-- see if the file exists
local function file_exists(file)
	local f = io.open(file, "rb")
	if f then
		f:close()
	end
	return f ~= nil
end

-- get all lines from a file, returns an empty
-- list/table if the file does not exist
local function lines_from(file)
	if not file_exists(file) then
		return {}
	end
	local lines = {}
	for line in io.lines(file) do
		lines[#lines + 1] = line
	end
	return lines
end

-- tests the functions above
local file = "input"
local lines = lines_from(file)

-- Solution Starts here

local target = "XMAS"

---@diagnostic disable-next-line: redefined-local
local function count_xmas_at_index(lines, line_idx, char_idx)
	local count = 0

	local line = lines[line_idx]

	local test_words = {}
	-- Forward
	test_words[#test_words + 1] = line:sub(char_idx, char_idx + 3)
	-- Backward
	test_words[#test_words + 1] = line:sub(char_idx - 3, char_idx):reverse()

	local up_right = ""
	local down_right = ""
	local up_left = ""
	local down_left = ""
	local up = ""
	local down = ""
	for offset = 0, 3 do
		local up_idx = line_idx - offset
		local down_idx = line_idx + offset
		local right_idx = char_idx + offset
		local left_idx = char_idx - offset

		if up_idx >= 1 then
			up = up .. lines[up_idx]:sub(char_idx, char_idx)

			up_right = up_right .. lines[up_idx]:sub(right_idx, right_idx)
			up_left = up_left .. lines[up_idx]:sub(left_idx, left_idx)
		end

		if down_idx <= #lines then
			down = down .. lines[down_idx]:sub(char_idx, char_idx)

			down_right = down_right .. lines[down_idx]:sub(right_idx, right_idx)
			down_left = down_left .. lines[down_idx]:sub(left_idx, left_idx)
		end
	end
	test_words[#test_words + 1] = up_right
	test_words[#test_words + 1] = down_right
	test_words[#test_words + 1] = up_left
	test_words[#test_words + 1] = down_left
	test_words[#test_words + 1] = up
	test_words[#test_words + 1] = down

	for _, v in ipairs(test_words) do
		if v == target then
			count = count + 1
		end
	end

	return count
end

local xmas_count = 0
-- print all line numbers and their contents
---@diagnostic disable-next-line: unused-local
for line_idx, line in ipairs(lines) do
	for char_idx in line:gmatch("()X") do
		xmas_count = xmas_count + count_xmas_at_index(lines, line_idx, char_idx)
	end
end

io.output():write(xmas_count)