/**
 * In-app update: decide what to offer, and on which platform.
 *
 * TRACES: UR-077 | DR-217
 *
 * Until this existed there was no upgrade path at all. Somebody who installed a
 * `.AppImage` or ran the NSIS installer stayed on that version permanently and
 * had no way to learn a newer one existed — the release notes were the only
 * announcement, and nothing in the app ever read them.
 *
 * ## Two platforms, two answers
 *
 * `tauri-plugin-updater` replaces the running application's own files. That is
 * possible on Linux and Windows and impossible on Android, where installing an
 * APK is the package installer's job and an app may not overwrite itself. So
 * the plugin is compiled only for desktop (see `Cargo.toml`'s
 * `cfg(not(any(target_os = "android", target_os = "ios")))` table) and Android
 * gets the honest alternative: a link to the releases page.
 *
 * That asymmetry is the whole reason this module is a pure decision function
 * plus a thin caller. `decideUpdateAction` takes the platform and what the
 * endpoint said and returns *what to offer*; the Svelte side does the offering.
 * The alternative — `if (platform() === "android")` sprinkled through a
 * component — is exactly the shape that has bitten this codebase before.
 *
 * ## Versions
 *
 * Comparison is left to the updater plugin on desktop, which compares against
 * the version baked into the bundle. `isNewerVersion` exists for the Android
 * path, where nothing native is available to do it, and for tests.
 */

import { createLogger } from "$lib/utils/logger";

const log = createLogger("UpdateCheck");

/** Where a user goes to fetch a build by hand. */
export const RELEASES_URL = "https://gitea.tourolle.paris/dtourolle/jellytau/releases";

/** What the UI should offer the user. */
export type UpdateAction =
  /** Nothing to do — already current, or the check failed and we stay quiet. */
  | { kind: "none" }
  /** Desktop: the plugin can download, verify and install this itself. */
  | { kind: "install"; version: string; notes: string | null }
  /** Android: we can only point at the download. */
  | { kind: "open-releases"; version: string; url: string };

/**
 * Compare two semver-ish version strings.
 *
 * Deliberately small: JellyTau's versions are `MAJOR.MINOR.PATCH` with an
 * optional `-rc1`/`-beta` suffix (build-release.yml keys prerelease off exactly
 * those). A pre-release sorts *below* the same numeric version, so 0.9.2-rc1
 * does not offer itself as an upgrade to somebody on 0.9.2.
 *
 * Returns true when `candidate` is strictly newer than `current`.
 */
export function isNewerVersion(candidate: string, current: string): boolean {
  const parse = (raw: string) => {
    const cleaned = raw.trim().replace(/^v/, "");
    const [core, ...rest] = cleaned.split("-");
    const parts = core.split(".").map((n) => Number.parseInt(n, 10));
    return {
      nums: [parts[0] || 0, parts[1] || 0, parts[2] || 0],
      // Any suffix at all makes it a pre-release.
      pre: rest.length > 0,
    };
  };

  const a = parse(candidate);
  const b = parse(current);

  for (let i = 0; i < 3; i++) {
    if (a.nums[i] !== b.nums[i]) return a.nums[i] > b.nums[i];
  }
  // Same numbers: a release beats a pre-release, nothing beats a release.
  return b.pre && !a.pre;
}

/** What a platform can do about an available update. */
export type UpdateCapability = "install" | "link-only";

/**
 * Map a platform string (from `@tauri-apps/plugin-os`) to what it can do.
 *
 * Android is link-only because the updater plugin is not compiled there at all;
 * calling it would throw rather than degrade.
 */
export function updateCapability(platform: string): UpdateCapability {
  return platform === "android" || platform === "ios" ? "link-only" : "install";
}

/**
 * Decide what to offer.
 *
 * `available` is null when the endpoint reported no newer version, or when the
 * check failed — the caller collapses both, because the UI treatment is the
 * same and a failed update check must never interrupt somebody watching
 * something.
 */
export function decideUpdateAction(
  platform: string,
  available: { version: string; notes?: string | null } | null,
): UpdateAction {
  if (!available) return { kind: "none" };

  if (updateCapability(platform) === "link-only") {
    return { kind: "open-releases", version: available.version, url: RELEASES_URL };
  }

  return { kind: "install", version: available.version, notes: available.notes ?? null };
}

/**
 * Check for an update and return what to offer.
 *
 * Everything here is best-effort: a server that is down, an endpoint that
 * 404s, or a machine with no network must produce a quiet "none", never an
 * error the user sees. An update check is not something the user asked for.
 */
export async function checkForUpdate(): Promise<UpdateAction> {
  try {
    const { platform } = await import("@tauri-apps/plugin-os");
    const current = platform();

    if (updateCapability(current) === "link-only") {
      // Nothing native to ask on Android. Offering the releases page
      // unconditionally would nag on every launch, so the mobile path is
      // surfaced from Settings on demand rather than checked automatically.
      return { kind: "none" };
    }

    const { check } = await import("@tauri-apps/plugin-updater");
    const update = await check();
    if (!update) return { kind: "none" };

    log.info("update available", update.version);
    return decideUpdateAction(current, { version: update.version, notes: update.body ?? null });
  } catch (error) {
    log.warn("update check failed; staying quiet", error);
    return { kind: "none" };
  }
}

/**
 * Download, verify and install a desktop update, then relaunch.
 *
 * The signature check happens inside the plugin against the public key in
 * `tauri.conf.json` — an artifact that does not verify is refused there, which
 * is the entire security value of the updater. `onProgress` is fed the fraction
 * downloaded so the UI can show something during what may be a 100 MB fetch.
 */
export async function installUpdate(onProgress?: (fraction: number) => void): Promise<void> {
  const { check } = await import("@tauri-apps/plugin-updater");
  const update = await check();
  if (!update) return;

  let downloaded = 0;
  let contentLength = 0;

  await update.downloadAndInstall((event) => {
    switch (event.event) {
      case "Started":
        contentLength = event.data.contentLength ?? 0;
        break;
      case "Progress":
        downloaded += event.data.chunkLength;
        if (contentLength > 0) onProgress?.(downloaded / contentLength);
        break;
      case "Finished":
        onProgress?.(1);
        break;
    }
  });

  const { relaunch } = await import("@tauri-apps/plugin-process");
  await relaunch();
}