const TIKTOK_AUTH_URL = "https://www.tiktok.com/v2/auth/authorize";
const TIKTOK_TOKEN_URL = "https://open.tiktokapis.com/v2/oauth/token/";
const TIKTOK_USER_INFO_URL = "https://open.tiktokapis.com/v2/user/info/";
const TIKTOK_VIDEO_LIST_URL = "https://open.tiktokapis.com/v2/video/list/";

const CLIENT_KEY = process.env.TIKTOK_CLIENT_KEY!;
const CLIENT_SECRET = process.env.TIKTOK_CLIENT_SECRET!;

function getRedirectUri(): string {
    return process.env.NODE_ENV === "production"
        ? process.env.TIKTOK_REDIRECT_URI_PROD!
        : process.env.TIKTOK_REDIRECT_URI_DEV!;
}

// ── PKCE helpers ──────────────────────────────────────────────
export function generateCodeVerifier(): string {
    const charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    let result = "";
    const array = new Uint8Array(64);
    crypto.getRandomValues(array);
    for (let i = 0; i < 64; i++) {
        result += charset[array[i] % charset.length];
    }
    return result;
}

export async function generateCodeChallenge(verifier: string): Promise<string> {
    const data = new TextEncoder().encode(verifier);
    const digest = await globalThis.crypto.subtle.digest("SHA-256", data);
    const bytes = Array.from(new Uint8Array(digest));
    return btoa(bytes.map((b) => String.fromCharCode(b)).join(""))
        .replace(/\+/g, "-")
        .replace(/\//g, "_")
        .replace(/=+$/, "");
}
// ──────────────────────────────────────────────────────────────

export function getTikTokAuthUrl(state: string, codeChallenge: string): string {
    const params = new URLSearchParams({
        client_key: CLIENT_KEY,
        response_type: "code",
        // video.list is used as a fallback to compute total views from all videos.
        scope: "user.info.basic,user.info.stats,video.list",
        redirect_uri: getRedirectUri(),
        state,
        code_challenge: codeChallenge,
        code_challenge_method: "S256",
        // "select_account" seul est ignoré par TikTok si une session est active.
        // On passe les deux pour forcer l'affichage du sélecteur de compte à chaque fois.
        prompt: "select_account",
        force_login: "true",
    });
    return `${TIKTOK_AUTH_URL}?${params.toString()}`;
}

export interface TikTokTokenResponse {
    access_token: string;
    refresh_token: string;
    open_id: string;
    expires_in: number;
    refresh_expires_in: number;
    token_type: string;
    scope: string;
    error?: string;
    error_description?: string;
}

export async function exchangeCodeForTokens(code: string, codeVerifier: string): Promise<TikTokTokenResponse> {
    const body = new URLSearchParams({
        client_key: CLIENT_KEY,
        client_secret: CLIENT_SECRET,
        code,
        grant_type: "authorization_code",
        redirect_uri: getRedirectUri(),
        code_verifier: codeVerifier,
    });

    const res = await fetch(TIKTOK_TOKEN_URL, {
        method: "POST",
        headers: { "Content-Type": "application/x-www-form-urlencoded" },
        body: body.toString(),
    });

    const data = await res.json();

    if (!res.ok || data.error) {
        throw new Error(data.error_description || data.error || "TikTok token exchange failed");
    }

    return data;
}

export async function refreshAccessToken(refreshToken: string): Promise<TikTokTokenResponse> {
    const body = new URLSearchParams({
        client_key: CLIENT_KEY,
        client_secret: CLIENT_SECRET,
        grant_type: "refresh_token",
        refresh_token: refreshToken,
    });

    const res = await fetch(TIKTOK_TOKEN_URL, {
        method: "POST",
        headers: { "Content-Type": "application/x-www-form-urlencoded" },
        body: body.toString(),
    });

    const data = await res.json();

    if (!res.ok || data.error) {
        throw new Error(data.error_description || data.error || "TikTok token refresh failed");
    }

    return data;
}

export interface TikTokUserStats {
    followers: number;
    likes: number;
    videoCount: number;
    views: number;
    profileViews: number;
    username: string;
    displayName: string;
    avatarUrl: string;
}

async function fetchTotalVideoViews(accessToken: string): Promise<number> {
    const fields = "id,view_count";
    let cursor = 0;
    let totalViews = 0;

    for (let page = 0; page < 50; page++) {
        const res = await fetch(`${TIKTOK_VIDEO_LIST_URL}?fields=${fields}`, {
            method: "POST",
            headers: {
                Authorization: `Bearer ${accessToken}`,
                "Content-Type": "application/json",
            },
            body: JSON.stringify({ max_count: 20, cursor }),
        });

        const data = await res.json();

        if (!res.ok || data.error?.code !== "ok") {
            throw new Error(data.error?.message || "TikTok video list fetch failed");
        }

        const videos = Array.isArray(data.data?.videos) ? data.data.videos : [];
        for (const video of videos) {
            totalViews += Number(video?.view_count ?? 0);
        }

        const hasMore = Boolean(data.data?.has_more);
        if (!hasMore) {
            break;
        }

        const nextCursor = Number(data.data?.cursor ?? cursor + videos.length);
        if (!Number.isFinite(nextCursor) || nextCursor <= cursor) {
            break;
        }

        cursor = nextCursor;
    }

    return totalViews;
}

export async function fetchUserStats(accessToken: string, openId: string): Promise<TikTokUserStats> {
    const fields = "follower_count,following_count,likes_count,video_count,video_view_count,profile_view_count,display_name,avatar_url";
    const url = `${TIKTOK_USER_INFO_URL}?fields=${fields}`;

    const res = await fetch(url, {
        headers: {
            Authorization: `Bearer ${accessToken}`,
        },
    });

    const data = await res.json();

    if (!res.ok || data.error?.code !== "ok") {
        throw new Error(data.error?.message || "TikTok user info fetch failed");
    }

    const user = data.data?.user ?? {};
    let views = user.video_view_count ?? user.profile_view_count ?? 0;

    // Some TikTok apps do not receive video_view_count in user.info.stats.
    // In that case we compute total views from the account video list.
    if (user.video_view_count == null) {
        try {
            const computedViews = await fetchTotalVideoViews(accessToken);
            if (computedViews > 0) {
                views = computedViews;
            }
        } catch (err) {
            console.warn("[TikTok views fallback error]", err);
        }
    }

    return {
        followers: user.follower_count ?? 0,
        likes: user.likes_count ?? 0,
        videoCount: user.video_count ?? 0,
        views,
        profileViews: user.profile_view_count ?? 0,
        username: openId,
        displayName: user.display_name ?? "",
        avatarUrl: user.avatar_url ?? "",
    };
}