# All files / src/theme ColorSchemeProvider.tsx

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     "use client";
    import {
      createContext,
      useContext,
      useEffect,
      useMemo,
      type ReactElement,
      type ReactNode,
    } from "react";
    import { useMediaQuery } from "../media-queries/useMediaQuery.js";
    import { type UseStateInitializer, type UseStateSetter } from "../types.js";
    import { useLocalStorage } from "../useLocalStorage.js";
    import { backgroundColorVar } from "./cssVars.js";
    import { getContrastRatio } from "./utils.js";

    /** @remarks \@since 6.0.0 */
    export type ColorScheme = "light" | "dark";

    /** @remarks \@since 6.0.0 */
    export type ColorSchemeMode = ColorScheme | "system";
    /** @remarks \@since 6.0.0 */
    export type SetColorSchemeMode = UseStateSetter<ColorSchemeMode>;

    /** @remarks \@since 6.0.0 */
    export interface ColorSchemeContext {
      /**
       * The current color scheme that is being used. This is only useful when the
       * {@link colorSchemeMode} is set to `"system"`.
       */
      colorScheme: ColorScheme;

      /**
       * The current color scheme mode that is being used by your app that should
       * default to the `$color-scheme` SCSS variable. If the
       * {@link setColorSchemeMode} is called, this will update to that new value.
       *
       * TODO: Figure out how to document this
       *
       * - `colorScheme` - only `light` or `dark` -- only useful when the `colorSchemeMode` is set to `system`
       * - `colorSchemeMode` - current **user** defined color scheme behavior? should default to `$color-scheme`, but will change based on `setColorSchemeMode`
       */
      colorSchemeMode: ColorSchemeMode;

      /**
       * A function to update the color scheme.
       *
       * @see {@link useColorScheme} for an example usage
       */
      setColorSchemeMode: SetColorSchemeMode;
    }

    const context = createContext<ColorSchemeContext>({
      colorScheme: "light",
      colorSchemeMode: "light",
      setColorSchemeMode() {
        if (process.env.NODE_ENV !== "production") {
          throw new Error("The `ColorSchemeProvider` has not been initialized.");
        }
      },
    });
    context.displayName = "ColorScheme";
    const { Provider } = context;

    /** @remarks \@since 6.0.0 */
    export type DefaultColorScheme = UseStateInitializer<ColorScheme>;

    /**
     * @example
     * Lazy Load Configurable Themes
     * ```tsx
     * import type { ChangeEvent, ReactElement } from "react";
     * import { lazy } from "react";
     * import { createRoot } from "react-doc/client";
     * import { Checkbox, ColorSchemeProvider, useColorScheme } from "@react-md/core";
     *
     * const DarkTheme = lazy(() => import("./DarkTheme"));
     * const SystemTheme = lazy(() => import("./SystemTheme"));
     *
     * function App(): ReactElement {
     *   const { colorScheme, colorSchemeMode, setColorSchemeMode } =
     *     useColorScheme();
     *
     *   const onChange = (event: ChangeEvent<HTMLInputElement>): void => {
     *     const { value } = event.currentTarget;
     *     if (value === "light" || value === "dark" || value === "system") {
     *       setColorSchemeMode(value);
     *     }
     *   };
     *
     *   return (
     *     <>
     *       {colorSchemeMode === "dark" && <DarkTheme />}
     *       {colorSchemeMode === "system" && <SystemTheme />}
     *       <Checkbox
     *         label="Light"
     *         value="light"
     *         checked={colorSchemeMode === "light"}
     *         onChange={onChange}
     *       />
     *       <Checkbox
     *         label="Dark"
     *         value="dark"
     *         checked={colorSchemeMode === "dark"}
     *         onChange={onChange}
     *       />
     *       <Checkbox
     *         label="System"
     *         value="system"
     *         checked={colorSchemeMode === "system"}
     *         onChange={onChange}
     *       />
     *     </>
     *   );
     * }
     *
     *
     * const root = createRoot(document.getElementById("root"));
     * root.render(
     *   <ColorSchemeProvider>
     *     <App />
     *   </ColorSchemeProvider>
     * );
     *
     * // DarkTheme.tsx
     * import { useHtmlClassName } from "@react-md/core";
     *
     * import styles from "./DarkTheme.module.scss";
     *
     * export default function DarkTheme(): null {
     *   useHtmlClassName(styles.theme);
     *   return null
     * }
     *
     * // DarkTheme.module.scss
     * @use "@react-md/core";
     *
     * .theme {
     *   @include core.use-dark-theme;
     * }
     * ```
     *
     * @remarks \@since 6.0.0
     */
    export function useColorScheme(): Readonly<ColorSchemeContext> {
      return useContext(context);
    }

    /** @remarks \@since 6.0.0 */
    export interface ColorSchemeProviderProps {
      /**
       * The current color scheme mode that is being used by your app. This should
       * match the `$color-scheme` SCSS variable.
       *
       * @defaultValue `"light"`
       */
      mode?: ColorSchemeMode;

      /**
       * Set this to a string like `"colorScheme"` if you want to store the user's
       * color scheme preference in local storage.
       *
       * @defaultValue `""`
       */
      localStorageKey?: string;

      /**
       * Set this to `true` to prevent a `<meta name="color-scheme" content="{COLOR_SCHEME}">`
       * from being added to the `document.head`.
       *
       * @defaultValue `false`
       */
      disableMetaTag?: boolean;
      children: ReactNode;
    }

    /**
     * **Client Component**
     *
     * @see {@link useColorScheme} for an example usage.
     * @remarks \@since 6.0.0
     */
    export function ColorSchemeProvider(
      props: ColorSchemeProviderProps
    ): ReactElement {
      const {
        children,
        mode = "light",
        localStorageKey = "",
        disableMetaTag,
      } = props;
      const { value: colorSchemeMode, setValue: setColorSchemeMode } =
        useLocalStorage({
          key: localStorageKey,
          defaultValue: mode,
          deserializer: (item) =>
            item === "light" || item === "dark" || item === "system" ? item : mode,
        });

      const prefersDarkTheme = useMediaQuery(
        "(prefers-color-scheme: dark)",
        colorSchemeMode !== "system"
      );
      const derivedColorScheme = prefersDarkTheme ? "dark" : "light";
      const colorScheme =
        colorSchemeMode === "system" ? derivedColorScheme : colorSchemeMode;

      const value = useMemo<ColorSchemeContext>(
        () => ({
          colorScheme,
          colorSchemeMode,
          setColorSchemeMode,
        }),
        [colorScheme, colorSchemeMode, setColorSchemeMode]
      );

      useEffect(() => {
        if (disableMetaTag || document.querySelector('meta[name="color-scheme"]')) {
          return;
        }

        // Adding the meta tag allows the default browser styles for form inputs to
        // be updated as well.
        //
        // Chrome and Firefox:
        // - the input type="number"'s spinner color will update from grey to white
        // - native `<select>` background color updates from grey/white to a dark color
        //
        // Chrome:
        // - the date/time/datetime icons will change from black to white
        // - the date/time/datetime pickers will use a darker theme instead of white
        const meta = document.createElement("meta");
        meta.name = "color-scheme";
        meta.content = colorSchemeMode === "system" ? colorScheme : colorSchemeMode;
        document.head.appendChild(meta);

        return () => {
          document.head.removeChild(meta);
        };
      }, [colorScheme, colorSchemeMode, disableMetaTag, mode]);

      return <Provider value={value}>{children}</Provider>;
    }