scaffold the CLI, logging and turn research into TODOs

src/logging.rs

@@ -0,0 +1,54 @@
+use tracing::Level;
+use tracing_subscriber::{Layer as _, layer::SubscriberExt as _, util::SubscriberInitExt as _};
+
+pub const DEFAULT_LOG_LEVEL: Level = if cfg!(debug_assertions) {
+    Level::DEBUG // debug builds
+} else {
+    Level::WARN // release builds
+};
+
+fn level_to_index(level: Level) -> u8 {
+    match level {
+        Level::TRACE => 0,
+        Level::DEBUG => 1,
+        Level::INFO => 2,
+        Level::WARN => 3,
+        Level::ERROR => 4,
+    }
+}
+
+fn index_to_level(index: u8) -> Level {
+    match index {
+        0 => Level::TRACE,
+        1 => Level::DEBUG,
+        2 => Level::INFO,
+        3 => Level::WARN,
+        4.. => Level::ERROR,
+    }
+}
+
+fn level_from_verbosity(verbosity: u8) -> Level {
+    index_to_level(level_to_index(DEFAULT_LOG_LEVEL).saturating_sub(verbosity))
+}
+
+pub fn init_tracing(verbosity: u8) -> anyhow::Result<()> {
+    let terminal_layer = tracing_subscriber::fmt::layer()
+        .without_time()
+        .compact()
+        .boxed();
+
+    let level = level_from_verbosity(verbosity);
+
+    tracing_subscriber::registry()
+        .with(terminal_layer)
+        .with(
+            tracing_subscriber::EnvFilter::builder()
+                .with_default_directive(level.into())
+                .from_env()?,
+        )
+        .init();
+
+    tracing::info!("logging with level {level}");
+
+    Ok(())
+}