hanzo.ai/components/code.tsx

import { bundledLanguages, getSingletonHighlighter, type BundledLanguage } from 'shiki'
import { codeTheme } from '@hanzo/ui/core'
import type { LineProps } from '@hanzo/ui/marketing'
import { Line } from '@/components/ui'

/**
 * A code sample, highlighted where the page is built.
 *
 * A server component: shiki runs once, during the export, and the page ships
 * the coloured spans — no highlighter reaches the browser. A client component
 * that shows code takes this as a prop from the server page that owns the
 * sample, the way ProductLanding's `code.source` does.
 *
 * The theme is @hanzo/ui's `codeTheme` (Dracula dark, GitHub Light light),
 * written as `light-dark(<light>, <dark>)`, so the page's `color-scheme` —
 * which @hanzo/appearance sets with the theme class — picks the palette. The
 * tokens are the theme's. The ground is not Dracula's blue-violet #282a36: the
 * site is monochrome, so the dark ground is the design system's own neutral
 * `--card` (#0f0f0f) and the light one GitHub Light's white; the frame around
 * the block stays the page's.
 *
 * A language shiki does not ship (or none) is set as plain text in the theme's
 * ink rather than failing the build.
 *
 * Every token reads at AA on the light ground: GitHub Light's orange (#E36209)
 * is 3.49:1 on its white, so a light ink under 4.5:1 is darkened, hue kept,
 * until it clears it (`legible`). The dark half is Dracula's as shipped.
 */
export type CodeProps = { code: string; lang?: string } & Omit<LineProps, 'children'>

const grammar = (lang?: string): BundledLanguage | 'text' =>
  lang && lang in bundledLanguages ? (lang as BundledLanguage) : 'text'

/** `#rgb` or `#rrggbb` as its three channels, 0–255; null for anything else. */
function channels(hex: string): [number, number, number] | null {
  const m = /^#([0-9a-f]{3}|[0-9a-f]{6})$/i.exec(hex.trim())
  if (!m) return null
  const h = m[1].length === 3 ? [...m[1]].map((c) => c + c).join('') : m[1]
  return [0, 2, 4].map((i) => parseInt(h.slice(i, i + 2), 16)) as [number, number, number]
}

/** WCAG 2 relative luminance. */
const luminance = (c: [number, number, number]) => {
  const [r, g, b] = c.map((v) => (v / 255 <= 0.03928 ? v / 255 / 12.92 : ((v / 255 + 0.055) / 1.055) ** 2.4))
  return 0.2126 * r + 0.7152 * g + 0.0722 * b
}

const ratio = (a: [number, number, number], b: [number, number, number]) => {
  const [hi, lo] = [luminance(a), luminance(b)].sort((x, y) => y - x)
  return (hi + 0.05) / (lo + 0.05)
}

/** `ink` darkened in 5% steps, hue kept, until it reads at 4.5:1 on `ground`. */
function legible(ink: string, ground: string): string {
  const [c, g] = [channels(ink), channels(ground)]
  if (!c || !g) return ink
  for (let k = 0; k <= 20; k++) {
    const shade = c.map((v) => Math.round(v * (1 - k * 0.05))) as [number, number, number]
    if (ratio(shade, g) >= 4.5) return k === 0 ? ink : `#${shade.map((v) => v.toString(16).padStart(2, '0')).join('')}`
  }
  return ink
}

/** A token's `light-dark(<light>, <dark>)` with its light ink made legible on `ground`. */
const readable = (color: string | undefined, ground: string) => {
  const m = color && /^light-dark\(([^,]+),\s*(.+)\)$/.exec(color)
  return m ? `light-dark(${legible(m[1], ground)}, ${m[2]})` : color
}

export async function Code({ code, lang, ...props }: CodeProps) {
  const language = grammar(lang)
  const shiki = await getSingletonHighlighter({ themes: [codeTheme.dark, codeTheme.light], langs: [] })
  if (language !== 'text') await shiki.loadLanguage(language)
  const dark = shiki.getTheme(codeTheme.dark)
  const light = shiki.getTheme(codeTheme.light)
  const { tokens } = shiki.codeToTokens(code.replace(/\n$/, ''), {
    lang: language,
    themes: codeTheme,
    defaultColor: 'light-dark()',
  })
  return (
    <Line
      render="pre"
      display="block"
      m={0}
      p={16}
      overflowX="auto"
      whiteSpace="pre"
      fontFamily="$mono"
      fontSize="$2"
      lineHeight="var(--leading-relaxed)"
      // inline-style: the light theme's ground and both themes' ink, read from shiki at build; the dark ground is the design system's neutral card.
      style={{
        backgroundColor: `light-dark(${light.bg}, var(--card))`,
        color: `light-dark(${light.fg}, ${dark.fg})`,
      }}
      {...props}
    >
      <code>
        {tokens.map((line, i) => (
          <span key={i}>
            {line.map((t, j) => (
              // inline-style: each token's colour is the code theme's, computed by shiki per token.
              <span key={j} style={{ color: readable(t.htmlStyle?.color, light.bg) }}>
                {t.content}
              </span>
            ))}
            {i < tokens.length - 1 ? '\n' : null}
          </span>
        ))}
      </code>
    </Line>
  )
}