.pathlib

#!/bin/sh /dev/null
# vim: ft=bash:

__pat_safe() { expr "${1-}" : '[^[*!?:]*$' > /dev/null; }

if [ -z "${BASH_VERSION:-}" ]; then
    # posix shells can't do variable indirection or pattern substitution
    # directly, so we need to use eval and assorted commands

    # https://stackoverflow.com/a/36235741/370695
    __var_safe() { expr "${1-}" : '[[:alpha:]_][[:alnum:]_]*$' > /dev/null; }

    pathlist_append() {
        if __var_safe "${1-}" && [ -d "${2-}" ]; then
            eval "export ${1}=\"\${${1}:+\$${1}:}\$2\""
        fi
    }

    pathlist_prepend() {
        if __var_safe "${1-}" && [ -d "${2-}" ]; then
            eval "export ${1}=\"\$2\${${1}:+:\$${1}}\""
        fi
    }

    pathlist_has() {
        if __var_safe "${1-}" && __pat_safe "${2-}"; then
            local SAFE_DIR="$(printf '%s' "${2}" | sed 's/[$.*[\^]/\\&/g')"
            eval "printf '%s\\n' \"\${${1}}\"" | grep "\\(:\\|^\\)${SAFE_DIR}\\(:\\|$\\)" > /dev/null
            return $?
        fi
        return 1
    }

    pathlist_remove() {
        if __var_safe "${1-}" && __pat_safe "${2-}"; then
            #local NEW_VALUE="$(eval printf '%s' \"\${${1}}\" | awk -v REM="${2}" -v RS=: -v ORS=: '$0 != REM' | sed 's/:$//')"
            # adapted from https://www.linuxjournal.com/content/removing-duplicate-path-entries
            local NEW_VALUE="$(eval printf '%s' \"\${${1}}\" | awk -v REM="${2}" -v RS=: '($0 != REM) {a[$0]; printf("%s%s", length(a) > 1 ? ":" : "", $0)}')"
            eval "export ${1}=\"${NEW_VALUE}\""
        fi
    }

    pathlist_dedupe() {
        if __var_safe "${1-}"; then
            local NEW_VALUE="$(eval printf '%s' \"\${${1}}\" | awk -v RS=: '!($0 in a) {a[$0]; printf("%s%s", length(a) > 1 ? ":" : "", $0)}')"
            eval "export ${1}=\"${NEW_VALUE}\""
        fi
    }
else
    # bash has enough functionality that everything can be done with builtins

    pathlist_append()  { [ -n "$1" -a -d "$2" ] && export "$1"="${!1:+${!1}:}$2"; }

    pathlist_prepend() { [ -n "$1" -a -d "$2" ] && export "$1"="$2${!1:+:${!1}}"; }

    pathlist_has() {
        if [ -n "$1" ] && __pat_safe "${2-}"; then
            if [ "${!1}" = "$2" ]; then # exact match
                return 0
            else # try to remove the path component...
                local __VALUE="${!1}"
                local __LENGTH="${#__VALUE}"
                __VALUE="${__VALUE//":$2:"/":"}"
                __VALUE="${__VALUE/#"$2:"/}"
                __VALUE="${__VALUE/%":$2"/}"
                # ...and check whether the length changed
                [ "${#__VALUE}" -ne ${__LENGTH} ] && return 0
            fi
            #expr "${!1}" : "$(printf '%s' "$2" | sed 's/[$.*[\^]/\\&/g;s/\(.*\)/\\(\1:.\\+\\|.\\+:\1:.\\+\\|\1$\\|.\\+:\1$\\)/')" > /dev/null
            #return $?
        fi
        return 1
    }

    pathlist_remove() {
        # https://stackoverflow.com/a/19587970/370695
        if [ -n "$1" ] && __pat_safe "${2-}"; then
            local __VALUE="${!1}"
            local __LENGTH="${#__VALUE}"

            while :; do # remove from the middle until nothing happens
                __VALUE="${__VALUE//":$2:"/":"}"
                [ ${#__VALUE} -eq ${__LENGTH} ] && break
                __LENGTH="${#__VALUE}"
            done

            __VALUE="${__VALUE/#"$2:"/}"
            __VALUE="${__VALUE/%":$2"/}"

            if [ "${__VALUE}" = "$2" ]; then
                export "$1"=""
            else
                export "$1"="${__VALUE}"
            fi
        fi
    }

    pathlist_dedupe() {
        local -A __KEYS
        local -a __LIST
        local __VALUE
        readarray -t __LIST <<< "${!1//":"/$'\n'}"
        for ENTRY in "${__LIST[@]}"; do
            if [ "${__KEYS["${ENTRY}"]-0}" -eq 0 ]; then
                if [ "${#__KEYS[@]}" -gt 0 ]; then
                    __VALUE="${__VALUE}:${ENTRY}"
                else
                    __VALUE="${ENTRY}"
                fi
                __KEYS["${ENTRY}"]=1
            fi
        done
        export "$1"="${__VALUE}"
    }
fi

pathlist_cond_append() {
    pathlist_has "$1" "$2" || pathlist_append "$1" "$2"
}

pathlist_cond_prepend() {
    pathlist_has "$1" "$2" || pathlist_prepend "$1" "$2"
}

pathlist_head() {
    pathlist_remove "$1" "$2"
    pathlist_prepend "$1" "$2"
}

pathlist_cond_head() {
    pathlist_has "$1" "$2" && pathlist_head "$1" "$2"
}

pathlist_tail() {
    pathlist_remove "$1" "$2"
    pathlist_append "$1" "$2"
}

pathlist_cond_tail() {
    pathlist_has "$1" "$2" && pathlist_tail "$1" "$2"
}