package engine

import (
	"os"
	"reflect"

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

// Definition contains reusable application rules for a configuration type.
// Secret is a pure predicate that can add sensitivity to semantic paths.
// Definitions should be treated as read-only after being shared.
type Definition[T any] struct {
	Defaults func() T
	Resolve  func(*T, *Resolution) error
	Validate func(*T, *Validation)
	Version  *VersionRule
	Secret   func(Path) bool

	sequenceIdentityRegistrations []sequenceIdentityRegistration
}

// Options contains the application definition and per-load input selections.
// Imports enables traversal of declarations in a selected main document; an
// absent source has no main declarations to traverse. Overlay selects one fixed
// overlay and requires filesystem context for NoSource. Overrides contain only
// values explicitly supplied by an application CLI.
type Options[T any] struct {
	Definition        Definition[T]
	Imports           bool
	Overlay           string
	Filesystem        *FilesystemContext
	Overrides         []Override
	SourceVersionMode sourceVersionMode
	ImportDefaults    ImportDefaults
	destination       Path
	placementMode     placementMode
}

// FilesystemContext supplies filesystem roots for imports and overlays. For an
// absent host input, Root is required and BaseDir may be omitted to use Root as
// the import base. Native contexts still require both BaseDir and Root.
type FilesystemContext struct {
	BaseDir string
	Root    string
	FS      *Filesystem
}

// Override describes one explicitly supplied application override. Value uses
// parser-neutral built-in scalars, nil, []any, or map[string]any; Flag is a safe
// display name and must not contain a raw argument or value.
type Override struct {
	Path  Path
	Value any
	Flag  string
}

// Resolution exposes entry-state input provenance, surviving-input presence, and
// audited application resolution changes. A resolver must not retain or
// concurrently use the context.
type Resolution struct {
	state *resolutionState
}

// VersionRule declares the input path and application checker for a schema version.
// At that path, string and decimal-integer input is supplied as Version.Text.
type VersionRule struct {
	Path  Path
	Check func(Version, *Validation) error
}

// Version preserves the absent, null, and textual states of a schema-version input.
// Text is the exact spelling of accepted string or decimal-integer input.
type Version struct {
	Present bool
	Null    bool
	Text    string
}

// Loaded is a short-lived generic carrier for a successful configuration load.
// Inspection is frozen independently of Config and does not retain application values.
type Loaded[T any] struct {
	Config     T
	Inspection *Inspection
}

// Inspection owns frozen load snapshots and detached query state.
type Inspection struct {
	metadata         Metadata
	sources          []SourceInfo
	contexts         map[string]ResourceContext
	diagnostics      []Diagnostic
	baseline         *document.Node
	input            *document.Node
	inputOrigins     map[string]Origin
	preCLI           *document.Node
	preCLIOrigins    map[string]Origin
	postDecodeApps   []historyApplication
	final            *document.Node
	immutableLookup  *documentLookup
	resolution       []resolutionSnapshot
	resolutionReplay []resolutionSnapshot
	applications     []historyApplication
	inheritance      []inheritanceOperation
	secrets          map[string]bool
	secretReferences map[string]string
}

// Metadata returns detached effective presence, origin, and history records.
func (r *Inspection) Metadata() Metadata {
	if r == nil {
		return Metadata{}
	}
	return cloneMetadata(r.metadata)
}

// Sources returns a detached list of sources used by the load.
func (r *Inspection) Sources() []SourceInfo {
	if r == nil {
		return nil
	}
	return cloneSourceInfos(r.sources)
}

// SourceContext returns a passive filesystem view for an acquired source.
// Unknown IDs and sources without a filesystem context return false.
func (r *Inspection) SourceContext(id string) (ResourceContext, bool) {
	if r == nil {
		return ResourceContext{}, false
	}
	context, ok := r.contexts[id]
	return context, ok
}

// Diagnostics returns detached nonfatal diagnostics from the load.
func (r *Inspection) Diagnostics() []Diagnostic {
	if r == nil {
		return nil
	}
	return cloneDiagnostics(r.diagnostics)
}

// Load parses and strictly decodes zero or one selected source, explicitly enabled
// imports, and one selected overlay. It accepts at most one Options value and
// returns no result when any error is reported.
func Load[T any](source Source, secrets SecretBinding, supplied ...Options[T]) (*Loaded[T], error) {
	return loadWithSecretLookup(source, secrets, os.LookupEnv, supplied...)
}

func loadWithSecretLookup[T any](source Source, secrets SecretBinding, lookup secretLookup, supplied ...Options[T]) (*Loaded[T], error) {
	return loadWithSecretLookupLimit(source, secrets, lookup, historyNodeLimit, supplied...)
}

func loadWithSecretLookupLimit[T any](source Source, secrets SecretBinding, lookup secretLookup, historyLimit int, supplied ...Options[T]) (*Loaded[T], error) {
	if len(supplied) > 1 {
		return nil, (&diagnosticAccumulator{diagnostics: []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "Load accepts at most one options value")}}).loadError()
	}
	var options Options[T]
	if len(supplied) == 1 {
		options = supplied[0]
	}
	input, diagnostics := normalizeInput(loadInput{
		source: source, imports: options.Imports, filesystem: options.Filesystem,
		destination: options.destination.clone(), placementMode: options.placementMode,
	}, options.Overlay)
	defaults, policy, settingsDiagnostics := loadSettings(options.ImportDefaults, options.Definition, options.SourceVersionMode)
	diagnostics = append(diagnostics, settingsDiagnostics...)
	diagnostics = append(diagnostics, overlayOptionDiagnostics(options.Overlay)...)
	if len(diagnostics) != 0 {
		return nil, (&diagnosticAccumulator{diagnostics: diagnostics}).loadError()
	}
	definition := options.Definition
	definition.sequenceIdentityRegistrations = nil
	request := loadRequest[T]{
		main:       input,
		definition: definition, importDefaults: defaults, sequencePolicy: policy, overlay: options.Overlay,
		overrides: options.Overrides, ordinary: true,
		sourceVersionMode: options.SourceVersionMode,
		effectiveVersion:  effectiveSourceVersionRuleForPlacement(options.Definition.Version, input.destination, options.SourceVersionMode, input.placementMode),
	}
	return executeLoadRequest(request, secrets, lookup, historyLimit)
}

func executeLoadRequest[T any](request loadRequest[T], secrets SecretBinding, lookup secretLookup, historyLimit int) (*Loaded[T], error) {
	accumulator := diagnosticAccumulator{}
	accounting := &importAccounting{}
	policy := acquisitionPolicy{
		importDefaults: request.importDefaults,
		sequencePolicy: request.sequencePolicy,
		importLimits:   defaultImportLimits(),
	}

	var schema *schemaDescriptor
	if request.sourceVersionMode != sourceVersionModeDefault {
		var schemaIssue *schemaIssue
		schema, schemaIssue = buildSchema(reflect.TypeFor[T](), secrets)
		if schemaIssue != nil {
			accumulator.add(diagnosticFromSchemaIssue(schemaIssue))
			return nil, accumulator.loadError()
		}
	}
	versionState := &sourceVersionState{
		localRule: request.definition.Version, effectiveRule: request.protectionVersion(), mode: request.sourceVersionMode,
	}
	state := &acquisitionState{accounting: accounting, versionState: versionState}
	accumulator.versionState = versionState
	directiveContext := rootDirectiveContextLayered
	ordinaryOverlay := ""
	if request.ordinary {
		directiveContext = rootDirectiveContextSource
		ordinaryOverlay = request.overlay
	}
	input, diagnostics := acquireInput(inputAcquisitionRequest{
		input: request.main, role: sourceVersionMain, directiveContext: directiveContext,
		protectionRule:  request.protectionVersion(),
		ordinaryOverlay: ordinaryOverlay,
	}, policy, state, &tierAcquisitionState{visited: make(map[resourceIdentity]importRoute)})
	request.main.source = input.source
	accumulator.sources = input.sources
	accumulator.add(versionState.diagnostics...)
	reportedVersionDiagnostics := len(versionState.diagnostics)
	accumulator.add(diagnostics...)
	if hasErrors(diagnostics) {
		return nil, accumulator.loadError()
	}
	if schema == nil {
		var schemaIssue *schemaIssue
		schema, schemaIssue = buildSchema(reflect.TypeFor[T](), secrets)
		if schemaIssue != nil {
			accumulator.add(diagnosticFromSchemaIssue(schemaIssue))
			return nil, accumulator.loadError()
		}
	}
	if request.ordinary && (input.document != nil || input.composition != nil) {
		input.composition, diagnostics = compositionForInputWithPolicy(input, policy.sequencePolicy)
		if len(diagnostics) != 0 {
			accumulator.add(diagnostics...)
			return nil, accumulator.loadError()
		}
		input.document = input.composition.root
	}
	if request.sourceVersionMode == sourceVersionModeDefault && request.ordinary {
		versionDiagnostics := checkVersion(request.definition.Version, input.document)
		accumulator.add(versionDiagnostics...)
		if hasErrors(versionDiagnostics) {
			return nil, accumulator.loadError()
		}
	}
	if request.ordinary {
		versionState.locateMainVersion(input.document)
		input, diagnostics = applyInputLayers(request.main.source, request.main.filesystem, request.overlay, versionState.effectiveRule, policy.sequencePolicy, input)
	} else {
		input, diagnostics = assembleLayeredInput(request, input, policy, state)
	}
	accumulator.add(versionState.diagnostics[reportedVersionDiagnostics:]...)
	accumulator.sources = input.sources
	accumulator.add(diagnostics...)
	if hasErrors(diagnostics) {
		return nil, accumulator.loadError()
	}
	request.effectiveVersion = versionState.effectiveRule
	if request.ordinary && input.parsed.source != nil {
		input, diagnostics = completeOrdinaryResourceContexts(input, request.main)
		if len(diagnostics) != 0 {
			accumulator.add(diagnostics...)
			return nil, accumulator.loadError()
		}
	}
	var expanded bool
	var effectiveVersion *VersionRule
	input, effectiveVersion, expanded, diagnostics = expandStructuralInheritance(input, request.protectionVersion(), policy.sequencePolicy)
	if len(diagnostics) != 0 {
		accumulator.add(diagnostics...)
		return nil, accumulator.loadError()
	}
	if expanded {
		request.effectiveVersion = effectiveVersion
		versionState.effectiveRule = effectiveVersion
	}

	base := overridePreparationInput{root: input.document}
	if input.composition != nil {
		base.inputBytes = input.composition.inputBytes
		base.inputNodes = input.composition.inputNodes
	}
	preparedOverrides, diagnostics := preparePostStructuralOverrides(base, input.sources, request.overrides, request.protectionVersion(), defaultImportLimits())
	accumulator.add(diagnostics...)
	if hasErrors(diagnostics) {
		return nil, accumulator.loadError()
	}
	input.sources = preparedOverrides.sources
	accumulator.sources = input.sources

	decodeDefinition := request.definition
	decodeDefinition.Version = request.protectionVersion()
	decoded, diagnostics := decodeLoadInput(schema, decodeDefinition, input)
	accumulator.add(diagnostics...)
	if len(diagnostics) != 0 {
		return nil, accumulator.loadError()
	}
	decodeContext := decodeContext{}
	if decodeDefinition.Version != nil {
		decodeContext.versionPath = &decodeDefinition.Version.Path
	}
	assigned, issues := applyDecodedOverrides(schema, decoded, preparedOverrides, decodeContext)
	if len(issues) != 0 {
		for _, issue := range issues {
			accumulator.add(diagnosticFromDecodeIssue(issue))
		}
		return nil, accumulator.loadError()
	}
	postDecode := preparePostDecodeOverrideContext(input, decoded, assigned)
	resolved, diagnostics := resolveLoadInput(schema, request.definition, input, postDecode)
	accumulator.add(diagnostics...)
	if hasErrors(diagnostics) {
		return nil, accumulator.loadError()
	}
	counter := newRetainedNodeCounter(historyLimit)
	inspection, admitted := prepareInspectionHistory(resolved, counter)
	if !admitted {
		accumulator.add(Diagnostic{Code: CodeExplainLimitExceeded, Severity: SeverityError, Message: "retained configuration history exceeds the node limit"})
		return nil, accumulator.loadError()
	}
	historyApplications := make([]historyApplication, 0, len(inspection.applications)+len(inspection.postDecodeApps))
	historyApplications = append(historyApplications, inspection.applications...)
	historyApplications = append(historyApplications, inspection.postDecodeApps...)
	if !addInspectionHistory(counter, inspection) {
		accumulator.add(Diagnostic{Code: CodeExplainLimitExceeded, Severity: SeverityError, Message: "retained configuration history exceeds the node limit"})
		return nil, accumulator.loadError()
	}

	// Detach resolver-borrowed values before reference mutation or validation.
	configuration, ownershipIssue := detachLoadConfiguration(schema, resolved.configuration, cloneUnresolvedSecrets)
	if ownershipIssue != nil {
		accumulator.add(*ownershipIssue)
		return nil, accumulator.loadError()
	}
	secretResolution := resolveSecretReferences(reflect.ValueOf(&configuration).Elem(), schema, resolved.referenceInput, lookup)
	accumulator.add(secretResolution.diagnostics...)
	if hasErrors(secretResolution.diagnostics) {
		return nil, accumulator.loadError()
	}
	identityDiagnostics := validateFinalSequenceIdentities(resolved.referenceInput, policy.sequencePolicy)
	accumulator.add(identityDiagnostics...)
	if hasErrors(identityDiagnostics) {
		return nil, accumulator.loadError()
	}
	if request.definition.Validate != nil {
		diagnostics = runValidation(&configuration, request.definition.Validate, schema, resolved.final, resolved.referenceInput, secretResolution.lookups)
		accumulator.add(diagnostics...)
		if hasErrors(diagnostics) {
			return nil, accumulator.loadError()
		}
	}
	resolved.configuration = configuration
	// Publication detaches equal-valued validator replacements, preserving the
	// validated secret state, then finalizes metadata and sensitivity.
	return publishLoadResult(schema, request.definition, resolved, inspection, historyApplications, secretResolution.references, &accumulator)
}