# A task list. The runtime owns the list: the index always names an item,
# stays on it when items are inserted or removed before it, stops at the
# ends, and a failed event leaves the list as it was.
record Task {
  title: text
  done = 0
}

state tasks: list of Task
state at: index of tasks
state made = 0

input typed = text
input up = key ArrowUp
input down = key ArrowDown
input toggle = key Space
input drop = key Delete
input top = key Home
input bottom = key End
input again = key KeyD
input shout = key KeyS

on typed {
  tasks.append(Task { title: typed })
  at = tasks.last
  made = made + 1
}
on up.down { at = at - 1 }
on down.down { at = at + 1 }
on toggle.down { at.done = !at.done }
on drop.down { tasks.remove(at) }
on top.down { at = tasks.first }
on bottom.down { at = tasks.last }
# A copy goes before the current task, which stays current.
on again.down { tasks.insert(at, Task { title: tasks[at].title, done: tasks[at].done }) }
on shout.down { tasks[at].title = "{at.title}!" }

view count = tasks.count
view position = at.position
view current = if tasks.count > 0 { at.title } else { "(empty)" }
view status = if tasks.count > 0 { "{at.position + 1}/{tasks.count}" } else { "empty" }
view finished = at.done              # no value while the list is empty

# One row per task. A surface computes only the rows it shows.
view board = each task in tasks {
  title = task.title
  mark = if task.done { "x" } else { " " }
  here = task.position == at.position
}