PO::read_entry( resource $f, int $lineno )

	function read_entry($f, $lineno = 0) {
		$entry = new Translation_Entry();
		// where were we in the last step
		// can be: comment, msgctxt, msgid, msgid_plural, msgstr, msgstr_plural
		$context = '';
		$msgstr_index = 0;
		while (true) {
			$lineno++;
			$line = PO::read_line($f);
			if (!$line)  {
				if (feof($f)) {
					if (self::is_final($context))
						break;
					elseif (!$context) // we haven't read a line and eof came
						return null;
					else
						return false;
				} else {
					return false;
				}
			}
			if ($line == "\n") continue;
			$line = trim($line);
			if (preg_match('/^#/', $line, $m)) {
				// the comment is the start of a new entry
				if (self::is_final($context)) {
					PO::read_line($f, 'put-back');
					$lineno--;
					break;
				}
				// comments have to be at the beginning
				if ($context && $context != 'comment') {
					return false;
				}
				// add comment
				$this->add_comment_to_entry($entry, $line);
			} elseif (preg_match('/^msgctxt\s+(".*")/', $line, $m)) {
				if (self::is_final($context)) {
					PO::read_line($f, 'put-back');
					$lineno--;
					break;
				}
				if ($context && $context != 'comment') {
					return false;
				}
				$context = 'msgctxt';
				$entry->context .= PO::unpoify($m[1]);
			} elseif (preg_match('/^msgid\s+(".*")/', $line, $m)) {
				if (self::is_final($context)) {
					PO::read_line($f, 'put-back');
					$lineno--;
					break;
				}
				if ($context && $context != 'msgctxt' && $context != 'comment') {
					return false;
				}
				$context = 'msgid';
				$entry->singular .= PO::unpoify($m[1]);
			} elseif (preg_match('/^msgid_plural\s+(".*")/', $line, $m)) {
				if ($context != 'msgid') {
					return false;
				}
				$context = 'msgid_plural';
				$entry->is_plural = true;
				$entry->plural .= PO::unpoify($m[1]);
			} elseif (preg_match('/^msgstr\s+(".*")/', $line, $m)) {
				if ($context != 'msgid') {
					return false;
				}
				$context = 'msgstr';
				$entry->translations = array(PO::unpoify($m[1]));
			} elseif (preg_match('/^msgstr\[(\d+)\]\s+(".*")/', $line, $m)) {
				if ($context != 'msgid_plural' && $context != 'msgstr_plural') {
					return false;
				}
				$context = 'msgstr_plural';
				$msgstr_index = $m[1];
				$entry->translations[$m[1]] = PO::unpoify($m[2]);
			} elseif (preg_match('/^".*"$/', $line)) {
				$unpoified = PO::unpoify($line);
				switch ($context) {
					case 'msgid':
						$entry->singular .= $unpoified; break;
					case 'msgctxt':
						$entry->context .= $unpoified; break;
					case 'msgid_plural':
						$entry->plural .= $unpoified; break;
					case 'msgstr':
						$entry->translations[0] .= $unpoified; break;
					case 'msgstr_plural':
						$entry->translations[$msgstr_index] .= $unpoified; break;
					default:
						return false;
				}
			} else {
				return false;
			}
		}

		$have_translations = false;
		foreach ( $entry->translations as $t ) {
			if ( $t || ('0' === $t) ) {
				$have_translations = true;
				break;
			}
		}
		if ( false === $have_translations ) {
			$entry->translations = array();
		}

		return array('entry' => $entry, 'lineno' => $lineno);
	}