/**
 * @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).expects("whitespace");

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

  // WIP, need to be able to escape braces correctly

  /** @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 = Choose(
    Brace.map((text) => ({ text })),
    BasicWord
  );

  const CommandTerminator = Choose(
    /** @type {Peg.Pattern<unknown>} */ (Regex(/[\n;]/y)).expects(
      "NEWLINE | ;"
    ),
    End()
  );
  /** @type {Peg.Pattern<Notcl.Command>} */
  const Command = Choose(
    CommandTerminator.map(() => []),
    Sequence(
      Word,
      AtLeast(
        0,
        Sequence(PreWordWhitespace, Word).map(([_padding, word]) => word)
      ),
      Choose(Sequence(PreWordWhitespace, Word), CommandTerminator)
    ).map(([word, moreWords, _end]) => [word].concat(moreWords))
  ).expects("COMMAND");

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

  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>`,
        ];
      }
    },
  };
})();