-- Copyright (C) 2018-2021 by KittenOS NEO contributors
--
-- Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.
--
-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
-- THIS SOFTWARE.

-- event: Implements pull/listen semantics in a consistent way for a given process.
-- This is similar in API to OpenOS's event framework, but is per-process.
-- To make this work, a function is shared.
-- This function needs access to the caller's NEO in order to ensure that NEO system functions are covered.
-- This can do less checks than usual as it only affects the caller.

-- Global forces reference to prevent duplication
newEvent = function (neo)
 local listeners = {}
 local translations = {}
 local timers = {}
 local oldRA = neo.requestAccess
 local function doPush(tp, tag, ...)
  if tp == "k.timer" then
   local f = timers[tag]
   timers[tag] = nil
   if f then
    f(...)
   end
  end
  local listeners2 = {}
  for k, _ in pairs(listeners) do
   table.insert(listeners2, k)
  end
  for _, v in ipairs(listeners2) do
   v(tp, tag, ...)
  end
 end
 neo.requestAccess = function (perm, handler)
  return oldRA(perm, function (...)
   doPush(...)
   if handler then
    handler(...)
   end
  end)
 end
 local function doPull()
  local ev = {coroutine.yield()}
  doPush(table.unpack(ev))
  return ev
 end
 return {
  listen = function (p1, p2)
   if type(p2) == "function" then
    local t = function (...)
     local evn = ...
     if evn == p1 then
      p2(...)
     end
    end
    translations[p2] = t
    listeners[t] = true
   else
    listeners[p1] = true
   end
  end,
  ignore = function (func)
   if translations[func] then
    listeners[translations[func]] = nil
    translations[func] = nil
   end
   listeners[func] = nil
  end,
  -- Arguments are filtering.
  -- For example, to filter for timers with a given tag, use pull("k.timer", tag)
  -- Note the explicit discouragement of timeout-pulls. Use runAt or the complex form of sleep.
  pull = function (...)
   local filter = {...}
   while true do
    local ev = doPull()
    local err = false
    for i = 1, #filter do
     err = err or (filter[i] ~= ev[i])
    end
    if not err then return table.unpack(ev) end
   end
  end,
  -- Run a function at a specified uptime.
  runAt = function (time, func)
   timers[neo.scheduleTimer(time)] = func
  end,
  -- Sleeps until a time (unless time is nil, in which case sleeps forever), but can be woken up before then.
  -- This allows using an async API as a synchronous one with optional time-to-failure.
  sleepTo = function (time, wakeUpPoll)
   local timerHit = false
   local oWUP = wakeUpPoll
   wakeUpPoll = function ()
    if oWUP then
     return timerHit or (oWUP())
    end
    return timerHit
   end
   if time then
    timers[neo.scheduleTimer(time)] = function () timerHit = true end
   end
   while true do
    local ev = doPull()
    if wakeUpPoll() then return end
   end
  end
 }
end
return newEvent