Barrier and Karabiner-Elements integration using Hammerspoon

barrier_karabiner.lua

knu = require("knu") -- https://github.com/knu/hs-knu

-- Switch between Karabiner-Elements profiles as Barrier enters a different host
do
  -- Configure Barrier (https://github.com/debauchee/barrier) to output log to ~/Library/Logs/barrier.log
  local logFile = os.getenv("HOME") .. "/Library/Logs/barrier.log"
  local lineNo = 1
  local host = nil
  local defaultProfile = "Default"
  local profileForHost = function (host)
    -- Return the name of a profile suitable for host
    if host == "your-windows-host-name" then
      return "Windows"
    elseif host == "your-linux-host-name" then
      return "Linux"
    else
      -- This function is not called when switching back to this host,
      -- but it's good to fall back to the default profile. (or in
      -- case you have another Mac host)
      return defaultProfile
    end
  end
  local watcher = hs.pathwatcher.new(
    logFile,
    function (_files, flagTables)
      for _, flagTable in ipairs(flagTables) do
        if flagTable.itemCreated or flagTable.itemRemoved or flagTable.itemRenamed then
          -- itemRenamed occurs when the log file is rotated
          lineNo = 1
          break
        elseif flagTable.itemModified then
          break
        end
      end

      local f = io.popen(knu.utils.shelljoin("tail", "-n+" .. lineNo, logFile))
      local profile = nil
      for line in f:lines() do
        lineNo = lineNo + 1
        local m = line:match("%] INFO: switch from \".*\" to \"(.*)\" at ")
        if m ~= nil then
          host = m
          goto continue
        end
        if line:match("%] INFO: entering screen") ~= nil then
          profile = defaultProfile
        elseif line:match("%] INFO: leaving screen") ~= nil then
          profile = profileForHost(host)
        end
        ::continue::
      end
      f:close()
      if profile ~= nil then
        knu.keyboard.switchKarabinerProfile(profile)
      end
    end
  )

  knu.runtime.guard(watcher)
  watcher:start()
end