Derive a concrete type from a schematic type

TypeFromSpec.ts

type Spec = Atom | Dict | List;
type Atom = "bool" | "int8" | "uint8" | "int16" | "uint16" | "int32" | "uint32" | "float32" | "float64" | "string" | "varuint" | "varint" | "buffer"
interface Dict { [key: string]: Spec }
interface List extends Array<Spec> { }

type TypeFromSpec<S extends Spec> = CondTypeFromAtom<S> | CondTypeFromDict<S> | CondTypeFromList<S>;
type TypeFromAtom<S extends Atom> = string;
type TypeFromDict<S extends Dict> = { [P in keyof S]: TypeFromSpec<S[P]> }
type TypeFromList<S extends List> = { [P in keyof S]: TypeFromSpec<S[P] extends Spec ? S[P] : never> }
type CondTypeFromAtom<S> = S extends Atom ? TypeFromAtom<S> : never;
type CondTypeFromDict<S> = S extends Dict ? TypeFromDict<S> : never;
type CondTypeFromList<S> = S extends List ? TypeFromList<S> : never;

const enum Buffer { }
interface Schema<S extends Dict> {
    encode(data: TypeFromDict<S>): Buffer;
    decode(data: Buffer): TypeFromDict<S>;
}

function build<S extends Dict>(schema: S): Schema<S>;