Practising lua by making a calendar thing.

calendar.lua

#!/usr/bin/env lua

function february(year)
	if year == nil or year == "context" then year = os.date("%Y"); end
	if year%4==0 and (year%100~=0 or year%400==0) then
		return 29
	else
		return 28
	end
end

-- month is 1 .. 12, where January = 1 and December = 12
function weekday(year, month, day)
	local h = 0
	month = month or 1
	day = day or 1
	if month < 3 then
		month = month + 12
		year = year - 1
	end
	h = day + math.floor((month + 1)*26/10)
	h = h + year + math.floor(year / 4)
	h = h + 6*math.floor(year / 100) + math.floor(year / 400)
	h = h % 7
	return (h + 5) % 7 + 1	
end

function get_months(year, month, day)
	day = day
	local padding = ""
	local result = {
		title = "",
		week = "",
		days = "",
		lines = {}
	}
	
	for i = 1,7 do
		result.week = result.week .. string.sub(days[i], 1, 2) .. " "
	end
	
	result.week = string.sub(result.week,1,# result.week - 1)
	
	for i = 2,((# result.week - # (months[month][1] .. " " .. year))/2) do
		padding = padding .. " "
	end
	
	result.title = "<" .. padding .. result.title .. months[month][1] .. " " .. year
	while (# result.title) < (# result.week)-1 do
		result.title = result.title .. " "
	end
	result.title = result.title .. ">"
	
	if day ~= nil then
		result.title = string.gsub(result.title, "<", "{")
		result.title = string.gsub(result.title, ">", "}")
	end
	
	for i = 1,months[month][2] do
		if day ~= nil and i == day+0 then
			result.days = result.days .. "## "
		else
			result.days = result.days..string.format("%2d", i) .. " "
		end
	end
	
	for i = 1,weekday(year, month, 1)-1 do
		result.days = "   " .. result.days
	end
	
	local i = 1
	
	while i < (# result.days) do
		local j = i + (# result.week)
		table.insert(result.lines, string.sub(result.days, i, j))
		i = j + 1
	end
	
	for i = 1,# result.lines do
		result.lines[i] = string.sub(result.lines[i],1,(# result.lines[i])-1)
	end
	
	while (# result.lines[# result.lines]) < (# result.week) do
		result.lines[# result.lines] = result.lines[# result.lines] .. " "
	end
	
	while # result.lines < 6 do
		local line = ""
		while (# line) < (# result.week) do
			line = line .. " "
		end
		table.insert(result.lines, line)
	end
	
	return result
end

-- year = four digit year (or more digits if you're planning a trip far into the future)
-- month = current month, 1 to 12, January = 1 and December = 12
-- day = current day, 1 to 28, 29, 30 or 31
-- rows
-- cols
-- range = {1, 12} for full year, {1, 3} for Jan-Mar, etc. 0 = last year's december, 13 = next year's January.
function print_calendar(year, month, day, rows, cols, range)
	local calendar = {}
	for i = range[1],range[2] do
		if i == month+0 and year == os.date("%Y") then
			table.insert(calendar, get_months(year, i, day))	
		else
			if i == 0 then
				table.insert(calendar, get_months(year-1, i+12))		
			elseif i == 13 then
				table.insert(calendar, get_months(year+1, i-12))		
			else
				table.insert(calendar, get_months(year, i))
			end
		end
	end

	if arg[1] ~= nil then
		local title = year .. " Calendar"
		local line = ""
		while # line < ((# cols + 1)*(#calendar[1].week) + (# tab)*(# cols) - (# title))/2 do
			line = line .. " "
		end
		line = line .. title
		while # line < (# cols + 1)*(#calendar[1].week) + (# tab)*(# cols) do
			line = line .. " "
		end
		print(string.char(27) .. "[7m" .. line .. string.char(27) .. "[0m")
	end
	
	for a,b in pairs(rows) do
		if cols[1] ~= 0 then
			for h,i in pairs(cols) do
				calendar[b].title = calendar[b].title .. tab .. calendar[b+i].title
				calendar[b].week = calendar[b].week .. tab .. calendar[b+i].week
				for c = 1,6 do
					calendar[b].lines[c] = calendar[b].lines[c] .. tab .. calendar[b+i].lines[c]
				end
			end
		end
		calendar[b].title = string.gsub(calendar[b].title, "<", string.char(27) .. "[7m" .. string.char(27) .. "[2m" .. " ")
		calendar[b].title = string.gsub(calendar[b].title, ">", " " .. string.char(27) .. "[0m")
		calendar[b].title = string.gsub(calendar[b].title, "{", string.char(27) .. "[7m" .. " ", 1)
		calendar[b].title = string.gsub(calendar[b].title, "}", " " .. string.char(27) .. "[0m", 1)
		calendar[b].week = string.gsub(calendar[b].week, "Mo", string.char(27) .. "[4m" .. "Mo")
		calendar[b].week = string.gsub(calendar[b].week, "Su", "Su" .. string.char(27) .. "[0m")
		print(calendar[b].title)
		print(calendar[b].week)
		for key,value in pairs(calendar[b].lines) do
			value = string.gsub(value, "#", string.char(27) .. "[7m" .. string.format("%2d", day+0), 1)
			value = string.gsub(value, "#", string.char(27) .. "[0m", 1)
			print(value)
		end
	end
end

days = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" }
months = {
	{"January",31},
	{"February",february(arg[1] or os.date("%Y"))},
	{"March",31},
	{"April",30},
	{"May",31},
	{"June",30},
	{"July",31},
	{"August",31},
	{"September",30},
	{"October",31},
	{"November",30},
	{"December",31},
}
tab = "    "
local help = false
if arg[1] == nil then
	help = true
end
if arg[2] ~= nil then
	if arg[2] ~= "wide" then
		tab = ""
		while # tab < arg[2]+0 do
			tab = tab .. " "
		end	
	elseif arg[3] ~= nil then
		tab = ""
		while # tab < arg[3]+0 do
			tab = tab .. " "
		end
	end
end

if arg[1] == "context" then
	-- 3 month calendar view
	print_calendar(os.date("%Y"), os.date("%m"), os.date("%d"), {1}, {1,2}, {os.date("%m") - 1, os.date("%m") + 1})
elseif arg[2] == "wide" then
	-- 1 month calendar view for current year
	print_calendar(arg[1] or os.date("%Y"), os.date("%m"), os.date("%d"), {1, 5, 9}, {1, 2, 3}, {1, 12})
elseif arg[1] ~= nil then
	-- 12 month calendar view for given year
	print_calendar(arg[1] or os.date("%Y"), os.date("%m"), os.date("%d"), {1, 4, 7, 10}, {1, 2}, {1, 12})
else
	-- 1 month calendar view for current year
	print_calendar(os.date("%Y"), os.date("%m"), os.date("%d"), {1}, {0}, {os.date("%m"), os.date("%m")})
end

if help == true then
	local usage = "" .. arg[-1] .. " " .. arg[0] .. " "
	print("Usage:")
	print(usage, "\t# Shows calendar for this month.")
	print(usage .. "context", "# Shows 3 month calendar.")
	print(usage .. os.date("%Y"), "\t# Show calendar for given year.")
	print(usage .. os.date("%Y") .. " 1", "\t# Above but with 1 space between months.")
end