import { splitWordmark } from "./brand";
import { WORDMARK_METRICS } from "./wordmarkMetrics";

// A wordmark's width as the DISPLAY FACE sets it, in em of its font size —
// so a layout can reserve it before the web font has loaded. The export
// header's wordmark drops its text when the text does not fit beside the
// icons (export/app/components/Header.tsx); measured in the fallback face,
// which is narrower, a title could fit, show, and then vanish when Archivo
// arrived. Reserving this width makes the decision the same either way.
//
// The lead is weight 720 and the suffix 380 (common/components/Wordmark.tsx),
// both at wdth 118; each character is its advance from the vendored font
// (lib/wordmarkMetrics.ts, generated) plus `letterSpacingEm`, kerning left
// out, and MARGIN more: the web font Google serves renders 0.2–2.4 % wider
// than the vendored file's advances sum to (measured in Chromium). The header
// sets this as the wordmark's MIN-width, not its width: where a platform
// renders the text wider still, the box grows with it (and the text drops a
// little sooner) rather than clipping its last letter. A character the table
// does not hold counts as UNMAPPED_EM, wider than any it does.

const UNMAPPED_EM = 1.25;
const MARGIN = 1.03;

function advanceEm(cp: number, wght: 720 | 380): number {
  const { ranges, advances, unitsPerEm } = WORDMARK_METRICS;
  let offset = 0;
  for (const [first, last] of ranges) {
    if (cp >= first && cp <= last) return advances[wght][offset + cp - first] / unitsPerEm;
    offset += last - first + 1;
  }
  return UNMAPPED_EM;
}

export function wordmarkWidthEm(title: string, lead: string | undefined, letterSpacingEm = 0): number {
  const parts = splitWordmark(title, lead);
  let em = 0;
  for (const [text, wght] of [
    [parts.lead, 720],
    [parts.suffix, 380],
  ] as const) {
    for (const ch of text) em += advanceEm(ch.codePointAt(0)!, wght) + letterSpacingEm;
  }
  return Math.round(em * MARGIN * 1000) / 1000;
}