package engine

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

// collectionCorrespondence describes matching at one concrete registered path.
// A negative index denotes an identity present only at the other endpoint.
type collectionCorrespondence struct {
	path         Path
	eligible     bool
	structural   bool
	entryToFinal []int
	finalToEntry []int
}

type resolutionCorrespondence struct {
	collections map[string]collectionCorrespondence
}

func (c resolutionCorrespondence) clone() resolutionCorrespondence {
	result := resolutionCorrespondence{collections: make(map[string]collectionCorrespondence, len(c.collections))}
	for key, collection := range c.collections {
		collection.path = collection.path.clone()
		collection.entryToFinal = append([]int(nil), collection.entryToFinal...)
		collection.finalToEntry = append([]int(nil), collection.finalToEntry...)
		result.collections[key] = collection
	}
	return result
}

func buildResolutionCorrespondence(entry, final *document.Node, policy sequencePolicy) resolutionCorrespondence {
	result := resolutionCorrespondence{collections: make(map[string]collectionCorrespondence)}
	var indexes mappingIndex
	var visit func(*document.Node, *document.Node, Path)
	visit = func(before, after *document.Node, path Path) {
		if fields, registered := policy.identityFieldsAt(path); registered &&
			((before != nil && before.Kind == document.Sequence) || (after != nil && after.Kind == document.Sequence)) {
			result.collections[path.String()] = matchResolutionCollection(before, after, path, fields)
			return
		}
		if before != nil && before.Kind == document.Mapping {
			for _, item := range before.Mapping {
				var next *document.Node
				if after != nil && after.Kind == document.Mapping {
					if position := indexes.find(after, item.Key); position >= 0 {
						next = after.Mapping[position].Value
					}
				}
				visit(item.Value, next, path.Key(item.Key))
			}
		}
		if after != nil && after.Kind == document.Mapping {
			for _, item := range after.Mapping {
				if before == nil || before.Kind != document.Mapping || indexes.find(before, item.Key) < 0 {
					visit(nil, item.Value, path.Key(item.Key))
				}
			}
		}
	}
	visit(entry, final, Path{})
	return result
}

func matchResolutionCollection(before, after *document.Node, path Path, fields []string) collectionCorrespondence {
	result := collectionCorrespondence{path: path.clone()}
	prior, priorIssues := validateNormalizedSequenceIdentityFrom(before, path, fields, sequenceIdentityDiagnosticCodes{}, 0, sequencePayloadRecord)
	later, laterIssues := validateNormalizedSequenceIdentityFrom(after, path, fields, sequenceIdentityDiagnosticCodes{}, 0, sequencePayloadRecord)
	if len(priorIssues) != 0 || len(laterIssues) != 0 {
		return result
	}
	result.eligible = true
	result.entryToFinal = make([]int, len(before.Sequence))
	result.finalToEntry = make([]int, len(after.Sequence))
	for i := range result.entryToFinal {
		result.entryToFinal[i] = -1
	}
	for i := range result.finalToEntry {
		result.finalToEntry[i] = -1
	}
	result.structural = len(prior) != len(later)
	for tuple, previous := range prior {
		if current, found := later[tuple]; found {
			result.entryToFinal[previous.index] = current.index
			result.finalToEntry[current.index] = previous.index
			if previous.index != current.index {
				result.structural = true
			}
		} else {
			result.structural = true
		}
	}
	return result
}

// entryPath translates a surviving final record prefix; additions have no entry.
// Paths outside eligible collections and wholly absent final positions stay positional.
func (c resolutionCorrespondence) entryPath(path Path) (Path, bool) {
	if !path.valid() {
		return Path{}, false
	}
	for depth := 0; depth < len(path.segments); depth++ {
		prefix := Path{segments: path.segments[:depth]}
		collection, found := c.collections[prefix.String()]
		if !found || !collection.eligible {
			continue
		}
		compatible := true
		for i, segment := range collection.path.segments {
			if segment.kind == pathSegmentKey && path.segments[i].kind == pathSegmentIndex {
				compatible = false
				break
			}
		}
		index, ok := schemaIndex(path.segments[depth])
		if !compatible || !ok || index >= len(collection.finalToEntry) {
			continue
		}
		previous := collection.finalToEntry[index]
		if previous < 0 {
			return Path{}, false
		}
		translated := path.clone()
		translated.segments[depth] = pathSegment{kind: pathSegmentIndex, index: previous}
		return translated, true
	}
	return path.clone(), true
}