-- Parsed as per W3's CSS Standard
-- Guidelines: https://www.w3.org/TR/css-syntax-3/

-- A string to number function was not coded in
-- I just used tonumber()

return function(CSSSource)

    local parserPosition = 1
    local lengthOfSource = CSSSource:len()
    local tokens = {} -- A collection of CSS-specific tokens
    local currentToken; -- The current token being used by the parser.
    local currentPoint; -- the current character indexed by the parser

    local function CreateToken(Type)
        local Token = {
            TokenType = Type;
            Value = "";
            Data = "";
            Flag = "";
            Unit = ""; -- used by <dimension-token>
            Repr = ""; -- used by <dimension-token>
        }
        return Token
    end

    local function EmitToken(Token)
        table.insert(tokens, Token)
    end

    local function AreCodePointsValidEscape(point1, point2)
        if (point1 == "\\") then
            if (point2 ~= "\n") then
                return true
            end
        end
    end

    local function IsCodePointNameStart(point)
        if (point:match("[%d_A-Za-z]")) then
            return true
        end
    end

    local function IsCodePointName(point)
        if (point:match("[%d%-A-Za-z]")) then
            return true
        end
    end

    local function DoThreeCodePointsStartIdentifier(point1, point2, point3)
        if (point1 == "-") then
            if (IsCodePointNameStart(point2) or AreCodePointsValidEscape(point2,point3)) then
                return true
            end
        elseif (IsCodePointNameStart(point1)) then
            return true
        elseif (point1 == "\\") then
            if (AreCodePointsValidEscape(point1, point2)) then
                return true
            end
        end
    end

    local function DoThreeCodePointsStartNumber(point1, point2, point3)
        if (point1 == "+" or point1 == "-") then
            if (point2:match("%d")) then
                return true
            elseif (point2 == ".") then
                if (point3:match("%d")) then
                    return true

                end
            else
                return false
            end
        elseif (point1 == ".") then
            if (point2:match("%d")) then
                return true
            else
                return false
            end
        elseif (point1:match("%d")) then
            return true
        end
    end

    -- vvv Get number/int from string
    local function ConsumeNumber()
        local repr = ""
        local typ = "integer"
        local value
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        currentPoint = CSSSource:sub(parserPosition, parserPosition)
        if (currentPoint == "+" or currentPoint == "-") then
            parserPosition = parserPosition + 1
            repr = repr .. currentPoint
            currentPoint = CSSSource:sub(parserPosition, parserPosition)
        end

        while (currentPoint:match("%d")) do
            repr = repr .. currentPoint
            parserPosition = parserPosition + 1
            currentPoint = CSSSource:sub(parserPosition, parserPosition)
        end

        local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)

        if (currentPoint == "." and nextCodePoint:match("%d")) then
            repr = repr .. "." .. nextCodePoint
            parserPosition = parserPosition + 2 -- consume . and digit
            typ = "number"
            currentPoint = CSSSource:sub(parserPosition, parserPosition)
            while (currentPoint:match("%d")) do
                repr = repr .. currentPoint
                parserPosition = parserPosition + 1
                currentPoint = CSSSource:sub(parserPosition, parserPosition)
            end
            nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)   -- Redefine next code point. !IMPORTANT
        end

        local nextNextCodePoint = CSSSource:sub(parserPosition+2, parserPosition+2)
        local continueWith_E_Parsing = false
        if (currentPoint == "e" or currentPoint == "E") then
            if (nextCodePoint == "+" or nextCodePoint == "-") then
                if (nextNextCodePoint:match("%d")) then
                    parserPosition = parserPosition + 3
                    repr = repr .. currentPoint .. nextCodePoint .. nextNextCodePoint
                    continueWith_E_Parsing = true
                end
            else
                if (nextCodePoint:match("%d")) then
                    parserPosition = parserPosition + 2
                    repr = repr .. currentPoint .. nextCodePoint
                    continueWith_E_Parsing = true
                end
            end
            if (continueWith_E_Parsing) then
                typ = "number"
                currentPoint = CSSSource:sub(parserPosition, parserPosition)
                while (currentPoint:match("%d")) do
                    repr = repr .. currentPoint
                    parserPosition = parserPosition + 1
                    currentPoint = CSSSource:sub(parserPosition, parserPosition)
                end
            end
        end

        value = tonumber(repr)
        return repr, value, typ
    end

    local function ConsumeName()
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        local result = ""
        while (parserPosition < lengthOfSource) do
            if (IsCodePointName(currentPoint)) then
                result = result .. currentPoint
                parserPosition = parserPosition + 1
                currentPoint = CSSSource:sub(parserPosition, parserPosition)
            else
                break
            end
        end
        return result
    end

    local function ConsumeNumericToken()
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        local repr, value, typ = ConsumeNumber()

        local nextCodePoint = CSSSource:sub(parserPosition, parserPosition)
        local nextNextCodePoint = CSSSource:sub(parserPosition + 1, parserPosition + 1)
        local currentToken -- stops it from affecting global 'currentToken'
        if (DoThreeCodePointsStartIdentifier(currentPoint, nextCodePoint, nextNextCodePoint)) then
            currentToken = CreateToken("<dimenion-token>")
            currentToken.Repr = repr
            currentToken.Value = value
            currentToken.Flag = typ

            local name = ConsumeName()

            currentToken.Unit = name
            EmitToken(currentToken)
        elseif (currentPoint == "%") then
            currentToken = CreateToken("<percentage-token>")
            currentToken.Repr = repr
            currentToken.Value = value
            currentToken.Flag = typ
            EmitToken(currentToken)
        else
            currentToken = CreateToken("<number-token>")
            currentToken.Repr = repr
            currentToken.Value = value
            currentToken.Flag = typ
            EmitToken(currentToken)
        end
    end

    local function ConsumeString()
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        local stringEndPoint = currentPoint == "'" and "'" or '"' -- Tells when to end the string
        -- Consume a string token
        local stringToken = CreateToken("<string-token>")
        while (parserPosition < lengthOfSource) do
            parserPosition = parserPosition + 1
            currentPoint = CSSSource:sub(parserPosition, parserPosition)
            if (currentPoint == "\\") then
                -- Escape character. Check if it is a valid escape
                -- Then consume one
            elseif (currentPoint == "\n") then
                -- Parse error. Should not expect new-line
                stringToken = CreateToken("<bad-string-token>") -- Overwrites the original string token
                EmitToken(stringToken)
                -- Reconsume token. Do not move parser position.
                break
            elseif (currentPoint == stringEndPoint) then
                -- Done with string. Move one. Emit it.
                EmitToken(stringToken)
                parserPosition = parserPosition + 1
                currentPoint = CSSSource:sub(parserPosition, parserPosition)
                break
            else
                -- Add to the string value
                stringToken.Value = currentPoint
            end
        end
        return stringToken
    end

    local function ConsumeWhitespace()
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        local token

        if (currentPoint:match("%s")) then
            token = CreateToken("<whitespace-token>")
        end

        while (currentPoint:match("%s")) do
            token.Value = token.Value .. currentPoint
            parserPosition = parserPosition + 1
            currentPoint = CSSSource:sub(parserPosition, parserPosition)
        end

        if (token) then
            table.insert(tokens, token)
            return token
        end
    end

    local function ConsumeURL()
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        local urlToken = CreateToken("<url-token>")
        ConsumeWhitespace()
        if (currentPoint == '"' or currentPoint == "'") then
            local stringToken = ConsumeString()
            if (stringToken.TokenType == "<bad-string-token>") then
                -- consume remnants of a bad url
            else
                urlToken.Value = stringToken.Value
                ConsumeWhitespace()
                if (currentPoint == ")") then
                    parserPosition = parserPosition + 1
                    return
                else
                    -- consume remnants of a bad url
                end
            end
        end
        while (parserPosition < lengthOfSource) do
            if (currentPoint == "(" or currentPoint == '"' or currentPoint == "'") then
                -- parse error. consume remnants of bad url
            elseif (currentPoint == "\\") then
                -- escape character
            else
                urlToken.Value = urlToken.Value .. currentPoint
                parserPosition = parserPosition + 1
                currentPoint = CSSSource:sub(parserPosition, parserPosition)
            end
        end
        return urlToken
    end

    local function ConsumeIdentLikeToken()
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        local name = ConsumeName()
        if (name == "url") then
            if (currentPoint == "(") then
                parserPosition = parserPosition + 1 -- Consume (
                local urlToken = ConsumeURL()
                EmitToken(urlToken)
            end
        elseif (currentPoint == "(") then
            -- function token
            local functionToken = CreateToken("<function-token>")
            functionToken.Value = name
            EmitToken(functionToken)
        else
            local identToken = CreateToken("<ident-token>")
            identToken.Value = name
            EmitToken(identToken)
        end
    end



    -- Here begins the actual parser

    local function ConsumeToken()
        local localToken
        -- WARNING: this function uses the stream - not given code points
        -- It will adjust the parserPosition
        if (currentPoint:match("%s")) then
            -- Consume as much whitespace as possible
            ConsumeWhitespace()
        elseif (currentPoint == '"' or currentPoint == "'") then
            ConsumeString()
        elseif (currentPoint == "#") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            local nextNextCodePoint = CSSSource:sub(parserPosition+2, parserPosition+2)
            local nNNextCodePoint = CSSSource:sub(parserPosition+3, parserPosition+3)
            if (IsCodePointName(nextCodePoint) or AreCodePointsValidEscape(nextCodePoint, nextNextCodePoint)) then -- DOES NOT SUPPORT non-ASCII code points
                localToken = CreateToken("<hash-token>")
                if (DoThreeCodePointsStartIdentifier(nextCodePoint, nextNextCodePoint, nNNextCodePoint)) then
                    localToken.Flag = "id"
                end
                local result = ""
                while (parserPosition < lengthOfSource) do
                    parserPosition = parserPosition + 1
                    currentPoint = CSSSource:sub(parserPosition, parserPosition)
                    if (IsCodePointName(currentPoint)) then
                        result = result .. currentPoint
                    else
                        break
                    end
                end
                localToken.Value = result
                EmitToken(localToken)
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == "(") then
            localToken = CreateToken("<(-token>")
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint == ")") then
            localToken = CreateToken("<)-token>")
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint == ",") then
            localToken = CreateToken("<comma-token>")
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint == "*") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            if (nextCodePoint == "=") then
                parserPosition = parserPosition + 2 -- Consume current AND next point
                localToken = CreateToken("<substring-match-token>")
                EmitToken(localToken)
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == "-") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            local nextNextCodePoint = CSSSource:sub(parserPosition+2, parserPosition+2)
            local nNNextCodePoint = CSSSource:sub(parserPosition+3, parserPosition+3)
            if (DoThreeCodePointsStartNumber(currentPoint, nextCodePoint, nextNextCodePoint)) then
                ConsumeNumericToken()
            elseif (DoThreeCodePointsStartIdentifier(currentPoint, nextCodePoint, nextNextCodePoint)) then
                ConsumeIdentLikeToken()
            elseif (nextCodePoint == "-" and nextNextCodePoint == ">") then
                localToken = CreateToken("<CDC-token>")
                EmitToken(localToken)
                parserPosition = parserPosition + 3
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == "+") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            local nextNextCodePoint = CSSSource:sub(parserPosition+2, parserPosition+2)
            if (DoThreeCodePointsStartNumber(currentPoint, nextCodePoint, nextNextCodePoint)) then
                ConsumeNumericToken()
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == ".") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            local nextNextCodePoint = CSSSource:sub(parserPosition+2, parserPosition+2)
            if (DoThreeCodePointsStartNumber(currentPoint, nextCodePoint, nextNextCodePoint)) then
                ConsumeNumericToken()
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == "/") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            if (nextCodePoint == "*") then
                parserPosition = parserPosition + 2
                -- consume everything until next asterisk followed by /
                while (currentPoint ~= "*" and nextCodePoint ~= "/") do
                    parserPosition = parserPosition + 1
                    currentPoint = CSSSource:sub(parserPosition, parserPosition)
                    nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
                end
                ConsumeToken() -- Is this even needed...?
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == ":") then
            localToken = CreateToken("<colon-token>")
            localToken.Value = currentPoint
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint == ";") then
            localToken = CreateToken("<semicolon-token>")
            localToken.Value = currentPoint
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint == "<") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            local nextNextCodePoint = CSSSource:sub(parserPosition+2, parserPosition+2)
            local nNNextCodePoint = CSSSource:sub(parserPosition+3, parserPosition+3)
            if (nextCodePoint == "!" and nextNextCodePoint == "-" and nNNextCodePoint == "-") then
                parserPosition = parserPosition + 4
                -- Consume current and next three points
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == "@") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            local nextNextCodePoint = CSSSource:sub(parserPosition+2, parserPosition+2)
            local nNNextCodePoint = CSSSource:sub(parserPosition+3, parserPosition+3)
            if (DoThreeCodePointsStartIdentifier(nextCodePoint,nextNextCodePoint,  nNNextCodePoint)) then
                parserPosition = parserPosition + 1
                local name = ConsumeName()
                localToken = CreateToken("<at-keyword-token>")
                localToken.Value = name
                EmitToken(localToken)
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == "]") then
            localToken = CreateToken("<]-token>")
            localToken.Value = currentPoint
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint == "^") then
            local nextCodePoint = CSSSource:sub(parserPosition+1, parserPosition+1)
            if (nextCodePoint == "=") then
                parserPosition = parserPosition + 2
                localToken = CreateToken("<prefix-match-token>")
                EmitToken(localToken)
            else
                localToken = CreateToken("<delim-token>")
                localToken.Value = currentPoint
                EmitToken(localToken)
                parserPosition = parserPosition + 1
            end
        elseif (currentPoint == "}") then
            localToken = CreateToken("<}-token>")
            localToken.Value = currentPoint
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint == "{") then
            localToken = CreateToken("<{-token>")
            localToken.Value = currentPoint
            EmitToken(localToken)
            parserPosition = parserPosition + 1
        elseif (currentPoint:match("%d")) then
            ConsumeNumericToken()
        end
    end


    while (parserPosition < lengthOfSource) and wait(0.25) do
        currentPoint = CSSSource:sub(parserPosition, parserPosition)
        ConsumeToken()
    end

    print("CSS Tokenizing done.")

    return tokens
end