1 files changed, 113 insertions, 0 deletions
diff --git a/src/cli/completion.rs b/src/cli/completion.rs
new file mode 100644
index 00000000..f049175d
--- /dev/null
+++ b/src/cli/completion.rs
@@ -0,0 +1,113 @@
+use std::io::Write;
+
+use clap_complete::{generate, Shell};
+
+pub(super) const SUPPORTED_SHELLS: [&str; 5] = ["bash", "elvish", "fish", "powershell", "zsh"];
+
+pub(super) fn supported_shells_usage() -> String {
+    SUPPORTED_SHELLS.join("|")
+}
+
+pub(super) fn run_completion_command(args: &[String]) -> std::io::Result<i32> {
+    let Some(shell) = args.first().map(String::as_str) else {
+        print_completion_help();
+        return Ok(2);
+    };
+    if matches!(shell, "help" | "--help" | "-h") {
+        print_completion_help();
+        return Ok(0);
+    }
+    if args.len() != 1 {
+        print_completion_help();
+        return Ok(2);
+    }
+
+    let Some(shell) = parse_shell(shell) else {
+        eprintln!("unknown shell: {shell}");
+        print_completion_help();
+        return Ok(2);
+    };
+
+    let mut command = super::spec::command();
+    if matches!(shell, Shell::Zsh) {
+        let mut output = Vec::new();
+        generate(shell, &mut command, "herdr", &mut output);
+        let script = String::from_utf8(output).map_err(|err| {
+            std::io::Error::new(std::io::ErrorKind::InvalidData, err.utf8_error())
+        })?;
+        std::io::stdout().write_all(space_separated_zsh_long_options(&script).as_bytes())?;
+    } else {
+        generate(shell, &mut command, "herdr", &mut std::io::stdout());
+    }
+    Ok(0)
+}
+
+fn space_separated_zsh_long_options(script: &str) -> String {
+    let mut output = String::with_capacity(script.len());
+    let mut rest = script;
+
+    while let Some(start) = rest.find("--") {
+        output.push_str(&rest[..start]);
+        let candidate = &rest[start + 2..];
+        let name_len = candidate
+            .chars()
+            .take_while(|ch| ch.is_ascii_alphanumeric() || *ch == '-')
+            .map(char::len_utf8)
+            .sum::<usize>();
+        if name_len > 0 && candidate[name_len..].starts_with("=[") {
+            output.push_str("--");
+            output.push_str(&candidate[..name_len]);
+            output.push('[');
+            rest = &candidate[name_len + 2..];
+        } else {
+            output.push_str("--");
+            rest = candidate;
+        }
+    }
+
+    output.push_str(rest);
+    output
+}
+
+fn parse_shell(shell: &str) -> Option<Shell> {
+    match shell {
+        value if value == SUPPORTED_SHELLS[0] => Some(Shell::Bash),
+        value if value == SUPPORTED_SHELLS[1] => Some(Shell::Elvish),
+        value if value == SUPPORTED_SHELLS[2] => Some(Shell::Fish),
+        value if value == SUPPORTED_SHELLS[3] => Some(Shell::PowerShell),
+        value if value == SUPPORTED_SHELLS[4] => Some(Shell::Zsh),
+        _ => None,
+    }
+}
+
+fn print_completion_help() {
+    eprintln!("usage: herdr completion <{}>", supported_shells_usage());
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn parses_supported_shells() {
+        assert!(matches!(
+            super::parse_shell("zsh"),
+            Some(clap_complete::Shell::Zsh)
+        ));
+        assert!(matches!(
+            super::parse_shell("powershell"),
+            Some(clap_complete::Shell::PowerShell)
+        ));
+        assert!(super::parse_shell("tcsh").is_none());
+    }
+
+    #[test]
+    fn zsh_long_options_use_space_separated_arguments() {
+        let script =
+            "'--cwd=[]:PATH:_files' \\\n'--json[]' \\\n'--split=[]:DIRECTION:(right down)' \\";
+        let normalized = super::space_separated_zsh_long_options(script);
+        assert!(normalized.contains("'--cwd[]:PATH:_files'"));
+        assert!(normalized.contains("'--json[]'"));
+        assert!(normalized.contains("'--split[]:DIRECTION:(right down)'"));
+        assert!(!normalized.contains("--cwd=[]"));
+        assert!(!normalized.contains("--split=[]"));
+    }
+}