Default to user's previously selected session

Closes: #109

cosmic-greeter-config/src/lib.rs

@@ -0,0 +1,48 @@
+// Copyright 2024 System76 <info@system76.com>
+// SPDX-License-Identifier: GPL-3.0-only
+
+pub mod user;
+
+use std::{collections::HashMap, num::NonZeroU32};
+
+use cosmic_config::{cosmic_config_derive::CosmicConfigEntry, CosmicConfigEntry};
+use serde::{Deserialize, Serialize};
+
+pub const APP_ID: &str = "com.system76.CosmicGreeter";
+pub const CONFIG_VERSION: u64 = 1;
+
+#[derive(Debug, Clone, Default, PartialEq, CosmicConfigEntry, Deserialize, Serialize)]
+#[version = 1]
+#[id = "com.system76.CosmicGreeter"]
+pub struct Config {
+    #[serde(skip_serializing_if = "HashMap::is_empty")]
+    pub users: HashMap<NonZeroU32, user::UserState>,
+}
+
+impl Config {
+    pub fn load() -> (Self, Option<cosmic_config::Config>) {
+        crate::load()
+    }
+}
+
+pub(crate) fn load<C>() -> (C, Option<cosmic_config::Config>)
+where
+    C: Default + CosmicConfigEntry,
+{
+    match cosmic_config::Config::new(APP_ID, CONFIG_VERSION) {
+        Ok(handler) => {
+            let config = C::get_entry(&handler)
+                .inspect_err(|(errors, _)| {
+                    for err in errors {
+                        log::error!("{err}")
+                    }
+                })
+                .unwrap_or_else(|(_, config)| config);
+            (config, Some(handler))
+        }
+        Err(e) => {
+            log::error!("Failed to get settings for `{APP_ID}` (v {CONFIG_VERSION}): {e:?}");
+            (C::default(), None)
+        }
+    }
+}

cosmic-greeter-config/src/user.rs

@@ -0,0 +1,20 @@
+// Copyright 2024 System76 <info@system76.com>
+// SPDX-License-Identifier: GPL-3.0-only
+
+use std::num::NonZeroU32;
+
+use serde::{Deserialize, Serialize};
+
+/// Per user state for Greeter.
+#[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
+pub struct UserState {
+    #[serde(skip_serializing_if = "invalid_uid")]
+    pub uid: NonZeroU32,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub last_session: Option<String>,
+}
+
+// Only serialize users not system accounts
+const fn invalid_uid(uid: &NonZeroU32) -> bool {
+    uid.get() < 1000
+}