JSON literal verification in TypeScript type system

json.ts

/*
  JSON literal verification in TypeScript type system (version 3.1 for workgroups)
  now powerd by tail recursion (you can blame @ackwell for telling me to and
  @s5bug for doing it)
*/

type HEX_CHARS =
  | "0"
  | "1"
  | "2"
  | "3"
  | "4"
  | "5"
  | "6"
  | "7"
  | "8"
  | "9"
  | "a"
  | "b"
  | "c"
  | "d"
  | "e"
  | "f"
  | "A"
  | "B"
  | "C"
  | "D"
  | "E"
  | "F";

type EXCLUDE_CHARS =
  | '"'
  | "\\"
  | "\u0000"
  | "\u0001"
  | "\u0002"
  | "\u0003"
  | "\u0004"
  | "\u0005"
  | "\u0006"
  | "\u0007"
  | "\u0008"
  | "\u0009"
  | "\u000A"
  | "\u000B"
  | "\u000C"
  | "\u000D"
  | "\u000E"
  | "\u000F"
  | "\u0010"
  | "\u0011"
  | "\u0012"
  | "\u0013"
  | "\u0014"
  | "\u0015"
  | "\u0016"
  | "\u0017"
  | "\u0018"
  | "\u0019"
  | "\u001A"
  | "\u001B"
  | "\u001C"
  | "\u001D"
  | "\u001E"
  | "\u001F";

type ZeroOrMore<M extends string, T extends string> = M extends `${T}${infer R}`
  ? R extends ZeroOrMore<R, T>
    ? M
    : never
  : M extends ``
  ? M
  : never;

type SUBTRACT_TABLE = {
  readonly "1": 0;
  readonly "2": 1;
  readonly "3": 2;
  readonly "4": 3;
};

type Subtract<T extends number> = `${T}` extends keyof SUBTRACT_TABLE
  ? SUBTRACT_TABLE[`${T}`]
  : never;

type CODEPOINT<S extends string, C extends number = 4> = C extends 0
  ? S extends ``
    ? S
    : never
  : S extends `${infer H}${infer R}`
  ? H extends HEX_CHARS
    ? R extends CODEPOINT<R, Subtract<C>>
      ? S
      : never
    : never
  : never;

type WHITESPACE = "\u0020" | "\u000A" | "\u000D" | "\u0009";
type BACKSLASH = "\\";
type ESCAPE = "\\" | '"' | "/" | "b" | "f" | "n" | "r" | "t" | "u";
type CHAR = string;

type JsonBoolean = "true" | "false";
type JsonNull = "null";
type JsonLiteral = JsonBoolean | JsonNull;

type JsonStringContents<T extends string> = T extends `${BACKSLASH}u${infer U}`
  ? U extends `${CODEPOINT<U>}${infer R}`
    ? R extends JsonStringContents<R>
      ? T
      : never
    : never
  : T extends `${BACKSLASH}${ESCAPE}${infer U}`
  ? U extends JsonStringContents<U>
    ? T
    : never
  : T extends `${CHAR}${infer U}`
  ? T extends `${EXCLUDE_CHARS}${infer U}`
    ? never
    : U extends JsonStringContents<U>
    ? T
    : never
  : T extends ``
  ? T
  : never;

type JsonString<T extends string> = T extends `"${infer U}"`
  ? U extends JsonStringContents<U>
    ? T
    : never
  : never;

type JsonNumber<T extends string> = T extends `${number}`
  ? T
  : T extends `${number}.${number}`
  ? T
  : T extends `-${number}`
  ? T
  : T extends `-${number}.${number}`
  ? T
  : never;

type JsonElement<T extends string> = T extends JsonValue<T>
  ? T
  : T extends `${JsonValue<infer H>},${infer R}`
  ? R extends JsonElement<R>
    ? T
    : never
  : never;

type JsonElements<T extends string> = T extends ZeroOrMore<T, WHITESPACE>
  ? T
  : JsonElement<T>;

type JsonArray<T extends string> = T extends `[${infer U}]`
  ? U extends JsonElements<U>
    ? T
    : never
  : never;

type JsonMember<T extends string> = T extends `${JsonString<
  infer H
>}:${infer R}`
  ? R extends JsonValue<R>
    ? T
    : never
  : never;

type JsonMembers<T extends string> = T extends `${WHITESPACE}${infer U}`
  ? U extends JsonMember<U>
    ? T
    : never
  : T extends `${infer U}${WHITESPACE}`
  ? U extends JsonMember<U>
    ? T
    : never
  : T extends `${JsonMember<infer H>},${infer R}`
  ? R extends JsonMembers<R>
    ? T
    : never
  : T extends JsonMember<T>
  ? T
  : never;

type JsonObject<T extends string> = T extends `{${infer U}}`
  ? U extends JsonMembers<U>
    ? T
    : never
  : never;

type JsonValue<T extends string> = T extends `${WHITESPACE}${infer U}`
  ? U extends JsonValue<U>
    ? T
    : never
  : T extends `${infer U}${WHITESPACE}`
  ? U extends JsonValue<U>
    ? T
    : never
  : T extends JsonString<T>
  ? T
  : T extends JsonArray<T>
  ? T
  : T extends JsonObject<T>
  ? T
  : T extends JsonNumber<T>
  ? T
  : T extends JsonLiteral
  ? T
  : never;

function asValue<T extends string>(j: JsonValue<T>) {}

asValue(`"Hello, world!"`);
asValue(`"\\u0000"`);

asValue(`{"hello": "world"}`);
asValue(`["hello", "world"]`);
asValue(`{"hello": {"world": "!"}}`);
asValue(`[{"hello": "world"}]`);
asValue(`{"hello": ["world"]}`);

asValue(`true`);
asValue(`false`);
asValue(`null`);

asValue(`3.141592653589793`);
asValue(`-3.141592653589793`);

// @ts-expect-error
asValue(`"Hello,\nworld!"`);
// @ts-expect-error
asValue(`"\\u000g"`);

export {};