var openParentheses = "(".charCodeAt(0);
var closeParentheses = ")".charCodeAt(0);
var singleQuote = "'".charCodeAt(0);
var doubleQuote = '"'.charCodeAt(0);
var backslash = "\\".charCodeAt(0);
var slash = "/".charCodeAt(0);
var comma = ",".charCodeAt(0);
var colon = ":".charCodeAt(0);
var star = "*".charCodeAt(0);
var uLower = "u".charCodeAt(0);
var uUpper = "U".charCodeAt(0);
var plus = "+".charCodeAt(0);
var isUnicodeRange = /^[a-f0-9?-]+$/i;

module.exports = function(input) {
  var tokens = [];
  var value = input;

  var next,
    quote,
    prev,
    token,
    escape,
    escapePos,
    whitespacePos,
    parenthesesOpenPos;
  var pos = 0;
  var code = value.charCodeAt(pos);
  var max = value.length;
  var stack = [{ nodes: tokens }];
  var balanced = 0;
  var parent;

  var name = "";
  var before = "";
  var after = "";

  while (pos < max) {
    // Whitespaces
    if (code <= 32) {
      next = pos;
      do {
        next += 1;
        code = value.charCodeAt(next);
      } while (code <= 32);
      token = value.slice(pos, next);

      prev = tokens[tokens.length - 1];
      if (code === closeParentheses && balanced) {
        after = token;
      } else if (prev && prev.type === "div") {
        prev.after = token;
      } else if (
        code === comma ||
        code === colon ||
        (code === slash &&
          value.charCodeAt(next + 1) !== star &&
          (!parent ||
            (parent && parent.type === "function" && parent.value !== "calc")))
      ) {
        before = token;
      } else {
        tokens.push({
          type: "space",
          sourceIndex: pos,
          value: token
        });
      }

      pos = next;

      // Quotes
    } else if (code === singleQuote || code === doubleQuote) {
      next = pos;
      quote = code === singleQuote ? "'" : '"';
      token = {
        type: "string",
        sourceIndex: pos,
        quote: quote
      };
      do {
        escape = false;
        next = value.indexOf(quote, next + 1);
        if (~next) {
          escapePos = next;
          while (value.charCodeAt(escapePos - 1) === backslash) {
            escapePos -= 1;
            escape = !escape;
          }
        } else {
          value += quote;
          next = value.length - 1;
          token.unclosed = true;
        }
      } while (escape);
      token.value = value.slice(pos + 1, next);

      tokens.push(token);
      pos = next + 1;
      code = value.charCodeAt(pos);

      // Comments
    } else if (code === slash && value.charCodeAt(pos + 1) === star) {
      token = {
        type: "comment",
        sourceIndex: pos
      };

      next = value.indexOf("*/", pos);
      if (next === -1) {
        token.unclosed = true;
        next = value.length;
      }

      token.value = value.slice(pos + 2, next);
      tokens.push(token);

      pos = next + 2;
      code = value.charCodeAt(pos);

      // Operation within calc
    } else if (
      (code === slash || code === star) &&
      parent &&
      parent.type === "function" &&
      parent.value === "calc"
    ) {
      token = value[pos];
      tokens.push({
        type: "word",
        sourceIndex: pos - before.length,
        value: token
      });
      pos += 1;
      code = value.charCodeAt(pos);

      // Dividers
    } else if (code === slash || code === comma || code === colon) {
      token = value[pos];

      tokens.push({
        type: "div",
        sourceIndex: pos - before.length,
        value: token,
        before: before,
        after: ""
      });
      before = "";

      pos += 1;
      code = value.charCodeAt(pos);

      // Open parentheses
    } else if (openParentheses === code) {
      // Whitespaces after open parentheses
      next = pos;
      do {
        next += 1;
        code = value.charCodeAt(next);
      } while (code <= 32);
      parenthesesOpenPos = pos;
      token = {
        type: "function",
        sourceIndex: pos - name.length,
        value: name,
        before: value.slice(parenthesesOpenPos + 1, next)
      };
      pos = next;

      if (name === "url" && code !== singleQuote && code !== doubleQuote) {
        next -= 1;
        do {
          escape = false;
          next = value.indexOf(")", next + 1);
          if (~next) {
            escapePos = next;
            while (value.charCodeAt(escapePos - 1) === backslash) {
              escapePos -= 1;
              escape = !escape;
            }
          } else {
            value += ")";
            next = value.length - 1;
            token.unclosed = true;
          }
        } while (escape);
        // Whitespaces before closed
        whitespacePos = next;
        do {
          whitespacePos -= 1;
          code = value.charCodeAt(whitespacePos);
        } while (code <= 32);
        if (parenthesesOpenPos < whitespacePos) {
          if (pos !== whitespacePos + 1) {
            token.nodes = [
              {
                type: "word",
                sourceIndex: pos,
                value: value.slice(pos, whitespacePos + 1)
              }
            ];
          } else {
            token.nodes = [];
          }
          if (token.unclosed && whitespacePos + 1 !== next) {
            token.after = "";
            token.nodes.push({
              type: "space",
              sourceIndex: whitespacePos + 1,
              value: value.slice(whitespacePos + 1, next)
            });
          } else {
            token.after = value.slice(whitespacePos + 1, next);
          }
        } else {
          token.after = "";
          token.nodes = [];
        }
        pos = next + 1;
        code = value.charCodeAt(pos);
        tokens.push(token);
      } else {
        balanced += 1;
        token.after = "";
        tokens.push(token);
        stack.push(token);
        tokens = token.nodes = [];
        parent = token;
      }
      name = "";

      // Close parentheses
    } else if (closeParentheses === code && balanced) {
      pos += 1;
      code = value.charCodeAt(pos);

      parent.after = after;
      after = "";
      balanced -= 1;
      stack.pop();
      parent = stack[balanced];
      tokens = parent.nodes;

      // Words
    } else {
      next = pos;
      do {
        if (code === backslash) {
          next += 1;
        }
        next += 1;
        code = value.charCodeAt(next);
      } while (
        next < max &&
        !(
          code <= 32 ||
          code === singleQuote ||
          code === doubleQuote ||
          code === comma ||
          code === colon ||
          code === slash ||
          code === openParentheses ||
          (code === star &&
            parent &&
            parent.type === "function" &&
            parent.value === "calc") ||
          (code === slash &&
            parent.type === "function" &&
            parent.value === "calc") ||
          (code === closeParentheses && balanced)
        )
      );
      token = value.slice(pos, next);

      if (openParentheses === code) {
        name = token;
      } else if (
        (uLower === token.charCodeAt(0) || uUpper === token.charCodeAt(0)) &&
        plus === token.charCodeAt(1) &&
        isUnicodeRange.test(token.slice(2))
      ) {
        tokens.push({
          type: "unicode-range",
          sourceIndex: pos,
          value: token
        });
      } else {
        tokens.push({
          type: "word",
          sourceIndex: pos,
          value: token
        });
      }

      pos = next;
    }
  }

  for (pos = stack.length - 1; pos; pos -= 1) {
    stack[pos].unclosed = true;
  }

  return stack[0].nodes;
};