class PoHeader

class PoHeader {
    
    /**
     * Language code.
     *
     * @var string
     */
    protected $langcode;
    
    /**
     * Formula for the plural form.
     *
     * @var string
     */
    protected $pluralForms;
    
    /**
     * Author(s) of the file.
     *
     * @var string[]
     */
    protected $authors;
    
    /**
     * Date the po file got created.
     *
     * @var string
     */
    protected $poDate;
    
    /**
     * Human readable language name.
     *
     * @var string
     */
    protected $languageName;
    
    /**
     * Name of the project the translation belongs to.
     *
     * @var string
     */
    protected $projectName;
    
    /**
     * Constructor, creates a PoHeader with default values.
     *
     * @param string $langcode
     *   Language code.
     */
    public function __construct($langcode = NULL) {
        $this->langcode = $langcode;
        // Ignore errors when run during site installation before
        // date_default_timezone_set() is called.
        $this->poDate = @date("Y-m-d H:iO");
        $this->pluralForms = 'nplurals=2; plural=(n > 1);';
    }
    
    /**
     * Gets the plural form.
     *
     * @return string
     *   Plural form component from the header, for example:
     *   'nplurals=2; plural=(n > 1);'.
     */
    public function getPluralForms() {
        return $this->pluralForms;
    }
    
    /**
     * Set the human readable language name.
     *
     * @param string $languageName
     *   Human readable language name.
     */
    public function setLanguageName($languageName) {
        $this->languageName = $languageName;
    }
    
    /**
     * Gets the human readable language name.
     *
     * @return string
     *   The human readable language name.
     */
    public function getLanguageName() {
        return $this->languageName;
    }
    
    /**
     * Set the project name.
     *
     * @param string $projectName
     *   Human readable project name.
     */
    public function setProjectName($projectName) {
        $this->projectName = $projectName;
    }
    
    /**
     * Gets the project name.
     *
     * @return string
     *   The human readable project name.
     */
    public function getProjectName() {
        return $this->projectName;
    }
    
    /**
     * Populate internal values from a string.
     *
     * @param string $header
     *   Full header string with key-value pairs.
     */
    public function setFromString($header) {
        // Get an array of all header values for processing.
        $values = $this->parseHeader($header);
        // There is only one value relevant for our header implementation when
        // reading, and that is the plural formula.
        if (!empty($values['Plural-Forms'])) {
            $this->pluralForms = $values['Plural-Forms'];
        }
    }
    
    /**
     * Generate a Gettext PO formatted header string based on data set earlier.
     */
    public function __toString() {
        $output = '';
        $isTemplate = empty($this->languageName);
        $output .= '# ' . ($isTemplate ? 'LANGUAGE' : $this->languageName) . ' translation of ' . ($isTemplate ? 'PROJECT' : $this->projectName) . "\n";
        if (!empty($this->authors)) {
            $output .= '# Generated by ' . implode("\n# ", $this->authors) . "\n";
        }
        $output .= "#\n";
        // Add the actual header information.
        $output .= "msgid \"\"\n";
        $output .= "msgstr \"\"\n";
        $output .= "\"Project-Id-Version: PROJECT VERSION\\n\"\n";
        $output .= "\"POT-Creation-Date: " . $this->poDate . "\\n\"\n";
        $output .= "\"PO-Revision-Date: " . $this->poDate . "\\n\"\n";
        $output .= "\"Last-Translator: NAME <EMAIL@ADDRESS>\\n\"\n";
        $output .= "\"Language-Team: LANGUAGE <EMAIL@ADDRESS>\\n\"\n";
        $output .= "\"MIME-Version: 1.0\\n\"\n";
        $output .= "\"Content-Type: text/plain; charset=utf-8\\n\"\n";
        $output .= "\"Content-Transfer-Encoding: 8bit\\n\"\n";
        $output .= "\"Plural-Forms: " . $this->pluralForms . "\\n\"\n";
        $output .= "\n";
        return $output;
    }
    
    /**
     * Parses a Plural-Forms entry from a Gettext Portable Object file header.
     *
     * @param string $plural_forms
     *   The Plural-Forms entry value.
     *
     * @return array|bool
     *   An indexed array of parsed plural formula data. Containing:
     *   - 'nplurals': The number of plural forms defined by the plural formula.
     *   - 'plurals': Array of plural positions keyed by plural value.
     *   False when there is no plural string.
     *
     * @throws \Exception
     */
    public function parsePluralForms($plural_forms) {
        $plurals = [];
        // First, delete all whitespace.
        $plural_forms = strtr($plural_forms, [
            " " => "",
            "\t" => "",
        ]);
        // Select the parts that define nplurals and plural.
        $nplurals = strstr($plural_forms, "nplurals=");
        if (strpos($nplurals, ";")) {
            // We want the string from the 10th char, because "nplurals=" length is 9.
            $nplurals = substr($nplurals, 9, strpos($nplurals, ";") - 9);
        }
        else {
            return FALSE;
        }
        $plural = strstr($plural_forms, "plural=");
        if (strpos($plural, ";")) {
            // We want the string from the 8th char, because "plural=" length is 7.
            $plural = substr($plural, 7, strpos($plural, ";") - 7);
        }
        else {
            return FALSE;
        }
        // If the number of plurals is zero, we return a default result.
        if ($nplurals == 0) {
            return [
                $nplurals,
                [
                    'default' => 0,
                ],
            ];
        }
        // Calculate possible plural positions of different plural values. All known
        // plural formula's are repetitive above 100.
        // For data compression we store the last position the array value
        // changes and store it as default.
        $element_stack = $this->parseArithmetic($plural);
        if ($element_stack !== FALSE) {
            for ($i = 0; $i <= 199; $i++) {
                $plurals[$i] = $this->evaluatePlural($element_stack, $i);
            }
            $default = $plurals[$i - 1];
            $plurals = array_filter($plurals, function ($value) use ($default) {
                return $value != $default;
            });
            $plurals['default'] = $default;
            return [
                $nplurals,
                $plurals,
            ];
        }
        else {
            throw new \Exception('The plural formula could not be parsed.');
        }
    }
    
    /**
     * Parses a Gettext Portable Object file header.
     *
     * @param string $header
     *   A string containing the complete header.
     *
     * @return array
     *   An associative array of key-value pairs.
     */
    private function parseHeader($header) {
        $header_parsed = [];
        $lines = array_map('trim', explode("\n", $header));
        foreach ($lines as $line) {
            if ($line) {
                [
                    $tag,
                    $contents,
                ] = explode(":", $line, 2);
                $header_parsed[trim($tag)] = trim($contents);
            }
        }
        return $header_parsed;
    }
    
    /**
     * Parses and sanitizes an arithmetic formula into a plural element stack.
     *
     * While parsing, we ensure, that the operators have the right
     * precedence and associativity.
     *
     * @param string $string
     *   A string containing the arithmetic formula.
     *
     * @return array|bool
     *   A stack of values and operations to be evaluated. False if the formula
     *   could not be parsed.
     */
    private function parseArithmetic($string) {
        // Operator precedence table.
        $precedence = [
            "(" => -1,
            ")" => -1,
            "?" => 1,
            ":" => 1,
            "||" => 3,
            "&&" => 4,
            "==" => 5,
            "!=" => 5,
            "<" => 6,
            ">" => 6,
            "<=" => 6,
            ">=" => 6,
            "+" => 7,
            "-" => 7,
            "*" => 8,
            "/" => 8,
            "%" => 8,
        ];
        // Right associativity.
        $right_associativity = [
            "?" => 1,
            ":" => 1,
        ];
        $tokens = $this->tokenizeFormula($string);
        // Parse by converting into infix notation then back into postfix
        // Operator stack - holds math operators and symbols.
        $operator_stack = [];
        // Element Stack - holds data to be operated on.
        $element_stack = [];
        foreach ($tokens as $token) {
            $current_token = $token;
            // Numbers and the $n variable are simply pushed into $element_stack.
            if (is_numeric($token)) {
                $element_stack[] = $current_token;
            }
            elseif ($current_token == "n") {
                $element_stack[] = '$n';
            }
            elseif ($current_token == "(") {
                $operator_stack[] = $current_token;
            }
            elseif ($current_token == ")") {
                $top_op = array_pop($operator_stack);
                while (isset($top_op) && $top_op != "(") {
                    $element_stack[] = $top_op;
                    $top_op = array_pop($operator_stack);
                }
            }
            elseif (!empty($precedence[$current_token])) {
                // If it's an operator, then pop from $operator_stack into
                // $element_stack until the precedence in $operator_stack is less
                // than current, then push into $operator_stack.
                $top_op = array_pop($operator_stack);
                while (isset($top_op) && $precedence[$top_op] >= $precedence[$current_token] && !($precedence[$top_op] == $precedence[$current_token] && !empty($right_associativity[$top_op]) && !empty($right_associativity[$current_token]))) {
                    $element_stack[] = $top_op;
                    $top_op = array_pop($operator_stack);
                }
                if ($top_op) {
                    // Return element to top.
                    $operator_stack[] = $top_op;
                }
                // Parentheses are not needed.
                $operator_stack[] = $current_token;
            }
            else {
                return FALSE;
            }
        }
        // Flush operator stack.
        $top_op = array_pop($operator_stack);
        while ($top_op != NULL) {
            $element_stack[] = $top_op;
            $top_op = array_pop($operator_stack);
        }
        $return = $element_stack;
        // Now validate stack.
        $previous_size = count($element_stack) + 1;
        while (count($element_stack) < $previous_size) {
            $previous_size = count($element_stack);
            for ($i = 2; $i < count($element_stack); $i++) {
                $op = $element_stack[$i];
                if (!empty($precedence[$op])) {
                    if ($op == ":") {
                        $f = $element_stack[$i - 2] . "):" . $element_stack[$i - 1] . ")";
                    }
                    elseif ($op == "?") {
                        $f = "(" . $element_stack[$i - 2] . "?(" . $element_stack[$i - 1];
                    }
                    else {
                        $f = "(" . $element_stack[$i - 2] . $op . $element_stack[$i - 1] . ")";
                    }
                    array_splice($element_stack, $i - 2, 3, $f);
                    break;
                }
            }
        }
        // If only one element is left, the number of operators is appropriate.
        return count($element_stack) == 1 ? $return : FALSE;
    }
    
    /**
     * Tokenize the formula.
     *
     * @param string $formula
     *   A string containing the arithmetic formula.
     *
     * @return array
     *   List of arithmetic tokens identified in the formula.
     */
    private function tokenizeFormula($formula) {
        $formula = str_replace(" ", "", $formula);
        $tokens = [];
        for ($i = 0; $i < strlen($formula); $i++) {
            if (is_numeric($formula[$i])) {
                $num = $formula[$i];
                $j = $i + 1;
                while ($j < strlen($formula) && is_numeric($formula[$j])) {
                    $num .= $formula[$j];
                    $j++;
                }
                $i = $j - 1;
                $tokens[] = $num;
            }
            elseif ($pos = strpos(" =<>!&|", $formula[$i])) {
                $next = $formula[$i + 1];
                switch ($pos) {
                    case 1:
                    case 2:
                    case 3:
                    case 4:
                        if ($next == '=') {
                            $tokens[] = $formula[$i] . '=';
                            $i++;
                        }
                        else {
                            $tokens[] = $formula[$i];
                        }
                        break;
                    case 5:
                        if ($next == '&') {
                            $tokens[] = '&&';
                            $i++;
                        }
                        else {
                            $tokens[] = $formula[$i];
                        }
                        break;
                    case 6:
                        if ($next == '|') {
                            $tokens[] = '||';
                            $i++;
                        }
                        else {
                            $tokens[] = $formula[$i];
                        }
                        break;
                }
            }
            else {
                $tokens[] = $formula[$i];
            }
        }
        return $tokens;
    }
    
    /**
     * Evaluate the plural element stack using a plural value.
     *
     * Using an element stack, which represents a plural formula, we calculate
     * which plural string should be used for a given plural value.
     *
     * An example of plural formula parting and evaluation:
     *   Plural formula: 'n!=1'
     * This formula is parsed by parseArithmetic() to a stack (array) of elements:
     *   array(
     *     0 => '$n',
     *     1 => '1',
     *     2 => '!=',
     *   );
     * The evaluatePlural() method evaluates the $element_stack using the plural
     * value $n. Before the actual evaluation, the '$n' in the array is replaced
     * by the value of $n.
     *   For example: $n = 2 results in:
     *   array(
     *     0 => '2',
     *     1 => '1',
     *     2 => '!=',
     *   );
     * The stack is processed until only one element is (the result) is left. In
     * every iteration the top elements of the stack, up until the first operator,
     * are evaluated. After evaluation the arguments and the operator itself are
     * removed and replaced by the evaluation result. This is typically 2
     * arguments and 1 element for the operator.
     *   Because the operator is '!=' the example stack is evaluated as:
     *   $f = (int) 2 != 1;
     *   The resulting stack is:
     *   array(
     *     0 => 1,
     *   );
     * With only one element left in the stack (the final result) the loop is
     * terminated and the result is returned.
     *
     * @param array $element_stack
     *   Array of plural formula values and operators create by parseArithmetic().
     * @param int $n
     *   The @count number for which we are determining the right plural position.
     *
     * @return int
     *   Number of the plural string to be used for the given plural value.
     *
     * @see parseArithmetic()
     *
     * @throws \Exception
     */
    protected function evaluatePlural($element_stack, $n) {
        $count = count($element_stack);
        $limit = $count;
        // Replace the '$n' value in the formula by the plural value.
        for ($i = 0; $i < $count; $i++) {
            if ($element_stack[$i] === '$n') {
                $element_stack[$i] = $n;
            }
        }
        // We process the stack until only one element is (the result) is left.
        // We limit the number of evaluation cycles to prevent an endless loop in
        // case the stack contains an error.
        while (isset($element_stack[1])) {
            for ($i = 2; $i < $count; $i++) {
                // There's no point in checking non-symbols. Also, switch(TRUE) would
                // match any case and so it would break.
                if (is_bool($element_stack[$i]) || is_numeric($element_stack[$i])) {
                    continue;
                }
                $f = NULL;
                $length = 3;
                $delta = 2;
                switch ($element_stack[$i]) {
                    case '==':
                        $f = $element_stack[$i - 2] == $element_stack[$i - 1];
                        break;
                    case '!=':
                        $f = $element_stack[$i - 2] != $element_stack[$i - 1];
                        break;
                    case '<=':
                        $f = $element_stack[$i - 2] <= $element_stack[$i - 1];
                        break;
                    case '>=':
                        $f = $element_stack[$i - 2] >= $element_stack[$i - 1];
                        break;
                    case '<':
                        $f = $element_stack[$i - 2] < $element_stack[$i - 1];
                        break;
                    case '>':
                        $f = $element_stack[$i - 2] > $element_stack[$i - 1];
                        break;
                    case '+':
                        $f = $element_stack[$i - 2] + $element_stack[$i - 1];
                        break;
                    case '-':
                        $f = $element_stack[$i - 2] - $element_stack[$i - 1];
                        break;
                    case '*':
                        $f = $element_stack[$i - 2] * $element_stack[$i - 1];
                        break;
                    case '/':
                        $f = $element_stack[$i - 2] / $element_stack[$i - 1];
                        break;
                    case '%':
                        $f = $element_stack[$i - 2] % $element_stack[$i - 1];
                        break;
                    case '&&':
                        $f = $element_stack[$i - 2] && $element_stack[$i - 1];
                        break;
                    case '||':
                        $f = $element_stack[$i - 2] || $element_stack[$i - 1];
                        break;
                    case ':':
                        $f = $element_stack[$i - 3] ? $element_stack[$i - 2] : $element_stack[$i - 1];
                        // This operator has 3 preceding elements, instead of the default 2.
                        $length = 5;
                        $delta = 3;
                        break;
                }
                // If the element is an operator we remove the processed elements and
                // store the result.
                if (isset($f)) {
                    array_splice($element_stack, $i - $delta, $length, $f);
                    break;
                }
            }
        }
        if (!$limit) {
            throw new \Exception('The plural formula could not be evaluated.');
        }
        return (int) $element_stack[0];
    }

}