Implement the headless SSH server

crates/bds-server/src/boot.rs

@@ -0,0 +1,121 @@
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BootMode {
+    Desktop,
+    Server,
+    Tui,
+}
+
+impl BootMode {
+    pub fn resolve(value: Option<&str>) -> Self {
+        match value.map(str::trim).map(str::to_ascii_lowercase).as_deref() {
+            Some("server") => Self::Server,
+            Some("tui") => Self::Tui,
+            _ => Self::Desktop,
+        }
+    }
+
+    pub fn effective(self, platform: Platform, env: &HashMap<String, String>) -> Self {
+        if self != Self::Desktop {
+            return self;
+        }
+        match platform {
+            Platform::MacOs if has_any(env, &["SSH_CONNECTION", "SSH_CLIENT", "SSH_TTY"]) => {
+                Self::Tui
+            }
+            Platform::Unix if !has_any(env, &["DISPLAY", "WAYLAND_DISPLAY"]) => Self::Tui,
+            _ => Self::Desktop,
+        }
+    }
+
+    pub fn components(self) -> BootComponents {
+        match self {
+            Self::Desktop => BootComponents {
+                engine_host: true,
+                ssh_daemon: false,
+                desktop_ui: true,
+                local_tui: false,
+            },
+            Self::Server => BootComponents {
+                engine_host: true,
+                ssh_daemon: true,
+                desktop_ui: false,
+                local_tui: false,
+            },
+            Self::Tui => BootComponents {
+                engine_host: true,
+                ssh_daemon: true,
+                desktop_ui: false,
+                local_tui: true,
+            },
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Platform {
+    MacOs,
+    Unix,
+    Windows,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct BootComponents {
+    pub engine_host: bool,
+    pub ssh_daemon: bool,
+    pub desktop_ui: bool,
+    pub local_tui: bool,
+}
+
+fn has_any(env: &HashMap<String, String>, keys: &[&str]) -> bool {
+    keys.iter()
+        .any(|key| env.get(*key).is_some_and(|value| !value.is_empty()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn modes_resolve_and_initialize_only_their_components() {
+        assert_eq!(BootMode::resolve(None), BootMode::Desktop);
+        assert_eq!(BootMode::resolve(Some("SERVER")), BootMode::Server);
+        assert_eq!(BootMode::resolve(Some("tui")), BootMode::Tui);
+        assert!(BootMode::Desktop.components().desktop_ui);
+        assert!(!BootMode::Server.components().desktop_ui);
+        assert!(!BootMode::Tui.components().desktop_ui);
+        assert!(BootMode::Tui.components().local_tui);
+    }
+
+    #[test]
+    fn desktop_falls_back_only_when_the_platform_is_headless() {
+        let empty = HashMap::new();
+        assert_eq!(
+            BootMode::Desktop.effective(Platform::Unix, &empty),
+            BootMode::Tui
+        );
+        assert_eq!(
+            BootMode::Desktop.effective(Platform::MacOs, &empty),
+            BootMode::Desktop
+        );
+        assert_eq!(
+            BootMode::Desktop.effective(Platform::Windows, &empty),
+            BootMode::Desktop
+        );
+        let display = HashMap::from([("DISPLAY".into(), ":0".into())]);
+        assert_eq!(
+            BootMode::Desktop.effective(Platform::Unix, &display),
+            BootMode::Desktop
+        );
+        let ssh = HashMap::from([("SSH_TTY".into(), "/dev/tty".into())]);
+        assert_eq!(
+            BootMode::Desktop.effective(Platform::MacOs, &ssh),
+            BootMode::Tui
+        );
+        assert_eq!(
+            BootMode::Server.effective(Platform::Unix, &empty),
+            BootMode::Server
+        );
+    }
+}