ConfigKit/internal/engine/overlay.go

package engine

import (
	"slices"
	"strings"

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

type overlayRecord struct {
	change    Change
	displaced []displacedDefinition
}

type displacedDefinition struct {
	path   Path
	origin Origin
}

func overlayDocuments(base *composedDocument, overlay *document.Node) (*composedDocument, []Diagnostic) {
	if base == nil || base.root == nil || base.root.Kind != document.Mapping || overlay == nil || overlay.Kind != document.Mapping {
		return nil, []Diagnostic{{
			Code: CodeOverlayInvalid, Severity: SeverityError,
			Message: "overlay overlay requires mapping document roots",
		}}
	}
	result := cloneComposedDocument(base)
	mergeOverlayOrigin(result.origins, Path{}, overlay.Location, LayerOverlay)
	mergeOverlayMappings(result, result.root, overlay, Path{}, LayerOverlay, true)
	result.applications = append(result.applications, historyApplication{layer: LayerOverlay, value: overlay})
	return result, nil
}

func mergeOverlayMappings(result *composedDocument, target, overlay *document.Node, current Path, layer Layer, recordReplacements bool) {
	for _, incoming := range overlay.Mapping {
		path := current.Key(incoming.Key)
		index := documentEntryIndex(target.Mapping, incoming.Key)
		if index < 0 {
			cloned := incoming
			cloned.Value = document.Clone(incoming.Value)
			target.Mapping = append(target.Mapping, cloned)
			collectOverlayOrigins(result.origins, incoming.Value, path, layer)
			continue
		}

		existing := target.Mapping[index].Value
		if existing.Kind == document.Mapping && incoming.Value.Kind == document.Mapping {
			mergeOverlayOrigin(result.origins, path, incoming.Value.Location, layer)
			mergeOverlayMappings(result, existing, incoming.Value, path, layer, recordReplacements)
			continue
		}

		displaced := displacedOrigins(existing, result.origins, path)
		previous := cloneOrigin(result.origins[path.String()])
		deleteOriginSubtree(result.origins, path)
		target.Mapping[index] = incoming
		target.Mapping[index].Value = document.Clone(incoming.Value)
		collectOverlayOrigins(result.origins, incoming.Value, path, layer)
		if recordReplacements {
			result.overlays = append(result.overlays, overlayRecord{
				change: Change{
					Path: path.clone(), Origin: overlayOrigin(layer, incoming.Value.Location),
					Previous: previousOrigins(previous),
				},
				displaced: displaced,
			})
		}
	}
}

func collectOverlayOrigins(origins map[string]Origin, node *document.Node, path Path, layer Layer) {
	origins[path.String()] = overlayOrigin(layer, node.Location)
	switch node.Kind {
	case document.Mapping:
		for _, entry := range node.Mapping {
			collectOverlayOrigins(origins, entry.Value, path.Key(entry.Key), layer)
		}
	case document.Sequence:
		for index, child := range node.Sequence {
			collectOverlayOrigins(origins, child, path.Index(index), layer)
		}
	}
}

func mergeOverlayOrigin(origins map[string]Origin, path Path, location document.Location, layer Layer) {
	pointer := path.String()
	origin := cloneOrigin(origins[pointer])
	origin.Layer = layer
	origin.Locations = append(origin.Locations, publicLocation(location))
	origins[pointer] = origin
}

func overlayOrigin(layer Layer, location document.Location) Origin {
	return Origin{Layer: layer, Locations: []Location{publicLocation(location)}}
}

func previousOrigins(origin Origin) []Origin {
	if origin.Layer == "" {
		return nil
	}
	return []Origin{origin}
}

func displacedOrigins(node *document.Node, origins map[string]Origin, path Path) []displacedDefinition {
	var displaced []displacedDefinition
	collectDisplacedOrigins(&displaced, node, origins, path, Origin{})
	slices.SortFunc(displaced, func(left, right displacedDefinition) int {
		return strings.Compare(left.path.String(), right.path.String())
	})
	return displaced
}

func collectDisplacedOrigins(displaced *[]displacedDefinition, node *document.Node, origins map[string]Origin, path Path, inherited Origin) {
	origin, ok := origins[path.String()]
	if !ok {
		origin = cloneOrigin(inherited)
		origin.Locations = []Location{publicLocation(node.Location)}
	}
	*displaced = append(*displaced, displacedDefinition{path: path.clone(), origin: cloneOrigin(origin)})
	switch node.Kind {
	case document.Mapping:
		for _, entry := range node.Mapping {
			collectDisplacedOrigins(displaced, entry.Value, origins, path.Key(entry.Key), origin)
		}
	case document.Sequence:
		for index, child := range node.Sequence {
			collectDisplacedOrigins(displaced, child, origins, path.Index(index), origin)
		}
	}
}

func deleteOriginSubtree(origins map[string]Origin, path Path) {
	prefix := path.String()
	for pointer := range origins {
		if pointer == prefix || strings.HasPrefix(pointer, prefix+"/") {
			delete(origins, pointer)
		}
	}
}

func cloneOriginIndex(origins map[string]Origin) map[string]Origin {
	cloned := make(map[string]Origin, len(origins))
	for pointer, origin := range origins {
		cloned[pointer] = cloneOrigin(origin)
	}
	return cloned
}

func cloneOverlayRecords(records []overlayRecord) []overlayRecord {
	cloned := make([]overlayRecord, len(records))
	for index, record := range records {
		cloned[index].change = cloneChange(record.change)
		cloned[index].displaced = make([]displacedDefinition, len(record.displaced))
		for displacedIndex, displaced := range record.displaced {
			cloned[index].displaced[displacedIndex] = displacedDefinition{
				path: displaced.path.clone(), origin: cloneOrigin(displaced.origin),
			}
		}
	}
	return cloned
}