- Mech Fabricator can be built. Contruction path is almost the same as for lathes, but you'll require 2 Matter Bins, 1 Manipulator, 1 Micro-Laser and 1 Console Screen.

- Added design for mech fabricator circuitboard.
- Added origin_tech for some mech equipment.
- Examining mecha chassis will show what construction step you're currently on.
- Made Gygax construction reversible.
- Moved global_iterator.dm and construction_datum.dm to code/datums/helper_datums
- Split mecha_construction.dm into mecha_parts.dm and mecha_construction_paths.dm
- Fixed wrong logic for mecha dna-checks.

git-svn-id: http://tgstation13.googlecode.com/svn/trunk@1402 316c924e-a436-60f5-8080-3fe189b3f50e

code/datums/helper_datums/construction_datum.dm

@@ -0,0 +1,110 @@
+#define FORWARD -1
+#define BACKWARD 1
+
+/datum/construction
+	var/list/steps
+	var/atom/holder
+	var/result
+	var/list/steps_desc
+
+	New(atom)
+		..()
+		holder = atom
+		if(!holder) //don't want this without a holder
+			spawn
+				del src
+		set_desc(steps.len)
+		return
+
+	proc/next_step()
+		steps.len--
+		if(!steps.len)
+			spawn_result()
+		else
+			set_desc(steps.len)
+		return
+
+	proc/action(atom/used_atom,mob/user as mob)
+		return
+
+	proc/check_step(atom/used_atom,mob/user as mob) //check last step only
+		var/valid_step = is_right_key(used_atom)
+		if(valid_step)
+			if(custom_action(valid_step, used_atom, user))
+				next_step()
+				return 1
+		return 0
+
+	proc/is_right_key(atom/used_atom) // returns current step num if used_atom is of the right type.
+		var/list/L = steps[steps.len]
+		if(istype(used_atom, text2path(L["key"])))
+			return steps.len
+		return 0
+
+	proc/custom_action(step, used_atom, user)
+		return 1
+
+	proc/check_all_steps(atom/used_atom,mob/user as mob) //check all steps, remove matching one.
+		for(var/i=1;i<=steps.len;i++)
+			var/list/L = steps[i];
+			if(istype(used_atom, text2path(L["key"])))
+				if(custom_action(i, used_atom, user))
+					steps[i]=null;//stupid byond list from list removal...
+					clear_nulls(steps);
+					if(!steps.len)
+						spawn_result()
+					return 1
+		return 0
+
+
+	proc/spawn_result()
+		if(result)
+			new result(get_turf(holder))
+			spawn()
+				del holder
+		return
+
+	proc/clear_nulls(list/L)
+		while(null in L)
+			L -= null
+		return
+
+	proc/set_desc(index as num)
+		var/list/step = steps[index]
+		holder.desc = step["desc"]
+		return
+
+/datum/construction/reversible
+	var/index
+
+	New(atom)
+		..()
+		index = steps.len
+		return
+
+	proc/update_index(diff as num)
+		index+=diff
+		if(index==0)
+			spawn_result()
+		else
+			set_desc(index)
+		return
+
+	is_right_key(atom/used_atom) // returns index step
+		var/list/L = steps[index]
+		if(istype(used_atom, L["key"]))
+			return FORWARD //to the first step -> forward
+		else if(L["backkey"] && istype(used_atom, L["backkey"]))
+			return BACKWARD //to the last step -> backwards
+		return 0
+
+	check_step(atom/used_atom,mob/user as mob)
+		var/diff = is_right_key(used_atom)
+		if(diff)
+			if(custom_action(index, diff, used_atom, user))
+				update_index(diff)
+				return 1
+		return 0
+
+	custom_action(index, diff, used_atom, user)
+		return 1