import esbuild from "esbuild";
import process from "process";
import { builtinModules as builtins } from "node:module";
import { copyFileSync, mkdirSync, existsSync, readdirSync, statSync, readFileSync, writeFileSync, unlinkSync, watch as fsWatch } from "fs";
import { join } from "path";
import esbuildSvelte from "esbuild-svelte";
import { sveltePreprocess } from "svelte-preprocess";

const banner =
  `/*
THIS IS A GENERATED/BUNDLED FILE BY ESBUILD
if you want to view the source, please visit the github repository of this plugin
*/
`;

const prod = (process.argv[2] === "production");

// Clean up build artifacts that aren"t needed (main.css, main.js, font files)
const CLEANUP_BUILD_ARTIFACTS = true; // Set to false if you need to debug these files

// Function to copy directory recursively
function copyDir(src, dest) {
  if (!existsSync(dest)) {
    mkdirSync(dest, { recursive: true });
  }

  const files = readdirSync(src);

  for (const file of files) {
    const srcPath = join(src, file);
    const destPath = join(dest, file);

    if (statSync(srcPath).isDirectory()) {
      copyDir(srcPath, destPath);
    } else {
      copyFileSync(srcPath, destPath);
      console.log(`📁 Copied: ${srcPath} → ${destPath}`);
    }
  }
}

// Neutralises `new Function(...)` literals in the bundled output.
//
// All such literals come from dependencies, never from our own source, and every
// one is dead code in our usage:
//   - diff2html/@profoundlogic/hogan: 2x template compilers reachable only via
//     Hogan.compile(), which diff2html invokes only for runtime `rawTemplates`.
//     We use diff2html's precompiled defaults, so these never run.
//
// We rewrite them to a throwing stub so the bundle contains no `new Function(`
// literal, which clears the Obsidian scanner's "Dynamic Code Execution" warning. The
// build FAILS if the count drifts from EXPECTED_NEW_FUNCTION_COUNT, so a dependency
// change can never silently reintroduce a live (or un-neutralised) dynamic-eval path.
//
// 2 = Hogan.
const EXPECTED_NEW_FUNCTION_COUNT = 2;
const NEW_FUNCTION_STUB = "VKBlockedDynamicFn";
function neutraliseDynamicEval(outfile) {
  if (!existsSync(outfile)) return;
  let contents = readFileSync(outfile, "utf-8");
  const matches = contents.match(/new Function\s*\(/g) || [];
  if (matches.length !== EXPECTED_NEW_FUNCTION_COUNT) {
    throw new Error(
      `neutraliseDynamicEval: expected ${EXPECTED_NEW_FUNCTION_COUNT} ` +
        `\`new Function(\` literals in ${outfile} but found ${matches.length}. ` +
        `A dependency changed — re-audit which library introduced/removed the ` +
        `call and confirm it is unreachable before updating EXPECTED_NEW_FUNCTION_COUNT.`,
    );
  }
  // Throwing stub: callable as `new VKBlockedDynamicFn(...)` with any args.
  const stubDecl =
    `function ${NEW_FUNCTION_STUB}(){throw new Error("Dynamic code execution is disabled in this build.")}`;
  contents = contents.replace(/new Function\s*\(/g, `new ${NEW_FUNCTION_STUB}(`);
  // Insert the stub right after the generated banner comment (a hoisted function
  // declaration is in scope for the whole module regardless of position).
  const bannerEnd = contents.indexOf("*/");
  if (bannerEnd !== -1) {
    const insertAt = contents.indexOf("\n", bannerEnd) + 1;
    contents = contents.slice(0, insertAt) + stubDecl + "\n" + contents.slice(insertAt);
  } else {
    contents = `${stubDecl}\n${contents}`;
  }
  writeFileSync(outfile, contents);
  console.log(
    `🛡️  Neutralised ${matches.length} \`new Function(\` literal(s) in ${outfile}`,
  );
}

// Runs the dynamic-eval neutralisation on every build and rebuild, for both dev and
// production, so the dev bundle matches what ships and the post-build step is
// exercised continuously rather than only at release time. Registered last so it
// transforms the finalised main.js.
const dynamicEvalPlugin = {
  name: "neutralise-dynamic-eval",
  setup(build) {
    build.onEnd(() => {
      neutraliseDynamicEval(build.initialOptions.outfile);
    });
  },
};

// Plugin to merge CSS files into styles.css and cleanup build artifacts
const cssMergerPlugin = {
  name: "css-merger",
  setup(build) {
    build.onEnd(() => {
      // esbuild outputs CSS as main.css (based on outfile: main.js)
      const generatedCss = "main.css";
      const customCssDir = "Styles";
      const outputCss = "styles.css";

      let mergedCss = "";

      // Read generated CSS from dependencies if it exists
      if (existsSync(generatedCss)) {
        mergedCss += readFileSync(generatedCss, "utf-8");
        mergedCss += "\n\n/* Custom Styles */\n\n";
      }

      // Append custom CSS files from styles directory
      if (existsSync(customCssDir)) {
        const cssFiles = readdirSync(customCssDir)
          .filter(file => file.endsWith(".css"))
          .sort();

        for (const cssFile of cssFiles) {
          const cssPath = join(customCssDir, cssFile);
          mergedCss += readFileSync(cssPath, "utf-8");
          mergedCss += "\n\n";
          console.log(`📦 Merged: ${cssPath}`);
        }
      }

      // Write merged CSS to styles.css
      writeFileSync(outputCss, mergedCss);
      console.log(`✅ Generated: ${outputCss}`);

      // Clean up build artifacts if enabled
      if (CLEANUP_BUILD_ARTIFACTS) {
        // Remove main.css (intermediate CSS file)
        if (existsSync(generatedCss)) {
          unlinkSync(generatedCss);
          console.log(`🗑️  Removed: ${generatedCss}`);
        }

        // Remove KaTeX font files
        let anyRemoved = false;
        const fontExtensions = [".woff", ".woff2", ".ttf"];
        const files = readdirSync(".");
        for (const file of files) {
          const ext = file.substring(file.lastIndexOf("."));
          if (fontExtensions.includes(ext)) {
            unlinkSync(file);
            anyRemoved = true;
          }
        }
        if (anyRemoved) {
          console.log("🗑️  Removed KaTeX Font Files");
        }
      }
    });
  }
};

const buildOptions = {
  plugins: [
    esbuildSvelte({
      compilerOptions: { css: "injected" },
      preprocess: sveltePreprocess(),
    }),
    cssMergerPlugin,
    dynamicEvalPlugin,
  ],
  banner: {
    js: banner,
  },
  entryPoints: ["main.ts"],
  bundle: true,
  define: {
    "process.env.NODE_ENV": JSON.stringify(prod ? "production" : "development"),
  },
  external: [
    "obsidian",
    "electron",
    "@codemirror/autocomplete",
    "@codemirror/collab",
    "@codemirror/commands",
    "@codemirror/language",
    "@codemirror/lint",
    "@codemirror/search",
    "@codemirror/state",
    "@codemirror/view",
    "@lezer/common",
    "@lezer/highlight",
    "@lezer/lr",
    ...builtins],
  format: "cjs",
  target: "es2022",
  logLevel: "info",
  sourcemap: prod ? false : "inline",
  treeShaking: true,
  outfile: "main.js",
  minify: prod,
  loader: {
    ".css": "css",
    ".svg": "text",
    ".png": "dataurl",
    ".ttf": "file",
    ".woff": "file",
    ".woff2": "file",
  },
};

if (prod) {
  await esbuild.build(buildOptions);
  console.log("✅ Production build complete!");
} else {
  const ctx = await esbuild.context(buildOptions);
  await ctx.watch();

  // Watch Styles directory for CSS changes
  if (existsSync("Styles")) {
    fsWatch("Styles", { recursive: true }, (_eventType, filename) => {
      if (filename && filename.endsWith(".css")) {
        console.log(`🔄 CSS file changed: ${filename} - Rebuilding...`);
        ctx.rebuild();
      }
    });
  }
}