Introduce document module

This module holds the automerge `AutoCommit` document now with all the
necessary methods around it we need.

Additionally this commit prepares the use of a hard-coded byte
representation to construct the document. This will allow us to
independently create documents across peers as all peers will create the
_same_ document schema whenever they do it. More about it here:

<https://automerge.org/docs/cookbook/modeling-data/#setting-up-an-initial-document-structure>

src/document.rs

@@ -0,0 +1,82 @@
+use std::fmt;
+
+use anyhow::Result;
+use automerge::{AutoCommit, AutoSerde, Patch};
+
+const DOCUMENT_OBJ_ID: &str = "doc";
+
+const DOCUMENT_SCHEMA: [u8] = [1, 2, 3];
+
+#[derive(Debug)]
+pub struct Document {
+    doc: RefCell<AutoCommit>,
+}
+
+impl Document {
+    pub fn new() -> Self {
+        let doc = AutoCommit::new();
+        doc.put_object(automerge::ROOT, DOCUMENT_OBJ_ID, ObjType::Text)
+            .expect("inserting text object '{DOCUMENT_OBJ_ID}' at root");
+        Self {
+            doc: RefCell::new(doc),
+        }
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Self {
+        let doc = AutoCommit::load(bytes).expect("load automerge document from bytes");
+        Self {
+            doc: RefCell::new(doc),
+        }
+    }
+
+    pub fn update(&mut self, position: i32, del: i32, text: &str) -> Result<()> {
+        let mut doc = self.doc.borrow_mut();
+        doc.splice_text(&root, position as usize, del as isize, text)?;
+        // Move the diff pointer forward to current position
+        doc.update_diff_cursor();
+        Ok(())
+    }
+
+    pub fn load_incremental(&mut self, bytes: &[u8]) -> Result<()> {
+        let mut doc = self.doc.borrow_mut();
+        doc.load_incremental(&bytes)?;
+        Ok(())
+    }
+
+    pub fn diff_incremental(&mut self) -> Vec<Patch> {
+        let mut doc = self.doc.borrow_mut();
+        doc.diff_incremental()
+    }
+
+    pub fn text(&self) -> String {
+        let doc = self.doc.borrow();
+        let obj = doc.get(automerge::ROOT, DOCUMENT_OBJ_ID);
+        doc.text(&obj)
+            .expect("text to be given in automerge document")
+    }
+
+    pub fn save(&mut self) -> Vec<u8> {
+        let mut doc = self.doc.borrow_mut();
+        doc.save()
+    }
+
+    pub fn save_incremental(&mut self) -> Vec<u8> {
+        let mut doc = self.doc.borrow_mut();
+        doc.save_incremental()
+    }
+}
+
+impl Default for Document {
+    fn default() -> Self {
+        Self::from_bytes(&DOCUMENT_SCHEMA)
+    }
+}
+
+impl fmt::Debug for Document {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut doc = self.doc.borrow();
+        let json = serde_json::to_string_pretty(&AutoSerde::from(doc))
+            .expect("serialize automerge document to JSON");
+        write!(f, "{}", json)
+    }
+}

src/main.rs

@@ -20,19 +20,20 @@
 
 mod application;
 mod config;
+mod document;
 mod network;
 mod operation;
-mod window;
 mod textbuffer;
+mod window;
 
 use self::application::AardvarkApplication;
-use self::window::AardvarkWindow;
 use self::textbuffer::AardvarkTextBuffer;
+use self::window::AardvarkWindow;
 
 use config::{GETTEXT_PACKAGE, LOCALEDIR, PKGDATADIR};
 use gettextrs::{bind_textdomain_codeset, bindtextdomain, textdomain};
-use gtk::{gio, glib};
 use gtk::prelude::*;
+use gtk::{gio, glib};
 
 fn main() -> glib::ExitCode {
     // Set up gettext translations