module.exports = function(css, options){
  options = options || {};

  /**
   * Positional.
   */

  var lineno = 1;
  var column = 1;

  /**
   * Update lineno and column based on `str`.
   */

  function updatePosition(str) {
    var lines = str.match(/\n/g);
    if (lines) lineno += lines.length;
    var i = str.lastIndexOf('\n');
    column = ~i ? str.length - i : column + str.length;
  }

  /**
   * Mark position and patch `node.position`.
   */

  function position() {
    var start = { line: lineno, column: column };
    if (!options.position) return positionNoop;

    return function(node){
      node.position = {
        start: start,
        end: { line: lineno, column: column },
        source: options.source
      };

      whitespace();
      return node;
    }
  }

  /**
   * Return `node`.
   */

  function positionNoop(node) {
    whitespace();
    return node;
  }

  /**
   * Error `msg`.
   */

  function error(msg) {
    var err = new Error(msg + ' near line ' + lineno + ':' + column);
    err.filename = options.source;
    err.line = lineno;
    err.column = column;
    err.source = css;
    throw err;
  }

  /**
   * Parse stylesheet.
   */

  function stylesheet() {
    return {
      type: 'stylesheet',
      stylesheet: {
        rules: rules()
      }
    };
  }

  /**
   * Opening brace.
   */

  function open() {
    return match(/^{\s*/);
  }

  /**
   * Closing brace.
   */

  function close() {
    return match(/^}/);
  }

  /**
   * Parse ruleset.
   */

  function rules() {
    var node;
    var rules = [];
    whitespace();
    comments(rules);
    while (css.charAt(0) != '}' && (node = atrule() || rule())) {
      rules.push(node);
      comments(rules);
    }
    return rules;
  }

  /**
   * Match `re` and return captures.
   */

  function match(re) {
    var m = re.exec(css);
    if (!m) return;
    var str = m[0];
    updatePosition(str);
    css = css.slice(str.length);
    return m;
  }

  /**
   * Parse whitespace.
   */

  function whitespace() {
    match(/^\s*/);
  }

  /**
   * Parse comments;
   */

  function comments(rules) {
    var c;
    rules = rules || [];
    while (c = comment()) rules.push(c);
    return rules;
  }

  /**
   * Parse comment.
   */

  function comment() {
    var pos = position();
    if ('/' != css.charAt(0) || '*' != css.charAt(1)) return;

    var i = 2;
    while (null != css.charAt(i) && ('*' != css.charAt(i) || '/' != css.charAt(i + 1))) ++i;
    i += 2;

    var str = css.slice(2, i - 2);
    column += 2;
    updatePosition(str);
    css = css.slice(i);
    column += 2;

    return pos({
      type: 'comment',
      comment: str
    });
  }

  /**
   * Parse selector.
   */

  function selector() {
    var m = match(/^([^{]+)/);
    if (!m) return;
    return trim(m[0]).split(/\s*,\s*/);
  }

  /**
   * Parse declaration.
   */

  function declaration() {
    var pos = position();

    // prop
    var prop = match(/^(\*?[-#\/\*\w]+(\[[0-9a-z_-]+\])?)\s*/);
    if (!prop) return;
    prop = trim(prop[0]);

    // :
    if (!match(/^:\s*/)) return error("property missing ':'");

    // val
    var val = match(/^((?:'(?:\\'|.)*?'|"(?:\\"|.)*?"|\([^\)]*?\)|[^};])+)/);
    if (!val) return error('property missing value');

    var ret = pos({
      type: 'declaration',
      property: prop,
      value: trim(val[0])
    });

    // ;
    match(/^[;\s]*/);

    return ret;
  }

  /**
   * Parse declarations.
   */

  function declarations() {
    var decls = [];

    if (!open()) return error("missing '{'");
    comments(decls);

    // declarations
    var decl;
    while (decl = declaration()) {
      decls.push(decl);
      comments(decls);
    }

    if (!close()) return error("missing '}'");
    return decls;
  }

  /**
   * Parse keyframe.
   */

  function keyframe() {
    var m;
    var vals = [];
    var pos = position();

    while (m = match(/^((\d+\.\d+|\.\d+|\d+)%?|[a-z]+)\s*/)) {
      vals.push(m[1]);
      match(/^,\s*/);
    }

    if (!vals.length) return;

    return pos({
      type: 'keyframe',
      values: vals,
      declarations: declarations()
    });
  }

  /**
   * Parse keyframes.
   */

  function atkeyframes() {
    var pos = position();
    var m = match(/^@([-\w]+)?keyframes */);

    if (!m) return;
    var vendor = m[1];

    // identifier
    var m = match(/^([-\w]+)\s*/);
    if (!m) return error("@keyframes missing name");
    var name = m[1];

    if (!open()) return error("@keyframes missing '{'");

    var frame;
    var frames = comments();
    while (frame = keyframe()) {
      frames.push(frame);
      frames = frames.concat(comments());
    }

    if (!close()) return error("@keyframes missing '}'");

    return pos({
      type: 'keyframes',
      name: name,
      vendor: vendor,
      keyframes: frames
    });
  }

  /**
   * Parse supports.
   */

  function atsupports() {
    var pos = position();
    var m = match(/^@supports *([^{]+)/);

    if (!m) return;
    var supports = trim(m[1]);

    if (!open()) return error("@supports missing '{'");

    var style = comments().concat(rules());

    if (!close()) return error("@supports missing '}'");

    return pos({
      type: 'supports',
      supports: supports,
      rules: style
    });
  }

  /**
   * Parse host.
   */

  function athost() {
    var pos = position();
    var m = match(/^@host */);

    if (!m) return;

    if (!open()) return error("@host missing '{'");

    var style = comments().concat(rules());

    if (!close()) return error("@host missing '}'");

    return pos({
      type: 'host',
      rules: style
    });
  }

  /**
   * Parse media.
   */

  function atmedia() {
    var pos = position();
    var m = match(/^@media *([^{]+)/);

    if (!m) return;
    var media = trim(m[1]);

    if (!open()) return error("@media missing '{'");

    var style = comments().concat(rules());

    if (!close()) return error("@media missing '}'");

    return pos({
      type: 'media',
      media: media,
      rules: style
    });
  }

  /**
   * Parse paged media.
   */

  function atpage() {
    var pos = position();
    var m = match(/^@page */);
    if (!m) return;

    var sel = selector() || [];

    if (!open()) return error("@page missing '{'");
    var decls = comments();

    // declarations
    var decl;
    while (decl = declaration()) {
      decls.push(decl);
      decls = decls.concat(comments());
    }

    if (!close()) return error("@page missing '}'");

    return pos({
      type: 'page',
      selectors: sel,
      declarations: decls
    });
  }

  /**
   * Parse document.
   */

  function atdocument() {
    var pos = position();
    var m = match(/^@([-\w]+)?document *([^{]+)/);
    if (!m) return;

    var vendor = trim(m[1]);
    var doc = trim(m[2]);

    if (!open()) return error("@document missing '{'");

    var style = comments().concat(rules());

    if (!close()) return error("@document missing '}'");

    return pos({
      type: 'document',
      document: doc,
      vendor: vendor,
      rules: style
    });
  }

  /**
   * Parse import
   */

  function atimport() {
    return _atrule('import');
  }

  /**
   * Parse charset
   */

  function atcharset() {
    return _atrule('charset');
  }

  /**
   * Parse namespace
   */

  function atnamespace() {
    return _atrule('namespace')
  }

  /**
   * Parse non-block at-rules
   */

  function _atrule(name) {
    var pos = position();
    var m = match(new RegExp('^@' + name + ' *([^;\\n]+);'));
    if (!m) return;
    var ret = { type: name };
    ret[name] = trim(m[1]);
    return pos(ret);
  }

  /**
   * Parse at rule.
   */

  function atrule() {
    if (css[0] != '@') return;

    return atkeyframes()
      || atmedia()
      || atsupports()
      || atimport()
      || atcharset()
      || atnamespace()
      || atdocument()
      || atpage()
      || athost();
  }

  /**
   * Parse rule.
   */

  function rule() {
    var pos = position();
    var sel = selector();

    if (!sel) return;
    comments();

    return pos({
      type: 'rule',
      selectors: sel,
      declarations: declarations()
    });
  }

  return stylesheet();
};

/**
 * Trim `str`.
 */

function trim(str) {
  return str ? str.replace(/^\s+|\s+$/g, '') : '';
}