Hammerspoon... spoon. Binds Hyper+Key to switch to a particular app and when pressed again switches between the windows of that app (across spaces). Cycle order between windows is determined by the order of focus received, most recently first. To use: place file in .hammerspoon directory and add 'require("hyper_plus")' to 'init.lua'

hyper_plus.lua

--------------------------
-- DEFINE YOUR APP + SHORTCUT KEY COMBINATIONS
--------------------------
shortcut_key_and_app = {
  { 'f', 'Firefox'  }, -- "F" for "Browser"
  { 'e', 'Code'     }, -- "E" for "Editor"
  { 'v', 'Finder'   }, -- "V" for "Finder"
  { 't', 'iTerm2'   }, -- "T" for "Terminal"
}


--------------------------
-- GLOBAL VARIABLES
--------------------------
hyper_modifiers_keys = {'shift', 'ctrl', 'alt', 'cmd'} -- Mapped to Caps Lock in Karabiner-Elements
hyper_pressed = false
idx_to_focus_hcl = 1  -- index of the window to focus from the hyper cycle window list
-- Window filter: will keep track of all visible windows across spaces
-- sources: https://github.com/Hammerspoon/hammerspoon/issues/1460
--          https://github.com/Hammerspoon/hammerspoon/issues/1260
-- When reloading hs config, we have to go through our workspaces 
-- manually for the wf to detect the windows there 
wf = hs.window.filter.new():setCurrentSpace(nil):keepActive()


--------------------------
-- SET UP
--------------------------
registered_apps = {}
for i, app in ipairs(shortcut_key_and_app) do 
  registered_apps[app[2]] = {shortcut_key=app[1], window_focus_list={}, window_hyper_cycle_list={}}
end


--------------------------
-- HELPER FUNCTIONS
--------------------------
function deepcopy(orig)
  local orig_type = type(orig)
  local copy
  if orig_type == 'table' then
      copy = {}
      for orig_key, orig_value in next, orig, nil do
          copy[deepcopy(orig_key)] = deepcopy(orig_value)
      end
      setmetatable(copy, deepcopy(getmetatable(orig)))
  else -- number, string, boolean, etc
      copy = orig
  end
  return copy
end

function window_list_remove(window_list, id)
  for i, winfo in ipairs(window_list) do
    if winfo.id == id then 
      -- Removes element at index i and re-orders/re-indexes the list
      table.remove(window_list, i)
      return i
    end
  end
end

function window_list_add(window_list, window_info)
  window_list_remove(window_list, window_info.id)
  -- Append window to window list:
  window_list[#window_list + 1] = window_info
end

function get_index_after_remove(next_index, index_to_remove, length_list)
  if length_list == 1 then return 1 end
  local current_index = next_index + 1
  if current_index > length_list then current_index = 1 end
  if current_index > index_to_remove then
    current_index = current_index - 1
  elseif current_index == index_to_remove and current_index == length_list then
    current_index = 1
  end 
  next_index = current_index - 1
  if next_index == 0 then next_index = (length_list - 1) end
  return next_index
end


--------------------------
-- WF WINDOW WATHCER
--------------------------
function wf_callback(window_object, app_name, event_name)
  if registered_apps[app_name] ~= nil then -- check if app to which window belongs is in registered apps
    if event_name == hs.window.filter.windowFocused then
      -- Just before closing a window with focus the focus will transfer onto the previous window
      -- that had focus before. The closed window won't exists anymore (i.e. is not standard anymore).
      -- In order to keep the window_hyper_cycle_list order we should skip any further code in this block
      for i, w in pairs(registered_apps[app_name].window_focus_list) do 
        if w.window:isStandard() ~= true then return end
      end
      window_list_add(registered_apps[app_name].window_focus_list, {id=window_object:id(), window=window_object})
      if hyper_pressed ~= true then
        registered_apps[app_name].window_hyper_cycle_list = deepcopy(registered_apps[app_name].window_focus_list)
        idx_to_focus_hcl = #registered_apps[app_name].window_hyper_cycle_list - 1
      end
    elseif event_name == hs.window.filter.windowDestroyed
    or event_name == hs.window.filter.windowHidden
    or event_name == hs.window.filter.windowMinimized 
    then
      local length_list = #registered_apps[app_name].window_hyper_cycle_list
      -- Remove window from both window lists:
      window_list_remove(registered_apps[app_name].window_focus_list, window_object:id())
      index_to_remove = window_list_remove(registered_apps[app_name].window_hyper_cycle_list, window_object:id())
      -- Calculate index of window to focus on next hyper cycle iteration:
      idx_to_focus_hcl = get_index_after_remove(idx_to_focus_hcl, index_to_remove, length_list)
    end
  end
  hyper_pressed = false
end

-- Listen for following window events and execute callback when event observered
wf:subscribe(
  {hs.window.filter.windowDestroyed, hs.window.filter.windowHidden, 
  hs.window.filter.windowMinimized, hs.window.filter.windowFocused,}, 
  wf_callback
)


--------------------------
-- BINDING HYPER SHORTCUTS
--------------------------
for app_name, app_info in pairs(registered_apps) do
  hs.hotkey.bind(hyper_modifiers_keys, app_info.shortcut_key, function()
    if hs.application.get(app_name):isFrontmost() and #app_info.window_focus_list > 1
    then
      hyper_pressed = true
      -- Focus window
      app_info.window_hyper_cycle_list[idx_to_focus_hcl].window:focus()
      -- Update next index
      idx_to_focus_hcl = idx_to_focus_hcl - 1
      if idx_to_focus_hcl == 0 then idx_to_focus_hcl = #app_info.window_hyper_cycle_list end
    else
      hs.application.get(app_name):activate(true)
      -- hs.application.open(app)  -- does not work with Finder
    end
  end)
end