Schema.ts

type SchemaType = PrimitiveSchema | ObjectSchema | ParametrizedObjectSchema;

interface PrimitiveSchema<T = any> {
	kind: "primitive";
	type: T;
}

interface Fields {
	[name: string]: SchemaType;
}

interface ObjectSchema<TFields extends Fields = Fields> {
	kind: "object";
	fields: TFields;
}

interface ParametrizedObjectSchema<
	TParams = object,
	TFields extends Fields = Fields
> {
	kind: "parametrized-object";
	params: TParams;
	fields: TFields;
}

type AsSchema<T extends SchemaType> = T;

type QueryIn<
	TSchema extends { [key: string]: any }
> = TSchema extends ObjectSchema ? { [TName in keyof TSchema["fields"]]?: QueryIn<TSchema["fields"][TName]> }
	: TSchema extends PrimitiveSchema ? true
	: TSchema extends ParametrizedObjectSchema ? {
			params: {
				[TName in keyof TSchema["params"]]:
					TSchema["params"][TName]
			};
			fields: {
				[TName in keyof TSchema["fields"]]?: QueryIn<
					TSchema["fields"][TName]
				>
			};
	  }
	: never;

type QueryResult<
	TSchema extends { [key: string]: any },
	T extends { [key: string]: any }
> = TSchema extends ObjectSchema
	? Pick<
			{
				[TName in keyof TSchema["fields"] & keyof T]: QueryResult<
					TSchema["fields"][TName],
					T[TName]
				>
			},
			keyof T & keyof TSchema["fields"]
	  >
	: TSchema extends PrimitiveSchema
	? TSchema["type"]
	: TSchema extends ParametrizedObjectSchema
	? Pick<
			{
				[TName in keyof TSchema["fields"] &
					keyof T["fields"]]: QueryResult<
					TSchema["fields"][TName],
					T["fields"][TName]
				>
			},
			keyof T["fields"] & keyof TSchema["fields"]
	  >
	: never;

class QueryBuilder<TSchema extends QuerySchema> {
	public query<T extends QueryIn<TSchema>>(
		type: T
	): QueryResult<QuerySchema, T> {
		throw "";
	}
}

// generated
type QuerySchema = AsSchema<{
	kind: "object";
	fields: {
		licenseByName: {
			kind: "parametrized-object";
			params: {
				name: string;
			};
			fields: {
				description: PrimitiveSchema<string>;
			};
		};
		author: {
			kind: "object";
			fields: {
				name: PrimitiveSchema<string>;
				email: PrimitiveSchema<string>;
			};
		};
	};
}>;

const schema: QueryBuilder<QuerySchema> = null!;

const r = schema.query({
	licenseByName: {
		params: {
			name: "test"
		},
		fields: { description: true }
	},
	author: { email: true, name: true }
});
//r.licenseByName.description;
//r.author.