import {cp, copyFile, lstat, mkdir, readdir, realpath, symlink} from 'node:fs/promises';
import {dirname, join, relative, sep} from 'node:path';

export const under=(path,base)=>path===base||path.startsWith(base+sep);

/**
 * Copy a release tree for npm or pnpm layouts.
 * In-tree symlinks are rewritten as relative links inside `to` so the package is relocatable.
 * Symlinks that escape `from` but stay under `root` are materialized; anything else is rejected.
 */
export async function copyReleaseTree(from,to,{root=from,filter=async()=>true}={}) {
  from=await realpath(from);
  root=await realpath(root);
  async function walk(srcDir,destDir) {
    await mkdir(destDir,{recursive:true});
    for(const entry of await readdir(srcDir,{withFileTypes:true})) {
      const srcPath=join(srcDir,entry.name);
      if(!await filter(srcPath))continue;
      const destPath=join(destDir,entry.name);
      if(entry.isSymbolicLink()){
        const target=await realpath(srcPath).catch(()=>null);
        if(!target||(!under(target,from)&&!under(target,root)))
          throw new Error(`Release source contains a symbolic link: ${srcPath}`);
        if(under(target,from)){
          const mapped=join(to,relative(from,target));
          await symlink(relative(dirname(destPath),mapped),destPath);
          continue;
        }
        await cp(target,destPath,{recursive:true,dereference:true,filter});
        continue;
      }
      if(entry.isDirectory()){
        await walk(srcPath,destPath);
        continue;
      }
      if(entry.isFile()){
        await copyFile(srcPath,destPath);
        continue;
      }
      // Rare non-file entries (sockets/devices) should never ship.
      throw new Error(`Release source contains an unsupported file type: ${srcPath}`);
    }
  }
  await walk(from,to);
}