Storage<T>
                           development documentation

IMPORTANT

    *   Should be renamed

        Storage<T> is too long. Rust variables basically views between 3 and
        5-6 characters. Vec, Box, i32, u32, HashMap, HashSet, ...
        e.g.: Bag<T> could be fine.

        Name ideas:
            
            * Storage<T>|    
            * Store<T>  |
            * Strg<T>   |
            * Bag<T>    |   (L)     * * * * *
            * Bg<T>     |
            * Dal<T>    | 
            * Fd<T>     |
            * Data<T>   |
            * Dt<T>     |
            * Dta<T>    |
            * Peel<T>   |   (L)     * * *
            * Shell<T>  |
            * Shl<T>    |
            * Rind<T>   |
            * Layer<T>  |
            * Sack<T>   |
            * Pack<T>   |   (L)     * * * * *
            * Pop<T>    |
            * Pod<T>

Issues to solve
===============

    * Delete item?
        
        Delete item from FS and from Memory. Vec item could be removed,
        but a single Pop?

        Example

            impl<T, I> Vec<Pack<T>> {
                pub fn remove_item_by_id(&mut self, id: I) {..}
            }

    * Move item between storages?

        Move one Pack<T> from one storage to another one,
        when both of them has the same type T.

        This should be a kind of create new and remove the old one.

    * Single file storage

        Should be able to use a single file as a storage; in cases when we do
        not need any vector of the same type files.

        E.g.: config files, or helper files like let mut units: Pack<Units> =
        Pack::load_or_init("path")?;

    * Issue with single file storage

        How can we use a default implementation when the file does not exist
        yet? I mean we have a user conig, but we have a new user.

    * Pack::from_storage(&storageA)?;



    * Schema versions?

        Migrate easily and safely from one schema to a new one. Using easy
        development process to be sure, a schema has a schema backup history, so
        it can be up from older shcema automatically.

        In the recent version we use a kind of ~~ load_from() ~~ method, but it
        is not soo easy and not soo clear to use.

    * OBJECT ID any type? Not just &str
    * OBJECT ID automatic generation
    * Multy THREAD? Prevent racecondition

    * Pack as a struct field?

    struct Repository {
        #[path="/config"]
        config: Pack<Config>,
        #[path="/users"]
        users: Vec<Pack<User>>,
        #[path="/issues"]
        issues: Vec<Pack<Issue>>,
        ..
    }

    impl Repository {
        pub fn new(id: &str) -> PackResult<Self, Error> {
            let storage = Storage::load_or_init("data/repositories/", id);
            Repository {
                config: storage.file_from("config")?,
                users: storage.folder_from("./users/")?,
                issues: storage.folder_from("./folder")?
            }
        }
    }

Ideas

    A few ideas about the required design:

    struct Pack<T> {
        data: T,
        path: &'static str
    }

    impl<T> Deref for Pack<T> {..}
             |
             |
             *---  Implementing deref() means we can access the inner DATA
                   READ ONLY.

    struct Guard<'a, T> {
        data: &'a mut T,
        path: &'static str
    }

    impl<'a, T> Deref for Guard<'a, T> {..}

    impl<'a, T> DerefMut for Guard<'a, T> {..}
                    |
                    |
                    *---    Implementing deref_mut() means we have acces for
                            inner DATA as MUTABLE.

    impl<'a, T> Drop for Guard<'a, T> {..}
                 |
                 |
                 *---  Drop Guard<'a, T> automatically, and perform File save
                       on DATA OBJECT

    struct VecPack<T> {
        data: Vec<Pack<T>>,
        path: &'static str
    }

Init a Pack OBJECT

    Pack should be inited by loading from path, or create and save a new copy by
    its storage.

    e.g.:

        let config: Pack<Config> = Pack::load_from_path("path")?;

        let products: Vec<Pack<Product>> = Pack::load_from_path("path")?;
                |
                |
                *--- and then --> products.add_new(new_product)?;

        let config: Pack<Config> = Pack::load_or_init("path")?;

Pack variants

    Pack<T>
    PackVec<T>
    ---
    Vec<Pack<T>>
    HashMap<String, Pack<T>>

    let mut m = Storage::new("data");
    m.add(&mut Vec<Pack<T>>, T);

    let products: Storage<Pack<Product>> = Storage::load_or_init(..)?;
    products.push(new_product1)?;
    products.push(new_product2)?;

    let mut products: PackVec<Product> = PackVec::new("/data/products");
    products.push(new_product1)?;
    products.push(new_product2)?;

    Pack<T>
    
        +   deref(&self)  -> &T
        +   deref_mut(&mut self) -> &mut T
        +   save(&self) -> PackResult<()>
        +   update(&mut self, f: FnMut) -> R
        +   get(&self, f: Fn) -> R
        +   map(&self, f: F) -> R

        ::  load(path: &'static str) -> PackResult<Pack<T>>
        ::  load_or_init(path: &'static str) -> PackResult<Pack<T>>

        fn <T>try_load() -> PackResult<Pack<T>>
        where
            T: Serialize + Deserialize + TryFrom
        -------------
            1. Try open file
            2. Try read file content to buffer
            3. Try deserialize buffer to the given type
                |
                |
                *-- If SUCCESS  => returns the Pack<T>
                |
                *-- If ERROR    => try From<previous_type>

        pub trait TryLoad<T>
        where
            T: From<P>
            P: Deserialize {
            
            fn <P>try_load() -> PackResult<P>
        }

        save()
        -------------
            1. Try serialize OBJECT DATA
            2. Try write_all to the given path

    VecPack<T>

        + deref(&self) -> &Vec<Pack<T>>

            It's like an iter().

        ! deref_mut(&mut self) -> &mut Vec<Pack<T>>
       
            Ezt lehet nem kellene engedni
            csak a VecPack<T> apin keresztül
            Helyette iter_mut()

        + push(&mut self, T) -> PackResult<ID>

            Or add()..
            Add a new elem into the VecPack<T>

        + check_id_available(&self, id: ID) -> bool
        
        + push_with_id(&mut self, T, id: ID) -> PackResult<()>
        
        + get_by_id(id: I) -> Option<&Pack<T>>          / Option<&T>
        
        + get_mut_by_id(id: I) -> Option<&mut Pack<T>>  / Option<PackGuard<'_, T>>
        
        + iter() -> &Vec<Pack<T>>
        
        + into_iter(&mut self) -> &mut Vec<Pack<T>>
       
        + move(&mut self, index: I, to: D) -> PackResult<()>
       
        + remove(&mut self, index: I) -> PackResult<T>
        
        + get_path(&self) -> Path

        let struct Repository {
            id: String,
            config: Pack<Config>,
            users: PackVec<User>,
            products: PackVec<Product>
        }

        let mut repositories: Pack<Vec<String>> =
            Pack::load_or_init("/data/repositores")?;

        let mut repos: Vec<Repository> = repositores
                                            .iter()
                                            .map(|r| i.init())
                                            .collect();

Pack methods

    * save(&self) -> PackResult<Self>   <----- result Self is not sure
    *


    let product_storage: Storage<Product> = Storage::load_or_init("/products")?;
    let p1 = product_storage.new(Product::new())?;

    let mut products: Vec<Pack<Product>> = Vec::new();
    products.push(p1);


Storage<Vec<Pack<T>>>

Schema Version Management (SVM)

    We need an easy to use solution to manage schema updates and data migration
    with ZERO ERROR.
    
    trait TryFrom {
        type From: TryFrom;
        fn try_from() -> PackResult<Self> {}
    }