import type { BuildPixelDensitySrcSetParams } from "imgix-url-builder"
import { buildPixelDensitySrcSet, buildURL } from "imgix-url-builder"

import type { ImageFieldImage } from "../types/value/image"
import { imageThumbnail as isImageThumbnailFilled } from "./isFilled"

/** The default pixel densities used to generate a `srcset` value. */
const DEFAULT_PIXEL_DENSITIES = [1, 2, 3]

/** Configuration for `asImagePixelDensitySrcSet()`. */
type AsImagePixelDensitySrcSetConfig = Omit<BuildPixelDensitySrcSetParams, "pixelDensities"> &
	Partial<Pick<BuildPixelDensitySrcSetParams, "pixelDensities">>

/** The return type of `asImagePixelDensitySrcSet()`. */
type AsImagePixelDensitySrcSetReturnType<Field extends ImageFieldImage | null | undefined> =
	Field extends ImageFieldImage<"filled">
		? {
				/** The image field's URL with imgix URL parameters (if given). */
				src: string

				/**
				 * A pixel-density-based `srcset` attribute value for the image field with imgix URL
				 * parameters (if given).
				 */
				srcset: string
			}
		: null

/**
 * Creates a pixel-density-based `srcset` from an image field with optional image transformations
 * via imgix URL parameters.
 *
 * If a `pixelDensities` parameter is not given, the following pixel densities will be used by
 * default: 1, 2, 3.
 *
 * @example
 * 	;```ts
 * 	const srcset = asImagePixelDensitySrcSet(document.data.photo, {
 * 		pixelDensities: [1, 2],
 * 		sat: -100,
 * 	})
 * 	// => {
 * 	//   src: "https://images.prismic.io/repo/image.png?sat=-100",
 * 	//   srcset: "https://images.prismic.io/repo/image.png?sat=-100&dpr=1 1x, " +
 * 	//           "https://images.prismic.io/repo/image.png?sat=-100&dpr=2 2x"
 * 	// }
 * 	```
 *
 * @param field - An image field (or one of its responsive views) from which to get an image URL.
 * @param config - An object of imgix URL API parameters. The `pixelDensities` parameter defines the
 *   resulting `srcset` pixel densities.
 * @returns A `srcset` attribute value for the image field with imgix URL parameters, or `null` if
 *   the field is empty.
 * @see Learn how to optimize images with imgix: {@link https://prismic.io/docs/fields/image}
 * @see imgix URL parameters reference: {@link https://docs.imgix.com/apis/rendering}
 */
export const asImagePixelDensitySrcSet = <Field extends ImageFieldImage | null | undefined>(
	field: Field,
	config: AsImagePixelDensitySrcSetConfig = {},
): AsImagePixelDensitySrcSetReturnType<Field> => {
	if (field && isImageThumbnailFilled(field)) {
		// We are using destructuring to omit `pixelDensities` from the
		// object we will pass to `buildURL()`.
		const { pixelDensities = DEFAULT_PIXEL_DENSITIES, ...imgixParams } = config

		return {
			src: buildURL(field.url, imgixParams),
			srcset: buildPixelDensitySrcSet(field.url, {
				...imgixParams,
				pixelDensities,
			}),
		} as AsImagePixelDensitySrcSetReturnType<Field>
	} else {
		return null as AsImagePixelDensitySrcSetReturnType<Field>
	}
}