import {useCallback, useEffect, useRef, useState} from 'react';
import {useEditUserPreferences, useUserPreferences} from '@/hooks/user-preferences';

export type ThemeMode = 'light' | 'dark' | 'system';
export type ResolvedThemeMode = 'light' | 'dark';

function getSystemTheme(): ResolvedThemeMode {
    if (typeof window === 'undefined' || typeof window.matchMedia !== 'function') {
        return 'light';
    }

    return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
}

function applyThemeClass(resolvedTheme: ResolvedThemeMode) {
    document.documentElement.classList.toggle('dark', resolvedTheme === 'dark');
}

// In the embedded admin, Ember owns the DOM theme: it manages both the `dark`
// class and the dark stylesheet, and installs its own prefers-color-scheme
// listener. The class-toggling and media-query effects below are only a fallback
// for running this hook standalone (no EmberBridge), so they must not fight Ember.
function isEmberManaged(): boolean {
    return typeof window !== 'undefined' && Boolean(window.EmberBridge);
}

async function preloadAdminThemeStylesheet() {
    await window.EmberBridge?.state.preloadAdminThemeStylesheet?.();
}

function applyAdminTheme(mode: ThemeMode, resolvedTheme: ResolvedThemeMode) {
    if (window.EmberBridge?.state.applyAdminThemePreference) {
        void window.EmberBridge.state.applyAdminThemePreference(mode);
    } else {
        applyThemeClass(resolvedTheme);
    }
}

export function useTheme() {
    const {data: preferences} = useUserPreferences();
    const {mutateAsync: editPreferences, isPending: isEditingPreferences} = useEditUserPreferences();
    const [systemTheme, setSystemTheme] = useState<ResolvedThemeMode>(getSystemTheme);
    const [pendingTheme, setPendingTheme] = useState<ThemeMode | null>(null);
    const [isPendingTheme, setIsPendingTheme] = useState(false);
    const pendingRef = useRef(false);

    const persistedTheme: ThemeMode = preferences?.nightShift ?? 'light';
    const theme: ThemeMode = pendingTheme ?? persistedTheme;
    const resolvedTheme: ResolvedThemeMode = theme === 'system' ? systemTheme : theme;

    useEffect(() => {
        if (isEmberManaged() || typeof window === 'undefined' || typeof window.matchMedia !== 'function') {
            return;
        }

        const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
        const handleChange = (event: MediaQueryListEvent) => {
            setSystemTheme(event.matches ? 'dark' : 'light');
        };

        setSystemTheme(mediaQuery.matches ? 'dark' : 'light');
        if (typeof mediaQuery.addEventListener === 'function') {
            mediaQuery.addEventListener('change', handleChange);
        } else {
            mediaQuery.addListener(handleChange);
        }

        return () => {
            if (typeof mediaQuery.removeEventListener === 'function') {
                mediaQuery.removeEventListener('change', handleChange);
            } else {
                mediaQuery.removeListener(handleChange);
            }
        };
    }, []);

    useEffect(() => {
        if (isEmberManaged()) {
            return;
        }
        applyThemeClass(resolvedTheme);
    }, [resolvedTheme]);

    // Clear the optimistic selection once the persisted preference catches up, so
    // the menu indicator settles on the new value without flickering back via the
    // brief window where the refetched preferences query has no data.
    useEffect(() => {
        if (pendingTheme !== null && persistedTheme === pendingTheme) {
            setPendingTheme(null);
        }
    }, [pendingTheme, persistedTheme]);

    const setTheme = useCallback(async (mode: ThemeMode) => {
        if (pendingRef.current || mode === theme) {
            return;
        }

        pendingRef.current = true;
        setIsPendingTheme(true);
        // Reflect the choice immediately; cleared on rollback (catch) or once the
        // persisted preference matches (effect above).
        setPendingTheme(mode);

        try {
            const nextResolvedTheme = mode === 'system' ? systemTheme : mode;
            await preloadAdminThemeStylesheet().catch((error) => {
                // eslint-disable-next-line no-console
                console.error('[Theme] Failed to preload admin theme stylesheet:', error);
            });
            applyAdminTheme(mode, nextResolvedTheme);
            await editPreferences({nightShift: mode});
        } catch (error) {
            setPendingTheme(null);
            applyAdminTheme(theme, resolvedTheme);
            // eslint-disable-next-line no-console
            console.error('[Theme] Failed to update appearance preference:', error);
        } finally {
            pendingRef.current = false;
            setIsPendingTheme(false);
        }
    }, [editPreferences, resolvedTheme, systemTheme, theme]);

    return {
        theme,
        resolvedTheme,
        setTheme,
        isSettingTheme: isEditingPreferences || isPendingTheme
    } as const;
}
