/**
 * Proxy API client
 *
 * Handles API requests to GlyphDiff proxy API for fetching font metadata.
 * Provides error handling, pagination support, and type-safe responses.
 *
 * Proxy API normalizes font data from Google Fonts and Fontshare into a single
 * unified format, eliminating the need for client-side normalization.
 *
 * Fallback: If proxy API fails, falls back to Fontshare API for development.
 *
 * @see https://api.glyphdiff.com/api/v1/fonts
 */

import { api } from '$shared/api/api';
import { buildQueryString } from '$shared/lib/utils';
import type { QueryParams } from '$shared/lib/utils';
import type { UnifiedFont } from '../../model/types';
import type {
    FontCategory,
    FontSubset,
} from '../../model/types';

/**
 * Proxy API base URL
 */
const PROXY_API_URL = 'https://api.glyphdiff.com/api/v1/fonts' as const;

/**
 * Whether to use proxy API (true) or fallback (false)
 *
 * Set to true when your proxy API is ready:
 *   const USE_PROXY_API = true;
 *
 * Set to false to use Fontshare API as fallback during development:
 *   const USE_PROXY_API = false;
 *
 * The app will automatically fall back to Fontshare API if the proxy fails.
 */
const USE_PROXY_API = true;

/**
 * Proxy API parameters
 *
 * Maps directly to the proxy API query parameters
 */
export interface ProxyFontsParams extends QueryParams {
    /**
     * Font provider filter ("google" or "fontshare")
     * Omit to fetch from both providers
     */
    provider?: 'google' | 'fontshare';

    /**
     * Font category filter
     */
    category?: FontCategory;

    /**
     * Character subset filter
     */
    subset?: FontSubset;

    /**
     * Search query (e.g., "roboto", "satoshi")
     */
    q?: string;

    /**
     * Sort order for results
     * "name" - Alphabetical by font name
     * "popularity" - Most popular first
     * "lastModified" - Recently updated first
     */
    sort?: 'name' | 'popularity' | 'lastModified';

    /**
     * Number of items to return (pagination)
     */
    limit?: number;

    /**
     * Number of items to skip (pagination)
     * Use for pagination: offset = (page - 1) * limit
     */
    offset?: number;
}

/**
 * Proxy API response
 *
 * Includes pagination metadata alongside font data
 */
export interface ProxyFontsResponse {
    /** Array of unified font objects */
    fonts: UnifiedFont[];

    /** Total number of fonts matching the query */
    total: number;

    /** Limit used for this request */
    limit: number;

    /** Offset used for this request */
    offset: number;
}

/**
 * Fetch fonts from proxy API
 *
 * If proxy API fails or is unavailable, falls back to Fontshare API for development.
 *
 * @param params - Query parameters for filtering and pagination
 * @returns Promise resolving to proxy API response
 * @throws ApiError when request fails
 *
 * @example
 * ```ts
 * // Fetch all sans-serif fonts from Google
 * const response = await fetchProxyFonts({
 *     provider: 'google',
 *     category: 'sans-serif',
 *     limit: 50,
 *     offset: 0
 * });
 *
 * // Search fonts across all providers
 * const searchResponse = await fetchProxyFonts({
 *     q: 'roboto',
 *     limit: 20
 * });
 *
 * // Fetch fonts with pagination
 * const page1 = await fetchProxyFonts({ limit: 50, offset: 0 });
 * const page2 = await fetchProxyFonts({ limit: 50, offset: 50 });
 * ```
 */
export async function fetchProxyFonts(
    params: ProxyFontsParams = {},
): Promise<ProxyFontsResponse> {
    // Try proxy API first if enabled
    if (USE_PROXY_API) {
        try {
            const queryString = buildQueryString(params);
            const url = `${PROXY_API_URL}${queryString}`;

            console.log('[fetchProxyFonts] Fetching from proxy API', { params, url });

            const response = await api.get<ProxyFontsResponse>(url);

            // Validate response has fonts array
            if (!response.data || !Array.isArray(response.data.fonts)) {
                console.error('[fetchProxyFonts] Invalid response from proxy API', response.data);
                throw new Error('Proxy API returned invalid response');
            }

            console.log('[fetchProxyFonts] Proxy API success', {
                count: response.data.fonts.length,
            });
            return response.data;
        } catch (error) {
            console.warn('[fetchProxyFonts] Proxy API failed, using fallback', error);

            // Check if it's a network error or proxy not available
            const isNetworkError = error instanceof Error
                && (error.message.includes('Failed to fetch')
                    || error.message.includes('Network')
                    || error.message.includes('404')
                    || error.message.includes('500'));

            if (isNetworkError) {
                // Fall back to Fontshare API
                console.log('[fetchProxyFonts] Using Fontshare API as fallback');
                return await fetchFontshareFallback(params);
            }

            // Re-throw other errors
            if (error instanceof Error) {
                throw error;
            }
            throw new Error(`Failed to fetch fonts from proxy API: ${String(error)}`);
        }
    }

    // Use Fontshare API directly
    console.log('[fetchProxyFonts] Using Fontshare API (proxy disabled)');
    return await fetchFontshareFallback(params);
}

/**
 * Fallback to Fontshare API when proxy is unavailable
 *
 * Maps proxy API params to Fontshare API params and normalizes response
 */
async function fetchFontshareFallback(
    params: ProxyFontsParams,
): Promise<ProxyFontsResponse> {
    // Import dynamically to avoid circular dependency
    const { fetchFontshareFonts } = await import('$entities/Font/api/fontshare/fontshare');
    const { normalizeFontshareFonts } = await import('$entities/Font/lib/normalize/normalize');

    // Map proxy params to Fontshare params
    const fontshareParams = {
        q: params.q,
        categories: params.category ? [params.category] : undefined,
        page: params.offset ? Math.floor(params.offset / (params.limit || 50)) + 1 : undefined,
        limit: params.limit,
    };

    const response = await fetchFontshareFonts(fontshareParams);
    const normalizedFonts = normalizeFontshareFonts(response.fonts);

    return {
        fonts: normalizedFonts,
        total: response.count_total,
        limit: params.limit || response.count,
        offset: params.offset || 0,
    };
}

/**
 * Fetch font by ID
 *
 * Convenience function for fetching a single font by ID
 * Note: This fetches a page and filters client-side, which is not ideal
 * For production, consider adding a dedicated endpoint to the proxy API
 *
 * @param id - Font ID (family name for Google, slug for Fontshare)
 * @returns Promise resolving to font or undefined
 *
 * @example
 * ```ts
 * const roboto = await fetchProxyFontById('Roboto');
 * const satoshi = await fetchProxyFontById('satoshi');
 * ```
 */
export async function fetchProxyFontById(
    id: string,
): Promise<UnifiedFont | undefined> {
    const response = await fetchProxyFonts({ limit: 1000, q: id });

    if (!response || !response.fonts) {
        console.error('[fetchProxyFontById] No fonts in response', { response });
        return undefined;
    }

    return response.fonts.find(font => font.id === id);
}