<?php

declare(strict_types=1);

namespace App\Controllers;

use App\Libraries\BookApi;
use App\Libraries\Mongo;

class Books extends BaseController
{
    private BookApi $api;

    /** School level groupings for the browse homepage. */
    private const LEVELS = [
        ['key' => 'th',  'label' => 'Bậc Tiểu học',    'grades' => [1, 2, 3, 4, 5]],
        ['key' => 'thcs','label' => 'Bậc THCS',        'grades' => [6, 7, 8, 9]],
        ['key' => 'thpt','label' => 'Bậc THPT',        'grades' => [10, 11, 12]],
    ];

    /**
     * Subject display order: important subjects first, the rest alphabetical.
     * Values are matched after diacritics/case normalization (e.g. "Vật lí" → "vat li").
     */
    private const SUBJECT_PRIORITY = [
        'Toán'                                => 10,
        'Đại số'                              => 10,
        'Giải tích'                           => 10,
        'Hình học'                            => 10,
        'Tiếng Việt'                          => 20,
        'Ngữ văn'                             => 20,
        'Tiếng Anh'                           => 30,
        'Vật lí'                              => 40,
        'Hóa học'                             => 50,
        'Sinh học'                            => 60,
        'Lịch sử'                             => 70,
        'Địa lí'                              => 80,
        'Giáo dục công dân'                   => 90,
        'Giáo dục Kinh tế và Pháp luật'       => 95,
        'Giáo dục Quốc phòng'                 => 96,
        'Giáo dục thể chất'                   => 97,
        'Tin học'                             => 110,
        'Công nghệ'                           => 120,
        'Kĩ thuật'                            => 125,
        'Tự nhiên và Xã hội'                  => 130,
        'Khoa học'                            => 135,
        'Đạo đức'                             => 140,
        'Hoạt động trải nghiệm'               => 150,
        'Âm nhạc'                             => 160,
        'Mĩ thuật'                            => 170,
        'Atlat Địa lí'                        => 181,
        'Bài giải'                            => 199,
    ];

    /** Cache of normalized subject → rank. */
    private array $subjectRankCache = [];

    public function __construct()
    {
        $this->api = new BookApi();
    }

    /**
     * Catalog: browse view when no filters; grouped, paginated list when filtered.
     */
    public function index()
    {
        $grade     = $this->request->getGet('lop');
        $publisher = $this->request->getGet('nxb');
        $subject   = $this->request->getGet('mon');
        $q         = trim((string) $this->request->getGet('q'));
        $page      = max(1, (int) ($this->request->getGet('trang') ?: 1));
        $perPage   = 48;

        try {
            $books = $this->api->catalog();
        } catch (\Throwable $e) {
            return view('pages/error_api', ['message' => $e->getMessage()]);
        }

        $isFiltered = ($grade !== null && $grade !== '')
            || ($publisher !== null && $publisher !== '')
            || ($subject !== null && $subject !== '')
            || $q !== '';

        // ------- Browse homepage (no filters): level → grade → subjects -------
        if (! $isFiltered) {
            return $this->browseView($books);
        }

        // ------- Filtered list view -------
        $filtered = array_values(array_filter($books, function ($b) use ($grade, $publisher, $subject, $q) {
            if ($grade !== null && $grade !== '' && (string) $b['grade'] !== (string) $grade) return false;
            if ($publisher !== null && $publisher !== '' && $b['publisher'] !== $publisher) return false;
            if ($subject !== null && $subject !== '' && $b['subject'] !== $subject) return false;
            if ($q !== '' && mb_strpos($b['search'] ?? '', mb_strtolower($q)) === false) return false;
            return true;
        }));

        // Group key: by subject when a grade is chosen, else by grade
        $hasGrade = $grade !== null && $grade !== '';
        $groupFn = $hasGrade
            ? fn($b) => $b['subject'] !== '' ? $b['subject'] : 'Khác'
            : fn($b) => $b['grade'] !== '' ? 'Lớp ' . $b['grade'] : 'Không phân lớp';

        // sort: group label, then title (within grade groups keep subject order too)
        if ($hasGrade) {
            usort($filtered, function ($a, $b2) use ($groupFn) {
                $cmp = $this->compareSubjects($groupFn($a), $groupFn($b2));
                return $cmp ?: strcmp((string) $a['title'], (string) $b2['title']);
            });
        } else {
            usort($filtered, function ($a, $b2) {
                $ga = (int) ($a['grade'] ?: 99);
                $gb = (int) ($b2['grade'] ?: 99);
                return $ga <=> $gb
                    ?: $this->compareSubjects((string) $a['subject'], (string) $b2['subject'])
                    ?: strcmp((string) $a['title'], (string) $b2['title']);
            });
        }

        $total     = count($filtered);
        $totalPage = max(1, (int) ceil($total / $perPage));
        $page      = min($page, $totalPage);
        $slice     = array_slice($filtered, ($page - 1) * $perPage, $perPage);

        // group the page slice for rendering
        $grouped = [];
        foreach ($slice as $b) {
            $grouped[$groupFn($b)][] = $b;
        }
        if ($hasGrade) {
            // group by subject, ordered by subject priority
            uksort($grouped, fn($a, $b2) => $this->compareSubjects($a, $b2));
        } else {
            ksort($grouped, SORT_NATURAL);
        }

        return view('books/index', [
            'grouped'    => $grouped,
            'total'      => $total,
            'page'       => $page,
            'totalPage'  => $totalPage,
            'grades'     => $this->gradeList($books),
            'publishers' => $this->facet($books, 'publisher'),
            'subjects'   => $this->facet($books, 'subject'),
            'filters'    => ['lop' => $grade, 'nxb' => $publisher, 'mon' => $subject, 'q' => $q],
        ]);
    }

    /**
     * Build the grouped browse homepage.
     */
    private function browseView(array $books): string
    {
        $publishers = $this->facet($books, 'publisher');

        // grade => [subject => count], grade => total
        $byGrade = [];
        foreach ($books as $b) {
            $g = (string) $b['grade'];
            if ($g === '') {
                $g = '0';
            }
            $byGrade[$g]['total'] = ($byGrade[$g]['total'] ?? 0) + 1;
            $s = $b['subject'] !== '' ? $b['subject'] : 'Khác';
            $byGrade[$g]['subjects'][$s] = ($byGrade[$g]['subjects'][$s] ?? 0) + 1;
            // keep up to 5 cover previews per grade (spread across subjects)
            $used = array_column($byGrade[$g]['covers'] ?? [], 'subject');
            if (count($byGrade[$g]['covers'] ?? []) < 5 && ! in_array($s, $used, true)) {
                $byGrade[$g]['covers'][] = ['id' => $b['id'], 'title' => $b['title'], 'subject' => $s];
            }
        }

        $levels = [];
        foreach (self::LEVELS as $lv) {
            $grades = [];
            foreach ($lv['grades'] as $g) {
                if (isset($byGrade[(string) $g])) {
                    $subs = $byGrade[(string) $g]['subjects'] ?? [];
                    uksort($subs, fn($a, $b2) => $this->compareSubjects($a, $b2));
                    $grades[] = [
                        'grade'   => $g,
                        'total'   => $byGrade[(string) $g]['total'],
                        'subjects'=> $subs,
                        'covers'  => $byGrade[(string) $g]['covers'] ?? [],
                    ];
                }
            }
            if ($grades) {
                $levels[] = ['label' => $lv['label'], 'grades' => $grades];
            }
        }

        return view('books/browse', [
            'total'      => count($books),
            'levels'     => $levels,
            'publishers' => $publishers,
        ]);
    }

    private function gradeList(array $books): array
    {
        $grades = [];
        foreach ($books as $b) {
            if ($b['grade'] !== '') {
                $grades[(int) $b['grade']] = true;
            }
        }
        $grades = array_keys($grades);
        sort($grades);
        return $grades;
    }

    /**
     * Comparator for subjects: priority rank first, then Vietnamese-awarded
     * alphabetical (normalized to strip diacritics). "Khác" / empty last.
     */
    private function compareSubjects(string $a, string $b): int
    {
        $ra = $this->subjectRank($a);
        $rb = $this->subjectRank($b);
        if ($ra !== $rb) {
            return $ra <=> $rb;
        }
        // equal rank → compare stripped-of-diacritics names, then raw names
        $na = $this->normalizeSubject($a);
        $nb = $this->normalizeSubject($b);
        if ($na !== $nb) {
            return strcmp($na, $nb);
        }
        return strcmp($a, $b);
    }

    /** Rank for a subject name: priority index, 500 for unknown, 999 for "Khác"/empty. */
    private function subjectRank(string $name): int
    {
        $key = $this->normalizeSubject($name);
        if ($key === '' || $key === 'khac') {
            return 999;
        }
        if (isset($this->subjectRankCache[$key])) {
            return $this->subjectRankCache[$key];
        }
        $rank = 500;
        foreach (self::SUBJECT_PRIORITY as $subject => $r) {
            if ($this->normalizeSubject($subject) === $key) {
                $rank = $r;
                break;
            }
        }
        $this->subjectRankCache[$key] = $rank;
        return $rank;
    }

    /** Lowercase + strip diacritics + collapse whitespace for matching. */
    private function normalizeSubject(string $s): string
    {
        static $map = null;
        if ($map === null) {
            $map = [
                'à'=>'a','á'=>'a','ạ'=>'a','ả'=>'a','ã'=>'a','â'=>'a','ầ'=>'a','ấ'=>'a','ậ'=>'a','ẩ'=>'a','ẫ'=>'a','ă'=>'a','ằ'=>'a','ắ'=>'a','ặ'=>'a','ẳ'=>'a','ẵ'=>'a',
                'è'=>'e','é'=>'e','ẹ'=>'e','ẻ'=>'e','ẽ'=>'e','ê'=>'e','ề'=>'e','ế'=>'e','ệ'=>'e','ể'=>'e','ễ'=>'e',
                'ì'=>'i','í'=>'i','ị'=>'i','ỉ'=>'i','ĩ'=>'i',
                'ò'=>'o','ó'=>'o','ọ'=>'o','ỏ'=>'o','õ'=>'o','ô'=>'o','ồ'=>'o','ố'=>'o','ộ'=>'o','ổ'=>'o','ỗ'=>'o','ơ'=>'o','ờ'=>'o','ớ'=>'o','ợ'=>'o','ở'=>'o','ỡ'=>'o',
                'ù'=>'u','ú'=>'u','ụ'=>'u','ủ'=>'u','ũ'=>'u','ư'=>'u','ừ'=>'u','ứ'=>'u','ự'=>'u','ử'=>'u','ữ'=>'u',
                'ỳ'=>'y','ý'=>'y','ỵ'=>'y','ỷ'=>'y','ỹ'=>'y',
                'đ'=>'d','ĩ'=>'i','ũ'=>'u',
            ];
        }
        $s = mb_strtolower($s);
        $s = strtr($s, $map);
        return (string) preg_replace('/\s+/', ' ', trim($s));
    }

    private function facet(array $books, string $key): array
    {
        $out = [];
        foreach ($books as $b) {
            $out[$b[$key]] = ($out[$b[$key]] ?? 0) + 1;
        }
        if ($key === 'subject') {
            uksort($out, fn($a, $b2) => $this->compareSubjects($a, $b2));
        } else {
            uksort($out, fn($a, $b2) => strcoll($a, $b2));
        }
        return $out;
    }

    /**
     * Book detail + PDF viewer.
     */
    public function show(string $id)
    {
        $book = $this->api->book($id);
        if (! $book) {
            throw \CodeIgniter\Exceptions\PageNotFoundException::forPageNotFound();
        }

        $stats = Mongo::col('stats')->findOne(['_id' => 'book:' . $id]);
        $downloads = $stats['downloads'] ?? 0;

        return view('books/show', [
            'book'      => $book,
            'downloads' => $downloads,
            'countdown' => (int) env('download.countdown', 15),
        ]);
    }
}