package configkit

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
}

// Options contains the application definition and per-load input selections.
// Imports enables explicit path and glob imports; Profile selects one fixed profile
// overlay; Overrides contains only values explicitly supplied by an application CLI.
type Options[T any] struct {
	Definition Definition[T]
	Imports    bool
	Profile    string
	Filesystem *FilesystemContext
	Overrides  []Override
}

// FilesystemContext supplies filesystem roots for imports and profiles.
type FilesystemContext struct {
	BaseDir string
	Root    string
}

// 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 surviving-input presence and records 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.
type VersionRule struct {
	Path  Path
	Check func(Version, *Validation) error
}

// Version preserves the absent, null, and string states of a schema-version input.
type Version struct {
	Present bool
	Null    bool
	Text    string
}

// Result is a successful independently owned configuration load.
type Result[T any] struct {
	Config T

	metadata         Metadata
	sources          []SourceInfo
	diagnostics      []Diagnostic
	baseline         *document.Node
	input            *document.Node
	inputOrigins     map[string]Origin
	final            *document.Node
	resolution       []resolutionSnapshot
	applications     []historyApplication
	secrets          map[string]bool
	secretReferences map[string]string
}

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

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

// Diagnostics returns detached nonfatal diagnostics from the load.
func (r *Result[T]) 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 profile. It accepts at most one Options value and
// returns no result when any error is reported.
func Load[T any](source Source, supplied ...Options[T]) (*Result[T], error) {
	return loadWithSecretLookup(source, os.LookupEnv, supplied...)
}

func loadWithSecretLookup[T any](source Source, lookup secretLookup, supplied ...Options[T]) (*Result[T], error) {
	accumulator := diagnosticAccumulator{}
	options, diagnostics := selectOptions(source, supplied)
	if len(diagnostics) != 0 {
		accumulator.add(diagnostics...)
		return nil, accumulator.loadError()
	}

	parsed, diagnostics := parseSource(source, "source-1", defaultParseLimits())
	if len(diagnostics) != 0 {
		if parsed.source != nil {
			accumulator.sources = append(accumulator.sources, *parsed.source)
		}
		accumulator.add(diagnostics...)
		return nil, accumulator.loadError()
	}

	inputDocument := parsed.document
	var composition *composedDocument
	if options.Imports {
		composition, accumulator.sources, diagnostics = loadImportedDocuments(source, options.Filesystem, parsed, options.Definition.Version, defaultImportLimits())
		if len(diagnostics) != 0 {
			accumulator.add(diagnostics...)
			return nil, accumulator.loadError()
		}
		inputDocument = composition.root
	} else {
		if parsed.source != nil {
			accumulator.sources = append(accumulator.sources, *parsed.source)
		}
		if options.Filesystem != nil && !activeProfile(options.Profile) {
			if diagnostic := validateFilesystemContext(source, options.Filesystem, parsed); diagnostic != nil {
				accumulator.add(*diagnostic)
				return nil, accumulator.loadError()
			}
		}
	}
	if !options.Imports && inputDocument != nil {
		directiveDiagnostics := disabledDirectiveDiagnostics(inputDocument, Path{})
		if len(directiveDiagnostics) != 0 {
			accumulator.add(directiveDiagnostics...)
			return nil, accumulator.loadError()
		}
	}

	schema, schemaIssue := buildSchema(reflect.TypeFor[T]())
	if schemaIssue != nil {
		accumulator.add(diagnosticFromSchemaIssue(schemaIssue))
		return nil, accumulator.loadError()
	}

	versionDiagnostics := checkVersion(options.Definition.Version, inputDocument)
	accumulator.add(versionDiagnostics...)
	if hasErrors(versionDiagnostics) {
		return nil, accumulator.loadError()
	}
	if activeProfile(options.Profile) {
		if composition == nil {
			composition, diagnostics = composeDocuments(inputDocument)
			if len(diagnostics) != 0 {
				accumulator.add(diagnostics...)
				return nil, accumulator.loadError()
			}
			composition.inputBytes = parsed.bytes
			composition.inputNodes = countInputNodes(parsed.document)
		}
		composition, accumulator.sources, diagnostics = loadProfileDocument(
			source, options.Filesystem, parsed, composition, accumulator.sources,
			options.Profile, options.Definition.Version, defaultImportLimits(),
		)
		if len(diagnostics) != 0 {
			accumulator.add(diagnostics...)
			return nil, accumulator.loadError()
		}
		inputDocument = composition.root
	}
	if len(options.Overrides) != 0 {
		if composition == nil {
			if inputDocument == nil {
				composition = &composedDocument{root: &document.Node{Kind: document.Mapping}, origins: make(map[string]Origin)}
			} else {
				composition, diagnostics = composeDocuments(inputDocument)
				if len(diagnostics) != 0 {
					accumulator.add(diagnostics...)
					return nil, accumulator.loadError()
				}
				composition.inputBytes = parsed.bytes
				composition.inputNodes = countInputNodes(inputDocument)
			}
		}
		composition, accumulator.sources, diagnostics = applyOverrides(
			composition, accumulator.sources, options.Overrides, options.Definition.Version, defaultImportLimits(),
		)
		if len(diagnostics) != 0 {
			accumulator.add(diagnostics...)
			return nil, accumulator.loadError()
		}
		inputDocument = composition.root
	}

	defaults := reflect.Zero(reflect.TypeFor[T]())
	if options.Definition.Defaults != nil {
		defaults = reflect.ValueOf(options.Definition.Defaults())
	}
	decoded, decodeIssues := decodeConfiguration(schema, defaults, inputDocument)
	if len(decodeIssues) != 0 {
		for _, issue := range decodeIssues {
			accumulator.add(diagnosticFromDecodeIssue(issue))
		}
		return nil, accumulator.loadError()
	}
	if composition != nil {
		applyCompositionOrigins(&decoded, composition.origins)
	}

	configuration := decoded.value.Interface().(T)
	metadata := metadataFromDecoded(decoded)
	if composition != nil {
		applyOverlayMetadata(&metadata, composition.overlays)
	}
	final := decoded.final
	var resolutionSnapshots []resolutionSnapshot
	if options.Definition.Resolve != nil {
		resolved := runResolution(&configuration, options.Definition.Resolve, schema, decoded, inputDocument)
		accumulator.add(resolved.diagnostics...)
		if hasErrors(resolved.diagnostics) {
			return nil, accumulator.loadError()
		}
		final = resolved.final
		resolutionSnapshots = resolved.snapshots
		applyResolutionMetadata(&metadata, resolved)
	}
	applications := []historyApplication(nil)
	if composition != nil {
		applications = cloneHistoryApplications(composition.applications)
	} else if inputDocument != nil {
		applications = []historyApplication{{layer: LayerBase, value: inputDocument}}
	}
	if !historyNodesWithinLimit(decoded.baseline, decoded.final, final, applications, resolutionSnapshots) {
		accumulator.add(Diagnostic{Code: CodeExplainLimitExceeded, Severity: SeverityError, Message: "retained configuration history exceeds the node limit"})
		return nil, accumulator.loadError()
	}
	// Resolver assignments may borrow application-owned mutable values. Detach
	// before secret resolution mutates reference fields or validation sees them.
	detached, ownershipIssue := cloneConfiguration(schema, reflect.ValueOf(configuration), defaultProjectionLimits())
	if ownershipIssue != nil {
		accumulator.add(diagnosticFromDecodeIssue(decodeIssueFromProjection(ownershipIssue)))
		return nil, accumulator.loadError()
	}
	configuration = detached.Interface().(T)
	secretResolution := resolveSecretReferences(reflect.ValueOf(&configuration).Elem(), schema, inputDocument, lookup)
	accumulator.add(secretResolution.diagnostics...)
	if hasErrors(secretResolution.diagnostics) {
		return nil, accumulator.loadError()
	}
	if options.Definition.Validate != nil {
		validationDiagnostics := runValidation(&configuration, options.Definition.Validate, schema, final, inputDocument, secretResolution.lookups)
		accumulator.add(validationDiagnostics...)
		if hasErrors(validationDiagnostics) {
			return nil, accumulator.loadError()
		}
	}
	// A read-only validator can replace a value with an equal borrowed object.
	// Projected mutation checks cannot detect that alias, so detach at publication.
	published, ownershipIssue := cloneConfigurationState(schema, reflect.ValueOf(configuration), defaultProjectionLimits(), true)
	if ownershipIssue != nil {
		accumulator.add(diagnosticFromDecodeIssue(decodeIssueFromProjection(ownershipIssue)))
		return nil, accumulator.loadError()
	}
	configuration = published.Interface().(T)
	finalizeMetadataPaths(&metadata, final, applications, decoded.baseline, decoded.final)
	secrets := classifySecretPaths(schema, options.Definition.Secret, metadata, final, applications, decoded.baseline, decoded.final)
	return &Result[T]{
		Config:           configuration,
		metadata:         metadata,
		sources:          cloneSourceInfos(accumulator.sources),
		diagnostics:      canonicalDiagnostics(accumulator.diagnostics),
		baseline:         decoded.baseline,
		input:            decoded.final,
		inputOrigins:     cloneOriginIndex(decoded.origins),
		final:            final,
		resolution:       resolutionSnapshots,
		applications:     applications,
		secrets:          secrets,
		secretReferences: cloneSecretReferences(secretResolution.references),
	}, nil
}

func selectOptions[T any](source Source, supplied []Options[T]) (Options[T], []Diagnostic) {
	if len(supplied) > 1 {
		return Options[T]{}, []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "Load accepts at most one options value")}
	}
	var options Options[T]
	if len(supplied) == 1 {
		options = supplied[0]
	}
	var diagnostics []Diagnostic
	definition := options.Definition
	if !validProfileName(options.Profile) {
		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "profile name must contain only ASCII letters, digits, underscore, or hyphen"))
	}
	if options.Filesystem != nil {
		diagnostics = append(diagnostics, filesystemOptionDiagnostics(source, options.Filesystem)...)
	}
	if source.kind == sourceNone && options.Imports {
		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "NoSource cannot enable imports"))
	}
	if source.kind == sourceNone && options.Profile != "" && options.Profile != "default" {
		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "NoSource cannot select an active profile"))
	}
	if options.Filesystem == nil && (source.kind == sourceBytes || source.kind == sourceReader) && (options.Imports || activeProfile(options.Profile)) {
		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "byte and reader imports or profiles require filesystem context"))
	}
	if definition.Version != nil {
		if !definition.Version.Path.valid() {
			diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "schema-version path is invalid"))
		}
		if definition.Version.Check == nil {
			diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "schema-version rule requires a checker"))
		}
	}
	return options, canonicalDiagnostics(diagnostics)
}

func optionDiagnostic(code Code, message string) Diagnostic {
	return Diagnostic{Code: code, Severity: SeverityError, Message: message}
}

func disabledDirectiveDiagnostics(node *document.Node, path Path) []Diagnostic {
	var diagnostics []Diagnostic
	if node.Kind == document.Mapping {
		for _, entry := range node.Mapping {
			childPath := path.Key(entry.Key)
			if entry.Key == "_configkit" {
				location := Location{SourceID: entry.KeyLocation.SourceID, Line: entry.KeyLocation.Line, Column: entry.KeyLocation.Column}
				diagnostics = append(diagnostics, Diagnostic{
					Code: CodeImportDisabled, Severity: SeverityError, Path: childPath,
					Message: "configuration directives require imports to be enabled", Primary: &location,
				})
			}
			diagnostics = append(diagnostics, disabledDirectiveDiagnostics(entry.Value, childPath)...)
		}
	} else if node.Kind == document.Sequence {
		for index, child := range node.Sequence {
			diagnostics = append(diagnostics, disabledDirectiveDiagnostics(child, path.Index(index))...)
		}
	}
	return diagnostics
}

func checkVersion(rule *VersionRule, root *document.Node) []Diagnostic {
	if rule == nil {
		return nil
	}
	version := Version{}
	node, present := documentAtPath(root, rule.Path)
	if present {
		version.Present = true
		switch node.Kind {
		case document.Null:
			version.Null = true
		case document.String:
			version.Text = node.Text
		default:
			location, _ := nearestDocumentLocation(root, rule.Path)
			primary := documentLocationPointer(location)
			return []Diagnostic{{
				Code: CodeVersionType, Severity: SeverityError, Path: rule.Path.clone(),
				Message: "schema version must be a string or null", Primary: primary,
			}}
		}
	}
	state := &validationState{
		active: true, errorCode: CodeVersionError, warningCode: CodeVersionWarning,
		invalidPath: CodeVersionError, document: root,
	}
	validation := &Validation{state: state}
	err := rule.Check(version, validation)
	state.active = false
	if err != nil && !hasErrors(state.diagnostics) {
		location, _ := nearestDocumentLocation(root, rule.Path)
		state.diagnostics = append(state.diagnostics, Diagnostic{
			Code: CodeVersionHookFailed, Severity: SeverityError, Path: rule.Path.clone(),
			Message: "schema-version check failed", Primary: documentLocationPointer(location),
		})
	}
	return canonicalDiagnostics(state.diagnostics)
}

func documentAtPath(root *document.Node, path Path) (*document.Node, bool) {
	if root == nil || !path.valid() {
		return nil, false
	}
	current := root
	for _, segment := range path.segments {
		switch current.Kind {
		case document.Mapping:
			if segment.kind == pathSegmentIndex {
				return nil, false
			}
			found := false
			for _, entry := range current.Mapping {
				if entry.Key == segment.key {
					current = entry.Value
					found = true
					break
				}
			}
			if !found {
				return nil, false
			}
		case document.Sequence:
			index, ok := schemaIndex(segment)
			if !ok || index >= len(current.Sequence) {
				return nil, false
			}
			current = current.Sequence[index]
		default:
			return nil, false
		}
	}
	return current, true
}

func documentLocationPointer(location document.Location) *Location {
	if !locationKnown(location) {
		return nil
	}
	return &Location{SourceID: location.SourceID, Line: location.Line, Column: location.Column}
}

func diagnosticFromSchemaIssue(issue *schemaIssue) Diagnostic {
	return Diagnostic{Code: issue.code, Severity: SeverityError, Path: issue.path.clone(), Message: issue.message}
}

func diagnosticFromDecodeIssue(issue decodeIssue) Diagnostic {
	return Diagnostic{
		Code: issue.code, Severity: SeverityError, Path: issue.path.clone(), Message: issue.message,
		Primary: documentLocationPointer(issue.location),
	}
}

func hasErrors(diagnostics []Diagnostic) bool {
	for _, diagnostic := range diagnostics {
		if diagnostic.Severity == SeverityError {
			return true
		}
	}
	return false
}