type Holder {
  file: dever.system.File
  label: Int
}

verify() (ok: Bool) {
  created = dever.io.create("created")
  dever.io.write(created, dever.bytes.fromText("hello"))
  dever.io.close(created)
  refused = createFailed(result(dever.io.create("created")))
  file = dever.io.open("input")
  holder = Holder { file = file
    label = 1 }
  copied = holder
  copied.label = 2
  first_read = dever.io.read(holder.file, 2)
  files = [copied.file]
  second_read = readAlias(first(files))
  last_read = dever.io.read(file, 99)
  end = dever.io.read(file, 1)
  dever.io.close(copied.file)
  closed_read = readFailed(result(dever.io.read(file, 1)))
  closed_write = writeFailed(result(dever.io.write(holder.file, dever.bytes.fromText(""))))
  closed_close = closeFailed(result(dever.io.close(file)))
  dever.io.println("hello")
  reads = first_read == dever.io.ReadState.Read(dever.bytes.fromText("ab")) and second_read == dever.io.ReadState.Read(dever.bytes.fromText("cd")) and last_read == dever.io.ReadState.Read(dever.bytes.fromText("e"))
  ok = refused and holder.label == 1 and copied.label == 2 and reads and end == dever.io.ReadState.End and closed_read and closed_write and closed_close
}

readAlias(file: null) (state: dever.io.ReadState) {
  state = dever.io.ReadState.End
}
readAlias(file: dever.system.File) (state: dever.io.ReadState) {
  state = dever.io.read(file, 2)
}

missing() () {
  file = dever.io.open("missing-file")
}

invalid() () {
  file = dever.io.open("input")
  state = dever.io.read(file, 0)
}

print() () {
  dever.io.println("hello")
}

createFailed(value: dever.io.OpenResult.Opened(file)) (ok: Bool) recover("test observes expected I/O failure") {
  ok = false
}
createFailed(value: dever.io.OpenResult.Failed(message)) (ok: Bool) recover("test observes expected I/O failure") {
  ok = length(message) > 0
}

readFailed(value: dever.io.ReadResult.Done(state)) (ok: Bool) recover("test observes expected I/O failure") {
  ok = false
}
readFailed(value: dever.io.ReadResult.Failed(message)) (ok: Bool) recover("test observes expected I/O failure") {
  ok = length(message) > 0
}

writeFailed(value: dever.io.WriteResult.Done) (ok: Bool) recover("test observes expected I/O failure") {
  ok = false
}
writeFailed(value: dever.io.WriteResult.Failed(message)) (ok: Bool) recover("test observes expected I/O failure") {
  ok = length(message) > 0
}

closeFailed(value: dever.io.CloseResult.Closed) (ok: Bool) recover("test observes expected I/O failure") {
  ok = false
}
closeFailed(value: dever.io.CloseResult.Failed(message)) (ok: Bool) recover("test observes expected I/O failure") {
  ok = length(message) > 0
}