improve configurability

src/config.rs

@@ -0,0 +1,103 @@
+use anyhow::{Context, Error, Result};
+use serde::{Deserialize, Serialize};
+use std::path::{Path, PathBuf};
+
+#[derive(Debug)]
+pub struct Config {
+    pub from: PathBuf,
+    pub to: PathBuf,
+}
+
+#[derive(Debug, Default, Serialize, Deserialize)]
+struct ConfigFile {
+    pub from: Option<PathBuf>,
+    pub to: Option<PathBuf>,
+}
+
+pub fn config() -> Result<Config> {
+    use clap::Arg;
+
+    let matches = clap::App::new("audio-conv")
+        .version(clap::crate_version!())
+        .about("Converts audio files")
+        .arg(
+            Arg::with_name("config")
+                .short("c")
+                .long("config")
+                .required(false)
+                .takes_value(true)
+                .help("path to an audio-conv config file, defaults to \"audio-conv.yaml\""),
+        )
+        .arg(
+            Arg::with_name("from")
+                .short("f")
+                .long("from")
+                .required(false)
+                .takes_value(true)
+                .help("from directory path"),
+        )
+        .arg(
+            Arg::with_name("to")
+                .short("t")
+                .long("to")
+                .required(false)
+                .takes_value(true)
+                .help("to directory path"),
+        )
+        .get_matches();
+
+    let current_dir = std::env::current_dir().context("could not get current directory")?;
+
+    let config_path = matches.value_of_os("config");
+    let force_load = config_path.is_some();
+    let config_path = config_path
+        .map(AsRef::<Path>::as_ref)
+        .unwrap_or_else(|| AsRef::<Path>::as_ref("audio-conv.yaml"));
+    let config_path = current_dir.join(config_path);
+
+    let config_file = load_config_file(&config_path)
+        .with_context(|| format!("failed loading config file \"{}\"", config_path.display()))?;
+
+    if force_load && config_file.is_none() {
+        return Err(Error::msg(format!(
+            "could not find config file \"{}\"",
+            config_path.display()
+        )));
+    }
+
+    Ok(Config {
+        from: matches
+            .value_of_os("from")
+            .map(AsRef::<Path>::as_ref)
+            .or_else(|| {
+                config_file
+                    .as_ref()
+                    .map(|c| c.from.as_ref().map(AsRef::as_ref))
+                    .flatten()
+            })
+            .map(|p| current_dir.join(p))
+            .ok_or_else(|| Error::msg("\"from\" not configured"))?,
+        to: matches
+            .value_of_os("to")
+            .map(AsRef::<Path>::as_ref)
+            .or_else(|| {
+                config_file
+                    .as_ref()
+                    .map(|c| c.to.as_ref().map(AsRef::as_ref))
+                    .flatten()
+            })
+            .map(|p| current_dir.join(p))
+            .ok_or_else(|| Error::msg("\"to\" not configured"))?,
+    })
+}
+
+fn load_config_file(path: &Path) -> Result<Option<ConfigFile>> {
+    let mut file = match std::fs::File::open(path) {
+        Ok(file) => file,
+        Err(err) if err.kind() == std::io::ErrorKind::NotFound => return Ok(None),
+        Err(err) => return Err(Error::new(err)),
+    };
+    let config: ConfigFile =
+        serde_yaml::from_reader(&mut file).context("could not read config file")?;
+    Ok(Some(config))
+}