caws

#!/bin/bash

# Like the 'aws' cli except caches results

# http://redsymbol.net/articles/unofficial-bash-strict-mode/

set -euo pipefail
IFS=$'\n\t'

#set -x

# Produce short hash just as insurance in case the directory scheme
# produces a collision. For example "s3 ls a@" and "s3 ls a_" both
# wind up in .caws-cache/s3/ls/a/ so there needs to be a final
# disambiguation.
function hexsum {
    printf "%x" $(echo -n $@ | cksum | cut -d' ' -f 1)
}

# https://stackoverflow.com/a/17841619/68127
function join_by { local IFS="$1"; shift; echo "$*"; }

function args_to_dir {
    local -a dir_safe_args
    for arg in $@
    do
	xlated=$(echo -n $arg | tr --delete --complement 'a-zA-Z0-9_')
	dir_safe_args+=( $xlated  )
    done

    join_by "/" ${dir_safe_args[@]}
}

CAWS_CACHE_DIR=${CAWS_CACHE_DIR-.caws-cache}

cached_output_dir="${CAWS_CACHE_DIR}/$(args_to_dir $@)/$(hexsum $@)"

mkdir -p $cached_output_dir

cached_output=$cached_output_dir/output

if [[ ! -f $cached_output ]]
then
    maybe_cached_output=$(mktemp --tmpdir=$cached_output_dir 'maybe_outputXXXXX.out')
    trap "rm -f $maybe_cached_output" EXIT
    maybe_error_output=$cached_output_dir/last-error.out

    set +e
    aws $@ >$maybe_cached_output 2>$maybe_error_output
    error_code=$?
    set -e
    if [[ $error_code != 0 ]]
    then
	cat 1>&2 $maybe_error_output
	exit $error_code
    else
	mv $maybe_cached_output $cached_output
    fi
fi

cat $cached_output
exit