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 {
		return nil, invalidOverlayDocument()
	}
	assembly := newAssemblyAccumulator(cloneComposedDocument(base))
	if diagnostics := assembly.applyOverlay(overlay, nil, nil, LayerOverlay); len(diagnostics) != 0 {
		return nil, diagnostics
	}
	return assembly.current, nil
}

func invalidOverlayDocument() []Diagnostic {
	return []Diagnostic{{
		Code: CodeOverlayInvalid, Severity: SeverityError,
		Message: "overlay requires mapping document roots",
	}}
}

func (a *assemblyAccumulator) applyOverlay(overlay *document.Node, incomingOrigins map[string]Origin, applications []historyApplication, layer Layer) []Diagnostic {
	if a == nil || a.current == nil || a.current.root == nil || a.current.root.Kind != document.Mapping || overlay == nil || overlay.Kind != document.Mapping {
		return invalidOverlayDocument()
	}
	mergeOriginContribution(a.current.origins, Path{}, incomingOrigin(incomingOrigins, Path{}, overlay, layer))
	mergeOverlayMappings(a.current, a.current.root, overlay, Path{}, layer, true, incomingOrigins, &a.index)
	if len(applications) == 0 {
		a.current.applications = append(a.current.applications, historyApplication{layer: layer, value: overlay})
	} else {
		for _, application := range applications {
			application.layer = layer
			a.current.applications = append(a.current.applications, application)
		}
	}
	return nil
}

func mergeOverlayMappings(result *composedDocument, target, overlay *document.Node, current Path, layer Layer, recordReplacements bool, incomingOrigins map[string]Origin, index *mappingIndex) {
	mergeRecursiveMappings(target, overlay, current, index, recursiveMergeHooks{
		added: func(path Path, incoming *document.Node) {
			collectOverlayOriginsFrom(result.origins, incomingOrigins, incoming, path, layer)
		},
		combined: func(path Path, incoming *document.Node) {
			mergeOriginContribution(result.origins, path, incomingOrigin(incomingOrigins, path, incoming, layer))
		},
		replaced: func(path Path, existing, incoming *document.Node) {
			displaced := displacedOrigins(existing, result.origins, path)
			previous := cloneOrigin(result.origins[path.String()])
			deleteOriginSubtree(result.origins, path, existing)
			collectOverlayOriginsFrom(result.origins, incomingOrigins, incoming, path, layer)
			if recordReplacements {
				result.overlays = append(result.overlays, overlayRecord{
					change: Change{
						Path: path.clone(), Origin: incomingOrigin(incomingOrigins, path, incoming, layer),
						Previous: previousOrigins(previous),
					},
					displaced: displaced,
				})
			}
		},
	})
}

func collectOverlayOrigins(origins map[string]Origin, node *document.Node, path Path, layer Layer) {
	collectOverlayOriginsFrom(origins, nil, node, path, layer)
}

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

func mergeOverlayOrigin(origins map[string]Origin, path Path, location document.Location, layer Layer) {
	mergeOriginContribution(origins, path, overlayOrigin(layer, location))
}

func mergeOriginContribution(origins map[string]Origin, path Path, incoming Origin) {
	pointer := path.String()
	origin := origins[pointer]
	origin.Layer = incoming.Layer
	origin.Locations = append(origin.Locations, incoming.Locations...)
	origins[pointer] = origin
}

func incomingOrigin(origins map[string]Origin, path Path, node *document.Node, layer Layer) Origin {
	if origin, ok := origins[path.String()]; ok {
		origin = cloneOrigin(origin)
		origin.Layer = layer
		return origin
	}
	return overlayOrigin(layer, node.Location)
}

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, node *document.Node) {
	delete(origins, path.String())
	switch node.Kind {
	case document.Mapping:
		for _, entry := range node.Mapping {
			deleteOriginSubtree(origins, path.Key(entry.Key), entry.Value)
		}
	case document.Sequence:
		for index, child := range node.Sequence {
			deleteOriginSubtree(origins, path.Index(index), child)
		}
	}
}

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
}