/**
 * @typedef {Notcl.Command[]} Notcl.Script
 * @typedef {Notcl.Word[]} Notcl.Command
 * @typedef {object} Notcl.Word
 * @property {string} text
 */

var Notcl = (() => {
  const { AtLeast, Choose, End, Regex, Sequence, Use } = Peg;

  const InterCommandWhitespace = Regex(/\s+/y).expects("whitespace");

  const Comment = Regex(/#.*\n/y).expects("#");

  const PreCommand = AtLeast(0, Choose(InterCommandWhitespace, Comment));

  const PreWordWhitespace = Regex(/[^\S\n;]*/y);

  const BasicWord = Regex(/[^\s;]+/y).map(([word]) => ({ text: word }));

  // WIP, need to be able to escape braces correctly
  // WIP, error if anything after closing brace

  /** @type {Peg.Pattern<string>} */
  const Brace = Sequence(
    Regex(/\{/y).expects("{"),
    AtLeast(
      0,
      Choose(
        Use(() => Brace).map((text) => `{${text}}`),
        Regex(/[^{}]+/y).map(([text]) => text)
      )
    ),
    Regex(/\}/y).expects("}")
  ).map(([_left, fragments, _right]) => fragments.join(""));

  const Word = Sequence(
    PreWordWhitespace,
    Choose(
      Brace.map((text) => ({ text })),
      BasicWord
    )
  ).map(([_padding, word]) => word);

  const CommandTerminator = Sequence(
    PreWordWhitespace,
    Choose(/** @type {Peg.Pattern<unknown>} */ (Regex(/[\n;]/y)), End())
  );

  /** @type {Peg.Pattern<Notcl.Command>} */
  const Command = Sequence(PreCommand, AtLeast(0, Word), CommandTerminator).map(
    ([_padding, words, _end]) => words
  );

  /** @type {Peg.Pattern<Notcl.Script>} */
  const Script = Sequence(AtLeast(0, Command), End()).map(
    ([commands, _eof]) => commands
  );

  const ERROR_CONTEXT = /(?<=([^\n]{0,50}))([^\n]{0,50})/y;

  return {
    /**
     * Parse out a Notcl script into an easier-to-interpret representation.
     * No script is actually executed yet.
     *
     * @param {string} code to parse
     * @returns {[true, Notcl.Script] | [false, string]} parsed list of commands, or error message on failure
     */
    parse(code) {
      /* Preprocess */
      // fold line endings
      code = code.replace(/(?<!\\)((\\\\)*)\\\n/g, "$1");

      /* Parse */
      const commands = Script(code, 0);

      if (commands[0]) {
        return [true, commands[1]];
      } else {
        const [, errorPos, expected] = commands;
        ERROR_CONTEXT.lastIndex = errorPos;
        const [, before, after] = /** @type {RegExpExecArray} */ (
          ERROR_CONTEXT.exec(code)
        );
        return [
          false,
          `<pre>Error at position ${commands[1]}
${escapeHtml(before + "" + after)}
${"-".repeat(before.length)}^

Expected: ${escapeHtml(expected)}</pre>`,
        ];
      }
    },
  };
})();