-- #REQUIRES mqueue.lua
-- #REQUIRES comms.lua
-- #REQUIRES log.lua
-- #REQUIRES util.lua

local PROTOCOLS = comms.PROTOCOLS
local RPLC_TYPES = comms.RPLC_TYPES

PLC_S_COMMANDS = {
    SCRAM = 0,
    ENABLE = 1,
    ISS_CLEAR = 2
}

local PERIODICS = {
    KEEP_ALIVE = 1.0
}

-- PLC supervisor session
function new_session(id, for_reactor, in_queue, out_queue)
    local log_header = "plc_session(" .. id .. "): "

    local self = {
        id = id,
        for_reactor = for_reactor,
        in_q = in_queue,
        out_q = out_queue,
        commanded_state = false,
        -- connection properties
        seq_num = 0,
        r_seq_num = nil,
        connected = true,
        received_struct = false,
        plc_conn_watchdog = util.new_watchdog(3),
        last_rtt = 0,
        -- when to next retry one of these requests
        periodics = {
            last_update = 0,
            keep_alive = 0
        },
        retry_times = {
            struct_req = 0,
            scram_req = 0,
            enable_req = 0
        },
        -- session database
        sDB = {
            last_status_update = 0,
            control_state = false,
            overridden = false,
            degraded = false,
            iss_status = {
                dmg_crit = false,
                ex_hcool = false,
                ex_waste = false,
                high_temp = false,
                no_fuel = false,
                no_cool = false,
                timed_out = false
            },
            mek_status = {
                heating_rate = 0,

                status = false,
                burn_rate = 0,
                act_burn_rate = 0,
                temp = 0,
                damage = 0,
                boil_eff = 0,
                env_loss = 0,

                fuel = 0,
                fuel_need = 0,
                fuel_fill = 0,
                waste = 0,
                waste_need = 0,
                waste_fill = 0,
                cool_type = "?",
                cool_amnt = 0,
                cool_need = 0,
                cool_fill = 0,
                hcool_type = "?",
                hcool_amnt = 0,
                hcool_need = 0,
                hcool_fill = 0
            },
            mek_struct = {
                heat_cap = 0,
                fuel_asm = 0,
                fuel_sa = 0,
                fuel_cap = 0,
                waste_cap = 0,
                cool_cap = 0,
                hcool_cap = 0,
                max_burn = 0
            }
        }
    }

    local _copy_iss_status = function (iss_status)
        self.sDB.iss_status.dmg_crit  = iss_status[1]
        self.sDB.iss_status.ex_hcool  = iss_status[2]
        self.sDB.iss_status.ex_waste  = iss_status[3]
        self.sDB.iss_status.high_temp = iss_status[4]
        self.sDB.iss_status.no_fuel   = iss_status[5]
        self.sDB.iss_status.no_cool   = iss_status[6]
        self.sDB.iss_status.timed_out = iss_status[7]
    end

    local _copy_status = function (mek_data)
        self.sDB.mek_status.status        = mek_data[1]
        self.sDB.mek_status.burn_rate     = mek_data[2]
        self.sDB.mek_status.act_burn_rate = mek_data[3]
        self.sDB.mek_status.temp          = mek_data[4]
        self.sDB.mek_status.damage        = mek_data[5]
        self.sDB.mek_status.boil_eff      = mek_data[6]
        self.sDB.mek_status.env_loss      = mek_data[7]

        self.sDB.mek_status.fuel          = mek_data[8]
        self.sDB.mek_status.fuel_need     = mek_data[9]
        self.sDB.mek_status.fuel_fill     = mek_data[10]
        self.sDB.mek_status.waste         = mek_data[11]
        self.sDB.mek_status.waste_need    = mek_data[12]
        self.sDB.mek_status.waste_fill    = mek_data[13]
        self.sDB.mek_status.cool_type     = mek_data[14]
        self.sDB.mek_status.cool_amnt     = mek_data[15]
        self.sDB.mek_status.cool_need     = mek_data[16]
        self.sDB.mek_status.cool_fill     = mek_data[17]
        self.sDB.mek_status.hcool_type    = mek_data[18]
        self.sDB.mek_status.hcool_amnt    = mek_data[19]
        self.sDB.mek_status.hcool_need    = mek_data[20]
        self.sDB.mek_status.hcool_fill    = mek_data[21]
    end

    local _copy_struct = function (mek_data)
        self.sDB.mek_struct.heat_cap  = mek_data[1]
        self.sDB.mek_struct.fuel_asm  = mek_data[2]
        self.sDB.mek_struct.fuel_sa   = mek_data[3]
        self.sDB.mek_struct.fuel_cap  = mek_data[4]
        self.sDB.mek_struct.waste_cap = mek_data[5]
        self.sDB.mek_struct.cool_cap  = mek_data[6]
        self.sDB.mek_struct.hcool_cap = mek_data[7]
        self.sDB.mek_struct.max_burn  = mek_data[8]
    end

    local _get_ack = function (pkt)
        if pkt.length == 1 then
            return pkt.data[1]
        else
            log._warning(log_header .. "RPLC ACK length mismatch")
            return nil
        end
    end

    local _handle_packet = function (message)
        local checks_ok = true

        -- handle an incoming packet from the PLC
        rplc_pkt = message.get()

        -- check sequence number
        if self.r_seq_num == nil then
            self.r_seq_num = rplc_pkt.scada_frame.seq_num()
        elseif self.r_seq_num >= rplc_pkt.scada_frame.seq_num() then
            log._warning(log_header .. "sequence out-of-order: last = " .. self.r_seq_num .. ", new = " .. rplc_pkt.scada_frame.seq_num())
            checks_ok = false
        else
            self.r_seq_num = rplc_pkt.scada_frame.seq_num()
        end

        -- check reactor ID
        if rplc_pkt.id ~= for_reactor then
            log._warning(log_header .. "RPLC packet with ID not matching reactor ID: reactor " .. self.for_reactor .. " != " .. rplc_pkt.id)
            checks_ok = false
        end

        -- process packet
        if checks_ok then
            -- feed watchdog
            self.plc_conn_watchdog.feed()

            -- handle packet by type
            if rplc_pkt.type == RPLC_TYPES.KEEP_ALIVE then
                -- keep alive reply
                if rplc_pkt.length == 2 then
                    local srv_start = rplc_pkt.data[1]
                    local plc_send = rplc_pkt.data[2]
                    local srv_now = util.time()
                    self.last_rtt = srv_now - srv_start

                    if self.last_rtt < 0 then
                        log._warning(log_header .. "PLC KEEP_ALIVE round trip time less than 0 (" .. trip_time .. ")") 
                    elseif trip_time > 1000 then
                        log._warning(log_header .. "PLC KEEP_ALIVE round trip time > 1s (" .. trip_time .. ")")
                    end

                    log._debug(log_header .. "RPLC RTT = ".. trip_time .. "ms")
                else
                    log._debug(log_header .. "RPLC keep alive packet length mismatch")
                end
            elseif rplc_pkt.type == RPLC_TYPES.STATUS then
                -- status packet received, update data
                if rplc_pkt.length >= 5 then
                    self.sDB.last_status_update = rplc_pkt.data[1]
                    self.sDB.control_state = rplc_pkt.data[2]
                    self.sDB.overridden = rplc_pkt.data[3]
                    self.sDB.degraded = rplc_pkt.data[4]
                    self.sDB.mek_status.heating_rate = rplc_pkt.data[5]

                    -- attempt to read mek_data table
                    if rplc_pkt.data[6] ~= nil then
                        local status = pcall(_copy_status, rplc_pkt.data[6])
                        if status then
                            -- copied in status data OK
                        else
                            -- error copying status data
                            log._error(log_header .. "failed to parse status packet data")
                        end
                    end
                else
                    log._debug(log_header .. "RPLC status packet length mismatch")
                end
            elseif rplc_pkt.type == RPLC_TYPES.MEK_STRUCT then
                -- received reactor structure, record it
                if rplc_pkt.length == 8 then
                    local status = pcall(_copy_struct, rplc_pkt.data)
                    if status then
                        -- copied in structure data OK
                    else
                        -- error copying structure data
                        log._error(log_header .. "failed to parse struct packet data")
                    end
                else
                    log._debug(log_header .. "RPLC struct packet length mismatch")
                end
            elseif rplc_pkt.type == RPLC_TYPES.MEK_SCRAM then
                -- SCRAM acknowledgement
                local ack = _get_ack(rplc_pkt)
                if ack then
                    self.sDB.control_state = false
                elseif ack == false then
                    log._warning(log_header .. "SCRAM failed!")
                end
            elseif rplc_pkt.type == RPLC_TYPES.MEK_ENABLE then
                -- enable acknowledgement
                local ack = _get_ack(rplc_pkt)
                if ack then
                    self.sDB.control_state = true
                elseif ack == false then
                    log._warning(log_header .. "enable failed!")
                end
            elseif rplc_pkt.type == RPLC_TYPES.MEK_BURN_RATE then
                -- burn rate acknowledgement
                if _get_ack(rplc_pkt) == false then
                    log._warning(log_header .. "burn rate update failed!")
                end
            elseif rplc_pkt.type == RPLC_TYPES.ISS_STATUS then
                -- ISS status packet received, copy data
                if rplc_pkt.length == 7 then
                    local status = pcall(_copy_iss_status, rplc_pkt.data)
                    if status then
                        -- copied in ISS status data OK
                    else
                        -- error copying ISS status data
                        log._error(log_header .. "failed to parse ISS status packet data")
                    end
                else
                    log._debug(log_header .. "RPLC ISS status packet length mismatch")
                end
            elseif rplc_pkt.type == RPLC_TYPES.ISS_ALARM then
                -- ISS alarm
                self.sDB.overridden = true
                if rplc_pkt.length == 7 then
                    local status = pcall(_copy_iss_status, rplc_pkt.data)
                    if status then
                        -- copied in ISS status data OK
                    else
                        -- error copying ISS status data
                        log._error(log_header .. "failed to parse ISS status packet data")
                    end
                else
                    log._debug(log_header .. "RPLC ISS alarm packet length mismatch")
                end
            elseif rplc_pkt.type == RPLC_TYPES.ISS_CLEAR then
                -- ISS clear acknowledgement
                if _get_ack(rplc_pkt) == false then
                    log._warning(log_header .. "ISS clear failed")
                end
            else
                log._debug(log_header .. "handler received unsupported RPLC packet type " .. rplc_pkt.type)
            end
        end
    end

    local _send = function (msg_type, msg)
        local s_pkt = comms.scada_packet()
        local r_pkt = comms.rplc_packet()

        r_pkt.make(self.id, msg_type, msg)
        s_pkt.make(self.seq_num, PROTOCOLS.RPLC, r_pkt.raw_sendable())

        self.out_q.push_packet(s_pkt)
        self.seq_num = self.seq_num + 1
    end

    -- PUBLIC FUNCTIONS --

    local get_id = function () return self.id end

    local get_db = function () return self.sDB end

    local close = function () self.connected = false end

    local check_wd = function (timer)
        return timer == self.plc_conn_watchdog.get_timer()
    end

    local get_struct = function ()
        if self.received_struct then
            return self.sDB.mek_struct
        else
            -- @todo: need a system in place to re-request this periodically
            return nil
        end
    end

    local iterate = function ()
        if self.connected then
            ------------------
            -- handle queue --
            ------------------

            if not self.in_q.empty() then
                -- get a new message to process
                local message = self.in_q.pop()

                if message.qtype == mqueue.TYPE.PACKET then
                    _handle_packet(message.message)
                elseif message.qtype == mqueue.TYPE.COMMAND then
                    -- handle instruction

                end
            end

            ----------------------
            -- update periodics --
            ----------------------

            local elapsed = os.clock() - self.periodics.last_update

            self.periodics.keep_alive = self.periodics.keep_alive + elapsed

            if self.periodics.keep_alive >= PERIODICS.KEEP_ALIVE then
                _send(RPLC_TYPES.KEEP_ALIVE, { util.time() })
                self.periodics.keep_alive = 0
            end

            self.periodics.last_update = os.clock()
        end

        return self.connected
    end

    return {
        get_id = get_id,
        get_db = get_db,
        close = close,
        check_wd = check_wd,
        get_struct = get_struct,
        iterate = iterate
    }
end