type sandbox {
  data: (handle gap-buffer)
  value: (handle stream byte)
}

fn initialize-sandbox _self: (addr sandbox) {
  var self/esi: (addr sandbox) <- copy _self
  var data-ah/eax: (addr handle gap-buffer) <- get self, data
  allocate data-ah
  var data/eax: (addr gap-buffer) <- lookup *data-ah
  initialize-gap-buffer data, 0x1000/4KB
  var value-ah/eax: (addr handle stream byte) <- get self, value
  populate-stream value-ah, 0x1000/4KB
}

## some helpers for tests

fn initialize-sandbox-with _self: (addr sandbox), s: (addr array byte) {
  var self/esi: (addr sandbox) <- copy _self
  var data-ah/eax: (addr handle gap-buffer) <- get self, data
  allocate data-ah
  var data/eax: (addr gap-buffer) <- lookup *data-ah
  initialize-gap-buffer-with data, s
}

fn allocate-sandbox-with _out: (addr handle sandbox), s: (addr array byte) {
  var out/eax: (addr handle sandbox) <- copy _out
  allocate out
  var out-addr/eax: (addr sandbox) <- lookup *out
  initialize-sandbox-with out-addr, s
}

fn add-grapheme-to-sandbox _self: (addr sandbox), c: grapheme {
  var self/esi: (addr sandbox) <- copy _self
  var data-ah/eax: (addr handle gap-buffer) <- get self, data
  var data/eax: (addr gap-buffer) <- lookup *data-ah
  add-grapheme-at-gap data, c
}

fn delete-grapheme-before-cursor _self: (addr sandbox) {
  var self/esi: (addr sandbox) <- copy _self
  var data-ah/eax: (addr handle gap-buffer) <- get self, data
  var data/eax: (addr gap-buffer) <- lookup *data-ah
  delete-before-gap data
}

fn render-sandbox screen: (addr screen), _self: (addr sandbox), _x: int, _y: int {
  clear-screen screen
  var self/esi: (addr sandbox) <- copy _self
  var data-ah/eax: (addr handle gap-buffer) <- get self, data
  var _data/eax: (addr gap-buffer) <- lookup *data-ah
  var data/edx: (addr gap-buffer) <- copy _data
  var x/eax: int <- copy _x
  var y/ecx: int <- copy _y
  x, y <- render-gap-buffer-wrapping-right-then-down screen, data, x, y, 0x20/xmax, 0x20/ymax, x, y, 1/true
  y <- increment
  var value-ah/eax: (addr handle stream byte) <- get self, value
  var value/eax: (addr stream byte) <- lookup *value-ah
  var dummy/eax: int <- draw-stream-rightward screen, value, _x, 0x30/xmax, y, 7/fg=grey, 0/bg
}

fn edit-sandbox _self: (addr sandbox), key: byte {
  var self/esi: (addr sandbox) <- copy _self
  var g/edx: grapheme <- copy key
  {
    compare g, 8/backspace
    break-if-!=
    delete-grapheme-before-cursor self
    return
  }
  {
    compare g, 0x12/ctrl-r
    break-if-!=
    # ctrl-r: run function outside sandbox
    # required: fn (addr screen), (addr keyboard)
    # Mu will pass in the real screen and keyboard.
    return
  }
  {
    compare g, 0x13/ctrl-s
    break-if-!=
    # ctrl-s: run sandbox(es)
    var data-ah/eax: (addr handle gap-buffer) <- get self, data
    var _data/eax: (addr gap-buffer) <- lookup *data-ah
    var data/ecx: (addr gap-buffer) <- copy _data
    var value-ah/eax: (addr handle stream byte) <- get self, value
    var value/eax: (addr stream byte) <- lookup *value-ah
    run data, value
    return
  }
  add-grapheme-to-sandbox self, g
}