factor storage out to a trait object

src/taskstorage/inmemory.rs

@@ -0,0 +1,101 @@
+use crate::operation::Operation;
+use crate::taskstorage::{TaskMap, TaskStorage};
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use uuid::Uuid;
+
+#[derive(PartialEq, Debug, Clone)]
+pub struct InMemoryStorage {
+    // The current state, with all pending operations applied
+    tasks: HashMap<Uuid, TaskMap>,
+
+    // The version at which `operations` begins
+    base_version: u64,
+
+    // Operations applied since `base_version`, in order.
+    //
+    // INVARIANT: Given a snapshot at `base_version`, applying these operations produces `tasks`.
+    operations: Vec<Operation>,
+}
+
+impl InMemoryStorage {
+    pub fn new() -> InMemoryStorage {
+        InMemoryStorage {
+            tasks: HashMap::new(),
+            base_version: 0,
+            operations: vec![],
+        }
+    }
+}
+
+impl TaskStorage for InMemoryStorage {
+    /// Get an (immutable) task, if it is in the storage
+    fn get_task(&self, uuid: &Uuid) -> Option<TaskMap> {
+        match self.tasks.get(uuid) {
+            None => None,
+            Some(t) => Some(t.clone()),
+        }
+    }
+
+    /// Create a task, only if it does not already exist.  Returns true if
+    /// the task was created (did not already exist).
+    fn create_task(&mut self, uuid: Uuid, task: TaskMap) -> bool {
+        if let ent @ Entry::Vacant(_) = self.tasks.entry(uuid) {
+            ent.or_insert(task);
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Set a task, overwriting any existing task.
+    fn set_task(&mut self, uuid: Uuid, task: TaskMap) {
+        self.tasks.insert(uuid, task);
+    }
+
+    /// Delete a task, if it exists.  Returns true if the task was deleted (already existed)
+    fn delete_task(&mut self, uuid: &Uuid) -> bool {
+        if let Some(_) = self.tasks.remove(uuid) {
+            true
+        } else {
+            false
+        }
+    }
+
+    fn get_task_uuids<'a>(&'a self) -> Box<dyn Iterator<Item = Uuid> + 'a> {
+        Box::new(self.tasks.keys().map(|u| u.clone()))
+    }
+
+    /// Add an operation to the list of operations in the storage.  Note that this merely *stores*
+    /// the operation; it is up to the TaskDB to apply it.
+    fn add_operation(&mut self, op: Operation) {
+        self.operations.push(op);
+    }
+
+    /// Get the current base_version for this storage -- the last version synced from the server.
+    fn base_version(&self) -> u64 {
+        return self.base_version;
+    }
+
+    /// Get the current set of outstanding operations (operations that have not been sync'd to the
+    /// server yet)
+    fn operations<'a>(&'a self) -> Box<dyn Iterator<Item = &'a Operation> + 'a> {
+        Box::new(self.operations.iter())
+    }
+
+    /// Apply the next version from the server.  This replaces the existing base_version and
+    /// operations.  It's up to the caller (TaskDB) to ensure this is done consistently.
+    fn update_version(&mut self, version: u64, new_operations: Vec<Operation>) {
+        // ensure that we are applying the versions in order..
+        assert_eq!(version, self.base_version + 1);
+        self.base_version = version;
+        self.operations = new_operations;
+    }
+
+    /// Record the outstanding operations as synced to the server in the given version.
+    fn local_operations_synced(&mut self, version: u64) {
+        assert_eq!(version, self.base_version + 1);
+        self.base_version = version;
+        self.operations = vec![];
+    }
+}