platform/templates/apply.js

const { join } = require("path")
const { readFileSync, writeFileSync, existsSync, readdirSync, lstatSync, copyFileSync, mkdirSync, rmSync } = require('fs')
const { spawnSync } = require('child_process')

function update (current, template) {
  if (template !== undefined && Object.keys(template).length > 0) {
    let value = current ?? {}
    for (const [k, v] of Object.entries(template)) {
      if(value[k] !== v) {
        console.log('updating ', k, 'to', v)
      }
      value[k] = v
    }
    return value
  }
  return current
}
function copyFiles(source, target, replaces) {
  const files = readdirSync(source)
  for (const f of files) {
    const sourceFile = join(source, f)
    const targetFile = join(target, f)
    if (lstatSync(sourceFile).isDirectory()) {
      if (!existsSync(targetFile)) {
        mkdirSync(targetFile, {recursive: true})
      }
      copyFiles(sourceFile, targetFile, replaces)
    } else {
      if( f.startsWith('~')) {
        // File should be removed from target folder
        const newTargetFile = join(target, f.substring(1))
        if (existsSync(newTargetFile)) {
          rmSync(newTargetFile)
        }
      } else {
        if( replaces.includes(targetFile) && existsSync(targetFile)) {
          // We need replace content of file as defined.
          rmSync(targetFile)
        }
        if (!existsSync(targetFile)) {
          // Copy if not exists.
          copyFileSync(sourceFile, targetFile)
        }
      }
    }
  }
}
function updatePackage(packageRoot, templates) {
  const pkgFile = join(packageRoot, 'package.json')

  const packageSource = readFileSync(pkgFile)
  const currentPackage = JSON.parse(packageSource)

  let template
  for (const t of templates) {
    if( t.isDefault) {
      template = t
    }

    // Allow to configure explicit template selection
    if( currentPackage.template === t.package.name) {
      template = t
      break
    }

    if (t.package.peerDependencies !== undefined) {
      const peers = Object.keys(t.package.peerDependencies)
      const deps = Object.keys(currentPackage.dependencies ?? {})
      const devDeps = Object.keys(currentPackage.devDependencies ?? {})
      if( peers.length > 0 && (peers.every((v) => deps.includes(v)) || peers.every((v) => devDeps.includes(v)))) {
        // If we had every peer dep in package.
        template = t
      }
    }
  }
  console.log('updating => ', currentPackage.name, ' with template', template.package.name)
  
  const packageJson = template.package

  currentPackage.devDependencies = update(currentPackage.devDependencies, packageJson.devDependencies )
  currentPackage.dependencies = update(currentPackage.dependencies, packageJson.dependencies )
  currentPackage.scripts = update(currentPackage.scripts, packageJson.scripts )

  const newPackage = JSON.stringify(currentPackage, undefined, 2)

  if (packageSource !== newPackage) {
    writeFileSync(pkgFile, newPackage.trim() + '\n')
  }

  // Copy missing files.

  copyFiles(template.root, packageRoot, (template.package['#replaces'] ?? []).map(f => join(packageRoot, f)) )
}

function listPackages() {
  const out = spawnSync('rush', ['list', '--json'], { encoding : 'utf8' }).stdout
  const projects = JSON.parse(out)
  return projects.projects.map(it => it.fullPath)
}

console.log('running at:', __dirname)

const templates = readdirSync(__dirname)
  .map(d => join(__dirname, d))
  .filter(d => lstatSync(d).isDirectory() && existsSync(join(d, 'package.json')) )
  .map(d => ({
    root: d, 
    isDefault: d.endsWith('default'),
    package: JSON.parse(readFileSync(join(d, 'package.json')))
  }))

console.log('Detected templates:', templates.map(t => (t.package.name + ':' + t.package.version)))

const projects = listPackages()
for (const p of projects) {
  updatePackage(p, templates)
}