const axios = require('axios');

// MCCS is on Zoho's US data centre; users on another DC would need accounts.zoho.<tld>
const ACCOUNTS_URL = 'https://accounts.zoho.com';
// profile.READ is only for showing who's signed in; the dashboard itself needs requests.READ
const SCOPES = 'SDPOnDemand.requests.READ,AaaServer.profile.READ';

// zoho reports most failures as a 200 with an error field, not an http error
function zohoError(data, fallback) {
    const err = new Error('Zoho: ' + (data?.error || fallback));
    err.zoho = true;
    return err;
}

function createZohoAuth({ clientId, clientSecret, redirectUri }) {
    // the page Zoho shows to approve the dashboard; state ties the callback to this browser
    function authorizeUrl(state) {
        const params = new URLSearchParams({
            client_id: clientId,
            response_type: 'code',
            scope: SCOPES,
            redirect_uri: redirectUri,
            state,
            // offline is what gets us a refresh token; consent makes zoho issue one every time
            access_type: 'offline',
            prompt: 'consent'
        });
        return `${ACCOUNTS_URL}/oauth/v2/auth?${params}`;
    }

    async function tokenRequest(fields) {
        const params = new URLSearchParams({ client_id: clientId, client_secret: clientSecret, ...fields });
        const res = await axios.post(`${ACCOUNTS_URL}/oauth/v2/token`, params);
        if (!res.data?.access_token) throw zohoError(res.data, 'no access token');
        return res.data;
    }

    async function exchangeCode(code) {
        const data = await tokenRequest({ grant_type: 'authorization_code', redirect_uri: redirectUri, code });
        if (!data.refresh_token) throw zohoError(data, 'no refresh token');
        return {
            accessToken: data.access_token,
            refreshToken: data.refresh_token,
            expiresAt: Date.now() + (data.expires_in || 3600) * 1000
        };
    }

    // access tokens last about an hour; the refresh token lasts until revoked
    async function refreshAccessToken(refreshToken) {
        const data = await tokenRequest({ grant_type: 'refresh_token', refresh_token: refreshToken });
        return {
            accessToken: data.access_token,
            expiresAt: Date.now() + (data.expires_in || 3600) * 1000
        };
    }

    // zoho keeps at most 20 refresh tokens per user per client and silently drops the oldest,
    // so revoke on sign-out rather than leaving them to pile up
    async function revokeToken(refreshToken) {
        await axios.post(`${ACCOUNTS_URL}/oauth/v2/token/revoke`, new URLSearchParams({ token: refreshToken }));
    }

    async function getUser(accessToken) {
        try {
            const res = await axios.get(`${ACCOUNTS_URL}/oauth/user/info`, {
                headers: { Authorization: `Zoho-oauthtoken ${accessToken}` }
            });
            return {
                name: res.data.Display_Name || [res.data.First_Name, res.data.Last_Name].filter(Boolean).join(' ') || null,
                email: res.data.Email || null
            };
        } catch (err) {
            // only cosmetic; the page just says "Signed in" without a name
            console.warn('Could not read Zoho profile:', err.response?.data || err.message);
            return { name: null, email: null };
        }
    }

    return {
        authorizeUrl,
        exchangeCode,
        refreshAccessToken,
        revokeToken,
        getUser
    };
}

module.exports = {
    createZohoAuth
};