Improved (tracking) unit marker widget

function widget:GetInfo() return {
    name    = "Tracking Unit Marker",
    desc    = "[v1.0.0] Modified Sprung's unit_marker.lua. Marks spotted buildings and units of interest, updates location and building progress.",
    author  = "rollmops",
    date    = "2022-08-29",
    license = "GNU GPL v2",
    layer   = -1,
    enabled = true,
} end

-- the main modification is to remember the text and the position of the last marker for each unit (by unit I mean buildings also), and, if the same unitID is spotted in another location, or the text needs to be changed (e.g., building progress increased), to remove the previous marker and to make the new one.

-- in the original code, a spotted unit was remembered (in knownUnits) and no new markers were being issued for it. I removed this functionality.

-- non-commented parts are mostly the original Sprung's code.

local unitList
local activeDefID = {}

-- associative arrays, where keys are 'unitID's, to save the position and the text of the last marker of a given unit.
local lastMarkerText = {}
local lastPos = {}

-- since issuing spMarkerErasePosition (to remove the old marker) and then spMarkerAddPoint (to make a new marker) doesn't seem to work in cases where location is not changed (the new marker disappears after less than 1 second, I think it is somehow related to both commands being processed in the same drawing frame?), I made an ugly hack, namely, after spMarkerErasePosition, I defer the creation of the new marker: the text and the position of the new marker are stored in markersToMake, (keys are again 'unitID's), then the script counts 'frames_defer' game frames, and only then spMarkerAddPoint is issued.
local markersToMake = {}
local frames_defer = 15

local markingActive = false

local sp = Spring
local spGetAIInfo           = sp.GetAIInfo
local spGetPlayerInfo       = sp.GetPlayerInfo
local spGetSpectatingState  = sp.GetSpectatingState
local spGetTeamInfo         = sp.GetTeamInfo
local spGetUnitDefID        = sp.GetUnitDefID
local spGetUnitHealth       = sp.GetUnitHealth
local spGetUnitPosition     = sp.GetUnitPosition
local spIsUnitAllied        = sp.IsUnitAllied
local spMarkerAddPoint      = sp.MarkerAddPoint
local spMarkerErasePosition = sp.MarkerErasePosition
local sputGetHumanName      = sp.Utilities.GetHumanName

-- for debug
local Echo = sp.Echo

-- for additional feature: for markers of building in progress, add the game time at which the specified building progress was spotted
local spGetGameSeconds = sp.GetGameSeconds

if VFS.FileExists("LuaUI/Configs/unit_marker_local.lua", nil, VFS.RAW) then
    unitList = VFS.Include("LuaUI/Configs/unit_marker_local.lua", nil, VFS.RAW)
else
    unitList = VFS.Include("LuaUI/Configs/unit_marker.lua")
end

-- modified options_path, so there will be a separate settings menu for the modified unit maker
options_path = 'Settings/Interface/Trackign Unit Marker'

options_order = { 'enableAll', 'disableAll', 'unitslabel'}
options = {
    enableAll = {
        type='button',
        name= "Enable All",
        desc = "Marks all listed units.",
        path = options_path .. "/Presets",
        OnChange = function ()
            for i = 1, #options_order do
                local opt = options_order[i]
                local find = string.find(opt, "_mark")
                local name = find and string.sub(opt,0,find-1)
                local ud = name and UnitDefNames[name]
                if ud then
                    options[opt].value = true
                end
            end
            for unitDefID in pairs(unitList) do
                activeDefID[unitDefID] = true
            end
            if not markingActive then
                widgetHandler:UpdateCallIn('UnitEnteredLos')
                markingActive = true
            end
        end,
        noHotkey = true,
    },
    disableAll = {
        type='button',
        name= "Disable All",
        desc = "Mark nothing.",
        path = options_path .. "/Presets",
        OnChange = function ()
            for i = 1, #options_order do
                local opt = options_order[i]
                local find = string.find(opt, "_mark")
                local name = find and string.sub(opt,0,find-1)
                local ud = name and UnitDefNames[name]
                if ud then
                    options[opt].value = false
                end
            end
            for unitDefID,_ in pairs(unitList) do
                activeDefID[unitDefID] = false
            end
            if markingActive then
                widgetHandler:RemoveCallIn('UnitEnteredLos')
                markingActive = false
            end
        end,
        noHotkey = true,
    },
    unitslabel = {name = "unitslabel", type = 'label', value = "Individual Toggles", path = options_path},
}

for unitDefID in pairs(unitList) do
    local ud = UnitDefs[unitDefID]
    options[ud.name .. "_mark"] = {
        name = "  " .. sputGetHumanName(ud) or "",
        type = 'bool',
        value = false,
        OnChange = function (self)
            activeDefID[unitDefID] = self.value
            if self.value and not markingActive then
                widgetHandler:UpdateCallIn('UnitEnteredLos')
                markingActive = true
            end
        end,
        noHotkey = true,
    }
    options_order[#options_order+1] = ud.name .. "_mark"
end

local function refreshCallin()
    if not markingActive then
        widgetHandler:RemoveCallIn("UnitEnteredLos")
    end
    if spGetSpectatingState() then
        widgetHandler:RemoveCallIn("UnitEnteredLos")
    elseif markingActive then
        widgetHandler:UpdateCallIn('UnitEnteredLos')
    end
end

widget.PlayerChanged = refreshCallin
widget.Initialize = refreshCallin
widget.TeamDied = refreshCallin

function widget:UnitEnteredLos (unitID, teamID)
    if spIsUnitAllied(unitID) or spGetSpectatingState() then
        return
    end

    local unitDefID = spGetUnitDefID (unitID)
    if not unitDefID or not activeDefID[unitDefID] then
        return
    end

    local data = unitList[unitDefID]
    if not data then
        return
    end

    local markerText = data.markerText or sputGetHumanName(UnitDefs[unitDefID])

    if data.show_owner then
        local _,playerID,_,isAI = spGetTeamInfo(teamID, false)
        local owner_name
        if isAI then
            local _,botName,_,botType = spGetAIInfo(teamID)
            owner_name = (botType or "AI") .." - " .. (botName or "unnamed")
        else
            owner_name = spGetPlayerInfo(playerID, false) or "nobody"
        end

        markerText = markerText .. " (" .. owner_name .. ")"
    end

    local _, _, _, _, buildProgress = spGetUnitHealth(unitID)
    if buildProgress < 1 then
        markerText = markerText .. " (" .. math.floor(100 * buildProgress) .. "% at " ..  os.date( "%M:%S", spGetGameSeconds()) .. ")"
    end

    local x, y, z = spGetUnitPosition(unitID)

    -- if there were no markers issued for the given unitID, make a marker immediately
    if not lastMarkerText[unitID] then
        spMarkerAddPoint (x, y, z, markerText, true)

    -- if there was a marker, but the text of it or the location of the unit has changed, remove the existing marker and save the details of the new marker, which will be actually made after 'frames_defer' game frames, see widget:GameFrame below).
    elseif markerText ~= lastMarkerText[unitID] or x ~= lastPos[unitID][1] or y ~= lastPos[unitID][2] or z ~= lastPos[unitID][3] then
        spMarkerErasePosition(lastPos[unitID][1], lastPos[unitID][2], lastPos[unitID][3])
        markersToMake[unitID] = { x, y, z, markerText, frames_defer }
    end

    -- save the text and position of the marker as last known.
    lastPos[unitID] = {x, y, z}
    lastMarkerText[unitID] = markerText

end

-- each game frame, loop over all the deferred markers and decrease their deferment counters. For a maker that its counter reached zero, issue marker command and remove its details from markersToMake
function widget:GameFrame()
    for u, m in pairs(markersToMake) do
        if m[5] > 0 then
            markersToMake[u][5] = markersToMake[u][5] - 1
        else
            spMarkerAddPoint ( m[1], m[2], m[3], m[4], true)
            markersToMake[u] = nil
        end
    end
end

-- if a unit destroyed, remove both actual and deferred markers and all the related info.
function widget:UnitDestroyed(unitID, unitDefID, unitTeam)
    markersToMake[unitID] = nil
    lastMarkerText[unitID] = nil
    if lastPos[unitID] then spMarkerErasePosition(lastPos[unitID][1], lastPos[unitID][2], lastPos[unitID][3]) end
    lastPos[unitID] = nil
end