import { resolvePreviewUrl } from '../../config/assets';
import type { ApiCategory, ApiWorksheet } from '../../services/content-api';

export interface CategoryTab {
    id: string;
    name: string;
    icon: string;
}

export interface CategoryItem {
    id: string;
    title: string;
    subtitle: string;
    icon: string;
    previewImg: string;
    ageBand: string;
    difficultyLabel: string;
    path: string;
    available: boolean;
    likes: string;
    downloads: string;
    date: string;
    updatedAt: string;
    skeleton?: boolean;
}

export interface CategoryDataset {
    sidebarTabs: CategoryTab[];
    groups: Map<string, CategoryItem[]>;
}

export const BASE_TABS: CategoryTab[] = [
    { id: 'all', name: '全部', icon: '📋' },
    { id: 'hot', name: '热门推荐', icon: '🔥' },
    { id: 'top-downloads', name: '下载最多', icon: '📥' },
];
const DIFFICULTY_LABELS = ['入门', '基础', '进阶', '挑战'];

/** 比较任意长度的非负十进制计数；微信运行时无需 BigInt，也不丢失 64 位精度。 */
export function compareCountDescending(left: string, right: string): number {
    const a = left.replace(/^0+(?=\d)/, '');
    const b = right.replace(/^0+(?=\d)/, '');
    return a.length !== b.length
        ? b.length - a.length
        : a === b
          ? 0
          : a < b
            ? 1
            : -1;
}

function time(value: string): number {
    const parsed = Date.parse(value);
    return Number.isFinite(parsed) ? parsed : 0;
}

/** 保留原页面交互：最近更新的两项置顶，其余下载量降序，并列按稳定 ID。 */
function sortWorksheets(items: CategoryItem[]): CategoryItem[] {
    const byId = (a: CategoryItem, b: CategoryItem) =>
        a.id < b.id ? -1 : a.id === b.id ? 0 : 1;
    const sorted = [...items].sort(
        (a, b) => time(b.updatedAt) - time(a.updatedAt) || byId(a, b),
    );
    return [
        ...sorted.slice(0, 2),
        ...sorted
            .slice(2)
            .sort(
                (a, b) =>
                    compareCountDescending(a.downloads, b.downloads) ||
                    byId(a, b),
            ),
    ];
}

/** 只展示本次接口返回的分类；并发下架导致目录缺失的题型直接丢弃。 */
export function buildCategoryDataset(
    categories: ApiCategory[],
    worksheets: ApiWorksheet[],
): CategoryDataset {
    const reservedIds = new Set(BASE_TABS.map((tab) => tab.id));
    const groups = new Map<string, CategoryItem[]>();
    const icons = new Map<string, string>();
    for (const category of categories) {
        if (reservedIds.has(category.id) || groups.has(category.id))
            throw new Error('分类数据异常，请稍后重试');
        groups.set(category.id, []);
        icons.set(category.id, category.icon || '📄');
    }
    for (const row of worksheets) {
        const group = groups.get(row.category);
        if (!group) continue;
        const date = row.contentUpdatedAt || row.createdAt;
        group.push({
            id: row.id,
            title: row.title,
            subtitle: row.subtitle,
            icon: icons.get(row.category) || '📄',
            previewImg: resolvePreviewUrl(row.previewImg),
            ageBand: `${row.ageMin}-${row.ageMax}岁`,
            difficultyLabel: DIFFICULTY_LABELS[row.difficulty - 1] || '基础',
            path: row.path,
            available: Boolean(row.path),
            likes: row.likes,
            downloads: row.downloads,
            date: Number.isFinite(Date.parse(date))
                ? new Date(date).toISOString().slice(0, 10)
                : '',
            updatedAt: row.updatedAt,
        });
    }
    return {
        sidebarTabs: [
            ...BASE_TABS,
            ...categories.map(({ id, name, icon }) => ({ id, name, icon })),
        ],
        groups,
    };
}

/** 两个榜单沿用旧页面含义：热门推荐按收藏数，下载最多按下载数，各取前 12。 */
export function getCategoryItems(
    dataset: CategoryDataset | null,
    categoryId: string,
    keyword = '',
): CategoryItem[] {
    if (!dataset) return [];
    let items: CategoryItem[];
    if (
        categoryId === 'all' ||
        categoryId === 'hot' ||
        categoryId === 'top-downloads'
    ) {
        const all = sortWorksheets(Array.from(dataset.groups.values()).flat());
        if (categoryId === 'all') items = all;
        else {
            const key = categoryId === 'hot' ? 'likes' : 'downloads';
            items = all
                .sort((a, b) => compareCountDescending(a[key], b[key]))
                .slice(0, 12);
        }
    } else items = sortWorksheets(dataset.groups.get(categoryId) || []);
    const kw = keyword.trim().toLowerCase();
    return kw
        ? items.filter(
              (item) =>
                  item.title.toLowerCase().includes(kw) ||
                  item.subtitle.toLowerCase().includes(kw),
          )
        : items;
}