1 files changed, 220 insertions, 0 deletions
diff --git a/src/UtfString.php b/src/UtfString.php
new file mode 100644
index 0000000..8815e58
--- /dev/null
+++ b/src/UtfString.php
@@ -0,0 +1,220 @@
+<?php
+
+namespace SqlParser;
+
+/**
+ * Implements array-like access for UTF-8 strings.
+ *
+ * In this library, this class should be used to parse UTF-8 queries.
+ */
+class UtfString implements \ArrayAccess
+{
+
+    /**
+     * The raw, multibyte string.
+     *
+     * @var string
+     */
+    private $str = '';
+
+    /**
+     * The index of current byte.
+     *
+     * For ASCII strings, the byte index is equal to the character index.
+     *
+     * @var int
+     */
+    private $byteIdx = 0;
+
+    /**
+     * The index of current character.
+     *
+     * For non-ASCII strings, some characters occupy more than one byte and
+     * the character index will have a lower value than the byte index.
+     *
+     * @var int
+     */
+    private $charIdx = 0;
+
+    /**
+     * The length of the string (in bytes).
+     *
+     * @var int
+     */
+    private $buffLen = 0;
+
+    /**
+     * The length of the string (in characters).
+     *
+     * @var int
+     */
+    private $charLen = 0;
+
+    /**
+     * Constructor.
+     *
+     * @param string $str
+     */
+    public function __construct($str)
+    {
+        $this->str = $str;
+        $this->byteIdx = 0;
+        $this->charIdx = 0;
+        // TODO: `strlen($str)` might return a wrong length when function
+        // overloading is enabled.
+        // https://php.net/manual/ro/mbstring.overload.php
+        $this->byteLen = strlen($str);
+        $this->charLen = mb_strlen($str);
+    }
+
+    /**
+     * Checks if the given offset exists.
+     *
+     * @param int $offset
+     *
+     * @return bool
+     */
+    public function offsetExists($offset)
+    {
+        return $offset < $charLen;
+    }
+
+    /**
+     * Gets the character at given offset.
+     *
+     * @param int $offset
+     *
+     * @return string
+     */
+    public function offsetGet($offset)
+    {
+        if (($offset < 0) || ($offset >= $this->charLen)) {
+            return null;
+        }
+
+        $delta = $offset - $this->charIdx;
+
+        if ($delta > 0) {
+            // Fast forwarding.
+            while ($delta-- > 0) {
+                $this->byteIdx += static::getCharLength($this->str[$this->byteIdx]);
+                ++$this->charIdx;
+            }
+        } elseif ($delta < 0) {
+            // Rewinding.
+            while ($delta++ < 0) {
+                do {
+                    $byte = ord($this->str[--$this->byteIdx]);
+                } while ((128 <= $byte) && ($byte < 192));
+                --$this->charIdx;
+            }
+        }
+
+        $bytesCount = static::getCharLength($this->str[$this->byteIdx]);
+
+        $ret = '';
+        for ($i = 0; $bytesCount-- > 0; ++$i) {
+            $ret .= $this->str[$this->byteIdx + $i];
+        }
+
+        return $ret;
+    }
+
+    /**
+     * Sets the value of a character.
+     *
+     * @param int $offset
+     * @param string $value
+     */
+    public function offsetSet($offset, $value)
+    {
+        throw new \Exception('Not implemented.');
+    }
+
+    /**
+     * Unsets an index.
+     *
+     * @param int $offset
+     */
+    public function offsetUnset($offset)
+    {
+        throw new \Exception('Not implemented.');
+    }
+
+    /**
+     * Gets the length of an UTF-8 character.
+     *
+     * According to RFC 3629, a UTF-8 character can have at most 4 bytes.
+     * However, this implemenation supports UTF-8 characters containing up to 6
+     * bytes.
+     *
+     * @see http://tools.ietf.org/html/rfc3629
+     *
+     * @param string $byte
+     *
+     * @return int
+     */
+    private static function getCharLength($byte)
+    {
+        $byte = ord($byte);
+        if ($byte < 128) {
+            return 1;
+        } elseif ($byte < 224) {
+            return 2;
+        } elseif ($byte < 240) {
+            return 3;
+        } elseif ($byte < 248) {
+            return 4;
+        } elseif ($byte === 252) {
+            return 5; // unofficial
+        }
+        return 6; // unofficial
+    }
+
+    /**
+     * Returns the number of remaining characters.
+     *
+     * @return int
+     */
+    public function remaining()
+    {
+        if ($this->charIdx < $this->charLen) {
+            return $this->charLen - $this->charIdx;
+        }
+        return 0;
+    }
+
+    /**
+     * Returns the length in characters of the string.
+     *
+     * @return int
+     */
+    public function length()
+    {
+        return $this->charLen;
+    }
+
+    /**
+     * Gets the values of the indexes.
+     *
+     * @param int &$byte
+     * @param int &$char
+     */
+    public function getIndexes(&$byte, &$char)
+    {
+        $byte = $this->byteIdx;
+        $char = $this->charIdx;
+    }
+
+    /**
+     * Sets the values of the indexes.
+     *
+     * @param int $byte
+     * @param int $char
+     */
+    public function setIndexes($byte = 0, $char = 0)
+    {
+        $this->byteIdx = $byte;
+        $this->charIdx = $char;
+    }
+}