local fullPath = shell.getRunningProgram()
local dir = fullPath:match("^(.*/)") or ""

local config = dofile(dir..'taskguard.cfg')

local clearances = { { computer_id = 1, clearance_level = 1, time_granted = os.clock() } }

local function split(str, divider)
    local t = {}
    for part in string.gmatch(str, "([^" .. divider .. "]+)") do
        table.insert(t, part)
    end
    return t
end

local function hash(str)
    local hash = 0
    for i = 1, #str do
        hash = (hash * 31 + string.byte(str, i)) % 65536
    end
    return string.format("%04X", hash)
end


local function check_for_outdated_sessions()
    local expired = 0
    for i = #clearances, 1, -1 do
        if (os.clock() - clearances[i].time_granted) > config.clearance_expiry then
            table.remove(clearances, i)
            expired = expired + 1
        end
    end
    print("Removed " .. expired .. " expired clearance(s). " ..
          #clearances .. " active session(s) remain.")
end



rednet.open(config.modem_side)
rednet.host('tg', config.name)
print("Server started, waiting for requests...")

while true do
    local id, msg, proto = rednet.receive('tg')
    check_for_outdated_sessions()
    msg_parts = split(msg, ',')
    if msg_parts[1] == 'validate_clearance' then
        print("Beginning transaction for clearance query with "..id)
        local target_id = tonumber(msg_parts[2])
        local requested_clearance = tonumber(msg_parts[3])
        local has_clearance = false

        for i, entry in ipairs(clearances) do
            if entry.computer_id == target_id and entry.clearance_level >= requested_clearance then
                -- Auth granted
                rednet.send(id, 'granted', 'tg')
                print('Finished transaction, granted')
                has_clearance = true
            end
        end

        if has_clearance == false then
            -- Auth not granted
            rednet.send(id, 'failed', 'tg')
            print('Finished transaction, failed')
        end
        print("EOP")
    elseif  msg_parts[1] == 'authenticate' then
        print("Beginning transaction for authentication with "..id)
        local card_holder = msg_parts[2]
        local card_clearance = msg_parts[3]
        local card_hash = hash(card_holder..','..card_clearance..','..msg_parts[4])
        local key_file = fs.open(dir..config.key_file, 'r')
        local card_authentic = false

        while true do
            local trusted_hash = key_file.readLine()
            if trusted_hash == card_hash then
                table.insert(clearances, { computer_id = tonumber(id), clearance_level = tonumber(card_clearance), time_granted = os.clock() })
                rednet.send(id, "authentication successful", "tg")
                print("Granted card "..card_hash.." clearance level "..card_clearance)

                card_authentic = true
            end
            if not line then break end -- Stop when EOF reached
        end

        key_file.close()
        
        if card_authentic == false then
            print("Unknown card "..card_hash)
            rednet.send(id, "authentication failed", "tg")
        end
        print("Transaction finished")
    end
end