Simple Hammerspoon Configuration

init.lua

-- for simpler binding of keys, define the modifiers ahead of time. 
local hyper = {"cmd","alt","ctrl","shift"}
local meh = {"alt","ctrl","shift"}

-- grid size determines how the windows can be split into a grid
-- laid out evenly onto the desktop
-- grid margins defines spacing on x and y between windows and the menu 
-- bar/monitor edges 0x0 if you want no space between windows.

-- for the case where you only ever need to move a window between three
-- equally sized windows, '3x1' is sufficient grid size.
gridSize = '3x1'
gridMargins = '10x10'

-- set the dimensions. If  you need to cover two different
-- grid sizes you'll have to set them locally inside the 
-- window management functions
hs.grid.setGrid(gridSize)
hs.grid.setMargins(gridMargins)

-- setting it to false, although this is false by default. It will
-- prevent window wiggling before setting into place which is
-- annoying
hs.window.setFrameCorrectness =false

-- function to move the active window to designated coordinates 
-- based on the defined grid
function setWindow(w,h,x,y)
	if hs.window.focusedWindow() then
		local win = hs.window.frontmostWindow()
		local id = win:id()
		local screen = win:screen()
		cell = hs.grid.get(win, screen)
		cell.w = w
		cell.h = h
		cell.x = x
		cell.y = y
		hs.grid.set(win, cell, screen)
	end
end

-- 
hs.hotkey.bind(meh, "j", function()
  -- assuming you only use one gridSize, setting them specifically for
  -- each function is unnecessary. If you do want to use more, you can
  -- define it like this
	hs.grid.setGrid('3x1')
  -- setWindow function takes four arguments, w, h, x, and y. w represents
  -- width of the window according to the defined grid. In 3x1 '1' will take
  -- up 1/3 of the width of the screen. h represents height and since the grid
  -- is 1 high, 1 will take up 100% of the vertical space. x is the horizontal 
  -- axis and y the vertical axis. All movement is assuming you start from top
  -- left. 0,0 would indicate it does not move at all from top left, so it will
  -- take up the left most section of the screen. the next two will take up the
  -- second and third section of the screen. In cases with larger grids, you'd 
  -- change the numbers to match the translation you want relative to the new 
  -- grid size
	setWindow(1,1,0,0)
	hs.grid.setGrid(gridSize)
end)

hs.hotkey.bind(meh, "k", function()
	hs.grid.setGrid('3x1')
	setWindow(1,1,1,0)
	hs.grid.setGrid(gridSize)
end)

hs.hotkey.bind(meh, "l", function()
	hs.grid.setGrid('3x1')
	setWindow(1,1,2,0)
	hs.grid.setGrid(gridSize)
end)

-- directional movement of focus between windows

-- I use hyper hjkl to move between windows relative to their
-- position on screen. Note that this is buggy and there are
-- cases where it won't find any eligble windows or a window
-- will stop being eligible. I wouldn't use this to replace
-- other cmd - tab alternatives you may have
hs.hotkey.bind(hyper, "h", function()
  -- this will focus the next eligble window to the west of the active window.
	hs.window.focusedWindow().focusWindowWest()
  -- this will show an alert of the new window you focus.
  -- This is entirely optional and you can delete this if
  -- you don't like it
	hs.alert(hs.window.focusedWindow():title())
end)

hs.hotkey.bind(hyper, "j", function()
	hs.window.focusedWindow().focusWindowSouth()
	hs.alert(hs.window.focusedWindow():title())
end)

hs.hotkey.bind(hyper, "k", function()
	hs.window.focusedWindow().focusWindowNorth()
	hs.alert(hs.window.focusedWindow():title())
end)
hs.hotkey.bind(hyper, "l", function()

	hs.window.focusedWindow().focusWindowEast()
	hs.alert(hs.window.focusedWindow():title())
end)


-- window swap alternative to command tab
-- this creates a list of open applications that you 
-- can fuzzy search type to swap between applications
-- This emulates functionality of something like rofi
-- on linux or contexts (https://contexts.co/) on MacOS

hs.hotkey.bind(hyper, 'space', function() 

	local switcher = hs.chooser.new(function(choice) 
		if not choice then return end
		hs.application.launchOrFocusByBundleID(choice.id)
	end)

	local windows = hs.fnutils.map(hs.window.filter.new():getWindows(), function(win)


		if win ~= hs.window.focusedWindow() then
			return {
				text = win:title(),
				subText = win:application():title(),
				image = hs.image.imageFromAppBundle(win:application():bundleID()),
				id = win:application():bundleID()
			}
		end
	end)


	switcher
		:query(nil)
		:placeholderText('Switch to...')
		:width(22)
		:searchSubText(true)
		:choices(windows)
		:show()
	end)

I'd suggest looking at the hammerspoon docs if you need more information on what is going on in any fo the api functions used here.

https://www.hammerspoon.org/docs/index.html