#!/usr/bin/env node
// Joins finished slides into one horizontal preview strip (webp), at most 2048 px on the long edge.
// Usage: node scripts/slides-strip.mjs --output strip.webp --gap 16 slide-1.png slide-2.png ...
// Options: --output <file> (required), --gap <px> (default 16), --height <px> (upper limit; the strip is shrunk to fit 2048 px wide).
let sharp
try {
  sharp = (await import('sharp')).default
} catch {
  console.error('This script needs the sharp package. Run `npm install sharp` in the Skill folder (Node 20.9 or newer), then try again.')
  process.exit(1)
}
function fail(message) { console.error(message); process.exit(1) }

const a = process.argv.slice(2)
const opt = { height: 640, gap: 16 }
const files = []
let output
for (let i = 0; i < a.length; i += 1) {
  const k = a[i]
  if (k === '--output' || k === '--height' || k === '--gap') {
    const v = a[i + 1]
    if (v === undefined || v.startsWith('--')) fail(`Flag ${k} needs a value.`)
    i += 1
    if (k === '--output') output = v
    else {
      const n = Number(v)
      if (!Number.isInteger(n) || n < 1 || n > 4000) fail(`${k} must be a whole number of pixels (1 to 4000).`)
      opt[k.slice(2)] = n
    }
  } else if (k.startsWith('--')) fail(`Unknown flag ${k}. Known: --output, --height, --gap`)
  else files.push(k)
}
if (!files.length || !output) fail('Usage: node scripts/slides-strip.mjs --output strip.webp slide-1.png slide-2.png ...')
const metas = await Promise.all(files.map((f) => sharp(f).metadata().catch(() => fail(`Cannot read image: ${f}`))))
const aspect = metas.reduce((n, m) => n + m.width / m.height, 0)
const fit = Math.floor((2048 - opt.gap * (files.length - 1)) / aspect) - files.length
const height = Math.max(1, Math.min(opt.height, fit))
const tiles = await Promise.all(files.map((f) => sharp(f).resize({ height }).toBuffer({ resolveWithObject: true })))
const width = tiles.reduce((n, t) => n + t.info.width, 0) + opt.gap * (tiles.length - 1)
let left = 0
const composite = tiles.map((t) => { const c = { input: t.data, left, top: 0 }; left += t.info.width + opt.gap; return c })
await sharp({ create: { width, height, channels: 3, background: '#1a100a' } }).composite(composite).webp({ quality: 82 }).toFile(output)
console.log(`${output} ${width}x${height}`)