/**
 * Naming the mesh's own images by what they are.
 *
 * **A digest is not knowable until something is built** (novox/hq 04-ISSUES/025). A manifest in a
 * repository can pin a third-party image, because somebody can ask a registry what a tag points
 * at. It cannot pin an image the mesh builds itself: mesh-controller, mesh-builder, mesh-route-proxy,
 * the per-module runtimes and the provisioners exist in no registry, so there is no manifest
 * digest to write down. The catalogue ships sixty-four zeros for them, which parses, resolves,
 * composes — and stops on the machine.
 *
 * The lab used to answer that with a registry of its own: raise one inside the scenario, push
 * everything into it, and rewrite every reference — third-party ones included — to the digest it
 * assigned. **That registry does not exist in production, so the lab was testing a fiction**, and
 * the fiction hid the bootstrap problems it was supposed to find.
 *
 * What is true instead is two things:
 *
 *   - **Third-party images are pulled from the internet.** They are left exactly as written, and
 *     the machine fetches them over its `egress` uplink the way any machine does.
 *   - **The mesh's own images are built and handed over.** They are loaded onto the machine from
 *     the workstation that built them, and named by the digest of their own image configuration —
 *     a bare `sha256:…`, which mesh-host accepts as "an image this machine already holds"
 *     (mesh-host, *an image may be named by the digest of its own configuration*).
 *
 * So the rewriting that remains is only the second kind, and it matches on the **repository**,
 * because that is the part a person writes and the only part a placeholder digest does not say.
 */

/** What the lab loaded onto a machine, and what a declaration should call it. */
export interface HeldImage {
  /** As the scenario asked for it, a tag this workstation holds: `mesh-runtime-postgres:development`. */
  requested: string;
  /** What a manifest names it by, with no tag and no digest: `mesh-runtime-postgres`. */
  repository: string;
  /**
   * The reference a declaration uses: a bare `sha256:<64 hex>`.
   *
   * The image's own ID — the digest of its configuration — which `docker load` preserves, so the
   * name is the same on the workstation that built it and on every machine it was handed to.
   */
  reference: string;
}

/** `alpine:3.20` and `alpine` both mean `alpine`; `foo/bar:1` means `foo/bar`. */
export function repositoryOf(reference: string): string {
  const withoutDigest = reference.split("@")[0] ?? reference;
  const lastColon = withoutDigest.lastIndexOf(":");
  const lastSlash = withoutDigest.lastIndexOf("/");
  return lastColon > lastSlash ? withoutDigest.slice(0, lastColon) : withoutDigest;
}

/**
 * Whether a reference names an image the mesh builds for itself.
 *
 * **Derived from the shape the build produces, not from a list of names.** `make image
 * builder-image provisioner-image objectstore-image redis-provisioner-image proxy-image` in
 * mesh-controller and `scripts/build-module-runtime.sh` here both tag their output `mesh-<something>`
 * with no registry host and no upstream organisation — that is what "built here, published
 * nowhere" looks like, and a hardcoded list would go stale the first time a module is added.
 *
 * The absence of a slash carries the weight: `ghcr.io/mailu/admin` and
 * `registry.example/novox/www` both say where they are fetched from, and a bare
 * `mesh-runtime-plex` says there is nowhere.
 */
export function isMeshBuilt(reference: string): boolean {
  const repository = repositoryOf(reference);
  return !repository.includes("/") && repository.startsWith("mesh-");
}

/**
 * Registries an anonymous pull works against.
 *
 * Not a list of what is trusted — a list of where no account is needed. Everything else wants one,
 * and a scenario machine has none.
 */
const PUBLIC_REGISTRIES = [
  "docker.io", "ghcr.io", "quay.io", "lscr.io", "gcr.io", "registry.k8s.io",
  "public.ecr.aws", "mcr.microsoft.com", "docker.elastic.co", "registry.gitlab.com",
];

/** The registry a reference names, or "" when it names none and so means Docker Hub. */
export function registryOf(reference: string): string {
  const first = repositoryOf(reference).split("/")[0] ?? "";
  // A first segment is a registry only if it looks like a host: `novox/www` is an organisation on
  // Docker Hub; `registry.example/novox/www` is somewhere else entirely.
  return first.includes(".") || first.includes(":") ? first : "";
}

/**
 * Whether the workstation has to hand this image over rather than let the machine fetch it.
 *
 * **Two reasons, one consequence.** An image the mesh builds for itself exists in no registry at
 * all. An image in the operator's *private* registry exists in one the machines have no account
 * for, and the pull fails with `no basic auth credentials` — which is not something more patience
 * fixes. Either way the machine cannot get it alone, so the workstation, which does hold the
 * credential, exports it and loads it.
 *
 * **This stands in for something, and it is worth saying what.** In a finished mesh these are built
 * by the mesh's builder and published to the mesh's own store, and every machine pulls them from
 * there with a credential the mesh granted it. Until that store exists there is nowhere for them to
 * come from — and handing them over is the closest honest thing to it, rather than a registry the
 * lab invents, which is exactly what was just removed.
 */
export function mustBeHandedOver(reference: string): boolean {
  if (isMeshBuilt(reference)) return true;
  const registry = registryOf(reference);
  return registry !== "" && !PUBLIC_REGISTRIES.includes(registry);
}

/**
 * Replace every reference to one of the mesh's own images with the image the machine holds.
 *
 * Matching is on the repository and ignores whatever digest was written down — a manifest says
 * `mesh-runtime-postgres@sha256:0000…` and means *the runtime this machine was given*.
 *
 * **Everything else is left exactly as it is.** `postgres@sha256:7456…`, `gitea/gitea@sha256:…`
 * and `ghcr.io/mailu/admin@sha256:…` are pulled from the internet over the machine's uplink, which
 * is what a real machine does and the reason the lab's own registry is gone.
 */
export function pinnedInto(text: string, held: HeldImage[]): string {
  let out = text;
  for (const image of held) {
    const escaped = image.repository.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
    // Optionally a registry, then the repository, then any digest. Anchored on a quote or
    // whitespace so a longer repository ending in a shorter one is not half-replaced.
    out = out.replaceAll(
      new RegExp(`(?<=^|["\\s])(?:[A-Za-z0-9_.:-]+\\/)*${escaped}@sha256:[0-9a-f]{64}`, "g"),
      image.reference,
    );
  }
  return out;
}

/** The reference for one repository, or undefined if this scenario loaded no such image. */
export function referenceFor(held: HeldImage[], repository: string): string | undefined {
  return held.find((image) => image.repository === repository)?.reference;
}

/** Whether anything is still pinned to a placeholder, which would fail on the machine. */
export function stillUnpinned(text: string): string[] {
  return [...text.matchAll(/([A-Za-z0-9_.:/-]+)@sha256:0{64}/g)].map((m) => m[1]!);
}