# Git-kv, a simple Key-Value store synchronized with a Git repository

This library is a simple implementation of a Git repository that can be read
and/or modified. It offers two ways to create such a local repository:
1) The local repository can be created in a serialized state
2) The local repository can be created from a remote repository

The first method has the advantage of not requiring an internet connection. The
serialized state can be created with the `mgit` tool:
```sh
$ mgit https://github.com/mirage/mirage <<EOF
> save db.pack
> quit
$ ls db.pack
db.pack
```

The disadvantage is that the serialized state may be out of sync with the state
of the remote repository. In this case, the user has access to the `pull`
function, which allows the internet state of the local repository to be
re-synchronised with the remote repository.
```ocaml
let contents_of_file filename =
  let ic = open_in filename in
  let ln = in_channel_length ic in
  let rs = Bytes.create ln in
  really_input ic rs 0 ln ;
  Bytes.unsafe_to_string rs

let _ =
  Git_kv.of_octets ctx 
    ~remote:"git@github.com:mirage/mirage.git"
    (contents_of_file "db.pack") >>= fun t ->
  Git_kv.pull t >>= fun diff ->
  ...
```

The second method initiates a connection to the remote repository in order to
download its state and reproduce a synchronised internal state. The type of
connections supported are described in the given `ctx`. We recommend the
tutorial about [Mimic][mimic] to understand its use.
```sh
let _ =
  Git_kv.connect ctx "git@github.com:mirage/mirage.git" >>= fun t ->
  ...
```

The user can manipulate the repository as an [RW][mirage-kv-rw] repository. Any
change to the repository requires a new commit. These changes will be sent to
the remote repository by default. If the user does not want to push modifications,
they can use `Git_kv.Make.Local` which provide functions without `push`. If the
user knows that they will do many changes and they don't want to change all of
them and do a `push` only at the end, they can use `Git_kv.Make.batch`.
```ocaml
module Store = Git_kv.Make (Pclock)

let new_file_locally_and_remotely t =
  Store.set t Mirage_kv.Key.(empty / "foo") "foo" >>= fun () ->
  ...

let new_file_locally t =
  Git_kv.pull t >>= fun _diff ->
  Store.Local.set t Mirage_kv.Key.(empty / "foo") "foo" >>= fun () ->
  ...

let batch_operations t =
  Store.batch t @@ fun t ->
  Store.set t Mirage_kv.Key.(empty / "bar") "bar" >>= fun () ->
  Store.remove t Mirage_kv.Key.(empty / "foo")
```

[mimic]: https://dinosaure.github.io/mimic/mimic/index.html
[mirage-kv-rw]: https://github.com/mirage/mirage-kv