import { useRef, useEffect } from 'react';

/**
 * Debug hook showing which props updated between two renders
 * @example
 *
 * const MyComponent = React.memo(props => {
 *   useWhyDidYouUpdate('MyComponent', props);
 *   return <div...;
 * });
 *
 * @link https://usehooks.com/useWhyDidYouUpdate/
 */
export default function useWhyDidYouUpdate(name, props) {
    // Get a mutable ref object where we can store props ...
    // ... for comparison next time this hook runs.
    const previousProps = useRef() as any;

    useEffect(() => {
        if (previousProps.current) {
            // Get all keys from previous and current props
            const allKeys = Object.keys({ ...previousProps.current, ...props });
            // Use this object to keep track of changed props
            const changesObj = {};
            // Iterate through keys
            allKeys.forEach(key => {
                // If previous is different from current
                if (previousProps.current[key] !== props[key]) {
                    // Add to changesObj
                    changesObj[key] = {
                        from: previousProps.current[key],
                        to: props[key],
                    };
                }
            });

            // If changesObj not empty then output to console
            if (Object.keys(changesObj).length) {
                console.log('[why-did-you-update]', name, changesObj);
            }
        }

        // Finally update previousProps with current props for next hook call
        previousProps.current = props;
    });
}