async function readLines(ctx, path) {
  const b4 = ctx.b4a
  if (path === '-') return bareStdin(ctx).split('\n')
  const b = await ctx.vfs.readFile(path)
  if (!b) return null
  return b4.toString(b).split('\n')
}

async function run(ctx, argv) {
  let c1 = true
  let c2 = true
  let c3 = true
  const paths = []
  for (let i = 1; i < argv.length; i++) {
    const a = argv[i]
    if (a === '-h' || a === '--help') {
      ctx.console.log(
        'usage: comm [-123] FILE1 FILE2\nCompare sorted files; columns: only FILE1, only FILE2, both.'
      )
      return
    }
    if (a === '-1') c1 = false
    else if (a === '-2') c2 = false
    else if (a === '-3') c3 = false
    else if (a.startsWith('-')) {
      ctx.console.error('comm: unsupported option ' + a)
      ctx.exitCode = 1
      return
    } else paths.push(a)
  }
  if (paths.length !== 2) {
    ctx.console.error('usage: comm [-123] FILE1 FILE2')
    ctx.exitCode = 1
    return
  }
  const A = await readLines(ctx, paths[0])
  const B = await readLines(ctx, paths[1])
  if (!A || !B) {
    ctx.console.error('comm: missing input file')
    ctx.exitCode = 1
    return
  }
  const trimNl = (arr) => {
    if (arr.length && arr[arr.length - 1] === '') arr.pop()
    return arr
  }
  const a = trimNl(A.slice())
  const b = trimNl(B.slice())
  let i = 0
  let j = 0
  while (i < a.length || j < b.length) {
    if (i >= a.length) {
      if (c2) ctx.console.log('\t' + b[j])
      j++
      continue
    }
    if (j >= b.length) {
      if (c1) ctx.console.log(a[i])
      i++
      continue
    }
    const cmp = a[i].localeCompare(b[j])
    if (cmp < 0) {
      if (c1) ctx.console.log(a[i])
      i++
    } else if (cmp > 0) {
      if (c2) ctx.console.log('\t' + b[j])
      j++
    } else {
      if (c3) ctx.console.log('\t\t' + a[i])
      i++
      j++
    }
  }
}