#!/bin/bash
set -e

# Check if gh CLI is installed
if ! command -v gh &> /dev/null; then
  echo "gh CLI is not installed. Please install it from https://cli.github.com/."
  exit 1
fi

# Get the current branch name
current_branch=$(git rev-parse --abbrev-ref HEAD)
if [ -z "$current_branch" ]; then
  echo "Could not determine the current branch. Please run this script within a Git repository."
  exit 1
fi

# Try to get the upstream (tracking) branch as the base branch
base_branch=$(git rev-parse --abbrev-ref --symbolic-full-name "@{u}" 2>/dev/null || true)
if [ -n "$base_branch" ]; then
  echo "Found upstream branch: $base_branch"
fi

# Count commits between base_branch and current_branch (if base_branch exists)
if [ -n "$base_branch" ]; then
  commit_count=$(git rev-list --count "${base_branch}..${current_branch}")
else
  commit_count=0
fi

# If no commits are found, try using the previous branch
if [ "$commit_count" -eq 0 ]; then
  previous_branch=$(git rev-parse --abbrev-ref @{-1} 2>/dev/null || true)
  # Check if previous_branch is literally "@{-1}" which indicates an unresolved value.
  if [ "$previous_branch" = "@{-1}" ]; then
    previous_branch=""
  fi
  if [ -n "$previous_branch" ] && [ "$previous_branch" != "$current_branch" ]; then
    alt_commit_count=$(git rev-list --count "${previous_branch}..${current_branch}")
    if [ "$alt_commit_count" -gt 0 ]; then
      echo "No commits found between ${base_branch:-'upstream'} and ${current_branch}."
      echo "Falling back to previous branch: $previous_branch"
      base_branch="$previous_branch"
      commit_count=$alt_commit_count
    fi
  fi
fi

# If still no base branch or no commits found, prompt the user for the base branch
if [ -z "$base_branch" ] || [ "$commit_count" -eq 0 ]; then
  echo "No commits found between the detected base branch and ${current_branch}."
  read -rp "Enter the base branch for the PR: " base_branch
  commit_count=$(git rev-list --count "${base_branch}..${current_branch}")
  if [ "$commit_count" -eq 0 ]; then
    echo "No commits found between ${base_branch} and ${current_branch}. Exiting."
    exit 1
  fi
fi

echo "Base branch: $base_branch"
echo "Number of commits from ${base_branch} to ${current_branch}: $commit_count"

# Generate the PR title based on the commit count
if [ "$commit_count" -eq 1 ]; then
  echo "The diff contains one commit. Auto-generating PR title from the commit message."
  pr_title=$(git log "${base_branch}..${current_branch}" -1 --pretty=%s)
else
  echo "Warning: The diff contains ${commit_count} commits."
  read -rp "Enter the PR title: " pr_title
fi

# Create a draft PR using the gh command (without a PR body)
echo "Creating a draft PR for branch '${current_branch}' against base branch '${base_branch}'..."
gh pr create --draft --base "$base_branch" --head "$current_branch" --title "$pr_title"

echo "Draft PR has been created."