[Gem/Placement] Detect Esc key while building

Issue: #416

In order to cancel construction, one must select the building being
constructed.  This, however, is error prone.  There is a short time
window in which to do this.  One also must select the building.

An alternative option would be to automatically select the unit.
However, that prevents giving the building multiple orders.  As such, we
detect usage of the escape key.  If the builder is selected and
building, we cancel construction of the building.

src/gem/placement.j

@@ -18,6 +18,7 @@
 // - If there are no registered units, then nothing will be placed. Rather, the
 //   placement structure will be replaced by `null`.
 // - If all unit types have a weight of `0.0`, placement behavior is undefined.
+// - Certain guarantees of Orc style construction are expected.
 
 globals
 
@@ -27,9 +28,13 @@ globals
 	// unless some sort of error is encountered.
 	constant integer Gem_Placement___PLACEMENT_UNIT_ID = 'h006'
 
+	constant integer Gem_Placement___CANCEL_ORDER_ID = 851976
+
 	// The lumber cost for the placement structure.
 	constant integer Gem_Placement___PLACEMENT_UNIT_COST = 1
 
+	unit array Gem_Placement___Constructing
+
 	// Each player has their own unique pool, which contains up to date unit
 	// types and weights.
 	unitpool array Gem_Placement___POOL
@@ -245,17 +250,47 @@ function Gem_Placement__Clear_Weight takes player the_player, integer unit_type
 	call Gem_Placement__Set_Weight (the_player, unit_type, 0.00)
 endfunction
 
+function Gem_Placement___Start takes nothing returns nothing
+	local unit which = GetTriggerUnit ()
+	local player whom
+	local integer whom_id
+
+	if GetUnitTypeId (which) != Gem_Placement___PLACEMENT_UNIT_ID then
+		return
+	endif
+
+	set whom = GetTriggerPlayer ()
+	set whom_id = GetPlayerId (whom)
+
+	set Gem_Placement___Constructing [whom_id] = which
+endfunction
+
+function Gem_Placement___Escape takes nothing returns nothing
+	local player whom = GetTriggerPlayer ()
+	local integer whom_id = GetPlayerId (whom)
+	local unit builder = Gem_Player__Get_Miner (whom)
+
+	if not IsUnitSelected (builder, whom) then
+		return
+	endif
+
+	call IssueImmediateOrderById (Gem_Placement___Constructing [whom_id], Gem_Placement___CANCEL_ORDER_ID)
+	set Gem_Placement___Constructing [whom_id] = null
+endfunction
+
 // Keeps track of when placement structures have had construction cancelled.
 // The primary purpose of this function is to refund lumber if a placement
 // phase is currently active.
 function Gem_Placement___Cancel takes nothing returns boolean
 	local player the_player
+	local integer whom_id
 
 	if GetUnitTypeId (GetTriggerUnit ()) != Gem_Placement___PLACEMENT_UNIT_ID then
 		return false
 	endif
 
 	set the_player = GetTriggerPlayer ()
+	set whom_id = GetPlayerId (the_player)
 
 	if Gem_Placement__Is_Active (the_player) then
 		// As the constant 'ConstructionRefundRate' has been set to zero, we need
@@ -265,13 +300,16 @@ function Gem_Placement___Cancel takes nothing returns boolean
 		call SetPlayerState (the_player, PLAYER_STATE_RESOURCE_LUMBER, GetPlayerState (the_player, PLAYER_STATE_RESOURCE_LUMBER) + Gem_Placement___PLACEMENT_UNIT_COST)
 	endif
 
+	set Gem_Placement___Constructing [whom_id] = null
+
 	return false
 endfunction
 
 // The core of the system. Deals with placement structures that have finished
 // construction, turning them into registered unit types.
 function Gem_Placement___Placement takes nothing returns boolean
 	local player the_player
+	local integer whom_id
 	local integer index__player
 	local unit old
 
@@ -290,6 +328,9 @@ function Gem_Placement___Placement takes nothing returns boolean
 		return false
 	endif
 
+	set whom_id = GetPlayerId (the_player)
+	set Gem_Placement___Constructing [whom_id] = null
+
 	set Gem_Placement___Placed [index__player] = Gem_Placement___Placed [index__player] + 1
 
 	call ShowUnit (old, false)
@@ -317,9 +358,17 @@ function Gem_Placement__Initialize takes nothing returns boolean
 	local player the_player
 	local integer index__player
 
+	local trigger trigger__escape
+	local trigger trigger__start
 	local trigger trigger__cancel
 	local trigger trigger__placement
 
+	set trigger__escape = CreateTrigger ()
+	call TriggerAddCondition (trigger__escape, Condition (function Gem_Placement___Escape))
+
+	set trigger__start = CreateTrigger ()
+	call TriggerAddCondition (trigger__start, Condition (function Gem_Placement___Start))
+
 	set trigger__cancel = CreateTrigger ()
 	call TriggerAddCondition (trigger__cancel, Condition (function Gem_Placement___Cancel))
 
@@ -331,6 +380,8 @@ function Gem_Placement__Initialize takes nothing returns boolean
 		set the_player = Player (index__player)
 		set Gem_Placement___POOL [index__player] = CreateUnitPool ()
 
+		call TriggerRegisterPlayerEvent (trigger__escape, the_player, EVENT_PLAYER_END_CINEMATIC)
+		call TriggerRegisterPlayerUnitEvent (trigger__start, the_player, EVENT_PLAYER_UNIT_CONSTRUCT_START, null)
 		call TriggerRegisterPlayerUnitEvent (trigger__cancel, the_player, EVENT_PLAYER_UNIT_CONSTRUCT_CANCEL, null)
 		call TriggerRegisterPlayerUnitEvent (trigger__placement, the_player, EVENT_PLAYER_UNIT_CONSTRUCT_FINISH, null)