n")
	application.sequences = []sequenceHistoryContribution{{path: Keys("items"), mode: sequenceHistoryAppend, offset: 1, length: 1}}
	application.sequencesByPath = indexSequenceHistoryContributions(application.sequences)
	applyHistoryApplication(&root, application, new(mappingIndex))
	items, present := documentAtPath(root, Keys("records").Index(0).Key("helper").Key("items"))
	if !present || len(items.Sequence) != 2 {
		t.Fatalf("indexed helper lost its local sequence operation: %#v", items)
	}
}

func TestLayeredUpsertExplanationFollowsStructuralOrder(t *testing.T) {
	t.Parallel()
	type config struct {
		Records []map[string]any `yaml:"records"`
	}
	loaded, err := testGroupedLoad(loadRequest[config]{
		main:      loadInput{source: Bytes("main", []byte("configkit:\n  sequences: [{destination: [records], key: id}]\nrecords: [{id: b, value: new-b}, {id: c, value: new-c}, {id: a, value: new-a}]\n"))},
		underlays: []loadGroup{{inputs: []loadInput{{source: Bytes("lower", []byte("records: [{id: a, value: old-a}, {id: b, value: old-b, removed: old}]\n"))}}}},
	})
	if err != nil {
		t.Fatal(err)
	}
	explanation, ok := loaded.Explain(Keys("records"))
	if !ok || len(explanation.History) == 0 {
		t.Fatal("missing collection history")
	}
	for _, change := range explanation.History {
		if change.Origin.Operation == ChangeDecoding {
			t.Fatal("structural upsert was misreported as a decoding reconciliation")
		}
	}
	if last := explanation.History[len(explanation.History)-1]; last.After.YAML != explanation.Effective.YAML || last.Origin.Layer != LayerMain {
		t.Fatalf("main contribution did not produce the effective collection: %#v", last)
	}
	removed, ok := loaded.Explain(Keys("records").Index(1).Key("removed"))
	if !ok || len(removed.History) == 0 || removed.Effective.Present {
		t.Fatalf("missing displaced field history: %#v, %v", removed, ok)
	}
	if last := removed.History[len(removed.History)-1]; last.After.Present || last.Origin.Layer != LayerMain || last.Origin.Operation == ChangeDecoding {
		t.Fatalf("upsert removal attribution = %#v", last)
	}
}

func TestProjectedSequenceHistoryAgreesAcrossMetadataAndExplanation(t *testing.T) {
	policy := mustCompileSequenceIdentityPolicy(t, []sequenceIdentityRegistration{{selector: sequenceIdentitySelector{literalSequenceSelector("records")}, identityFields: []string{"id"}}})
	composed, diagnostics := composeDocumentsWithPolicy(policy,
		parseCompositionDocument(t, "first", "records: [{id: first, token: public}]"),
		parseCompositionDocument(t, "second", "records: [{id: second, token: private}]"),
	)
	if len(diagnostics) != 0 {
		t.Fatalf("compose diagnostics = %#v", diagnostics)
	}
	path := Keys("records").Index(1).Key("token")
	baseline := &document.Node{Kind: document.Mapping}
	model := sourceHistoryModelForInspection(baseline, composed.root, composed.origins, composed.applications, composed.overlays)
	metadata := Metadata{historyModel: model}
	finalizeEffectiveMetadataPaths(&metadata, composed.root)
	if !metadata.hasHistoricalPath(path) {
		t.Fatalf("projected metadata omitted shifted path %s: %#v", path, metadata.HistoricalPaths())
	}

	inspection := &Inspection{metadata: metadata, history: model, final: composed.root}
	inspection.secrets = classifySecretPaths(nil, func(candidate Path) bool {
		return reflect.DeepEqual(candidate, path)
	}, metadata)
	explanation, ok := inspection.Explain(path)
	if !ok || !explanation.Effective.Redacted {
		t.Fatalf("shifted explanation = %#v, %v", explanation, ok)
	}
	var foundSecondOrigin bool
	for _, change := range explanation.History {
		for _, location := range change.Origin.Locations {
			foundSecondOrigin = foundSecondOrigin || location.SourceID == "second"
		}
	}
	if !foundSecondOrigin {
		t.Fatalf("shifted history lost second source attribution: %#v", explanation.History)
	}
	var rendered bytes.Buffer
	if err := inspection.WriteExplanation(&rendered, path); err != nil {
		t.Fatal(err)
	}
	if !strings.Contains(rendered.String(), `path: "/records/1/token"`) || strings.Contains(rendered.String(), "private") {
		t.Fatalf("shifted explanation rendering is incomplete or unsafe: %s", rendered.String())
	}
}

func TestReplacedProjectedSensitiveRecordRemainsRedacted(t *testing.T) {
	policy := mustCompileSequenceIdentityPolicy(t, []sequenceIdentityRegistration{{selector: sequenceIdentitySelector{literalSequenceSelector("records")}, identityFields: []string{"id"}}})
	composed, diagnostics := composeDocumentsWithPolicy(policy,
		parseCompositionDocument(t, "first", "records: [{id: first, token: public}]"),
		parseCompositionDocument(t, "second", "records: [{id: second, token: PRIVATE-RECORD-CANARY}]"),
	)
	if len(diagnostics) != 0 {
		t.Fatalf("compose diagnostics = %#v", diagnostics)
	}
	applications := append([]historyApplication(nil), composed.applications...)
	applications = append(applications, historyApplication{
		layer: LayerOverlay,
		value: parseCompositionDocument(t, "replacement", "records: [{id: replacement, token: visible}]"),
	})
	final := applications[len(applications)-1].value
	path := Keys("records").Index(1).Key("token")
	baseline := &document.Node{Kind: document.Mapping}
	model := sourceHistoryModelForInspection(baseline, final, nil, applications, nil)
	metadata := Metadata{historyModel: model}
	finalizeEffectiveMetadataPaths(&metadata, final)
	inspection := &Inspection{metadata: metadata, history: model, final: final}
	inspection.secrets = classifySecretPaths(nil, func(candidate Path) bool {
		return reflect.DeepEqual(candidate, path)
	}, metadata)
	explanation, ok := inspection.Explain(path)
	if !ok || explanation.Effective.Present {
		t.Fatalf("replaced shifted record explanation = %#v, %v", explanation, ok)
	}
	var rendered bytes.Buffer
	if err := inspection.WriteExplanation(&rendered, path); err != nil {
		t.Fatal(err)
	}
	if strings.Contains(rendered.String(), "PRIVATE-RECORD-CANARY") || !strings.Contains(rendered.String(), "[REDACTED]") {
		t.Fatalf("replaced sensitive history leaked or was not redacted: %s", rendered.String())
	}
}

func sourceHistoryModelForInspection(baseline, final *document.Node, origins map[string]Origin, applications []historyApplication, records []overlayRecord) *historyModel {
	builder := newHistoryBuilder()
	builder.observeBaseline(baseline)
	builder.setScratch(baseline)
	builder.observeSourceEvidence(final, origins, applications, records)
	builder.model.final = final
	return builder.freeze()
}

func TestMappedUpsertProjectsSensitiveReplacementEvidence(t *testing.T) {
	lowerRoot := parseCompositionDocument(t, "lower", `records:
  - id: first
  - id: middle
  - id: last
    token: MAPPED-SECRET-CANARY
`)
	higherRoot := parseCompositionDocument(t, "higher", `records:
  - id: last
    token: visible
  - id: first
  - id: added
`)
	lower, _ := documentAtPath(lowerRoot, Keys("records"))
	higher, _ := documentAtPath(higherRoot, Keys("records"))
	combined, diagnostics := combineSequence(
		lower, higher,
		sequenceCombinationPolicy(sequenceModeUpsert, "id"),
		sequenceCombinationContext{destination: Keys("records")},
	)
	if len(diagnostics) != 0 {
		t.Fatalf("combine diagnostics = %#v", diagnostics)
	}
	secretPath := Keys("records").Index(2).Key("token")
	secretNode, present := documentAtPath(lowerRoot, Keys("records").Index(2).Key("token"))
	if !present {
		t.Fatal("sensitive source token is missing")
	}
	secretNode.Sensitive = true
	application := historyApplication{
		layer: LayerOverlay, value: higherRoot,
		sequences: []sequenceHistoryContribution{{
			path: Keys("records"), mode: sequenceHistoryMapped,
			items: combined.higherItems, replacements: combined.replacements,
		}},
	}
	application.sequencesByPath = indexSequenceHistoryContributions(application.sequences)
	applications := []historyApplication{{value: lowerRoot}, application}
	replayed := &document.Node{Kind: document.Mapping}
	for _, current := range applications {
		applyHistoryApplication(&replayed, current, new(mappingIndex))
	}
	replayedRecords, _ := documentAtPath(replayed, Keys("records"))
	if !reflect.DeepEqual(replayedRecords.Sequence, combined.value.Sequence) {
		t.Fatalf("replayed value = %#v, want combination = %#v", replayedRecords.Sequence, combined.value.Sequence)
	}
	finalRoot := document.Clone(lowerRoot)
	finalRecords, _ := documentAtPath(finalRoot, Keys("records"))
	finalRecords.Sequence = document.Clone(combined.value).Sequence

	baseline := &document.Node{Kind: document.Mapping}
	model := sourceHistoryModelForInspection(baseline, finalRoot, nil, applications, nil)
	metadata := Metadata{historyModel: model}
	finalizeEffectiveMetadataPaths(&metadata, finalRoot)
	inspection := &Inspection{metadata: metadata, history: model, final: finalRoot}
	secretRule := func(candidate Path) bool { return reflect.DeepEqual(candidate, secretPath) }
	inspection.secrets = classifySecretPaths(nil, secretRule, metadata)
	explanation, ok := inspection.Explain(secretPath)
	if !ok || !explanation.Effective.Redacted {
		t.Fatalf("mapped replacement explanation = %#v, %v", explanation, ok)
	}
	var rendered bytes.Buffer
	if err := inspection.WriteExplanation(&rendered, secretPath); err != nil {
		t.Fatal(err)
	}
	if strings.Contains(rendered.String(), "MAPPED-SECRET-CANARY") || !strings.Contains(rendered.String(), "[REDACTED]") {
		t.Fatalf("mapped replacement history leaked or was not redacted: %s", rendered.String())
	}
}

func TestSequenceHistoryReplaysCombinationEvidence(t *testing.T) {
	tests := []struct {
		name      string
		operation sequenceMode
		lower     string
		higher    string
	}{
		{
			name:      "append",
			operation: sequenceModeAppend,
			lower:     "records: [{id: first}, {id: last}]\n",
			higher:    "records: [{id: added}]\n",
		},
		{
			name:      "upsert",
			operation: sequenceModeUpsert,
			lower: `records:
  - id: first
    label: same
    nested: {removed: lower}
  - id: middle
  - id: last
    nested: {removed: lower}
`,
			higher: `records:
  - id: last
    nested: {kept: higher}
  - id: first
    label: same
  - id: added
`,
		},
		{
			name:      "replace",
			operation: sequenceModeReplace,
			lower:     "records: [{id: discarded}]\n",
			higher:    "records: [{id: replacement}]\n",
		},
	}
	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			lowerRoot := parseCompositionDocument(t, "lower", test.lower)
			higherRoot := parseCompositionDocument(t, "higher", test.higher)
			lower, _ := documentAtPath(lowerRoot, Keys("records"))
			higher, _ := documentAtPath(higherRoot, Keys("records"))
			fields := []string(nil)
			if test.operation != sequenceModeReplace {
				fields = []string{"id"}
			}
			combined, diagnostics := combineSequence(lower, higher, sequenceCombinationPolicy(test.operation, fields...), sequenceCombinationContext{destination: Keys("records")})
			if len(diagnostics) != 0 {
				t.Fatalf("combine diagnostics = %#v", diagnostics)
			}

			application := historyApplication{
				layer: LayerOverlay,
				value: higherRoot,
				sequences: []sequenceHistoryContribution{
					sequenceHistoryContributionForCombination(Keys("records"), test.operation, higher, combined),
				},
			}
			if len(combined.higherItems) != 0 {
				combined.higherItems[0].outputIndex++
			}
			if len(combined.replacements) != 0 {
				combined.replacements[0].outputIndex++
			}
			application.sequencesByPath = indexSequenceHistoryContributions(application.sequences)
			replayed := document.Clone(lowerRoot)
			applyHistoryApplication(&replayed, application, new(mappingIndex))
			got, present := documentAtPath(replayed, Keys("records"))
			if !present || !reflect.DeepEqual(got.Sequence, combined.value.Sequence) {
				t.Fatalf("replayed sequence = %#v, want combination = %#v", got, combined.value.Sequence)
			}
		})
	}
}

func TestMappedSequenceHistoryReplacesWholeRecordsAndKeepsDisplacedEvidence(t *testing.T) {
	lowerRoot := parseCompositionDocument(t, "lower", `records:
  - id: first
    label: same
  - id: middle
  - id: last
    nested: {removed: LOWER-CANARY}
`)
	higherRoot := parseCompositionDocument(t, "higher", `records:
  - id: last
    nested: {kept: higher}
  - id: first
    label: same
  - id: added
`)
	lower, _ := documentAtPath(lowerRoot, Keys("records"))
	higher, _ := documentAtPath(higherRoot, Keys("records"))
	combined, diagnostics := combineSequence(
		lower, higher,
		sequenceCombinationPolicy(sequenceModeUpsert, "id"),
		sequenceCombinationContext{destination: Keys("records")},
	)
	if len(diagnostics) != 0 {
		t.Fatal(diagnostics)
	}
	application := historyApplication{
		layer: LayerOverlay, value: higherRoot,
		sequences: []sequenceHistoryContribution{{
			path: Keys("records"), mode: sequenceHistoryMapped,
			items: combined.higherItems, replacements: combined.replacements,
		}},
	}
	application.sequencesByPath = indexSequenceHistoryContributions(application.sequences)
	clonedApplications := cloneHistoryApplications([]historyApplication{application})
	clonedApplications[0].sequences[0].items[0].outputIndex = 99
	clonedApplications[0].sequences[0].replacements[0].outputIndex = 99
	if application.sequences[0].items[0].outputIndex == 99 || application.sequences[0].replacements[0].outputIndex == 99 {
		t.Fatal("cloned mapped history aliases its source projections")
	}

	query := Keys("records").Index(2).Key("nested").Key("removed")
	operationPath, relevant := applicationOperationPath(application, query, nil)
	if !relevant || operationPath.String() != "/records/2" {
		t.Fatalf("removed descendant operation = %s, %v", operationPath.String(), relevant)
	}
	localPath, ok := historyApplicationLocalPath(application, Keys("records").Index(2).Key("nested").Key("kept"))
	if !ok || localPath.String() != "/records/0/nested/kept" {
		t.Fatalf("mapped effective path localizes to %s, %v", localPath.String(), ok)
	}
	origin := historyApplicationOrigin(application, operationPath, nil)
	if len(origin.Locations) != 1 || origin.Locations[0].SourceID != "higher" {
		t.Fatalf("replacement operation origin = %#v", origin)
	}
	var walkedMappedPath bool
	walkHistoryApplication(application, func(local, effective Path, _ *document.Node) {
		if local.String() == "/records/0/nested/kept" && effective.String() == "/records/2/nested/kept" {
			walkedMappedPath = true
		}
	})
	if !walkedMappedPath {
		t.Fatal("history walk did not project a noncontiguous incoming item")
	}

	replayed := document.Clone(lowerRoot)
	applyHistoryApplication(&replayed, application, new(mappingIndex))
	sequence, _ := documentAtPath(replayed, Keys("records"))
	if _, present := documentAtPath(sequence.Sequence[2], Keys("nested", "removed")); present {
		t.Fatal("whole-record replacement retained an omitted descendant")
	}
	if value, present := documentAtPath(sequence.Sequence[2], Keys("nested", "kept")); !present || value.Text != "higher" {
		t.Fatalf("replacement descendant = %#v, %v", value, present)
	}
	if sequence.Sequence[1].Mapping[0].Value.Text != "middle" {
		t.Fatal("unchanged neighboring record moved or changed")
	}
	if value, present := documentAtPath(lowerRoot, Keys("records").Index(2).Key("nested").Key("removed")); !present || value.Text != "LOWER-CANARY" {
		t.Fatalf("displaced lower contribution was not retained as raw history: %#v, %v", value, present)
	}
	if got := application.sequences[0].replacements; !reflect.DeepEqual(got, combined.replacements) || len(got) != 2 {
		t.Fatalf("replacement evidence lost equal-valued or noncontiguous events: %#v", got)
	}
}

func TestHistorySourceSequenceApplicationsUseAssignedCoordinates(t *testing.T) {
	t.Parallel()

	policy := mustCompileSequenceIdentityPolicy(t, []sequenceIdentityRegistration{{
		selector:       sequenceIdentitySelector{literalSequenceSelector("collections"), anyMappingSequenceSelector(), literalSequenceSelector("records")},
		identityFields: []string{"id"},
	}})
	first := parseCompositionDocument(t, "source-1", "collections: {north: {records: [{id: a, value: first}]}}\n")
	second := parseCompositionDocument(t, "source-2", "collections: {north: {records: [{id: b, value: second}]}}\n")
	composed, diagnostics := composeDocumentsWithPolicy(policy, first, second)
	if len(diagnostics) != 0 {
		t.Fatalf("compose diagnostics = %#v", diagnostics)
	}
	builder := newHistoryBuilder()
	builder.observeSourceEvidence(composed.root, composed.origins, composed.applications, composed.overlays)
	model := builder.freeze()

	appendedPath := Keys("collections", "north", "records").Index(1).Key("value")
	selections := model.selectHistory(appendedPath)
	foundSecond := false
	for _, selection := range selections {
		if selection.role == historyRoleContribution && selection.attribution.origin.Locations[0].SourceID == "source-2" {
			foundSecond = true
		}
	}
	if !foundSecond {
		t.Fatalf("appended source was not attributed at its assigned index: %#v", selections)
	}
	for _, selection := range model.selectHistory(Keys("collections", "north", "records").Index(0).Key("value")) {
		if selection.role == historyRoleContribution && selection.attribution.origin.Locations[0].SourceID == "source-2" {
			t.Fatalf("later source acquired an earlier append index: %#v", selection)
		}
	}
	local, ok := historyApplicationLocalPath(composed.applications[1], appendedPath)
	if !ok || local.String() != "/collections/north/records/0/value" {
		t.Fatalf("assigned append path localizes to %s, %v", local.String(), ok)
	}
}

func TestHistorySourceSequenceReplacementTracksMappedAndWholeSides(t *testing.T) {
	t.Parallel()

	lowerRoot := parseCompositionDocument(t, "lower", `records:
  - id: first
  - id: middle
  - id: last
    nested: {removed: lower}
`)
	higherRoot := parseCompositionDocument(t, "higher", `records:
  - id: last
    nested: {kept: higher}
  - id: first
  - id: added
`)
	lower, _ := documentAtPath(lowerRoot, Keys("records"))
	higher, _ := documentAtPath(higherRoot, Keys("records"))
	combined, diagnostics := combineSequence(
		lower, higher, sequenceCombinationPolicy(sequenceModeUpsert, "id"),
		sequenceCombinationContext{destination: Keys("records")},
	)
	if len(diagnostics) != 0 {
		t.Fatal(diagnostics)
	}
	finalRoot := document.Clone(lowerRoot)
	finalSequence, _ := documentAtPath(finalRoot, Keys("records"))
	*finalSequence = *document.Clone(combined.value)
	lowerOrigins := make(map[string]Origin)
	collectOverlayOrigins(lowerOrigins, lowerRoot, Path{}, LayerMain)
	higherOrigins := make(map[string]Origin)
	collectOverlayOrigins(higherOrigins, higherRoot, Path{}, LayerOverlay)
	assembly := newAssemblyAccumulator(&composedDocument{root: finalRoot, origins: lowerOrigins})
	applyOverlaySequenceEvidence(
		assembly, Keys("records"), lower, higher, combined,
		collectionPolicyResolution{operation: sequenceModeUpsert}, higherOrigins, collectionPolicyScope{}, LayerOverlay,
	)
	higherApplication := historyApplication{
		layer: LayerOverlay, value: higherRoot,
		sequences: []sequenceHistoryContribution{{
			path: Keys("records"), mode: sequenceHistoryMapped,
			items: combined.higherItems, replacements: combined.replacements,
		}},
	}
	higherApplication.sequencesByPath = indexSequenceHistoryContributions(higherApplication.sequences)
	applications := []historyApplication{
		{layer: LayerMain, value: lowerRoot}, higherApplication,
	}
	builder := newHistoryBuilder()
	builder.observeSourceEvidence(finalRoot, assembly.current.origins, applications, assembly.current.overlays)
	model := builder.freeze()

	removedPath := Keys("records").Index(2).Key("nested").Key("removed")
	removed := model.selectHistory(removedPath)
	var lowerContribution, removal bool
	for _, selection := range removed {
		if selection.role == historyRoleContribution && selection.attribution.origin.Locations[0].SourceID == "lower" {
			lowerContribution = true
		}
		if selection.role == historyRoleOperation {
			removal = selection.before && !selection.after
		}
	}
	if !lowerContribution || !removal {
		t.Fatalf("omitted descendant evidence = %#v", removed)
	}

	introducedPath := Keys("records").Index(2).Key("nested").Key("kept")
	introduced := model.selectHistory(introducedPath)
	var higherContribution, introduction bool
	for _, selection := range introduced {
		if selection.role == historyRoleContribution && selection.attribution.origin.Locations[0].SourceID == "higher" {
			higherContribution = true
		}
		if selection.role == historyRoleOperation {
			introduction = !selection.before && selection.after
		}
	}
	if !higherContribution || !introduction {
		t.Fatalf("mapped introduced descendant evidence = %#v", introduced)
	}
	if local, ok := historyApplicationLocalPath(higherApplication, introducedPath); !ok || local.String() != "/records/0/nested/kept" {
		t.Fatalf("mapped path localizes to %s, %v", local.String(), ok)
	}
	if selections := model.selectHistory(Keys("records").Index(2).Key("nested").Key("removed")); len(selections) > 0 {
		for _, selection := range selections {
			if selection.role == historyRoleContribution && selection.attribution.origin.Locations[0].SourceID == "higher" {
				t.Fatalf("unaddressed source acquired removed-record attribution: %#v", selections)
			}
		}
	}

	wholeLower := parseCompositionDocument(t, "whole-lower", "records: [{id: old, nested: {removed: old}}]\n")
	wholeHigher := parseCompositionDocument(t, "whole-higher", "records: [{id: new, nested: {added: new}}]\n")
	wholeLowerSequence, _ := documentAtPath(wholeLower, Keys("records"))
	wholeHigherSequence, _ := documentAtPath(wholeHigher, Keys("records"))
	whole, diagnostics := combineSequence(
		wholeLowerSequence, wholeHigherSequence, sequenceCombinationPolicy(sequenceModeReplace),
		sequenceCombinationContext{destination: Keys("records")},
	)
	if len(diagnostics) != 0 {
		t.Fatal(diagnostics)
	}
	wholeFinal := document.Clone(wholeLower)
	wholeFinalSequence, _ := documentAtPath(wholeFinal, Keys("records"))
	*wholeFinalSequence = *document.Clone(whole.value)
	wholeLowerOrigins := make(map[string]Origin)
	collectOverlayOrigins(wholeLowerOrigins, wholeLower, Path{}, LayerMain)
	wholeHigherOrigins := make(map[string]Origin)
	collectOverlayOrigins(wholeHigherOrigins, wholeHigher, Path{}, LayerOverlay)
	wholeAssembly := newAssemblyAccumulator(&composedDocument{root: wholeFinal, origins: wholeLowerOrigins})
	applyOverlaySequenceEvidence(
		wholeAssembly, Keys("records"), wholeLowerSequence, wholeHigherSequence, whole,
		collectionPolicyResolution{operation: sequenceModeReplace}, wholeHigherOrigins, collectionPolicyScope{}, LayerOverlay,
	)
	wholeHigherApplication := historyApplication{
		layer: LayerOverlay, value: wholeHigher,
		sequences: []sequenceHistoryContribution{sequenceHistoryContributionForCombination(Keys("records"), sequenceModeReplace, wholeHigherSequence, whole)},
	}
	wholeHigherApplication.sequencesByPath = indexSequenceHistoryContributions(wholeHigherApplication.sequences)
	wholeBuilder := newHistoryBuilder()
	wholeBuilder.observeSourceEvidence(wholeFinal, wholeAssembly.current.origins, []historyApplication{
		{layer: LayerMain, value: wholeLower}, wholeHigherApplication,
	}, wholeAssembly.current.overlays)
	wholeModel := wholeBuilder.freeze()
	if len(wholeAssembly.current.overlays) != 1 {
		t.Fatalf("whole-sequence replacement records = %#v", wholeAssembly.current.overlays)
	}
	wholeIntroductions := wholeAssembly.current.overlays[0].introduced
	if len(wholeIntroductions) != 5 {
		t.Fatalf("whole-sequence introduced paths = %#v", wholeIntroductions)
	}
	var introducedNested bool
	for _, fact := range wholeIntroductions {
		if sameConcreteHistoryPath(fact.path, Keys("records").Index(0).Key("nested").Key("added")) {
			introducedNested = true
		}
	}
	if !introducedNested {
		t.Fatalf("whole-sequence nested introduction missing: %#v", wholeIntroductions)
	}
	oldWholePath := Keys("records").Index(0).Key("nested").Key("removed")
	newWholePath := Keys("records").Index(0).Key("nested").Key("added")
	oldWhole := wholeModel.selectHistory(oldWholePath)
	newWhole := wholeModel.selectHistory(newWholePath)
	if len(oldWhole) < 2 || oldWhole[len(oldWhole)-1].role != historyRoleOperation || !oldWhole[len(oldWhole)-1].before || oldWhole[len(oldWhole)-1].after {
		t.Fatalf("whole-sequence removed descendant selections = %#v", oldWhole)
	}
	if len(newWhole) < 2 || newWhole[len(newWhole)-1].role != historyRoleOperation || newWhole[len(newWhole)-1].before || !newWhole[len(newWhole)-1].after {
		t.Fatalf("whole-sequence introduced descendant selections = %#v", newWhole)
	}
}

func mustParsePath(t *testing.T, value string) Path {
	t.Helper()
	path, err := ParsePath(value)
	if err != nil {
		t.Fatal(err)
	}
	return path
}