const { getDefaultConfig } = require("expo/metro-config");
const { resolve } = require("metro-resolver");
const fs = require("fs");
const path = require("path");

const projectRoot = __dirname;
const serverSrcRoot = path.resolve(projectRoot, "../server/src");
const relaySrcRoot = path.resolve(projectRoot, "../relay/src");
const customWebPlatform = (process.env.PASEO_WEB_PLATFORM ?? "")
  .trim()
  .replace(/^\./, "")
  .toLowerCase();

const config = getDefaultConfig(projectRoot);
const defaultResolveRequest = config.resolver.resolveRequest ?? resolve;
config.transformer.asyncRequireModulePath = require.resolve(
  "@expo/metro-config/build/async-require"
);

function isLocalModuleImport(moduleName) {
  return (
    moduleName.startsWith("./") ||
    moduleName.startsWith("../") ||
    moduleName.startsWith("@/") ||
    path.isAbsolute(moduleName)
  );
}

function resolveWithCustomWebOverlay(context, moduleName, platform) {
  const shouldResolveCustomWebVariant =
    platform === "web" &&
    customWebPlatform.length > 0 &&
    customWebPlatform !== "web" &&
    isLocalModuleImport(moduleName);

  if (shouldResolveCustomWebVariant) {
    const overlayContext = {
      ...context,
      // Resolve only "<custom-platform>.<ext>" variants in overlay mode.
      sourceExts: context.sourceExts.map((ext) => `${customWebPlatform}.${ext}`),
      preferNativePlatform: false,
    };

    try {
      return defaultResolveRequest(overlayContext, moduleName, null);
    } catch {
      // Ignore overlay misses and continue with normal web resolution.
    }
  }

  return defaultResolveRequest(context, moduleName, platform);
}

config.resolver.resolveRequest = (context, moduleName, platform) => {
  const origin = context.originModulePath;
  if (
    origin &&
    (origin.startsWith(serverSrcRoot) || origin.startsWith(relaySrcRoot)) &&
    moduleName.endsWith(".js")
  ) {
    const tsModuleName = moduleName.replace(/\.js$/, ".ts");
    const candidatePath = path.resolve(path.dirname(origin), tsModuleName);
    if (fs.existsSync(candidatePath)) {
      return resolveWithCustomWebOverlay(context, tsModuleName, platform);
    }
  }

  return resolveWithCustomWebOverlay(context, moduleName, platform);
};

module.exports = config;