---------------
-- ## ftcsv, a fairly fast csv library written in pure lua
--
-- It works well for CSVs that can easily be fully loaded into memory (easily
-- up to a hundred MBs). Currently, there isn't a "large" file mode with
-- proper readers and writers for ingesting CSVs in bulk with a fixed amount
-- of memory
--
-- @author Shakil Thakur
-- @copyright 2016
-- @license MIT
---------------

local ftcsv = {}

-- load an entire file into memory
local function loadFile(textFile)
    local file = io.open(textFile, "r")
    if not file then error("File not found at " .. textFile) end
    local allLines = file:read("*all")
    file:close()
    return allLines
end

-- finds the end of an escape sequence
local function findClosingQuote(i, inputLength, inputString, quote, doubleQuoteEscape)
    local doubleQuoteEscape = doubleQuoteEscape
    while i <= inputLength do
        -- print(i)
        local currentChar = string.byte(inputString, i)
        local nextChar = string.byte(inputString, i+1)
        -- this one deals with " double quotes that are escaped "" within single quotes "
        -- these should be turned into a single quote at the end of the field
        if currentChar == quote and nextChar == quote then
            doubleQuoteEscape = true
            i = i + 2
        -- identifies the escape toggle
        elseif currentChar == quote and nextChar ~= quote then
            return i-1, doubleQuoteEscape
        else
            i = i + 1
        end
    end
end

-- creates a new field and adds it to the main table
local function createNewField(inputString, quote, fieldStart, i, line, fieldNum, doubleQuoteEscape, fieldsToKeep)
    -- print(lineNum, fieldNum, fieldStart, i-1)
    -- so, if we just recently de-escaped, we don't want the trailing \"
    -- if fieldsToKeep == nil then
    -- local fieldsToKeep = fieldsToKeep
    local output = line[fieldNum]
    if fieldsToKeep == nil or fieldsToKeep[fieldNum] then
        -- print(fieldsToKeep)
        -- print("b4", i, fieldNum, line[fieldNum])
        if string.byte(inputString, i-1) == quote then
            -- print("Skipping last \"")
            line[fieldNum] = string.sub(inputString, fieldStart, i-2)
        else
            line[fieldNum] = string.sub(inputString, fieldStart, i-1)
        end
        -- print("aft", i, fieldNum, line[fieldNum])
        -- remove the double quotes (if they existed)
        if doubleQuoteEscape then
            -- print("QUOTE REPLACE")
            -- print(line[fieldNum])
            line[fieldNum] = line[fieldNum]:gsub('""', '"')
            return false
        end
    end
end

-- creates the headers after reading through to the first line
local function createHeaders(line, rename, fieldsToKeep)
    -- print("CREATING HEADERS")
    local headers = {}
    for i = 1, #line do
        if rename[line[i]] then
            -- print("RENAMING", line[i], rename[line[i]])
            headers[i] = rename[line[i]]
        else
            headers[i] = line[i]
        end
    end
    if fieldsToKeep ~= nil then
        for i = 1, #fieldsToKeep do
            fieldsToKeep[fieldsToKeep[i]] = true
        end
    end
    return headers, 0, true, fieldsToKeep
end

-- main function used to parse
function ftcsv.parse(inputFile, delimiter, options)
    -- each line in outResults holds another table
    local outResults = {}
    outResults[1] = {}

    -- delimiter MUST be one character
    assert(#delimiter == 1 and type(delimiter) == "string", "the delimiter must be of string type and exactly one character")
    local delimiter = string.byte(delimiter)

    -- OPTIONS yo
    local header = true
    local rename = {}
    local fieldsToKeep = nil
    local ofieldsToKeep = nil
    local loadFromString = false
    if options then
        if options.headers ~= nil then
            assert(type(options.headers) == "boolean", "ftcsv only takes the boolean 'true' or 'false' for the optional parameter 'headers' (default 'true'). You passed in '" .. tostring(options.headers) .. "' of type '" .. type(options.headers) .. "'.")
            header = options.headers
        end
        if options.rename ~= nil then
            assert(type(options.rename) == "table", "ftcsv only takes in a key-value table for the optional parameter 'rename'. You passed in '" .. tostring(options.rename) .. "' of type '" .. type(options.rename) .. "'.")
            rename = options.rename
        end
        if options.fieldsToKeep ~= nil then
            assert(type(options.fieldsToKeep) == "table", "ftcsv only takes in a list (as a table) for the optional parameter 'fieldsToKeep'. You passed in '" .. tostring(options.fieldsToKeep) .. "' of type '" .. type(options.fieldsToKeep) .. "'.")
            ofieldsToKeep = options.fieldsToKeep
        end
        if options.loadFromString ~= nil then
            assert(type(options.loadFromString) == "boolean", "ftcsv only takes a boolean value for optional parameter 'loadFromString'. You passed in '" .. tostring(options.loadFromString) .. "' of type '" .. type(options.loadFromString) .. "'.")
            loadFromString = options.loadFromString
        end
    end

    local inputString
    if loadFromString then
        inputString = inputFile
    else
        inputString = loadFile(inputFile)
    end

    local CR = string.byte("\r")
    local LF = string.byte("\n")
    local quote = string.byte("\"")
    local doubleQuoteEscape = false
    local fieldStart = 1
    local fieldNum = 1
    local lineNum = 1
    local skipChar = 0
    local inputLength = #inputString
    local headerField = {}
    local headerSet = false
    local i = 1

    -- keep track of my chars!
    local currentChar, nextChar = string.byte(inputString, i), string.byte(inputString, i+1)

    while i <= inputLength do
        -- go by two chars at a time!
        -- currentChar = string.byte(inputString, i)
        nextChar = string.byte(inputString, i+1)
        -- print(i, string.char(currentChar), string.char(nextChar))

        -- keeps track of characters to "skip" while going through the encoding process
        -- if skipChar == 0 then

            -- empty string
            if currentChar == quote and nextChar == quote then
                -- print("EMPTY STRING")
                skipChar = 1
                fieldStart = i + 2
                -- print("fs+2:", fieldStart)

            -- identifies the escape toggle
            elseif currentChar == quote and nextChar ~= quote then
                -- print("ESCAPE TOGGLE")
                fieldStart = i + 1
                i, doubleQuoteEscape = findClosingQuote(i+1, inputLength, inputString, quote, doubleQuoteEscape)
                -- print("I VALUE", i, doubleQuoteEscape)
                skipChar = 1
            -- end

            -- create some fields if we can!
            elseif currentChar == delimiter then
                -- for that first field
                if not headerSet and lineNum == 1 then
                    headerField[fieldNum] = fieldNum
                end
                -- create the new field
                -- print(headerField[fieldNum])
                doubleQuoteEscape = createNewField(inputString, quote, fieldStart, i, outResults[lineNum], headerField[fieldNum], doubleQuoteEscape, fieldsToKeep)

                fieldNum = fieldNum + 1
                fieldStart = i + 1
                -- print("fs+1:", fieldStart)
            -- end

            -- newline?!
            elseif ((currentChar == CR and nextChar == LF) or currentChar == LF) then
                -- keep track of headers
                if not headerSet and lineNum == 1 then
                    headerField[fieldNum] = fieldNum
                end

                -- create the new field
                doubleQuoteEscape = createNewField(inputString, quote, fieldStart, i, outResults[lineNum], headerField[fieldNum], doubleQuoteEscape, fieldsToKeep)

                -- if we have headers then we gotta do something about it
                if header and lineNum == 1 and not headerSet then
                    headerField, lineNum, headerSet, fieldsToKeep = createHeaders(outResults[lineNum], rename, ofieldsToKeep)
                end

                lineNum = lineNum + 1
                outResults[lineNum] = {}
                fieldNum = 1
                fieldStart = i + 1
                -- print("fs:", fieldStart)
                if (currentChar == CR and nextChar == LF) then
                    -- print("CRLF DETECTED")
                    skipChar = 1
                    fieldStart = fieldStart + 1
                    -- print("fs:", fieldStart)
                end
            end

        i = i + 1 + skipChar
        if (skipChar > 0) then
            currentChar = string.byte(inputString, i)
        else
            currentChar = nextChar
        end
        skipChar = 0
    end

    -- if the line doesn't end happily (with a quote/newline), the last char will be forgotten.
    -- this should take care of that.
    createNewField(inputString, quote, fieldStart, i, outResults[lineNum], headerField[fieldNum], doubleQuoteEscape, fieldsToKeep)
    -- end

    -- clean up last line if it's weird (this happens when there is a CRLF newline at end of file)
    -- doing a count gets it to pick up the oddballs
    local finalLineCount = 0
    for _, value in pairs(outResults[lineNum]) do
        finalLineCount = finalLineCount + 1
    end
    local initialLineCount = 0
    for _, value in pairs(outResults[1]) do
        initialLineCount = initialLineCount + 1
    end
    -- print("Final/Initial", finalLineCount, initialLineCount)
    if finalLineCount ~= initialLineCount then
        outResults[lineNum] = nil
    end

    return outResults
end

-- a function that delimits " to "", used by the writer
local function delimitField(field)
    if field:find('"') then
        return field:gsub('"', '""')
    else
        return field
    end
end

-- a function that compiles some lua code to quickly print out the csv
local function writer(inputTable, dilimeter, headers)
    -- they get re-created here if they need to be escaped so lua understands it based on how
    -- they came in
    local headers = headers
    for i = 1, #headers do
        if inputTable[1][headers[i]] == nil then
            error("the field '" .. headers[i] .. "' doesn't exist in the table")
        end
        if headers[i]:find('"') then
            headers[i] = headers[i]:gsub('"', '\\"')
        end
    end

    local outputFunc = [[
        local state, i = ...
        local d = state.delimitField
        i = i + 1;
        if i > state.tableSize then return nil end;
        return i, '"' .. d(state.t[i]["]] .. table.concat(headers, [["]) .. '"]] .. dilimeter .. [["' .. d(state.t[i]["]]) .. [["]) .. '"\r\n']]

    -- print(outputFunc)

    local state = {}
    state.t = inputTable
    state.tableSize = #inputTable
    state.delimitField = delimitField

    return load(outputFunc), state, 0

end

-- takes the values from the headers in the first row of the input table
local function extractHeaders(inputTable)
    headers = {}
    for key, _ in pairs(inputTable[1]) do
        headers[#headers+1] = key
    end

    -- lets make the headers alphabetical
    table.sort(headers)

    return headers
end

-- turns a lua table into a csv
-- works really quickly with luajit-2.1, because table.concat life
function ftcsv.encode(inputTable, delimiter, options)
    local output = {}

    -- dilimeter MUST be one character
    assert(#delimiter == 1 and type(delimiter) == "string", "the delimiter must be of string type and exactly one character")
    local delimiter = delimiter

    -- grab the headers from the options if they are there
    local headers = nil
    if options then
        if options.headers ~= nil then
            assert(type(options.headers) == "table", "ftcsv only takes in a list (as a table) for the optional parameter 'headers'. You passed in '" .. tostring(options.headers) .. "' of type '" .. type(options.headers) .. "'.")
            headers = options.headers
        end
    end
    if headers == nil then
        headers = extractHeaders(inputTable)
    end

    -- newHeaders are needed if there are quotes within the header
    -- because they need to be escaped
    local newHeaders = {}
    for i = 1, #headers do
        if headers[i]:find('"') then
            newHeaders[i] = headers[i]:gsub('"', '""')
        else
            newHeaders[i] = headers[i]
        end
    end
    output[1] = '"' .. table.concat(newHeaders, '","') .. '"\r\n'

    -- add each line by line.
    for i, line in writer(inputTable, delimiter, headers) do
        output[i+1] = line
    end
    return table.concat(output)
end

return ftcsv