Fix useTheme hook

[NicholasBoll]

🐛 Bug Report

The useTheme hook is used in 3 distinct ways:

• Inside a functional component
• Inside a styled function
• Inside a class component

All use-cases will use the getFilledTheme utility function or fall back to the default Canvas theme if no theme was found.

There is actually 2 distinct functions: A hook that can access the ThemeContext and a utility function. At the moment, the way it is implemented shouldn't cause any real issues, but every use of the CK styled function that doesn't have a predefined theme is throwing a silently-ignored error which isn't very efficient.

I propose useTheme is broken out to 2 distinct functions:

function isCanvasTheme(input: object): input is EmotionCanvasTheme {
  return input.hasOwnProperty('canvas');
}

function getThemeFromWindow(): any {
  // should we do any validation here? The shape could be anything... We're returning `any` and pretending things will be okay
  return typeof window !== 'undefined' && get(window, 'window.workday.canvas.theme');
}

// to be used in `styled` and class components
export function getTheme(theme?: PartialEmotionCanvasTheme): EmotionCanvasTheme {
  if (theme && isCanvasTheme(theme)) {
    return getFilledTheme(theme);
  }

  const windowTheme = getThemeFromWindow();
  if (windowTheme) {
    return getFilledTheme({canvas: windowTheme});
  }

  return {canvas: defaultCanvasTheme};
}

// to be used in functional components
export function useTheme(theme?: PartialEmotionCanvasTheme): EmotionCanvasTheme {
  const contextTheme = React.useContext(ThemeContext);

  if (theme && isCanvasTheme(theme)) {
    return getFilledTheme(theme);
  }

  if (isCanvasTheme(contextTheme)) {
    return getFilledTheme(contextTheme);
  }

  const windowTheme = getThemeFromWindow();
  if (windowTheme) {
    return getFilledTheme({canvas: windowTheme});
  }

  return {canvas: defaultCanvasTheme};
}

AC

• Update components that current useTheme to use the new methods
• Deprecate old useTheme methods
• Document changes
• Review current usage & plan for migration

look into #864 and if that can be somewhat addressed here