package engine

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

// composedDocument is the private handoff between source assembly and later
// precedence layers. Claims remain ordered by source and declaration traversal;
// origins retain every source that contributes to a composite mapping.
type composedDocument struct {
	root           *document.Node
	claims         []compositionClaim
	sequenceRanges []sequenceRange
	origins        map[string]Origin
	overlays       []overlayRecord
	applications   []historyApplication
	inputBytes     int64
	inputNodes     int
}

// assemblyAccumulator owns one mutable working document. Acquired trees held by
// history applications are separate from its root and remain unchanged.
type assemblyAccumulator struct {
	current *composedDocument
	index   mappingIndex
}

func newAssemblyAccumulator(owned *composedDocument) *assemblyAccumulator {
	return &assemblyAccumulator{current: owned}
}

// cloneComposedDocument detaches mutable composition and provenance state;
// history application trees are immutable and retain their existing sharing.
func cloneComposedDocument(base *composedDocument) *composedDocument {
	return &composedDocument{
		root: document.Clone(base.root), claims: cloneCompositionClaims(base.claims),
		sequenceRanges: cloneSequenceRanges(base.sequenceRanges),
		origins:        cloneOriginIndex(base.origins), overlays: cloneOverlayRecords(base.overlays),
		applications: cloneHistoryApplications(base.applications),
		inputBytes:   base.inputBytes, inputNodes: base.inputNodes,
	}
}

type compositionClaim struct {
	path        Path
	kind        document.Kind
	location    Location
	sourceIndex int
}

type compositionClaims struct {
	ordered []compositionClaim
	byPath  map[string][]compositionClaim
}

// sequenceRange records where one source's sequence items were assigned in the
// composed sequence at path. End is exclusive.
type sequenceRange struct {
	sourceIndex int
	path        Path
	start       int
	end         int
}

// composeDocuments recursively joins disjoint mapping entries. Source order
// controls only output traversal and diagnostics: every non-mapping overlap is
// rejected before a result is assembled.
func composeDocuments(inputs ...*document.Node) (*composedDocument, []Diagnostic) {
	return composeDocumentsWithPolicy(sequencePolicy{}, inputs...)
}

// composeDocumentsWithPolicy composes one strict tier using the registered
// sequence rules when policy contains registrations. The ordinary adapter above
// deliberately preserves the existing unregistered behavior for current callers.
func composeDocumentsWithPolicy(policy sequencePolicy, inputs ...*document.Node) (*composedDocument, []Diagnostic) {
	if len(inputs) == 0 {
		return nil, []Diagnostic{compositionInvalidDiagnostic("strict composition requires at least one document", nil)}
	}

	collected := compositionClaims{byPath: make(map[string][]compositionClaim)}
	for sourceIndex, input := range inputs {
		if input == nil || input.Kind != document.Mapping {
			var location *Location
			if input != nil {
				converted := publicLocation(input.Location)
				location = &converted
			}
			return nil, []Diagnostic{compositionInvalidDiagnostic("strict composition requires mapping document roots", location)}
		}
		collected.append(input, Path{}, sourceIndex)
	}

	checked := make(map[string]struct{}, len(collected.byPath))
	for _, claim := range collected.ordered {
		pointer := claim.path.String()
		if _, seen := checked[pointer]; seen {
			continue
		}
		checked[pointer] = struct{}{}
		claims := collected.byPath[pointer]
		if len(claims) < 2 || allMappingClaims(claims) || (allSequenceClaims(claims) && policy.registered(claim.path)) {
			continue
		}
		return nil, []Diagnostic{compositionConflictDiagnostic(claim.path, claims)}
	}

	validated, ranges, diagnostics := validateRegisteredSequences(inputs, collected.ordered, policy)
	if len(diagnostics) != 0 {
		return nil, diagnostics
	}

	root := document.Clone(inputs[0])
	index := new(mappingIndex)
	for sourceIndex, input := range inputs[1:] {
		mergeComposedMappings(root, input, Path{}, index, sourceIndex+1, policy, validated)
	}
	applications := make([]historyApplication, 0, len(inputs))
	for _, input := range inputs {
		applications = append(applications, historyApplication{layer: LayerBase, value: input})
	}
	origins := compositionOrigins(collected.ordered)
	completeCompositionOrigins(root, Path{}, origins)
	return &composedDocument{
		root:           root,
		claims:         cloneCompositionClaims(collected.ordered),
		sequenceRanges: cloneSequenceRanges(ranges),
		origins:        origins,
		applications:   applications,
	}, nil
}

// Conflict claims treat sequences atomically, but inspection needs origins for
// every descendant. Preserve composite mapping claims while filling those gaps.
func completeCompositionOrigins(node *document.Node, path Path, origins map[string]Origin) {
	pointer := path.String()
	if _, present := origins[pointer]; !present {
		origins[pointer] = Origin{Layer: LayerBase, Locations: []Location{publicLocation(node.Location)}}
	}
	switch node.Kind {
	case document.Mapping:
		for _, entry := range node.Mapping {
			completeCompositionOrigins(entry.Value, path.Key(entry.Key), origins)
		}
	case document.Sequence:
		for index, child := range node.Sequence {
			completeCompositionOrigins(child, path.Index(index), origins)
		}
	}
}

func (c *compositionClaims) append(node *document.Node, path Path, sourceIndex int) {
	claim := compositionClaim{
		path:        path.clone(),
		kind:        node.Kind,
		location:    publicLocation(node.Location),
		sourceIndex: sourceIndex,
	}
	c.ordered = append(c.ordered, claim)
	pointer := path.String()
	c.byPath[pointer] = append(c.byPath[pointer], claim)

	if node.Kind != document.Mapping {
		return
	}
	for _, entry := range node.Mapping {
		c.append(entry.Value, path.Key(entry.Key), sourceIndex)
	}
}

func allSequenceClaims(claims []compositionClaim) bool {
	for _, claim := range claims {
		if claim.kind != document.Sequence {
			return false
		}
	}
	return true
}

type validatedSequence struct {
	items []*document.Node
}

func validateRegisteredSequences(inputs []*document.Node, claims []compositionClaim, policy sequencePolicy) (map[string]map[int]validatedSequence, []sequenceRange, []Diagnostic) {
	itemsByPath := make(map[string]map[int]validatedSequence)
	identitiesByPath := make(map[string]map[string]Location)
	lengthsByPath := make(map[string]int)
	var ranges []sequenceRange
	for _, claim := range claims {
		if claim.kind != document.Sequence {
			continue
		}
		identityField, registered := policy.identityFields[claim.path.String()]
		if !registered {
			continue
		}
		node, ok := documentAtPath(inputs[claim.sourceIndex], claim.path)
		if !ok || node.Kind != document.Sequence {
			continue
		}
		pathKey := claim.path.String()
		identities := identitiesByPath[pathKey]
		if identities == nil {
			identities = make(map[string]Location, len(node.Sequence))
			identitiesByPath[pathKey] = identities
		}
		start := lengthsByPath[pathKey]
		contribution := validatedSequence{items: node.Sequence}
		for itemIndex, item := range node.Sequence {
			itemPath := claim.path.Index(itemIndex)
			if item == nil || item.Kind != document.Mapping {
				location := (*Location)(nil)
				if item != nil {
					converted := publicLocation(item.Location)
					location = &converted
				}
				return nil, nil, []Diagnostic{{
					Code: CodeComposeInvalid, Severity: SeverityError,
					Path: itemPath, Message: "registered sequence items must be mappings", Primary: location,
				}}
			}
			fieldIndex := documentEntryIndex(item.Mapping, identityField)
			if fieldIndex < 0 {
				location := publicLocation(item.Location)
				return nil, nil, []Diagnostic{{
					Code: CodeComposeInvalid, Severity: SeverityError,
					Path: itemPath, Message: "registered sequence item is missing its identity field",
					Primary: &location,
				}}
			}
			field := item.Mapping[fieldIndex].Value
			if field == nil || field.Kind != document.String {
				location := publicLocation(item.Mapping[fieldIndex].ValueLocation)
				if field != nil {
					location = publicLocation(field.Location)
				}
				return nil, nil, []Diagnostic{{
					Code: CodeComposeInvalid, Severity: SeverityError,
					Path: itemPath.Key(identityField), Message: "registered sequence identity must be a string",
					Primary: &location,
				}}
			}
			if first, duplicate := identities[field.Text]; duplicate {
				current := publicLocation(field.Location)
				return nil, nil, []Diagnostic{{
					Code: CodeComposeConflict, Severity: SeverityError,
					Path: claim.path.clone(), Message: "registered sequence contains duplicate identities",
					Primary: &first, Related: []Location{current},
				}}
			}
			identities[field.Text] = publicLocation(field.Location)
		}
		if itemsByPath[pathKey] == nil {
			itemsByPath[pathKey] = make(map[int]validatedSequence)
		}
		itemsByPath[pathKey][claim.sourceIndex] = contribution
		lengthsByPath[pathKey] = start + len(node.Sequence)
		ranges = append(ranges, sequenceRange{
			sourceIndex: claim.sourceIndex, path: claim.path.clone(), start: start, end: start + len(node.Sequence),
		})
	}
	return itemsByPath, ranges, nil
}

func mergeComposedMappings(target, incoming *document.Node, path Path, index *mappingIndex, sourceIndex int, policy sequencePolicy, validated map[string]map[int]validatedSequence) {
	for _, incomingEntry := range incoming.Mapping {
		entryPath := path.Key(incomingEntry.Key)
		position := index.find(target, incomingEntry.Key)
		if position < 0 {
			cloned := incomingEntry
			cloned.Value = document.Clone(incomingEntry.Value)
			index.append(target, cloned)
			continue
		}
		current := target.Mapping[position].Value
		if current.Kind == document.Sequence && incomingEntry.Value.Kind == document.Sequence && policy.registered(entryPath) {
			contribution := validated[entryPath.String()][sourceIndex]
			if contribution.items != nil {
				for _, item := range contribution.items {
					current.Sequence = append(current.Sequence, document.Clone(item))
				}
			}
			continue
		}
		mergeDisjointMappingsAtPath(current, incomingEntry.Value, entryPath, index, sourceIndex, policy, validated)
	}
}

func mergeDisjointMappingsAtPath(target, incoming *document.Node, path Path, index *mappingIndex, sourceIndex int, policy sequencePolicy, validated map[string]map[int]validatedSequence) {
	if target.Kind != document.Mapping || incoming.Kind != document.Mapping {
		return
	}
	mergeComposedMappings(target, incoming, path, index, sourceIndex, policy, validated)
}

func (p sequencePolicy) registered(path Path) bool {
	_, ok := p.identityFields[path.String()]
	return ok
}

func cloneSequenceRanges(ranges []sequenceRange) []sequenceRange {
	cloned := make([]sequenceRange, len(ranges))
	for i, assigned := range ranges {
		cloned[i] = assigned
		cloned[i].path = assigned.path.clone()
	}
	return cloned
}

func allMappingClaims(claims []compositionClaim) bool {
	for _, claim := range claims {
		if claim.kind != document.Mapping {
			return false
		}
	}
	return true
}

func mergeDisjointMappings(target, incoming *document.Node, index *mappingIndex) {
	for _, incomingEntry := range incoming.Mapping {
		position := index.find(target, incomingEntry.Key)
		if position < 0 {
			cloned := incomingEntry
			cloned.Value = document.Clone(incomingEntry.Value)
			index.append(target, cloned)
			continue
		}
		// Claim validation guarantees that the only remaining overlap is a
		// mapping pair. Empty mappings naturally contribute no child entries.
		mergeDisjointMappings(target.Mapping[position].Value, incomingEntry.Value, index)
	}
}

func documentEntryIndex(entries []document.Entry, key string) int {
	for index := range entries {
		if entries[index].Key == key {
			return index
		}
	}
	return -1
}

func compositionOrigins(claims []compositionClaim) map[string]Origin {
	origins := make(map[string]Origin, len(claims))
	for _, claim := range claims {
		pointer := claim.path.String()
		origin := origins[pointer]
		origin.Layer = LayerBase
		origin.Locations = append(origin.Locations, claim.location)
		origins[pointer] = origin
	}
	return origins
}

func applyCompositionOrigins(decoded *decodedConfiguration, origins map[string]Origin) {
	for pointer, origin := range origins {
		if _, present := decoded.presence[pointer]; present {
			decoded.origins[pointer] = cloneOrigin(origin)
		}
	}
}

func cloneCompositionClaims(claims []compositionClaim) []compositionClaim {
	cloned := make([]compositionClaim, len(claims))
	for index, claim := range claims {
		cloned[index] = claim
		cloned[index].path = claim.path.clone()
	}
	return cloned
}

func compositionInvalidDiagnostic(message string, location *Location) Diagnostic {
	return Diagnostic{
		Code: CodeComposeInvalid, Severity: SeverityError, Message: message,
		Primary: cloneLocation(location),
	}
}

func compositionConflictDiagnostic(path Path, claims []compositionClaim) Diagnostic {
	primary := claims[0].location
	related := make([]Location, 0, len(claims)-1)
	for _, claim := range claims[1:] {
		related = append(related, claim.location)
	}
	return Diagnostic{
		Code:     CodeComposeConflict,
		Severity: SeverityError,
		Path:     path.clone(),
		Message:  "configuration path is defined by multiple sources",
		Primary:  &primary,
		Related:  related,
	}
}

func publicLocation(location document.Location) Location {
	return Location{SourceID: location.SourceID, Line: location.Line, Column: location.Column}
}