bsky-social-app/scripts/icons/lib.mts

import fs from 'node:fs/promises'
import path from 'node:path'

import {format} from 'prettier'
import {optimize} from 'svgo'

import svgoConfig from '../../svgo.config.mjs'

export const GENERATED_HEADER = '// This file is generated by pnpm icons:generate. Do not edit.\n'

const STYLE_TOKEN = /^(?:Filled|Stroke\d*|Corner\d+|Rounded|Large)$/
const IDENTIFIER = /^[A-Za-z_$][\w$]*$/
const NUMBER = '[-+]?(?:\\d*\\.\\d+|\\d+\\.?)(?:[eE][-+]?\\d+)?'
const PATH_TOKEN = new RegExp(`[A-Za-z]|${NUMBER}`, 'y')
const PATH_ARGUMENTS = {
  A: 7,
  C: 6,
  H: 1,
  L: 2,
  M: 2,
  Q: 4,
  S: 4,
  T: 2,
  V: 1,
  Z: 0,
}

export const SOURCE_LANES = new Set([
  'brands',
  'community',
  'custom',
  'flags',
  'ui',
])

const CODEGEN_LANES = new Set(['brands', 'community', 'ui'])

function fail(file, message) {
  throw new Error(`${file}: ${message}`)
}

function walkElements(node, ancestors = [], result = []) {
  if (node.type === 'element') {
    result.push({node, ancestors})
    ancestors = [...ancestors, node]
  }
  for (const child of node.children ?? []) {
    walkElements(child, ancestors, result)
  }
  return result
}

function effectiveAttributes(entry) {
  return Object.assign(
    {},
    ...entry.ancestors.map(node => node.attributes ?? {}),
    entry.node.attributes ?? {},
  )
}

function tokenizePathData(data, file) {
  const tokens = []
  let index = 0
  while (index < data.length) {
    const whitespace = /^\s+/.exec(data.slice(index))
    if (whitespace) index += whitespace[0].length
    if (index >= data.length) break

    if (data[index] === ',') {
      if (typeof tokens.at(-1) !== 'number') {
        fail(file, `misplaced comma near ${JSON.stringify(data.slice(index, index + 16))}`)
      }
      index += 1
      const afterComma = /^\s*/.exec(data.slice(index))
      index += afterComma[0].length
      PATH_TOKEN.lastIndex = index
      const next = PATH_TOKEN.exec(data)
      if (!next || /[A-Za-z]/.test(next[0])) {
        fail(file, `misplaced comma near ${JSON.stringify(data.slice(index, index + 16))}`)
      }
    }

    PATH_TOKEN.lastIndex = index
    const match = PATH_TOKEN.exec(data)
    if (!match) fail(file, `malformed path data near ${JSON.stringify(data.slice(index, index + 16))}`)
    tokens.push(/[A-Za-z]/.test(match[0]) ? match[0] : Number(match[0]))
    index = PATH_TOKEN.lastIndex
  }
  return tokens
}

function rejectExternalUrls(value, file) {
  for (const match of value.matchAll(/url\s*\(\s*(?:(['"])(.*?)\1|([^)]*))\s*\)/gi)) {
    const target = (match[2] ?? match[3]).trim()
    if (!target.startsWith('#')) fail(file, `external URL ${JSON.stringify(target)} is not allowed`)
  }
}

export function validatePathData(data, file = '<path>') {
  if (typeof data !== 'string' || data.trim() === '') fail(file, 'path data is empty')
  const tokens = tokenizePathData(data, file)
  if (tokens[0] !== 'M' && tokens[0] !== 'm') fail(file, 'path data must begin with M or m')

  let index = 0
  let command
  while (index < tokens.length) {
    if (typeof tokens[index] === 'string') {
      command = tokens[index++]
      const upper = command.toUpperCase()
      if (!(upper in PATH_ARGUMENTS)) fail(file, `unsupported path command ${command}`)
      if (upper === 'Z') {
        command = undefined
        continue
      }
    } else if (!command) {
      fail(file, 'path arguments are missing a command')
    }

    const upper = command.toUpperCase()
    const argumentCount = PATH_ARGUMENTS[upper]
    let sets = 0
    while (index < tokens.length && typeof tokens[index] !== 'string') {
      if (index + argumentCount > tokens.length) fail(file, `${command} has too few arguments`)
      const args = tokens.slice(index, index + argumentCount)
      if (args.some(value => typeof value !== 'number' || !Number.isFinite(value))) {
        fail(file, `${command} has an invalid number`)
      }
      if (upper === 'A' && ![0, 1].includes(args[3])) fail(file, 'arc large-arc-flag must be 0 or 1')
      if (upper === 'A' && ![0, 1].includes(args[4])) fail(file, 'arc sweep-flag must be 0 or 1')
      index += argumentCount
      sets += 1
    }
    if (sets === 0) fail(file, `${command} has no arguments`)
  }
}

function validateViewBox(value, file) {
  if (!value) fail(file, 'missing viewBox')
  const numbers = value.trim().split(/[\s,]+/).map(Number)
  if (numbers.length !== 4 || numbers.some(number => !Number.isFinite(number))) {
    fail(file, `invalid viewBox ${JSON.stringify(value)}`)
  }
  if (numbers[2] <= 0 || numbers[3] <= 0) fail(file, 'viewBox width and height must be positive')
  return numbers.join(' ')
}

function rejectDangerousContent(entries, file, {raw = false} = {}) {
  for (const {node} of entries) {
    if (
      ['foreignObject', 'image', 'script', 'text', 'use'].includes(node.name) ||
      (!raw && node.name === 'style')
    ) {
      fail(file, `unsupported <${node.name}> element`)
    }
    for (const [name, value] of Object.entries(node.attributes ?? {})) {
      if (/^on/i.test(name)) fail(file, `event handler attribute ${name} is not allowed`)
      if ((name === 'href' || name === 'xlink:href') && !value.startsWith('#')) {
        fail(file, `external reference ${JSON.stringify(value)} is not allowed`)
      }
      rejectExternalUrls(value, file)
    }
    if (node.name === 'style') {
      const css = (node.children ?? [])
        .filter(child => child.type === 'text')
        .map(child => child.value)
        .join('')
      rejectExternalUrls(css, file)
      if (/@import/i.test(css)) {
        fail(file, 'external resources in <style> are not allowed')
      }
    }
  }
}

function inspectSvg(root, file, lane) {
  const entries = walkElements(root)
  const svgEntries = entries.filter(entry => entry.node.name === 'svg')
  const documentElements = (root.children ?? []).filter(child => child.type === 'element')
  if (
    svgEntries.length !== 1 ||
    svgEntries[0].ancestors.length !== 0 ||
    documentElements.length !== 1 ||
    documentElements[0] !== svgEntries[0].node
  ) {
    fail(file, 'expected exactly one root <svg> element')
  }
  const viewBox = validateViewBox(svgEntries[0].node.attributes?.viewBox, file)
  rejectDangerousContent(entries, file, {raw: lane === 'custom'})

  if (lane === 'custom') {
    const safeRawElements = new Set([
      'circle',
      'clipPath',
      'defs',
      'ellipse',
      'g',
      'line',
      'linearGradient',
      'path',
      'polygon',
      'polyline',
      'radialGradient',
      'rect',
      'stop',
      'style',
      'svg',
    ])
    const unsupported = entries.find(entry => !safeRawElements.has(entry.node.name))
    if (unsupported) fail(file, `unsupported <${unsupported.node.name}> element in custom/`)
  }

  for (const entry of entries.filter(entry => entry.node.name === 'path')) {
    validatePathData(entry.node.attributes?.d, file)
  }

  return {entries, viewBox}
}

function validateOrdinaryAttributes(entries, file, lane) {
  const presentation = new Set([
    'clip-rule',
    'fill',
    'fill-rule',
    'stroke',
    'stroke-linecap',
    'stroke-linejoin',
    'stroke-width',
  ])
  const allowedByElement = {
    g: presentation,
    path: new Set(['d', ...presentation]),
    svg: new Set(['viewBox', 'xmlns', ...presentation]),
  }
  for (const {node} of entries) {
    const allowed = allowedByElement[node.name]
    for (const [name, value] of Object.entries(node.attributes ?? {})) {
      if (!allowed.has(name)) {
        fail(file, `unsupported ${name} attribute on <${node.name}> in ${lane}/`)
      }
      if ((name === 'fill-rule' || name === 'clip-rule') && value !== 'evenodd') {
        fail(file, `unsupported ${name} ${JSON.stringify(value)} in ${lane}/`)
      }
    }
  }
}

function validateOrdinarySourceSemantics(entries, file, lane) {
  for (const entry of entries.filter(entry => entry.node.name === 'path')) {
    const attributes = effectiveAttributes(entry)
    for (const name of ['fill-rule', 'clip-rule']) {
      if (attributes[name] && attributes[name] !== 'evenodd') {
        fail(file, `unsupported ${name} ${JSON.stringify(attributes[name])} in ${lane}/`)
      }
    }
  }
}

function validateOrdinaryIcon(root, file, lane) {
  const {entries, viewBox} = inspectSvg(root, file, lane)
  const allowed = new Set(['g', 'path', 'svg'])
  const unsupported = entries.find(entry => !allowed.has(entry.node.name))
  if (unsupported) fail(file, `unsupported <${unsupported.node.name}> element in ${lane}/`)
  validateOrdinaryAttributes(entries, file, lane)

  const paths = entries.filter(entry => entry.node.name === 'path')
  if (paths.length !== 1) {
    fail(
      file,
      `${lane}/ generated icons must optimize to exactly one path; found ${paths.length} (move raw multi-path artwork to custom/)`,
    )
  }

  const attributes = effectiveAttributes(paths[0])
  const fill = attributes.fill ?? 'black'
  const stroke = attributes.stroke ?? 'none'
  const hasFill = fill !== 'none'
  const hasStroke = stroke !== 'none'
  if (hasFill === hasStroke) fail(file, 'each path must use either fill or stroke, not both')

  let description
  if (hasStroke) {
    const strokeWidth = Number(attributes['stroke-width'] ?? 1)
    if (![1, 1.5, 2].includes(strokeWidth)) fail(file, `unsupported stroke-width ${strokeWidth}`)
    const strokeLinecap = attributes['stroke-linecap'] ?? 'butt'
    const strokeLinejoin = attributes['stroke-linejoin'] ?? 'miter'
    if (!['butt', 'round', 'square'].includes(strokeLinecap)) fail(file, `unsupported stroke-linecap ${strokeLinecap}`)
    if (!['bevel', 'miter', 'round'].includes(strokeLinejoin)) fail(file, `unsupported stroke-linejoin ${strokeLinejoin}`)
    description = {path: attributes.d, strokeLinecap, strokeLinejoin, strokeWidth}
  } else {
    description = {path: attributes.d, strokeWidth: 0}
  }

  return {description, viewBox}
}

function validateFlexibleIcon(root, file, lane) {
  const {entries, viewBox} = inspectSvg(root, file, lane)
  const allowed = new Set(['circle', 'g', 'path', 'rect', 'svg'])
  const unsupported = entries.find(entry => !allowed.has(entry.node.name))
  if (unsupported) fail(file, `unsupported <${unsupported.node.name}> element in ${lane}/`)

  const drawable = entries.filter(entry => ['circle', 'path', 'rect'].includes(entry.node.name))
  if (drawable.length === 0) fail(file, 'icon has no drawable elements after optimization')
  const elements = drawable.map(entry => {
    const attributes = effectiveAttributes(entry)
    const common = {
      fill: attributes.fill ?? 'black',
      stroke: attributes.stroke ?? 'none',
      strokeLinecap: attributes['stroke-linecap'],
      strokeLinejoin: attributes['stroke-linejoin'],
      strokeWidth: attributes['stroke-width'] ? Number(attributes['stroke-width']) : undefined,
      type: entry.node.name,
    }
    if (entry.node.name === 'path') {
      return {...common, d: attributes.d, fillRule: attributes['fill-rule'], clipRule: attributes['clip-rule']}
    }
    if (entry.node.name === 'circle') {
      return {...common, cx: Number(attributes.cx ?? 0), cy: Number(attributes.cy ?? 0), r: Number(attributes.r)}
    }
    return {
      ...common,
      height: Number(attributes.height),
      rx: attributes.rx ? Number(attributes.rx) : undefined,
      ry: attributes.ry ? Number(attributes.ry) : undefined,
      width: Number(attributes.width),
      x: Number(attributes.x ?? 0),
      y: Number(attributes.y ?? 0),
    }
  })
  if (elements.some(element => Object.values(element).some(value => typeof value === 'number' && !Number.isFinite(value)))) {
    fail(file, 'shape has invalid numeric attributes')
  }
  return {elements, viewBox}
}

export function tokensForSemanticName(name) {
  return name.match(/[A-Z]+(?=[A-Z][a-z]|\d|$)|[A-Z]?[a-z]+|\d+/g) ?? []
}

export function semanticName(exportName) {
  const parts = exportName.replaceAll('Stoke', 'Stroke').split('_')
  const styleIndex = parts.findIndex(part => STYLE_TOKEN.test(part))
  return (styleIndex === -1 ? parts : parts.slice(0, styleIndex)).join('')
}

export function normalizeExportName(exportName) {
  const parts = exportName.replaceAll('Stoke', 'Stroke').split('_')
  const styleIndex = parts.findIndex(part => STYLE_TOKEN.test(part))
  if (styleIndex === -1) return parts.join('')
  return [parts.slice(0, styleIndex).join(''), ...parts.slice(styleIndex)].join('_')
}

function validateUiExportName(exportName, file) {
  const parts = exportName.split('_')
  const styleIndex = parts.findIndex(part => STYLE_TOKEN.test(part))
  const styles = styleIndex === -1 ? [] : parts.slice(styleIndex)
  const hasVariant = styles.some(part => part === 'Filled' || /^Stroke\d+$/.test(part))
  const hasCorner = styles.some(part => /^Corner\d+$/.test(part))
  if (
    styleIndex <= 0 ||
    styles.some(part => !STYLE_TOKEN.test(part)) ||
    !hasVariant ||
    !hasCorner ||
    !styles.includes('Rounded')
  ) {
    fail(
      file,
      'UI icon names must have a semantic name followed only by style tokens, including Filled or StrokeN, CornerN, and Rounded',
    )
  }
}

function validateUiSizeName(exportName, viewBox, file) {
  const [, , width, height] = viewBox.split(' ').map(Number)
  const isLarge = width === 64 && height === 64
  const namedLarge = exportName.split('_').includes('Large')
  if (isLarge !== namedLarge) {
    fail(file, 'the Large style token must be present if and only if the viewBox is 64x64')
  }
}

export function assignFamilies(icons) {
  const byNamespace = Map.groupBy(icons, icon => icon.namespace)
  for (const namespaceIcons of byNamespace.values()) {
    const buckets = Map.groupBy(namespaceIcons, icon => tokensForSemanticName(semanticName(icon.exportName))[0])
    for (const bucket of buckets.values()) {
      const distinct = [...new Map(bucket.map(icon => [semanticName(icon.exportName), tokensForSemanticName(semanticName(icon.exportName))])).values()]
      let prefix = distinct[0]
      if (distinct.length > 1) {
        prefix = prefix.slice(0, distinct.reduce((length, tokens) => {
          let index = 0
          while (index < length && prefix[index] === tokens[index]) index += 1
          return index
        }, prefix.length))
      }
      if (prefix.length === 0) throw new Error(`could not derive a family for ${bucket.map(icon => icon.exportName).join(', ')}`)
      const family = prefix.join('')
      for (const icon of bucket) icon.family = family
    }
  }
  return icons
}

function namespaceForLane(lane) {
  if (lane === 'brands' || lane === 'community') return lane
  return ''
}

function cleanObject(value) {
  return Object.fromEntries(Object.entries(value).filter(([, item]) => item !== undefined))
}

export async function readIconSource(sourceRoot, relativePath) {
  const [lane, ...rest] = relativePath.split(path.sep)
  if (!SOURCE_LANES.has(lane)) fail(relativePath, `unclassified source directory ${lane}`)
  if (rest.length !== 1) fail(relativePath, 'nested icon source directories are not supported')
  const filename = rest[0]
  const source = await fs.readFile(path.join(sourceRoot, relativePath), 'utf8')
  let originalRoot
  let optimizedRoot
  let result
  try {
    result = optimize(source, {
      ...svgoConfig,
      path: relativePath,
      plugins: [
        {name: 'captureOriginal', fn(root) { originalRoot = structuredClone(root) }},
        ...svgoConfig.plugins,
        {name: 'captureOptimized', fn(root) { optimizedRoot = structuredClone(root) }},
      ],
    })
  } catch (error) {
    fail(relativePath, `malformed SVG: ${error.message}`)
  }

  const original = inspectSvg(originalRoot, relativePath, lane)
  if (!CODEGEN_LANES.has(lane)) {
    return {codegen: false, lane, optimized: result.data, relativePath, warnings: []}
  }

  const exportName = filename.slice(0, -path.extname(filename).length)
  if (path.extname(filename) !== '.svg') fail(relativePath, 'icon sources must use the .svg extension')
  if (!IDENTIFIER.test(exportName)) fail(relativePath, `filename must be a valid TypeScript export name; got ${exportName}`)
  if (!/^[A-Z]/.test(exportName)) fail(relativePath, 'generated icon filenames must begin with an uppercase letter')
  if (normalizeExportName(exportName) !== exportName) {
    fail(relativePath, `non-canonical export name; rename it to ${normalizeExportName(exportName)}.svg`)
  }
  if (lane === 'ui') {
    validateUiExportName(exportName, relativePath)
    validateUiSizeName(exportName, original.viewBox, relativePath)
  }

  if (lane !== 'brands') validateOrdinarySourceSemantics(original.entries, relativePath, lane)
  const data = lane === 'brands' ? validateFlexibleIcon(optimizedRoot, relativePath, lane) : validateOrdinaryIcon(optimizedRoot, relativePath, lane)
  const [, , width, height] = data.viewBox.split(' ').map(Number)
  const warnings =
    (width === 24 && height === 24) || (width === 64 && height === 64)
      ? []
      : [`${relativePath}: non-standard viewBox ${data.viewBox}; expected 24x24 or 64x64`]
  return {
    ...data,
    codegen: true,
    exportName,
    lane,
    namespace: namespaceForLane(lane),
    optimized: result.data,
    relativePath,
    warnings,
  }
}

async function listFiles(root) {
  const result = []
  async function visit(directory, prefix = '') {
    for (const entry of await fs.readdir(directory, {withFileTypes: true})) {
      const relative = path.join(prefix, entry.name)
      if (entry.isDirectory()) await visit(path.join(directory, entry.name), relative)
      else result.push(relative)
    }
  }
  await visit(root)
  return result.sort()
}

export async function discoverIconSources(sourceRoot) {
  const files = await listFiles(sourceRoot)
  const unclassified = files.filter(file => file.endsWith('.svg') && !SOURCE_LANES.has(file.split(path.sep)[0]))
  if (unclassified.length > 0) throw new Error(`unclassified SVG sources:\n${unclassified.join('\n')}`)
  return files.filter(file => file.endsWith('.svg') && file.split(path.sep)[0] !== 'flags')
}

function relativeImport(fromModule, targetModule) {
  let result = path.posix.relative(path.posix.dirname(fromModule), targetModule)
  if (!result.startsWith('.')) result = `./${result}`
  return result
}

function renderSingleIcon(icon) {
  const description = icon.description
  const properties = [`path: ${JSON.stringify(description.path)}`, `viewBox: ${JSON.stringify(icon.viewBox)}`]
  if (description.strokeWidth > 0) {
    properties.push(`strokeWidth: ${description.strokeWidth}`)
    if (description.strokeLinecap !== 'butt') properties.push(`strokeLinecap: ${JSON.stringify(description.strokeLinecap)}`)
    if (description.strokeLinejoin !== 'miter') properties.push(`strokeLinejoin: ${JSON.stringify(description.strokeLinejoin)}`)
  }
  return `export const ${icon.exportName} = createSinglePathSVG({\n  ${properties.join(',\n  ')},\n})\n`
}

function renderFlexibleIcon(icon) {
  return `export const ${icon.exportName} = createSVG({\n  elements: ${JSON.stringify(icon.elements.map(cleanObject), null, 2).replaceAll('\n', '\n  ')},\n  viewBox: ${JSON.stringify(icon.viewBox)},\n})\n`
}

function renderModule(modulePath, icons, aliases) {
  const factoryNames = new Set()
  const imports = []
  for (const icon of icons) {
    if (icon.elements) factoryNames.add('createSVG')
    else factoryNames.add('createSinglePathSVG')
  }
  const templatePath = relativeImport(modulePath, 'TEMPLATE')
  const sections = [GENERATED_HEADER.trimEnd()]
  if (factoryNames.size > 0) {
    imports.push({
      code: `import {${[...factoryNames].sort().join(', ')}} from ${JSON.stringify(templatePath)}`,
      source: templatePath,
    })
  }
  for (const alias of aliases) {
    if (alias.targetModule === modulePath) continue
    const targetPath = relativeImport(modulePath, alias.targetModule)
    imports.push({
      code: `import {${alias.targetExport} as ${alias.localName}} from ${JSON.stringify(targetPath)}`,
      source: targetPath,
    })
  }
  if (imports.length > 0) {
    sections.push(
      imports
        .sort((a, b) => a.source.localeCompare(b.source) || a.code.localeCompare(b.code))
        .map(entry => entry.code)
        .join('\n'),
    )
  }
  for (const icon of icons) {
    sections.push(icon.elements ? renderFlexibleIcon(icon) : renderSingleIcon(icon))
  }
  for (const alias of aliases) {
    sections.push(`/** @deprecated Import ${alias.targetExport} from \`#/components/icons/${alias.targetModule}\` instead. */\nexport const ${alias.exportName} = ${alias.localName}\n`)
  }
  return `${sections.join('\n\n')}\n`
}

export async function scanIconImports(scanRoot, outputRoot) {
  const files = (await listFiles(scanRoot)).filter(file => /\.[cm]?[jt]sx?$/.test(file))
  const outputRelative = path.relative(scanRoot, outputRoot)
  const imports = []
  for (const relative of files) {
    if (relative === outputRelative || relative.startsWith(`${outputRelative}${path.sep}`)) continue
    const contents = await fs.readFile(path.join(scanRoot, relative), 'utf8')
    for (const match of contents.matchAll(/import\s+(?:type\s+)?\{([^}]*)\}\s+from\s+['"]#\/components\/icons\/([^'"]+)['"]/g)) {
      const modulePath = match[2]
      if (!modulePath.split('/').every(part => IDENTIFIER.test(part))) {
        fail(relative, `invalid icon module path ${JSON.stringify(modulePath)}`)
      }
      for (const raw of match[1].split(',')) {
        const specifier = raw.trim().replace(/^type\s+/, '')
        if (!specifier) continue
        const exportName = specifier.split(/\s+as\s+/)[0].trim()
        if (IDENTIFIER.test(exportName)) imports.push({exportName, modulePath, sourceFile: relative})
      }
    }
  }
  return imports
}

export async function buildIconSet({outputRoot, scanRoot, sourceRoot}) {
  const sourcePaths = await discoverIconSources(sourceRoot)
  const sources = await Promise.all(sourcePaths.map(relative => readIconSource(sourceRoot, relative)))
  const icons = assignFamilies(sources.filter(source => source.codegen))
  const exportMap = new Map()
  const normalizedExportMap = new Map()
  for (const icon of icons) {
    if (exportMap.has(icon.exportName)) {
      fail(icon.relativePath, `duplicate export ${icon.exportName} also provided by ${exportMap.get(icon.exportName).relativePath}`)
    }
    icon.modulePath = path.posix.join(icon.namespace, icon.family)
    exportMap.set(icon.exportName, icon)
    const normalized = normalizeExportName(icon.exportName)
    if (normalizedExportMap.has(normalized)) {
      fail(icon.relativePath, `normalized export collision with ${normalizedExportMap.get(normalized).relativePath}`)
    }
    normalizedExportMap.set(normalized, icon)
  }

  const imports = await scanIconImports(scanRoot, outputRoot)
  const modules = new Map()
  function moduleData(modulePath) {
    if (!modules.has(modulePath)) modules.set(modulePath, {aliases: [], icons: []})
    return modules.get(modulePath)
  }
  for (const icon of icons) moduleData(icon.modulePath).icons.push(icon)

  const deprecatedImports = []
  const holdouts = []
  const aliasKeys = new Set()
  for (const imported of imports) {
    const icon = exportMap.get(imported.exportName) ?? normalizedExportMap.get(normalizeExportName(imported.exportName))
    if (!icon || (imported.modulePath === icon.modulePath && imported.exportName === icon.exportName)) continue
    deprecatedImports.push({...imported, targetModule: icon.modulePath})
    const legacyFile = path.join(outputRoot, `${imported.modulePath}.tsx`)
    let handwritten = false
    try {
      const contents = await fs.readFile(legacyFile, 'utf8')
      handwritten = !contents.startsWith(GENERATED_HEADER)
    } catch {}
    if (handwritten && !modules.has(imported.modulePath)) {
      holdouts.push({...imported, targetModule: icon.modulePath})
      continue
    }
    const key = `${imported.modulePath}:${imported.exportName}`
    if (aliasKeys.has(key)) continue
    aliasKeys.add(key)
    moduleData(imported.modulePath).aliases.push({
      exportName: imported.exportName,
      localName: imported.modulePath === icon.modulePath ? icon.exportName : `Canonical${imported.exportName}`,
      targetExport: icon.exportName,
      targetModule: icon.modulePath,
    })
  }

  const tsOutputs = new Map()
  for (const [modulePath, data] of modules) {
    if (data.icons.length > 0) {
      const target = path.join(outputRoot, `${modulePath}.tsx`)
      try {
        const contents = await fs.readFile(target, 'utf8')
        if (!contents.startsWith(GENERATED_HEADER)) {
          fail(
            path.relative(process.cwd(), target),
            'generated output would overwrite a handwritten module; rename the SVG family or move the handwritten code',
          )
        }
      } catch (error) {
        if (error?.code !== 'ENOENT') throw error
      }
    }
    data.icons.sort((a, b) => a.exportName.localeCompare(b.exportName))
    data.aliases.sort((a, b) => a.exportName.localeCompare(b.exportName))
    tsOutputs.set(
      `${modulePath}.tsx`,
      await format(renderModule(modulePath, data.icons, data.aliases), {
        arrowParens: 'avoid',
        bracketSameLine: true,
        bracketSpacing: false,
        parser: 'typescript',
        semi: false,
        singleQuote: true,
        trailingComma: 'all',
      }),
    )
  }
  const svgOutputs = new Map(sources.map(source => [source.relativePath, source.optimized]))
  const warnings = sources.flatMap(source => source.warnings)
  return {deprecatedImports, holdouts, icons, svgOutputs, tsOutputs, warnings}
}

export async function applyIconSet({check, outputRoot, result, sourceRoot}) {
  const differences = []
  async function compareOrWrite(root, relative, contents) {
    const target = path.join(root, relative)
    let current
    try { current = await fs.readFile(target, 'utf8') } catch {}
    if (current === contents) return
    differences.push(path.relative(process.cwd(), target))
    if (!check) {
      await fs.mkdir(path.dirname(target), {recursive: true})
      await fs.writeFile(target, contents)
    }
  }

  for (const [relative, contents] of result.svgOutputs) await compareOrWrite(sourceRoot, relative, contents)
  for (const [relative, contents] of result.tsOutputs) await compareOrWrite(outputRoot, relative, contents)

  const existing = await listFiles(outputRoot)
  for (const relative of existing.filter(file => file.endsWith('.tsx') && !result.tsOutputs.has(file))) {
    const target = path.join(outputRoot, relative)
    const contents = await fs.readFile(target, 'utf8')
    if (!contents.startsWith(GENERATED_HEADER)) continue
    differences.push(path.relative(process.cwd(), target))
    if (!check) await fs.unlink(target)
  }
  return [...new Set(differences)].sort()
}