image_constrain_size_for_editor( int $width, int $height, string|array $size = 'medium', string $context = null )

function image_constrain_size_for_editor( $width, $height, $size = 'medium', $context = null ) {
	global $content_width;

	$_wp_additional_image_sizes = wp_get_additional_image_sizes();

	if ( ! $context )
		$context = is_admin() ? 'edit' : 'display';

	if ( is_array($size) ) {
		$max_width = $size[0];
		$max_height = $size[1];
	}
	elseif ( $size == 'thumb' || $size == 'thumbnail' ) {
		$max_width = intval(get_option('thumbnail_size_w'));
		$max_height = intval(get_option('thumbnail_size_h'));
		// last chance thumbnail size defaults
		if ( !$max_width && !$max_height ) {
			$max_width = 128;
			$max_height = 96;
		}
	}
	elseif ( $size == 'medium' ) {
		$max_width = intval(get_option('medium_size_w'));
		$max_height = intval(get_option('medium_size_h'));

	}
	elseif ( $size == 'medium_large' ) {
		$max_width = intval( get_option( 'medium_large_size_w' ) );
		$max_height = intval( get_option( 'medium_large_size_h' ) );

		if ( intval( $content_width ) > 0 ) {
			$max_width = min( intval( $content_width ), $max_width );
		}
	}
	elseif ( $size == 'large' ) {
		/*
		 * We're inserting a large size image into the editor. If it's a really
		 * big image we'll scale it down to fit reasonably within the editor
		 * itself, and within the theme's content width if it's known. The user
		 * can resize it in the editor if they wish.
		 */
		$max_width = intval(get_option('large_size_w'));
		$max_height = intval(get_option('large_size_h'));
		if ( intval($content_width) > 0 ) {
			$max_width = min( intval($content_width), $max_width );
		}
	} elseif ( ! empty( $_wp_additional_image_sizes ) && in_array( $size, array_keys( $_wp_additional_image_sizes ) ) ) {
		$max_width = intval( $_wp_additional_image_sizes[$size]['width'] );
		$max_height = intval( $_wp_additional_image_sizes[$size]['height'] );
		// Only in admin. Assume that theme authors know what they're doing.
		if ( intval( $content_width ) > 0 && 'edit' === $context ) {
			$max_width = min( intval( $content_width ), $max_width );
		}
	}
	// $size == 'full' has no constraint
	else {
		$max_width = $width;
		$max_height = $height;
	}

	/**
	 * Filters the maximum image size dimensions for the editor.
	 *
	 * @since WP-2.5.0
	 *
	 * @param array        $max_image_size An array with the width as the first element,
	 *                                     and the height as the second element.
	 * @param string|array $size           Size of what the result image should be.
	 * @param string       $context        The context the image is being resized for.
	 *                                     Possible values are 'display' (like in a theme)
	 *                                     or 'edit' (like inserting into an editor).
	 */
	list( $max_width, $max_height ) = apply_filters( 'editor_max_image_size', array( $max_width, $max_height ), $size, $context );

	return wp_constrain_dimensions( $width, $height, $max_width, $max_height );
}