package engine

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

// Metadata provides detached effective presence/origin and chronological history
// queries for a load. Its zero value contains no paths.
type Metadata struct {
	effectivePaths map[string]Path
	fields         map[string]FieldInfo
	historyBuilder *historyBuilder
	historyModel   *historyModel
}

// Lookup returns information for an effective path. Unknown and invalid paths
// return false.
func (m Metadata) Lookup(path Path) (FieldInfo, bool) {
	info, ok := m.effectiveField(path)
	if !ok {
		return FieldInfo{}, false
	}
	detached := cloneFieldInfo(info)
	detached.Origin.Inheritance = projectInheritanceSteps(detached.Origin)
	return detached, true
}

// IsExplicit reports whether a surviving input contribution, including one
// inherited from a sibling, explicitly defined path.
func (m Metadata) IsExplicit(path Path) bool {
	info, ok := m.effectiveField(path)
	return ok && info.Explicit
}

func (m Metadata) effectiveField(path Path) (FieldInfo, bool) {
	if !path.valid() {
		return FieldInfo{}, false
	}
	pointer := path.String()
	candidate, ok := m.effectivePaths[pointer]
	if !ok || !matchesPathShape(path, candidate) {
		return FieldInfo{}, false
	}
	info, ok := m.fields[pointer]
	return info, ok
}

// History returns detached definition, inheritance, and resolution records for path. A record's
// Path can be an ancestor when that container operation replaced or removed path.
// Removed historical paths can have history even though Lookup returns false.
// Unknown and invalid paths return nil.
func (m Metadata) History(path Path) []Change {
	model := m.historyEvidence()
	if model == nil || !model.hasObservedShape(path) {
		return nil
	}
	selections := model.selectHistory(path)
	if len(selections) == 0 {
		return nil
	}
	changes := make([]Change, 0, len(selections))
	for _, selection := range selections {
		if !metadataHistoryRole(selection.role) || !selection.hasAttribution {
			continue
		}
		var previous []Origin
		if len(selection.previous) != 0 {
			previous = make([]Origin, len(selection.previous))
			for index, origin := range selection.previous {
				previous[index] = cloneOrigin(origin)
			}
		}
		changes = append(changes, Change{
			Path:         selection.reportedPath.clone(),
			Origin:       cloneOrigin(selection.attribution.origin),
			Previous:     previous,
			Reasons:      append([]string(nil), selection.attribution.reasons...),
			Dependencies: clonePaths(selection.attribution.dependencies),
		})
	}
	if len(changes) == 0 {
		return nil
	}
	return changes
}

// HistoricalPaths returns the paths observed during loading, including effective
// paths and paths removed by overlays, inheritance, or recorded resolution. It includes default
// paths and the root, but not paths that never existed. The zero Metadata returns
// an empty slice.
//
// Paths are detached, unique by canonical JSON Pointer, and sorted by that
// spelling. Like ParsePath results, numeric tokens are resolved contextually;
// one pointer can identify a mapping key in an earlier layer and a sequence index
// in a later one. Use History to inspect definitions and Lookup to check whether
// a path remains effective. Enumeration exposes no configuration values and does
// not perform another load or resolve secrets.
func (m Metadata) HistoricalPaths() []Path {
	return m.historyEvidence().historicalPaths()
}

func (m Metadata) historyEvidence() *historyModel {
	if m.historyModel != nil {
		return m.historyModel
	}
	if m.historyBuilder != nil {
		return m.historyBuilder.model
	}
	return nil
}

// Textual pointers are lookup keys, but explicit key/index kinds remain part of
// the query. Candidate paths are constructed from actual document containers.
func matchesPathShape(query, candidate Path) bool {
	if !query.valid() || len(query.segments) != len(candidate.segments) {
		return false
	}
	for i, segment := range query.segments {
		actual := candidate.segments[i]
		if !pathTokenSpellingEqual(segment, actual) {
			return false
		}
		if actual.kind == pathSegmentIndex {
			switch segment.kind {
			case pathSegmentIndex:
				if segment.index != actual.index {
					return false
				}
			case pathSegmentParsed:
				index, ok := schemaIndex(segment)
				if !ok || index != actual.index {
					return false
				}
			default:
				return false
			}
		} else if segment.kind == pathSegmentIndex {
			return false
		}
	}
	return true
}

func (m Metadata) hasHistoricalPath(path Path) bool {
	return m.historyEvidence().hasObservedShape(path)
}

func freezeMetadataHistory(m *Metadata, final *document.Node) {
	finalizeEffectiveMetadataPaths(m, final)
	builder := m.historyBuilder
	if builder == nil || !builder.prefixReady {
		panic("configkit: metadata history prefix is not ready")
	}
	builder.model.final = final
	m.historyModel = builder.freeze()
	m.historyBuilder = nil
}

func finalizeEffectiveMetadataPaths(m *Metadata, final *document.Node) {
	m.effectivePaths = effectivePathIndex(final)
}

// effectivePathIndex records document-derived paths with their contextual segment
// kinds. Callers retain no aliases to the walked tree or its paths.
func effectivePathIndex(final *document.Node) map[string]Path {
	paths := make(map[string]Path)
	walkDocument(final, Path{}, func(path Path, _ *document.Node) {
		paths[path.String()] = path.clone()
	})
	return paths
}