Create initial project structure

The initial project structure includes the base scaffolding of the
application as well as the ability to fetch the repo list from the
remote endpoint.

src/main.rs

@@ -0,0 +1,93 @@
+use crate::cli::Cli;
+use crate::config::Config;
+use crate::error::ConfigError;
+use crate::error::DredgeError;
+use clap::Parser;
+use std::ffi::OsString;
+use std::path::PathBuf;
+use crate::cli::Commands;
+
+pub(crate) mod cli;
+mod commands;
+mod config;
+mod error;
+
+/// The default basename of the main configuration file.
+const CONFIG_FILE_NAME: &str = "dredge.toml";
+
+/// The XDG directory prefix.
+const CONFIG_PREFIX: &str = "dredge";
+
+/// Locate the absolute path to the saved configuration file on disk.
+///
+/// If given an optional `path` to a configuration file, and that file
+/// exists on disk, the absoulte path to that file will be returned.
+/// Otherwise, the XDG configuration path will be used.  If neither the
+/// optional `path` parameter refers to an existing file on disk, nor a
+/// suitable configuration file can be located within the XDG configuration
+/// path, the `None` variant will be returned.
+fn locate_config_file(path: Option<OsString>) -> Option<PathBuf> {
+    log::trace!("locate_config_file({path:?})");
+
+    match path {
+        Some(path) => {
+            let p = PathBuf::from(path);
+            log::debug!("Checking if path {p:?} exists");
+            p.try_exists().map(|_| Some(p)).unwrap_or(None)
+        }
+        None => {
+            let xdg_dirs = xdg::BaseDirectories::with_prefix(CONFIG_PREFIX).ok()?;
+            let search_paths: Vec<PathBuf> = vec![xdg_dirs.get_config_home()]
+                .into_iter()
+                .chain(xdg_dirs.get_config_dirs())
+                .collect();
+
+            log::debug!(
+                "Searching configuration directories for {CONFIG_FILE_NAME} {search_paths:?}"
+            );
+            xdg_dirs.find_config_file(CONFIG_FILE_NAME)
+        }
+    }
+}
+
+/// Attempt to create a default configuration file in the XDG configuration
+/// path.  Any sub-directories of the XDG configuration path which do not
+/// already exist will be created automatically.
+///
+/// # Errors:
+///
+/// This returns a `ConfigError` if a problem occured which prevented either
+/// the creation of the directory tree, or in writing the default configuration
+/// to the file.
+fn create_default_config_file() -> Result<PathBuf, ConfigError> {
+    log::trace!("create_default_config_file()");
+
+    let xdg_dirs = xdg::BaseDirectories::with_prefix(CONFIG_PREFIX)?;
+    let config_path = xdg_dirs.place_config_file(CONFIG_FILE_NAME)?;
+    let default_config = toml::to_string_pretty(&Config::default())?;
+    std::fs::write(&config_path, default_config)?;
+    Ok(config_path)
+}
+
+#[async_std::main]
+async fn main() -> Result<(), DredgeError> {
+    let args = Cli::parse();
+
+    // -- Initialize logging
+    let log_level = args.log_level.clone();
+    femme::with_level(log::LevelFilter::from(log_level));
+
+    // -- Load and parse configuration file
+    let config_file =
+        locate_config_file(args.config).map_or_else(create_default_config_file, Ok)?;
+    log::debug!("Using configuration file {config_file:?}");
+
+    #[allow(unused_variables)]
+    let config = Config::try_from(config_file.as_ref())?;
+
+    match args.command {
+        Commands::Repo(repo_args) => commands::repo::handler(&config, &repo_args).await?,
+    }
+
+    Ok(())
+}