#!/bin/bash
# Script to create a new shell script and open it for editing

APP=$(basename $0)

#######################################################################
# Set default options
#######################################################################
NEWSH_SCRIPT_TYPE=bash
NEWSH_USE_ABS_PATH=0
NEWSH_NO_EXEC_FLAG=0
NEWSH_TRUNC_SCRIPT=0
NEWSH_SCRIPT_FILE=

#######################################################################
# Usage information
#######################################################################
usage()
{
    cat <<-EOM
Usage: $APP OPTIONS <new-shell-script-filename>

OPTIONS
    -t <type>       Type of script to create (bash/python/ruby/expect)
    -a              Use absolute path to binary instead of the env wrapper
    -x              Don't make the file executable
    -f              Overwrite the script file if it already exists
    -h              Display this help message

$APP will abort if the specified filename already exists
EOM
}

#######################################################################
# Get path to binary
#######################################################################
get_binary_path()
{
    local binary=$1
    local env_path=$(which env)
    local bin_path=$(which $binary)

    if [[ -z "$bin_path" ]]
    then
        echo "$APP: fatal: Cannot find $binary" >&2
        exit 1
    fi

    case "$NEWSH_USE_ABS_PATH" in
    0)
        # Use env as the path specifier
        NEWSH_BINARY_PATH="$env_path $binary"
        ;;

    1)
        # Use absolute path to the binary as the path specifier
        NEWSH_BINARY_PATH="$bin_path"
        ;;

    *)
        echo "$APP: fatal: Corrupted internal state!" >&2
        echo "$APP: USE_ABS_PATH=$NEWSH_USE_ABS_PATH" >&2
        exit 2
        ;;
    esac
}


#######################################################################
# Verify command line switches
#######################################################################
while getopts "t:axfh" OPTION
do
    case "$OPTION" in
    h)
        usage
        exit 0
        ;;

    t)
        NEWSH_SCRIPT_TYPE=$OPTARG
        ;;

    a)
        NEWSH_USE_ABS_PATH=1
        ;;

    x)
        NEWSH_NO_EXEC_FLAG=1
        ;;

    f)
        NEWSH_TRUNC_SCRIPT=1
        ;;

    \?)
        exit 1
        ;;

    :)
        echo "$APP: Option -$OPTARG requires an argument" >&2
        exit 1
        ;;
    esac
done

shift $((OPTIND - 1))
NEWSH_SCRIPT_FILE=$1

if [[ -z "$NEWSH_SCRIPT_FILE" ]]
then
    echo "$APP: fatal: Missing script file!" >&2
    exit 1
fi

if [[ -e "$NEWSH_SCRIPT_FILE" ]]
then
    if [[ "$NEWSH_TRUNC_SCRIPT" == "0" ]]
    then
        echo "$APP: fatal: Existing script file $NEWSH_SCRIPT_FILE" >&2
        exit 1
    elif [[ "$NEWSH_TRUNC_SCRIPT" == "1" ]]
    then
        echo "$APP: overwriting existing script file $NEWSH_SCRIPT_FILE" >&2
    fi
fi

get_binary_path $NEWSH_SCRIPT_TYPE
(cat <<-EOF
#!$NEWSH_BINARY_PATH
# Autogenerated by $APP on $(date +%F) at $(date +%T%z)

EOF
) > "$NEWSH_SCRIPT_FILE"

# Check and make file executable
if [[ "$NEWSH_NO_EXEC_FLAG" == "0" ]]
then
    chmod +x "$NEWSH_SCRIPT_FILE"
fi