#!/usr/bin/env bash
# update a git repository and copy its contents to a directory 
set -o errexit
set -o nounset
set -o pipefail
if [[ "${TRACE-0}" == "1" ]]; then
    set -o xtrace
fi

help() {
    echo "Update a git repository and copy the files to OUTDIR"
    echo "Intended for use with static websites"
    echo
    echo "Usage: ./site-update.sh [-b BRANCH|d SRCDIR|f FILE|h|p] OUTDIR"
    echo "Options"
    echo "b BRANCH    git branch to update, defaults to the current branch in SRCDIR"
    echo "d SRCDIR    directory containing git repository to update, defaults to current working directory"
    echo "f FILE      update a batch of repositories, as defined in FILE"
    echo "h           print this help message"
    echo "p           publish files only, do not update"
}

get_changes() {
    git fetch origin
    if [[ $(git status | grep behind) ]]; then
        git merge origin/"${BRANCH}"
    fi
}

change_directory() {
    if [[ -n "$SRCDIR" ]]; then
        cd "${SRCDIR}"
    fi
}

checkout_branch() {
    if [[ -n "$BRANCH" ]]; then
        git checkout "${BRANCH}"
    else 
        BRANCH=$(git branch --show-current)
    fi
}

copy_to_dest () {
    cp -r "${SRCDIR}/." "${OUTDIR}"
}

update_publish() {
    if [[ -n "$SRCDIR" ]]; then
        cd "${SRCDIR}"
    fi
    if [[ -n "$BRANCH" ]]; then
        git checkout "${BRANCH}"
    else 
        BRANCH=$(git branch --show-current)
    fi
    if [[ "$PUBONLY" == false ]]; then
        get_changes
    fi
    if diff "${SRCDIR}" "${OUTDIR}" >/dev/null; then
        echo "No changes detected."
    else
        copy_to_dest
    fi
}

main() {
    srcdirlen=${#SRCDIR}
    if [[ ${SRCDIR:(-1)} == '/' ]]; then
        SRCDIR=${SRCDIR:0:-1}
    fi
    if [[ -f "$FILE" ]]; then
        while read -r src out rem; do
            # use rem as dummy variable to guarantee out countains one word
            echo "${src} | ${out} | ${rem}"
        done < "${FILE}" 
    else
        update_publish
    fi
}

SRCDIR=$(pwd)
BRANCH=
FILE=
PUBONLY=false
OUTDIR=

while getopts ":hd:f:b:p" option; do
    case $option in
        b) # select branch
            BRANCH=$OPTARG;;
        f) # file listing directories
            FILE=$OPTARG;;
        d) # directory to act on
            SRCDIR=$OPTARG;;
        h) #display help
            help
            exit;;
        p) #publish only, do not update
            PUBONLY=true;;
        \?) #invalid option
            echo "Error: Invalid option"
            exit;;
    esac
done
    
if [[ -z "$FILE" ]]; then
    OUTDIR="${@:$OPTIND:1}"
    echo "$OUTDIR"
    if [[ ! -d "$OUTDIR" ]]; then
        echo "Directory \"${OUTDIR}\" does not exist"
        exit 1
    fi
fi

main