module.exports = grammar({
  name: 'xml',

  rules: {
    source_file: $ => repeat($._item),

    _item: $ => choice(
      $.element,
      $.comment,
      $.text,
      $._whitespace
    ),

    // XML element
    element: $ => seq(
      '<',
      $.tag_name,
      repeat($.attribute),
      choice(
        seq('>', repeat($._item), '</', $.tag_name, '>'),
        '/>'
      )
    ),

    // Tag name
    tag_name: $ => /[A-Za-z][A-Za-z0-9_-]*/,

    // Attribute
    attribute: $ => seq(
      $.attribute_name,
      '=',
      $.attribute_value
    ),

    // Attribute name
    attribute_name: $ => /[A-Za-z][A-Za-z0-9_-]*/,

    // Attribute value
    attribute_value: $ => choice(
      seq('"', $.quoted_value, '"'),
      seq("'", $.quoted_value, "'")
    ),

    // Quoted value content
    quoted_value: $ => /[^"']*/,

    // XML comment
    comment: $ => token(seq('<!--', /[^-]*(?:-[^-]+)*/, '-->')),

    // Text content
    text: $ => /[^<]+/,

    // Whitespace
    _whitespace: $ => /\s+/
  },

  extras: $ => [
    /\s/,
    $.comment
  ]
});