--[[
  MIDI Grid: preview daemon.

  Runs quietly in the background and owns every preview note-on/note-off.
  The action scripts never defer, so they always exit instantly and Reaper
  never shows its "already running" prompt no matter how fast keys repeat.

  Started automatically by the action scripts; you never need to run it.
]]
local dir = ({ reaper.get_action_context() })[2]:match("@?(.*[\\/])")
local G = dofile(dir .. "midigrid_lib.lua")

-- Refuse to start a second copy.
local hb = tonumber(G.getTemp("hb", "0")) or 0
if os.time() - hb <= 3 then return end

local sounding = {}
local releaseAt = 0
local lastSeq = tonumber(G.getTemp("seq", "0")) or 0

local function allOff()
  for _, p in ipairs(sounding) do
    reaper.StuffMIDIMessage(0, 0x80, p, 0)
  end
  sounding = {}
end

local function loop()
  G.setTemp("hb", os.time())

  local seq = tonumber(G.getTemp("seq", "0")) or 0
  if seq ~= lastSeq then
    lastSeq = seq
    -- A new request cuts whatever is still sounding, so fast arrowing
    -- retriggers cleanly instead of piling notes up.
    allOff()
    local vel = math.floor(G.getNum("vel", 96))
    for s in tostring(G.getTemp("pitches", "")):gmatch("%d+") do
      local p = tonumber(s)
      if p and p >= 0 and p <= 127 then
        sounding[#sounding + 1] = p
        reaper.StuffMIDIMessage(0, 0x90, p, vel)
      end
    end
    releaseAt = reaper.time_precise() + (tonumber(G.getTemp("dur", "0.4")) or 0.4)
  end

  if #sounding > 0 and reaper.time_precise() >= releaseAt then
    allOff()
  end

  -- Pending "stop at end of bar" request, posted by the play-one-bar action.
  local stopAt = tonumber(G.getTemp("stopat", ""))
  if stopAt then
    local playing = (reaper.GetPlayState() % 2) == 1
    -- Stop a little BEFORE the bar line, not on it, or a note sitting exactly
    -- on the next bar line sounds.
    --
    -- GetPlayPosition2 reports the block REAPER is about to render, rather
    -- than what you are currently hearing. Testing against that removes the
    -- render-ahead entirely, so the lead only has to cover this loop's own
    -- polling interval (~33ms at frame rate) instead of both. That is why
    -- 35ms suffices here where 60ms was needed against GetPlayPosition.
    --
    -- Polling cannot do better than its own interval; for a sample-accurate
    -- bar boundary use the loop-bar action instead, which lets REAPER's audio
    -- engine handle the edge.
    local lead = G.getNum("stoplead", 0.035)
    if playing and reaper.GetPlayPosition2() >= stopAt - lead then
      -- Stopping can move the edit cursor depending on preferences, and the
      -- edit cursor is the grid cursor, so put it back.
      local cur = reaper.GetCursorPosition()
      reaper.CSurf_OnStop()
      reaper.SetEditCurPos(cur, false, false)
      G.setTemp("stopat", "")
    elseif not playing
       and reaper.time_precise() > (tonumber(G.getTemp("stoparm", "0")) or 0) then
      -- Transport stopped by other means; drop the pending request.
      G.setTemp("stopat", "")
    end
  end

  -- Grid mode borrows the record arm/monitor state of the edited track so
  -- preview plays through its instrument. Give it back as soon as grid mode
  -- is off or the editor is gone -- here rather than in an action script, so
  -- closing the editor puts the project back too.
  if G.getTemp("savedarm", "") ~= ""
     and (not G.isActive() or not reaper.MIDIEditor_GetActive()) then
    G.restoreRouting()
  end

  -- Restore the loop range and repeat state the loop-bar action borrowed,
  -- once transport has stopped. Doing it here rather than in the action
  -- script means the project is put back even if you stop with Space.
  local savedLoop = G.getTemp("savedloop", "")
  if savedLoop ~= "" then
    local playing = (reaper.GetPlayState() % 2) == 1
    if not playing
       and reaper.time_precise() > (tonumber(G.getTemp("stoparm", "0")) or 0) then
      local a, b = savedLoop:match("^([%-%d%.eE+]+),([%-%d%.eE+]+)$")
      if a and b then
        reaper.GetSet_LoopTimeRange(true, true, tonumber(a), tonumber(b), false)
      end
      reaper.GetSetRepeat(tonumber(G.getTemp("savedrep", "0")) or 0)
      G.setTemp("savedloop", "")
    end
  end

  reaper.defer(loop)
end

-- Never leave a note hanging, or a borrowed record arm unreturned, if the
-- daemon is terminated or Reaper quits.
reaper.atexit(function() allOff() ; G.restoreRouting() end)
loop()