<?php

namespace BigFish\PDF417;

/**
 * Computes the Reed Solomon correction factors.
 */
class ReedSolomon
{
    private $factors = [

        // Level 0
        [
            27, 917,
        ],

        // Level 1
        [
            522, 568, 723, 809,
        ],

        // Level 2
        [
            237, 308, 436, 284, 646, 653, 428, 379
        ],

        // Level 3
        [
            274, 562, 232, 755, 599, 524, 801, 132, 295, 116, 442, 428, 295, 42,
            176, 65
        ],

        // Level 4
        [
            361, 575, 922, 525, 176, 586, 640, 321, 536, 742, 677, 742, 687,
            284, 193, 517, 273, 494, 263, 147, 593, 800, 571, 320, 803, 133,
            231, 390, 685, 330, 63, 410,
        ],

        // Level 5
        [
            539, 422, 6, 93, 862, 771, 453, 106, 610, 287, 107, 505, 733, 877,
            381, 612, 723, 476, 462, 172, 430, 609, 858, 822, 543, 376, 511,
            400, 672, 762, 283, 184, 440, 35, 519, 31, 460, 594, 225, 535, 517,
            352, 605, 158, 651, 201, 488, 502, 648, 733, 717, 83, 404, 97, 280,
            771, 840, 629, 4, 381, 843, 623, 264, 543,
        ],

        // Level 6
        [
            521, 310, 864, 547, 858, 580, 296, 379, 53, 779, 897, 444, 400, 925,
            749, 415, 822, 93, 217, 208, 928, 244, 583, 620, 246, 148, 447, 631,
            292, 908, 490, 704, 516, 258, 457, 907, 594, 723, 674, 292, 272, 96,
            684, 432, 686, 606, 860, 569, 193, 219, 129, 186, 236, 287, 192,
            775, 278, 173, 40, 379, 712, 463, 646, 776, 171, 491, 297, 763, 156,
            732, 95, 270, 447, 90, 507, 48, 228, 821, 808, 898, 784, 663, 627,
            378, 382, 262, 380, 602, 754, 336, 89, 614, 87, 432, 670, 616, 157,
            374, 242, 726, 600, 269, 375, 898, 845, 454, 354, 130, 814, 587,
            804, 34, 211, 330, 539, 297, 827, 865, 37, 517, 834, 315, 550, 86,
            801, 4, 108, 539,
        ],

        // Level 7
        [
            524, 894, 75, 766, 882, 857, 74, 204, 82, 586, 708, 250, 905, 786,
            138, 720, 858, 194, 311, 913, 275, 190, 375, 850, 438, 733, 194,
            280, 201, 280, 828, 757, 710, 814, 919, 89, 68, 569, 11, 204, 796,
            605, 540, 913, 801, 700, 799, 137, 439, 418, 592, 668, 353, 859,
            370, 694, 325, 240, 216, 257, 284, 549, 209, 884, 315, 70, 329, 793,
            490, 274, 877, 162, 749, 812, 684, 461, 334, 376, 849, 521, 307,
            291, 803, 712, 19, 358, 399, 908, 103, 511, 51, 8, 517, 225, 289,
            470, 637, 731, 66, 255, 917, 269, 463, 830, 730, 433, 848, 585, 136,
            538, 906, 90, 2, 290, 743, 199, 655, 903, 329, 49, 802, 580, 355,
            588, 188, 462, 10, 134, 628, 320, 479, 130, 739, 71, 263, 318, 374,
            601, 192, 605, 142, 673, 687, 234, 722, 384, 177, 752, 607, 640,
            455, 193, 689, 707, 805, 641, 48, 60, 732, 621, 895, 544, 261, 852,
            655, 309, 697, 755, 756, 60, 231, 773, 434, 421, 726, 528, 503, 118,
            49, 795, 32, 144, 500, 238, 836, 394, 280, 566, 319, 9, 647, 550,
            73, 914, 342, 126, 32, 681, 331, 792, 620, 60, 609, 441, 180, 791,
            893, 754, 605, 383, 228, 749, 760, 213, 54, 297, 134, 54, 834, 299,
            922, 191, 910, 532, 609, 829, 189, 20, 167, 29, 872, 449, 83, 402,
            41, 656, 505, 579, 481, 173, 404, 251, 688, 95, 497, 555, 642, 543,
            307, 159, 924, 558, 648, 55, 497, 10,
        ],

        // Level 8
        [
            352, 77, 373, 504, 35, 599, 428, 207, 409, 574, 118, 498, 285, 380,
            350, 492, 197, 265, 920, 155, 914, 299, 229, 643, 294, 871, 306, 88,
            87, 193, 352, 781, 846, 75, 327, 520, 435, 543, 203, 666, 249, 346,
            781, 621, 640, 268, 794, 534, 539, 781, 408, 390, 644, 102, 476,
            499, 290, 632, 545, 37, 858, 916, 552, 41, 542, 289, 122, 272, 383,
            800, 485, 98, 752, 472, 761, 107, 784, 860, 658, 741, 290, 204, 681,
            407, 855, 85, 99, 62, 482, 180, 20, 297, 451, 593, 913, 142, 808,
            684, 287, 536, 561, 76, 653, 899, 729, 567, 744, 390, 513, 192, 516,
            258, 240, 518, 794, 395, 768, 848, 51, 610, 384, 168, 190, 826, 328,
            596, 786, 303, 570, 381, 415, 641, 156, 237, 151, 429, 531, 207,
            676, 710, 89, 168, 304, 402, 40, 708, 575, 162, 864, 229, 65, 861,
            841, 512, 164, 477, 221, 92, 358, 785, 288, 357, 850, 836, 827, 736,
            707, 94, 8, 494, 114, 521, 2, 499, 851, 543, 152, 729, 771, 95, 248,
            361, 578, 323, 856, 797, 289, 51, 684, 466, 533, 820, 669, 45, 902,
            452, 167, 342, 244, 173, 35, 463, 651, 51, 699, 591, 452, 578, 37,
            124, 298, 332, 552, 43, 427, 119, 662, 777, 475, 850, 764, 364, 578,
            911, 283, 711, 472, 420, 245, 288, 594, 394, 511, 327, 589, 777,
            699, 688, 43, 408, 842, 383, 721, 521, 560, 644, 714, 559, 62, 145,
            873, 663, 713, 159, 672, 729, 624, 59, 193, 417, 158, 209, 563, 564,
            343, 693, 109, 608, 563, 365, 181, 772, 677, 310, 248, 353, 708,
            410, 579, 870, 617, 841, 632, 860, 289, 536, 35, 777, 618, 586, 424,
            833, 77, 597, 346, 269, 757, 632, 695, 751, 331, 247, 184, 45, 787,
            680, 18, 66, 407, 369, 54, 492, 228, 613, 830, 922, 437, 519, 644,
            905, 789, 420, 305, 441, 207, 300, 892, 827, 141, 537, 381, 662,
            513, 56, 252, 341, 242, 797, 838, 837, 720, 224, 307, 631, 61, 87,
            560, 310, 756, 665, 397, 808, 851, 309, 473, 795, 378, 31, 647, 915,
            459, 806, 590, 731, 425, 216, 548, 249, 321, 881, 699, 535, 673,
            782, 210, 815, 905, 303, 843, 922, 281, 73, 469, 791, 660, 162, 498,
            308, 155, 422, 907, 817, 187, 62, 16, 425, 535, 336, 286, 437, 375,
            273, 610, 296, 183, 923, 116, 667, 751, 353, 62, 366, 691, 379, 687,
            842, 37, 357, 720, 742, 330, 5, 39, 923, 311, 424, 242, 749, 321,
            54, 669, 316, 342, 299, 534, 105, 667, 488, 640, 672, 576, 540, 316,
            486, 721, 610, 46, 656, 447, 171, 616, 464, 190, 531, 297, 321, 762,
            752, 533, 175, 134, 14, 381, 433, 717, 45, 111, 20, 596, 284, 736,
            138, 646, 411, 877, 669, 141, 919, 45, 780, 407, 164, 332, 899, 165,
            726, 600, 325, 498, 655, 357, 752, 768, 223, 849, 647, 63, 310, 863,
            251, 366, 304, 282, 738, 675, 410, 389, 244, 31, 121, 303, 263,
        ],
    ];

    /**
     * Computes the solomon reed correction codewords for given data code words.
     *
     * @param  array   $data  Data code words.
     * @param  integer $level Correction level (0-8).
     * @return array          Correction code words.
     */
    public function compute(array $data, $level)
    {
        if (!isset($this->factors[$level])) {
            $msg = sprintf('Invalid correction level given: "%s". Valid values are 0-8.', $level);
            throw new \InvalidArgumentException($msg);
        }

        // Number of correction code words
        $count = pow(2, $level + 1);

        // Correction factors for the given level
        $factors = $this->factors[$level];

        // Correction code words array, prepopulated with zeros
        $ecWords = array_fill(0, $count, 0);

        // Index of the last correction code word
        $last = $count - 1;

        // Do the math
        foreach ($data as $key => $value) {
            $temp = ($value + $ecWords[$last]) % 929;

            for ($i = $last; $i >= 0; $i -= 1) {
                $add = isset($ecWords[$i - 1]) ? $ecWords[$i - 1] : 0;
                $ecWords[$i] = ($add + 929 - ($temp * $factors[$i]) % 929) % 929;
            }
        }

        foreach($ecWords as &$word) {
            if ($word > 0) {
                $word = 929 - $word;
            }
        }
        unset($word);

        return array_reverse($ecWords);
    }
}