const safeTags = new Map<string, string>()

function safeTagFor(locale: string) {
	let safeTag = safeTags.get(locale)
	if (safeTag == null) {
		safeTag = new Intl.Locale(locale).baseName
		safeTags.set(locale, safeTag)
	}
	return safeTag
}

type DisplayNamesWrapper = Intl.DisplayNames & {
	of(tag: string): string | undefined
}

const displayNamesDicts = new Map<string, DisplayNamesWrapper>()

function getWrapperKey(locale: string, options: Intl.DisplayNamesOptions) {
	return JSON.stringify({ ...options, locale })
}

export function createDisplayNames(
	locale: string,
	options: Intl.DisplayNamesOptions = { type: 'language' },
) {
	const wrapperKey = getWrapperKey(locale, options)
	let wrapper = displayNamesDicts.get(wrapperKey)

	if (wrapper == null) {
		const dict = new Intl.DisplayNames(locale, options)

		const badTags: string[] = []

		wrapper = {
			resolvedOptions() {
				return dict.resolvedOptions()
			},
			of(tag: string) {
				let attempt = 0

				lookupLoop: do {
					let lookup: string
					switch (attempt) {
						case 0:
							lookup = tag
							break
						case 1:
							lookup = safeTagFor(tag)
							break
						default:
							break lookupLoop
					}

					if (badTags.includes(lookup)) continue

					try {
						return dict.of(lookup)
					} catch {
						console.warn(
							`Failed to get display name for ${lookup} using dictionary for ${
								this.resolvedOptions().locale
							}`,
						)
						badTags.push(lookup)
						continue
					}
				} while (++attempt < 5)

				return undefined
			},
		}

		displayNamesDicts.set(wrapperKey, wrapper)
	}

	return wrapper
}

export function useDisplayNames(
	locale: string | (() => string) | Ref<string>,
	options?:
		| (Intl.DisplayNamesOptions | undefined)
		| (() => Intl.DisplayNamesOptions | undefined)
		| Ref<Intl.DisplayNamesOptions | undefined>,
) {
	const $locale = toRef(locale)
	const $options = toRef(options)

	return computed(() => createDisplayNames($locale.value, $options.value))
}