restructure project into a virtual manifest

- remove redundant readme
- de-duplicate Cargo.toml information using workspace inheritance
- rename "pacdef_core" to "pacdef"
- move "crates/main/main.rs" to "crates/pacdef/src/main.rs"

crates/pacdef/src/config.rs

@@ -0,0 +1,99 @@
+use std::fs::{create_dir_all, read_to_string, File};
+use std::io::{ErrorKind, Write};
+use std::path::Path;
+
+use anyhow::{bail, Context, Result};
+use serde_derive::{Deserialize, Serialize};
+
+// Update the master README if fields change.
+/// Config for the program, as listed in `$XDG_CONFIG_HOME/pacdef/pacdef.yaml`.
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Config {
+    /// The AUR helper to use for Arch Linux.
+    #[serde(default = "aur_helper")]
+    pub aur_helper: String,
+    /// Additional arguments to pass to `aur_helper` when removing a package.
+    #[serde(default)]
+    pub aur_rm_args: Vec<String>,
+    /// Install Flatpak packages system-wide
+    #[serde(default = "yes")]
+    pub flatpak_systemwide: bool,
+    /// Warn the user when a group is not a symlink.
+    #[serde(default = "yes")]
+    pub warn_not_symlinks: bool,
+    /// Backends the user does not want to use even though the binary exists.
+    #[serde(default)]
+    pub disabled_backends: Vec<String>,
+    /// Choose whether to use pipx instead of pip for python package management
+    #[serde(default = "pip")]
+    pub pip_binary: String,
+}
+
+fn yes() -> bool {
+    true
+}
+
+fn aur_helper() -> String {
+    "paru".into()
+}
+
+fn pip() -> String {
+    "pip".into()
+}
+
+impl Config {
+    /// Load the config from the associated file.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the config file exists but cannot be
+    /// read, its contents are not UTF-8, or the file is malformed.
+    pub fn load(config_file: &Path) -> Result<Self> {
+        let from_file = read_to_string(config_file);
+
+        let content = match from_file {
+            Ok(content) => content,
+            Err(e) => {
+                if e.kind() == ErrorKind::NotFound {
+                    bail!(crate::Error::ConfigFileNotFound)
+                }
+                bail!("unexpected error occured: {e:?}");
+            }
+        };
+
+        serde_yaml::from_str(&content).context("parsing yaml config")
+    }
+
+    /// Save the instance of [`Config`] to disk.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the config file cannot be saved to disk.
+    pub fn save(&self, file: &Path) -> Result<()> {
+        let content = serde_yaml::to_string(&self).context("converting Config to yaml")?;
+
+        let parent = file.parent().context("getting parent of config dir")?;
+        if !parent.is_dir() {
+            create_dir_all(parent)
+                .with_context(|| format!("creating dir {}", parent.to_string_lossy()))?;
+        }
+
+        let mut output = File::create(file).context("creating default config file")?;
+        write!(output, "{content}").context("writing default config")?;
+
+        Ok(())
+    }
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            aur_helper: "paru".into(),
+            aur_rm_args: vec![],
+            flatpak_systemwide: true,
+            warn_not_symlinks: true,
+            disabled_backends: vec![],
+            pip_binary: "pip".into(),
+        }
+    }
+}