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--- libecho:classes:persistence [2022/05/20 18:06] – lee
+++ libecho:classes:persistence [2023/08/06 19:36] (current) – removed lee
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-====== LibEcho.Persistence ======
-Most web browsers only allow for 10 megs (though some are as low as 5) of on-disk storage per origin. This not only has to contain the current game state, but also all previous game states in the game history. This is a particular problem with very large and/or complicated Twine games.
-In an attempt to minimize this issue, LibEcho uses a defaults and delta Persistence system. "Persistent Objects", be they characters within the game and their statistics and inventory, articles of clothing and their state, etc etc, are all defined  at initialization time, <i>outside</i> of SugarCube's game history stack. Later, when an object's state is changed, only the differences from the object's initially defined default state are stored within SugarCube's game history stack. This greatly reduces the game's localstorage footprint (versus storing every object's full state within every game history moment), while still allowing the flexibility for almost all objects to be modified and tracked in the story history.
-All persistent objects must ultimately derive from the PersistentObject class.
-Each PersistentObject has a readonly "id" field (hereafter referred to as the "Persistence ID"), a simple alphanumeric-underscore string (whitespace, punctuation, and special symbols are not allowed).
-A PersistentObject may be the "child" of another PersistentObject. This is tracked in the id field via a dot notation. For example, each Person object contains a GeneralInventory object that tracks what the Person is carrying. If the game contains a Person with the id of "joe", then the id of Joe's GeneralInventory object might be "joe.inventory". Likewise, the actual contents of that GeneralInventory might be stored as "joe.inventory.contents", an array called "contents" within the joe.inventory object.
-You won't generally need to worry too much about this id hierarchy, though. LibEcho takes care of most of it for you. The vast majority of the time, you'll only need to know the ids of toplevel objects that you have explicitly created: "joe", "cocktail_dress", etc.
-===== How It Works =====
-The implementation of PersistentObject isn't very straightforward to read.  Here's a high level overview of how it works.
-There are three layers of data associated with a PersistentObject.
-The lowest layer is called the "object layer", and comprises properties that are defined in the actual subclass itself, in the constructor, in the usual way.  These data are generally default values that will be the same on any object of a given type, although they can be overridden by higher layers of data.
-Unless you are actually extending LibEcho itself, you will probably never really need to deal with the object layer in your story.
-The middle layer is called the "defaults layer".  These data are defined by the story author in a JS file, using the static function PersistentObject.define().  This is used to define every specific concrete object in the game, by registering its Persistence ID, PersistentObject subclass, and default properties.  These data will override any properties that are set on the object itself in the class constructor.
-Finally, the top layer is called the "sugarcube layer".  This layer is stored within Sugarcube's state history, and overrides data in the layers below it.  If you change a property on an object to something different than the value you defined in the defaults layer, the new value will be stored in the sugarcube layer and will override the data in the defaults and object layers.  If you delete the property or set it back to the value you defined in the defaults layer, it will be removed from Sugarcube's state history, and the value from the defaults layer will be used once again.
-In this way, only the changes from the default data are stored in Sugarcube's limited-size story history, yet all properties on any PersistentObject can be mutable.
-These three layers are implemented by returning a Proxy object from the PersistentObject constructor.  The Proxy's handler intercepts all property accesses to the PersistentObject and routes them through our own code that handles the layered data levels.
-This handler also replaces all references to PersistentObjects stored within Sugarcube's state history with a placeholder object that tracks the real PersistentObject's 'id' field, and then reinstantiates the real PersistentObject when it is fetched back from the Sugarcube datastore.  This allows for circular graphs of PersistentObjects to be stored within Sugarcube's state history without causing a covfefe.  You still can't have circular graphs of non-PersistentObjects, but as long as there is a PersistentObject somewhere in the graph that keeps the circle from circling back on itself, things should work.  It's not the most efficient way to do things, but I think it's the best way short of patching Sugarcube itself.
-Please look at the [[Tutorial]] for more details.  This implementation works decently well, but there are some gotchas to look out for that are sort of hacked around, particularly in the constructors of subclasses.
-===== LibEcho.Persistence.PersistentObject =====
-Inherits from: Nothing
-The PersistentObject is the class from which all of the more complex persistent data types are derived. People, Apparel, Transformable attributes, Inventories of various sorts, and many other classes of objects, are all are ultimately derived from PersistentObject.
-//**ALERT!  MAKE NOTE!  ALERT!**//
-//**You should never instantiate a PersistentObject directly!  Instead, you must define it with PersistentObject.define(), and then either store the result somewhere or re-fetch it with PersistentObject.fetch() when you want to use it.**//
-If you try to instantiate a PersistentObject directly, rather than wrapping it in a call to fetch(), the Proxy object will get confused about what to do with properties that are set in subclass constructors, and you'll have an unhappy day.  fetch() wraps things up with some hackery-magic and makes things behave as you'd expect for the most part.
-==== Static Functions ====
-=== PersistentObject.define( id, objectClass=PersistentObject, defaults={}, allowRedefine=false ) ===
-Defines the default data for a PersistentObject (or subclass thereof) within your game. PersistentObject.define() must only be called at initialization time, from story javascript or initialization passages.  The results of trying to use this function after the game has started are undefined.
-  * id: the Persistence ID of the object being defined.
-  * objectClass: the class of the object being defined.  PersistentObject or subclass thereof.
-  * defaults: a mapping of property names to data for the object's default data.
-  * allowRedefine: if true, the object may be redefined.  This is used internally and you probably shouldn't mess with it unless you are sure of what you are doing.
-  * Returns: An instantiated instance of the object that was defined.
-  * Throws: Error if the object is being redefined (and allowRedefine=false) or if the previously defined object does not have a valid class associated with it.
-All PersistentObjects (and subclasses) must be defined using this method before they can be used within the game.  See the [[Tutorial]] for a better explanation of all of this.
-Example:<code>
-LibEcho.PersistentObject.define( "joe", LibEcho.Person.Man, {
-	"name":               "Joe",
-	"lastName":           "Blow",
-	"inventory.contents": [ "revolver" ],
-	"apparel.contents":   [ "boxers", "jeans", "tshirt", "socks", "tennisshoes" ]
-});</code>
-=== PersistentObject.fetch( id, forceClass=undefined ) ===
-Given a persistence ID, returns the appropriate instantiated object (a PersistentObject or subclass).
-  * id: the Persistence ID of the object being fetched.
-  * forceClass: If set, overrides the class associated with the object ID and uses the given class instead.  This is used internally and you probably shouldn't mess with it unless you are sure of what you are doing.
-  * Returns: An instantiated instance of the object defined with the given id.
-  * Throws: Error if the object does not have a valid class associated with it.
-==== Properties ====
-=== .id ===
-This object's Persistence ID, as defined with PersistentObject.define().
-  * Type: String
-  * Automatic
-  * ReadOnly
-=== .parent ===
-This object's parent.  For example, the parent of the object with the id "joe.inventory" would be the object with the id "joe".
-  * Type: PersistentObject or undefined
-  * Automatic
-  * ReadOnly
-=== .name ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .nameIsProper ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .nameIrregularArticle ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .genericName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .genericNameIsProper ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .genericNameIrregularArticle ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .aName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .AName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .aGenericName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .AGenericName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .theName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .TheName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .theGenericName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .TheGenericName ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .image ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .thumbnail ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .equals( o ) ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .toString() ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .clone() ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .toJSON() ===
-FIXME
-  * Type: type
-  * Optional Required
-=== .someProperty ===
-FIXME
-  * Type: type
-  * Optional Required

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