feat: relation field and picker

internal/domain/contenttype/contentTypeDomain.go

@@ -13,6 +13,7 @@ var (
 	ErrInvalidIcon         = errors.New("invalid content type icon")
 	ErrInvalidField        = errors.New("invalid field")
 	ErrHasEntries          = errors.New("the content type still has entries")
+	ErrReferenced          = errors.New("the content type is the target of a relation field")
 	ErrSchemaIncompatible  = errors.New("the schema is incompatible with the stored entries")
 )
 
@@ -26,6 +27,7 @@ const (
 	TypeDate     FieldType = "date"
 	TypeSelect   FieldType = "select"
 	TypeMedia    FieldType = "media"
+	TypeRelation FieldType = "relation"
 )
 
 const (
@@ -54,6 +56,7 @@ type Field struct {
 	Min      any       `json:"min"`
 	Max      any       `json:"max"`
 	Options  []string  `json:"options"`
+	Relation *Relation `json:"relation"`
 }
 
 type ContentType struct {

internal/domain/contenttype/fieldKinds.go

@@ -21,6 +21,7 @@ var kinds = map[FieldType]kind{
 	TypeDate:     {accepts: isDate, measure: dateDays, bound: dateDays, unique: true},
 	TypeSelect:   {accepts: isString, unique: true},
 	TypeMedia:    {accepts: isMediaID},
+	TypeRelation: {},
 }
 
 func MediaID(value any) (uint32, bool) {

internal/domain/contenttype/fieldSchema.go

@@ -63,7 +63,7 @@ func (f Field) validSchema() bool {
 	if f.Unique && !fieldKind.unique {
 		return false
 	}
-	return f.validOptions() && f.validBounds(fieldKind) && f.validDefault()
+	return f.validRelation() && f.validOptions() && f.validBounds(fieldKind) && f.validDefault()
 }
 
 func (f Field) validOptions() bool {
@@ -109,7 +109,7 @@ func (f Field) validDefault() bool {
 	if f.Default == nil {
 		return true
 	}
-	if f.Type == TypeMedia {
+	if f.Type == TypeMedia || f.Type == TypeRelation {
 		return false
 	}
 	return !f.Unique && f.Violation(f.Default) == ""

internal/domain/contenttype/fieldValue.go

@@ -3,6 +3,9 @@ package contenttype
 import "slices"
 
 func (f Field) Violation(value any) string {
+	if f.Type == TypeRelation {
+		return f.relationViolation(value)
+	}
 	fieldKind, known := kinds[f.Type]
 	if !known || !fieldKind.accepts(value) {
 		return RuleType

internal/domain/contenttype/relationField.go

@@ -0,0 +1,134 @@
+package contenttype
+
+const MaxRelationIDs = 50
+
+type RelationKind string
+
+const (
+	RelationOneToOne   RelationKind = "one_to_one"
+	RelationOneToMany  RelationKind = "one_to_many"
+	RelationManyToMany RelationKind = "many_to_many"
+)
+
+type Relation struct {
+	ContentType string       `json:"content_type"`
+	Kind        RelationKind `json:"kind"`
+}
+
+func (r Relation) validKind() bool {
+	return r.Kind == RelationOneToOne || r.Kind == RelationOneToMany || r.Kind == RelationManyToMany
+}
+
+func (f Field) validRelation() bool {
+	if f.Type != TypeRelation {
+		return f.Relation == nil
+	}
+	return f.Relation != nil && f.Relation.ContentType != "" && f.Relation.validKind()
+}
+
+func (f Field) IsRelation() bool {
+	return f.Type == TypeRelation && f.Relation != nil
+}
+
+func (f Field) HoldsManyRelations() bool {
+	return f.IsRelation() && f.Relation.Kind == RelationManyToMany
+}
+
+func (f Field) IsExclusiveRelation() bool {
+	return f.IsRelation() && f.Relation.Kind == RelationOneToOne
+}
+
+func (f Field) RelationIDs(value any) ([]uint32, bool) {
+	if value == nil {
+		return []uint32{}, true
+	}
+	if !f.HoldsManyRelations() {
+		id, ok := MediaID(value)
+		if !ok {
+			return nil, false
+		}
+		return []uint32{id}, true
+	}
+	return manyRelationIDs(value)
+}
+
+func manyRelationIDs(value any) ([]uint32, bool) {
+	var items []any
+	switch typed := value.(type) {
+	case []any:
+		items = typed
+	case []uint32:
+		for _, id := range typed {
+			items = append(items, id)
+		}
+	default:
+		return nil, false
+	}
+	if len(items) > MaxRelationIDs {
+		return nil, false
+	}
+	ids := make([]uint32, 0, len(items))
+	seen := make(map[uint32]bool, len(items))
+	for _, item := range items {
+		id, ok := MediaID(item)
+		if !ok || seen[id] {
+			return nil, false
+		}
+		seen[id] = true
+		ids = append(ids, id)
+	}
+	return ids, true
+}
+
+func (f Field) relationViolation(value any) string {
+	if _, ok := f.RelationIDs(value); !ok {
+		return RuleType
+	}
+	return ""
+}
+
+func EmptyRelation(field Field, value any) bool {
+	if !field.HoldsManyRelations() {
+		return false
+	}
+	ids, ok := field.RelationIDs(value)
+	return ok && len(ids) == 0
+}
+
+type RelationRef struct {
+	Field Field
+	IDs   []uint32
+}
+
+func RelationRefs(fields []Field, data map[string]any) []RelationRef {
+	var refs []RelationRef
+	for _, field := range RelationFields(fields) {
+		if ids, ok := field.RelationIDs(data[field.Key]); ok && len(ids) > 0 {
+			refs = append(refs, RelationRef{Field: field, IDs: ids})
+		}
+	}
+	return refs
+}
+
+func RelationFields(fields []Field) []Field {
+	var relations []Field
+	for _, field := range fields {
+		if field.IsRelation() {
+			relations = append(relations, field)
+		}
+	}
+	return relations
+}
+
+func ReferencesType(fields []Field, key string) bool {
+	for _, field := range RelationFields(fields) {
+		if field.Relation.ContentType == key {
+			return true
+		}
+	}
+	return false
+}
+
+func SameRelation(left Field, right Field) bool {
+	return left.IsRelation() && right.IsRelation() && *left.Relation == *right.Relation
+}