package engine

import (
	"errors"
	"math"
	"path/filepath"
	"reflect"
	"strings"
	"testing"
	"time"

	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
)

type overrideLifecycleSettings struct {
	Target  string            `yaml:"target"`
	Count   int               `yaml:"count"`
	Enabled bool              `yaml:"enabled"`
	Text    string            `yaml:"text"`
	Items   []string          `yaml:"items"`
	Maybe   *string           `yaml:"maybe"`
	Labels  map[string]string `yaml:"labels"`
	APIKey  Secret            `yaml:"api_key"`
}

type overrideLifecycleConfig struct {
	Version  string                    `yaml:"version"`
	Settings overrideLifecycleSettings `yaml:"settings"`
}

func TestOverridesRunAtHighestInputPrecedenceBeforeResolutionAndValidation(t *testing.T) {
	directory := t.TempDir()
	mainPath := writeImportFile(t, directory, "main.yml", "configkit:\n  imports: [{path: base.yml}]\nversion: v1\n")
	writeImportFile(t, directory, "base.yml", `settings:
  target: base
  count: 4
  enabled: true
  text: base
  items: [base]
  maybe: base
  labels: {base: retained}
  api_key: BASE_SECRET
`)
	writeImportFile(t, directory, filepath.Join("overlays", "testing.yml"), `settings:
  target: overlay
  labels: {overlay: retained}
`)
	validated := false
	overrides := []Override{
		{Path: Keys("settings", "target"), Value: " cli ", Flag: "--target"},
		{Path: Keys("settings", "count"), Value: 0, Flag: "--count"},
		{Path: Keys("settings", "enabled"), Value: false, Flag: "--enabled"},
		{Path: Keys("settings", "text"), Value: "", Flag: "--text"},
		{Path: Keys("settings", "items"), Value: []any{}, Flag: "--items"},
		{Path: Keys("settings", "maybe"), Value: nil, Flag: "--maybe"},
		{Path: Keys("settings", "labels"), Value: map[string]any{"cli": "selected"}, Flag: "--label"},
		{Path: Keys("settings", "api_key"), Value: "CLI_SECRET", Flag: "--api-key-env"},
	}
	result, err := testLoadWithSecretLookup(File(mainPath), func(name string) (string, bool) {
		if name != "CLI_SECRET" {
			t.Fatalf("looked up superseded secret name %q", name)
		}
		return "credential-value", true
	}, Options[overrideLifecycleConfig]{
		Imports: true, Overlay: "testing", Overrides: overrides,
		Definition: Definition[overrideLifecycleConfig]{
			Defaults: func() overrideLifecycleConfig {
				return overrideLifecycleConfig{Settings: overrideLifecycleSettings{Target: "default", Count: 9, Text: "default", Items: []string{"default"}}}
			},
			Version: &VersionRule{Path: Keys("version"), Check: func(version Version, validation *Validation) error {
				if version.Text != "v1" {
					validation.Error(Keys("version"), "unsupported version")
				}
				return nil
			}},
			Resolve: func(configuration *overrideLifecycleConfig, resolution *Resolution) error {
				Normalize(resolution, Keys("settings", "target"), &configuration.Settings.Target, strings.TrimSpace(configuration.Settings.Target), "trimmed target")
				return nil
			},
			Validate: func(configuration *overrideLifecycleConfig, validation *Validation) {
				validated = configuration.Settings.Target == "cli" && configuration.Settings.APIKey.Value() == "credential-value"
			},
		},
	})
	if err != nil {
		t.Fatalf("testLoadWithSecretLookup() error = %v", err)
	}
	want := overrideLifecycleSettings{
		Target: "cli", Labels: map[string]string{"base": "retained", "overlay": "retained", "cli": "selected"},
		APIKey: result.Config.Settings.APIKey,
	}
	if !validated || result.Config.Settings.Count != 0 || result.Config.Settings.Enabled || result.Config.Settings.Text != "" ||
		len(result.Config.Settings.Items) != 0 || result.Config.Settings.Items == nil || result.Config.Settings.Maybe != nil ||
		result.Config.Settings.Target != want.Target || !reflect.DeepEqual(result.Config.Settings.Labels, want.Labels) {
		t.Fatalf("effective settings = %#v", result.Config.Settings)
	}
	sources := result.Sources()
	if len(sources) != 3+len(overrides) || sources[0].Layer != LayerBase || sources[1].Layer != LayerBase || sources[2].Layer != LayerOverlay {
		t.Fatalf("sources = %#v", sources)
	}
	for index, override := range overrides {
		if sources[index+3].Layer != LayerCLI || sources[index+3].Label != override.Flag || sources[index+3].Path != "" {
			t.Fatalf("CLI source %d = %#v", index, sources[index+3])
		}
	}
	history := result.Metadata().History(Keys("settings", "target"))
	wantLayers := []Layer{LayerDefault, LayerBase, LayerOverlay, LayerCLI, LayerResolution}
	if got := historyLayers(history); !reflect.DeepEqual(got, wantLayers) {
		t.Fatalf("target history layers = %#v, want %#v; history %#v", got, wantLayers, history)
	}
}

func TestOverridesSupportDefaultsOnlyMapMergeListReplacementAndNumericKeys(t *testing.T) {
	type config struct {
		Labels  map[string]string `yaml:"labels"`
		Items   []int             `yaml:"items"`
		Numbers map[string]int    `yaml:"numbers"`
		Dynamic any               `yaml:"dynamic"`
	}
	labels := map[string]any{"0": "zero", "new": "value"}
	items := []any{0, 2}
	dynamic := map[string]any{
		"int": int8(1), "uint": uint16(2), "float": float32(3.5), "bool": false,
		"null": nil, "list": []any{"value"}, "map": map[string]any{"key": "value"},
	}
	result, err := testLoad(NoSource(), Options[config]{
		Definition: Definition[config]{Defaults: func() config {
			return config{Labels: map[string]string{"kept": "default"}, Items: []int{9}}
		}},
		Overrides: []Override{
			{Path: parseOverrideTestPath(t, "/labels"), Value: labels, Flag: "--labels"},
			{Path: Keys("items"), Value: items, Flag: "--items"},
			{Path: parseOverrideTestPath(t, "/numbers/0"), Value: 7, Flag: "--number"},
			{Path: Keys("dynamic"), Value: dynamic, Flag: "--dynamic"},
		},
	})
	labels["new"] = "mutated"
	items[0] = 99
	dynamic["int"] = 99
	if err != nil {
		t.Fatal(err)
	}
	if !reflect.DeepEqual(result.Config.Labels, map[string]string{"kept": "default", "0": "zero", "new": "value"}) || !reflect.DeepEqual(result.Config.Items, []int{0, 2}) || result.Config.Numbers["0"] != 7 || result.Config.Dynamic.(map[string]any)["int"] != int64(1) {
		t.Fatalf("defaults-only overrides = %#v", result.Config)
	}
	var effective strings.Builder
	if err := result.WriteEffective(&effective); err != nil {
		t.Fatal(err)
	}
	if strings.Contains(effective.String(), "mutated") || !strings.Contains(effective.String(), "new: value") {
		t.Fatalf("detached effective output = %q", effective.String())
	}
	if info, ok := result.Metadata().Lookup(Keys("labels", "0")); !ok || !info.Explicit || info.Origin.Layer != LayerCLI {
		t.Fatalf("numeric mapping key metadata = %#v, %v", info, ok)
	}
}

func TestOverrideValidationRejectsPathsOverlapValuesAndProtectedTargets(t *testing.T) {
	type config struct {
		Version string         `yaml:"version"`
		Scalar  string         `yaml:"scalar"`
		Items   []string       `yaml:"items"`
		Nested  map[string]any `yaml:"nested"`
		Unknown string         `yaml:"unknown"`
	}
	base := Bytes("override-errors.yml", []byte("version: 4\nscalar: value\nitems: [one]\nnested: {}\n"))
	version := &VersionRule{Path: Keys("version"), Check: func(Version, *Validation) error { return nil }}
	cycle := map[string]any{}
	cycle["self"] = cycle
	deep := any("leaf")
	for range maxDocumentDepth + 1 {
		deep = []any{deep}
	}
	for _, test := range []struct {
		name      string
		overrides []Override
		code      Code
	}{
		{name: "root", overrides: []Override{{Path: Keys(), Value: "x", Flag: "--root"}}, code: CodeOverrideInvalidPath},
		{name: "index", overrides: []Override{{Path: Keys("items").Index(0), Value: "x", Flag: "--item"}}, code: CodeOverrideInvalidPath},
		{name: "parsed sequence index", overrides: []Override{{Path: parseOverrideTestPath(t, "/items/0"), Value: "x", Flag: "--item"}}, code: CodeOverrideInvalidPath},
		{name: "scalar ancestor", overrides: []Override{{Path: Keys("scalar", "child"), Value: "x", Flag: "--child"}}, code: CodeOverrideInvalidPath},
		{name: "duplicate", overrides: []Override{{Path: Keys("scalar"), Value: "a", Flag: "--first"}, {Path: Keys("scalar"), Value: "b", Flag: "--second"}}, code: CodeOverrideDuplicate},
		{name: "overlap", overrides: []Override{{Path: Keys("nested"), Value: map[string]any{}, Flag: "--nested"}, {Path: Keys("nested", "child"), Value: "x", Flag: "--child"}}, code: CodeOverrideOverlap},
		{name: "unsupported", overrides: []Override{{Path: Keys("scalar"), Value: time.Second, Flag: "--scalar"}}, code: CodeOverrideInvalidValue},
		{name: "cycle", overrides: []Override{{Path: Keys("nested"), Value: cycle, Flag: "--nested"}}, code: CodeOverrideInvalidValue},
		{name: "nonfinite", overrides: []Override{{Path: Keys("scalar"), Value: math.Inf(1), Flag: "--scalar"}}, code: CodeOverrideInvalidValue},
		{name: "depth", overrides: []Override{{Path: Keys("nested"), Value: deep, Flag: "--nested"}}, code: CodeOverrideLimitExceeded},
		{name: "record bytes", overrides: []Override{{Path: Keys("scalar"), Value: strings.Repeat("x", maxSourceBytes+1), Flag: "--scalar"}}, code: CodeOverrideLimitExceeded},
		{name: "directive path", overrides: []Override{{Path: Keys("configkit", "x"), Value: true, Flag: "--directive"}}, code: CodeOverrideDirective},
		{name: "directive value", overrides: []Override{{Path: Keys("nested"), Value: map[string]any{"configkit": map[string]any{}}, Flag: "--nested"}}, code: CodeOverrideDirective},
		{name: "version", overrides: []Override{{Path: Keys("version"), Value: "v2", Flag: "--version"}}, code: CodeOverrideVersion},
		{name: "version ancestor", overrides: []Override{{Path: Keys("version"), Value: map[string]any{"child": "v2"}, Flag: "--version"}}, code: CodeOverrideVersion},
		{name: "label", overrides: []Override{{Path: Keys("scalar"), Value: "x", Flag: "\nCANARY"}}, code: CodeOverrideInvalidLabel},
	} {
		t.Run(test.name, func(t *testing.T) {
			result, err := testLoad(base, Options[config]{Definition: Definition[config]{Version: version}, Overrides: test.overrides})
			if result != nil {
				t.Fatalf("result = %#v, want nil", result)
			}
			loadError := requireSecretLoadCode(t, err, test.code)
			if strings.Contains(fmtLoadError(loadError), strings.Repeat("x", 64)) {
				t.Fatal("override diagnostic leaked a raw value")
			}
		})
	}
}

func TestOverrideOverlapIndexPreservesFirstAcceptedSource(t *testing.T) {
	type config struct {
		Nested map[string]any `yaml:"nested"`
	}
	base := Bytes("override-overlap.yml", []byte("nested: {}\n"))
	_, err := testLoad(base, Options[config]{Overrides: []Override{
		{Path: Keys("nested"), Value: map[string]any{}, Flag: "--nested"},
		{Path: Keys("nested", "first"), Value: "one", Flag: "--first"},
		{Path: Keys("nested", "second"), Value: "two", Flag: "--second"},
	}})
	if err == nil {
		t.Fatal("load succeeded with overlapping overrides")
	}
	var loadErr *LoadError
	if !errors.As(err, &loadErr) {
		t.Fatalf("error = %T %v, want *LoadError", err, err)
	}
	diagnostics := loadErr.Diagnostics()
	var conflicts []Diagnostic
	for _, diagnostic := range diagnostics {
		if diagnostic.Code == CodeOverrideOverlap {
			conflicts = append(conflicts, diagnostic)
		}
	}
	if len(conflicts) != 2 {
		t.Fatalf("overlap diagnostics = %#v, want two conflicts", diagnostics)
	}
	for index, path := range []string{"/nested/first", "/nested/second"} {
		if conflicts[index].Path.String() != path || len(conflicts[index].Related) != 1 || conflicts[index].Related[0].SourceID != "source-2" {
			t.Fatalf("conflict[%d] = %#v, want path %q related to first CLI source", index, conflicts[index], path)
		}
	}
}

func TestOverrideOverlapIndexIncludesAcceptedPathWithInvalidValue(t *testing.T) {
	type config struct {
		Nested map[string]any `yaml:"nested"`
	}
	base := Bytes("override-value-overlap.yml", []byte("nested: {}\n"))
	_, err := testLoad(base, Options[config]{Overrides: []Override{
		{Path: Keys("nested"), Value: time.Second, Flag: "--nested"},
		{Path: Keys("nested", "child"), Value: "value", Flag: "--child"},
	}})
	if err == nil {
		t.Fatal("load succeeded with an invalid value and overlapping path")
	}
	var loadErr *LoadError
	if !errors.As(err, &loadErr) {
		t.Fatalf("error = %T %v, want *LoadError", err, err)
	}
	var invalidValue, overlap bool
	for _, diagnostic := range loadErr.Diagnostics() {
		switch diagnostic.Code {
		case CodeOverrideInvalidValue:
			invalidValue = diagnostic.Path.String() == "/nested"
		case CodeOverrideOverlap:
			overlap = diagnostic.Path.String() == "/nested/child" && len(diagnostic.Related) == 1 && diagnostic.Related[0].SourceID == "source-2"
		}
	}
	if !invalidValue || !overlap {
		t.Fatalf("diagnostics = %#v, want invalid parent value and child overlap related to its source", loadErr.Diagnostics())
	}
}

func TestRejectedOverridePathDoesNotCauseOverlap(t *testing.T) {
	type config struct {
		Scalar string `yaml:"scalar"`
	}
	base := Bytes("override-rejected-overlap.yml", []byte("scalar: value\n"))
	_, err := testLoad(base, Options[config]{Overrides: []Override{
		{Path: Keys("scalar", "child"), Value: "invalid", Flag: "--child"},
		{Path: Keys("scalar"), Value: "valid", Flag: "--scalar"},
	}})
	if err == nil {
		t.Fatal("load succeeded with a path traversing a scalar")
	}
	var loadErr *LoadError
	if !errors.As(err, &loadErr) {
		t.Fatalf("error = %T %v, want *LoadError", err, err)
	}
	diagnostics := loadErr.Diagnostics()
	if len(diagnostics) != 1 || diagnostics[0].Code != CodeOverrideInvalidPath || diagnostics[0].Path.String() != "/scalar/child" {
		t.Fatalf("diagnostics = %#v, want only the invalid descendant path", diagnostics)
	}
}

func TestVersionRejectedOverridePathDoesNotCauseOverlap(t *testing.T) {
	type config struct {
		Nested map[string]any `yaml:"nested"`
	}
	base := Bytes("override-version-overlap.yml", []byte("nested: {}\n"))
	version := &VersionRule{Path: Keys("nested", "locked"), Check: func(Version, *Validation) error { return nil }}
	_, err := testLoad(base, Options[config]{
		Definition: Definition[config]{Version: version},
		Overrides: []Override{
			{Path: Keys("nested"), Value: map[string]any{}, Flag: "--nested"},
			{Path: Keys("nested", "other"), Value: "allowed", Flag: "--other"},
		},
	})
	if err == nil {
		t.Fatal("load succeeded despite an override of a schema-version ancestor")
	}
	var loadErr *LoadError
	if !errors.As(err, &loadErr) {
		t.Fatalf("error = %T %v, want *LoadError", err, err)
	}
	diagnostics := loadErr.Diagnostics()
	if len(diagnostics) != 1 || diagnostics[0].Code != CodeOverrideVersion || diagnostics[0].Path.String() != "/nested" {
		t.Fatalf("diagnostics = %#v, want only the protected ancestor path", diagnostics)
	}
}

func TestEscapedOverrideKeysStayDistinctFromMultipleSegments(t *testing.T) {
	type config struct {
		Nested map[string]any `yaml:"nested"`
	}
	base := Bytes("override-escaped-keys.yml", []byte("nested: {}\n"))
	_, err := testLoad(base, Options[config]{Overrides: []Override{
		{Path: Keys("nested", "a/b"), Value: "single key", Flag: "--single"},
		{Path: Keys("nested", "a", "b"), Value: "nested key", Flag: "--nested"},
	}})
	if err != nil {
		t.Fatalf("load rejected distinct escaped path tokens: %v", err)
	}
}

func TestOverrideCannotReplaceSchemaVersionAncestor(t *testing.T) {
	type schemaConfig struct {
		Version string `yaml:"version"`
	}
	type config struct {
		Schema schemaConfig `yaml:"schema"`
	}
	_, err := testLoad(Bytes("version.yml", []byte("schema: {version: 4}\n")), Options[config]{
		Definition: Definition[config]{Version: &VersionRule{Path: Keys("schema", "version"), Check: func(Version, *Validation) error { return nil }}},
		Overrides:  []Override{{Path: Keys("schema"), Value: map[string]any{"other": "value"}, Flag: "--schema"}},
	})
	requireSecretLoadCode(t, err, CodeOverrideVersion)
}

func TestOverrideDecodeFailureUsesFlagSourceWithoutRawValue(t *testing.T) {
	type config struct {
		Count int `yaml:"count"`
	}
	result, err := testLoad(Bytes("base.yml", []byte("count: 1\n")), Options[config]{Overrides: []Override{{
		Path: Keys("missing"), Value: "RAW-ARG-CANARY", Flag: "--missing",
	}}})
	if result != nil {
		t.Fatalf("result = %#v", result)
	}
	var loadError *LoadError
	if !errors.As(err, &loadError) {
		t.Fatalf("error = %T", err)
	}
	diagnostics := loadError.Diagnostics()
	sources := loadError.Sources()
	if len(diagnostics) != 1 || diagnostics[0].Code != CodeDecodeUnknownField || diagnostics[0].Primary == nil ||
		len(sources) != 2 || sources[1].Label != "--missing" || diagnostics[0].Primary.SourceID != sources[1].ID {
		t.Fatalf("diagnostics/sources = %#v / %#v", diagnostics, sources)
	}
	if strings.Contains(fmtLoadError(loadError), "RAW-ARG-CANARY") {
		t.Fatal("decode failure leaked override value")
	}
}

func TestOverrideTypeMismatchUsesNormalStrictDecode(t *testing.T) {
	type config struct {
		Count int `yaml:"count"`
	}
	_, err := testLoad(Bytes("base.yml", []byte("count: 1\n")), Options[config]{Overrides: []Override{{
		Path: Keys("count"), Value: "not-an-integer", Flag: "--count",
	}}})
	loadError := requireSecretLoadCode(t, err, CodeDecodeType)
	if loadError.Diagnostics()[0].Primary == nil || loadError.Sources()[1].Label != "--count" || strings.Contains(fmtLoadError(loadError), "not-an-integer") {
		t.Fatalf("type mismatch diagnostics/sources = %#v / %#v", loadError.Diagnostics(), loadError.Sources())
	}
}

func TestOverrideEqualReplacementStillAppearsInHistory(t *testing.T) {
	type config struct {
		Value string `yaml:"value"`
	}
	result, err := testLoad(Bytes("equal.yml", []byte("value: same\n")), Options[config]{Overrides: []Override{{Path: Keys("value"), Value: "same", Flag: "--value"}}})
	if err != nil {
		t.Fatal(err)
	}
	if got := historyLayers(result.Metadata().History(Keys("value"))); !reflect.DeepEqual(got, []Layer{LayerDefault, LayerBase, LayerCLI}) {
		t.Fatalf("equal override history = %#v", result.Metadata().History(Keys("value")))
	}
}

func TestAffectedOverrideOriginsSortEscapedPointers(t *testing.T) {
	existingInput := parseCompositionDocument(t, "source-1", `values:
  z: old
  a/b: slash
  a~b: tilde
  nested: {x: old}
`)
	existing, diagnostics := composeDocuments(existingInput)
	if len(diagnostics) != 0 {
		t.Fatal(diagnostics)
	}
	incoming := parseCompositionDocument(t, "source-2", `values:
  z: new
  a/b: new
  a~b: new
  nested: {x: new}
`)
	existingValues, ok := documentAtPath(existing.root, Keys("values"))
	if !ok {
		t.Fatal("existing values mapping is missing")
	}
	incomingValues, ok := documentAtPath(incoming, Keys("values"))
	if !ok {
		t.Fatal("incoming values mapping is missing")
	}
	displaced := affectedOverrideOrigins(existingValues, incomingValues, existing.origins, Keys("values"), &mappingIndex{})
	want := []string{"/values", "/values/a~0b", "/values/a~1b", "/values/nested", "/values/nested/x", "/values/z"}
	if len(displaced) != len(want) {
		t.Fatalf("displaced definitions = %d, want %d", len(displaced), len(want))
	}
	for i, definition := range displaced {
		if got := definition.path.String(); got != want[i] {
			t.Fatalf("displaced[%d] path = %q, want %q", i, got, want[i])
		}
	}
}

func TestOverrideAggregateLimitsFailBeforeApplication(t *testing.T) {
	base, diagnostics := composeDocuments(&document.Node{Kind: document.Mapping})
	if len(diagnostics) != 0 {
		t.Fatal(diagnostics)
	}
	base.inputNodes = 1
	_, diagnostics = preparePostStructuralOverrides(overridePreparationInput{
		root: base.root, inputBytes: base.inputBytes, inputNodes: base.inputNodes,
	}, nil, []Override{{Path: Keys("value"), Value: "x", Flag: "--value"}}, nil, importLimits{sources: 1, bytes: 1, nodes: 2})
	if len(diagnostics) != 1 || diagnostics[0].Code != CodeOverrideLimitExceeded || len(base.root.Mapping) != 0 {
		t.Fatalf("bounded preparation = %#v; base %#v", diagnostics, base.root)
	}
}

func TestPreparedOverrideBatchDetachesInputsAndAllocatesSourcesInOrder(t *testing.T) {
	base, diagnostics := composeDocuments(parseCompositionDocument(t, "base", "settings: {}\n"))
	if len(diagnostics) != 0 {
		t.Fatal(diagnostics)
	}
	sources := []SourceInfo{{ID: "source-1", Label: "base", Layer: LayerBase, Kind: SourceKindMapping}}
	firstValue := map[string]any{"nested": map[string]any{"name": "original"}}
	secondValue := []any{map[string]any{"enabled": true}}
	batch, diagnostics := preparePostStructuralOverrides(overridePreparationInput{
		root: base.root, inputBytes: base.inputBytes, inputNodes: base.inputNodes,
	}, sources, []Override{
		{Path: Keys("settings", "first"), Value: firstValue, Flag: "--first"},
		{Path: Keys("settings", "second"), Value: secondValue, Flag: "--second"},
	}, nil, defaultImportLimits())
	if len(diagnostics) != 0 {
		t.Fatalf("prepare post-structural overrides: %#v", diagnostics)
	}
	if len(batch.overrides) != 2 || len(batch.sources) != 3 {
		t.Fatalf("prepared counts = %d overrides, %d sources", len(batch.overrides), len(batch.sources))
	}
	for index, want := range []string{"source-2", "source-3"} {
		if batch.overrides[index].source.ID != want || batch.sources[index+1].ID != want {
			t.Errorf("prepared source %d = %#v / %#v, want %s", index, batch.overrides[index].source, batch.sources[index+1], want)
		}
	}
	if batch.sources[1].Label != "--first" || batch.sources[2].Label != "--second" {
		t.Fatalf("synthetic source order = %#v", batch.sources)
	}

	firstValue["nested"].(map[string]any)["name"] = "changed after preparation"
	preparedName, found := documentAtPath(batch.overrides[0].value, Keys("nested", "name"))
	if !found || preparedName.Text != "original" {
		t.Fatalf("prepared override aliases input value: %#v, %v", preparedName, found)
	}
	preparedName.Text = "changed prepared snapshot"
	if firstValue["nested"].(map[string]any)["name"] != "changed after preparation" {
		t.Fatal("prepared override mutation changed caller input")
	}
	batch.sources[0].Label = "changed batch source"
	if sources[0].Label != "base" {
		t.Fatal("prepared source list aliases the input source list")
	}
	if len(base.root.Mapping) != 1 || base.root.Mapping[0].Value.Kind != document.Mapping || len(base.root.Mapping[0].Value.Mapping) != 0 {
		t.Fatalf("preparation mutated assembled input: %#v", base.root)
	}
}

func TestPostStructuralOverridePreparationRejectsInheritanceDirectives(t *testing.T) {
	base, diagnostics := composeDocuments(parseCompositionDocument(t, "base", "child: {}\nitems: []\n"))
	if len(diagnostics) != 0 {
		t.Fatal(diagnostics)
	}
	tests := []struct {
		name     string
		override Override
		path     string
	}{
		{
			name:     "supplied path",
			override: Override{Path: Keys("child", "extends"), Value: "parent", Flag: "--extends"},
			path:     "/child/extends",
		},
		{
			name:     "nested value",
			override: Override{Path: Keys("items"), Value: []any{map[string]any{"extends": "parent"}}, Flag: "--items"},
			path:     "/items/0/extends",
		},
	}
	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			_, diagnostics := preparePostStructuralOverrides(overridePreparationInput{
				root: base.root, inputBytes: base.inputBytes, inputNodes: base.inputNodes,
			}, nil, []Override{test.override}, nil, defaultImportLimits())
			if len(diagnostics) != 1 || diagnostics[0].Code != CodeOverrideDirective || diagnostics[0].Path.String() != test.path {
				t.Fatalf("post-structural diagnostics = %#v, want directive at %s", diagnostics, test.path)
			}
		})
	}
}

func historyLayers(history []Change) []Layer {
	layers := make([]Layer, len(history))
	for index, change := range history {
		layers[index] = change.Origin.Layer
	}
	return layers
}

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

func fmtLoadError(loadError *LoadError) string {
	var output strings.Builder
	_ = WriteDiagnostics(&output, loadError.Diagnostics())
	return loadError.Error() + output.String()
}

func TestApplyDecodedOverridesUsesSchemaAndPreservesTypedOwnership(t *testing.T) {
	t.Parallel()
	type child struct {
		Name    string `yaml:"name"`
		Enabled bool   `yaml:"enabled"`
	}
	type config struct {
		Nested  child            `yaml:"nested"`
		Labels  map[string]child `yaml:"labels"`
		Items   []child          `yaml:"items"`
		Empty   []string         `yaml:"empty"`
		Count   int              `yaml:"count"`
		Enabled bool             `yaml:"enabled"`
		Label   string           `yaml:"label"`
		Small   namedSmall       `yaml:"small"`
		Text    validatedText    `yaml:"text"`
		Delay   time.Duration    `yaml:"delay"`
		APIKey  Secret           `yaml:"api_key"`
		Maybe   *string          `yaml:"maybe"`
	}
	defaultMaybe := "default"
	defaults := config{
		Nested: child{Name: "default", Enabled: true},
		Labels: map[string]child{"default": {Name: "default", Enabled: true}},
		Items:  []child{{Name: "default", Enabled: true}},
		Empty:  []string{"default"},
		Count:  8, Enabled: true, Label: "default", Small: 7, Text: "default", Delay: time.Second,
		Maybe: &defaultMaybe,
	}
	input := parseDocumentForDecode(t, "nested: {name: source, enabled: true}\nlabels: {old: {name: source, enabled: true}}\nitems: [{name: discarded, enabled: true}]\nempty: [source]\ncount: 7\nenabled: true\nlabel: source\nsmall: 3\ntext: source\ndelay: 1s\napi_key: SOURCE_SECRET\nmaybe: source\n")
	schema, schemaIssue := buildSchema(reflect.TypeFor[config](), testSecretBinding())
	if schemaIssue != nil {
		t.Fatalf("buildSchema() issue = %#v", schemaIssue)
	}
	decoded, decodeIssues := decodeConfiguration(schema, reflect.ValueOf(defaults), input)
	if len(decodeIssues) != 0 {
		t.Fatalf("decodeConfiguration() issues = %#v", decodeIssues)
	}
	batch, diagnostics := preparePostStructuralOverrides(overridePreparationInput{root: input}, nil, []Override{
		{Path: Keys("nested"), Value: map[string]any{"enabled": false}, Flag: "--nested"},
		{Path: Keys("labels"), Value: map[string]any{
			"old": map[string]any{"enabled": false}, "new": map[string]any{"name": "cli"},
		}, Flag: "--labels"},
		{Path: Keys("items"), Value: []any{map[string]any{"name": "replacement"}}, Flag: "--items"},
		{Path: Keys("empty"), Value: []any{}, Flag: "--empty"},
		{Path: Keys("count"), Value: 0, Flag: "--count"},
		{Path: Keys("enabled"), Value: false, Flag: "--enabled"},
		{Path: Keys("label"), Value: "", Flag: "--label"},
		{Path: Keys("small"), Value: 0, Flag: "--small"},
		{Path: Keys("text"), Value: "cli text", Flag: "--text"},
		{Path: Keys("delay"), Value: "250ms", Flag: "--delay"},
		{Path: Keys("api_key"), Value: "CLI_SECRET", Flag: "--api-key"},
		{Path: Keys("maybe"), Value: nil, Flag: "--maybe"},
	}, nil, defaultImportLimits())
	if len(diagnostics) != 0 {
		t.Fatalf("preparePostStructuralOverrides() diagnostics = %#v", diagnostics)
	}
	result, issues := applyDecodedOverrides(schema, decoded, batch, decodeContext{})
	if len(issues) != 0 {
		t.Fatalf("applyDecodedOverrides() issues = %#v", issues)
	}
	got := result.value.Interface().(config)
	if got.Nested != (child{Name: "source", Enabled: false}) || !reflect.DeepEqual(got.Labels, map[string]child{
		"default": {Name: "default", Enabled: true},
		"old":     {Name: "source", Enabled: false},
		"new":     {Name: "cli"},
	}) || !reflect.DeepEqual(got.Items, []child{{Name: "replacement"}}) || got.Count != 0 || got.Enabled ||
		got.Empty == nil || len(got.Empty) != 0 || got.Label != "" || got.Small != 0 ||
		got.Text != "cli text" || got.Delay != 250*time.Millisecond || got.APIKey.name != "CLI_SECRET" || got.Maybe != nil {
		t.Fatalf("post-decode configuration = %#v", got)
	}
	if result.preCLI == result.final || !reflect.DeepEqual(result.preCLI, decoded.final) || len(result.overrides) != len(batch.overrides) {
		t.Fatalf("result snapshots/contributions = pre:%p final:%p overrides:%d", result.preCLI, result.final, len(result.overrides))
	}
	if _, explicit := result.presence["/items/0/enabled"]; explicit {
		t.Fatalf("replacement list inherited presence from its discarded item: %#v", result.presence)
	}
	if result.presence["/items/0/name"].location.SourceID != batch.overrides[2].source.ID ||
		result.presence["/nested"].location.SourceID != "source-1" ||
		result.origins["/items/0/name"].Layer != LayerCLI || result.origins["/nested/name"].Layer != LayerBase ||
		result.origins["/nested/enabled"].Layer != LayerCLI || result.origins["/labels/default/name"].Layer != LayerDefault {
		t.Fatalf("presence/origins = %#v / %#v", result.presence, result.origins)
	}
	if node, ok := documentAtPath(result.final, Keys("items").Index(0).Key("enabled")); !ok || node.Kind != document.Boolean || node.Text != "false" {
		t.Fatalf("replacement list default projection = %#v", node)
	}

	got.Labels["new"] = child{Name: "mutated"}
	result.overrides[0].value.Mapping[0].Value.Text = "changed"
	if decoded.value.Interface().(config).Labels["old"].Name != "source" || batch.overrides[0].value.Mapping[0].Value.Text != "false" {
		t.Fatal("post-decode result mutation reached the pre-CLI value or prepared batch")
	}
}

func TestApplyDecodedOverridesRejectsSchemaErrorsWithoutPartialResult(t *testing.T) {
	t.Parallel()
	type config struct {
		Nested struct {
			Kept int `yaml:"kept"`
		} `yaml:"nested"`
		Count int `yaml:"count"`
	}
	input := parseDocumentForDecode(t, "nested: {kept: 1}\ncount: 2\n")
	schema := mustSchemaFor[config](t)
	decoded, issues := decodeConfiguration(schema, reflect.ValueOf(config{}), input)
	if len(issues) != 0 {
		t.Fatalf("decodeConfiguration() issues = %#v", issues)
	}
	for _, test := range []struct {
		name     string
		override Override
		code     Code
	}{
		{name: "unknown nested field", override: Override{Path: Keys("nested"), Value: map[string]any{"unknown": 1}, Flag: "--nested"}, code: CodeDecodeUnknownField},
		{name: "invalid type", override: Override{Path: Keys("count"), Value: "not an integer", Flag: "--count"}, code: CodeDecodeType},
	} {
		t.Run(test.name, func(t *testing.T) {
			batch, diagnostics := preparePostStructuralOverrides(overridePreparationInput{root: input}, nil, []Override{test.override}, nil, defaultImportLimits())
			if len(diagnostics) != 0 {
				t.Fatalf("preparePostStructuralOverrides() diagnostics = %#v", diagnostics)
			}
			result, issues := applyDecodedOverrides(schema, decoded, batch, decodeContext{})
			if len(issues) == 0 || issues[0].code != test.code {
				t.Fatalf("decode issues = %#v, want code %q", issues, test.code)
			}
			if result.value.IsValid() || result.final != nil {
				t.Fatalf("failed assignment returned a partial result: %#v", result)
			}
			original := decoded.value.Interface().(config)
			if original.Count != 2 || original.Nested.Kept != 1 {
				t.Fatal("failed assignment mutated the pre-CLI decoded value")
			}
		})
	}
}