import { anglebrackets, braces, Item, keyvalue, opseq, seq } from "./block";

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');

export function variantInitFor(variantName: string | undefined) : Item[] {
    return variantName === void 0 ? [] : [variantFor(variantName)];
}

export function variantFor(variantName: string): Item {
    return keyvalue('_variant', JSON.stringify(variantName));
}

export function renderVariant([variantName, t]: [string, SimpleType]): Item {
    let fields: Item[];
    switch (t.kind) {
        case 'unit':
            fields = [];
            break;
        case 'ref':
        case 'set':
        case 'dictionary':
        case 'array':
            fields = [keyvalue('value', renderType(t))];
            break;
        case 'record':
            fields = Array.from(t.fields).map(([nn, tt]) => keyvalue(nn, renderType(tt)));
            break;
        default:
            ((_: never) => {})(t);
            throw new Error("Unreachable");
    }
    return braces(variantFor(variantName), ... fields);
}

export function renderType(t: Type): Item {
    switch (t.kind) {
        case 'union': return opseq('never', ' | ', ...
            Array.from(t.variants).flatMap(renderVariant));
        case 'unit': return 'null';
        case 'ref': return t.typeName;
        case 'set': return seq('_.KeyedSet', anglebrackets(
            renderType(t.type),
            '_embedded'));
        case 'dictionary': return seq('_.KeyedDictionary', anglebrackets(
            renderType(t.key),
            renderType(t.value),
            '_embedded'));
        case 'array': return seq('Array', anglebrackets(renderType(t.type)));
        case 'record': return braces(... Array.from(t.fields).map(([nn, tt]) =>
            keyvalue(nn, renderType(tt))));
        default:
            ((_: never) => {})(t);
            throw new Error("Unreachable");
    }
}