--[[
  midigrid_lib.lua -- shared library for the MIDI Grid quick-entry mode.

  Design notes:
    * No window, no gfx. All feedback goes through OSARA speech.
    * The cursor is Reaper's OWN edit cursor (time) plus the MIDI editor's
      active_note_row (pitch). We never keep a private cursor, so grid mode
      and normal OSARA editing can be interleaved freely.
    * Grid size is read from MIDI_GetGrid(), so the user's existing
      grid-size keybindings (1-9 in the MIDI editor) drive it.
    * Persistent state is only: active, hold, root, scale, vel, chan.
]]

local M = {}

local EXT = "midigrid"

--------------------------------------------------------------------- state

function M.get(k, default)
  local v = reaper.GetExtState(EXT, k)
  if v == "" then return default end
  return v
end

function M.getNum(k, default)
  return tonumber(M.get(k, tostring(default))) or default
end

function M.set(k, v)
  reaper.SetExtState(EXT, k, tostring(v), true)
end

-- Transient state (preview requests, daemon heartbeat). Never persisted:
-- these change on every keypress and must not hit reaper.ini.
function M.setTemp(k, v) reaper.SetExtState(EXT, k, tostring(v), false) end

function M.getTemp(k, default)
  local v = reaper.GetExtState(EXT, k)
  if v == "" then return default end
  return v
end

function M.isActive() return M.get("active", "0") == "1" end
function M.isHold()   return M.get("hold",   "0") == "1" end

--------------------------------------------------------------------- speech

-- OSARA exposes osara_outputMessage; fall back to the console if absent so
-- the scripts are still debuggable on a machine without OSARA.
function M.say(msg)
  if reaper.APIExists("osara_outputMessage") then
    reaper.osara_outputMessage(msg)
  else
    reaper.ShowConsoleMsg(tostring(msg) .. "\n")
  end
end

--------------------------------------------------------------- editor/take

-- Returns hwnd, take for the active MIDI editor, or nil plus a reason.
function M.editor()
  local hwnd = reaper.MIDIEditor_GetActive()
  if not hwnd then return nil, nil, "No MIDI editor open" end
  local take = reaper.MIDIEditor_GetTake(hwnd)
  if not take or not reaper.TakeIsMIDI(take) then
    return nil, nil, "No MIDI take in editor"
  end
  return hwnd, take, nil
end

-- Forward a keystroke to whatever it would normally do when grid mode is off.
-- Accepts a numeric command id or a named command string such as
-- "_OSARA_NEXTCHORD".
function M.passThrough(cmd)
  local hwnd = reaper.MIDIEditor_GetActive()
  local id = cmd
  if type(cmd) == "string" then id = reaper.NamedCommandLookup(cmd) end
  if not id or id == 0 then return false end
  if hwnd then
    reaper.MIDIEditor_OnCommand(hwnd, id)
  else
    reaper.Main_OnCommand(id, 0)
  end
  return true
end

----------------------------------------------------------------- note names

local PC_NAMES = { "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B" }

-- Reaper's displayed octave depends on the "midioctoffs" preference so that
-- our speech matches what OSARA and the editor say. With the default offset
-- of 1, note 60 reads as C5.
local function octaveOffset()
  if reaper.SNM_GetIntConfigVar then
    return reaper.SNM_GetIntConfigVar("midioctoffs", 1)
  end
  return 1
end

function M.noteName(pitch)
  local pc = pitch % 12
  local oct = math.floor(pitch / 12) - 1 + octaveOffset()
  return PC_NAMES[pc + 1] .. tostring(oct)
end

--------------------------------------------------------------------- scales

M.SCALES = {
  { name = "major",             steps = { 0, 2, 4, 5, 7, 9, 11 } },
  { name = "natural minor",     steps = { 0, 2, 3, 5, 7, 8, 10 } },
  { name = "harmonic minor",    steps = { 0, 2, 3, 5, 7, 8, 11 } },
  { name = "melodic minor",     steps = { 0, 2, 3, 5, 7, 9, 11 } },
  { name = "dorian",            steps = { 0, 2, 3, 5, 7, 9, 10 } },
  { name = "phrygian",          steps = { 0, 1, 3, 5, 7, 8, 10 } },
  { name = "lydian",            steps = { 0, 2, 4, 6, 7, 9, 11 } },
  { name = "mixolydian",        steps = { 0, 2, 4, 5, 7, 9, 10 } },
  { name = "locrian",           steps = { 0, 1, 3, 5, 6, 8, 10 } },
  { name = "major pentatonic",  steps = { 0, 2, 4, 7, 9 } },
  { name = "minor pentatonic",  steps = { 0, 3, 5, 7, 10 } },
  { name = "blues",             steps = { 0, 3, 5, 6, 7, 10 } },
  { name = "whole tone",        steps = { 0, 2, 4, 6, 8, 10 } },
  { name = "chromatic",         steps = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 } },
}

function M.scaleIndex()
  local n = M.getNum("scale", 1)
  if n < 1 or n > #M.SCALES then n = 1 end
  return math.floor(n)
end

function M.scaleRoot() return math.floor(M.getNum("root", 0)) % 12 end

function M.scaleName()
  return M.noteNamePc(M.scaleRoot()) .. " " .. M.SCALES[M.scaleIndex()].name
end

function M.noteNamePc(pc) return PC_NAMES[(pc % 12) + 1] end

-- Set of pitch classes belonging to the current scale.
local function scalePcSet()
  local root = M.scaleRoot()
  local set = {}
  for _, s in ipairs(M.SCALES[M.scaleIndex()].steps) do
    set[(root + s) % 12] = true
  end
  return set
end

function M.inScale(pitch) return scalePcSet()[pitch % 12] == true end

-- Step to the next pitch of the current scale in direction dir (+1 / -1).
-- Notes already off-scale simply move to the nearest scale tone in that
-- direction, so foreign notes never trap the cursor.
function M.scaleStep(pitch, dir)
  local set = scalePcSet()
  local p = pitch
  for _ = 1, 24 do
    p = p + dir
    if p < 0 or p > 127 then return nil end
    if set[p % 12] then return p end
  end
  return nil
end

------------------------------------------------------------ cursor / pitch

function M.getPitch(hwnd)
  local p = reaper.MIDIEditor_GetSetting_int(hwnd, "active_note_row")
  if not p or p < 0 or p > 127 then p = 60 end
  return p
end

function M.setPitch(hwnd, pitch)
  reaper.MIDIEditor_SetSetting_int(hwnd, "active_note_row", pitch)
end

------------------------------------------------------------------ the grid

-- Grid length in quarter notes, as configured in the MIDI editor.
function M.gridQN(take)
  local grid = reaper.MIDI_GetGrid(take)
  if not grid or grid <= 0 then grid = 1 end
  return grid
end

-- Speak grid sizes as musical fractions ("1/16", "1 bar") rather than raw
-- quarter-note counts.
function M.gridLabel(g)
  -- Length of one bar in quarter notes, at the cursor's time signature.
  local num = 4
  local ts_num, ts_den = reaper.TimeMap_GetTimeSigAtTime(0, reaper.GetCursorPosition())
  if ts_num and ts_den and ts_den > 0 then num = ts_num * (4 / ts_den) end
  if math.abs(g - num) < 1e-6 then return "1 bar" end
  if g > num then
    local bars = g / num
    return ("%g bars"):format(bars)
  end
  local frac = 4 / g
  if math.abs(frac - math.floor(frac + 0.5)) < 1e-6 then
    return ("1/%d"):format(math.floor(frac + 0.5))
  end
  return ("%.3g QN"):format(g)
end

-- The grid cell the edit cursor currently sits in.
-- Cells are aligned to the project timeline (QN 0), matching Reaper's own
-- grid lines rather than the item start.
-- Returns: startQN, endQN, cellIndex, gridQN
function M.cell(take)
  local g = M.gridQN(take)
  local qn = reaper.TimeMap2_timeToQN(0, reaper.GetCursorPosition())
  local idx = math.floor(qn / g + 1e-9)
  return idx * g, (idx + 1) * g, idx, g
end

function M.cellPPQ(take)
  local a, b = M.cell(take)
  return reaper.MIDI_GetPPQPosFromProjQN(take, a),
         reaper.MIDI_GetPPQPosFromProjQN(take, b)
end

-- Move the edit cursor to the start of cell index idx.
function M.gotoCell(take, idx)
  local g = M.gridQN(take)
  local t = reaper.TimeMap2_QNToTime(0, idx * g)
  if t < 0 then t = 0 end
  reaper.SetEditCurPos(t, true, false)
end

--[[
  Put the cursor on the nearest cell boundary to time t (the edit cursor by
  default), without leaving the item.

  Entering grid mode uses this instead of jumping to the item start: wherever
  you were already listening stays where you are, only tidied onto a real cell
  so the first left/right press moves a whole cell rather than a remainder.

  Returns the cell index landed on.
]]
function M.snapCursorToCell(take, t)
  local g = M.gridQN(take)
  local item = reaper.GetMediaItemTake_Item(take)
  local lo = reaper.GetMediaItemInfo_Value(item, "D_POSITION")
  local hi = lo + reaper.GetMediaItemInfo_Value(item, "D_LENGTH")

  t = t or reaper.GetCursorPosition()
  local idx = math.floor(reaper.TimeMap2_timeToQN(0, t) / g + 0.5)

  -- A cursor outside the item pulls back to the first or last cell the item
  -- covers. The first is the cell containing the item start, which is where
  -- plain "open in editor" used to land.
  local loIdx = math.floor(reaper.TimeMap2_timeToQN(0, lo) / g + 1e-9)
  local hiIdx = math.ceil(reaper.TimeMap2_timeToQN(0, hi) / g - 1e-9) - 1
  if hiIdx < loIdx then hiIdx = loIdx end
  if idx < loIdx then idx = loIdx elseif idx > hiIdx then idx = hiIdx end

  M.gotoCell(take, idx)
  return idx
end

------------------------------------------------------------- note queries

-- A cell counts as occupied by a note if the note overlaps it at all, so
-- held notes spanning several cells register in every cell they cover.
-- The 1-tick slack keeps float rounding at cell boundaries from producing
-- phantom overlaps.
local SLACK = 1

function M.noteInCell(take, pitch, ppqA, ppqB)
  local _, notecnt = reaper.MIDI_CountEvts(take)
  for i = 0, notecnt - 1 do
    local ok, sel, muted, sppq, eppq, chan, p, vel = reaper.MIDI_GetNote(take, i)
    if ok and p == pitch and sppq < ppqB - SLACK and eppq > ppqA + SLACK then
      return i, sppq, eppq, chan, vel, sel, muted
    end
  end
  return nil
end

function M.noteEndingAt(take, pitch, ppq)
  local _, notecnt = reaper.MIDI_CountEvts(take)
  for i = 0, notecnt - 1 do
    local ok, _, _, sppq, eppq, _, p = reaper.MIDI_GetNote(take, i)
    if ok and p == pitch and math.abs(eppq - ppq) <= SLACK then return i, sppq, eppq end
  end
  return nil
end

function M.noteStartingAt(take, pitch, ppq)
  local _, notecnt = reaper.MIDI_CountEvts(take)
  for i = 0, notecnt - 1 do
    local ok, _, _, sppq, eppq, _, p = reaper.MIDI_GetNote(take, i)
    if ok and p == pitch and math.abs(sppq - ppq) <= SLACK then return i, sppq, eppq end
  end
  return nil
end

-- All pitches sounding anywhere inside the current cell, low to high.
function M.pitchesInCell(take, ppqA, ppqB)
  local out = {}
  local _, notecnt = reaper.MIDI_CountEvts(take)
  for i = 0, notecnt - 1 do
    local ok, _, muted, sppq, eppq, _, p = reaper.MIDI_GetNote(take, i)
    if ok and not muted and sppq < ppqB - SLACK and eppq > ppqA + SLACK then
      out[#out + 1] = p
    end
  end
  table.sort(out)
  -- de-duplicate unisons on different channels
  local uniq = {}
  for _, p in ipairs(out) do
    if uniq[#uniq] ~= p then uniq[#uniq + 1] = p end
  end
  return uniq
end

------------------------------------------------------------ octave jumps

-- Jump a whole octave, keeping the pitch class. Because the octave is
-- transpositionally neutral, a scale tone stays a scale tone, so this needs
-- no scale awareness at all -- unlike scaleStep it just adds 12.
-- Returns nil at the ends of the MIDI range rather than clamping, so the
-- caller can say "top" instead of pretending it moved.
function M.octaveStep(pitch, dir)
  local p = pitch + 12 * dir
  if p < 0 or p > 127 then return nil end
  return p
end

------------------------------------------------------ jumping to real notes

--[[
  Arrowing cell by cell is right inside a dense bar and tedious across an
  empty one. These jump straight to a note that is actually there, along the
  three axes you can be looking down:

    column -- the pitches sounding in the cell you are on, up or down
    row    -- the same pitch, forwards or backwards in time
    any    -- the next note in the take whatever its pitch

  Two rules they all share. They ignore muted notes, because a muted note is
  not audible content and stopping on one would be a lie. And, apart from the
  column jump, they anchor on note *starts*, so a note sustained over eight
  cells is one stop rather than eight.
]]

-- Nearest pitch sounding in the cell strictly above (dir 1) or below (dir -1)
-- `pitch`. The cell's pitches arrive sorted, so the first match in the right
-- direction is the nearest one.
function M.pitchInCellToward(take, ppqA, ppqB, pitch, dir)
  local ps = M.pitchesInCell(take, ppqA, ppqB)
  if dir > 0 then
    for i = 1, #ps do if ps[i] > pitch then return ps[i] end end
  else
    for i = #ps, 1, -1 do if ps[i] < pitch then return ps[i] end end
  end
  return nil
end

-- Nearest note start beyond the current cell in direction dir.
--   opts.pitch -- restrict to this one pitch (row navigation)
--   opts.near  -- when several notes share the winning position, prefer the
--                one closest to this pitch, so jumping into a chord lands
--                where you were rather than at its bottom
-- Returns startPPQ, pitch, or nil when there is nothing that way.
function M.nextNoteStart(take, ppqA, ppqB, dir, opts)
  opts = opts or {}
  local bestPos, bestPitch
  local _, notecnt = reaper.MIDI_CountEvts(take)

  for i = 0, notecnt - 1 do
    local ok, _, muted, sppq, _, _, p = reaper.MIDI_GetNote(take, i)
    local wanted = ok and not muted and (not opts.pitch or p == opts.pitch)
    local beyond = wanted and
      (dir > 0 and sppq > ppqB - SLACK or dir < 0 and sppq < ppqA - SLACK)

    if beyond then
      local better
      if not bestPos then
        better = true
      elseif math.abs(sppq - bestPos) <= SLACK then
        -- Same position: a chord. Break the tie towards opts.near.
        better = opts.near ~= nil and
          math.abs(p - opts.near) < math.abs(bestPitch - opts.near)
      elseif dir > 0 then
        better = sppq < bestPos
      else
        better = sppq > bestPos
      end
      if better then bestPos, bestPitch = sppq, p end
    end
  end

  return bestPos, bestPitch
end

-- Which grid cell a PPQ position falls in. Converted through quarter notes,
-- like everything else here, so it survives tempo changes.
function M.cellIndexAtPPQ(take, ppq)
  local g = M.gridQN(take)
  local qn = reaper.MIDI_GetProjQNFromPPQPos(take, ppq)
  return math.floor(qn / g + 1e-9)
end

-- Speak and sound the cell the cursor has landed in, naming the pitch cursor
-- as well when the cell holds more than one note and the answer is therefore
-- not obvious.
local function announceCell(take, pitch)
  local ppqA, ppqB = M.cellPPQ(take)
  local ps = M.pitchesInCell(take, ppqA, ppqB)
  local msg = M.cellPosText(take) .. ", " .. M.cellContentText(take)
  if pitch and #ps > 1 then msg = msg .. ", cursor " .. M.noteName(pitch) end
  M.say(msg)
  M.preview(ps)
end

-- Shared driver for the two octave actions.
function M.runOctave(dir)
  local hwnd, take, err = M.editor()
  if not take then M.say(err) return end

  local p = M.octaveStep(M.getPitch(hwnd), dir)
  if not p then M.say(dir > 0 and "top" or "bottom") return end
  M.setPitch(hwnd, p)

  local ppqA, ppqB = M.cellPPQ(take)
  local on = M.noteInCell(take, p, ppqA, ppqB) ~= nil
  M.say(M.noteName(p) .. (on and ", on" or ""))
  M.preview({ p })
end

-- Shared driver for the two column actions: next note up or down within the
-- cell the cursor is already on. Time does not move.
function M.runColumnJump(dir)
  local hwnd, take, err = M.editor()
  if not take then M.say(err) return end

  local ppqA, ppqB = M.cellPPQ(take)
  local p = M.pitchInCellToward(take, ppqA, ppqB, M.getPitch(hwnd), dir)
  if not p then
    M.say(dir > 0 and "No note above in this cell" or "No note below in this cell")
    return
  end

  M.setPitch(hwnd, p)
  M.say(M.noteName(p) .. ", on")
  M.preview({ p })
end

-- Shared driver for the two row actions: next note at the cursor's own pitch,
-- forwards or backwards. The pitch cursor does not move.
function M.runRowJump(dir)
  local hwnd, take, err = M.editor()
  if not take then M.say(err) return end

  local pitch = M.getPitch(hwnd)
  local ppqA, ppqB = M.cellPPQ(take)
  local pos = M.nextNoteStart(take, ppqA, ppqB, dir, { pitch = pitch })
  if not pos then
    M.say(("No %s %s"):format(dir > 0 and "later" or "earlier", M.noteName(pitch)))
    return
  end

  M.gotoCell(take, M.cellIndexAtPPQ(take, pos))
  announceCell(take, pitch)
end

-- Shared driver for the two any-note actions: the next note anywhere in the
-- take, moving both cursors.
function M.runNoteJump(dir)
  local hwnd, take, err = M.editor()
  if not take then M.say(err) return end

  local ppqA, ppqB = M.cellPPQ(take)
  local pos, p = M.nextNoteStart(take, ppqA, ppqB, dir, { near = M.getPitch(hwnd) })
  if not pos then
    M.say(dir > 0 and "No later notes" or "No earlier notes")
    return
  end

  M.setPitch(hwnd, p)
  M.gotoCell(take, M.cellIndexAtPPQ(take, pos))
  announceCell(take, p)
end

--------------------------------------------------------------------- edits

-- Toggle a note on/off at (current cell, pitch).
-- Returns "on", "off" or nil, plus a describing word for speech.
function M.toggleCell(take, pitch)
  local ppqA, ppqB = M.cellPPQ(take)
  local idx, sppq, eppq, chan, vel = M.noteInCell(take, pitch, ppqA, ppqB)

  reaper.Undo_BeginBlock2(0)
  local result, detail

  if idx then
    -- Cell is occupied: carve this cell out of whatever covers it.
    local startsInside = sppq >= ppqA - SLACK
    local endsInside   = eppq <= ppqB + SLACK
    if startsInside and endsInside then
      reaper.MIDI_DeleteNote(take, idx)
      detail = "removed"
    elseif startsInside then
      -- held note begins here and continues: shorten from the front
      reaper.MIDI_SetNote(take, idx, nil, nil, ppqB, nil, nil, nil, nil, true)
      detail = "shortened"
    elseif endsInside then
      -- held note ends here: shorten from the back
      reaper.MIDI_SetNote(take, idx, nil, nil, nil, ppqA, nil, nil, nil, true)
      detail = "shortened"
    else
      -- cell sits mid-way through a held note: split it in two
      reaper.MIDI_SetNote(take, idx, nil, nil, nil, ppqA, nil, nil, nil, true)
      reaper.MIDI_InsertNote(take, false, false, ppqB, eppq, chan, pitch, vel, true)
      detail = "split"
    end
    result = "off"
  else
    local v = math.floor(M.getNum("vel", 96))
    local c = math.floor(M.getNum("chan", 0))
    if M.isHold() then
      -- Join with neighbours of the same pitch so runs of adjacent cells
      -- become one sustained note rather than repeated attacks.
      local pi, _, _   = M.noteEndingAt(take, pitch, ppqA)
      local ni, nsppq, neppq = M.noteStartingAt(take, pitch, ppqB)
      if pi and ni then
        reaper.MIDI_SetNote(take, pi, nil, nil, nil, neppq, nil, nil, nil, true)
        reaper.MIDI_DeleteNote(take, ni)
        detail = "joined"
      elseif pi then
        reaper.MIDI_SetNote(take, pi, nil, nil, nil, ppqB, nil, nil, nil, true)
        detail = "extended"
      elseif ni then
        reaper.MIDI_SetNote(take, ni, nil, nil, ppqA, nil, nil, nil, nil, true)
        detail = "extended"
      else
        reaper.MIDI_InsertNote(take, false, false, ppqA, ppqB, c, pitch, v, true)
        detail = "added"
      end
    else
      reaper.MIDI_InsertNote(take, false, false, ppqA, ppqB, c, pitch, v, true)
      detail = "added"
    end
    result = "on"
  end

  reaper.MIDI_Sort(take)
  reaper.Undo_EndBlock2(0, "MIDI Grid: toggle " .. M.noteName(pitch), -1)
  return result, detail
end

------------------------------------------------------------------ playback

-- Start and end of the bar containing time t, plus the 1-based bar number.
function M.barBounds(t)
  local _, measures = reaper.TimeMap2_timeToBeats(0, t)
  return reaper.TimeMap2_beatsToTime(0, 0, measures),
         reaper.TimeMap2_beatsToTime(0, 0, measures + 1),
         measures + 1
end

--[[
  Play from the top of the bar the cursor is in, without losing your place.

  The edit cursor doubles as the grid cursor, so it is moved to the bar line
  only long enough to start playback and then put straight back. Restoring it
  passes seekplay=false so the restore cannot drag playback along with it.

  Playing from the bar line rather than the cursor is what makes fine
  subdivisions checkable: you hear the note in relation to the downbeat,
  which is the thing you are actually trying to judge.
]]
function M.playFromBar(stopAtBarEnd)
  local here = reaper.GetCursorPosition()
  local barPos, barEnd, barNum = M.barBounds(here)

  reaper.PreventUIRefresh(1)
  reaper.SetEditCurPos(barPos, false, true)
  -- GetPlayState bit 0 is "playing"; avoid bitwise ops for portability.
  if (reaper.GetPlayState() % 2) == 0 then
    reaper.CSurf_OnPlay()
  end
  reaper.SetEditCurPos(here, false, false)
  reaper.PreventUIRefresh(-1)

  if stopAtBarEnd then
    -- The daemon watches for this and stops transport, because an action
    -- script must never stay alive to wait for it.
    M.setTemp("stopat", barEnd)
    -- Grace period: play state takes a moment to report as playing, and
    -- without this the daemon would see "not playing" and cancel instantly.
    M.setTemp("stoparm", reaper.time_precise() + 0.5)
    M.ensureDaemon()
  else
    M.setTemp("stopat", "")
  end

  return barNum
end

--[[
  Loop the cursor's bar.

  Where the play-once action stops by polling -- and so can only be as precise
  as its polling interval -- this hands the boundary to REAPER's audio engine
  via the loop points, which is sample accurate. The next bar's downbeat can
  never leak in, at any tempo or grid size.

  The trade is that it repeats until you stop it with Space, rather than
  stopping itself. For checking placement that is arguably better: leave it
  looping and edit while it plays.

  Loop range and repeat state are saved and restored by the daemon once
  transport stops, so this does not quietly rearrange the project.
]]
function M.loopBar()
  local here = reaper.GetCursorPosition()
  local barPos, barEnd, barNum = M.barBounds(here)

  local s, e = reaper.GetSet_LoopTimeRange(false, true, 0, 0, false)
  M.setTemp("savedloop", ("%.17g,%.17g"):format(s, e))
  M.setTemp("savedrep", reaper.GetSetRepeat(-1))
  M.setTemp("stoparm", reaper.time_precise() + 0.5)
  M.setTemp("stopat", "") -- cancel any pending play-once stop

  reaper.PreventUIRefresh(1)
  reaper.GetSet_LoopTimeRange(true, true, barPos, barEnd, false)
  reaper.GetSetRepeat(1)
  reaper.SetEditCurPos(barPos, false, true)
  if (reaper.GetPlayState() % 2) == 0 then
    reaper.CSurf_OnPlay()
  end
  reaper.SetEditCurPos(here, false, false)
  reaper.PreventUIRefresh(-1)

  M.ensureDaemon()
  return barNum
end

---------------------------------------------------------------- time shift

--[[
  Move every note in the take by whole grid cells.

  Because the entire take moves together, notes cannot collide with each
  other -- the only thing at stake is the item's boundaries. Notes pushed
  outside them are not deleted, they simply stop sounding, and shifting back
  the other way restores them. The safe variant still refuses, because
  silently silencing part of a clip is exactly the kind of thing you want to
  be told about rather than discover later.

  Positions are converted through QN rather than offset in ticks, so a shift
  stays musically correct across tempo changes.

  Returns moved, outside. moved is nil when the shift was refused.
]]
function M.shiftAllNotes(take, cells, force)
  local _, notecnt = reaper.MIDI_CountEvts(take)
  if notecnt == 0 then return 0, 0 end

  local g = M.gridQN(take)
  local item = reaper.GetMediaItemTake_Item(take)
  local itemPos = reaper.GetMediaItemInfo_Value(item, "D_POSITION")
  local itemLen = reaper.GetMediaItemInfo_Value(item, "D_LENGTH")
  local loPPQ = reaper.MIDI_GetPPQPosFromProjTime(take, itemPos)
  local hiPPQ = reaper.MIDI_GetPPQPosFromProjTime(take, itemPos + itemLen)

  local moved, outside = {}, 0
  for i = 0, notecnt - 1 do
    local ok, _, _, s, e = reaper.MIDI_GetNote(take, i)
    if ok then
      local ns = reaper.MIDI_GetPPQPosFromProjQN(take,
        reaper.MIDI_GetProjQNFromPPQPos(take, s) + cells * g)
      local ne = reaper.MIDI_GetPPQPosFromProjQN(take,
        reaper.MIDI_GetProjQNFromPPQPos(take, e) + cells * g)
      moved[i] = { ns, ne }
      if ns < loPPQ - SLACK or ne > hiPPQ + SLACK then outside = outside + 1 end
    end
  end

  if outside > 0 and not force then return nil, outside end

  reaper.Undo_BeginBlock2(0)
  for i = 0, notecnt - 1 do
    local np = moved[i]
    if np then
      reaper.MIDI_SetNote(take, i, nil, nil, np[1], np[2], nil, nil, nil, true)
    end
  end
  reaper.MIDI_Sort(take)
  reaper.Undo_EndBlock2(0, "MIDI Grid: shift notes", -1)

  return notecnt, outside
end

-- Shared driver for the four shift actions: does the work and the speech.
function M.runShift(cells, force)
  local hwnd, take, err = M.editor()
  if not take then M.say(err) return end

  local moved, outside = M.shiftAllNotes(take, cells, force)
  local dir = cells < 0 and "left" or "right"

  if moved == nil then
    M.say(("Not shifted %s, %d %s would fall outside the item. Add Alt to force.")
      :format(dir, outside, outside == 1 and "note" or "notes"))
  elseif moved == 0 then
    M.say("No notes to shift")
  elseif outside > 0 then
    M.say(("Shifted %s, %d %s now outside the item and silent")
      :format(dir, outside, outside == 1 and "note" or "notes"))
  else
    M.say(("Shifted %s, %d %s"):format(dir, moved, moved == 1 and "note" or "notes"))
  end
end

--------------------------------------------------------------- note length

--[[
  Grow or shrink the note under the cursor by whole grid cells.

  This is how you sustain notes that already exist. It is deliberately
  independent of hold mode -- hold mode governs how *new* notes join as you
  enter them, whereas this edits an existing note's length in place, so it
  preserves velocity, channel and note identity. Toggling a note off and on
  again to make it join would silently reset its velocity to the default.

  Extending swallows any same-pitch notes it runs into, absorbing their tail
  if they reach further than the new end, so growing a note across repeated
  notes fuses the run rather than producing overlaps.
]]
function M.resizeNote(take, pitch, cells)
  local ppqA, ppqB = M.cellPPQ(take)
  local idx, sppq, eppq = M.noteInCell(take, pitch, ppqA, ppqB)
  if not idx then return nil end

  local g = M.gridQN(take)
  local startQN = reaper.MIDI_GetProjQNFromPPQPos(take, sppq)
  local endQN   = reaper.MIDI_GetProjQNFromPPQPos(take, eppq)

  local newEndQN = endQN + cells * g
  local clamped = false
  if newEndQN < startQN + g - 1e-9 then
    newEndQN = startQN + g -- never shrink below a single cell
    clamped = true
  end
  local newEnd = reaper.MIDI_GetPPQPosFromProjQN(take, newEndQN)

  reaper.Undo_BeginBlock2(0)

  local absorbed = 0
  if cells > 0 then
    -- Collect first, delete descending: deleting shifts later indices.
    local victims = {}
    local _, notecnt = reaper.MIDI_CountEvts(take)
    for i = 0, notecnt - 1 do
      local ok, _, _, s, e, _, p = reaper.MIDI_GetNote(take, i)
      if ok and p == pitch and i ~= idx and s > sppq + SLACK and s < newEnd - SLACK then
        victims[#victims + 1] = i
        if e > newEnd then newEnd = e end
      end
    end
    table.sort(victims, function(a, b) return a > b end)
    for _, i in ipairs(victims) do
      reaper.MIDI_DeleteNote(take, i)
      if i < idx then idx = idx - 1 end
      absorbed = absorbed + 1
    end
  end

  reaper.MIDI_SetNote(take, idx, nil, nil, nil, newEnd, nil, nil, nil, true)
  reaper.MIDI_Sort(take)
  reaper.Undo_EndBlock2(0, "MIDI Grid: resize note", -1)

  local lenCells = (reaper.MIDI_GetProjQNFromPPQPos(take, newEnd) - startQN) / g
  return math.floor(lenCells + 0.5), absorbed, clamped
end

-- Fuse every contiguous same-pitch note touching the one under the cursor
-- into a single sustained note. Returns how many notes were merged.
function M.joinRun(take, pitch)
  local ppqA, ppqB = M.cellPPQ(take)
  local idx, sppq, eppq = M.noteInCell(take, pitch, ppqA, ppqB)
  if not idx then return nil end

  local minS, maxE = sppq, eppq
  local victims = {}
  local seen = { [idx] = true }

  while true do
    local i, s = M.noteEndingAt(take, pitch, minS)
    if not i or seen[i] then break end
    seen[i] = true ; victims[#victims + 1] = i ; minS = s
  end
  while true do
    local i, _, e = M.noteStartingAt(take, pitch, maxE)
    if not i or seen[i] then break end
    seen[i] = true ; victims[#victims + 1] = i ; maxE = e
  end

  if #victims == 0 then return 0 end

  reaper.Undo_BeginBlock2(0)
  table.sort(victims, function(a, b) return a > b end)
  for _, i in ipairs(victims) do reaper.MIDI_DeleteNote(take, i) end
  -- Indices shifted; re-find the survivor by its unchanged start position.
  local keep = M.noteStartingAt(take, pitch, sppq)
  if keep then
    reaper.MIDI_SetNote(take, keep, nil, nil, minS, maxE, nil, nil, nil, true)
  end
  reaper.MIDI_Sort(take)
  reaper.Undo_EndBlock2(0, "MIDI Grid: join notes", -1)

  return #victims + 1
end

--------------------------------------------------------------------- chords

-- Stack `count` diatonic chord tones on `pitch`, skipping a scale degree
-- between each -- so in a major scale, degree 1 gives a major triad and
-- degree 2 a minor one, exactly as harmony expects. In the chromatic scale
-- this degenerates to stacked whole tones, which is arguably useless but at
-- least predictable.
function M.chordPitches(pitch, count)
  local ps = { pitch }
  local p = pitch
  for _ = 2, count do
    local a = M.scaleStep(p, 1); if not a then return nil end
    local b = M.scaleStep(a, 1); if not b then return nil end
    p = b
    ps[#ps + 1] = p
  end
  return ps
end

-- Toggle a whole chord in the current cell. If every tone is already
-- present the chord is removed; otherwise the missing tones are filled in.
-- Delegates to toggleCell so hold mode, splitting and trimming all behave
-- identically to single notes.
function M.toggleChord(take, pitches)
  local ppqA, ppqB = M.cellPPQ(take)
  local allPresent = true
  for _, p in ipairs(pitches) do
    if not M.noteInCell(take, p, ppqA, ppqB) then allPresent = false break end
  end

  reaper.Undo_BeginBlock2(0)
  local changed = {}
  for _, p in ipairs(pitches) do
    local here = M.noteInCell(take, p, ppqA, ppqB) ~= nil
    if allPresent or not here then
      M.toggleCell(take, p)
      changed[#changed + 1] = p
    end
  end
  reaper.Undo_EndBlock2(0, "MIDI Grid: toggle chord", -1)
  return (allPresent and "off" or "on"), changed
end

------------------------------------------------------------------ velocity

-- Adjust velocity by delta. If a note sits at the cursor cell and pitch, its
-- velocity changes; otherwise the default for newly inserted notes does.
-- Returns "note" or "default", and the resulting value.
function M.nudgeVelocity(take, pitch, delta)
  local ppqA, ppqB = M.cellPPQ(take)
  local idx, _, _, _, vel = M.noteInCell(take, pitch, ppqA, ppqB)
  if idx then
    local v = math.max(1, math.min(127, math.floor(vel + delta)))
    reaper.Undo_BeginBlock2(0)
    reaper.MIDI_SetNote(take, idx, nil, nil, nil, nil, nil, nil, v, true)
    reaper.MIDI_Sort(take)
    reaper.Undo_EndBlock2(0, "MIDI Grid: set velocity", -1)
    return "note", v
  end
  local v = math.max(1, math.min(127, math.floor(M.getNum("vel", 96) + delta)))
  M.set("vel", v)
  return "default", v
end

------------------------------------------------------------ preview routing

--[[
  Preview notes leave through StuffMIDIMessage, i.e. the virtual MIDI
  keyboard, and Reaper feeds that to whatever tracks happen to be armed and
  monitoring. That is usually NOT the track whose item you are editing, so
  the grid would sound your notes through some unrelated instrument.

  Grid mode therefore borrows the record routing: the edited take's track is
  armed and monitoring with MIDI input, every other armed track is stood
  down so it cannot answer as well, and the previous state of every track we
  touched is remembered so it can be handed straight back.

  The borrow is undone when grid mode is switched off, when the MIDI editor
  closes, and on Reaper exit -- all three by the daemon, in the same way it
  restores the loop/repeat state the loop-bar action borrows.
]]

-- "All MIDI inputs, all channels": 4096 | (device << 5) | channel, with
-- device 63 meaning all. Anything narrower may exclude the virtual keyboard.
local ALL_MIDI_IN = 4096 + 63 * 32

local function trackByGUID(guid)
  for i = 0, reaper.CountTracks(0) - 1 do
    local tr = reaper.GetTrack(0, i)
    if reaper.GetTrackGUID(tr) == guid then return tr end
  end
end

local function armState(tr)
  return ("%s,%d,%d,%d"):format(
    reaper.GetTrackGUID(tr),
    reaper.GetMediaTrackInfo_Value(tr, "I_RECARM"),
    reaper.GetMediaTrackInfo_Value(tr, "I_RECMON"),
    reaper.GetMediaTrackInfo_Value(tr, "I_RECINPUT"))
end

-- Hand back every track's arm/monitor/input exactly as we found it.
function M.restoreRouting()
  local saved = M.getTemp("savedarm", "")
  M.setTemp("savedarm", "")
  M.setTemp("routed", "")
  if saved == "" then return false end
  for guid, arm, mon, inp in saved:gmatch("({[^}]*}),(%-?%d+),(%-?%d+),(%-?%d+)") do
    local tr = trackByGUID(guid)
    if tr then
      reaper.SetMediaTrackInfo_Value(tr, "I_RECARM",   tonumber(arm))
      reaper.SetMediaTrackInfo_Value(tr, "I_RECMON",   tonumber(mon))
      reaper.SetMediaTrackInfo_Value(tr, "I_RECINPUT", tonumber(inp))
    end
  end
  return true
end

-- Point preview at the track this take lives on. Cheap to call on every
-- keypress: it only touches the project when the target has changed.
function M.routePreview(take)
  if not take then return end
  local tr = reaper.GetMediaItemTake_Track(take)
  if not tr then return end
  local guid = reaper.GetTrackGUID(tr)
  if M.getTemp("routed", "") == guid then return end

  -- Give the previously borrowed track back before borrowing another.
  M.restoreRouting()

  local saved = {}
  for i = 0, reaper.CountTracks(0) - 1 do
    local t = reaper.GetTrack(0, i)
    local armed = reaper.GetMediaTrackInfo_Value(t, "I_RECARM") == 1
    if t == tr or armed then
      saved[#saved + 1] = armState(t)
      if t ~= tr then reaper.SetMediaTrackInfo_Value(t, "I_RECARM", 0) end
    end
  end

  reaper.SetMediaTrackInfo_Value(tr, "I_RECINPUT", ALL_MIDI_IN)
  reaper.SetMediaTrackInfo_Value(tr, "I_RECARM", 1)
  reaper.SetMediaTrackInfo_Value(tr, "I_RECMON", 1)

  M.setTemp("savedarm", table.concat(saved, ";"))
  M.setTemp("routed", guid)
end

------------------------------------------------------------------ audition

--[[
  Preview is handled by a separate always-running daemon script rather than
  by deferring here. The action scripts must exit immediately: if one is
  still alive when you press the same key again, Reaper puts up its
  "script is already running" prompt, which makes fast key repeat impossible.

  So preview() only posts a request and returns. The daemon owns all
  note-on/note-off timing.
]]
function M.preview(pitches, dur)
  if not pitches or #pitches == 0 then return end
  -- Sound through the instrument of the track being edited, not through
  -- whatever else happened to be armed.
  M.routePreview(select(2, M.editor()))
  M.setTemp("pitches", table.concat(pitches, ","))
  M.setTemp("dur", dur or M.getNum("previewdur", 0.4))
  M.setTemp("seq", (tonumber(M.getTemp("seq", "0")) or 0) + 1)
  M.ensureDaemon()
end

-- Start the preview daemon if it is not currently alive. The daemon stamps a
-- wall-clock heartbeat every cycle; anything older than a few seconds means
-- it is gone (Reaper restarted, script terminated) and we relaunch it.
function M.ensureDaemon()
  local hb = tonumber(M.getTemp("hb", "0")) or 0
  if os.time() - hb <= 3 then return end
  local id = reaper.NamedCommandLookup("_RSmidigrid_daemon")
  if id and id ~= 0 then reaper.Main_OnCommand(id, 0) end
end

--------------------------------------------------------------------- speech

-- "bar 3 beat 2" style position for the current cell.
function M.cellPosText(take)
  local a = select(1, M.cell(take))
  local t = reaper.TimeMap2_QNToTime(0, a)
  return reaper.format_timestr_pos(t, "", 2)
end

-- Describe the cell contents for speech, e.g. "C5, E5" or "empty".
function M.cellContentText(take)
  local ppqA, ppqB = M.cellPPQ(take)
  local ps = M.pitchesInCell(take, ppqA, ppqB)
  if #ps == 0 then return "empty" end
  local names = {}
  for _, p in ipairs(ps) do names[#names + 1] = M.noteName(p) end
  return table.concat(names, ", ")
end

return M