/**
 * @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("#")
    .map(() => []);

  const PreCommand = AtLeast(0, InterCommandWhitespace);

  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)
          .expects("{")
          .map((text) => `{${text}}`),
        Regex(/[^{}]+/y)
          .expects("text")
          .map(([text]) => text)
      )
    ),
    Regex(/\}/y).expects("}")
  ).map(([_left, fragments, _right]) => fragments.join(""));

  const Word = Choose(
    BasicWord,
    Brace.map((text) => ({ text }))
  );

  const CommandTerminator = Regex(/[\n;]/y)
    .expects("NEWLINE | ;")
    .map(() => true);

  /** @type {Peg.Pattern<Notcl.Command>} */
  const Command = Sequence(
    Word,
    AtLeast(
      0,
      Sequence(PreWordWhitespace, Word).map(([, word]) => word)
    ),
    AtLeast(0, PreWordWhitespace)
  ).map(([word, moreWords]) => [word].concat(moreWords));

  /** @type {Peg.Pattern<Notcl.Script>} */
  const Script = Sequence(
    AtLeast(
      0,
      Choose(
        PreWordWhitespace.map(() => []),
        CommandTerminator.map(() => []),
        Sequence(Comment, Choose(CommandTerminator, End())).map(() => []),
        Sequence(Command, Choose(CommandTerminator, End())).map(
          ([words]) => words
        )
      )
    ),
    End()
  ).map(([commands]) => commands.filter((command) => command.length > 0));

  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, errorPos, expected] = Script(code, 0);

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

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