import type { BunPlugin } from "bun";
import { createHash } from "node:crypto";
import { mkdirSync, rmSync, writeFileSync } from "node:fs";
import { createRequire } from "node:module";
import { basename, join } from "node:path";

export interface IslandInput {
  name: string;
  sourcePath: string;
}

export interface IslandBuildResult {
  assets: Array<{ name: string; hash: string; path: string }>;
  sharedChunks: string[];
}

/**
 * Generates the per-island browser entry.
 *
 * Never imports react-dom/server — islands are client-only.
 */
export function generateIslandEntry(input: IslandInput): string {
  return [
    "/** @jsxImportSource react */",
    `import Component from ${JSON.stringify(input.sourcePath)};`,
    `export const name = ${JSON.stringify(input.name)};`,
    `export default Component;`,
    "",
  ].join("\n");
}

/**
 * Compiles every island `.tsx` against React's JSX runtime.
 *
 * The repo's root tsconfig sets `jsxImportSource` to `@wrnexus/core`, so an
 * island would otherwise compile to WRNexus's HTML-string renderer and
 * silently never mount. A `@jsxImportSource` pragma applies only to the file
 * that carries it, so putting one in the generated entry does nothing for the
 * author's own component — the injection has to happen per source file, which
 * is what this plugin does. App-authored islands stay plain `.tsx`.
 */
export function reactJsxPlugin(): BunPlugin {
  return {
    name: "wrnexus-island-jsx",
    setup(build) {
      build.onLoad({ filter: /\.tsx$/ }, async (args) => {
        // Only first-party island sources need the pragma. Third-party .tsx
        // under node_modules is left alone so Bun's own handling is untouched.
        if (args.path.includes("node_modules")) return undefined;
        return {
          contents: `/** @jsxImportSource react */\n${await Bun.file(args.path).text()}`,
          loader: "tsx" as const,
        };
      });
    },
  };
}

export function assertReactAvailable(
  appRoot: string,
): { code: "WRN-ISLAND-REACT-MISSING"; message: string; severity: "error" } | null {
  const require = createRequire(join(appRoot, "package.json"));
  try {
    require.resolve("react");
    require.resolve("react-dom");
    return null;
  } catch {
    return {
      code: "WRN-ISLAND-REACT-MISSING",
      severity: "error",
      message:
        "This app imports a .tsx island but react and react-dom are not installed. " +
        "Run: bun add react react-dom",
    };
  }
}

/**
 * Bundles island entries. `splitting: true` is required so React is emitted
 * once as a shared chunk rather than duplicated into every island.
 */
export async function buildIslands(input: {
  islands: IslandInput[];
  outDir: string;
  /**
   * App root used to resolve the island mount runtime. When given, the runtime
   * is emitted as `runtime.js` in the SAME build as the islands.
   *
   * This is not a convenience: building the runtime separately gives it its own
   * copy of React, and a component rendered by one copy while importing hooks
   * from another fails with "Cannot read properties of null (reading
   * 'useState')". One build with splitting keeps React in a single shared chunk.
   */
  appRoot?: string;
}): Promise<IslandBuildResult> {
  if (input.islands.length === 0) return { assets: [], sharedChunks: [] };

  // Each island gets its own generated entry file named after the island.
  // Passing the component sources directly would dedupe two islands that share
  // a source file, and output order is not guaranteed to match input order —
  // both of which silently mismatch island names to bundles.
  //
  // The entries live inside outDir so `react` resolves from the app that
  // installed it, exactly as the island's own imports do.
  const entryDir = join(input.outDir, ".entries");
  mkdirSync(entryDir, { recursive: true });

  const islandNames = new Set(input.islands.map((island) => island.name));
  for (const island of input.islands) {
    writeFileSync(join(entryDir, `${island.name}.tsx`), generateIslandEntry(island), "utf8");
  }

  const entrypoints = input.islands.map((island) => join(entryDir, `${island.name}.tsx`));
  if (input.appRoot) {
    const resolveFrom = createRequire(join(input.appRoot, "package.json"));
    const runtimeEntry = join(entryDir, "runtime.ts");
    writeFileSync(
      runtimeEntry,
      `export * from ${JSON.stringify(resolveFrom.resolve("@wrnexus/react/browser"))};
`,
      "utf8",
    );
    entrypoints.push(runtimeEntry);
  }

  try {
    const result = await Bun.build({
      entrypoints,
      outdir: input.outDir,
      target: "browser",
      format: "esm",
      splitting: true,
      minify: true,
      plugins: [reactJsxPlugin()],
    });

    if (!result.success) {
      throw new AggregateError(result.logs, "Island bundling failed");
    }

    const assets: IslandBuildResult["assets"] = [];
    const sharedChunks: string[] = [];

    for (const output of result.outputs) {
      if (output.kind === "entry-point") {
        // Bun names an entry's output after its entry file, so the basename
        // identifies the island unambiguously.
        const stem = basename(output.path).replace(/\.js$/, "");
        if (stem === "runtime") continue;
        if (!islandNames.has(stem)) continue;
        assets.push({
          name: stem,
          hash: createHash("sha256").update(output.path).digest("hex").slice(0, 16),
          path: output.path,
        });
      } else if (output.kind === "chunk") {
        sharedChunks.push(output.path);
      }
    }

    return { assets, sharedChunks };
  } finally {
    rmSync(entryDir, { recursive: true, force: true });
  }
}