function ScanTrains()
    storage.trains = {}
    for _, train in pairs(game.train_manager.get_trains({})) do
        storage.trains[train.id] = train
    end
end

---comment Get the first locomotive in the front, if non, in the back, if none empty string
---@param train LuaTrain
function GetTrainName(train)
    if train.locomotives.front_movers[1] then
        return train.locomotives.front_movers[1].backer_name or ""
    elseif train.locomotives.back_movers[1] then
        return train.locomotives.back_movers[1].backer_name or ""
    end
    return ""
end

function GetTrainsInDepot()
    local trainsInDepot = 0
    for trainsID, train in pairs(storage.trains) do
        if train.state == defines.train_state.wait_station
            and train.station and train.station.backer_name == autotrainDepotName then
            trainsInDepot = trainsInDepot + 1
        end
    end
    local trainsInGroup = #game.train_manager.get_trains({ group = autotrainGroupName })
    return ("---autotrain-stats---\n%d:%d"):format(trainsInDepot, trainsInGroup)
end

function GetTrainPlayerKills()
    local trainKills = {}
    trainKills[#trainKills + 1] = "---train-player-kills---"
    ---@type LuaTrain
    for _, train in pairs(storage.trains) do
        for killedPlayerID, killedPlayerCount in pairs(train.killed_players) do
            trainKills[#trainKills + 1] = ("%s:%s:%s:%s:%d"):format(train.id, GetTrainName(train), killedPlayerID,
                game.players[killedPlayerID].name, killedPlayerCount)
        end
    end
    return table.concat(trainKills, "\n")
end

function GetTrainTotalKills()
    local trainKills = {}
    trainKills[#trainKills + 1] = "---train-total-kills---"
    ---@type LuaTrain
    for _, train in pairs(storage.trains) do
        trainKills[#trainKills + 1] = ("%s:%s:%d"):format(train.id, GetTrainName(train), train.kill_count)
    end
    return table.concat(trainKills, "\n")
end

--TODO: Seperate by surface
function GetTrainStates()
    local trainsWaiting = {}
    local trainsDriving = {}
    local trainsManual = {}
    local trainsProblems = {}
    for _, train in pairs(storage.trains) do
        local surfaceName
        if train.locomotives then
            if train.locomotives.front_movers[1] then
                surfaceName = train.locomotives.front_movers[1].surface.name
            end
        elseif train.locomotives.back_movers[1] then
            surfaceName = train.locomotives.back_movers[1].surface.name
        end
        if surfaceName then
            if train.state == defines.train_state.wait_station
                or train.state == defines.train_state.destination_full
                or train.state == defines.train_state.no_schedule
            then
                trainsWaiting[surfaceName] = (trainsWaiting[surfaceName] or 0) + 1
            elseif train.state == defines.train_state.on_the_path
                or train.state == defines.train_state.arrive_signal
                or train.state == defines.train_state.arrive_station
                or train.state == defines.train_state.wait_signal
            then
                trainsDriving[surfaceName] = (trainsDriving[surfaceName] or 0) + 1
            elseif train.state == defines.train_state.manual_control
                or train.state == defines.train_state.manual_control_stop
            then
                trainsManual[surfaceName] = (trainsManual[surfaceName] or 0) + 1
            elseif train.state == defines.train_state.no_path
            then
                trainsProblems[surfaceName] = (trainsProblems[surfaceName] or 0) + 1
            end
        end
    end
    local stateParts = {}
    stateParts[#stateParts + 1] = "---trains-states---\n"
    for _, surface in pairs(game.surfaces) do
        local surfaceName = surface.name
        stateParts[#stateParts + 1] = ("%s:%d:%d:%d:%d"):format(
            surfaceName,
            trainsDriving[surfaceName] or 0,
            trainsManual[surfaceName] or 0,
            trainsProblems[surfaceName] or 0,
            trainsWaiting[surfaceName] or 0)
    end
    return table.concat(stateParts, "\n")
end

---@class trainStat
trainStat = {
    trainID = 0,
    trainName = "",
    lastInventory = {},
    currentInventory = {},
    lastState = 0,
    lastStationUnitNumber = 0,
    currentStationUnitNumber = 0,
    totalCargoCount = 0,
    totalCargo = {},
    lastArrivalTime = 0,
    currentArrivalTime = 0,
    ---@type trip
    trips = {}
}
---@class trip
trip = {
    startStation = {},
    endStation = {},
    timeTaken = 0,
    tick = 0
}

---@param inv table[]
---@return table<string, table>
local function toLookup(inv)
    local t = {}
    for _, item in ipairs(inv) do
        local key = item.name .. ":" .. (item.quality or 0) -- eindeutiger Key
        t[key] = item.count
    end
    return t
end

---@param oldInv table[]
---@param newInv table[]
---@return table[]
local function inventoryDiff(oldInv, newInv)
    local oldLookup = toLookup(oldInv)
    local newLookup = toLookup(newInv)
    local diff = {}

    -- Items, die neu hinzugekommen oder verändert wurden
    for key, newCount in pairs(newLookup) do
        local oldCount = oldLookup[key] or 0
        if newCount ~= oldCount then
            local name, quality = key:match("([^:]+):([^:]+)")
            table.insert(diff, {
                name = name,
                quality = tonumber(quality),
                oldCount = oldCount,
                newCount = newCount,
                delta = newCount - oldCount
            })
        end
    end

    -- Items, die komplett entfernt wurden
    for key, oldCount in pairs(oldLookup) do
        if newLookup[key] == nil then
            local name, quality = key:match("([^:]+):([^:]+)")
            table.insert(diff, {
                name = name,
                quality = tonumber(quality),
                oldCount = oldCount,
                newCount = 0,
                delta = -oldCount
            })
        end
    end

    return diff
end


function onTrainStateChange(event)
    -- Train arrived at station, so we store current data
    ---@type LuaTrain
    local train = event.train

    local trainID = train.id
    ---@type trainStat
    local stat = storage.trainStats[trainID] or {}
    stat.trips = stat.trips or {}
    stat.trainID = trainID
    stat.trainName = GetTrainName(train)

    if event.train.state == defines.train_state.wait_station then
        if not train.station then return end
        if train.station.unit_number == stat.lastStationUnitNumber then return end

        stat.lastStationUnitNumber = stat.currentStationUnitNumber
        stat.lastInventory = stat.currentInventory
        stat.lastArrivalTime = stat.currentArrivalTime

        stat.currentStationUnitNumber = train.station.unit_number
        stat.currentInventory = train.get_contents()
        stat.currentArrivalTime = game.tick

        if stat.lastStationUnitNumber
            and stat.currentStationUnitNumber
            and (stat.lastStationUnitNumber ~= stat.currentStationUnitNumber) then
            local tripIdentifier = tostring(stat.lastStationUnitNumber) .. tostring(stat.currentStationUnitNumber)
            stat.trips[tripIdentifier] = {
                startStation = game.get_entity_by_unit_number(stat.lastStationUnitNumber),
                endStation = game.get_entity_by_unit_number(stat.currentStationUnitNumber),
                timeTaken = stat.currentArrivalTime - stat.lastArrivalTime,
                time = game.tick
            }
        end

        if stat.currentInventory and stat.lastInventory then
            --Get Total Cargo
            for key, value in pairs(inventoryDiff(stat.lastInventory, stat.currentInventory)) do
                stat.totalCargoCount = (stat.totalCargoCount or 0) + math.abs(value.delta)
            end
        end

        storage.trainStats[trainID] = stat
    end
    --log("inEvent")
end

--Checks if trip is still valid by checking of st
function isTripValid(trip, tripID, trainID)
    if trip.startStation == nil
        or trip.endStation == nil
        or trip.startStation.valid == false
        or trip.endStation.valid == false then
        --One station is nil so we delete this trip
        log("Deleting trip" .. tripID)
        storage.trainStats[trainID].trips[tripID] = nil
        return false
    end
    --Stations are valid, so we true
    return true
end

function SortTrips()
    for trainID, stat in pairs(storage.trainStats) do
        table.sort(stat.trips, function(a, b)
            return a.tick > b.tick
        end)
    end
end

function GetTrainTripStats()
    --SortTrips()
    local tripParts = {}
    local tripCount = 0
    tripParts[#tripParts + 1] = "---train-trips---\n"
    for trainID, stats in pairs(storage.trainStats) do
        for tripIndex, trip in pairs(stats.trips or {}) do
            if isTripValid(trip, tripIndex, trainID) then
                tripParts[#tripParts + 1] =
                    ("%d:%s:%s:%s:%s:%d"):format(
                        trainID,
                        stats.trainName,
                        trip.startStation.surface.name,
                        trip.startStation.backer_name,
                        trip.endStation.backer_name,
                        trip.timeTaken)
                tripCount = tripCount + 1
            end
            --To clean up, we delete this trip now
            stats.trips[tripIndex] = nil
        end
        if #tripParts > 400 then
            log("Sending at " .. tripCount .. " trips")
            SendChunked(table.concat(tripParts, "\n"))
            tripParts = {}
            tripParts[#tripParts + 1] = "---train-trips---\n"
        end
    end
    --tripParts[#tripParts+1] = "--train-fin--"
    SendChunked(table.concat(tripParts, "\n"))
    log("Counted " .. tripCount .. " trips")
    --return table.concat(tripParts,"\n")
end

function GetTrainStatistics()
    local trainParts = {}
    trainParts[#trainParts + 1] = "---train-total-statistics---\n"
    for trainID, stat in pairs(storage.trainStats) do
        trainParts[#trainParts + 1] = ("%d:%s:%d"):format(trainID, stat.trainName, stat.totalCargoCount or 0)
    end
    return table.concat(trainParts, "\n")
end

---Purges stats for trains that no longer exist
---@param trainID integer|nil If provided, purges only that train. If nil, purges all dead trains.
function PurgeDeadTrainStats(trainID)
    if trainID then
        -- Purge a specific train if it doesn't exist
        if not storage.trains[trainID] then
            storage.trainStats[trainID] = nil
            return true
        end
    else
        -- Purge all trains not in storage.trains
        for statTrainID in pairs(storage.trainStats) do
            if not storage.trains[statTrainID] then
                storage.trainStats[statTrainID] = nil
            end
        end
    end
    return false
end

function SendTrainStats()
    if options.enableTrains then
        ScanTrains()
        PurgeDeadTrainStats()
        local returnParts = {}
        returnParts[#returnParts + 1] = GetTrainPlayerKills()
        returnParts[#returnParts + 1] = GetTrainTotalKills()
        returnParts[#returnParts + 1] = GetTrainStates()
        returnParts[#returnParts + 1] = GetTrainStatistics()
        returnParts[#returnParts + 1] = GetTrainsInDepot()
        if options.enableTrainTrips then
            GetTrainTripStats()
        end
        log("Sending Train statistics")
        SendChunked(table.concat(returnParts, "\n"))
    end
end