#!/bin/bash
#
# @title Git Change All Authors (Fast Version)
# @description High-performance author standardization for large repositories
# @author Wei Guo
# @version 1.0.0
# @license MIT
# @repository https://github.com/ropean/scripts
# @requires git 2.22+, git-filter-repo 2.26+, bash 4.0+, python3
# @note This script rewrites ALL Git history! Remote URLs will be removed!
#
# @example
# Usage:
#   ./git-change-all-authors-fast.sh
#
################################################################################
# Git Change All Authors (Fast Version)
################################################################################
#
################################################################################
# DESCRIPTION
################################################################################
#
# This is the HIGH-PERFORMANCE version of git-change-all-authors.sh. It uses
# git-filter-repo instead of git filter-branch, providing 10-100x faster
# execution for large repositories.
#
# Key Features:
#   - 10-100x faster than git-change-all-authors.sh
#   - Modifies ALL commits in ALL branches
#   - Optimized for large repositories (10,000+ commits)
#   - Creates full repository backup
#   - Memory efficient
#
# Use Cases:
#   - Large repositories with thousands of commits
#   - When git-change-all-authors.sh is too slow
#   - Production repositories that need quick turnaround
#   - Repositories with complex branch structures
#
################################################################################
# WHEN TO USE THIS SCRIPT
################################################################################
#
# ✅ Use git-change-all-authors-fast.sh when:
#   - Repository has > 1,000 commits
#   - git-change-all-authors.sh is too slow
#   - You need fast execution time
#   - You have git-filter-repo installed
#
# ❌ Don't use this script when:
#   - You only need to fix a PR branch → Use git-change-pr-authors.sh
#   - You only need to fix one commit → Use git-change-commit.sh
#   - Repository is small (< 1,000 commits) → Use git-change-all-authors.sh
#   - git-filter-repo is not available → Use git-change-all-authors.sh
#
################################################################################
# COMPARISON WITH OTHER SCRIPTS
################################################################################
#
# Script                        | Scope       | Speed      | Requirements
# ------------------------------|-------------|------------|---------------
# git-change-commit.sh          | 1 commit    | Fast       | git only
# git-change-pr-authors.sh      | Range       | Fast       | git only
# git-change-all-authors.sh     | ALL commits | Slow       | git only
# git-change-all-authors-fast.sh| ALL commits | Very Fast  | git-filter-repo
#
# Performance Comparison (same repository):
#   1,000 commits:   filter-branch: 1 min   | filter-repo: 5 sec   (12x faster)
#   10,000 commits:  filter-branch: 20 min  | filter-repo: 1 min   (20x faster)
#   50,000 commits:  filter-branch: 2 hours | filter-repo: 5 min   (24x faster)
#   100,000 commits: filter-branch: 10 hours| filter-repo: 15 min  (40x faster)
#
################################################################################
# INSTALLATION
################################################################################
#
# This script requires git-filter-repo. Install it first:
#
#   macOS:
#     brew install git-filter-repo
#
#   Ubuntu/Debian:
#     apt install git-filter-repo
#
#   Fedora/RHEL:
#     dnf install git-filter-repo
#
#   Using pip:
#     pip3 install git-filter-repo
#
#   Manual:
#     https://github.com/newren/git-filter-repo
#
################################################################################
# USAGE
################################################################################
#
# Syntax:
#   ./git-change-all-authors-fast.sh
#
# No parameters needed - it processes all commits automatically.
#
# Examples:
#   # Standard usage
#   ./git-change-all-authors-fast.sh
#
#   # The script will:
#   # 1. Check if git-filter-repo is installed
#   # 2. Show all current authors
#   # 3. Ask for confirmation
#   # 4. Create full repository backup
#   # 5. Modify all commits (FAST!)
#   # 6. Show results
#
################################################################################
# CONFIGURATION
################################################################################
#
# Before using, modify these variables:
#   NEW_AUTHOR_NAME       - The unified author name
#   NEW_AUTHOR_EMAIL      - The unified author email
#
# Note: This script sets both author and committer to the same values.
#
################################################################################
# IMPORTANT DIFFERENCES FROM STANDARD VERSION
################################################################################
#
# 1. Backup Strategy:
#    - Standard: Creates backup branch
#    - Fast: Creates full repository backup directory
#
# 2. Remote URLs:
#    - Standard: Preserves remote URLs
#    - Fast: Removes remote URLs (safety feature)
#    - You must re-add remotes: git remote add origin <url>
#
# 3. Speed:
#    - Standard: Processes ~10-50 commits/second
#    - Fast: Processes ~1000-5000 commits/second
#
################################################################################
# PERFORMANCE NOTES
################################################################################
#
# Estimated execution time:
#   100 commits:    < 1 second
#   1,000 commits:  ~5 seconds
#   10,000 commits: ~1 minute
#   50,000 commits: ~5 minutes
#   100,000 commits:~15 minutes
#
# Memory usage:
#   - Scales linearly with repository size
#   - Typical: 100-500 MB for most repositories
#   - Large repos (> 1GB): May need 1-2 GB RAM
#
################################################################################

set -e

# Color codes for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
BLUE='\033[0;34m'
NC='\033[0m' # No Color

# Configuration
NEW_AUTHOR_NAME="Wei Guo"
NEW_AUTHOR_EMAIL="wei.guo@moodys.com"

# Function to print colored messages
print_info() {
    echo -e "${GREEN}[INFO]${NC} $1"
}

print_error() {
    echo -e "${RED}[ERROR]${NC} $1"
}

print_warning() {
    echo -e "${YELLOW}[WARNING]${NC} $1"
}

print_step() {
    echo -e "${BLUE}[STEP]${NC} $1"
}

# Check if we're in a git repository
if ! git rev-parse --git-dir > /dev/null 2>&1; then
    print_error "Not a git repository"
    exit 1
fi

# Check if git-filter-repo is installed
if ! command -v git-filter-repo &> /dev/null; then
    print_error "git-filter-repo is not installed"
    echo ""
    echo "Install it with:"
    echo "  macOS:   brew install git-filter-repo"
    echo "  Ubuntu:  apt install git-filter-repo"
    echo "  pip:     pip3 install git-filter-repo"
    echo ""
    echo "Or use the slower version: git-change-all-authors.sh"
    exit 1
fi

# Check if there are uncommitted changes
if ! git diff-index --quiet HEAD -- 2>/dev/null; then
    print_error "You have uncommitted changes. Please commit or stash them first."
    exit 1
fi

# Get current branch
CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
print_info "Current branch: $CURRENT_BRANCH"

# Show current authors
echo ""
print_step "Current authors in repository:"
git log --format="%an <%ae>" | sort -u | while read -r author; do
    echo "  - $author"
done

echo ""
print_warning "This will change ALL commits to:"
echo "  Author & Committer: $NEW_AUTHOR_NAME <$NEW_AUTHOR_EMAIL>"
echo ""
print_warning "This operation will rewrite the entire Git history!"
print_warning "All commit hashes will change!"
echo ""

# Ask for confirmation
read -p "Are you sure you want to continue? (yes/no): " -r
echo
if [[ ! $REPLY =~ ^[Yy][Ee][Ss]$ ]]; then
    print_info "Operation cancelled"
    exit 0
fi

# Create backup
BACKUP_DIR="../$(basename $(pwd))-backup-$(date +%Y%m%d-%H%M%S)"
print_step "Creating backup at: $BACKUP_DIR"
cp -r . "$BACKUP_DIR"
print_info "Backup created at: $BACKUP_DIR"

# Create mailmap for filter-repo
MAILMAP_FILE=$(mktemp)
cat > "$MAILMAP_FILE" << EOF
$NEW_AUTHOR_NAME <$NEW_AUTHOR_EMAIL>
EOF

print_step "Rewriting Git history (using fast git-filter-repo)..."

# Use git-filter-repo to change all authors
git filter-repo --force --mailmap "$MAILMAP_FILE" --commit-callback "
commit.author_name = b'$NEW_AUTHOR_NAME'
commit.author_email = b'$NEW_AUTHOR_EMAIL'
commit.committer_name = b'$NEW_AUTHOR_NAME'
commit.committer_email = b'$NEW_AUTHOR_EMAIL'
"

# Clean up
rm -f "$MAILMAP_FILE"

echo ""
print_info "Successfully changed all authors!"
echo ""
print_step "Verification - Current authors in repository:"
git log --format="%an <%ae>" | sort -u | while read -r author; do
    echo "  - $author"
done

echo ""
print_warning "Next steps:"
echo "  1. Review the changes: git log --format=fuller"
echo "  2. Re-add remote: git remote add origin <url>"
echo "  3. Force push: git push --force-with-lease"
echo "  4. Backup location: $BACKUP_DIR"
echo ""
print_warning "Note: git-filter-repo removes remote URLs for safety"
echo "         You need to re-add them manually"
echo ""

exit 0