Split crates and clean up structure of codebase (#294)

Co-authored-by: Jiahao XU <Jiahao_XU@outlook.com>

crates/bin/src/install_path.rs

@@ -0,0 +1,39 @@
+use std::{
+    path::{Path, PathBuf},
+    sync::Arc,
+};
+
+use binstall::helpers::statics::cargo_home;
+use log::debug;
+
+/// Fetch install path from environment
+/// roughly follows <https://doc.rust-lang.org/cargo/commands/cargo-install.html#description>
+///
+/// Return (install_path, is_custom_install_path)
+pub fn get_install_path<P: AsRef<Path>>(install_path: Option<P>) -> (Option<Arc<Path>>, bool) {
+    // Command line override first first
+    if let Some(p) = install_path {
+        return (Some(Arc::from(p.as_ref())), true);
+    }
+
+    // Environmental variables
+    if let Ok(p) = std::env::var("CARGO_INSTALL_ROOT") {
+        debug!("using CARGO_INSTALL_ROOT ({p})");
+        let b = PathBuf::from(p);
+        return (Some(Arc::from(b.join("bin"))), true);
+    }
+
+    if let Ok(p) = cargo_home() {
+        debug!("using ({}) as cargo home", p.display());
+        return (Some(p.join("bin").into()), false);
+    }
+
+    // Local executable dir if no cargo is found
+    let dir = dirs::executable_dir();
+
+    if let Some(d) = &dir {
+        debug!("Fallback to {}", d.display());
+    }
+
+    (dir.map(Arc::from), true)
+}