matcher.ts

export const matcher = <Input, Output>(value: Input) => {
  type Result = (value: Input) => Output;
  type Expression = (value: Input) => boolean;

  interface MatchCases {
    expression: Expression;
    result: Result;
  }

  const cases: MatchCases[] = [];
  let defaultCase: Result = () => {
    throw new Error("No default case provided");
  };

  function run(): Output {
    for (const { expression, result } of cases) {
      if (expression(value)) {
        return result(value);
      }
    }

    return defaultCase(value);
  }

  function setDefault(result: Result) {
    defaultCase = result;
    return run();
  }

  function addCase(expression: Expression, result: Result) {
    cases.push({ expression, result });
    return { case: addCase, default: setDefault };
  }

  return { case: addCase };
};

export const asyncMatcher = <Input, Output>(value: Input) => {
  type Result = (value: Input) => Output | Promise<Output>;
  type Expression = (value: Input) => boolean | Promise<boolean>;

  interface MatchCases {
    expression: Expression;
    result: Result;
  }

  const cases: MatchCases[] = [];
  let defaultCase: Result = () => {
    throw new Error("No default case provided");
  };

  async function run() {
    for (const { expression, result } of cases) {
      if (await expression(value)) {
        return await result(value);
      }
    }

    return defaultCase(value);
  }

  function setDefault(result: Result) {
    defaultCase = result;
    return run();
  }

  function addCase(expression: Expression, result: Result) {
    cases.push({ expression, result });
    return { case: addCase, default: setDefault };
  }

  return { case: addCase };
};