#!/bin/bash

# This script performs an incremental backup of the specified source directory,
# generates CRC32 checksums for only the files that are backed up or modified,
# and manages the deletion of old backups. The CRC32 checksum files are stored 
# in a dedicated subdirectory within the backup directory. You can also run the 
# script with the 'verification' argument to check the integrity of only the files 
# processed in the latest backup.
# 
# NOTE: This script is not tested and is intended for debugging purposes. Use with caution.

# Configuration
SOURCE_DIR="/chemin/vers/votre/dossier_source" # Replace with the path to your source directory
BACKUP_DIR="/chemin/vers/votre/dossier_backup" # Replace with the path to your backup directory
LOG_FILE="/chemin/vers/votre/fichier_log" # Replace with the path to your log file
RETENTION_PERIOD=60 # Number of days to retain deleted/modified files (2 months)
EMAIL="votre_email@example.com" # Replace with your email address
CRC_RETENTION_PERIOD=60 # Number of days to retain CRC checksum files

# Directory for CRC32 checksums within the backup directory
CRC_DIR="$BACKUP_DIR/.crc_checksums"
mkdir -p "$CRC_DIR" # Create the checksum directory if it does not exist

# Files for CRC32 checksums
SOURCE_CRC_FILE="$CRC_DIR/source_crc_checksums.txt"
BACKUP_CRC_FILE="$CRC_DIR/backup_crc_checksums.txt"

# Temporary files for CRC32 checksums of the current backup
CURRENT_BACKUP_CRC_FILE="$CRC_DIR/current_backup_crc_checksums.txt"

# Function to send an email in case of error
send_error_email() {
    SUBJECT="Backup Error on $(hostname)"
    MESSAGE="An error occurred during the backup on $(hostname) at $(date +'%Y-%m-%d %H:%M:%S'). Please check the log file at $LOG_FILE for details."
    echo "$MESSAGE" | mail -s "$SUBJECT" "$EMAIL"
}

# Function to log actions to the log file and send an email in case of error
log_action() {
    echo "$(date +'%Y-%m-%d %H:%M:%S') - $1" >> "$LOG_FILE"
    if [[ "$1" == "ERREUR"* ]]; then
        send_error_email
    fi
}

# Check if the source and backup directories exist
if [ ! -d "$SOURCE_DIR" ]; then
    log_action "ERREUR : The source directory '$SOURCE_DIR' does not exist."
    exit 1
fi

if [ ! -d "$BACKUP_DIR" ]; then
    log_action "The backup directory '$BACKUP_DIR' does not exist. Creating directory."
    mkdir -p "$BACKUP_DIR"
    if [ $? -ne 0 ]; then
        log_action "ERREUR : Unable to create the backup directory '$BACKUP_DIR'."
        exit 1
    fi
fi

# Function to generate CRC32 checksums only for files processed in the current backup
generate_crc_checksums() {
    # Generate checksums for source files
    find "$SOURCE_DIR" -type f -exec crc32 {} \; > "$SOURCE_CRC_FILE"
    if [ $? -ne 0 ]; then
        log_action "ERREUR : Unable to generate CRC32 checksums for the source directory."
        exit 1
    fi

    # Generate checksums for files in the backup directory
    find "$BACKUP_DIR" -type f ! -path "$CRC_DIR/*" -exec crc32 {} \; > "$CURRENT_BACKUP_CRC_FILE"
    if [ $? -ne 0 ]; then
        log_action "ERREUR : Unable to generate CRC32 checksums for the backup directory."
        exit 1
    fi
}

# Function to verify the integrity of files processed in the latest backup
verify_integrity() {
    if [ ! -f "$SOURCE_CRC_FILE" ] || [ ! -f "$CURRENT_BACKUP_CRC_FILE" ]; then
        log_action "ERREUR : Checksum files do not exist. Run the script without arguments to generate them."
        exit 1
    fi

    # Compare the checksums and store differences
    diff "$SOURCE_CRC_FILE" "$CURRENT_BACKUP_CRC_FILE" > /tmp/diff_output.txt
    if [ $? -eq 0 ]; then
        echo "La vérification de l'intégrité des fichiers a terminé avec succès."
        log_action "Backup integrity has been successfully verified."
    else
        log_action "ERREUR : Backup integrity check failed. Differences found between source and backup checksums."
        # Print the errors with file paths
        while IFS= read -r line; do
            echo "$line"
        done < /tmp/diff_output.txt
        exit 1
    fi
}

# Function to clean up old CRC32 checksum files
cleanup_old_crc_files() {
    find "$CRC_DIR" -type f -mtime +$CRC_RETENTION_PERIOD -exec rm -f {} \;
    if [ $? -ne 0 ]; then
        log_action "ERREUR : Unable to delete old CRC32 checksum files."
        exit 1
    fi
}

# If the 'verification' argument is provided, only perform the verification
if [ "$1" == "verification" ]; then
    verify_integrity
    exit 0
fi

# Incremental backup with error handling
# This section performs the incremental backup of the source directory to the backup directory
# Deleted files are moved to a dated subdirectory. The checksum directory is excluded from the backup.
rsync -av --delete --backup --backup-dir="$BACKUP_DIR/deleted/$(date +'%Y-%m-%d')" --exclude "$CRC_DIR/" "$SOURCE_DIR/" "$BACKUP_DIR/"
if [ $? -ne 0 ]; then
    log_action "ERREUR : The incremental backup failed."
    exit 1
fi

# Generate CRC32 checksums for the files processed in the latest backup
generate_crc_checksums

# Verify the integrity of the files processed in the latest backup
verify_integrity

# Delete old backups of deleted/modified files
find "$BACKUP_DIR/deleted" -type d -mtime +$RETENTION_PERIOD -exec rm -rf {} \;
if [ $? -ne 0 ]; then
    log_action "ERREUR : Unable to delete old backups."
    exit 1
fi

# Clean up old CRC32 checksum files
cleanup_old_crc_files

log_action "Incremental backup completed successfully."