import {assertNever} from "../utils";
import {Expression} from "./types";

export function evaluate(expr: Expression): number {
  switch (expr.type) {
    case "literal": {
      return expr.value;
    }

    case "binary": {
      switch (expr.operator) {
        case "+":
          return evaluate(expr.left) + evaluate(expr.right);
        case "-":
          return evaluate(expr.left) - evaluate(expr.right);
        case "*":
          return evaluate(expr.left) * evaluate(expr.right);
        case "/":
          return evaluate(expr.left) / evaluate(expr.right);
        /* istanbul ignore next */
        default: {
          return assertNever("Unexpected binary operator", expr.operator);
        }
      }
    }
    /* istanbul ignore next */
    default: {
      return assertNever("Unexpected expression type", expr);
    }
  }
}