Allow the player to automatize army movement

When you control a lot of provinces, and especially when auto-recruit is on, it's a lot of work having to move all of your armies one by one. There should be a way to automatically move armies in any direction. Here's my idea:

Create the code architecture

[x] Add new object in Country called AutoArrows, a list of AutoArrow
[x] Create AutoArrow class: has a source province and a destination province
[x] AutoArrows ignores any attempt to add a new AutoArrow that's a duplicate of an existing one
[x] AutoArrows listens to changes in all AutoArrow objects in the list. Whenever an arrow's information matches another one's, it deletes that arrow and its visuals
[x] Add new node in GameWorld2D called AutoArrowsNode2D, a list of AutoArrowNode2D
[x] Create AutoArrowNode2D class: contains an AutoArrow or, alternatively, can also take just a source province and a Vector2 destination

Draw the arrows on the world map

[x] AutoArrowNode draws an arrow using the information it has
[x] AutoArrowNode listens to changes in AutoArrow's provinces and updates the visuals accordingly
[x] Only show arrows when a province is selected (any province)
[x] Only show the playing country's arrows

Save the arrows between sessions

[x] Save the arrows for each Country
[x] Load the arrows for each Country

Add behavior

[x] At the end of a player's turn, the game goes through all of the country's arrows. For each arrow, checks if a controlled army is in the source province, and if so, creates and applies a new army movement action
[x] If more than one arrow points from the source province, splits the army evenly between each destination

Make the user able to add new arrows

[x] Have a new node that listens to mouse input for arrows
[x] When right click is pressed on a province, creates a new AutoArrowNode2D
[x] The AutoArrowNode2D points from the source province to the mouse cursor's position
[x] If the mouse cursor is on a valid destination, then the arrow snaps to the destination province
[x] If the right mouse button is released with a valid destination province, an AutoArrow is created and added to the Country's AutoArrows
[x] Players can add and remove arrows at any time, but they can only add them to their own country

Make the user able to remove arrows

[x] When a new arrow is created by the user that matches an existing arrow, it deletes the existing arrow instead of creating a new arrow
[x] A double right click on a province deletes all arrows going from that province

Synchronize between clients

[x] Sync the addition of an AutoArrow
[x] Sync the removal of an AutoArrow
[x] Non-server clients can only edit the AutoArrows of their locally controlled countries
[x] When it's a remote player's turn to play, you can't create or remove arrows

Note: no need to sync changes in AutoArrow properties because they de facto never change. Arrows are only added and removed, never modified.

SamTheBlow / grand-strategy-game

Allow the player to automatize army movement #149