First pass at a farm control program.

farm_control.lua

@@ -0,0 +1,81 @@
+-- Program to control a farm made with the create mod
+
+-- establish amounts of items to ensure
+local LEVELS = {}
+LEVELS["minecraft:oak_log"] = {4 * 64, "minecraft:oak_sapling"}
+
+local STORAGE = ""
+local HARVESTER = ""
+
+local HARVESTER_RELAY = ""
+
+local SLEEP_TIME = 10
+local HARVESTER_SIGNAL_TIME = 2
+
+-------------------------------- PROGRAM --------------------------------------
+
+function pull_items (src, dest)
+    local src = peripheral.wrap(src)
+    if src.size() < 1 return nil end
+    for slot, _ in pairs(src.list()) do
+        src.pushItems(dest, slot)
+    end
+end
+
+-- need to return the sources for items that need farming
+-- e.g. a sapling for wood
+function check_levels (levels, src)
+    local src = peripheral.wrap(src)
+    local amounts = {}
+    for _, item in pairs(src.list()) do
+        if amounts[item.name] == nil then
+            amounts[item.name] = item.count
+        else
+            amounts[item.name] = amounts[item.name] + item.count
+        end
+    end
+    local needs_farming = {}
+    for item, data in pairs(levels) do
+        if amounts[item] ~= nil and amounts[item] < data[1] then
+            table.insert(needs_farming, data[2])
+        end
+    end
+    if needs_farming[1] == nil then
+        return nil
+    else
+        return needs_farming
+    end
+end
+
+function load_stack(item_name, src, dest)
+    local src = peripheral.wrap(src)
+    for slot, item in pairs(src.list()) do
+        if item.name == item_name then
+            src.pushItems(dest, slot)
+            break
+        end
+    end
+end
+
+function send_harvester (relay_and_side)
+    local RELAY_COMMAND = "setOutput"
+    local relay, side = relay_and_side:match"(.+):(.+)"
+    peripheral.call(relay, RELAY_COMMAND, side, true)
+    os.sleep(HARVESTER_SIGNAL_TIME)
+    peripheral.call(relay, RELAY_COMMAND, side, false)
+end
+
+-- TODO make a different loop for crops controlled by a CLI arg
+-- the other loop doesn't need to load the harvester, but also doesn't need
+-- to send the harvester unless stock drops below a level
+while true do
+    local needs_farming = check_levels(LEVELS, STORAGE)
+    if needs_farming ~= nil then
+        for _, item in ipairs(needs_farming) do
+            load_stack(item, STORAGE, HARVESTER)
+        end
+    end
+    send_harvester()
+    os.sleep(SLEEP_TIME)
+    pull_items(HARVESTER, STORAGE)
+end