Add since command

nixprstatus/__main__.py

@@ -1,7 +1,9 @@
 import typer
+import json
 from typing import Annotated
 from rich.console import Console
 from nixprstatus.pr import pr_merge_status
+from nixprstatus.pr import commits_since
 
 app = typer.Typer()
 
@@ -38,6 +40,26 @@ def pr(
         console.print(output, highlight=False)
 
 
+@app.command()
+def since(
+    commit_sha: str,
+    target: str = "nixos-unstable",
+    waybar_format: Annotated[
+        bool, typer.Option(help="Output in format expected by waybar")
+    ] = False,
+):
+    """
+    Return the count of commits that has happened between the two refs.
+    """
+    count = commits_since(target, commit_sha)
+
+    if waybar_format:
+        output = {"text": str(count), "tooltip": f"{target}: {count}"}
+        typer.echo(json.dumps(output))
+        return
+    typer.echo(count)
+
+
 def main():
     app()