#!/bin/bash
set -euo pipefail

# Check if an ID was provided
if [ -z "${1:-}" ]; then
  echo "Usage: get_mr_diff <MR_ID> [BASE_REF]"
  echo "Example: get_mr_diff 1234 origin/develop"
  exit 1
fi

mr_id="$1"
base_ref="${2:-origin/develop}"   # target branch ref (default)

output_dir="/Users/arun/Downloads/fulldiff"
output_file="${output_dir}/MR-${mr_id}.diff"

mkdir -p "$output_dir"

# Make sure base ref exists/updated locally
# If base_ref is origin/<branch>, fetch that branch
if [[ "$base_ref" == origin/* ]]; then
  base_branch="${base_ref#origin/}"
  git fetch origin "$base_branch" >/dev/null 2>&1 || true
fi

# Fetch the specific MR head (Hidden GitLab Ref)
echo "⬇️  Fetching changes for MR ${mr_id}..."
git fetch origin "refs/merge-requests/${mr_id}/head" >/dev/null 2>&1

# Generate the NET diff (final changes only)
# Triple-dot uses merge-base(base_ref, FETCH_HEAD) -> FETCH_HEAD
echo "📝 Writing NET diff to file..."
git diff "$base_ref...FETCH_HEAD" > "$output_file"

echo "✅ Done! File saved at:"
echo "$output_file"