#!/bin/bash

PATSH_REPO=".patches"
PATSH_NAME="patsh"

function check_if_unchanged {
    unset -v LATEST_DIFF
    for file in "${PATSH_REPO}/${1}"-*.diff; do
        [[ "$file" -nt "${LATEST_DIFF}" ]] && LATEST_DIFF="$file"
    done
    if [ "$LATEST_DIFF" != "" ]; then
        patch -i "${LATEST_DIFF}" -o - "${PATSH_REPO}/${1}" 2> /dev/null | cmp - "${1}" > /dev/null
    else
        cmp "${PATSH_REPO}/${1}" "${1}" > /dev/null
    fi
}

function showhelp {
    cat <<EOF
${PATSH_NAME} -- dead simple patch/version control system

Usage:
    patsh [options] command [files...]

Options:
  -h        show this help
  -f        enforce commit if no changes

Commands:
  init      initialize stash area
  add       start tracking file changes
  save      store changes done to file
  restore   undo changes and rewind to last version
  diff      show changes between working copy and last version
  list      show stored versions
EOF
    exit 0
}

while [[ "$1" == -* ]]; do
    case "$1" in
        -f|--force)
            printf "${PATSH_NAME}: not implemented yet\n"
            ;;
        -h|--help)
            showhelp
            ;;
    esac
    shift
done

case "$1" in
    init)
        mkdir "${PATSH_REPO}" && \
        printf "${PATSH_NAME}: stash initialized\n"
        ;;
    add|a)
        while [ -e "$2" ]; do

        if [ ! -e "${PATSH_REPO}/$2" ]; then
            cp "$2" "${PATSH_REPO}/" && \
            printf "${PATSH_NAME}: tracked file: ${2}\n"
        else
            printf "${PATSH_NAME}: file already tracked\npat.sh: use ${0} save ${2} to commit changes\n"
        fi

        shift
        done
        ;;
    list|ls)
        while [ -e "$2" ]; do

        if [ ! -e "${PATSH_REPO}/$2" ]; then
            printf "${PATSH_NAME}: file not tracked\npat.sh: use ${0} add ${2} to track file\n"
            exit 0
        fi
        printf "${PATSH_NAME}: ${2}: saved patches\n"
        for file in "${PATSH_REPO}/${2}"-*.diff ; do
            basename "${file}"
        done | sort

        shift
        done
        ;;
    save|ci)
        while [ -e "$2" ]; do

        if [ ! -e "${PATSH_REPO}/$2" ]; then
            printf "${PATSH_NAME}: file ${2} not tracked\n"
        elif check_if_unchanged "$2"; then
            printf "${PATSH_NAME}: file ${2} not changed\n"
        else
            LATEST_DIFF="${PATSH_REPO}/$2-$(date +%s).diff"
            diff -u "${PATSH_REPO}/$2" "$2" > "${LATEST_DIFF}"
            printf "${PATSH_NAME}: changes written to %s\n" "${LATEST_DIFF}"
        fi

        shift
        done
        ;;
    restore|co)
        while [ -e "$2" ]; do

        unset -v LATEST_DIFF
        if [ ! -e "${PATSH_REPO}/$2" ]; then
            printf "${PATSH_NAME}: file ${2} not tracked\n"
            exit 0
        fi
        cp "${PATSH_REPO}/${2}" "${2}"
        for file in "${PATSH_REPO}/${2}"-*.diff; do
            [[ "$file" -nt "${LATEST_DIFF}" ]] && LATEST_DIFF="$file"
        done
        if [ "$LATEST_DIFF" != "" ]; then
            patch "${2}" < "${LATEST_DIFF}" > /dev/null
            printf "${PATSH_NAME}: reset to ${LATEST_DIFF}\n"
        else
            printf "${PATSH_NAME}: reset to original version\n"
        fi

        shift
        done
        ;;
    diff)
        while [ -e "$2" ]; do

        unset -v LATEST_DIFF
        printf "${PATSH_NAME}: ${2} working copy changes\n"
        for file in "${PATSH_REPO}/${2}"-*.diff; do
            [[ "$file" -nt "${LATEST_DIFF}" ]] && LATEST_DIFF="$file"
        done
        if [ "$LATEST_DIFF" != "" ]; then
            patch -i "${LATEST_DIFF}" -o - "${PATSH_REPO}/${2}" 2> /dev/null | diff --color=always - "${2}"
        else
            diff --color=always "${PATSH_REPO}/${2}" "${2}"
        fi

        shift
        done
        ;;
    *)
        if [ "$1" == "" ]; then showhelp; fi
        printf "${PATSH_NAME}: unknown operation: ${1}\n"
        ;;
esac