scalesApp/frontend/src/contexts/LicenseContext.jsx

import { createContext, useContext, useState, useEffect, useCallback, useRef } from 'react';
import api from '../services/api';

const LicenseContext = createContext(null);

const SERIAL_URL = process.env.REACT_APP_SERIAL_URL || 'http://localhost:5000';
const HEARTBEAT_MS = 30000;   // server releases a slot after 120s, so 4 missed beats

export const useLicense = () => {
    const ctx = useContext(LicenseContext);
    if (!ctx) throw new Error('useLicense must be used within LicenseProvider');
    return ctx;
};

/** Stable identifier for the bridge this browser is using.
 *
 *  The bridge deliberately never talks to Django, so the browser reports which
 *  station it is on. Built from the bridge address plus its COM port, so two
 *  browsers on the same station share one slot rather than consuming two.
 */
async function readStationKey() {
    try {
        const res = await fetch(`${SERIAL_URL}/status`);
        if (!res.ok) return null;
        const status = await res.json();
        const raw = `${SERIAL_URL}|${status.com_port || 'unknown'}`;
        // Short stable hash - this is an identifier, not a secret
        let hash = 0;
        for (let i = 0; i < raw.length; i++) {
            hash = ((hash << 5) - hash + raw.charCodeAt(i)) | 0;
        }
        return {
            station_key: `st-${Math.abs(hash).toString(36)}`,
            com_port: status.com_port || '',
            bridge_version: status.version || '',
        };
    } catch {
        return null;
    }
}

export function LicenseProvider({ children }) {
    const [state, setState] = useState({
        allowed: true,          // assume allowed until told otherwise, so a slow
        stationsUsed: null,     // first heartbeat never blocks a working station
        stationsLicensed: null,
        detail: null,
        stationKey: null,
    });
    const [status, setStatus] = useState(null);

    const stationRef = useRef(null);

    const beat = useCallback(async () => {
        if (!stationRef.current) {
            stationRef.current = await readStationKey();
        }
        const station = stationRef.current;
        if (!station) return;   // bridge unreachable; nothing to register

        try {
            const res = await api.post('/api/license/heartbeat/', station);
            setState({
                allowed: res.data.allowed,
                stationsUsed: res.data.stations_used,
                stationsLicensed: res.data.stations_licensed,
                detail: null,
                stationKey: station.station_key,
            });
        } catch (err) {
            if (err.response?.status === 403) {
                const d = err.response.data || {};
                setState({
                    allowed: false,
                    stationsUsed: d.stations_used ?? null,
                    stationsLicensed: d.stations_licensed ?? null,
                    detail: d.detail || 'Licence limit reached',
                    stationKey: station.station_key,
                });
            }
            // Other failures (server down) leave the previous state alone -
            // a licence check must not stop a working weighbridge.
        }
    }, []);

    useEffect(() => {
        beat();
        const timer = setInterval(beat, HEARTBEAT_MS);
        return () => clearInterval(timer);
    }, [beat]);

    const loadStatus = useCallback(async () => {
        try {
            const res = await api.get('/api/license/');
            setStatus(res.data);
            return res.data;
        } catch {
            return null;
        }
    }, []);

    useEffect(() => { loadStatus(); }, [loadStatus]);

    return (
        <LicenseContext.Provider value={{ ...state, status, refreshStatus: loadStatus }}>
            {children}
        </LicenseContext.Provider>
    );
}