// Each extension's `web.tsx`, built by vite on its own, apart from the app's bundle, and served for the app to import.

import { decodeBase64, encodeBase64 } from "@std/encoding/base64";
import { encodeHex } from "@std/encoding/hex";
import { fromFileUrl, join, resolve } from "@std/path";
import type { FrontendSource } from "@berry/api/extension-startup.ts";
import { denoExecutable } from "./deno.ts";
import type { FrontendBuild } from "./web-build.ts";
import { HOST_GLOBAL, HOST_MODULES } from "@berry/api/host.ts";

/** Where the app finds an extension's frontend. */
export type WebEntry = { module: string; styles: string[] };

const TYPES: Record<string, string> = {
  wasm: "application/wasm",
  svg: "image/svg+xml",
  png: "image/png",
  woff2: "font/woff2",
  json: "application/json",
};

const contentType = (file: string) =>
  TYPES[file.split(".").at(-1) ?? ""] ?? "application/octet-stream";

async function hash(text: string) {
  return encodeHex(await crypto.subtle.digest("SHA-256", new TextEncoder().encode(text))).slice(
    0,
    16,
  );
}

type CachedBuild = {
  pipeline: string;
  inputs: [string, string][];
  entry: WebEntry;
  files: { path: string; body: string; digest: string; binary: boolean; type: string }[];
};

const root = fromFileUrl(new URL("../", import.meta.url));
const builder = fromFileUrl(new URL("./web-build.ts", import.meta.url));
const pipelineFiles = [
  fromFileUrl(import.meta.url),
  builder,
  join(root, "deno.json"),
  join(root, "deno.lock"),
];
// the running build pipeline may predate edits that are waiting for a restart
const pipeline = await hash(JSON.stringify([
  Deno.version.deno,
  HOST_GLOBAL,
  HOST_MODULES,
  ...await Promise.all(pipelineFiles.map((path) => Deno.readTextFile(path))),
]));

async function inputs(paths: readonly string[]) {
  return await Promise.all(
    [...new Set(paths)].sort().map(async (path): Promise<[string, string]> => {
      if ((await Deno.stat(path)).isDirectory) {
        const entries = [];
        for await (const entry of Deno.readDir(path)) {
          entries.push([entry.name, entry.isDirectory, entry.isSymlink]);
        }
        return [path, await hash(JSON.stringify(entries.sort()))];
      }
      const bytes = await Deno.readFile(path);
      return [path, encodeHex(await crypto.subtle.digest("SHA-256", bytes))];
    }),
  );
}

export function extensionWeb({ cacheDirectory }: {
  cacheDirectory?: string;
} = {}) {
  /** Built files by url path; a build replaces its extension's files, and content-hashed names never change meaning. */
  const files = new Map<string, { body: string | Uint8Array<ArrayBuffer>; type: string }>();
  const paths = new Map<string, string[]>();

  return {
    /** Build an extension's frontend; a failed build leaves the previous one in place and rejects. */
    async build(
      name: string,
      entry: string,
      onSource?: (source: FrontendSource) => void,
    ): Promise<WebEntry> {
      entry = resolve(entry);
      const builtAfter = Date.now();
      const cache = cacheDirectory === undefined ? undefined : join(
        cacheDirectory,
        `${await hash(JSON.stringify([name, entry]))}.json`,
      );
      if (cache !== undefined) {
        try {
          const cached: CachedBuild = JSON.parse(await Deno.readTextFile(cache));
          if (
            cached.pipeline === pipeline &&
            JSON.stringify(cached.inputs) ===
              JSON.stringify(await inputs(cached.inputs.map(([path]) => path)))
          ) {
            const restored = await Promise.all(cached.files.map(async (file) => {
              if (await hash(file.body) !== file.digest) throw new Error("damaged artifact");
              return [file.path, {
                body: file.binary ? decodeBase64(file.body) : file.body,
                type: file.type,
              }] as const;
            }));
            if (
              [cached.entry.module, ...cached.entry.styles].some((path) =>
                !restored.some(([served]) => served === path)
              )
            ) throw new Error("missing artifact");
            for (const path of paths.get(name) ?? []) files.delete(path);
            for (const [path, file] of restored) files.set(path, file);
            paths.set(name, restored.map(([path]) => path));
            onSource?.("cache");
            return cached.entry;
          }
        } catch {
          // a missing, stale, or damaged cache is just a rebuild
        }
      }
      onSource?.("build");
      const { success, code, stdout, stderr } = await new Deno.Command(denoExecutable(), {
        args: ["run", "-A", "--quiet", "--config", join(root, "deno.json"), builder, entry],
        cwd: root,
        stdout: "piped",
        stderr: "piped",
      }).output();
      if (!success) {
        throw new Error(
          new TextDecoder().decode(stderr).trim() || `frontend build exited with code ${code}`,
        );
      }
      const { chunks, assets, dependencies }: FrontendBuild = JSON.parse(
        new TextDecoder().decode(stdout),
      );
      const css = assets.filter((o) => o.fileName.endsWith(".css"))
        .map((o) => String(o.source))
        .join("\n");

      // chunks import each other by name, so the module keeps its content-hashed one
      const module = `/ext/${name}/${chunks.find((chunk) => chunk.isEntry)!.fileName}`;
      const styles = css.trim() === "" ? [] : [`/ext/${name}/${await hash(css)}.css`];
      for (const path of paths.get(name) ?? []) files.delete(path);
      const scripts = chunks.map((chunk) => {
        const path = `/ext/${name}/${chunk.fileName}`;
        files.set(path, { body: chunk.code, type: "text/javascript; charset=utf-8" });
        return path;
      });
      if (styles.length > 0) files.set(styles[0], { body: css, type: "text/css; charset=utf-8" });
      const others = assets.filter((o) => !o.fileName.endsWith(".css")).map((asset) => {
        const path = `/ext/${name}/${asset.fileName}`;
        const body = asset.binary ? decodeBase64(asset.source) : asset.source;
        files.set(path, { body, type: contentType(asset.fileName) });
        return path;
      });
      paths.set(name, [...scripts, ...styles, ...others]);
      const built = { module, styles };
      if (cache !== undefined) {
        let temporary: string | undefined;
        try {
          const fingerprints = await inputs([...pipelineFiles, ...dependencies]);
          // do not cache a build whose inputs changed while vite was reading them
          const changed = await Promise.all(
            fingerprints.map(async ([path]) =>
              (await Deno.stat(path)).mtime!.getTime() > builtAfter
            ),
          );
          if (!changed.some(Boolean)) {
            const cached: CachedBuild = {
              pipeline,
              inputs: fingerprints,
              entry: built,
              files: await Promise.all(paths.get(name)!.map(async (path) => {
                const { body, type } = files.get(path)!;
                const encoded = typeof body === "string" ? body : encodeBase64(body);
                return {
                  path,
                  body: encoded,
                  digest: await hash(encoded),
                  binary: typeof body !== "string",
                  type,
                };
              })),
            };
            await Deno.mkdir(cacheDirectory!, { recursive: true, mode: 0o700 });
            temporary = await Deno.makeTempFile({ dir: cacheDirectory, prefix: ".build-" });
            await Deno.writeTextFile(temporary, JSON.stringify(cached));
            await Deno.rename(temporary, cache);
          }
        } catch (error) {
          console.error(`[berry] ${name} frontend cache:`, error);
        } finally {
          if (temporary !== undefined) await Deno.remove(temporary).catch(() => {});
        }
      }
      return built;
    },

    /** Answers a request for a built file; `undefined` for anything else. */
    serve(path: string): Response | undefined {
      const file = files.get(path);
      if (file === undefined) return undefined;
      return new Response(file.body, {
        headers: {
          "content-type": file.type,
          "cache-control": "public, max-age=31536000, immutable",
        },
      });
    },
  };
}

export type ExtensionWeb = ReturnType<typeof extensionWeb>;