#!/usr/bin/env bash
set -euo pipefail

url=$1
rev=$2
expHash=$3

hashType="${NIX_HASH_ALGO:-sha256}"
hashFormat=${hashFormat:-"--sri"}
rev="${rev:-tip}"

LOG() {
  echo "$@" >&2
}

die() {
  LOG "$@"
  exit 1
}

if [[ -z "$url" || "$url" == "--help" ]]; then
    die "Usage: nix-prefetch-hg URL [rev [EXPECTED-HASH]]"
fi

if [[ "${fetchSubrepos:-0}" == 1 ]]; then
    subrepoClause=S
else
    subrepoClause=
fi

# If the hash was given, a file with that hash may already be in the
# store.
if [[ -n "$expHash" ]]; then
    finalPath=$(nix-store --print-fixed-path --recursive "$hashType" "$expHash" hg-archive)
    if ! nix-store --check-validity "$finalPath" 2> /dev/null; then
        finalPath=
    fi
    hash="$expHash"
fi


# If we don't know the hash or a path with that hash doesn't exist,
# download the file and add it to the store.
if [[ -z "$finalPath" ]]; then
    # nix>=2.20 rejects adding symlinked paths to the store, so use realpath
    # to resolve to a physical path. https://github.com/NixOS/nix/issues/11941
    tmpPath="$(realpath "$(mktemp -d --tmpdir hg-checkout-tmp-XXXXXXXX)")"
    cleanup() { x=$?; rm -rf "$tmpPath"; exit $x; }; trap cleanup EXIT

    tmpArchive="$tmpPath/hg-archive"

    # Perform the checkout.
    if [[ "$url" != /* ]]; then
      tmpClone="$tmpPath/hg-clone"
      hg clone -q -y -U "$url" "$tmpClone" >&2
    else
      tmpClone=$url
    fi
    hg archive -q$subrepoClause -y -r "$rev" --cwd "$tmpClone" "$tmpArchive"
    rm -f "$tmpArchive/.hg_archival.txt"

    LOG "hg revision is $(cd "$tmpClone"; hg id -r "$rev" -i)"

    # Compute the hash.
    hash=$(nix-hash --type "$hashType" "${hashFormat:---sri}" "$tmpArchive")
    if [[ -z "${QUIET:-}" ]]; then LOG "hash is $hash"; fi

    # Add the downloaded file to the Nix store.
    finalPath=$(nix-store --add-fixed --recursive "$hashType" "$tmpArchive")

    if [[ -n "$expHash" && "$expHash" != "$hash" ]]; then
        die "ERROR: hash mismatch for URL \`$url'"
    fi


fi

if [[ -z "${QUIET:-}" ]]; then LOG "path is $finalPath"; fi

echo "$hash"

if [[ -n "${PRINT_PATH:-}" ]]; then
    echo "$finalPath"
fi
