local log    = require("scada-common.log")
local mqueue = require("scada-common.mqueue")
local util   = require("scada-common.util")

local coordinator = require("supervisor.session.coordinator")
local plc         = require("supervisor.session.plc")
local rtu         = require("supervisor.session.rtu")

-- Supervisor Sessions Handler

local svsessions = {}

local SESSION_TYPE = {
    RTU_SESSION = 0,
    PLC_SESSION = 1,
    COORD_SESSION = 2
}

svsessions.SESSION_TYPE = SESSION_TYPE

local self = {
    modem = nil,
    num_reactors = 0,
    rtu_sessions = {},
    plc_sessions = {},
    coord_sessions = {},
    next_rtu_id = 0,
    next_plc_id = 0,
    next_coord_id = 0
}

-- PRIVATE FUNCTIONS --

-- iterate all the given sessions
---@param sessions table
local function _iterate(sessions)
    for i = 1, #sessions do
        local session = sessions[i]  ---@type plc_session_struct|rtu_session_struct
        if session.open then
            local ok = session.instance.iterate()
            if ok then
                -- send packets in out queue
                while session.out_queue.ready() do
                    local msg = session.out_queue.pop()
                    if msg ~= nil and msg.qtype == mqueue.TYPE.PACKET then
                        self.modem.transmit(session.r_port, session.l_port, msg.message.raw_sendable())
                    end
                end
            else
                session.open = false
            end
        end
    end
end

-- cleanly close a session
---@param session plc_session_struct|rtu_session_struct
local function _shutdown(session)
    session.open = false
    session.instance.close()

    -- send packets in out queue (namely the close packet)
    while session.out_queue.ready() do
        local msg = session.out_queue.pop()
        if msg ~= nil and msg.qtype == mqueue.TYPE.PACKET then
            self.modem.transmit(session.r_port, session.l_port, msg.message.raw_sendable())
        end
    end

    log.debug("closed session " .. session.instance.get_id() .. " on remote port " .. session.r_port)
end

-- close connections
---@param sessions table
local function _close(sessions)
    for i = 1, #sessions do
        local session = sessions[i]  ---@type plc_session_struct
        if session.open then
            _shutdown(session)
        end
    end
end

-- check if a watchdog timer event matches that of one of the provided sessions
---@param sessions table
---@param timer_event number
local function _check_watchdogs(sessions, timer_event)
    for i = 1, #sessions do
        local session = sessions[i]  ---@type plc_session_struct
        if session.open then
            local triggered = session.instance.check_wd(timer_event)
            if triggered then
                log.debug("watchdog closing session " .. session.instance.get_id() .. " on remote port " .. session.r_port .. "...")
                _shutdown(session)
            end
        end
    end
end

-- delete any closed sessions
---@param sessions table
local function _free_closed(sessions)
    local f = function (session) return session.open end
    local on_delete = function (session) log.debug("free'ing closed session " .. session.instance.get_id() .. " on remote port " .. session.r_port) end

    util.filter_table(sessions, f, on_delete)
end

-- find a session by remote port
---@param list table
---@param port integer
---@return plc_session_struct|rtu_session_struct|nil
local function _find_session(list, port)
    for i = 1, #list do
        if list[i].r_port == port then return list[i] end
    end
    return nil
end

-- PUBLIC FUNCTIONS --

-- link the modem
---@param modem table
function svsessions.link_modem(modem)
    self.modem = modem
end

-- find an RTU session by the remote port
---@param remote_port integer
---@return rtu_session_struct|nil
function svsessions.find_rtu_session(remote_port)
    -- check RTU sessions
    return _find_session(self.rtu_sessions, remote_port)
end

-- find a PLC session by the remote port
---@param remote_port integer
---@return plc_session_struct|nil
function svsessions.find_plc_session(remote_port)
    -- check PLC sessions
    return _find_session(self.plc_sessions, remote_port)
end

-- find a PLC/RTU session by the remote port
---@param remote_port integer
---@return plc_session_struct|rtu_session_struct|nil
function svsessions.find_device_session(remote_port)
    -- check RTU sessions
    local s = _find_session(self.rtu_sessions, remote_port)

    -- check PLC sessions
    if s == nil then s = _find_session(self.plc_sessions, remote_port) end

    return s
end

-- find a coordinator session by the remote port
---@param remote_port integer
---@return nil
function svsessions.find_coord_session(remote_port)
    -- check coordinator sessions
    return _find_session(self.coord_sessions, remote_port)
end

-- get a session by reactor ID
---@param reactor integer
---@return plc_session_struct|nil session
function svsessions.get_reactor_session(reactor)
    local session = nil

    for i = 1, #self.plc_sessions do
        if self.plc_sessions[i].reactor == reactor then
            session = self.plc_sessions[i]
        end
    end

    return session
end

-- establish a new PLC session
---@param local_port integer
---@param remote_port integer
---@param for_reactor integer
---@param version string
---@return integer|false session_id
function svsessions.establish_plc_session(local_port, remote_port, for_reactor, version)
    if svsessions.get_reactor_session(for_reactor) == nil then
        ---@class plc_session_struct
        local plc_s = {
            open = true,
            reactor = for_reactor,
            version = version,
            l_port = local_port,
            r_port = remote_port,
            in_queue = mqueue.new(),
            out_queue = mqueue.new(),
            instance = nil
        }

        plc_s.instance = plc.new_session(self.next_plc_id, for_reactor, plc_s.in_queue, plc_s.out_queue)
        table.insert(self.plc_sessions, plc_s)

        log.debug("established new PLC session to " .. remote_port .. " with ID " .. self.next_plc_id)

        self.next_plc_id = self.next_plc_id + 1

        -- success
        return plc_s.instance.get_id()
    else
        -- reactor already assigned to a PLC
        return false
    end
end

-- establish a new RTU session
---@param local_port integer
---@param remote_port integer
---@param advertisement table
---@return integer session_id
function svsessions.establish_rtu_session(local_port, remote_port, advertisement)
    -- pull version from advertisement
    local version = table.remove(advertisement, 1)

    ---@class rtu_session_struct
    local rtu_s = {
        open = true,
        version = version,
        l_port = local_port,
        r_port = remote_port,
        in_queue = mqueue.new(),
        out_queue = mqueue.new(),
        instance = nil
    }

    rtu_s.instance = rtu.new_session(self.next_rtu_id, rtu_s.in_queue, rtu_s.out_queue, advertisement)
    table.insert(self.rtu_sessions, rtu_s)

    log.debug("established new RTU session to " .. remote_port .. " with ID " .. self.next_rtu_id)

    self.next_rtu_id = self.next_rtu_id + 1

    -- success
    return rtu_s.instance.get_id()
end

-- establish a new coordinator session
---@param local_port integer
---@param remote_port integer
---@param version string
---@return integer|false session_id
function svsessions.establish_coord_session(local_port, remote_port, version)
    ---@class coord_session_struct
    local coord_s = {
        open = true,
        version = version,
        l_port = local_port,
        r_port = remote_port,
        in_queue = mqueue.new(),
        out_queue = mqueue.new(),
        instance = nil
    }

    coord_s.instance = coordinator.new_session(self.next_coord_id, coord_s.in_queue, coord_s.out_queue)
    table.insert(self.coord_sessions, coord_s)

    log.debug("established new coordinator session to " .. remote_port .. " with ID " .. self.next_coord_id)

    self.next_coord_id = self.next_coord_id + 1

    -- success
    return coord_s.instance.get_id()
end

-- attempt to identify which session's watchdog timer fired
---@param timer_event number
function svsessions.check_all_watchdogs(timer_event)
    -- check RTU session watchdogs
    _check_watchdogs(self.rtu_sessions, timer_event)

    -- check PLC session watchdogs
    _check_watchdogs(self.plc_sessions, timer_event)

    -- check coordinator session watchdogs
    _check_watchdogs(self.coord_sessions, timer_event)
end

-- iterate all sessions
function svsessions.iterate_all()
    -- iterate RTU sessions
    _iterate(self.rtu_sessions)

    -- iterate PLC sessions
    _iterate(self.plc_sessions)

    -- iterate coordinator sessions
    _iterate(self.coord_sessions)
end

-- delete all closed sessions
function svsessions.free_all_closed()
    -- free closed RTU sessions
    _free_closed(self.rtu_sessions)

    -- free closed PLC sessions
    _free_closed(self.plc_sessions)

    -- free closed coordinator sessions
    _free_closed(self.coord_sessions)
end

-- close all open connections
function svsessions.close_all()
    -- close sessions
    _close(self.rtu_sessions)
    _close(self.plc_sessions)
    _close(self.coord_sessions)

    -- free sessions
    svsessions.free_all_closed()
end

return svsessions