#!/usr/bin/env bash
# darling-nix — run Nix commands inside a Darling prefix from the Linux host
#
# This is a convenience wrapper that sources the Nix profile inside a
# Darling shell and then exec's the given command.  It saves users from
# having to remember the long `darling shell bash -lc '...'` incantation
# every time.
#
# Usage:
#   darling-nix <command> [arguments ...]
#
# Examples:
#   darling-nix nix --version
#   darling-nix nix-instantiate --eval -E '1 + 1'
#   darling-nix nix eval --expr 'builtins.currentSystem'
#   darling-nix nix-build --expr 'derivation { name = "test"; builder = "/bin/bash"; args = ["-c" "echo ok > $out"]; system = "x86_64-darwin"; }'
#   darling-nix nix-env -qa hello
#   darling-nix nix repl
#
# Options:
#   --prefix <path>   Use a non-default Darling prefix
#   --help            Show this help message
#
# Environment:
#   DPREFIX           Override the default Darling prefix (~/.darling)
#   DARLING_NIX_VERBOSE  Set to 1 for debug output
#
# See: plan/05-phase3-nix-install.md (Task 3.4)

set -euo pipefail

# ── Defaults ────────────────────────────────────────────────────────────────

DARLING_PREFIX="${DPREFIX:-}"
VERBOSE="${DARLING_NIX_VERBOSE:-0}"

# ── Helpers ─────────────────────────────────────────────────────────────────

die() {
    echo "darling-nix: error: $*" >&2
    exit 1
}

debug() {
    if [ "$VERBOSE" = "1" ]; then
        echo "darling-nix: debug: $*" >&2
    fi
}

usage() {
    cat <<'EOF'
Usage: darling-nix [--prefix <path>] <command> [arguments ...]

Run Nix commands inside a Darling (macOS compatibility) prefix.

Options:
  --prefix <path>   Use a non-default Darling prefix (default: ~/.darling)
  --help            Show this help message

Environment:
  DPREFIX                Override the default Darling prefix
  DARLING_NIX_VERBOSE    Set to 1 for debug output

Examples:
  darling-nix nix --version
  darling-nix nix-instantiate --eval -E '1 + 1'
  darling-nix nix eval --expr 'builtins.currentSystem'
  darling-nix nix-env -qa hello
  darling-nix nix repl
EOF
    exit 0
}

# ── Argument Parsing ────────────────────────────────────────────────────────

while [ $# -gt 0 ]; do
    case "$1" in
        --prefix)
            [ $# -ge 2 ] || die "--prefix requires an argument"
            DARLING_PREFIX="$2"
            shift 2
            ;;
        --help|-h)
            usage
            ;;
        --)
            shift
            break
            ;;
        -*)
            # Could be a flag for the inner command (e.g. `darling-nix nix --version`)
            # so stop parsing our flags and treat everything as the command.
            break
            ;;
        *)
            break
            ;;
    esac
done

if [ $# -eq 0 ]; then
    die "no command specified (try --help)"
fi

# ── Preflight ───────────────────────────────────────────────────────────────

if ! command -v darling &>/dev/null; then
    die "darling is not installed or not in PATH"
fi

# Build the darling command with optional --prefix
DARLING_CMD=(darling)
if [ -n "$DARLING_PREFIX" ]; then
    DARLING_CMD+=(--prefix "$DARLING_PREFIX")
    debug "using prefix: $DARLING_PREFIX"
fi

# ── Build the inner command ─────────────────────────────────────────────────

# We need to carefully quote the user's arguments so they survive the
# bash -lc layer.  We use printf %q to produce shell-escaped versions
# of each argument.
ESCAPED_ARGS=""
for arg in "$@"; do
    ESCAPED_ARGS+=" $(printf '%q' "$arg")"
done

debug "inner command:${ESCAPED_ARGS}"
debug "darling cmd: ${DARLING_CMD[*]}"

# The inner script:
#   1. Sources the Nix profile so nix/nix-env/etc. are on PATH.
#   2. exec's the user's command (preserving exit code).
INNER_SCRIPT="
# Source Nix profile
if [ -e '/nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh' ]; then
    . '/nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh'
elif [ -e \"\\\$HOME/.nix-profile/etc/profile.d/nix.sh\" ]; then
    . \"\\\$HOME/.nix-profile/etc/profile.d/nix.sh\"
elif [ -e '/etc/profile.d/nix-darling.sh' ]; then
    . '/etc/profile.d/nix-darling.sh'
fi

# Verify nix is available
if ! command -v nix &>/dev/null && ! command -v nix-env &>/dev/null; then
    echo 'darling-nix: Nix does not appear to be installed in this prefix.' >&2
    echo 'darling-nix: Run ./scripts/install-nix-in-darling.sh first.' >&2
    exit 127
fi

exec${ESCAPED_ARGS}
"

# ── Execute ─────────────────────────────────────────────────────────────────

# Run the command inside Darling, forwarding the exit code.
# We use `bash -lc` to get a login shell (which sources /etc/profile.d/*).
exec "${DARLING_CMD[@]}" shell bash -lc "$INNER_SCRIPT"