import { useCallback, useEffect, useState } from 'react';

export type Density = 'comfortable' | 'compact';

const STORAGE_KEY = 'sencho.appearance.density';
const DEFAULT_DENSITY: Density = 'comfortable';

function isDensity(value: unknown): value is Density {
    return value === 'comfortable' || value === 'compact';
}

function readStoredDensity(): Density {
    if (typeof window === 'undefined') return DEFAULT_DENSITY;
    try {
        const raw = window.localStorage.getItem(STORAGE_KEY);
        return isDensity(raw) ? raw : DEFAULT_DENSITY;
    } catch {
        return DEFAULT_DENSITY;
    }
}

function applyDensityClass(density: Density) {
    if (typeof document === 'undefined') return;
    const body = document.body;
    if (!body) return;
    body.classList.toggle('density-compact', density === 'compact');
}

export function initializeDensity() {
    applyDensityClass(readStoredDensity());
}

export function useDensity(): [Density, (next: Density) => void] {
    const [density, setDensityState] = useState<Density>(readStoredDensity);

    useEffect(() => {
        applyDensityClass(density);
        try {
            if (window.localStorage.getItem(STORAGE_KEY) !== density) {
                window.localStorage.setItem(STORAGE_KEY, density);
            }
        } catch {
            // ignore; localStorage may be unavailable (private mode, quota)
        }
    }, [density]);

    useEffect(() => {
        function onStorage(event: StorageEvent) {
            if (event.key !== STORAGE_KEY) return;
            if (isDensity(event.newValue)) setDensityState(event.newValue);
        }
        window.addEventListener('storage', onStorage);
        return () => window.removeEventListener('storage', onStorage);
    }, []);

    const setDensity = useCallback((next: Density) => {
        setDensityState(next);
    }, []);

    return [density, setDensity];
}