import type {
    ColorSchemeSetup,
    ColorSchemeApi,
    ColorSchemeSubscriber,
    ColorSchemeConfig,
    ColorSchemeResolve,
} from './types';

function initiateColorScheme({ saveConfig, loadConfig, cssClass }: ColorSchemeSetup): ColorSchemeApi {
    const state: {
        listeners: Set<ColorSchemeSubscriber>;
        config: ColorSchemeConfig;
    } = {
        listeners: new Set<ColorSchemeSubscriber>(),
        config: loadConfig(),
    };

    const isDarkQuery = window.matchMedia('(prefers-color-scheme: dark)');

    const resolveSystem = (): ColorSchemeResolve => (isDarkQuery.matches ? 'dark' : 'light');
    const onSystemChange = (): void => {
        if (state.config !== 'system') return;
        updateDocument();
    };
    const currentState = () => {
        const config = state.config;
        const resolved = config === 'system' ? resolveSystem() : config;
        return { config, resolved };
    };
    const updateDocument = (): void => {
        const current = currentState();
        const root = document.documentElement;
        root.classList.remove(cssClass.light, cssClass.dark);
        root.classList.add(cssClass[current.resolved]);
        root.style.colorScheme = current.resolved === 'dark' ? 'dark' : 'light';
        state.listeners.forEach((listener) => listener(current));
    };

    // set initial color scheme and listen for system changes
    updateDocument();
    isDarkQuery.addEventListener('change', onSystemChange);

    return {
        get config() {
            return state.config;
        },
        set config(config) {
            if (config === state.config) return;
            state.config = config;
            updateDocument();
            saveConfig(config);
        },
        get currentState() {
            return currentState();
        },
        get resolvedSystem(): ColorSchemeResolve {
            return resolveSystem();
        },
        getRootCssClass(resolved = currentState().resolved) {
            return cssClass[resolved];
        },
        subscribe: (sub: ColorSchemeSubscriber): (() => void) => {
            state.listeners.add(sub);
            return (): void => {
                state.listeners.delete(sub);
            };
        },
        dispose: () => {
            state.listeners.clear();
            isDarkQuery.removeEventListener('change', onSystemChange);
        },
    };
}

const storageKey: string = 'color-scheme';
const scriptDataset = document.currentScript?.dataset;
const darkCssClass = scriptDataset?.darkClass || 'dark-theme';
const lightCssClass = scriptDataset?.lightClass || 'light-theme';

window.colorSchemeApi ??= initiateColorScheme({
    loadConfig(): ColorSchemeConfig {
        try {
            const config: string | null = localStorage.getItem(storageKey);
            return config === 'light' || config === 'dark' ? config : 'system';
        } catch {
            return 'system';
        }
    },
    saveConfig(config: ColorSchemeConfig): void {
        try {
            if (config === 'system') {
                localStorage.removeItem(storageKey);
            } else {
                localStorage.setItem(storageKey, config);
            }
        } catch {
            // Fallback to no-op if localStorage is not available
        }
    },
    cssClass: { light: lightCssClass, dark: darkCssClass },
});