feat: replace next-themes with a custom ThemeProvider

To be honest, next-themes was working fine. However since I use a theme
provider for Prism code blocks, some code is duplicated between this
app and the library. So I prefer to use a custom Provider without the
options I don't need.

4 files changed, 168 insertions, 0 deletions

diff --git a/src/utils/providers/index.ts b/src/utils/providers/index.ts
index a01200a..90dca15 100644
--- a/src/utils/providers/index.ts
+++ b/src/utils/providers/index.ts
@@ -1,3 +1,4 @@
 export * from './ackee-provider';
 export * from './motion-provider';
 export * from './prism-theme';
+export * from './theme-provider';
diff --git a/src/utils/providers/theme-provider/index.ts b/src/utils/providers/theme-provider/index.ts
new file mode 100644
index 0000000..3df4bde
--- /dev/null
+++ b/src/utils/providers/theme-provider/index.ts
@@ -0,0 +1 @@
+export * from './theme-provider';
diff --git a/src/utils/providers/theme-provider/theme-provider.test.tsx b/src/utils/providers/theme-provider/theme-provider.test.tsx
new file mode 100644
index 0000000..59a72cc
--- /dev/null
+++ b/src/utils/providers/theme-provider/theme-provider.test.tsx
@@ -0,0 +1,78 @@
+import { describe, expect, it } from '@jest/globals';
+import { render, screen as rtlScreen } from '@testing-library/react';
+import { type FC, useContext } from 'react';
+import { getThemeFromSystem } from '../../helpers';
+import { ThemeContext, ThemeProvider } from './theme-provider';
+
+const bodyPrefix = 'Current theme is:';
+
+const ComponentTest: FC = () => {
+  const { theme } = useContext(ThemeContext);
+
+  return (
+    <div>
+      {bodyPrefix} {theme}
+    </div>
+  );
+};
+
+describe('ThemeProvider', () => {
+  it('uses the default value when the provider is not used', () => {
+    const defaultValue = 'system';
+
+    render(<ComponentTest />);
+
+    expect(rtlScreen.getByText(new RegExp(bodyPrefix))).toHaveTextContent(
+      `${bodyPrefix} ${defaultValue}`
+    );
+  });
+
+  it('provides the given value to its children and set a matching attribute', () => {
+    const attribute = 'iure';
+    const theme = 'dark';
+
+    const { baseElement } = render(
+      <ThemeProvider
+        attribute={attribute}
+        defaultTheme={theme}
+        storageKey="dolores"
+      >
+        <ComponentTest />
+      </ThemeProvider>
+    );
+
+    expect(rtlScreen.getByText(new RegExp(bodyPrefix))).toHaveTextContent(
+      `${bodyPrefix} ${theme}`
+    );
+    expect(baseElement.parentElement?.getAttribute(`data-${attribute}`)).toBe(
+      theme
+    );
+    expect(baseElement.parentElement).toHaveStyle(`color-scheme: ${theme};`);
+  });
+
+  it('can resolve the preferred theme from user system settings', () => {
+    const attribute = 'qui';
+    const defaultTheme = 'system';
+    const resolvedTheme = getThemeFromSystem();
+
+    const { baseElement } = render(
+      <ThemeProvider
+        attribute={attribute}
+        defaultTheme={defaultTheme}
+        storageKey="modi"
+      >
+        <ComponentTest />
+      </ThemeProvider>
+    );
+
+    expect(rtlScreen.getByText(new RegExp(bodyPrefix))).toHaveTextContent(
+      `${bodyPrefix} ${defaultTheme}`
+    );
+    expect(baseElement.parentElement?.getAttribute(`data-${attribute}`)).toBe(
+      resolvedTheme
+    );
+    expect(baseElement.parentElement).toHaveStyle(
+      `color-scheme: ${resolvedTheme};`
+    );
+  });
+});
diff --git a/src/utils/providers/theme-provider/theme-provider.tsx b/src/utils/providers/theme-provider/theme-provider.tsx
new file mode 100644
index 0000000..b743a7f
--- /dev/null
+++ b/src/utils/providers/theme-provider/theme-provider.tsx
@@ -0,0 +1,88 @@
+import {
+  type Dispatch,
+  type FC,
+  type ReactNode,
+  type SetStateAction,
+  createContext,
+  useMemo,
+  useEffect,
+} from 'react';
+import { getDataAttributeFrom, getThemeFromSystem } from '../../helpers';
+import { useLocalStorage, useSystemColorScheme } from '../../hooks';
+
+const validThemes = ['dark', 'light', 'system'] as const;
+
+type Theme = (typeof validThemes)[number];
+
+type ThemeContextProps = {
+  resolvedTheme: Exclude<Theme, 'system'>;
+  setTheme: Dispatch<SetStateAction<Theme>>;
+  theme: Theme;
+};
+
+export const ThemeContext = createContext<ThemeContextProps>({
+  resolvedTheme: getThemeFromSystem(),
+  setTheme: (value) => value,
+  theme: 'system',
+});
+
+const validator = (value: unknown): value is Theme =>
+  typeof value === 'string' &&
+  (validThemes as readonly string[]).includes(value);
+
+export type ThemeProviderProps = {
+  /**
+   * The attribute name to append to document root.
+   */
+  attribute: string;
+  /**
+   * The provider children.
+   */
+  children?: ReactNode;
+  /**
+   * The default theme.
+   *
+   * @default 'system'
+   */
+  defaultTheme?: Theme;
+  /**
+   * The key to use in local storage.
+   */
+  storageKey: string;
+};
+
+export const ThemeProvider: FC<ThemeProviderProps> = ({
+  attribute,
+  children,
+  defaultTheme = 'system',
+  storageKey,
+}) => {
+  const [theme, setTheme] = useLocalStorage(
+    storageKey,
+    defaultTheme,
+    validator
+  );
+  const userColorScheme = useSystemColorScheme();
+  const resolvedTheme: Exclude<Theme, 'system'> =
+    theme === 'system' ? userColorScheme : theme;
+  const dataAttribute = getDataAttributeFrom(attribute);
+
+  useEffect(() => {
+    if (typeof window !== 'undefined') {
+      document.documentElement.setAttribute(dataAttribute, `${resolvedTheme}`);
+      document.documentElement.style.colorScheme = resolvedTheme;
+    }
+
+    return () => {
+      document.documentElement.removeAttribute(dataAttribute);
+    };
+  }, [dataAttribute, resolvedTheme]);
+
+  const value = useMemo(() => {
+    return { resolvedTheme, setTheme, theme };
+  }, [resolvedTheme, setTheme, theme]);
+
+  return (
+    <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>
+  );
+};