Vote v1.0 for CC without adv. computers

--[[
Vote v1.0 for CC without advanced computers by Espen
An example code for a voting system, inspired by ewart4fun

Thread: http://www.computercraft.info/forums2/index.php?/topic/5807-lua-voting-program/
--]]

-- [[ BEGINNING of FUNCTION DEFINITIONS ]] ---------------------------
-- Writes text centered, x- and y-axis position can be offset, and the line to be written can be cleared beforehand.
local function writeCentered( sText, nOffsetX, nOffsetY, color, bClearLine )
    local maxX, maxY = term.getSize()

    if nOffsetX == null then nOffsetX = 0 end
    local centeredX = (maxX / 2) - (string.len( sText ) / 2) + nOffsetX

    if nOffsetY == null then nOffsetY = 0 end
    local centeredY = (maxY / 2) + nOffsetY

    term.setCursorPos( centeredX, centeredY )
    if bClearLine then term.clearLine() end
    write( sText )
end


--[[
    Returns:
        0 - If login is ok.
        1 - If login failed.
        2 - If user already voted.
]]
local function checkLogin( sUser, sPwd )
    --[[
        ^%a     = first char has to be a letter
        %w*     = then there can follow an arbitrary number of alphanumeric characters
        :       = then a colon follows (which is used in the passwd file to delimit the usernames from their passwords)
        [01]    = then either a 0 or a 1 follows
        :       = then another colon follows (which is used in the passwd file to delimit the usernames from their passwords)
        .*$     = finally the pattern ends with an arbitrary number of any characters, i.e. empty passwords are allowed as well (use .+$ to ignore users with empty passwords).

        ( )     = Everything we encase in brackets will be extracted and returned as a separate value.
    ]]
    local credentials_pattern = "^(%a%w*):([01]):(.*)$" -- Example: "user123:0:secret"
    local bLoginOk = -1

    local hFile = fs.open( ".passwd", "r" )
    local line = hFile.readLine()
    while line do
        local user, hasVoted, pwd = string.match( line, credentials_pattern )
        if ( user and pwd ) and ( sUser == user ) then
            if ( sPwd == pwd ) then
                if ( hasVoted == "0" ) then
                    -- User found and password correct. Has not yet voted.
                    bLoginOk = 0
                    break
                else
                    -- User found and password correct. Has already voted.
                    bLoginOk = 1
                    break
                end
            else
                -- Password incorrect.
                --bLoginOk = -1  -- Unnecessary in the current code, as bLoginOk will not have changed from -1 when the program reaches this point.
                break
            end
        end

        -- Read the next line.
        line = hFile.readLine()
    end

    hFile:close()

    return bLoginOk
end

local function getLogin()
    local usrCurPosX, usrCurPosY, pwdCurPosX, pwdCurPosY
    local username = "", password

    while username == "" do
        writeCentered( "Username: ", -5, 0, nil, true )
        usrCurPosX, usrCurPosY = term.getCursorPos()
        writeCentered( "Password: ", -5, 1, nil, true )
        pwdCurPosX, pwdCurPosY = term.getCursorPos()

        term.setCursorPos( usrCurPosX, usrCurPosY )
        username = read()
        if username == "" then term.clear() end
    end

    term.setCursorPos( pwdCurPosX, pwdCurPosY )
    password = read("*")

    return username, password
end

-- Returns a table with candidates.
local function getCandidates()
    --[[
        [^:]+   = Each candidate name has to be comprised of at least one character, except colon.
    ]]
    local candidate_pattern = "[^:]+"
    local tCandidates = {}
    local candidate = nil


    local hFile = fs.open( ".candidates", "r" )
    local line = hFile.readLine()
    while line do
        candidate = string.match( line, candidate_pattern )

        if candidate then
            table.insert( tCandidates, candidate )
        end

        -- Read the next line.
        line = hFile.readLine()
    end

    hFile:close()
    return tCandidates
end

local function printVotingScreen( candidateList )
    term.clear()
    term.setCursorPos(1, 2)
    print( "Place your vote (type the corresponding numbers):\n" )
    for index, candidate in ipairs( candidateList ) do
        print( "\t("..index..") - "..candidate )
    end
    print( "\n\t(X) - Logout (vote later)." )
end

local function getVote( candidateList )
    while true do
        printVotingScreen( candidateList )

        local _, sChoice = os.pullEvent( "char" )
        local nChoice = tonumber( sChoice )

        -- Ask for confirmation of choice.
        if candidateList[ nChoice ] then
            write( "\nYou chose: ")
            print (candidateList[ nChoice ] )
            print( "(A)ccept or (C)ancel this choice." )
            while true do
                local _, sCommit = os.pullEvent( "char" )

                if sCommit and string.lower(sCommit) == "a" then return nChoice end
                if sCommit and string.lower(sCommit) == "c" then break end
            end
        end

        -- Logout
        if sChoice and string.lower(sChoice) == "x" then break end
    end
end

local function setHasVoted( voter )
    local users = {}
    local username, hasVoted, password
    local credentials_pattern = "^(%a%w*):([01]):(.*)$"

    -- Read old values into table 'users'.
    local hFile = fs.open( ".passwd", "r" )
    local line = hFile.readLine()
    while line do
        username, hasVoted, password = string.match( line, credentials_pattern )
        if username and hasVoted and password then
            users[username] = { hasVoted, password }
        end
        line = hFile.readLine()
    end
    hFile.close()

    -- Write changes to file.
    local hFile = fs.open( ".passwd", "w" )
    for user, _ in pairs(users) do
        if user == voter then
            hFile.writeLine(user..":1:"..users[user][2])
        else
            hFile.writeLine(user..":"..users[user][1]..":"..users[user][2])    -- users[user][1] is hasVoted and users[user][2] is password.
        end
    end
    hFile.close()
end

local function applyVote( tCandidateList, sVoter, nCandidateNum )
    local vote = nil
    local votes = {}
    local votedCandidate
    local votes_pattern = "^([^:]+):(%d+)$" -- Example: candidate3:27

    local hFile = fs.open( ".votes", "r" )
    local line = hFile.readLine()
    while line do
        candidate, vote = string.match( line, votes_pattern )
        if candidate and vote then votes[candidate] = vote end
        line = hFile.readLine()
    end

    votedCandidate = tCandidateList[ nCandidateNum ]
    if not votedCandidate then print(tCandidateList[ 1 ]) error( "The voted candidate isn't in the list of eligible candidates. This shouldn't happen, please fix me." ) end

    -- Initialize votes for candidate in case there are not votes for him yet.
    if not votes[votedCandidate] then
        votes[votedCandidate] = 0
    end

    -- Now finally increment his votes by 1.
    votes[votedCandidate] = votes[votedCandidate] + 1

    -- Write the changes back to file.
    local hFile = fs.open( ".votes", "w" )
    for candidate, vote in pairs(votes) do
        hFile.writeLine( candidate..":"..vote )
    end
    hFile.close()

    -- Set the hasVoted flag for the voter.
    setHasVoted( sVoter )
end

local function main()
    term.clear()
    local sUser, sPassword
    local candidateList
    local vote
    local loginState
    local validLogin = false

    -- Check for valid user.
    while not validLogin do
        sUser, sPassword = getLogin()
        -- Special login which quits the program to console. Remove if unwanted.
        if sUser == "exit to" and sPassword == "console" then return false end

        loginState = checkLogin( sUser, sPassword )

        if loginState == 0 then
            writeCentered( "[ Access Granted ]\n", 0, 3, colors.lime, true )
            validLogin = true
        elseif loginState == -1 then
            writeCentered( "[ Access Denied ]\n", 0, 3, colors.red, true )
        elseif loginState == 1 then
            writeCentered( "[ Already Voted ]\n", 0, 3, colors.purple, true )
        end

        sleep(1)    -- artificial cooldown before next try
    end

    -- Get the list of candidates and let the current user make a vote.
    candidateList = getCandidates()
    if #candidateList < 1 then
        term.clear()
        writeCentered( "No candidates to vote for." )
        writeCentered( "Please try again later.", 0, 1 )
        writeCentered( "Press ENTER to dismiss...", 0, 4 )
        local _, enter
        while enter ~= 28 do
            _, enter = os.pullEvent( "key" )
        end
        return true
    end

    -- Get a vote and apply it.
    vote = getVote( candidateList )
    if type(vote) == "number" then
        applyVote( candidateList, sUser, vote )
        term.clear()
        writeCentered( "Thank you for voting.", 0, 0, colors.yellow )
        writeCentered( "Have a nice day!", 0, 1, colors.yellow )
        sleep(3)
    end

    return true
end
-- [[ END of FUNCTION DEFINITIONS ]] ---------------------------

-- Prevent termination key-combo
nativePullEvent = os.pullEvent
os.pullEvent = os.pullEventRaw

-- Program loop
local running = true
while running do
    running = main()
end

-- Restore native os.pullEvent
os.pullEvent = nativePullEvent