garrysmod-coop/gamemode/weaponsystem.lua

local respawnDistance = CreateConVar(
    "gc_respawndistance",
    "75",
    FCVAR_ARCHIVE,
    "Distance a map item may move from its spawn before it is returned"
)

local respawnDelay = CreateConVar(
    "gc_itemrespawntime",
    "1",
    FCVAR_ARCHIVE,
    "Seconds before a collected or displaced map item respawns"
)

local trackedItems = {}
local suppressRespawns = false

local function IsRespawnable(ent)
    if not IsValid(ent) then return false end

    local className = ent:GetClass()
    return string.StartWith(className, "item_") or string.StartWith(className, "weapon_")
end

local function CaptureTemplate(ent)
    local bodygroups = {}
    for _, bodygroup in ipairs(ent:GetBodyGroups() or {}) do
        bodygroups[bodygroup.id] = ent:GetBodygroup(bodygroup.id)
    end

    return {
        className = ent:GetClass(),
        position = ent:GetPos(),
        angles = ent:GetAngles(),
        model = ent:GetModel(),
        skin = ent:GetSkin(),
        material = ent:GetMaterial(),
        color = ent:GetColor(),
        collisionGroup = ent:GetCollisionGroup(),
        name = ent:GetName(),
        keyValues = ent:GetKeyValues(),
        bodygroups = bodygroups
    }
end

local TrackItem
local RespawnItem

local function ScheduleRespawn(template)
    if suppressRespawns then return end

    timer.Simple(math.max(respawnDelay:GetFloat(), 0), function()
        if suppressRespawns then return end
        RespawnItem(template)
    end)
end

TrackItem = function(ent, template)
    if not IsValid(ent) or trackedItems[ent] then return end

    template = template or CaptureTemplate(ent)
    trackedItems[ent] = template

    ent:CallOnRemove("CustomCoopRespawnItem", function(removed)
        local savedTemplate = trackedItems[removed]
        trackedItems[removed] = nil

        if savedTemplate then
            ScheduleRespawn(savedTemplate)
        end
    end)
end

RespawnItem = function(template)
    local ent = ents.Create(template.className)
    if not IsValid(ent) then
        ErrorNoHalt("[custom_coop] Could not respawn " .. template.className .. "; retrying in 5 seconds\n")
        timer.Simple(5, function()
            if not suppressRespawns then RespawnItem(template) end
        end)
        return
    end

    -- Restore mapper-provided properties before Spawn. Position, angles and model
    -- are restored explicitly because GetKeyValues does not always include them.
    for key, value in pairs(template.keyValues or {}) do
        if key ~= "classname" and key ~= "origin" and key ~= "angles" and key ~= "hammerid" then
            ent:SetKeyValue(key, tostring(value))
        end
    end

    ent:SetPos(template.position + Vector(0, 0, 3))
    ent:SetAngles(template.angles)
    if template.model and template.model ~= "" then ent:SetModel(template.model) end
    if template.name and template.name ~= "" then ent:SetName(template.name) end
    ent:Spawn()
    ent:Activate()

    if not IsValid(ent) then
        ScheduleRespawn(template)
        return
    end

    ent:SetSkin(template.skin or 0)
    ent:SetMaterial(template.material or "")
    ent:SetColor(template.color or color_white)
    ent:SetCollisionGroup(template.collisionGroup or COLLISION_GROUP_NONE)
    for id, value in pairs(template.bodygroups or {}) do
        ent:SetBodygroup(id, value)
    end

    TrackItem(ent, template)
    ent:EmitSound("items/suitchargeok1.wav", 60, 100, 0.35)
end

hook.Add("OnEntityCreated", "CustomCoopTrackMapItems", function(ent)
    -- OnEntityCreated fires before keyvalues and map-created state are ready.
    timer.Simple(0, function()
        if IsRespawnable(ent) and ent:CreatedByMap() then
            TrackItem(ent)
        end
    end)
end)

hook.Add("WeaponEquip", "CustomCoopRespawnCollectedWeapon", function(weapon)
    local template = trackedItems[weapon]
    if not template then return end

    -- A newly acquired weapon becomes the player's inventory entity and is not
    -- removed. Detach it and immediately start a new respawn cycle for its slot.
    trackedItems[weapon] = nil
    weapon:RemoveCallOnRemove("CustomCoopRespawnItem")
    ScheduleRespawn(template)
end)

-- Prevent +use from dragging a map pickup away. Touch pickup still works, and
-- duplicate weapons are left to the engine's EquipAmmo path so they correctly
-- replenish reserve ammo and disappear only when ammo was actually accepted.
hook.Add("AllowPlayerPickup", "CustomCoopProtectMapItems", function(_, ent)
    if trackedItems[ent] then return false end
end)

timer.Create("CustomCoopReturnDisplacedItems", 1, 0, function()
    local maxDistance = math.max(respawnDistance:GetFloat(), 0)
    local maxDistanceSquared = maxDistance * maxDistance

    for ent, template in pairs(trackedItems) do
        if not IsValid(ent) then
            trackedItems[ent] = nil
        elseif not IsValid(ent:GetParent()) and ent:GetPos():DistToSqr(template.position) > maxDistanceSquared then
            SafeRemoveEntityDelayed(ent, 0)
        end
    end
end)

hook.Add("PlayerSpawn", "CustomCoopKeepWeaponsOnDeath", function(ply)
    timer.Simple(0, function()
        if IsValid(ply) then ply:ShouldDropWeapon(false) end
    end)
end)

hook.Add("PreCleanupMap", "CustomCoopPauseItemRespawns", function()
    suppressRespawns = true
    trackedItems = {}
end)

hook.Add("PostCleanupMap", "CustomCoopResumeItemRespawns", function()
    suppressRespawns = false
end)

hook.Add("ShutDown", "CustomCoopStopItemRespawns", function()
    suppressRespawns = true
end)