package engine

import "go.maximumdirect.net/configkit/internal/document"

type historyPathOrigin struct {
	path      Path
	origin    Origin
	sensitive bool
}

type historySourcePayloadKind uint8

const (
	historySourceApplicationPayload historySourcePayloadKind = iota
	historySourceOverlayPayload
	historySourceSummaryPayload
)

// historySourcePayload keeps source values and replacement facts under the
// shared model's ownership. Application documents remain shared when immutable.
type historySourcePayload struct {
	kind              historySourcePayloadKind
	application       historyApplication
	overlay           overlayRecord
	applicationRef    historyPayloadRef
	hasApplicationRef bool
	path              Path
	origin            Origin
}

func (builder *historyBuilder) observeBaseline(root *document.Node) {
	builder.requireOpen()
	if root == nil {
		return
	}
	builder.model.baseline = root
	payload := builder.nextPayload(historyPhaseBaseline)
	defaultAttribution := builder.addAttribution(Origin{Layer: LayerDefault}, nil, nil)
	walkDocument(root, Path{}, func(path Path, node *document.Node) {
		builder.addObservation(historyObservation{
			path: path, phase: historyPhaseBaseline, payload: payload,
			reportedPath: path, role: historyRoleDefinition,
			afterPresent: true, sensitive: node.Sensitive,
			attributionRef: defaultAttribution,
		})
	})
}

// observeSourceEvidence registers raw source contributions, replacement sides,
// and the surviving structural definition summaries in producer order.
func (builder *historyBuilder) observeSourceEvidence(root *document.Node, origins map[string]Origin, applications []historyApplication, records []overlayRecord) {
	builder.requireOpen()
	if len(applications) == 0 && len(records) == 0 {
		return
	}
	applicationsBySource := make(map[string]historyPayloadRef)
	applicationsByLayer := make(map[Layer][]historyPayloadRef)
	for index := range applications {
		application := applications[index]
		payload := builder.addSourcePayload(&application, nil)
		applicationsByLayer[application.layer] = append(applicationsByLayer[application.layer], payload)
		walkHistoryApplication(application, func(_, effective Path, node *document.Node) {
			if node.Location.SourceID != "" {
				applicationsBySource[node.Location.SourceID] = payload
			}
			origin := sourceApplicationOrigin(application, node)
			for _, location := range origin.Locations {
				if location.SourceID != "" {
					applicationsBySource[location.SourceID] = payload
				}
			}
			attribution := builder.addAttribution(origin, nil, nil)
			builder.addObservation(historyObservation{
				path: effective, phase: historyPhaseSources, payload: payload,
				reportedPath: effective, role: historyRoleContribution,
				afterPresent: true, sensitive: node.Sensitive,
				attributionRef: attribution,
			})
		})
	}
	for index := range records {
		record := records[index]
		payload := builder.addSourcePayload(nil, &record)
		applicationRef, hasApplication := sourceApplicationForRecord(record, applicationsBySource, applicationsByLayer)
		if hasApplication {
			owned := &builder.model.sourcePayloads[payload.id]
			owned.applicationRef = applicationRef
			owned.hasApplicationRef = true
		}
		for displacedIndex, displaced := range record.displaced {
			if sourceOriginRepresentedByOperation(builder.model, displaced.path, displaced.origin) {
				continue
			}
			definitionPayload := payload
			definitionPayload.substep = displacedIndex + 1
			definition := builder.addAttribution(displaced.origin, nil, nil)
			builder.addObservation(historyObservation{
				path: displaced.path, phase: historyPhaseSources, payload: definitionPayload,
				reportedPath: displaced.path, role: historyRoleDefinition,
				beforePresent:  true,
				attributionRef: definition,
			})
		}
		attribution := builder.addAttribution(record.change.Origin, nil, nil)
		for _, displaced := range record.displaced {
			builder.addObservation(historyObservation{
				path: displaced.path, phase: historyPhaseSources, payload: payload,
				reportedPath: record.change.Path, role: historyRoleOperation,
				beforePresent: true, attributionRef: attribution,
			})
		}
		for _, introduced := range record.introduced {
			builder.addObservation(historyObservation{
				path: introduced.path, phase: historyPhaseSources, payload: payload,
				reportedPath: record.change.Path, role: historyRoleOperation,
				afterPresent: true, sensitive: introduced.sensitive,
				attributionRef: attribution,
			})
		}
	}

	if root == nil {
		return
	}
	walkDocument(root, Path{}, func(path Path, node *document.Node) {
		origin, found := origins[path.String()]
		if !found || origin.Layer == "" || sourceOriginRepresentedByOperation(builder.model, path, origin) {
			return
		}
		payload := builder.addSourceSummary(path, origin)
		attribution := builder.addAttribution(origin, nil, nil)
		builder.addObservation(historyObservation{
			path: path, phase: historyPhaseSources, payload: payload,
			reportedPath: path, role: historyRoleCompositeDefinition,
			afterPresent: true, sensitive: node.Sensitive,
			attributionRef: attribution,
		})
	})
}

func sourceApplicationForRecord(record overlayRecord, bySource map[string]historyPayloadRef, byLayer map[Layer][]historyPayloadRef) (historyPayloadRef, bool) {
	for _, location := range record.change.Origin.Locations {
		if reference, found := bySource[location.SourceID]; found && location.SourceID != "" {
			return reference, true
		}
	}
	applications := byLayer[record.change.Origin.Layer]
	if len(applications) == 1 {
		return applications[0], true
	}
	return historyPayloadRef{}, false
}

func (builder *historyBuilder) addSourcePayload(application *historyApplication, overlay *overlayRecord) historyPayloadRef {
	payload := builder.nextPayload(historyPhaseSources)
	if payload.id != len(builder.model.sourcePayloads) {
		panic("configkit: source payload identifiers are out of order")
	}
	owned := historySourcePayload{}
	switch {
	case application != nil:
		owned.kind = historySourceApplicationPayload
		owned.application = cloneHistoryApplications([]historyApplication{*application})[0]
	case overlay != nil:
		owned.kind = historySourceOverlayPayload
		owned.overlay = cloneOverlayRecords([]overlayRecord{*overlay})[0]
	default:
		panic("configkit: source payload requires a producer")
	}
	builder.model.sourcePayloads = append(builder.model.sourcePayloads, owned)
	return payload
}

func (builder *historyBuilder) addSourceSummary(path Path, origin Origin) historyPayloadRef {
	payload := builder.nextPayload(historyPhaseSources)
	if payload.id != len(builder.model.sourcePayloads) {
		panic("configkit: source payload identifiers are out of order")
	}
	builder.model.sourcePayloads = append(builder.model.sourcePayloads, historySourcePayload{
		kind: historySourceSummaryPayload, path: path.clone(), origin: cloneOrigin(origin),
	})
	return payload
}

func sourceApplicationOrigin(application historyApplication, node *document.Node) Origin {
	origin := cloneOrigin(application.origin)
	origin.Layer = application.layer
	if node.Location.SourceID != "" {
		origin.Locations = []Location{publicLocation(node.Location)}
	}
	return origin
}

func sourceOriginRepresentedByOperation(model *historyModel, path Path, origin Origin) bool {
	for _, observationID := range model.observationsByPointer[path.String()] {
		observation := model.observations[observationID]
		if observation.phase != historyPhaseSources || observation.role != historyRoleOperation {
			continue
		}
		if !observation.afterPresent || !sameConcreteHistoryPath(path, observation.path) {
			continue
		}
		operationOrigin, ok := model.resolveAttribution(observation.attributionRef)
		if !ok {
			continue
		}
		if originRepresentedByChange(path, origin, Change{
			Path: observation.reportedPath, Origin: operationOrigin.origin,
		}) {
			return true
		}
	}
	return false
}

func originRepresentedByChange(path Path, origin Origin, change Change) bool {
	if change.Path.String() == path.String() {
		return originContainedBy(origin, change.Origin)
	}
	if !pathContains(change.Path, path) || origin.Layer != change.Origin.Layer || origin.Operation != change.Origin.Operation {
		return false
	}
	// A subtree replacement records descendant contributions only when their
	// source identities are present in the ancestor operation attribution.
	recordedSources := make(map[string]struct{}, len(change.Origin.Locations))
	for _, recorded := range change.Origin.Locations {
		recordedSources[recorded.SourceID] = struct{}{}
	}
	for _, location := range origin.Locations {
		if _, found := recordedSources[location.SourceID]; !found {
			return false
		}
	}
	return true
}