margin/src/model/fonts.ts

export type FontCategory = "serif" | "sans" | "display";

export interface BundledFont {
  id: string;
  label: string;
  family: string;
  category: FontCategory;
  regular: string;
  italic?: string;
  weight: string;
}

export const BUNDLED_FONTS: BundledFont[] = [
  { id: "literata", label: "Literata", family: "Literata", category: "serif", regular: "Literata-VF.ttf", italic: "Literata-Italic-VF.ttf", weight: "200 900" },
  { id: "eb-garamond", label: "EB Garamond", family: "EB Garamond", category: "serif", regular: "EBGaramond-VF.ttf", italic: "EBGaramond-Italic-VF.ttf", weight: "400 800" },
  { id: "lora", label: "Lora", family: "Lora", category: "serif", regular: "Lora-VF.ttf", italic: "Lora-Italic-VF.ttf", weight: "400 700" },
  { id: "source-serif", label: "Source Serif 4", family: "Source Serif 4", category: "serif", regular: "SourceSerif4-VF.ttf", italic: "SourceSerif4-Italic-VF.ttf", weight: "200 900" },
  { id: "fraunces", label: "Fraunces", family: "Fraunces", category: "display", regular: "Fraunces-VF.ttf", italic: "Fraunces-Italic-VF.ttf", weight: "100 900" },
  { id: "hanken", label: "Hanken Grotesk", family: "Hanken Grotesk", category: "sans", regular: "HankenGrotesk-VF.ttf", italic: "HankenGrotesk-Italic-VF.ttf", weight: "100 900" },
];

export type FontRef =
  | { kind: "bundled"; id: string }
  | { kind: "system"; family: string };

export interface BookFonts {
  body: FontRef;
  heading: FontRef;
}

export interface FontPairing {
  id: string;
  label: string;
  body: FontRef;
  heading: FontRef;
}

const bundled = (id: string): FontRef => ({ kind: "bundled", id });

export const FONT_PAIRINGS: FontPairing[] = [
  { id: "quiet-press", label: "Quiet Press", body: bundled("literata"), heading: bundled("literata") },
  { id: "classic", label: "Classic", body: bundled("eb-garamond"), heading: bundled("eb-garamond") },
  { id: "editorial", label: "Editorial", body: bundled("source-serif"), heading: bundled("fraunces") },
  { id: "modern", label: "Modern", body: bundled("lora"), heading: bundled("hanken") },
  { id: "contrast", label: "Contrast", body: bundled("literata"), heading: bundled("hanken") },
];

export const DEFAULT_FONTS: BookFonts = { body: bundled("literata"), heading: bundled("literata") };

const SERIF_FALLBACK = `Georgia, "Times New Roman", serif`;
const SANS_FALLBACK = `ui-sans-serif, system-ui, -apple-system, sans-serif`;

export function bundledFont(id: string): BundledFont | undefined {
  return BUNDLED_FONTS.find((f) => f.id === id);
}

export function encodeRef(ref: FontRef): string {
  return ref.kind === "bundled" ? `b:${ref.id}` : `s:${ref.family}`;
}

export function decodeRef(value: string): FontRef {
  return value.startsWith("s:") ? { kind: "system", family: value.slice(2) } : { kind: "bundled", id: value.slice(2) };
}

export function fontFamilyName(ref: FontRef): string {
  if (ref.kind === "system") return ref.family;
  return bundledFont(ref.id)?.family ?? "Literata";
}

export function fontLabel(ref: FontRef): string {
  if (ref.kind === "system") return ref.family;
  return bundledFont(ref.id)?.label ?? ref.id;
}

export function fontStack(ref: FontRef): string {
  if (ref.kind === "bundled") {
    const font = bundledFont(ref.id);
    if (!font) return SERIF_FALLBACK;
    return `"${font.family}", ${font.category === "sans" ? SANS_FALLBACK : SERIF_FALLBACK}`;
  }
  return `"${ref.family}", ${SERIF_FALLBACK}`;
}

export function refsEqual(a: FontRef, b: FontRef): boolean {
  if (a.kind !== b.kind) return false;
  return a.kind === "bundled" ? a.id === (b as { id: string }).id : a.family === (b as { family: string }).family;
}

export function pairingFor(fonts: BookFonts): string | null {
  const match = FONT_PAIRINGS.find((p) => refsEqual(p.body, fonts.body) && refsEqual(p.heading, fonts.heading));
  return match?.id ?? null;
}

export function fontsUsed(fonts: BookFonts): { bundled: BundledFont[]; system: string[] } {
  const usedBundled = new Map<string, BundledFont>();
  const usedSystem = new Set<string>();
  for (const ref of [fonts.body, fonts.heading]) {
    if (ref.kind === "bundled") {
      const font = bundledFont(ref.id);
      if (font) usedBundled.set(font.id, font);
    } else {
      usedSystem.add(ref.family);
    }
  }
  return { bundled: [...usedBundled.values()], system: [...usedSystem] };
}