Add lua option for accessing the FOF cooldown

This was requested by @AxemP.
The implementation is a bit more complicated than simply retrieving the
value since that is only updated when the weapon is fired. Instead, the
function calculates what the current value should be based on the code
from the function that updates the value when the weapon is fired.

Setting the value is disabled since the extra processing code could
alter the calculation a script does so that after setting the value,
reading it again would return a different value.

code/parse/lua.cpp

@@ -7081,6 +7081,40 @@ ADE_VIRTVAR(Capacity, l_WeaponBank, "number", "The actual capacity of a weapon b
 	return ade_set_error(L, "i", -1);
 }
 
+ADE_VIRTVAR(FOFCooldown, l_WeaponBank, "number", "The FOF cooldown value. A value of 0 means the default weapon FOF is used. A value of 1 means that the max FOF will be used", "number", "The cooldown value or -1 if invalid")
+{
+	ship_bank_h *bh = NULL;
+	float newValue = -1.f;
+	if(!ade_get_args(L, "o|i", l_WeaponBank.GetPtr(&bh), &newValue))
+		return ade_set_error(L, "f", -1.f);
+
+	if(!bh->IsValid())
+		return ade_set_error(L, "f", -1.f);
+
+	if (ADE_SETTING_VAR) {
+		LuaError(L, "This function does not support setting values yet!");
+		return ade_set_error(L, "f", -1.f);
+	}
+
+	switch(bh->type)
+	{
+		case SWH_PRIMARY:
+		{
+			auto wif = &Weapon_info[bh->sw->primary_bank_weapons[bh->bank]];
+			float reset_amount = (timestamp_until(bh->sw->last_primary_fire_stamp[bh->bank]) / 1000.0f) * wif->fof_reset_rate;
+			auto val = bh->sw->primary_bank_fof_cooldown[bh->bank] + reset_amount;
+			CLAMP(val, 0.0f, 1.0f);
+			return ade_set_args(L, "f", val);
+		}
+		case SWH_SECONDARY:
+		case SWH_TERTIARY:
+			LuaError(L, "FOF cooldown is not valid for secondary or tertiary banks!");
+			return ade_set_args(L, "f", -1.f);
+	}
+
+	return ade_set_error(L, "f", -1.f);
+}
+
 ADE_FUNC(isValid, l_WeaponBank, NULL, "Detects whether handle is valid", "boolean", "true if valid, false if handle is invalid, nil if a syntax/type error occurs")
 {
 	ship_bank_h *bh;