#!/bin/bash
# Script to backup folders to either a tarball or a Git repository
# Script expects to run at most on a daily basis. Any faster, and you risk
# overwriting a previous backup.

# Default environment variables used
BACKUP_METHOD=git
BACKUP_TS=$(date +%F)
BACKUP_DEBUG=false
BACKUP_SRC=''
BACKUP_DST=''
BACKUP_DB=''

APP=$(basename $0)

# Usage function will display the usage
usage()
{
    local backup=$APP
    local exit_code=$1

    [[ -z $exit_code ]] && exit_code=0

    echo "Usage: $backup [options] <source path>"
    echo "Options:"
    echo "    -s tar    Save to a tarball, format is backup-%Y-%m-%d.tar.gz"
    echo "              This is the default."
    echo "    -s git    Save to a git repository and tag the commit"
    echo
    echo "    -t <dst>  Specify the path to save the backup to. If omitted,"
    echo "              it defaults to ~/backups/\$(basename <src>)"
    echo
    echo "    -d <db>   Specify a MySQL database to backup in addition to"
    echo "              the files in the source path. This requires you to"
    echo "              save the MySQL root password in ~/.my.cnf"
    echo
    echo "    -h        Display this help message"

    exit $exit_code
}

# Die function will print the error message to stderr and abort the script
die()
{
    local exit_code=$1
    local backup=$APP
    shift

    for msg in "$@"
    do
        echo -e "$backup: $msg" >&2
    done

    exit $exit_code
}

# Sanity check
backup_sanity()
{
    if [[ -z $BACKUP_SRC ]]
    then
        die 1 "Need to specify a source"
    fi

    # Run basic sanity checks on env variables
    if [[ -z $BACKUP_DST ]]
    then
        BACKUP_DST=$HOME/backups/$(basename $BACKUP_SRC)
    fi

    mkdir -p $BACKUP_DST
    if [[ $? != 0 ]]
    then
        die 2 "Error creating backup folder"
    fi
}

# Retrieve data using rsync
backup_data()
{
    # Don't rsync if we are using tar as the backup method
    if [[ "$BACKUP_METHOD" != "tar" ]]
    then
        rsync -a $BACKUP_SRC $BACKUP_DST

        if [[ $? != 0 ]]
        then
            die 2 "Error syncing data from source $BACKUP_SRC"
        fi
    fi
}

# Backup the database
backup_db()
{
    if [[ ! -z $BACKUP_DB ]]
    then
        # Dump using mysqldump
        mysqldump -u root $BACKUP_DB >$BACKUP_DST/$BACKUP_DB.sql 2>/dev/null

        if [[ $? != 0 ]]
        then
            die 2 "Error dumping database $BACKUP_DB"
        fi
    fi
}

# Save the files to git repo or tarball
backup_save()
{
    if [[ "$BACKUP_METHOD" == "tar" ]]
    then
        cd $BACKUP_SRC
        local daily=$BACKUP_DST/backup-daily-$BACKUP_TS.tar.gz
        tar czf $daily .

        # Weekly tarballs every Sunday
        if [[ $(date +%w) == "0" ]]
        then
            local weekly=$BACKUP_DST/backup-weekly-$(date +%Y-%U).tar.gz
            ln $daily $weekly
        fi

        # Monthly tarballs on the first of every month
        if [[ $(date +%-d) == "1" ]]
        then
            local monthly=$BACKUP_DST/backup-monthly-$(date +%Y-%m).tar.gz
            ln $daily $monthly
        fi
    else
        cd $BACKUP_DST
        git init -q
        git config core.safecrlf false
        git add .
        git commit -m "Backup of $BACKUP_SRC on $BACKUP_TS"
        git tag -am "Daily ($BACKUP_TS) backup of $BACKUP_SRC" daily-$BACKUP_TS

        # Weekly tags every Sunday
        if [[ $(date +%w) == "0" ]]
        then
            local week=$(date +%Y-%U)
            git tag -am "Weekly ($week) backup of $BACKUP_SRC" weekly-$week
        fi

        # Monthly tags on the first of every month
        if [[ $(date +%-d) == "1" ]]
        then
            local month=$(date +%Y-%m)
            git tag -am "Monthly ($month) backup of $BACKUP_SRC" monthly-$month
        fi
    fi
}

while getopts :hs:t:d: OPTION
do
    case $OPTION in
    h)
        # Help
        usage 0
        ;;

    s)
        # Backup method
        if [[ "$OPTARG" == "git" || "$OPTARG" == "tar" ]]
        then
            BACKUP_METHOD=$OPTARG
        else
            die 1 "Backup method must be one of git or tar"
        fi
        ;;
    t)
        # Target folder
        BACKUP_DST=$OPTARG
        ;;

    d)
        # Database
        BACKUP_DB=$OPTARG
        ;;

    :)
        # Missing required argument
        die 1 "Missing argument for option -$OPTARG"
        ;;

    \?)
        # Invalid option
        die 1 "Invalid option: -$OPTARG"
        ;;

    esac
done

# Shift away the options
shift $(($OPTIND - 1))

BACKUP_SRC=$1
backup_sanity
backup_data
backup_db
backup_save