export interface WebFontFamilyDefinition {
  readonly family: string;
  readonly weights: readonly number[];
  readonly italic: boolean | readonly number[];
}

export interface LoadWebFontFamiliesOptions {
  readonly document: Document;
  readonly linkId: string;
  readonly families: readonly WebFontFamilyDefinition[];
}

function sortedUniqueWeights(weights: readonly number[]): number[] {
  return [...new Set(weights)].sort((left, right) => left - right);
}

function familyQuery(definition: WebFontFamilyDefinition): string {
  const weights = sortedUniqueWeights(definition.weights);
  if (weights.length === 0) {
    throw new Error(`Web font "${definition.family}" must declare at least one weight.`);
  }

  const italicWeights =
    definition.italic === true
      ? weights
      : definition.italic === false
        ? []
        : sortedUniqueWeights(definition.italic).filter((weight) => weights.includes(weight));
  const family = encodeURIComponent(definition.family);

  if (italicWeights.length === 0) {
    return `family=${family}:wght@${weights.map(String).join(';')}`;
  }

  const axes = [
    ...weights.map((weight) => `0,${String(weight)}`),
    ...italicWeights.map((weight) => `1,${String(weight)}`),
  ];
  return `family=${family}:ital,wght@${axes.join(';')}`;
}

export function buildWebFontStylesheetUrl(families: readonly WebFontFamilyDefinition[]): string {
  if (families.length === 0) {
    throw new Error('At least one web font family is required.');
  }

  return `https://fonts.googleapis.com/css2?${families.map(familyQuery).join('&')}&display=swap`;
}

export function loadWebFontFamilies({
  document,
  linkId,
  families,
}: LoadWebFontFamiliesOptions): () => void {
  const href = buildWebFontStylesheetUrl(families);
  const existing = document.getElementById(linkId);

  if (existing instanceof HTMLLinkElement && existing.getAttribute('href') === href) {
    return () => existing.remove();
  }
  existing?.remove();

  const link = document.createElement('link');
  link.id = linkId;
  link.rel = 'stylesheet';
  link.href = href;
  document.head.appendChild(link);

  return () => link.remove();
}