Create a themer

components/Theme.tsx

@@ -0,0 +1,178 @@
+import React, {
+  createContext,
+  ReactElement,
+  useContext,
+  useEffect,
+  useState,
+} from "react";
+
+type BuiltInThemes = "light" | "dark";
+
+export interface Theme {
+  name: BuiltInThemes | "custom";
+  palette: Palette;
+}
+
+export type SetThemeInput = BuiltInThemes | Partial<Palette>;
+
+export const PALETTE_NAMES = [
+  "--primary-background",
+  "--secondary-background",
+
+  "--primary-accent",
+  "--primary-accent-soft",
+  "--primary-accent-light",
+  "--primary-accent-dim",
+
+  "--secondary-accent",
+  "--secondary-accent-light",
+
+  "--primary-heading",
+  "--secondary-heading",
+
+  "--text",
+
+  "--form-invalid",
+
+  "--input-background",
+  "--input-placeholder-text",
+  "--input-text",
+
+  "--navbar-page-overlay",
+] as const;
+
+export const emptyPalette = PALETTE_NAMES.reduce(
+  (partial, varName) => ({
+    ...partial,
+    [varName]: "#c4e0f8",
+  }),
+  {} as Palette
+);
+
+const ThemeContext =
+  createContext<
+    | {
+        theme: Theme;
+        setTheme(input: SetThemeInput): void;
+        save(): void;
+        clearSaved(): void;
+      }
+    | undefined
+  >(undefined);
+
+export interface Props {
+  children?: ReactElement;
+}
+
+export function ThemeProvider(props: Props) {
+  const update = useForcedUpdate();
+  const [themeName, setThemeName] =
+    useState<Theme["name"] | undefined>(undefined);
+
+  const setTheme = (input: SetThemeInput) => {
+    if (typeof input === "string") {
+      PALETTE_NAMES.forEach((name) =>
+        document.body.style.setProperty(name, "")
+      );
+
+      if (input === "light") {
+        document.body.classList.remove("dark");
+      } else if (input === "dark") {
+        document.body.classList.add("dark");
+      }
+
+      setThemeName(input);
+    } else {
+      const properties = Object.keys(input) as PaletteNames[];
+
+      properties.forEach((property) =>
+        document.body.style.setProperty(
+          property,
+          input[property]?.trim() ?? null
+        )
+      );
+
+      setThemeName("custom");
+    }
+
+    update();
+  };
+
+  useEffect(() => {
+    const customPalette = getSavedPalette();
+
+    if (customPalette == null) {
+      setThemeName("light");
+    } else {
+      setTheme(customPalette);
+      setThemeName("custom");
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
+  return (
+    <ThemeContext.Provider
+      value={
+        themeName == null
+          ? undefined
+          : {
+              theme: {
+                name: themeName,
+                get palette() {
+                  return getCurrentPalette();
+                },
+              },
+              setTheme,
+              save: () => savePalette(getCurrentPalette()),
+              clearSaved: clearSavedPalette,
+            }
+      }
+    >
+      {props.children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useThemeContext() {
+  return useContext(ThemeContext);
+}
+
+export type PaletteNames = typeof PALETTE_NAMES[number];
+
+export type Palette = {
+  [key in PaletteNames]: string;
+};
+
+function getCurrentPalette() {
+  const styles = getComputedStyle(document.body);
+
+  return PALETTE_NAMES.reduce(
+    (partial, varName) => ({
+      ...partial,
+      [varName]: styles.getPropertyValue(varName).trim(),
+    }),
+    {} as Palette
+  );
+}
+
+function useForcedUpdate() {
+  const [fakeState, setFakeState] = useState(true);
+
+  return () => setFakeState(!fakeState);
+}
+
+const STORAGE_KEY = "csc-theme-palette";
+
+function getSavedPalette() {
+  const raw = localStorage.getItem(STORAGE_KEY);
+
+  return raw == null ? undefined : (JSON.parse(raw) as Palette);
+}
+
+function savePalette(palette: Palette) {
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(palette));
+}
+
+function clearSavedPalette() {
+  localStorage.removeItem(STORAGE_KEY);
+}

components/theme.tsx

@@ -1,36 +0,0 @@
-import React, { createContext, ReactElement, useEffect, useState } from "react";
-
-type Theme = "light" | "dark";
-
-const ThemeContext = createContext<{
-  theme: Theme;
-  setTheme(newTheme: Theme): void;
-}>({
-  theme: "light",
-  setTheme: () => {
-    throw new Error("Use ThemeProvider instead.");
-  },
-});
-
-interface Props {
-  theme: Theme;
-  children?: ReactElement;
-}
-
-export function ThemeProvider({ children, theme }: Props) {
-  const [currentTheme, setTheme] = useState(theme);
-
-  useEffect(() => {
-    if (currentTheme === "light") {
-      document.body.classList.remove("dark");
-    } else if (currentTheme === "dark") {
-      document.body.classList.add("dark");
-    }
-  }, [currentTheme]);
-
-  return (
-    <ThemeContext.Provider value={{ theme: currentTheme, setTheme }}>
-      {children}
-    </ThemeContext.Provider>
-  );
-}

pages/_app.tsx

@@ -2,7 +2,7 @@ import React, { ComponentType, ReactNode } from "react";
 import { NextComponentType, NextPageContext } from "next";
 import { AppProps as DefaultAppProps } from "next/app";
 import { MDXProvider } from "@mdx-js/react";
-import { ThemeProvider } from "../components/theme";
+import { ThemeProvider } from "../components/Theme";
 import { Navbar } from "../components/Navbar";
 import { Footer } from "../components/Footer";
 import { Link } from "../components/Link";
@@ -16,7 +16,7 @@ export default function App({ Component, pageProps }: AppProps): JSX.Element {
   const Layout = Component.Layout ?? DefaultLayout;
 
   return (
-    <ThemeProvider theme="light">
+    <ThemeProvider>
       <MDXProvider components={{ a: Link }}>
         <div className={styles.appContainer}>
           <Navbar />

pages/themer.module.css

@@ -0,0 +1,34 @@
+.page {
+  margin-bottom: calc(60rem / 16);
+}
+
+.controls {
+  display: flex;
+  justify-content: space-between;
+}
+
+.palette {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(calc(150rem / 16), 1fr));
+  row-gap: calc(20rem / 16);
+  column-gap: calc(40rem / 16);
+}
+
+.palette > * {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+}
+
+.colorSelector {
+  height: calc(75rem / 16);
+}
+
+.colorReset {
+  margin-bottom: calc(10rem / 16);
+  transition-duration: unset;
+}
+
+.colorName {
+  text-align: center;
+}

pages/themer.tsx

@@ -0,0 +1,67 @@
+import React from "react";
+import { useThemeContext, emptyPalette } from "components/Theme";
+import { Input } from "components/Input";
+import { Button } from "components/Button";
+
+import styles from "./themer.module.css";
+
+export default function Themer() {
+  const context = useThemeContext();
+  const palette = context?.theme.palette ?? emptyPalette;
+
+  return (
+    <main className={styles.page}>
+      <h1>Themer</h1>
+      <form onSubmit={(event) => event.preventDefault()}>
+        <div className={styles.controls}>
+          <Button
+            type="reset"
+            onClick={() => {
+              context?.clearSaved();
+              context?.setTheme("light");
+            }}
+          >
+            Reset to light mode
+          </Button>
+          <Button type="submit" onClick={() => context?.save()}>
+            Save
+          </Button>
+        </div>
+        <div className={styles.palette}>
+          {Object.entries(palette).map(([key, value]) => {
+            return (
+              <div key={key}>
+                <Input
+                  id={`color-${key}`}
+                  type="color"
+                  className={styles.colorSelector}
+                  value={value}
+                  onChange={(event) =>
+                    context?.setTheme({ [key]: event.target.value })
+                  }
+                />
+                <Button
+                  type="button"
+                  className={styles.colorReset}
+                  size="small"
+                  onClick={() => context?.setTheme({ [key]: "" })}
+                >
+                  Reset
+                </Button>
+                <code className={styles.colorName}>
+                  <label htmlFor={`color-${key}`}>
+                    {key
+                      .slice(2)
+                      .split("-")
+                      .map((word) => word[0].toUpperCase() + word.slice(1))
+                      .join(" ")}
+                  </label>
+                </code>
+              </div>
+            );
+          })}
+        </div>{" "}
+      </form>
+    </main>
+  );
+}