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
}

// Options contains the application definition and per-load input selections.
// Imports enables explicit path and glob imports; Overlay selects one fixed overlay;
// Overrides contains 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
}

// FilesystemContext supplies filesystem roots for imports and overlays.
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
	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) {
	options, diagnostics := selectOptions(source, supplied)
	if len(diagnostics) != 0 {
		return nil, (&diagnosticAccumulator{diagnostics: diagnostics}).loadError()
	}
	request := loadRequest[T]{
		main:       loadInput{source: source, imports: options.Imports, filesystem: options.Filesystem},
		definition: options.Definition, overlay: options.Overlay,
		overrides: options.Overrides, ordinary: true,
		sourceVersionMode: options.SourceVersionMode,
		effectiveVersion:  effectiveSourceVersionRule(options.Definition.Version, Path{}, options.SourceVersionMode),
	}
	return executeLoadRequest(request, secrets, lookup)
}

func executeLoadRequest[T any](request loadRequest[T], secrets SecretBinding, lookup secretLookup) (*Loaded[T], error) {
	accumulator := diagnosticAccumulator{}
	accounting := &importAccounting{}
	mainOptions := Options[T]{Definition: request.definition, Imports: request.main.imports, Filesystem: request.main.filesystem}
	mainOptions.SourceVersionMode = request.sourceVersionMode
	mainOptions.Definition.Version = request.protectionVersion()
	mainOptions.Overrides = request.overrides
	if request.ordinary {
		mainOptions.Overlay = request.overlay
	}

	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,
	}
	input, diagnostics := assembleBaseInputTrackedWithVersion(request.main.source, mainOptions, request.main.destination, accounting, nil, nil, versionState)
	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.sourceVersionMode == sourceVersionModeDefault {
		versionDiagnostics := checkVersion(request.definition.Version, input.document)
		accumulator.add(versionDiagnostics...)
		if hasErrors(versionDiagnostics) {
			return nil, accumulator.loadError()
		}
	}
	if request.ordinary {
		input, diagnostics = applyInputLayers(request.main.source, mainOptions, input)
	} else {
		input, diagnostics = assembleLayeredInput(request, input, accounting)
	}
	accumulator.add(versionState.diagnostics[reportedVersionDiagnostics:]...)
	accumulator.sources = input.sources
	accumulator.add(diagnostics...)
	if len(diagnostics) != 0 {
		return nil, accumulator.loadError()
	}
	if request.ordinary && input.parsed.source != nil {
		baseSources := make([]SourceInfo, 0, len(input.sources))
		for _, source := range input.sources {
			if source.Layer == LayerBase {
				baseSources = append(baseSources, source)
			}
		}
		if len(baseSources) != 0 && input.contexts[baseSources[0].ID].FS == nil {
			contexts, diagnostic := contextsForAcquiredSources(request.main.source, request.main.filesystem, input.parsed.source, baseSources)
			if diagnostic != nil {
				accumulator.add(*diagnostic)
				return nil, accumulator.loadError()
			}
			mergeResourceContexts(&input.contexts, contexts)
		}
	}
	if input.document != nil && containsInheritanceDirective(input.document) {
		composition, problems := compositionForInput(input)
		if len(problems) != 0 {
			accumulator.add(problems...)
			return nil, accumulator.loadError()
		}
		expanded, problems := expandInheritanceWithOrigins(composition.root, composition.origins, defaultProjectionLimits())
		if len(problems) != 0 {
			accumulator.add(problems...)
			return nil, accumulator.loadError()
		}
		if problem := inheritanceVersionDiagnostic(request.protectionVersion(), expanded); problem != nil {
			accumulator.add(*problem)
			return nil, accumulator.loadError()
		}
		input.composition = composition
		input.inheritance = expanded
		input.document = expanded.root
	}

	decodeDefinition := request.definition
	decodeDefinition.Version = request.protectionVersion()
	decoded, diagnostics := decodeLoadInput(schema, decodeDefinition, input)
	accumulator.add(diagnostics...)
	if len(diagnostics) != 0 {
		return nil, accumulator.loadError()
	}
	resolved, diagnostics := resolveLoadInput(schema, request.definition, input, decoded)
	accumulator.add(diagnostics...)
	if hasErrors(diagnostics) {
		return nil, accumulator.loadError()
	}
	if !historyNodesWithinLimit(decoded.baseline, decoded.final, resolved.final, resolved.applications, resolved.snapshots, input.inheritance) {
		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, input.document, lookup)
	accumulator.add(secretResolution.diagnostics...)
	if hasErrors(secretResolution.diagnostics) {
		return nil, accumulator.loadError()
	}
	if request.definition.Validate != nil {
		diagnostics = runValidation(&configuration, request.definition.Validate, schema, resolved.final, input.document, 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, secretResolution.references, &accumulator)
}