#!/usr/bin/env sh

warn() { printf >&2 '\033[1m%s:\033[m %s\n' acquire "$*" ;}
die() { warn "$@"; exit 64 ;}
missing() { [ ${#3} != 0 ] || { warn "missing a required $1: $2"; ok=0 ;} ;}

argue()
 { : \
 && for arg in "$@" \
    ;do : \
     && rhs="${arg#*=}" \
     && a="${arg%"$rhs"}" \
     && b="${a%=}" \
     &&  if [ ${#a} = ${#b} ] \
         || [ ${#b} = 0 ] \
        ;then : \
         && warn "ignoring bare argument: $arg" \
         && continue \
        ;fi \
     && lhs="${b#*[!-0-9A-Z_a-z]}" \
     &&  if [ ${#lhs} != ${#b} ] \
        ;then : \
         && warn "ignoring invalid key: $b" \
         && warn "it became invalid at: ${b#"${b%?"$lhs"}"}" \
         && continue \
        ;fi \
     && case "$lhs" in \
        (from) from="$rhs" ;; \
        (repo) repo="$rhs" ;; \
        (dest) dest="$rhs" ;; \
        (commit) commit="$rhs" ;; \
        (checksum) checksum="$rhs" ;; \
        (env) env="${rhs%%[!A-Za-z0-9_]*}" ;; \
        (*) warn "ignoring unknown key: $lhs" ;; \
        esac \
     || exit \
    ;done \
 && { [ "${#from}" != 0 ] || die "missing a required key: from" ;} \
 &&  if [ -n "$env" ] && [ ".${env#[0-9]}" = ".$env" ] \
    ;then : \
        "${commit:="$(printenv "${env}_COMMIT")"}" \
        "${checksum:="$(printenv "${env}_SHA256")"}" \
    ;fi \
 &&  if [ "$from" = github ] || [ "$from" = sourcehut ] \
    ;then : \
     && missing key repo "$repo" \
     && missing key commit "$commit" \
     && missing key checksum "$checksum" \
     && { [ $ok = 1 ] || exit 64 ;} \
     && username="${repo%%/*}" && project="${repo##*/}" \
     &&  if [ ".$username/$project" != ".$repo" ] \
        ;then : \
         && warn "invalid value for key: repo=$repo" \
         && die "expected format: repo=username/project" \
        ;fi \
     && remote_fn="$commit.tar.gz" \
     && local_fn="$username!$project-$remote_fn" \
     && pathy="$repo/archive/$remote_fn" \
     && case "$from" in
        (github)    remote_url="https://github.com/$pathy" ;; \
        (sourcehut) remote_url="https://git.sr.ht/~$pathy" ;; \
        esac \
     && sha256="$checksum" \
     && { [ "${#dest}" != 0 ] || dest="${repo##*/}" ;} \
    ;else : \
     && die "unknown value specified for \"from\": $from" \
    ;fi \
 || exit \
 ;}

ok=1 from= repo= commit= checksum= env= \
 && { [ "$#" == 0 ] || argue "$@" ;} \
 && { [ -d "/tmp" ] || die '/tmp must be mounted (or just exist)' ;} \
 && missing variable dest "$dest" \
 && missing variable local_fn "$local_fn" \
 && missing variable remote_url "$remote_url" \
 && missing variable sha256 "$sha256" \
 && { [ $ok = 1 ] || exit 64 ;} \
 && { : \
     && printf '%s  %s\n' "$sha256" "$local_fn" | sha256sum -c - >/dev/null 2>&1 \
     || wget -q "$remote_url" -O "$local_fn" \
     && printf '%s  %s\n' "$sha256" "$local_fn" | sha256sum -c - \
     || { sha256sum "$local_fn"; exit 1 ;} \
     ;} \
 && temp="$(mktemp -d)" \
 && tar -axof "$local_fn" -C "$temp" \
 && find "$temp" -mindepth 1 -maxdepth 1 >/tmp/files \
 && find "$temp" -mindepth 1 -maxdepth 1 -type d >/tmp/dirs \
 && { [ -d "$dest" ] || mkdir "$dest" ;} \
 && if [ "$(wc -l </tmp/files)" = 1 ] && [ "$(wc -l </tmp/dirs)" = 1 ] \
    ;then : \
     && find "$temp" -mindepth 2 -maxdepth 2 -exec cp -rp {} "$dest" + \
    ;else : \
     && cp -rp "$temp" "$dest" \
    ;fi \
;