-- Mungo is magical data format that easily chomps up silly datafiles
-- with the ferocity of a mongoose (mungos mungo). Then through parsing,
-- it can be excreted into tabular/associative/structured form!
-- [] are comments,
-- "", '', `` are string quotes
-- *-+|~>=# are the default list delimiters
--  (define more delimiters if you think you need to)
-- : is the mapping delimiter, used when associating keys with string values
do
	local LIST_DELIMITERS = "*-+|~>=#"
	local MAPPING_DELIMITER = ':'
	local WHITESPACE = " \t"
	local QUOTE = "'`\""
	local COMMENT_OPEN = '['
	local COMMENT_CLOSE = ']'
	-- Returns whether or not a file exists.
	local function FileExists(filename)
		local f = io.open(filename, "r")
		if f == nil then
			return false
		end
		f:close()
		return true
	end

	-- Convert Mungo format into Lua table
	function MungoToTable(filename)
		local result = {}
		if FileExists(filename) then
			local buffer = ""
			for line in io.lines(filename) do
				buffer = buffer .. line .. "\n"
			end

			local i = 1
			local lists = {}
			local delimiters = {}
			local delimiter_current = nil
			local comment = false
			local quote = false
			local t = nil
			local k = ""
			local v = ""
			local line_index = 1
			while i <= #buffer do
				local c = buffer:sub(i, i)
				-- Next line
				if c == '\n' then
					if quote then
						v = v .. c
					end
					line_index = line_index + 1
				elseif not comment and not quote then
					-- List delimiter
					if LIST_DELIMITERS:find(c, 1, true) then
						-- Map current key to a string value and create a new list item
						if t and delimiter_current == c then
							if #v == 0 then
								return nil, "Expected a value identifier but got list delimiter '" .. c .. "' on line " .. tostring(line_index)
							end
							t[k] = v
						-- Map current key to a list
						elseif not lists[c] then
							delimiter_current = c
							if #k > 0 and #v > 0 then
								return nil, "Unexpected list delimiter '" .. c .. "' on line " .. tostring(line_index)
							end
							if t and #v == 0 then
								return nil, "Expected a key identifier but got list delimiter '" .. c .. "' on line " .. tostring(line_index)
							end
							if not t then
								t = result 
							else
								t[v] = {}
								t = t[v]
							end
							lists[c] = t
							table.insert(delimiters, c)
						-- Map current key to a string value and return to a list on an upper level
						else
							delimiter_current = c
							if #v == 0 then
								return nil, "Expected a value identifier but got list delimiter '" .. c .. "' on line " .. tostring(line_index)
							end
							t[k] = v
							t = lists[c]
							local delimiter_index = nil
							for idx, delimiter in ipairs(delimiters) do
								if delimiter == c then
									delimiter_index = idx
									break
								end
							end

							if delimiter_index then
								while delimiter_index < #delimiters do
									lists[table.remove(delimiters)] = nil
								end
							end
						end
						k = ""
						v = ""
					-- Mapping delimiter, make current indentifier into the key, make new indentifier a value
					elseif c == MAPPING_DELIMITER then
						if not t then
							return nil, "Attempt to define mapping before a list was started on line " .. tostring(line_index)
						end
						if #v == 0 then
							return nil, "Expected a key identifier but got mapping delimiter '" .. c .. "' on line " .. tostring(line_index)
						end
						k = v
						v = ""
					elseif c == COMMENT_OPEN then
						comment = true
					elseif QUOTE:find(c, 1, true) then
						if not t then
							return nil, c .. " quote encountered before a list was started on line " .. tostring(line_index)
						end
						quote = c
					elseif not WHITESPACE:find(c, 1, true) then
						if not t then
							return nil, "Indentifier character '" .. c .. "' encountered before a list was started on line " .. tostring(line_index)
						end
						v = v .. c
					end
				elseif quote then
					if c == quote then
						quote = false
					else
						v = v .. c
					end
				elseif comment and c == COMMENT_CLOSE then
					comment = false				
				end
				i = i + 1
			end
			-- If we reached EOF mid-string, whine
			if #v == 0 or (#v > 0 and #k == 0) then
				return nil, "Expected a value identifier but got EOF on line " .. tostring(line_index)
			end
			if #k > 0 then
				t[k] = v
			end
		else
			return nil, "Failed to open '" .. filename .. "'"
		end

		-- Finally, return our resolved table.
		return result
	end
end