Add user choice on existing output file; don't just overwrite target

Cargo.toml

@@ -26,11 +26,29 @@ serde = { version = "1.0.185", features = ["derive"] }
 serde_json = "1.0.105"
 shell-escape = "0.1.5"
 sled = "0.34.7"
+strum = { version = "0.25.0", features = ["derive"] }
+strum_macros = "0.25.3"
 time = { version = "0.3", features = ["parsing", "macros"] }
-tokio = { version = "1.15", features = ["rt", "macros", "process", "fs", "signal"] }
+tokio = { version = "1.15", features = [
+    "rt",
+    "macros",
+    "process",
+    "fs",
+    "signal",
+] }
 tokio-process-stream = "0.4"
 tokio-stream = "0.1"
 
+[dev-dependencies]
+mktemp = "0.5.1"
+
+[target.'cfg(unix)'.dependencies]
+unix-named-pipe = "0.2"
+
+[target.'cfg(windows)'.dependencies.tokio]
+version = "1.15"
+features = ["net"]
+
 [profile.release]
 lto = true
 opt-level = "s"

src/command/args.rs

@@ -3,10 +3,11 @@ mod encode;
 mod vmaf;
 
 pub use encode::*;
+use strum::EnumCount;
 pub use vmaf::*;
 
 use crate::{command::encode::default_output_ext, ffprobe::Ffprobe};
-use clap::Parser;
+use clap::{Parser, ValueEnum};
 use std::{
     path::{Path, PathBuf},
     sync::Arc,
@@ -22,6 +23,10 @@ pub struct EncodeToOutput {
     #[arg(short, long)]
     pub output: Option<PathBuf>,
 
+    /// What to do if the output file already exists.
+    #[arg(long, default_value("rename"))]
+    pub on_duplicate: Option<OnDuplicate>,
+
     /// Set the output ffmpeg audio codec.
     /// By default 'copy' is used. Otherwise, if re-encoding is necessary, 'libopus' is default.
     ///
@@ -95,3 +100,30 @@ impl Sample {
         self.extension = output.extension().and_then(|e| e.to_str().map(Into::into));
     }
 }
+
+#[derive(Default, Clone, Copy, PartialEq, Eq, Debug, Hash, EnumCount)]
+pub enum OnDuplicate {
+    Overwrite,
+    Skip,
+    #[default]
+    Rename,
+    Ask,
+}
+
+impl ValueEnum for OnDuplicate {
+    fn value_variants<'a>() -> &'a [Self] {
+        let variants = &[Self::Overwrite, Self::Skip, Self::Rename, Self::Ask];
+        // safety check in case one forgets to add a new variant
+        debug_assert!(OnDuplicate::COUNT == variants.len());
+        variants
+    }
+
+    fn to_possible_value(&self) -> Option<clap::builder::PossibleValue> {
+        match self {
+            OnDuplicate::Overwrite => Some(clap::builder::PossibleValue::new("overwrite")),
+            OnDuplicate::Skip => Some(clap::builder::PossibleValue::new("skip")),
+            OnDuplicate::Rename => Some(clap::builder::PossibleValue::new("rename").help("Tries to rename the output file by appending and incrementing a number.\nE.g. `vid.av1.mkv` -> `vid.av1_1.mkv` -> `vid.av1_2.mkv` etc.")),
+            OnDuplicate::Ask => Some(clap::builder::PossibleValue::new("ask")),
+        }
+    }
+}