-- lzr_csv: RFC-4180-compliant Lua CSV Parser

-- NOTE: The "rules" mentioned in this file refer
-- to the rules mentioned in RFC 4180 under
-- section 2.


-- Rule 4: The value separator is comma
local SEP = ","

lzr_csv = {}

function lzr_csv.parse_csv(text) 
	-- List of all records so far
	-- (a record is a list of values)
	local records = {}
	-- The record we a currently working on and adding values to
	local currentRecord = {}
	-- Keep track of position in string
	local pos = 1
	-- Final position in string
	local lastPos = string.len(text)

	-- The current value we are parsing right now.
	-- When finished, it must be added to currentRecord.
	local currentValue = ""

	-- Status variables to change parsing state:

	-- If true, expects a LF character in the character check
	-- (required for CRLF check)
	local awaitingLF = false
	-- If true, we are currently parsing a quoted value,
	-- i.e. a value enclosed in quotes. As long this is true,
	-- the parsing rules are a bit different.
	local inQuotedValue = false
	-- If true, the previous character was a quote.
	-- Only used while inQuotedValue is true
	local prevWasQuote = false

	-- Begin of the main parsing loop
	while true do 
		-- We reached the end of the string
		if (pos > lastPos) then
			-- According to rule 2, a CRLF may or may not be at the end
			-- of the last record.
			if #currentRecord > 0 then
				-- There was no CRLF. So flush the final value
				-- to the list of records and call it a day.
				table.insert(currentRecord, currentValue)
				table.insert(records, currentRecord)
			end
			-- (If there *was* a CRLF,
			-- then currentRecord must be empty in which case
			-- no additional record should be added.)
			break
		end

		-- Get next character
		local c = string.sub(text, pos, pos)
		-- Rule 5: Values may be enclosed by quotes
		if inQuotedValue then
			-- This marks the "inside" of a quoted value
			if c == '"' then
				if prevWasQuote then
					currentValue = currentValue .. c
					prevWasQuote = false
				else
					prevWasQuote = true
				end
			else
				if prevWasQuote then
					-- This marks the *end* of a quoted value,
					-- special parsing will be deactivated.
					inQuotedValue = false
					prevWasQuote = false
					pos = pos - 1 
				else
					currentValue = currentValue .. c
				end
			end
		-- Rule 5: Values may be enclosed by quotes
		elseif (c == '"') then
			-- This marks the *beginning* of a quoted value,
			-- activate special parsing mode in next iteration.
			currentValue = ""
			prevWasQuote = false
			inQuotedValue = true
		-- Rule 1: Records must be separated by CRLF
		elseif (c == "\013") then -- CR (Carriage Return)
			if awaitingLF then
				minetest.log("error", "[lzr_csv] Carriage Return found but Line Feed expected (pos="..pos..")")
				return nil 
			end
			awaitingLF = true
		-- Rule 1: Records must be separated by CRLF
		elseif c == '\010' then -- LF (Line Feed)
			if not awaitingLF then
				minetest.log("error", "[lzr_csv] Line Feed found but there was no preceding Carriage Return (pos="..pos..")")
				return nil
			end
			table.insert(currentRecord, currentValue)
			local recordCopy = {}
			for l=1, #currentRecord do
				table.insert(recordCopy, currentRecord[l])
			end
			table.insert(records, recordCopy)
			currentRecord = {}
			currentValue = ""
			awaitingLF = false
		-- Rule 4: Values are separated by comma
		elseif c == SEP then
			table.insert(currentRecord, currentValue)
			currentValue = ""
		-- Parse a single normal character
		else
			if awaitingLF then
				minetest.log("error", "[lzr_csv] Line Feed character expected but other character found (pos="..pos..")")
				return nil
			end
			currentValue = currentValue .. c
		end
		pos = pos + 1
	end

	return records
end

-- Escapes the quote characters in the given string
local escape_quotes = function(str)
	return string.gsub(str, '"', '""')
end

function lzr_csv.write_csv(rows)
	local output_rows = {}
	for r=1, #rows do
		local values = table.copy(rows[r])
		for v=1, #values do
			-- Rule 5: Enclose each value with quotes.
			-- We enclose ALL values although this is
			-- not stricly neccessary, but keeps the code simpler.
			-- Rule 7: Quote characters within a value must be escaped
			values[v] = '"' .. escape_quotes(values[v]) .. '"'
		end
		-- Rule 4: Separate values by comma
		local output_row = table.concat(values, SEP)
		table.insert(output_rows, output_row)
	end
	-- Rule 1: Separate records by CRLF
	local output_all = table.concat(output_rows, "\013\010")
	return output_all
end