<?php
namespace FWIF;

use DateTime;
use DateTimeInterface;
use DateTimeZone;

class FWIF {
    public const CONTENT_TYPE = 'text/plain; charset=us-ascii'; // TODO: come up with a mime type

    public const DEFAULT = 0;
    public const DISCARD_MILLISECONDS = 0x01; // Always exclude the millisecond component from DateTime

    public const TYPE_NULL      = 0;    // NULL, no data
    public const TYPE_INTEGER   = 0x01; // LEB128, implicit length
    public const TYPE_FLOAT     = 0x02; // double precision IEEE 754, fixed length of 8 bytes
    public const TYPE_STRING    = 0x03; // UTF-8 string, terminated with TRAILER
    public const TYPE_BUFFER    = 0x04; // Buffer with binary data, prefixed with a LEB128 length
    public const TYPE_ARRAY     = 0x05; // List of values, terminated with TRAILER
    public const TYPE_OBJECT    = 0x06; // List of values with ASCII names, terminated with TRAILER
    public const TYPE_DATETIME  = 0x07; // A gregorian year, month and day as well as an hour, minute and seconds component, fixed length of * bytes
    
    public const TRAILER = 0xFF; // Termination byte

    private const CODECS = [
        self::TYPE_NULL => 'Null',
        self::TYPE_INTEGER => 'Integer',
        self::TYPE_FLOAT => 'Float',
        self::TYPE_STRING => 'String',
        self::TYPE_ARRAY => 'Array',
        self::TYPE_OBJECT => 'Object',
        self::TYPE_BUFFER => 'Buffer',
        self::TYPE_DATETIME => 'DateTime',
    ];

    private const UTF8 = '%^(?:' // https://www.w3.org/International/questions/qa-forms-utf-8.en
                        . '[\x09\x0A\x0D\x20-\x7E]'             // ASCII
                        . '|[\xC2-\xDF][\x80-\xBF]'             // non-overlong 2-byte
                        . '|\xE0[\xA0-\xBF][\x80-\xBF]'         // excluding overlongs
                        . '|[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}'  // straight 3-byte
                        . '|\xED[\x80-\x9F][\x80-\xBF]'         // excluding surrogates
                        . '|\xF0[\x90-\xBF][\x80-\xBF]{2}'      // planes 1-3
                        . '|[\xF1-\xF3][\x80-\xBF]{3}'          // planes 4-15
                        . '|\xF4[\x80-\x8F][\x80-\xBF]{2}'      // plane 16 
                        . ')*$%xs';

    private static function isAssocArray($array): bool {
        if(!is_array($array) || $array === [])
            return false;
        return array_keys($array) !== range(0, count($array) - 1);
    }

    // apparently this is faster than mb_check_encoding($string, 'utf-8');
    // on PHP 7.1 on Windows at least, perhaps investigate this later
    private static function isUTF8String(string $string): bool {
        return preg_match(self::UTF8, $string) === 1;
    }

    private static function detectType($data, int $flags): int {
        if(is_null($data))
            return self::TYPE_NULL;
        if(is_int($data))
            return self::TYPE_INTEGER;
        if(is_float($data))
            return self::TYPE_FLOAT;
        if(is_string($data))
            return self::isUTF8String($data) ? self::TYPE_STRING : self::TYPE_BUFFER;
        if(is_object($data) || self::isAssocArray($data)) {
            if($data instanceof DateTimeInterface)
                return self::TYPE_DATETIME;
            return self::TYPE_OBJECT;
        }
        if(is_array($data))
            return self::TYPE_ARRAY;
        throw new FWIFUnsupportedTypeException(gettype($data));
    }

    public static function encode($data, int $flags = self::DEFAULT): string {
        if($data instanceof FWIFSerializable)
            $data = $data->fwifSerialize();
        $type = self::detectType($data, $flags);
        return chr($type) . self::{'encode' . self::CODECS[$type]}($data, $flags);
    }

    public static function decode(string $data, int $flags = self::DEFAULT) {
        return self::decodeInternal(new FWIFDecodeStream($data), $flags);
    }

    private static function decodeInternal(FWIFDecodeStream $data, int $flags) {
        $type = $data->readByte();
        if(!array_key_exists($type, self::CODECS)) {
            $hexType = dechex($type); $hexPos = dechex($data->getPosition());
            throw new FWIFUnsupportedTypeException("Unsupported type {$type} (0x{$hexType}) at position {$data->getPosition()} (0x{$hexPos})");
        }
        return self::{'decode' . self::CODECS[$type]}($data, $flags);
    }

    private static function encodeNull($data, int $flags): string { return ''; }
    private static function decodeNull(FWIFDecodeStream $data, int $flags) { return null; }

    private static function encodeInteger(int $number, int $flags): string {
        $packed = ''; $more = 1; $negative = $number < 0; $size = PHP_INT_SIZE * 8;
        while($more) {
            $byte = $number & 0x7F;
            $number >>= 7;
            if($negative)
                $number |= (~0 << ($size - 7));
            if((!$number && !($byte & 0x40)) || ($number === -1 && ($byte & 0x40)))
                $more = 0;
            else
                $byte |= 0x80;
            $packed .= chr($byte);
        }
        return $packed;
    }
    private static function decodeInteger(FWIFDecodeStream $data, int $flags): int {
        $number = 0; $shift = 0; $o = 0; $size = PHP_INT_SIZE * 8;
        do {
            $byte = $data->readByte();
            $number |= ($byte & 0x7F) << $shift;
            $shift += 7;
        } while($byte & 0x80);
        if(($shift < $size) && ($byte & 0x40))
            $number |= (~0 << $shift);
        return $number;
    }

    private static function encodeFloat(float $number, int $flags): string {
        return pack('E', $number);
    }
    private static function decodeFloat(FWIFDecodeStream $data, int $flags): float {
        return unpack('E', $data->readString(8))[1];
    }

    private static function encodeString(string $string, int $flags): string {
        $packed = ''; $string = unpack('C*', mb_convert_encoding($string, 'utf-8'));
        foreach($string as $char)
            $packed .= chr($char);
        return $packed . chr(self::TRAILER);
    }
    private static function decodeAsciiString(FWIFDecodeStream $data, int $flags): string {
        $string = '';
        for(;;) {
            $byte = $data->readByte();
            if($byte === self::TRAILER)
                break;
            $string .= chr($byte);
        }
        return $string;
    }
    private static function decodeString(FWIFDecodeStream $data, int $flags): string {   // This should decode based on the utf-8 spec rather than just
        return mb_convert_encoding(self::decodeAsciiString($data, $flags), 'utf-8'); //  grabbing the FF terminated string representation.
    }

    private static function encodeArray(array $array, int $flags): string {
        $packed = '';
        foreach($array as $value)
            $packed .= self::encode($value, $flags);
        return $packed . chr(self::TRAILER);
    }
    private static function decodeArray(FWIFDecodeStream $data, int $flags): array {
        $array = [];
        for(;;) {
            if($data->readByte() === self::TRAILER)
                break;
            $data->stepBack();
            $array[] = self::decodeInternal($data, $flags);
        }
        return $array;
    }

    private static function encodeObject($object, int $flags): string {
        $packed = ''; $array = (array)$object;
        foreach($array as $name => $value)
            $packed .= $name . chr(self::TRAILER) . self::encode($value, $flags);
        return $packed . chr(self::TRAILER);
    }
    private static function decodeObject(FWIFDecodeStream $data, int $flags): object {
        $array = [];
        for(;;) {
            if($data->readByte() === self::TRAILER)
                break;
            $data->stepBack();
            $name = self::decodeAsciiString($data, $flags);
            $array[$name] = self::decodeInternal($data, $flags);
        }
        return (object)$array;
    }

    private static function encodeBuffer(string $buffer, int $flags): string {
        return self::encodeInteger(strlen($buffer), $flags) . $buffer;
    }
    private static function decodeBuffer(FWIFDecodeStream $data, int $flags): string {
        return $data->readString(self::decodeInteger($data, $flags));
    }

    private const DATETIME_FLAG_TIME   = 0x01;
    private const DATETIME_FLAG_MILLI  = 0x02;
    private const DATETIME_FLAG_MASK   = 0x03;

    private const DATETIME_YEAR_SIGN  = 0x800000;
    private const DATETIME_YEAR_MASK  = 0x3FFF;
    private const DATETIME_YEAR_SHIFT = 9;

    private const DATETIME_MONTH_MASK  = 0x0F;
    private const DATETIME_MONTH_SHIFT = 5;

    private const DATETIME_DAY_MASK = 0x1F;

    private const DATETIME_HOUR_MASK  = 0x1F;
    private const DATETIME_HOUR_SHIFT = 12;

    private const DATETIME_MINS_MASK  = 0x3F;
    private const DATETIME_MINS_SHIFT = 6;

    private const DATETIME_SECS_MASK = 0x3F;

    private const DATETIME_MILLI_MASK = 0xFFFFF;

    /*  One block     Chunked
        +--------+    +--------+  +--------+
      0 | YYYYYYY|    |YYYYYYYY|  |FFF.....|
      8 |YYYYYYYY|    |YYYYYYYM|  +--------+
     12 |    MMMM|    |MMMDDDDD|
     16 |   DDDDD|    +--------+
     24 |FFFHHHHH|    FHmS and U seperate       Semicombined FHmSU
     32 |  mmmmmm|    +--------+  +--------+    +--------+ +--------+
     40 |  SSSSSS|    |FFFHHHHH|  |UUUUUUUU|    |FFFHHHHH| |UUUUUUUU|
     48 |uuuuuuuu|    |mmmmmmSS|  |UUUUUUUU| OR |mmmmmmSS| |UUUUUUUU|
     56 |uuuuuuuu|    |SSSS....|  |UUUU....|    |SSSSUUUU| +--------+
     64 |uuuuuuuu|    +--------+  +--------+    +--------+
        +--------+    In both situations the upper byte of FHmS would always be present for the flags.
                      Meaning the thing would take up at least 4 bytes and at most 9 bytes with 1 unused bit.
                      Most situations I'd imagine you wouldn't really care about the milliseconds,
                       in which you end up with 7 bytes with 5 unused bits.
                      Is there a benefit to this over just using .NET-style ticks?
                      Yes, it can be entirely handled using just 32-bit integers.
     */

    private static function encodeDateTime(DateTimeInterface $dt, int $flags): string {
        static $utc = null;
        if($utc === null)
            $utc = new DateTimeZone('utc');

        if($dt->getTimezone()->getOffset($dt) !== 0)
            $dt = DateTime::createFromInterface($dt)->setTimezone($utc);

        $dtf = 0;

        $year  = (int)$dt->format('Y');
        $month = (int)$dt->format('n');
        $day   = (int)$dt->format('j');

        $subYear = $year < 0;
        if($subYear)
            $year = ~$year;
        
        $ymd  = $subYear ? self::DATETIME_YEAR_SIGN : 0;
        $ymd |= ( $year       & self::DATETIME_YEAR_MASK)  << self::DATETIME_YEAR_SHIFT;
        $ymd |= (($month - 1) & self::DATETIME_MONTH_MASK) << self::DATETIME_MONTH_SHIFT;
        $ymd |= (($day   - 1) & self::DATETIME_DAY_MASK);

        var_dump(str_pad(decbin($ymd), 24, '0', STR_PAD_LEFT));

        $hours  = (int)$dt->format('G');
        $mins   = (int)$dt->format('i');
        $secs   = (int)$dt->format('s');
        $millis = ($flags & self::DISCARD_MILLISECONDS) ? 0 : (int)$dt->format('u');

        // Add year, month, day

        if($hours > 0 || $mins > 0 || $secs > 0 || $millis > 0) {
            $dtf |= self::DATETIME_FLAG_TIME;
            $hms  = 0;
            $hms |= ($hours & self::DATETIME_HOUR_MASK) << self::DATETIME_HOUR_SHIFT;
            $hms |= ($mins  & self::DATETIME_MINS_MASK) << self::DATETIME_MINS_SHIFT;
            $hms |= ($secs  & self::DATETIME_SECS_MASK);

            var_dump(str_pad(decbin($hms), 17, '0', STR_PAD_LEFT));

            if($millis > 0) {
                $dtf    |= self::DATETIME_FLAG_MILLI;
                $millis &= self::DATETIME_MILLI_MASK;
                
                var_dump(str_pad(decbin($millis), 20, '0', STR_PAD_LEFT));
            }
        }

        echo "\r\n";

        return '';
    }
    private static function decodeDateTime(FWIFDecodeStream $data, int $flags): DateTimeInterface {
        return new \DateTime();
    }
}