local Lexer = {}
Lexer.__index = Lexer

function Lexer:eat(byte_count)
	for c in self.source:sub(self.i, self.i + byte_count - 1):gmatch"." do
		if c == "\n" then
			self.current_row = self.current_row + 1
			self.current_col = 1
		else
			self.current_col = self.current_col + 1
		end
	end
	
	self.i = self.i + byte_count
end

function Lexer:match(pattern)
	local m = self.source:sub(self.i):match("^" .. pattern)
	if m then
		self:eat(#m)
		self.last_match = m
		return m
	end
end

function Lexer:add(token_type, token_data)
	table.insert(self.result, {type = token_type, data = token_data, x = self.current_col, y = self.current_row})
end

function Lexer:get()
	if self:match"[0-9]+r[0-9a-zA-Z]+" or self:match"[0-9]+" then
		self:add("num", self.last_match)
	elseif self:match"if" then
		self:add("if", nil)
	elseif self:match"string" then
		self:add("stringkw", nil)
	elseif self:match"loop" then
		self:add("loop", nil)
	elseif self:match"return" then
		self:add("return", nil)
	elseif self:match"export" then
		self:add("export", nil)
	elseif self:match"[a-zA-Z_][a-zA-Z0-9_]*" then
		self:add("ident", self.last_match)
	elseif self:match"@[a-zA-Z_][a-zA-Z0-9_]*" then
		self:add("mod", self.last_match)
	elseif self:match"'" then
		local j = self.i
		local value = ""
		while j <= #self.source do
			local b = self.source:sub(j, j)
			
			if b == "'" then
				break
			elseif b == "\\" then
				j = j + 1
				b = self.source:sub(j, j)
				if b == "n" then
					b = "\n"
				elseif b == "b" then
					b = "\b"
				elseif b == "e" then
					b = "\x1B"
				elseif b == "r" then
					b = "\r"
				elseif b == "t" then
					b = "\t"
				elseif b == "x" then
					b = string.char(tonumber(self.source:sub(j + 1, j + 2), 16))
					j = j + 2
				else
					error("Unknown escape sequence")
				end
			end
			
			value = value .. b
			j = j + 1
		end
		self:eat(j - self.i + 1)
		self:add("string", value)
	elseif self:match"==" then
		self:add("==", nil)
	elseif self:match"!=" then
		self:add("!=", nil)
	elseif self:match">=" then
		self:add(">=", nil)
	elseif self:match"<=" then
		self:add("<=", nil)
	elseif self:match":" then
		self:add(":", nil)
	elseif self:match"%(" then
		self:add("(", nil)
	elseif self:match"%)" then
		self:add(")", nil)
	elseif self:match"->" then
		self:add("->", nil)
	elseif self:match"{" then
		self:add("{", nil)
	elseif self:match"}" then
		self:add("}", nil)
	elseif self:match"%s" then
		--self:add("ws", nil)
	else
		self:add(self.source:sub(self.i, self.i), nil)
		self:eat(1)
	end
end

function Lexer:go()
	while self.i <= #self.source do
		self:get()
	end
end

return function(source_code)
	return setmetatable({i = 1, source = source_code, result = {}, current_row = 1, current_col = 1}, Lexer)
end