export type Type =
    | { kind: 'union', variants: VariantMap } // zero: never
    | SimpleType

export type SimpleType = AtomicType | CompoundType
export type FieldType = AtomicType | CollectionType;

export type AtomicType =
    | { kind: 'unit' }
    | { kind: 'ref', typeName: string } // also for base types

export type CompoundType =
    | CollectionType
    | { kind: 'record', fields: FieldMap }

export type CollectionType =
    | { kind: 'array', type: AtomicType }
    | { kind: 'set', type: AtomicType }
    | { kind: 'dictionary', key: AtomicType, value: AtomicType }

export type VariantMap = Map<string, SimpleType>;
export type FieldMap = Map<string, FieldType>;

export namespace Type {
    export const union = (variants: VariantMap): Type => ({ kind: 'union', variants });
    export const unit = (): AtomicType => ({ kind: 'unit' });
    export const ref = (typeName: string): AtomicType => ({ kind: 'ref', typeName });
    export const record = (fields: FieldMap): CompoundType => ({ kind: 'record', fields });
    export const array = (type: AtomicType): CollectionType => ({ kind: 'array', type });
    export const set = (type: AtomicType): CollectionType => ({ kind: 'set', type });
    export const dictionary = (key: AtomicType, value: AtomicType): CollectionType => (
        { kind: 'dictionary', key, value });
}

export const ANY_TYPE: AtomicType = Type.ref('_val');