parsec/src/index.ts

declare const __parsed_brand: unique symbol;
export type Brand<T, B> = T & { [__parsed_brand]: B };
export type Parser<T> = (value: unknown) => T;

export class ParseError extends Error {
  name = "ParseError";
  shape: string;
  path: string;

  constructor(message: string, shape = "unknown", path = "") {
    super(message);
    this.shape = shape;
    this.path = path;
  }
}

const MismatchError = (expectedType: string, receivedValue: unknown) => {
  return new ParseError(
    `Expected: ${expectedType}, Received: ${typeof receivedValue} ${JSON.stringify(receivedValue)}`,
    expectedType,
  );
};

type TypeofType = "number" | "string" | "boolean" | "bigint" | "symbol";
const assertTypeof = <T>(val: unknown, expectedType: TypeofType): T => {
  // biome-ignore lint/suspicious/useValidTypeof: Safe through types
  if (typeof val !== expectedType) {
    throw MismatchError(expectedType, val);
  }

  return val as T;
};

export const Parse = {
  unknown(val: unknown): unknown {
    return val;
  },

  number(val: unknown): number {
    return assertTypeof<number>(val, "number");
  },

  string(val: unknown): string {
    return assertTypeof<string>(val, "string");
  },

  boolean(val: unknown): boolean {
    return assertTypeof<boolean>(val, "boolean");
  },

  bigint(val: unknown): bigint {
    return assertTypeof<bigint>(val, "bigint");
  },

  symbol(val: unknown): symbol {
    return assertTypeof<symbol>(val, "symbol");
  },

  null(val: unknown): null {
    if (val === null) {
      return val;
    }

    throw MismatchError("null", val);
  },

  undefined(val: unknown): undefined {
    if (val === undefined) {
      return val;
    }

    throw MismatchError("undefined", val);
  },

  literal<
    T extends string | number | boolean | bigint | symbol | null | undefined,
  >(literal: T): (val: unknown) => T {
    return (val: unknown) => {
      if (val === literal) {
        return val as T;
      }

      throw MismatchError(String(literal), val);
    };
  },

  int(val: unknown): number {
    const asNum = Parse.number(val);

    if (!Number.isInteger(asNum)) {
      throw MismatchError("integer", asNum);
    }

    return asNum;
  },

  nan(val: unknown): number {
    if (typeof val === "number" && Number.isNaN(val)) {
      return val;
    }

    throw MismatchError("NaN", val);
  },

  instanceOf<T>(classDef: { new(): T }): (val: unknown) => T {
    return (val: unknown) => {
      if (val instanceof classDef) {
        return val;
      }

      throw MismatchError(`instanceof ${classDef.name}`, val);
    };
  },

  arrayOf<T>(
    parser: (val: unknown) => T,
    shapeName = "Array",
  ): (val: unknown) => T[] {
    return (val: unknown) => {
      if (Array.isArray(val)) {
        return val.map((entry, index) => {
          try {
            return parser(entry);
          } catch (error) {
            if (error instanceof ParseError) {
              error.path += `${shapeName}[${index}]`;
              throw error;
            }

            throw error;
          }
        });
      }

      throw MismatchError(shapeName, val);
    };
  },

  // biome-ignore lint/suspicious/noExplicitAny: Could be fixed; intentionally kept simpler
  shape<T extends Record<string, Parser<any>>>(
    parsers: T,
    shapeName = "Shape",
  ): (val: unknown) => { [K in keyof T]: ReturnType<T[K]> } {
    return (val: unknown) => {
      if (val === null || typeof val !== "object") {
        throw MismatchError("object", val);
      }

      const result = {} as { [K in keyof T]: ReturnType<T[K]> };

      for (const key in parsers) {
        const value = (val as Record<string, unknown>)[key] ?? undefined;

        try {
          // biome-ignore lint/style/noNonNullAssertion: Logically guaranteed
          result[key] = parsers[key]!(value);
        } catch (error) {
          if (error instanceof ParseError) {
            error.path += `${shapeName}.${key}`;
            throw error;
          }

          throw error;
        }
      }

      return result;
    };
  },

  regex<T extends string>(
    regex: RegExp,
    shapeName = "Regex String",
  ): (val: unknown) => T {
    return (val: unknown) => {
      const asStr = Parse.string(val);
      if (regex.test(asStr)) {
        return val as T;
      }

      throw MismatchError(`${shapeName} (${regex.toString()})`, asStr);
    };
  },

  enum<E extends string>(
    enumDef: readonly E[],
    shapeName = "Enum",
  ): (val: unknown) => E {
    return (val: unknown) => {
      if (typeof val !== "string") {
        throw MismatchError("string", val);
      }

      if (!enumDef.includes(val as E)) {
        throw MismatchError(shapeName, val);
      }

      return val as E;
    };
  },

  optional<T>(
    parser: (val: unknown) => T,
    coerceNull = false,
  ): (val: unknown) => T | undefined {
    return (val: unknown) => {
      if (val === undefined || (coerceNull && val === null)) {
        return undefined;
      }

      return parser(val);
    };
  },

  nullable<T>(
    parser: (val: unknown) => T,
    coerceUndefined = false,
  ): (val: unknown) => T | null {
    return (val: unknown) => {
      if (val === null || (coerceUndefined && val === undefined)) {
        return null;
      }

      return parser(val);
    };
  },

  defaulted<T>(
    parser: (val: unknown) => T,
    defaultVal: T,
  ): (val: unknown) => T {
    return (val: unknown) => {
      if (val === undefined || val === null) {
        return defaultVal;
      }

      return parser(val);
    };
  },

  oneOf<T extends Parser<unknown>[]>(
    parsers: T,
    shapeName = "Union",
  ): (value: unknown) => ReturnType<T[number]> {
    return (value: unknown): ReturnType<T[number]> => {
      const errors: Error[] = [];

      for (const parser of parsers) {
        try {
          return parser(value) as ReturnType<T[number]>;
        } catch (error) {
          errors.push(
            error instanceof Error ? error : new Error(String(error)),
          );
        }
      }

      throw MismatchError(shapeName, value);
    };
  },
} as const;