module Polysemy.Time.At where

import Polysemy (intercept)
import Torsor (Torsor (add), difference)

import Polysemy.Time.Calendar (HasDate, date, dateToTime)
import qualified Polysemy.Time.Data.Time as Time
import Polysemy.Time.Data.Time (Time)
import Polysemy.Time.Data.TimeUnit (TimeUnit, addTimeUnit)

-- |Determine the current time adjusted for the difference between a custom instant and the time at which the program
-- was started.
dateCurrentRelative ::
  ∀ diff t d r .
  Torsor t diff =>
  Members [Time t d, AtomicState (t, t)] r =>
  Sem r t
dateCurrentRelative = do
  (startAt, startActual) <- atomicGet @(t, t)
  (`add` startAt) . (`difference` startActual) <$> Time.now @t @d

-- |Given real and adjusted start time, change all calls to 'Time.Now' and 'Time.Today' to be relative to that start
-- time.
-- This needs to be interpreted with a vanilla interpreter for 'Time' once more.
interceptTimeAtWithStart ::
  ∀ diff t d r a .
  Torsor t diff =>
  TimeUnit diff =>
  HasDate t d =>
  Members [Time t d, AtomicState (t, t)] r =>
  Sem r a ->
  Sem r a
interceptTimeAtWithStart =
  intercept @(Time t d) \case
    Time.Now ->
      dateCurrentRelative @diff @t @d
    Time.Today ->
      date <$> dateCurrentRelative @diff @t @d
    Time.Sleep t ->
      Time.sleep @t @d t
    Time.SetTime startAt -> do
      startActual <- Time.now @t @d
      atomicPut @(t, t) (startAt, startActual)
    Time.Adjust diff -> do
      atomicModify' @(t, t) \ (old, actual) -> (addTimeUnit diff old, actual)
    Time.SetDate startAt -> do
      startActual <- Time.now @t @d
      atomicPut @(t, t) (dateToTime startAt, startActual)
{-# inline interceptTimeAtWithStart #-}

-- |Interpret 'Time' so that the time when the program starts is @startAt@.
interceptTimeAt ::
  ∀ (diff :: Type) t d r a .
  TimeUnit diff =>
  Torsor t diff =>
  HasDate t d =>
  Members [Time t d, Embed IO] r =>
  t ->
  Sem r a ->
  Sem r a
interceptTimeAt startAt sem = do
  startActual <- Time.now @t @d
  tv <- newTVarIO (startAt, startActual)
  runAtomicStateTVar tv . interceptTimeAtWithStart @diff @t @d . raise $ sem
{-# inline interceptTimeAt #-}

-- |Change all calls to 'Time.Now' and 'Time.Today' to return the given start time.
-- This needs to be interpreted with a vanilla interpreter for 'Time' once more.
interceptTimeConstantState ::
  ∀ t d r a .
  HasDate t d =>
  Members [Time t d, AtomicState t] r =>
  Sem r a ->
  Sem r a
interceptTimeConstantState =
  intercept @(Time t d) \case
    Time.Now ->
      atomicGet
    Time.Today ->
      atomicGets @t date
    Time.Sleep t ->
      Time.sleep @t @d t
    Time.SetTime now ->
      atomicPut now
    Time.Adjust diff ->
      atomicModify' @t (addTimeUnit diff)
    Time.SetDate startAt ->
      atomicPut @t (dateToTime startAt)
{-# inline interceptTimeConstantState #-}

-- |Interpret 'Time' so that the time is always @startAt@.
--
-- The time can still be changed with 'Time.setTime', 'Time.adjust' and 'Time.setDate'.
interceptTimeConstant ::
  ∀ t d r a .
  HasDate t d =>
  Members [Time t d, Embed IO] r =>
  t ->
  Sem r a ->
  Sem r a
interceptTimeConstant startAt sem = do
  tv <- newTVarIO startAt
  runAtomicStateTVar tv . interceptTimeConstantState @t . raise $ sem
{-# inline interceptTimeConstant #-}

-- |Interpret 'Time' so that the time is always the time at the start of interpretation.
--
-- The time can still be changed with 'Time.setTime', 'Time.adjust' and 'Time.setDate'.
interceptTimeConstantNow ::
  ∀ t d r a .
  HasDate t d =>
  Members [Time t d, Embed IO] r =>
  Sem r a ->
  Sem r a
interceptTimeConstantNow sem = do
  now <- Time.now @t @d
  tv <- newTVarIO now
  runAtomicStateTVar tv . interceptTimeConstantState @t . raise $ sem
{-# inline interceptTimeConstantNow #-}