av-club/scripts/gen-docs.ts

#!/usr/bin/env bun
// Generate docs/SHARP.md from src/sharp/vocabulary.ts.
//
// The vocabulary table is what the validator enforces. Writing the reference by hand would mean two
// descriptions of one thing, and the doc would quietly stop being true the first time a bound
// changed. This makes the drift structurally impossible instead of a discipline problem.
//
// Run: bun run docs

import { INPUT_OPTIONS, OPERATIONS, OUTPUT_FORMATS, type Param } from "../src/sharp/vocabulary";
import { resolve, dirname } from "node:path";
import { fileURLToPath } from "node:url";

const ROOT = resolve(dirname(fileURLToPath(import.meta.url)), "..");

function describeParam(spec: Param): string {
  const base = (() => {
    switch (spec.kind) {
      case "int": return `integer, ${spec.min}–${spec.max}`;
      case "number": return `number, ${spec.min}–${spec.max}`;
      case "bool": return "boolean";
      case "enum": return spec.values.map((v) => `\`${v}\``).join(" · ");
      case "color": return "colour — a CSS string like `#ffffff`, or `{r, g, b, alpha}`";
      case "numberArray": return `array of ${spec.minLength === spec.maxLength ? spec.minLength : `${spec.minLength}–${spec.maxLength}`} numbers, each ${spec.min}–${spec.max}`;
      case "assetId": return "**asset id** (never a path)";
      case "string": return `string, up to ${spec.maxLength} chars`;
    }
  })();
  return spec.note ? `${base}. ${spec.note}` : base;
}

function paramTable(params: Record<string, Param>): string {
  const keys = Object.keys(params);
  if (!keys.length) return "_Takes no options._\n";

  return [
    "| Parameter | Accepts |",
    "|---|---|",
    ...keys.map((key) => `| \`${key}\` | ${describeParam(params[key]!)} |`),
    "",
  ].join("\n");
}

const lines: string[] = [
  "# sharp — the operation vocabulary",
  "",
  "**Generated from `src/sharp/vocabulary.ts` by `scripts/gen-docs.ts`. Do not edit by hand —",
  "run `bun run docs`.**",
  "",
  "Every operation is named what sharp names it and takes sharp's own arguments, so",
  "[sharp's documentation](https://sharp.pixelplumbing.com/api-operation) describes what each one",
  "*does*. This page describes what av-club *accepts*: the bounds, which exist because an unbounded",
  "number here is a denial of service rather than a picture.",
  "",
  "Requests go to `POST /v1/sharp` — see [API.md](API.md) for the envelope.",
  "",
  "```json",
  "{",
  '  "input": "as_9f86d081884c7d659a2feaa0c55ad015",',
  '  "options": { "failOn": "warning" },',
  '  "pipeline": [',
  '    { "rotate": {} },',
  '    { "resize": { "width": 1200, "fit": "inside", "withoutEnlargement": true } }',
  "  ],",
  '  "output": { "format": "avif", "options": { "quality": 55 } }',
  "}",
  "```",
  "",
  "## Three things that catch people",
  "",
  "**`rotate` with no angle applies the EXIF orientation.** Output is re-encoded and metadata is",
  "dropped, so a photo that looked upright in a phone's gallery arrives sideways on the web unless you",
  "include `{ \"rotate\": {} }`. This is the most commonly forgotten operation.",
  "",
  "**`resize` enlarges by default.** A 300px source asked for 800px comes back 800px and soft. Pass",
  "`withoutEnlargement: true` unless you actually want that.",
  "",
  "**Metadata is always stripped and there is no way to keep it.** `withMetadata` is deliberately not",
  "in this vocabulary — it is how a client's GPS coordinates end up published. Dimensions come back in",
  "the response instead.",
  "",
  "## Input options",
  "",
  "sharp's constructor options, passed as `options`.",
  "",
  paramTable(INPUT_OPTIONS),
  "`limitInputPixels` is **not** accepted: it is the decompression-bomb guard and is set by the",
  "server. A 1 KB PNG can expand to tens of gigabytes.",
  "",
  "## Operations",
  "",
  `${Object.keys(OPERATIONS).length} operations, run in the order given.`,
  "",
];

for (const [name, spec] of Object.entries(OPERATIONS)) {
  lines.push(`### \`${name}\``, "", spec.describe, "");
  if (spec.positional) {
    lines.push(
      `Takes \`${spec.positional}\` directly — \`{ "${name}": { "${spec.positional}": … } }\`.`,
      "",
    );
  }
  lines.push(paramTable(spec.params));
}

lines.push(
  "## Output formats",
  "",
  "Given as `output.format`, with `output.options` carrying the encoder settings. Defaults to `webp`.",
  "",
);

for (const [name, spec] of Object.entries(OUTPUT_FORMATS)) {
  lines.push(`### \`${name}\``, "", spec.describe, "", paramTable(spec.params));
}

const path = resolve(ROOT, "docs/SHARP.md");
await Bun.write(path, lines.join("\n"));
console.log(
  `[gen-docs] docs/SHARP.md — ${Object.keys(OPERATIONS).length} operations, ${Object.keys(OUTPUT_FORMATS).length} output formats`,
);