1 files changed, 58 insertions, 0 deletions
diff --git a/src/new_fields/Types.ts b/src/new_fields/Types.ts
new file mode 100644
index 000000000..416298a64
--- /dev/null
+++ b/src/new_fields/Types.ts
@@ -0,0 +1,58 @@
+import { Field, Opt } from "./Doc";
+import { List } from "./List";
+
+export type ToType<T> =
+    T extends "string" ? string :
+    T extends "number" ? number :
+    T extends "boolean" ? boolean :
+    T extends ListSpec<infer U> ? List<U> :
+    T extends { new(...args: any[]): infer R } ? R : never;
+
+export type ToConstructor<T> =
+    T extends string ? "string" :
+    T extends number ? "number" :
+    T extends boolean ? "boolean" : { new(...args: any[]): T };
+
+export type ToInterface<T> = {
+    [P in keyof T]: ToType<T[P]>;
+};
+
+// type ListSpec<T extends Field[]> = { List: FieldCtor<Head<T>> | ListSpec<Tail<T>> };
+export type ListSpec<T> = { List: FieldCtor<T> };
+
+// type ListType<U extends Field[]> = { 0: List<ListType<Tail<U>>>, 1: ToType<Head<U>> }[HasTail<U> extends true ? 0 : 1];
+
+export type Head<T extends any[]> = T extends [any, ...any[]] ? T[0] : never;
+export type Tail<T extends any[]> =
+    ((...t: T) => any) extends ((_: any, ...tail: infer TT) => any) ? TT : [];
+export type HasTail<T extends any[]> = T extends ([] | [any]) ? false : true;
+
+export interface Interface {
+    [key: string]: ToConstructor<Field> | ListSpec<Field>;
+    // [key: string]: ToConstructor<Field> | ListSpec<Field[]>;
+}
+
+export type FieldCtor<T extends Field> = ToConstructor<T> | ListSpec<T>;
+
+export function Cast<T extends FieldCtor<Field>>(field: Field | null | undefined, ctor: T): ToType<T> | null | undefined {
+    if (field !== undefined && field !== null) {
+        if (typeof ctor === "string") {
+            if (typeof field === ctor) {
+                return field as ToType<T>;
+            }
+        } else if (typeof ctor === "object") {
+            if (field instanceof List) {
+                return field as ToType<T>;
+            }
+        } else if (field instanceof (ctor as any)) {
+            return field as ToType<T>;
+        }
+    } else {
+        return field;
+    }
+    return undefined;
+}
+
+export function FieldValue<T extends Field>(field: Opt<Field> | Promise<Opt<Field>>): Opt<Field> {
+    return field instanceof Promise ? undefined : field;
+}