#! /bin/sh
#
# NAME
#   get - evaluate ./default.nix
#
# SYNOPSIS
#   get [-jlprs] [attrPath]
#
# DESCRIPTION
#   The command nix evaluates the Nix expression in ./default.nix.
#
# OPTIONS
#
#   -j    Format output as JSON. Implies -s.
#
#   -l    List attrNames, one per line.
#
#   -p    Pretty-print output. (Only effectiv in conjunction with -j.)
#
#   -r    If result looks is a string, then it will be written directly to
#         standard output rather than being formatted as JSON or Nix string
#         with quotes. Refs jq(1)'s --raw-output.
#
#   -s    Recursively evaluate list elements and attributes.
#         Refs nix-instantiate(1)'s --strict.
#
set -efu

args=$*

has_lopt() {
  echo "$args" | grep -q '\(^\|\s\)--'"$1"'\(\s\|$\)'
}

has_sopt() {
  echo "$args" | grep -q '\(^\|\s\)-[a-z]*'"$1"'[a-z]*\(\s\|$\)'
}

filter() { cat; }

if has_sopt j; then
  json=1
  strict=1
fi

if has_sopt l; then
  unset json
  unset strict
  filter() { sed 's/\({ \)\?\(\S\+\) = <CODE>; }\?/\2\n/g' | grep .; }
fi

if has_sopt p && has_sopt j; then
  filter() { jq .; }
fi

if has_sopt r; then
  raw_output=1
fi

if has_sopt s; then
  strict=1
fi


if x=$(nix-instantiate --json --eval -A NIX_PATH 2>/dev/null); then
  NIX_PATH=$(echo "$x" | jq -r .)
  export NIX_PATH
  unset x
fi

result=$(nix-instantiate \
  --eval \
  --argstr user-name "$LOGNAME" \
  --argstr host-name "$HOSTNAME" \
  ${json+--json} \
  ${strict+--strict} \
  $(
    for i; do
      echo "$i"
    done | sed -n '
      s/^[A-Za-z_][0-9A-Za-z_.-]*$/--attr &/p
      s/^\([0-9A-Za-z-]\+\)=\([0-9A-Za-z-]*\)$/--argstr \1-name \2/p
    '
  ))

case ${raw_output-0} in 1)
  case ${result:0:1} in \")
    result=$(echo "$result" | jq -e -r .)
  esac
esac

echo "$result" | filter