package engine

import (
	"errors"
	"os"
	"path/filepath"
	"reflect"
	"runtime"
	"testing"
)

type overlayTestConfig struct {
	Settings struct {
		Kept    string `yaml:"kept"`
		Changed string `yaml:"changed"`
		Added   string `yaml:"added"`
	} `yaml:"settings"`
	Values   []string          `yaml:"values"`
	Nullable *string           `yaml:"nullable"`
	Value    any               `yaml:"value"`
	Schema   map[string]string `yaml:"schema"`
}

func TestLoadAppliesSelectedOverlayAfterBaseAndBeforeDefaults(t *testing.T) {
	directory := t.TempDir()
	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
  imports: [{path: base.yml}]
settings:
  kept: main
  changed: base
values: [base, stale]
nullable: base
value: {child: base}
`)
	basePath := writeImportFile(t, directory, "base.yml", "settings: {added: imported}\n")
	overlayPath := writeImportFile(t, directory, "overlays/testing.yml", `settings:
  changed: overlay
values: [overlay]
nullable: null
value: scalar
`)

	result, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{
		Imports: true,
		Overlay: "testing",
		Definition: Definition[overlayTestConfig]{Defaults: func() overlayTestConfig {
			defaultValue := "default"
			return overlayTestConfig{
				Values: []string{"default"}, Nullable: &defaultValue,
				Settings: struct {
					Kept    string `yaml:"kept"`
					Changed string `yaml:"changed"`
					Added   string `yaml:"added"`
				}{Kept: "default", Changed: "default", Added: "default"},
			}
		}},
	})
	if err != nil {
		t.Fatal(err)
	}
	if result.Config.Settings.Kept != "main" || result.Config.Settings.Changed != "overlay" || result.Config.Settings.Added != "imported" {
		t.Fatalf("settings = %#v", result.Config.Settings)
	}
	if !reflect.DeepEqual(result.Config.Values, []string{"overlay"}) || result.Config.Nullable != nil || result.Config.Value != "scalar" {
		t.Fatalf("overlay values = values %#v nullable %#v value %#v", result.Config.Values, result.Config.Nullable, result.Config.Value)
	}
	sources := result.Sources()
	wantPaths := []string{canonicalTestPath(t, mainPath), canonicalTestPath(t, basePath), canonicalTestPath(t, overlayPath)}
	gotPaths := make([]string, len(sources))
	for index, source := range sources {
		gotPaths[index] = source.Path
	}
	if !reflect.DeepEqual(gotPaths, wantPaths) || sources[2].Layer != LayerOverlay {
		t.Fatalf("sources = %#v", sources)
	}
	changed, _ := result.Metadata().Lookup(Keys("settings", "changed"))
	kept, _ := result.Metadata().Lookup(Keys("settings", "kept"))
	if changed.Origin.Layer != LayerOverlay || changed.Origin.Locations[0].SourceID != "source-3" || kept.Origin.Layer != LayerBase {
		t.Fatalf("origins = changed %#v kept %#v", changed, kept)
	}
	if _, ok := result.Metadata().Lookup(Keys("value", "child")); ok {
		t.Fatal("removed child remains effective")
	}
	childHistory := result.Metadata().History(Keys("value", "child"))
	if len(childHistory) < 2 || childHistory[len(childHistory)-1].Path.String() != "/value" || childHistory[len(childHistory)-1].Origin.Layer != LayerOverlay {
		t.Fatalf("removed child history = %#v", childHistory)
	}
	if _, ok := result.Metadata().Lookup(Keys("values").Index(1)); ok {
		t.Fatal("removed sequence index remains effective")
	}
	indexHistory := result.Metadata().History(Keys("values").Index(1))
	if len(indexHistory) < 2 || indexHistory[len(indexHistory)-1].Path.String() != "/values" {
		t.Fatalf("removed sequence history = %#v", indexHistory)
	}
}

func TestLoadSelectedOverlayAppliesCollectionOperationsAndEvidence(t *testing.T) {
	t.Parallel()
	type item struct {
		ID       string `yaml:"id"`
		Value    string `yaml:"value"`
		Children []item `yaml:"children"`
	}
	type config struct {
		Items []item `yaml:"items"`
	}
	tests := []struct {
		name    string
		mode    string
		overlay string
		want    []item
	}{
		{
			name: "append",
			mode: "append",
			overlay: `configkit:
  sequences:
    - destination: [items]
      key: id
      mode: append
items: [{id: c, value: added}]
`,
			want: []item{{ID: "a", Value: "old"}, {ID: "b", Value: "kept"}, {ID: "c", Value: "added"}},
		},
		{
			name: "upsert replaces complete records at retained positions",
			mode: "upsert",
			overlay: `configkit:
  sequences:
    - destination: [items]
      key: id
      mode: upsert
items: [{id: a, value: new}]
`,
			want: []item{{ID: "a", Value: "new"}, {ID: "b", Value: "kept"}},
		},
		{
			name: "replace",
			mode: "replace",
			overlay: `configkit:
  sequences:
    - destination: [items]
      key: id
      mode: replace
items: [{id: c, value: replacement}]
`,
			want: []item{{ID: "c", Value: "replacement"}},
		},
	}
	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			directory := t.TempDir()
			mainPath := writeImportFile(t, directory, "main.yml", "items: [{id: a, value: old, children: [{id: child}]}, {id: b, value: kept}]\n")
			writeImportFile(t, directory, "overlays/testing.yml", test.overlay)
			result, err := testLoad[config](File(mainPath), Options[config]{Overlay: "testing"})
			if err != nil {
				t.Fatal(err)
			}
			if len(result.Config.Items) != len(test.want) {
				t.Fatalf("items = %#v, want %#v", result.Config.Items, test.want)
			}
			for index, want := range test.want {
				if result.Config.Items[index].ID != want.ID || result.Config.Items[index].Value != want.Value {
					t.Fatalf("items[%d] = %#v, want id %q value %q", index, result.Config.Items[index], want.ID, want.Value)
				}
			}
			if _, found := result.Metadata().Lookup(Keys("configkit")); found {
				t.Fatal("overlay collection controls reached application metadata")
			}
			if test.mode == "append" {
				base, _ := result.Metadata().Lookup(Keys("items").Index(0).Key("value"))
				added, _ := result.Metadata().Lookup(Keys("items").Index(2).Key("value"))
				if base.Origin.Layer != LayerBase || added.Origin.Layer != LayerOverlay {
					t.Fatalf("append origins = base %#v added %#v", base.Origin, added.Origin)
				}
				history := result.Metadata().History(Keys("items").Index(2).Key("value"))
				if len(history) == 0 || history[len(history)-1].Origin.Layer != LayerOverlay {
					t.Fatalf("append history = %#v", history)
				}
			}
			if test.mode == "upsert" {
				if _, found := result.Metadata().Lookup(Keys("items").Index(0).Key("children").Index(0)); found {
					t.Fatal("upsert retained a discarded child")
				}
				history := result.Metadata().History(Keys("items").Index(0).Key("children").Index(0))
				if len(history) < 2 {
					t.Fatalf("discarded child history = %#v", history)
				}
			}
		})
	}
}

func TestLoadSelectedOverlayReconcilesPendingAndRetainedCollectionPolicy(t *testing.T) {
	t.Parallel()
	requireCode := func(t *testing.T, main, overlay string, code Code) {
		t.Helper()
		directory := t.TempDir()
		mainPath := writeImportFile(t, directory, "main.yml", main)
		writeImportFile(t, directory, "overlays/testing.yml", overlay)
		_, err := testLoad[ordinarySequenceConfig](File(mainPath), Options[ordinarySequenceConfig]{Overlay: "testing"})
		var loadError *LoadError
		if !errors.As(err, &loadError) || len(loadError.Diagnostics()) == 0 || loadError.Diagnostics()[0].Code != code {
			t.Fatalf("load error = %#v, want %s", err, code)
		}
	}
	t.Run("key only validates retained records", func(t *testing.T) {
		requireCode(t, "items: [{id: duplicate}, {id: duplicate}]\n", `configkit:
  sequences:
    - destination: [items]
      key: id
`, CodeSequenceConflict)
	})

	t.Run("mode only retains lower identity", func(t *testing.T) {
		directory := t.TempDir()
		mainPath := writeImportFile(t, directory, "main.yml", `configkit:
  sequences:
    - destination: [items]
      key: id
      mode: append
items: [{id: base}]
`)
		writeImportFile(t, directory, "overlays/testing.yml", `configkit:
  sequences:
    - destination: [items]
      mode: append
items: [{id: overlay}]
`)
		result, err := testLoad[ordinarySequenceConfig](File(mainPath), Options[ordinarySequenceConfig]{Overlay: "testing"})
		if err != nil {
			t.Fatal(err)
		}
		if !reflect.DeepEqual(result.Config.Items, []ordinarySequenceItem{{ID: "base"}, {ID: "overlay"}}) {
			t.Fatalf("items = %#v", result.Config.Items)
		}
	})

	t.Run("lower explicit mode remains active when overlay omits it", func(t *testing.T) {
		directory := t.TempDir()
		mainPath := writeImportFile(t, directory, "main.yml", `configkit:
  sequences:
    - destination: [items]
      key: id
      mode: append
items: [{id: base}]
`)
		writeImportFile(t, directory, "overlays/testing.yml", "items: [{id: overlay}]\n")
		result, err := testLoad[ordinarySequenceConfig](File(mainPath), Options[ordinarySequenceConfig]{Overlay: "testing"})
		if err != nil || !reflect.DeepEqual(result.Config.Items, []ordinarySequenceItem{{ID: "base"}, {ID: "overlay"}}) {
			t.Fatalf("retained operation = %#v, %v", result, err)
		}
	})

	t.Run("overlay identity must agree with retained identity", func(t *testing.T) {
		requireCode(t, `configkit:
  sequences:
    - destination: [items]
      key: id
items: [{id: base}]
`, `configkit:
  sequences:
    - destination: [items]
      key: slug
items: [{id: overlay}]
`, CodeSequenceConflict)
	})

	t.Run("replace accepts null and append rejects it", func(t *testing.T) {
		for _, test := range []struct {
			mode string
			want Code
		}{
			{mode: "replace"},
			{mode: "append", want: CodeSequenceInvalid},
		} {
			overlay := "configkit:\n  sequences:\n    - destination: [items]\n      key: id\n      mode: " + test.mode + "\nitems: null\n"
			if test.want != "" {
				requireCode(t, "items: [{id: base}]\n", overlay, test.want)
				continue
			}
			directory := t.TempDir()
			mainPath := writeImportFile(t, directory, "main.yml", "items: [{id: base}]\n")
			writeImportFile(t, directory, "overlays/testing.yml", overlay)
			result, err := testLoad[ordinarySequenceConfig](File(mainPath), Options[ordinarySequenceConfig]{Overlay: "testing"})
			if err != nil || result.Config.Items != nil {
				t.Fatalf("replace null = %#v, %v", result, err)
			}
		}
	})

	t.Run("empty contributions and kind mismatches", func(t *testing.T) {
		for _, test := range []struct {
			name, mode, value string
			want              int
			wantCode          Code
		}{
			{name: "append empty", mode: "append", value: "[]", want: 1},
			{name: "upsert empty", mode: "upsert", value: "[]", want: 1},
			{name: "replace empty", mode: "replace", value: "[]", want: 0},
			{name: "append mapping", mode: "append", value: "{id: overlay}", wantCode: CodeSequenceInvalid},
		} {
			t.Run(test.name, func(t *testing.T) {
				overlay := "configkit:\n  sequences:\n    - destination: [items]\n      key: id\n      mode: " + test.mode + "\nitems: " + test.value + "\n"
				if test.wantCode != "" {
					requireCode(t, "items: [{id: base}]\n", overlay, test.wantCode)
					return
				}
				directory := t.TempDir()
				mainPath := writeImportFile(t, directory, "main.yml", "items: [{id: base}]\n")
				writeImportFile(t, directory, "overlays/testing.yml", overlay)
				result, err := testLoad[ordinarySequenceConfig](File(mainPath), Options[ordinarySequenceConfig]{Overlay: "testing"})
				if err != nil || len(result.Config.Items) != test.want {
					t.Fatalf("%s result = %#v, %v", test.name, result, err)
				}
			})
		}
	})
}

func TestLoadSelectedOverlayKeepsCollectionPoliciesIndependent(t *testing.T) {
	t.Parallel()
	directory := t.TempDir()
	mainPath := writeImportFile(t, directory, "main.yml", `configkit:
  sequences:
    - destination: [items]
      key: id
      mode: append
    - destination: [catalog, items]
      key: id
      mode: append
items: [{id: base}]
catalog: {items: [{id: catalog-base}]}
`)
	writeImportFile(t, directory, "overlays/testing.yml", `configkit:
  sequences:
    - destination: [items]
      mode: upsert
    - destination: [catalog, items]
      mode: append
items: [{id: base}]
catalog: {items: [{id: catalog-overlay}]}
`)
	result, err := testLoad[ordinarySequenceConfig](File(mainPath), Options[ordinarySequenceConfig]{Overlay: "testing"})
	if err != nil {
		t.Fatal(err)
	}
	if !reflect.DeepEqual(result.Config.Items, []ordinarySequenceItem{{ID: "base"}}) ||
		!reflect.DeepEqual(result.Config.Catalog.Items, []ordinarySequenceItem{{ID: "catalog-base"}, {ID: "catalog-overlay"}}) {
		t.Fatalf("independent overlay policies = items %#v, catalog %#v", result.Config.Items, result.Config.Catalog.Items)
	}
}

func TestLoadOverlaySelectionUsesOneFixedYAMLFile(t *testing.T) {
	directory := t.TempDir()
	mainPath := writeImportFile(t, directory, "main.yml", "settings: {kept: base}\n")
	writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: selected}\n")
	writeImportFile(t, directory, "profiles/testing.yml", "settings: {changed: legacy}\n")
	writeImportFile(t, directory, "overlays/default.yml", "settings: {changed: forbidden}\n")

	for _, name := range []string{"", "default"} {
		result, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{Overlay: name})
		if err != nil || result.Config.Settings.Changed != "" || len(result.Sources()) != 1 {
			t.Fatalf("inactive overlay %q = %#v, %v", name, result, err)
		}
	}
	selected, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{Overlay: "testing"})
	if err != nil || selected.Config.Settings.Changed != "selected" || len(selected.Sources()) != 2 ||
		selected.Sources()[1].Label != "overlays/testing.yml" || selected.Sources()[1].Layer != LayerOverlay {
		t.Fatalf("selected overlay = %#v, %v", selected, err)
	}

	t.Run("legacy directory is not selected", func(t *testing.T) {
		legacyDirectory := t.TempDir()
		legacyMain := writeImportFile(t, legacyDirectory, "main.yml", "settings: {kept: base}\n")
		writeImportFile(t, legacyDirectory, "profiles/testing.yml", "settings: {changed: legacy}\n")
		requireOverlayLoadCode(t, File(legacyMain), Options[overlayTestConfig]{Overlay: "testing"}, CodeOverlayMissing)
	})

	for _, name := range []string{"../testing", "testing.yml", "one,two", "with space", "é", "bad\x00name"} {
		t.Run(name, func(t *testing.T) {
			requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: name}, CodeOptionsInvalid)
		})
	}
	requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "missing"}, CodeOverlayMissing)
	writeImportFile(t, directory, "overlays/fallback.yaml", "settings: {changed: fallback}\n")
	requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "fallback"}, CodeOverlayMissing)
}

func TestLoadOverlayRejectsDirectivesVersionsAndBaseAliases(t *testing.T) {
	versionRule := &VersionRule{Path: Keys("schema", "version"), Check: func(version Version, _ *Validation) error {
		if !version.Present || version.Text != "4" {
			return errors.New("unexpected version")
		}
		return nil
	}}
	for _, test := range []struct {
		name    string
		overlay string
		code    Code
	}{
		{name: "root directive", overlay: "configkit: {}\n", code: CodeOverlayDirective},
		{name: "nested directive", overlay: "settings: {configkit: {}}\n", code: CodeOverlayDirective},
		{name: "equal integer version", overlay: "schema: {version: 4}\n", code: CodeOverlayVersion},
		{name: "ancestor scalar", overlay: "schema: null\n", code: CodeOverlayVersion},
	} {
		t.Run(test.name, func(t *testing.T) {
			directory := t.TempDir()
			mainPath := writeImportFile(t, directory, "main.yml", "schema: {version: 4}\n")
			writeImportFile(t, directory, "overlays/testing.yml", test.overlay)
			requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing", Definition: Definition[overlayTestConfig]{Version: versionRule}}, test.code)
		})
	}

	t.Run("mapping sibling is allowed", func(t *testing.T) {
		directory := t.TempDir()
		mainPath := writeImportFile(t, directory, "main.yml", "schema: {version: 4}\n")
		writeImportFile(t, directory, "overlays/testing.yml", "schema: {other: allowed}\n")
		result, err := testLoad[overlayTestConfig](File(mainPath), Options[overlayTestConfig]{Overlay: "testing", Definition: Definition[overlayTestConfig]{Version: versionRule}})
		if err != nil || result.Config.Schema["other"] != "allowed" {
			t.Fatalf("mapping sibling = %#v, %v", result, err)
		}
	})

	t.Run("overlay aliases imported base", func(t *testing.T) {
		directory := t.TempDir()
		mainPath := writeImportFile(t, directory, "main.yml", "configkit: {imports: [{path: overlays/testing.yml}]}\n")
		writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: value}\n")
		requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Imports: true, Overlay: "testing"}, CodeOverlayRepeated)
	})
}

func TestLoadOverlayKeepsBaseFailuresAndFilesystemContainment(t *testing.T) {
	t.Run("base parse precedes overlay", func(t *testing.T) {
		directory := t.TempDir()
		mainPath := writeImportFile(t, directory, "main.yml", "settings: [\n")
		writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: overlay}\n")
		requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing"}, CodeYAMLInvalid)
	})

	t.Run("overlay parse", func(t *testing.T) {
		directory := t.TempDir()
		mainPath := writeImportFile(t, directory, "main.yml", "{}\n")
		writeImportFile(t, directory, "overlays/testing.yml", "settings: [\n")
		loadError := requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing"}, CodeYAMLInvalid)
		if loadError.Diagnostics()[0].Primary.SourceID != "source-2" || len(loadError.Sources()) != 2 {
			t.Fatalf("overlay parse attribution = %#v / %#v", loadError.Diagnostics(), loadError.Sources())
		}
	})

	if runtime.GOOS == "linux" || runtime.GOOS == "darwin" {
		t.Run("symlink escape", func(t *testing.T) {
			root := t.TempDir()
			outside := t.TempDir()
			outsideOverlay := writeImportFile(t, outside, "testing.yml", "settings: {changed: outside}\n")
			if err := os.Mkdir(filepath.Join(root, "overlays"), 0o755); err != nil {
				t.Fatal(err)
			}
			if err := os.Symlink(outsideOverlay, filepath.Join(root, "overlays/testing.yml")); err != nil {
				t.Skipf("symlinks unavailable: %v", err)
			}
			mainPath := writeImportFile(t, root, "main.yml", "{}\n")
			requireOverlayLoadCode(t, File(mainPath), Options[overlayTestConfig]{Overlay: "testing"}, CodeOverlayOutsideRoot)
		})
	}

	t.Run("byte source context", func(t *testing.T) {
		directory := t.TempDir()
		writeImportFile(t, directory, "overlays/testing.yml", "settings: {changed: selected}\n")
		result, err := testLoad[overlayTestConfig](Bytes("s3://bucket/main.yml", []byte("{}\n")), Options[overlayTestConfig]{
			Overlay: "testing", Filesystem: &FilesystemContext{BaseDir: directory, Root: directory},
		})
		if err != nil || result.Config.Settings.Changed != "selected" {
			t.Fatalf("byte overlay = %#v, %v", result, err)
		}
		requireOverlayLoadCode(t, Bytes("memory.yml", []byte("{}\n")), Options[overlayTestConfig]{Overlay: "testing"}, CodeOptionsInvalid)
	})
}

func TestLoadOverlayCountsAgainstAggregateBudgets(t *testing.T) {
	for _, test := range []struct {
		name   string
		limits func(parsedSource, int) importLimits
	}{
		{name: "source count", limits: func(_ parsedSource, _ int) importLimits {
			return importLimits{sources: 1, bytes: maxTotalBytes, nodes: maxDocumentNodes}
		}},
		{name: "aggregate bytes", limits: func(main parsedSource, overlayBytes int) importLimits {
			return importLimits{sources: 2, bytes: main.bytes + int64(overlayBytes) - 1, nodes: maxDocumentNodes}
		}},
		{name: "aggregate nodes", limits: func(main parsedSource, _ int) importLimits {
			return importLimits{sources: 2, bytes: maxTotalBytes, nodes: countInputNodes(main.document) + 1}
		}},
	} {
		t.Run(test.name, func(t *testing.T) {
			directory := t.TempDir()
			mainPath := writeImportFile(t, directory, "main.yml", "{}\n")
			overlayData := "settings: {changed: selected}\n"
			writeImportFile(t, directory, "overlays/testing.yml", overlayData)
			main, diagnostics := parseSource(File(mainPath), "source-1", defaultParseLimits())
			if len(diagnostics) != 0 {
				t.Fatal(diagnostics)
			}
			base, diagnostics := composeDocuments(main.document)
			if len(diagnostics) != 0 {
				t.Fatal(diagnostics)
			}
			base.inputBytes = main.bytes
			base.inputNodes = countInputNodes(main.document)
			_, _, diagnostics = loadSelectedOverlayDocument(File(mainPath), nil, main, base, sourceInfos(main.source), "testing", nil, test.limits(main, len(overlayData)))
			if len(diagnostics) == 0 || diagnostics[0].Code != CodeOverlayLimitExceeded {
				t.Fatalf("diagnostics = %#v", diagnostics)
			}
		})
	}
}

func requireOverlayLoadCode(t *testing.T, source Source, options Options[overlayTestConfig], code Code) *LoadError {
	t.Helper()
	result, err := testLoad[overlayTestConfig](source, options)
	if result != nil || err == nil {
		t.Fatalf("result, error = %#v, %v", result, err)
	}
	var loadError *LoadError
	if !errors.As(err, &loadError) {
		t.Fatalf("error type = %T", err)
	}
	diagnostics := loadError.Diagnostics()
	if len(diagnostics) == 0 || diagnostics[0].Code != code {
		t.Fatalf("diagnostics = %#v, want %s", diagnostics, code)
	}
	return loadError
}