init.lua

-- ===========================================================================
-- Caps Layout Switcher — Hammerspoon config
-- ===========================================================================
-- Per-layout hotkeys for switching macOS keyboard layouts, plus a CapsLock
-- "tap" that toggles between the two most recent layouts.
--
--   • Tap CapsLock            -> toggle between the two most recent layouts
--   • Hold CapsLock + <letter> -> jump straight to a specific layout
--   • Hold CapsLock + 0        -> show & copy the current layout's source ID
--
-- CapsLock is physically remapped to F18 (via hidutil + a LaunchAgent) so it
-- behaves like a normal modifier with no "caps toggle". While CapsLock is held,
-- the modal below is active. CapsLock's normal ALL-CAPS function is disabled.
--
-- >>> CONFIGURE ME <<<  Edit the `layouts` table below with YOUR layouts.
-- Find your source IDs with `tools/list-input-sources` or by holding CapsLock+0
-- after the current layout is selected. See the README for details.
-- ===========================================================================

-- letter -> { human-readable name, sourceID }.  Pick mnemonic letters.
local layouts = {
  ["e"] = { "English (ABC)",        "com.apple.keylayout.ABC" },
  ["r"] = { "Russian (PC)",         "com.apple.keylayout.RussianWin" },
  ["k"] = { "Korean (2-Set)",       "com.apple.inputmethod.Korean.2SetKorean" },
  ["c"] = { "Chinese (Pinyin)",     "com.apple.inputmethod.SCIM.ITABC" },
  ["a"] = { "Armenian (HM QWERTY)", "com.apple.keylayout.Armenian-HMQWERTY" },
  ["d"] = { "Austrian (German)",    "com.apple.keylayout.Austrian" },
}

local function isIME(id) return id and id:find("inputmethod") ~= nil end

local function setTwice(id)
  hs.keycodes.currentSourceID(id)
  hs.timer.doAfter(0.05, function() hs.keycodes.currentSourceID(id) end)
end

-- Key subtlety: leaving an IME (Korean/Chinese/etc.) for a plain keyboard
-- layout. macOS updates the menu-bar icon, but the IME's input context in the
-- focused app is NOT torn down until a *different* source is selected. So we
-- first bounce through an intermediate layout (which breaks the IME), then set
-- the real target. For ordinary switches we just set the source twice (guards
-- against a race where the first set doesn't "take").
local function selectSource(targetID)
  local cur = hs.keycodes.currentSourceID()
  if isIME(cur) and not isIME(targetID) then
    -- intermediate must differ from the target and be an ENABLED layout
    local intermediate = (targetID == "com.apple.keylayout.ABC")
      and "com.apple.keylayout.Austrian" or "com.apple.keylayout.ABC"
    hs.keycodes.currentSourceID(intermediate)
    hs.timer.doAfter(0.10, function() setTwice(targetID) end)
  else
    setTwice(targetID)
  end
end

-- reverse index id -> name (for the on-screen labels)
local nameByID = {}
for _, def in pairs(layouts) do nameByID[def[2]] = def[1] end

-- ===== "Two most recent layouts" history =====
-- curLayout/prevLayout are updated ONLY for the final target layout, never for
-- the intermediate IME "bounce". We set a `programmatic` flag while switching
-- so the watcher below ignores those transient changes.
local curLayout = hs.keycodes.currentSourceID()
local prevLayout = nil
local programmatic = false

local function recordTarget(targetID)
  if targetID ~= curLayout then
    prevLayout = curLayout
    curLayout = targetID
  end
end

-- single entry point: remember target + set source + show a label
local function activate(targetID)
  if not targetID then return end
  programmatic = true
  recordTarget(targetID)
  selectSource(targetID)
  hs.timer.doAfter(0.3, function() programmatic = false end)  -- wait out the bounce
  hs.alert.closeAll()
  hs.alert.show(nameByID[targetID] or targetID, 0.6)
end

-- also track manual switches (via the menu bar), but ignore programmatic bounces
hs.keycodes.inputSourceChanged(function()
  if programmatic then return end
  local now = hs.keycodes.currentSourceID()
  if now ~= curLayout then
    prevLayout = curLayout
    curLayout = now
  end
end)

-- ===== CapsLock (=F18): hold + letter, or a short tap =====
-- While CapsLock is held the modal is active and letters switch layout.
-- A short tap with no letter toggles to the previous layout.
local capsModal = hs.hotkey.modal.new()
local tapCandidate = false      -- was this press a potential "tap" (no letter)?

for key, def in pairs(layouts) do
  local sourceID = def[2]
  capsModal:bind({}, key, function()
    tapCandidate = false        -- a letter was pressed => hold-combo, not a tap
    activate(sourceID)
  end)
end

-- CapsLock+0 — show the current layout's source ID (handy when adding layouts)
capsModal:bind({}, "0", function()
  tapCandidate = false
  local id = hs.keycodes.currentSourceID()
  hs.pasteboard.setContents(id)        -- also copy it to the clipboard
  hs.alert.show("Current source ID:\n" .. id .. "\n(copied to clipboard)", 3)
end)

-- capsWatcher is GLOBAL (no `local`), otherwise GC would kill the eventtap.
local F18 = hs.keycodes.map["f18"]
local TAP_MAX = 0.4                     -- max seconds for a press to count as a "tap"
local capsDown = false
local pressTime = 0

capsWatcher = hs.eventtap.new(
  { hs.eventtap.event.types.keyDown, hs.eventtap.event.types.keyUp },
  function(e)
    local isDown = (e:getType() == hs.eventtap.event.types.keyDown)
    if e:getKeyCode() == F18 then
      if isDown then
        capsDown = true
        tapCandidate = true
        pressTime = hs.timer.secondsSinceEpoch()
        capsModal:enter()
      else
        capsDown = false
        capsModal:exit()
        -- short press with no letter => tap => go to the previous layout
        if tapCandidate and (hs.timer.secondsSinceEpoch() - pressTime) < TAP_MAX then
          activate(prevLayout)
        end
      end
      return true            -- swallow the F18 key itself
    else
      if capsDown and isDown then tapCandidate = false end  -- any other key => not a tap
      return false
    end
  end)
capsWatcher:start()

hs.alert.show("Caps Layout Switcher loaded", 1.2)