// The v7 → v8 source transform. Deliberately regex-based and honest about
// it: simple top-level CJS patterns are converted mechanically, package
// specifiers are remapped, and everything the regexes cannot prove is
// reported as a note instead of guessed at.

// old specifier → new specifier
export const SPECIFIERS = {
  choo: '@choojs/core',
  'choo/html': '@choojs/html',
  'choo/html/raw': '@choojs/html/raw',
  'choo/component': '@choojs/component',
  nanohtml: '@choojs/html',
  'nanohtml/raw': '@choojs/html/raw',
  nanomorph: '@choojs/html/morph',
  nanocomponent: '@choojs/component',
  'choo-devtools': '@choojs/devtools'
}

// old specifier → guidance (no direct replacement package)
export const RETIRED = {
  nanobus: "built into @choojs/core — use app.emitter, or import Nanobus from '@choojs/core' internals is no longer needed",
  nanorouter: 'built into @choojs/core — app.route covers it',
  nanohref: 'built into @choojs/core — link handling is automatic',
  nanotiming: "built into @choojs/core — import from '@choojs/core/timing' if you need it directly",
  nanoraf: 'retired — use requestAnimationFrame, or rely on choo render batching',
  nanoquery: 'retired — state.query is built in; use URLSearchParams directly elsewhere',
  nanoassert: 'retired — use plain checks or node:assert',
  nanolru: 'retired — the component cache is built into @choojs/core',
  'choo-lazy-route': "replaced by lazy() from '@choojs/core': app.route('/x', lazy(() => import('./x.js')))",
  'choo-service-worker': 'kept as a concept; bankai v10 will inject the asset manifest — check docs before migrating this one'
}

export default function transform (source) {
  const notes = []
  let code = source

  // --- CJS → ESM, simple top-level forms ---

  // const { a, b } = require('x')
  code = code.replace(
    /^(\s*)(?:var|let|const)\s*\{([^}]+)\}\s*=\s*require\((['"])([^'"]+)\3\)\s*;?[^\S\n]*$/gm,
    (m, indent, names, q, spec) => `${indent}import {${names}} from '${spec}'`
  )

  // const X = require('x').default / .thing
  code = code.replace(
    /^(\s*)(?:var|let|const)\s+([A-Za-z_$][\w$]*)\s*=\s*require\((['"])([^'"]+)\3\)\.default\s*;?[^\S\n]*$/gm,
    (m, indent, name, q, spec) => `${indent}import ${name} from '${spec}'`
  )
  code = code.replace(
    /^(\s*)(?:var|let|const)\s+([A-Za-z_$][\w$]*)\s*=\s*require\((['"])([^'"]+)\3\)\.([A-Za-z_$][\w$]*)\s*;?[^\S\n]*$/gm,
    (m, indent, name, q, spec, prop) => `${indent}import { ${prop} as ${name} } from '${spec}'`
  )

  // const X = require('x')
  code = code.replace(
    /^(\s*)(?:var|let|const)\s+([A-Za-z_$][\w$]*)\s*=\s*require\((['"])([^'"]+)\3\)\s*;?[^\S\n]*$/gm,
    (m, indent, name, q, spec) => `${indent}import ${name} from '${spec}'`
  )

  // bare require('x') statements (side-effect imports)
  code = code.replace(
    /^(\s*)require\((['"])([^'"]+)\2\)\s*;?[^\S\n]*$/gm,
    (m, indent, q, spec) => `${indent}import '${spec}'`
  )

  // module.exports = X
  code = code.replace(/^(\s*)module\.exports\s*=\s*/gm, (m, indent, offset) => {
    return `${indent}export default `
  })

  // --- specifier remapping (imports and any requires we couldn't convert) ---

  code = code.replace(
    /(from\s*|import\s*\(\s*|import\s+|require\s*\(\s*)(['"])([^'"]+)\2/g,
    (m, lead, q, spec) => {
      if (SPECIFIERS[spec]) return `${lead}${q}${SPECIFIERS[spec]}${q}`
      if (RETIRED[spec]) {
        notes.push(`'${spec}': ${RETIRED[spec]}`)
      }
      return m
    }
  )

  // --- things we refuse to guess at ---

  if (/module\.exports\.[A-Za-z_$]/.test(code)) {
    notes.push('module.exports.<name> assignments found — convert to named `export` statements by hand')
  }
  if (/\brequire\s*\(/.test(code)) {
    notes.push('require() calls remain (non-top-level or dynamic) — convert to import/await import() by hand')
  }
  if (/\bexports\.[A-Za-z_$]/.test(code)) {
    notes.push('bare exports.<name> assignments found — convert to named `export` statements by hand')
  }

  return { code, changed: code !== source, notes: [...new Set(notes)] }
}