.gosh.sh

#!/usr/bin/env bash

# Default a variable named $1 to $2 unless already set.
# This is more readable than expansion syntax.
# E.g.,
#    default foo bar
# vice:
#    export FOO="${FOO:=$BAR}"
function default {
    if [ $# -ne 2 ]; then
        echo "usage: default <variable> <default value>" >&2
        echo "(got: $@)" >&2
        exit 1
    fi
    eval __=\$$1
    if [ -z "$__" ]; then
        export $1="$2"
    fi
}

# Default a variable named $1 to $2 unless already set,
# and be verbose about it. This is a verbose variant of
# the default function.
# E.g.,
#    vdefault foo bar
function vdefault {
    if [ $# -ne 2 ]; then
        echo "usage: vdefault <variable> <default value>" >&2
        echo "(got: $@)" >&2
        exit 1
    fi
    eval __=\$$1
    if [ -z "$__" ]; then
        echo "Variable \"$1\" is being defaulted to \"$2\"."
        export $1="$2"
    fi
}

# Returns 1 if the environment variable $1 is not set, 0 otherwise.
# E.g.,
#    assert_env PATH
function assert_env {
    if [ $# -ne 1 ]; then
        echo "usage: assert_env <variable>" >&2
        echo "(got: $@)" >&2
        exit 1
    fi
    eval __=\$$1
    if [ -z "$__" ]; then
        echo "$1 is not set" 1>&2
        return 1
    fi
    return 0
}

# Prompts the user to set a variable if it does not have a default value.
# E.g.,
#    prompt_env VERSION "VERSION is not set, please set it now: "
function prompt_env {
    if [ $# -ne 2 ]; then
        echo "usage: prompt_env <variable> <prompt>" >&2
        echo "(got: $@)" >&2
        exit 1
    fi
    eval __=\$$1
    if [ -z "$__" ]; then
        read -p "$2" REPLY
        if [ -z "$REPLY" ]; then
            echo "no response" >&2
            return 1
        fi
        export $1="$REPLY"
    fi
    return 0
}

# Sources the file named $1, if readable. The return code of the source
# operation is returned to allow for failure conditions when sourcing a
# file fails for any reason.
# E.g.,
#    assert_source template.sh
function assert_source {
    if [ $# -ne 1 ]; then
        echo "usage: assert_source <file>" >&2
        echo "(got: $@)" >&2
        exit 1
    fi
    if [ -r "$1" ]; then
        source "$1"
        RC=$?
        if [ $RC -ne 0 ]; then
            echo "assert_source: source failure in $1; returned $RC" >&2
            return $RC
        fi
    fi
    return 0
}

# Returns 1 if the command $1 is not found, 0 otherwise.
# E.g.,
#    require_cmd realpath
function require_cmd {
    if [ $# -ne 1 ]; then
        echo "usage: require_cmd <command>" >&2
        echo "(got: $@)" >&2
        exit 1
    fi
    _=$(which "$1" >/dev/null 2>&1)
    if [ $? -eq 1 ]; then
        echo "$1: command not found (and it is required)" 2>&2
        return 1
    fi
    return 0
}

# Pull in any GOSH_CONTRIB scripts found.
function use_gosh_contrib {
    assert_env GOSH_CONTRIB || return 1
    for contrib in "$GOSH_CONTRIB"/*.sh; do
        assert_source "$contrib" || return 1
    done
    return 0
}