add taskdb

src/taskdb.rs

@@ -0,0 +1,142 @@
+use crate::errors::Error;
+use chrono::{DateTime, Utc};
+use serde_json::Value;
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use uuid::Uuid;
+
+#[derive(PartialEq, Clone, Debug)]
+enum Operation {
+    Create {
+        uuid: Uuid,
+    },
+    Update {
+        uuid: Uuid,
+        property: String,
+        value: Value,
+        timestamp: DateTime<Utc>,
+    },
+}
+
+struct DB {
+    // The current state, with all pending operations applied
+    tasks: HashMap<Uuid, HashMap<String, Value>>,
+
+    // 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 DB {
+    fn new() -> DB {
+        DB {
+            tasks: HashMap::new(),
+            base_version: 0,
+            operations: vec![],
+        }
+    }
+
+    fn apply(&mut self, op: Operation) -> Result<(), Error> {
+        match op {
+            Operation::Create { uuid } => {
+                match self.tasks.entry(uuid) {
+                    Entry::Occupied(_) => {
+                        return Err(Error::DBError(format!("Task {} already exists", uuid)));
+                    }
+                    ent @ Entry::Vacant(_) => {
+                        ent.or_insert(HashMap::new());
+                    }
+                };
+            }
+            Operation::Update {
+                ref uuid,
+                ref property,
+                ref value,
+                timestamp: _,
+            } => {
+                match self.tasks.get_mut(uuid) {
+                    Some(task) => {
+                        task.insert(property.clone(), value.clone());
+                    }
+                    None => {
+                        return Err(Error::DBError(format!("Task {} does not exist", uuid)));
+                    }
+                };
+            }
+        };
+        self.operations.push(op);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use uuid::Uuid;
+
+    #[test]
+    fn test_apply_create() {
+        let mut db = DB::new();
+        let uuid = Uuid::new_v4();
+        let op = Operation::Create { uuid };
+        db.apply(op.clone()).unwrap();
+
+        let mut exp = HashMap::new();
+        exp.insert(uuid, HashMap::new());
+        assert_eq!(db.tasks, exp);
+        assert_eq!(db.operations, vec![op]);
+    }
+
+    #[test]
+    fn test_apply_create_exists() {
+        let mut db = DB::new();
+        let uuid = Uuid::new_v4();
+        db.apply(Operation::Create { uuid }).unwrap();
+        assert_eq!(
+            db.apply(Operation::Create { uuid }),
+            Err(Error::DBError(format!("Task {} already exists", uuid)))
+        );
+    }
+
+    #[test]
+    fn test_apply_create_update() {
+        let mut db = DB::new();
+        let uuid = Uuid::new_v4();
+        let op1 = Operation::Create { uuid };
+        db.apply(op1.clone()).unwrap();
+        let op2 = Operation::Update {
+            uuid,
+            property: String::from("title"),
+            value: Value::from("\"my task\""),
+            timestamp: Utc::now(),
+        };
+        db.apply(op2.clone()).unwrap();
+
+        let mut exp = HashMap::new();
+        let mut task = HashMap::new();
+        task.insert(String::from("title"), Value::from("\"my task\""));
+        exp.insert(uuid, task);
+        assert_eq!(db.tasks, exp);
+        assert_eq!(db.operations, vec![op1, op2]);
+    }
+
+    #[test]
+    fn test_apply_update_does_not_exist() {
+        let mut db = DB::new();
+        let uuid = Uuid::new_v4();
+        assert_eq!(
+            db.apply(Operation::Update {
+                uuid,
+                property: String::from("title"),
+                value: Value::from("\"my task\""),
+                timestamp: Utc::now(),
+            }),
+            Err(Error::DBError(format!("Task {} does not exist", uuid)))
+        );
+    }
+
+}