package engine

import (
	"bytes"
	"errors"
	"io/fs"
	"strconv"

	yamladapter "gitea.maximumdirect.net/eric/ConfigKit/internal/yaml"
)

func activeOverlay(name string) bool {
	return name != "" && name != "default"
}

func validOverlayName(name string) bool {
	if !activeOverlay(name) {
		return true
	}
	for _, character := range name {
		if (character >= 'a' && character <= 'z') ||
			(character >= 'A' && character <= 'Z') ||
			(character >= '0' && character <= '9') || character == '_' || character == '-' {
			continue
		}
		return false
	}
	return true
}

func loadSelectedOverlayDocument(source Source, context *FilesystemContext, main parsedSource, base *composedDocument, sources []SourceInfo, name string, rule *VersionRule, limits importLimits) (*composedDocument, []SourceInfo, []Diagnostic) {
	assembly := newAssemblyAccumulator(cloneComposedDocument(base))
	allSources, diagnostics := loadSelectedOverlayInto(source, context, main, assembly, sources, name, rule, limits)
	if len(diagnostics) != 0 {
		return nil, allSources, diagnostics
	}
	return assembly.current, allSources, nil
}

func loadSelectedOverlayInto(source Source, context *FilesystemContext, main parsedSource, base *assemblyAccumulator, sources []SourceInfo, name string, rule *VersionRule, limits importLimits) ([]SourceInfo, []Diagnostic) {
	return loadSelectedOverlayIntoWithVersion(source, context, main, base, sources, name, rule, limits, nil)
}

func loadSelectedOverlayIntoWithVersion(source Source, context *FilesystemContext, main parsedSource, base *assemblyAccumulator, sources []SourceInfo, name string, rule *VersionRule, limits importLimits, versionState *sourceVersionState, policies ...sequencePolicy) ([]SourceInfo, []Diagnostic) {
	var policy sequencePolicy
	if len(policies) != 0 {
		policy = policies[0]
	}
	if nativeContext(source, context) {
		access, basePath, mainPath, diagnostic := nativeFilesystemAccess(source, context)
		if diagnostic != nil {
			return cloneSourceInfos(sources), []Diagnostic{*diagnostic}
		}
		if diagnostic := validateNativeDirectories(access, basePath, mainPath); diagnostic != nil {
			return cloneSourceInfos(sources), []Diagnostic{*diagnostic}
		}
		if len(policies) == 0 {
			return loadSelectedOverlayWithAccessAndVersion(access, base, sources, name, rule, limits, versionState)
		}
		return loadSelectedOverlayWithAccessAndVersion(access, base, sources, name, rule, limits, versionState, policy)
	}
	rootPath, _, _, diagnostic := importFilesystem(source, context, main)
	if diagnostic != nil {
		return cloneSourceInfos(sources), []Diagnostic{*diagnostic}
	}
	access, err := openHostAccess(rootPath)
	if err != nil {
		value := globFilesystemDiagnostic(err, "configuration root could not be opened for the selected overlay", Location{})
		value.Primary = nil
		return cloneSourceInfos(sources), []Diagnostic{value}
	}
	if len(policies) == 0 {
		return loadSelectedOverlayWithAccessAndVersion(access, base, sources, name, rule, limits, versionState)
	}
	return loadSelectedOverlayWithAccessAndVersion(access, base, sources, name, rule, limits, versionState, policy)
}

func loadSelectedOverlayWithAccess(access *filesystemAccess, base *assemblyAccumulator, sources []SourceInfo, name string, rule *VersionRule, limits importLimits) ([]SourceInfo, []Diagnostic) {
	return loadSelectedOverlayWithAccessAndVersion(access, base, sources, name, rule, limits, nil)
}

func loadSelectedOverlayWithAccessAndVersion(access *filesystemAccess, base *assemblyAccumulator, sources []SourceInfo, name string, rule *VersionRule, limits importLimits, versionState *sourceVersionState, policies ...sequencePolicy) ([]SourceInfo, []Diagnostic) {
	var policy sequencePolicy
	if len(policies) != 0 {
		policy = policies[0]
	}
	closed := false
	defer func() {
		if !closed {
			_ = access.close()
		}
	}()
	overlayPath := access.join(access.rootPath, "overlays/"+name+".yml")
	canonical, err := access.canonical(overlayPath)
	if err != nil {
		code := CodeOverlayInvalid
		message := "selected overlay could not be resolved"
		if errors.Is(err, fs.ErrNotExist) {
			code, message = CodeOverlayMissing, "selected overlay does not exist"
		} else if errors.Is(err, fs.ErrPermission) {
			code, message = CodeImportPermission, "selected overlay cannot be accessed"
		}
		return cloneSourceInfos(sources), []Diagnostic{importDiagnostic(code, message, nil)}
	}
	if !access.contains(canonical) {
		return cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayOutsideRoot, "selected overlay resolves outside the configuration root", nil)}
	}
	for _, existing := range sources {
		if existing.Path != "" && existing.Path == canonical &&
			((access.native == nil && existing.Kind == SourceKindFile) ||
				(access.native != nil && existing.Kind == SourceKindFilesystem && existing.namespace == access.token)) {
			return cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayRepeated, "selected overlay is already present in the base source graph", nil)}
		}
	}
	if len(sources)+1 > limits.sources {
		return cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayLimitExceeded, "selected overlay exceeds the source-count limit", nil)}
	}

	if _, err := access.relative(canonical); err != nil {
		return cloneSourceInfos(sources), []Diagnostic{importDiagnostic(CodeOverlayOutsideRoot, "selected overlay could not be addressed inside the configuration root", nil)}
	}

	sourceID := "source-" + strconv.Itoa(len(sources)+1)
	overlayLocation := &Location{SourceID: sourceID}
	kind := SourceKindFile
	label := "overlays/" + name + ".yml"
	if access.native != nil {
		kind = SourceKindFilesystem
		label = access.label + "/" + canonical
	}
	overlaySource := SourceInfo{ID: sourceID, Label: label, Path: canonical, Layer: LayerOverlay, Kind: kind}
	if kind == SourceKindFilesystem {
		overlaySource.namespace = access.token
	}
	sources = append(cloneSourceInfos(sources), overlaySource)
	data, diagnostic := readOverlayFile(access, canonical, sourceID, limits.bytes-base.current.inputBytes)
	if diagnostic != nil {
		return sources, []Diagnostic{*diagnostic}
	}
	overlayRoot, issues := yamladapter.Parse(bytes.NewReader(data), sourceID, yamladapter.Limits{Depth: maxDocumentDepth, Nodes: maxDocumentNodes})
	if len(issues) != 0 {
		return sources, parserDiagnostics(sourceID, issues)
	}
	nodeCount := countInputNodes(overlayRoot)
	if base.current.inputNodes+nodeCount > limits.nodes {
		return sources, []Diagnostic{importDiagnostic(CodeOverlayLimitExceeded, "selected overlay exceeds the aggregate node limit", overlayLocation)}
	}
	if diagnostics := overlayDirectiveDiagnostics(overlayRoot, Path{}, len(policies) != 0); len(diagnostics) != 0 {
		return sources, diagnostics
	}
	var processed sourceVersionProcessingResult
	var failures []Diagnostic
	if len(policies) != 0 {
		if versionState != nil {
			processed, failures = versionState.processWithDirectiveContext(
				overlayRoot, sourceVersionContribution, Path{}, sourceID, placementModeMapping, rootDirectiveContextOverlay,
			)
		} else {
			processed = processSourceVersionWithDirectiveContext(
				overlayRoot, rule, sourceVersionContribution, Path{}, sourceVersionModeDefault, rootDirectiveContextOverlay,
			)
			failures = processed.diagnostics
		}
	} else {
		if versionState != nil && versionState.mode != sourceVersionModeDefault {
			processed, failures = versionState.process(overlayRoot, sourceVersionContribution, Path{}, sourceID, placementModeMapping)
		} else {
			processed = sourceVersionProcessingResult{payload: overlayRoot}
		}
	}
	if len(failures) != 0 {
		return sources, failures
	}
	overlayPayload := processed.payload
	if versionNode := fragmentVersionClaim(overlayPayload, rule); versionNode != nil {
		location := publicLocation(versionNode.Location)
		return sources, []Diagnostic{{
			Code: CodeOverlayVersion, Severity: SeverityError, Path: rule.Path.clone(),
			Message: "overlays cannot contribute to or replace the schema-version path", Primary: &location,
		}}
	}
	closeErr := access.close()
	closed = true
	if closeErr != nil {
		return sources, []Diagnostic{importDiagnostic(CodeImportRead, "configuration root could not be closed after reading the selected overlay", nil)}
	}

	var overlayDiagnostics []Diagnostic
	if len(policies) != 0 {
		overlayDiagnostics = base.applyOverlayWithCollectionPolicy(overlayPayload, nil, nil, LayerOverlay, policy, processed.sequences)
	} else {
		overlayDiagnostics = base.applyOverlay(overlayPayload, nil, nil, LayerOverlay)
	}
	if len(overlayDiagnostics) != 0 {
		return sources, overlayDiagnostics
	}
	base.current.inputBytes += int64(len(data))
	base.current.inputNodes += nodeCount
	return sources, nil
}

func readOverlayFile(access *filesystemAccess, name, sourceID string, remaining int64) ([]byte, *Diagnostic) {
	limit := min(int64(maxSourceBytes), remaining)
	if limit < 0 {
		limit = 0
	}
	data, failure := readRegularFile(name, access.stat, access.open, limit)
	if failure != nil {
		value := sourceReadDiagnostic(failure, sourceID, CodeOverlayLimitExceeded, "selected overlay exceeds a source or aggregate byte limit")
		return nil, &value
	}
	return data, nil
}