emigration: persists last cycle tick so that the behaviour is more consistent with respect to save-and-reloads

Author: master-spike

emigration.lua

@@ -4,13 +4,14 @@
 local GLOBAL_KEY = 'emigration' -- used for state change hooks and persistence
 
 enabled = enabled or false
+last_cycle_tick = last_cycle_tick or 0
 
 function isEnabled()
     return enabled
 end
 
 local function persist_state()
-    dfhack.persistent.saveSiteData(GLOBAL_KEY, {enabled=enabled})
+    dfhack.persistent.saveSiteData(GLOBAL_KEY, {enabled=enabled, last_cycle_tick=last_cycle_tick})
 end
 
 function desireToStay(unit,method,civ_id)
@@ -191,12 +192,20 @@ function checkmigrationnow()
     else
         for _, civ_id in pairs(merchant_civ_ids) do checkForDeserters('merchant', civ_id) end
     end
+
+    last_cycle_tick = dfhack.world.ReadCurrentTick() + 403200 * dfhack.world.ReadCurrentYear()
 end
 
 local function event_loop()
     if enabled then
-        checkmigrationnow()
-        dfhack.timeout(1, 'months', event_loop)
+        local current_tick = dfhack.world.ReadCurrentTick() + 403200 * dfhack.world.ReadCurrentYear()
+        if last_cycle_tick and (current_tick - last_cycle_tick < 33600) then
+            local timeout_ticks = last_cycle_tick - current_tick + 33600
+            dfhack.timeout(timeout_ticks, 'ticks', event_loop)
+        else
+            checkmigrationnow()
+            dfhack.timeout(1, 'months', event_loop)
+        end
     end
 end
 
@@ -210,8 +219,9 @@ dfhack.onStateChange[GLOBAL_KEY] = function(sc)
         return
     end
 
-    local persisted_data = dfhack.persistent.getSiteData(GLOBAL_KEY, {enabled=false})
+    local persisted_data = dfhack.persistent.getSiteData(GLOBAL_KEY, {enabled=false,last_cycle_tick=0})
     enabled = persisted_data.enabled
+    last_cycle_tick = persisted_data.last_cycle_tick
     event_loop()
 end