#!/usr/bin/env bash

set -eo pipefail

# Dumps all environment variables sorted alphabetically.  Uses zero byte as a
# delimiter since bash variables can not contain '\0'.
dumpEnv() {
    env -0 | sort -z
}

# Retrieves the value of variable name passed as $1 in dumped environment
# passed as $2 (see dumpEnv)
getByName() {
    local name="$1"
    local envFile="$2"
    grep -z "^${name}=" $envFile | cut -z -f2- -d '=' | tr -d '\0'
}

# Produces a diff of two given environment dumps, suitable for consumption by
# bash. Given environment dumps A and B (both generated by dumpEnv),
#
#     source A; source <(diffEnvs A B)
#
# shall be equivalent to
#
#     source B
#
diffEnvs() {
    local name
    local old="$1"
    local new="$2"

    while read -r -d '' line; do
        name=$(tr -d '\0' <<<"$line" | head -n1 | cut -f1 -d'=')
        if ! getByName "$name" "$new" >/dev/null; then
            echo "export -n '${name}'"
        fi
    done <"$old"

    while read -rd $'\0' line; do
        name=$(tr -d '\0' <<<"$line" | head -n1 | cut -f1 -d'=')
        if getByName "$name" "$old" >/dev/null; then
            # found in old env, check if values match
            if ! grep -z "^${line}\$" "$old" >/dev/null; then
                # variable has changed
                echo "export ${line@Q}"
            fi
        else
            # variable is new
            echo "export ${line@Q}"
        fi
    done <"$new"
}

usage() {
    echo "${BASH_SOURCE[0]} COMMAND"
    echo
    echo "Commands:"
    echo -e "\tstatus,s: Show cache status"
    echo -e "\treload,r: Recreate cache from .envrc"
    echo -e "\tclear,c: Remove cache file for current directory"
}

getCacheFilePath() {
    local cacheDir="${XDG_CACHE_HOME:-$HOME/.cache}/direnv-cache"
    echo "${cacheDir}/$(pwd | sha1sum | tr -d ' -')"
}

cmd="$1"

if ! [[ -e .envrc ]]; then
    echo "Error, no .envrc found in current directory"
    exit 1
fi

cacheFile=$(getCacheFilePath)

case $cmd in
    reload|r)
        echo "Re-creating cache"
        mkdir -p "$(dirname ${cacheFile})"
        dumpEnv > "${cacheFile}.pre"
        source <(direnv stdlib)
        if [[ .envrc -nt ${cacheFile}.recipe ]]; then
            direnv exec . true > /dev/null
        fi
        source "${cacheFile}.recipe"
        dumpEnv > "${cacheFile}.post"
        diffEnvs "${cacheFile}.pre" "${cacheFile}.post" > "$cacheFile"
        rm "${cacheFile}.pre" "${cacheFile}.post"
        echo "Environment cached in $cacheFile, telling direnv to reload"
        direnv reload
        ;;
    status|s)
        shift
        ls "$cacheFile" "$@"
        ;;
    clear|c)
        if [[ -e "$cacheFile" ]]; then
            rm "$cacheFile"
        fi
        ;;
    *)
        usage
        exit 1
esac