1 files changed, 133 insertions, 1 deletions
diff --git a/src/bin/cachedir.rs b/src/bin/cachedir.rs
index e7a11a9..4d35ae8 100644
--- a/src/bin/cachedir.rs
+++ b/src/bin/cachedir.rs
@@ -1,3 +1,135 @@
+//! `cachedir` is a tiny utility for tagging, finding, and untagging
+//! directories as cache directories, according to the
+//! <http://www.bford.info/cachedir/> specification.
+//!
+//! ~~~sh
+//! $ cachedir find $HOME
+//! $ cachedir tag $HOME/.cache
+//! $ cachedir find $HOME
+//! /home/liw/.cache
+//! $ cachedir untag $HOME/.cache
+//! $ cachedir find $HOME
+//! $
+//! ~~~
+
+use clap::{Parser, Subcommand};
+use std::fs::{read, remove_file, write};
+use std::path::{Path, PathBuf};
+use walkdir::{DirEntry, WalkDir};
+
+/// Name of tag file.
+const CACHEDIR_TAG: &str = "CACHEDIR.TAG";
+
+/// Prefix of contents of tag file.
+const TAG: &str = "Signature: 8a477f597d28d172789f06886806bc55";
+
+/// The main program.
 fn main() {
-    println!("Hello, world!");
+    if let Err(e) = real_main() {
+        eprintln!("ERROR: {}", e);
+        std::process::exit(1);
+    }
+}
+
+/// Fallible main program.
+fn real_main() -> anyhow::Result<()> {
+    let args = Args::parse();
+    match args.cmd {
+        Command::Find { dirs } => walk(&dirs, find)?,
+        Command::Tag { dirs } => walk(&dirs, tag)?,
+        Command::Untag { dirs } => walk(&dirs, untag)?,
+        Command::IsCache { dir } => is_cache(dir)?,
+    }
+    Ok(())
+}
+
+/// Command line arguments.
+#[derive(Debug, Parser)]
+struct Args {
+    #[clap(subcommand)]
+    cmd: Command,
+}
+
+/// Subcommands.
+#[derive(Debug, Subcommand)]
+enum Command {
+    /// Find cache directories starting at given directories.
+    Find { dirs: Vec<PathBuf> },
+    /// Add cache directory tag to given directories.
+    Tag { dirs: Vec<PathBuf> },
+    /// Remove cache directory tag from given directories.
+    Untag { dirs: Vec<PathBuf> },
+    /// Is the single given directory tagged as a cache directory?
+    IsCache { dir: PathBuf },
+}
+
+/// Is the given directory a cache?
+fn is_cache(dir: PathBuf) -> Result<(), std::io::Error> {
+    let filename = dir.join(CACHEDIR_TAG);
+    if !is_cachedir_tag(&filename)? {
+        std::process::exit(1);
+    }
+    Ok(())
+}
+
+/// Is the given directory a cache?
+fn find(entry: &DirEntry) -> Result<(), std::io::Error> {
+    let filename = tag_filename(entry);
+    if is_cachedir_tag(&filename)? {
+        println!("{}", entry.path().display());
+    }
+    Ok(())
+}
+
+/// Add a tag file to the given directory.
+fn tag(entry: &DirEntry) -> Result<(), std::io::Error> {
+    let filename = tag_filename(entry);
+    if !is_cachedir_tag(&filename)? {
+        write(filename, TAG)?;
+    }
+    Ok(())
+}
+
+/// Remove a tag file from the given directory.
+fn untag(entry: &DirEntry) -> Result<(), std::io::Error> {
+    let filename = tag_filename(entry);
+    if is_cachedir_tag(&filename)? {
+        remove_file(filename)?;
+    }
+    Ok(())
+}
+
+/// Iterate over all directories, call given function for each.
+fn walk<F>(dirs: &[PathBuf], mut func: F) -> Result<(), std::io::Error>
+where
+    F: FnMut(&DirEntry) -> Result<(), std::io::Error>,
+{
+    for dir in dirs {
+        for entry in WalkDir::new(dir) {
+            let entry = entry?;
+            if entry.metadata()?.is_dir() {
+                func(&entry)?;
+            }
+        }
+    }
+    Ok(())
+}
+
+/// Is the given file a cache directory tag?
+fn is_cachedir_tag(filename: &Path) -> Result<bool, std::io::Error> {
+    if filename.exists() {
+        let data = read(filename)?;
+        if data.len() >= TAG.len() {
+            Ok(&data[..TAG.len()] == TAG.as_bytes())
+        } else {
+            Ok(false)
+        }
+    } else {
+        Ok(false)
+    }
+}
+
+/// Return path to tag file in a directory.
+fn tag_filename(entry: &DirEntry) -> PathBuf {
+    entry.path().join(CACHEDIR_TAG)
 }