gerbeur/api/mail/styles.ts

/**
 * Carries each site style into email, so a digest looks like the site its
 * reader chose and the other emails like the instance's style. A mail client
 * takes no stylesheet of ours, so each style is resolved here into plain
 * values, which `layout.ts` inlines.
 *
 * What a theme defines is read from it through `theme-tokens.ts`, never
 * copied: the colors, the gradient, the font and the corner radii. What is
 * the email's own is stated here: how large it sets its type, how its card
 * stands out, which divider it draws, and which of the theme's own tokens
 * carry the touches that make it recognisable (Kanagawa's syntax hues,
 * GeoCities' rainbow, Melange's spice and warm shadow).
 *
 * @module
 */

import { STYLE_NAMES, type StyleName } from "../../shared/theme.ts";
import { readTokens, type Scheme } from "./theme-tokens.ts";

/**
 * The colors of one style in one scheme, by role, each read from a token of
 * its theme. The optional ones carry a style's particular touches.
 */
export interface EmailPalette {
  /** The page around the card (`--color-bg`). */
  outer: string;
  /** The card holding the content (`--color-surface`). */
  card: string;
  /** `--color-text`. */
  text: string;
  /** `--color-text-secondary`. */
  sec: string;
  /** `--color-text-muted`. */
  muted: string;
  /** Section titles, ranks and button fills (`--color-accent`). */
  accent: string;
  /** `--color-link`. */
  link: string;
  /** Text on an accent fill (`--color-on-accent`). */
  onAccent: string;
  /** Dividers and hairlines (`--color-border`). */
  rule: string;
  /** Pills and the reset link's box, as the site's badges (`--color-badge-bg`). */
  soft: string;
  /** Quoted comments and messages (`--color-text-secondary` unless set). */
  quote: string;
  /** Kanagawa's fujiGray dates; others use `muted`. */
  date?: string;
  /** Kanagawa's oniViolet wordmark; others use `text`. */
  brand?: string;
  /** GeoCities' ridged border. */
  border?: string;
  /** Melange's warm card shadow, translucent. */
  shadow?: string;
  /** The colors of GeoCities' rainbow or Melange's spice, left to right. */
  gradient?: string[];
}

/**
 * How a style draws an email. `layout.ts` builds every block from it, so
 * adding a style to `shared/theme.ts` means adding its {@link Recipe} here.
 */
export interface EmailStyle {
  /**
   * The theme's font stack (`--font-body`). Its first family is a web font
   * only Apple's mail apps load, through {@link webFont}; other clients fall
   * back along the stack.
   */
  font: string;
  /** The Google Fonts `family` parameter of the web font, if it is one. */
  webFont?: string;
  /** Multiplies every font size: Times sets its serif larger, Kanagawa its monospace smaller. */
  scale: number;
  /**
   * Corner radii, in pixels: the card's as the site's cards
   * (`--radius-xl`), the images' as its thumbnails (`--radius-md`), the
   * buttons' as its buttons (`--radius-lg`), the pills' as its badges
   * (`--radius-sm`). The avatars' is the email's own, since the site rounds
   * them with a literal 50% that some styles square.
   */
  radius: {
    card: number;
    img: number;
    btn: number;
    pill: number;
    avatar: number;
  };
  /** The heading: its size in pixels, weight, and Brutalist's uppercase and spacing. */
  title: {
    size: number;
    weight: number;
    upper?: boolean;
    spacing?: string;
    accent?: boolean;
  };
  /** The weight of titles of items, figures and names. */
  heavy: number;
  /** How the card stands out from the page. */
  frame: "none" | "hard" | "ridge" | "hairline" | "soft";
  /** The divider between sections; "gradient" draws the palette's. */
  rule: "hairline" | "thick" | "gradient";
  /** Draws the palette's gradient as a bar along the card's top. */
  bar?: boolean;
  /** Underlines links, for styles whose links are the color of the text. */
  linkUnderline?: boolean;
  light: EmailPalette;
  dark: EmailPalette;
}

/** The roles every style reads, and the token each is read from. */
const PALETTE_TOKENS = {
  outer: "--color-bg",
  card: "--color-surface",
  text: "--color-text",
  sec: "--color-text-secondary",
  muted: "--color-text-muted",
  accent: "--color-accent",
  link: "--color-link",
  onAccent: "--color-on-accent",
  rule: "--color-border",
  soft: "--color-badge-bg",
  quote: "--color-text-secondary",
} satisfies Partial<Record<keyof EmailPalette, string>>;

/**
 * What a style states about its email, beside what its theme defines: the
 * {@link EmailStyle} less the values read from the theme, the axes of its
 * web font, its avatars' radius, and the tokens of its own touches.
 */
interface Recipe
  extends Omit<EmailStyle, "font" | "webFont" | "radius" | "light" | "dark"> {
  /** The Google Fonts axes of the theme's first family; none for a system font. */
  webFontAxes?: string;
  avatarRadius: number;
  /** The tokens of the palette's optional roles, or of a base role it reads elsewhere. */
  tokens?: Partial<Record<keyof EmailPalette, string>>;
}

const RECIPES: Record<StyleName, Recipe> = {
  smooth: {
    webFontAxes: "wght@400;600;700",
    scale: 1,
    avatarRadius: 16,
    title: { size: 30, weight: 600 },
    heavy: 600,
    frame: "none",
    rule: "hairline",
  },
  brutalist: {
    webFontAxes: "wght@400;700",
    scale: 1,
    avatarRadius: 0,
    title: { size: 30, weight: 900, upper: true, spacing: "0.03em" },
    heavy: 700,
    frame: "hard",
    rule: "thick",
  },
  geocities: {
    scale: 1,
    avatarRadius: 0,
    title: { size: 30, weight: 700, accent: true },
    heavy: 700,
    frame: "ridge",
    rule: "gradient",
    bar: true,
    linkUnderline: true,
    tokens: { border: "--color-border", gradient: "--geo-rainbow" },
  },
  nyt: {
    webFontAxes: "ital@0;1",
    scale: 1.12,
    avatarRadius: 16,
    title: { size: 38, weight: 400 },
    heavy: 400,
    frame: "hairline",
    rule: "hairline",
    linkUnderline: true,
  },
  kanagawa: {
    webFontAxes: "ital,wght@0,400;0,600;1,400",
    scale: 0.9,
    avatarRadius: 4,
    title: { size: 26, weight: 600 },
    heavy: 600,
    frame: "hairline",
    rule: "hairline",
    tokens: {
      quote: "--kngw-string",
      date: "--kngw-comment",
      brand: "--kngw-keyword",
    },
  },
  melange: {
    webFontAxes: "wght@400;600",
    scale: 1,
    avatarRadius: 16,
    title: { size: 32, weight: 600 },
    heavy: 600,
    frame: "soft",
    rule: "hairline",
    bar: true,
    tokens: { shadow: "--shadow-color", gradient: "--mel-spice" },
  },
};

/**
 * Returns the palette of `style` in `scheme` from its theme's tokens. Every
 * color is flattened onto the card, as a translucent one shows on the site,
 * but the shadow, which falls on the page.
 */
function readPalette(
  style: StyleName,
  scheme: Scheme,
  own: Recipe["tokens"] = {},
): EmailPalette {
  const tokens = readTokens(style, scheme);
  const roles = { ...PALETTE_TOKENS, ...own };
  const palette = Object.fromEntries(
    Object.entries(roles)
      .filter(([role]) => role !== "shadow" && role !== "gradient")
      .map(([role, token]) => [role, tokens.color(token, "--color-surface")]),
  ) as unknown as EmailPalette;
  if (own.shadow) palette.shadow = tokens.color(own.shadow);
  if (own.gradient) palette.gradient = tokens.stops(own.gradient);
  return palette;
}

/** Returns the email look of `style`, its theme read in both schemes. */
function readStyle(style: StyleName): EmailStyle {
  const { webFontAxes, avatarRadius, tokens: own, ...recipe } = RECIPES[style];
  const tokens = readTokens(style, "light");
  const font = tokens.font("--font-body");
  const family = font.split(",")[0].replace(/'/g, "").replaceAll(" ", "+");
  return {
    ...recipe,
    font,
    webFont: webFontAxes ? `${family}:${webFontAxes}` : undefined,
    radius: {
      card: tokens.px("--radius-xl"),
      img: tokens.px("--radius-md"),
      btn: tokens.px("--radius-lg"),
      pill: tokens.px("--radius-sm"),
      avatar: avatarRadius,
    },
    light: readPalette(style, "light", own),
    dark: readPalette(style, "dark", own),
  };
}

/** Every style's email look, keyed by its name, read once at load. */
export const EMAIL_STYLES = Object.fromEntries(
  STYLE_NAMES.map((style) => [style, readStyle(style)]),
) as Record<StyleName, EmailStyle>;