env_functions

# These are functions for manipulating PATH in shell config files such that the
# config file being loaded multiple times doesn't result in duplicate PATH
# entries.
# This allows using the Emacs package
# https://github.com/purcell/exec-path-from-shell to set environment variables
# for Emacs.

# Source: https://heptapod.host/flowblok/shell-startup/-/blob/65940865dc584083a16b23e458ed4945920af694/.shell/env_functions
indirect_expand () {
    env |sed -n "s/^$1=//p"
}

# Usage: path_remove /path/to/bin [PATH]
# Eg, to remove ~/bin from $PATH
#     path_remove ~/bin PATH
path_remove () {
    local IFS=':'
    local newpath
    local dir
    local var=${2:-PATH}
    # Bash has ${!var}, but this is not portable.
    for dir in `indirect_expand "$var"`; do
        IFS=''
        if [ "$dir" != "$1" ]; then
            newpath=$newpath:$dir
        fi
    done
    export $var=${newpath#:}
}

# Usage: path_prepend /path/to/bin [PATH]
# Eg, to prepend ~/bin to $PATH
#     path_prepend ~/bin PATH
path_prepend () {
    # if the path is already in the variable,
    # remove it so we can move it to the front
    path_remove "$1" "$2"
    #[ -d "${1}" ] || return
    local var="${2:-PATH}"
    local value=`indirect_expand "$var"`
    export ${var}="${1}${value:+:${value}}"
}

# Usage: path_append /path/to/bin [PATH]
# Eg, to append ~/bin to $PATH
#     path_append ~/bin PATH
path_append () {
    path_remove "${1}" "${2}"
    #[ -d "${1}" ] || return
    local var=${2:-PATH}
    local value=`indirect_expand "$var"`
    export $var="${value:+${value}:}${1}"
}

# Usage: source_if_exists filename
source_if_exists () {
    if [ -r "$1" ]; then
        . "$1"
    fi
}

# Usage: indirect_expand PATH -> $PATH
indirect_expand () {
    env |sed -n "s/^$1=//p"
}

# Usage: path_remove /path/to/bin [PATH]
# Eg, to remove ~/bin from $PATH
#     path_remove ~/bin PATH
path_remove () {
    local IFS=':'
    local newpath
    local dir
    local var=${2:-PATH}
    # Bash has ${!var}, but this is not portable.
    for dir in `indirect_expand "$var"`; do
        IFS=''
        if [ "$dir" != "$1" ]; then
            newpath=$newpath:$dir
        fi
    done
    export $var=${newpath#:}
}

# Usage: path_prepend /path/to/bin [PATH]
# Eg, to prepend ~/bin to $PATH
#     path_prepend ~/bin PATH
path_prepend () {
    # if the path is already in the variable,
    # remove it so we can move it to the front
    path_remove "$1" "$2"
    #[ -d "${1}" ] || return
    local var="${2:-PATH}"
    local value=`indirect_expand "$var"`
    export ${var}="${1}${value:+:${value}}"
}

# Usage: path_append /path/to/bin [PATH]
# Eg, to append ~/bin to $PATH
#     path_append ~/bin PATH
path_append () {
    path_remove "${1}" "${2}"
    #[ -d "${1}" ] || return
    local var=${2:-PATH}
    local value=`indirect_expand "$var"`
    export $var="${value:+${value}:}${1}"
}

# Usage: source_if_exists filename
source_if_exists () {
    # Test whether "$1" exists and is readable.
    if [ -r "$1" ]; then
        . "$1"
    fi
}