From ea5add16b79013ec344a7f8143e0eb4de897b21a Mon Sep 17 00:00:00 2001
From: Weihang Lo <me@weihanglo.tw>
Date: Wed, 22 Apr 2026 19:26:33 -0400
Subject: [PATCH] feat: new example for simlple `apply`-like cli

---
 Cargo.toml        |   5 ++
 examples/apply.rs | 135 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 140 insertions(+)
 create mode 100644 examples/apply.rs

diff --git a/Cargo.toml b/Cargo.toml
index 89eaab2..80f89d7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -49,6 +49,11 @@ name = "patch_formatter"
 required-features = ["std", "color"]
 doc-scrape-examples = true
 
+[[example]]
+name = "apply"
+required-features = ["binary"]
+doc-scrape-examples = true
+
 [[test]]
 name = "compat"
 required-features = ["binary"]
diff --git a/examples/apply.rs b/examples/apply.rs
new file mode 100644
index 0000000..002432f
--- /dev/null
+++ b/examples/apply.rs
@@ -0,0 +1,135 @@
+//! A minimal patch-apply tool using diffy's multi-file patch support.
+//!
+//! Usage:
+//!
+//! ```console
+//! apply <patch-file> [target-dir]
+//! ```
+//!
+//! Applies a git-format patch file to a target directory
+//! (defaults to the current directory).
+//!
+//! Assumes the default `a/` and `b/` path prefixes
+//! from `git diff` and GNU `diff -u`.
+
+use std::fs;
+use std::path::Path;
+use std::process::ExitCode;
+
+use diffy::apply_bytes;
+use diffy::binary::BinaryPatch;
+use diffy::patch_set::FileOperation;
+use diffy::patch_set::ParseOptions;
+use diffy::patch_set::PatchKind;
+use diffy::patch_set::PatchSet;
+
+fn main() -> ExitCode {
+    let args: Vec<String> = std::env::args().collect();
+    if args.len() < 2 || args.len() > 3 {
+        eprintln!("usage: {} <patch-file> [target-dir]", args[0]);
+        return ExitCode::FAILURE;
+    }
+    let patch_file = Path::new(&args[1]);
+    let target_dir = args.get(2).map_or_else(|| Path::new("."), |p| Path::new(p));
+
+    if let Err(e) = apply_patch_file(patch_file, target_dir) {
+        eprintln!("error: {e}");
+        return ExitCode::FAILURE;
+    }
+    ExitCode::SUCCESS
+}
+
+fn apply_patch_file(patch_file: &Path, dst: &Path) -> Result<(), Box<dyn std::error::Error>> {
+    let content = fs::read(patch_file)?;
+
+    let patches = PatchSet::parse_bytes(&content, ParseOptions::gitdiff());
+
+    for file_patch in patches {
+        let file_patch = file_patch?;
+        let operation = {
+            let op = file_patch.operation();
+            // Rename/Copy paths come from git headers without a/b prefix.
+            let strip = match op {
+                FileOperation::Rename { .. } | FileOperation::Copy { .. } => 0,
+                _ => 1,
+            };
+            op.strip_prefix(strip)
+        };
+
+        match operation {
+            FileOperation::Create(path) => {
+                let target = dst.join(path_from_bytes(&path)?);
+                let patched = match file_patch.patch() {
+                    PatchKind::Text(patch) => apply_bytes(&[], patch)?,
+                    PatchKind::Binary(BinaryPatch::Marker) => continue,
+                    PatchKind::Binary(patch) => patch.apply(&[])?,
+                };
+                create_parent_dirs(&target)?;
+                fs::write(&target, patched)?;
+                eprintln!("create {}", target.display());
+            }
+            FileOperation::Delete(path) => {
+                let target = dst.join(path_from_bytes(&path)?);
+                fs::remove_file(&target)?;
+                eprintln!("delete {}", target.display());
+            }
+            FileOperation::Modify { original, modified } => {
+                let src_path = dst.join(path_from_bytes(&original)?);
+                let dst_path = dst.join(path_from_bytes(&modified)?);
+                let patched = match file_patch.patch() {
+                    PatchKind::Text(patch) => {
+                        let base = fs::read(&src_path)?;
+                        apply_bytes(&base, patch)?
+                    }
+                    PatchKind::Binary(BinaryPatch::Marker) => continue,
+                    PatchKind::Binary(patch) => {
+                        let base = fs::read(&src_path)?;
+                        patch.apply(&base)?
+                    }
+                };
+                create_parent_dirs(&dst_path)?;
+                fs::write(&dst_path, patched)?;
+                if src_path != dst_path {
+                    fs::remove_file(&src_path)?;
+                    eprintln!("rename {} -> {}", src_path.display(), dst_path.display());
+                } else {
+                    eprintln!("modify {}", dst_path.display());
+                }
+            }
+            FileOperation::Rename { from, to } => {
+                let src_path = dst.join(path_from_bytes(&from)?);
+                let dst_path = dst.join(path_from_bytes(&to)?);
+                create_parent_dirs(&dst_path)?;
+                fs::rename(&src_path, &dst_path)?;
+                eprintln!("rename {} -> {}", src_path.display(), dst_path.display());
+            }
+            FileOperation::Copy { from, to } => {
+                let src_path = dst.join(path_from_bytes(&from)?);
+                let dst_path = dst.join(path_from_bytes(&to)?);
+                create_parent_dirs(&dst_path)?;
+                fs::copy(&src_path, &dst_path)?;
+                eprintln!("copy {} -> {}", src_path.display(), dst_path.display());
+            }
+        }
+    }
+
+    Ok(())
+}
+
+#[cfg(unix)]
+fn path_from_bytes(bytes: &[u8]) -> Result<&Path, Box<dyn std::error::Error>> {
+    use std::os::unix::ffi::OsStrExt;
+    Ok(Path::new(std::ffi::OsStr::from_bytes(bytes)))
+}
+
+#[cfg(not(unix))]
+fn path_from_bytes(bytes: &[u8]) -> Result<&Path, Box<dyn std::error::Error>> {
+    Ok(Path::new(std::str::from_utf8(bytes)?))
+}
+
+fn create_parent_dirs(path: &Path) -> std::io::Result<()> {
+    if let Some(parent) = path.parent() {
+        fs::create_dir_all(parent)?;
+    }
+    Ok(())
+}