feat(postgres): Introduce chained error variants

Introduces error variants for external crate errors and internal
errors.

Additional context can be provided at sites where errors occur using a
simple `.context()` call.

1 files changed, 61 insertions, 1 deletions

diff --git a/finito-postgres/src/error.rs b/finito-postgres/src/error.rs
index 0fb30a99dcd7..aacc219f0418 100644
--- a/finito-postgres/src/error.rs
+++ b/finito-postgres/src/error.rs
@@ -2,8 +2,68 @@
 //! occur while dealing with persisted state machines.
 
 use std::result;
+use std::fmt::Display;
+use uuid::Uuid;
+
+// errors to chain:
+use serde_json::Error as JsonError;
+use postgres::Error as PgError;
 
 pub type Result<T> = result::Result<T, Error>;
 
 #[derive(Debug)]
-pub enum Error { SomeError }
+pub struct Error {
+    pub kind: ErrorKind,
+    pub context: Option<String>,
+}
+
+#[derive(Debug)]
+pub enum ErrorKind {
+    /// Errors occuring during JSON serialization of FSM types.
+    Serialization(String),
+
+    /// Errors occuring during communication with the database.
+    Database(String),
+
+    /// State machine could not be found.
+    FSMNotFound(Uuid),
+
+    /// Action could not be found.
+    ActionNotFound(Uuid),
+}
+
+impl <E: Into<ErrorKind>> From<E> for Error {
+    fn from(err: E) -> Error {
+        Error {
+            kind: err.into(),
+            context: None,
+        }
+    }
+}
+
+impl From<JsonError> for ErrorKind {
+    fn from(err: JsonError) -> ErrorKind {
+        ErrorKind::Serialization(err.to_string())
+    }
+}
+
+impl From<PgError> for ErrorKind {
+    fn from(err: PgError) -> ErrorKind {
+        ErrorKind::Database(err.to_string())
+    }
+}
+
+/// Helper trait that makes it possible to supply contextual
+/// information with an error.
+pub trait ResultExt<T> {
+    fn context<C: Display>(self, ctx: C) -> Result<T>;
+}
+
+impl <T, E: Into<Error>> ResultExt<T> for result::Result<T, E> {
+    fn context<C: Display>(self, ctx: C) -> Result<T> {
+        self.map_err(|err| Error {
+            context: Some(format!("{}", ctx)),
+            .. err.into()
+        })
+    }
+}