/**
 * rs-loader.ts — load the Reed-Solomon erasure WASM module.
 *
 * The same code runs in two contexts:
 *  - Extension popup (browser): fetch the WASM via `chrome.runtime.getURL`
 *    so the asset path resolves against the extension package. The WASM
 *    file is shipped from `public/codex/reed_solomon_erasure_bg.wasm`.
 *  - Vitest (Node + jsdom): read the WASM bytes from `node_modules`
 *    synchronously. We avoid the library's `fromCurrentDirectory*` helpers
 *    because they probe `__dirname`, which is unreliable when the test
 *    file is bundled by Vite.
 *
 * The instance is cached — WASM instantiation is non-trivial work and the
 * library is safe to reuse across encode / reconstruct calls.
 */

import { CodexError } from "../../shared/codex-types";
import { ReedSolomonErasure } from "./reed-solomon";

const WASM_RELATIVE_PATH = "codex/reed_solomon_erasure_bg.wasm";

let cached: Promise<ReedSolomonErasure> | null = null;

export function getReedSolomon(): Promise<ReedSolomonErasure> {
  if (!cached) cached = loadReedSolomon();
  return cached;
}

async function loadReedSolomon(): Promise<ReedSolomonErasure> {
  try {
    if (isExtensionPopup()) {
      const url = chrome.runtime.getURL(WASM_RELATIVE_PATH);
      const response = await fetch(url);
      if (!response.ok) {
        throw new Error(`fetch ${url} → ${response.status}`);
      }
      const bytes = new Uint8Array(await response.arrayBuffer());
      return ReedSolomonErasure.fromBytes(bytes);
    }

    const bytes = await readTestWasmBytes();
    return ReedSolomonErasure.fromBytes(bytes);
  } catch (err) {
    throw new CodexError(
      "RS_LIBRARY_FAILED",
      `Failed to load Reed-Solomon WASM module: ${err instanceof Error ? err.message : String(err)}`,
    );
  }
}

async function readTestWasmBytes(): Promise<Uint8Array<ArrayBuffer>> {
  if (import.meta.env.MODE !== "test") {
    throw new Error("Reed-Solomon WASM can only be loaded through chrome.runtime.getURL outside tests");
  }
  const { readNodeReedSolomonWasmBytes } = await import("./node-wasm");
  return readNodeReedSolomonWasmBytes();
}

function isExtensionPopup(): boolean {
  return (
    typeof chrome !== "undefined" &&
    typeof chrome.runtime !== "undefined" &&
    typeof chrome.runtime.getURL === "function"
  );
}

/** Reset the cache. Test-only — never called from production code. */
export function _resetReedSolomonCacheForTest(): void {
  cached = null;
}