source $stdenv/setup

set -euo pipefail

src=$(realpath $1)
out=$(realpath $2)

echo "Fetching $src to $out"

mkdir $out

# Configure cargo to fetch from a local copy of the crates.io registry

echo "Using rust registry from $rustRegistry"

cat <<EOF > $out/config
[registry]
index = "file://$rustRegistry"
EOF

export CARGO_HOME=$out
cd $src

if [[ ! -f Cargo.lock ]]; then
    echo
    echo "ERROR: The Cargo.lock file doesn't exist"
    echo
    echo "Cargo.lock is needed to make sure that depsSha256 doesn't change"
    echo "when the registry is updated."
    echo

    exit 1
fi

# We need to do the following string replacement so that 'cargo fetch'
# doesn't ignore the versions specified in Cargo.lock
set +u
substituteInPlace Cargo.lock \
    --replace "registry+https://github.com/rust-lang/crates.io-index" \
              "registry+file://$rustRegistry"
set -u

# Do any possible 'cargo update -p <pkgName> --precise <version>' ad-hoc updates
eval "$cargoUpdateHook"

# Do the fetch
cargo fetch --verbose

# Now that we have fetched everything, let's make the output deterministic

# Cargo uses the following directory structure for fetched data, where
# $indexHash is a hash of the registry index URL:
#
#
# /config:
#
#     Cargo config file. We'll delete this because it's not deterministic,
#     and instead recreate it just before running 'cargo build'.
#
# /registry/cache/$indexHash/:
#
#     This is where tarballs of registry package dependencies are kept
#     We'll need to keep this, but make sure $indexHash is a fixed name.
#
# /registry/index/$indexHash/:
#
#     A copy of the registry index is kept here. We can delete this, and
#     instead, just before running 'cargo build', we'll symlink this
#     directory to our static copy of the registry in the Nix store.
#
# /registry/src/$indexHash/{pkgName-pkgVersion}/:
#
#     Here cargo keeps extracted sources of the cached tarballs.
#     We'll just delete this because cargo will re-populate them from the
#     tarballs.
#
# /git/db/{domain-hash}/:
#
#     Here cargo keeps the `.git` directories of git dependencies.
#     We'll need to keep these, but make them deterministic.
#
# /git/checkouts/{domain-hash}/{branchName}/:
#
#     Here cargo keeps checked-out sources of the git dependencies.
#     We can delete this, because cargo will re-populate them from the above
#     `.git` directories.
#
# Let's start

# Remove cargo config file, which points to the ever-changing registry
rm $out/config

# Save the Cargo.lock file into the output, so that we don't have to do another
# 'cargo update' during the build (which would try to access the network) for
# any ad-hoc package updates (through $cargoUpdateHook).
#
# We need to replace the rustRegistry URL with something deterministic.
# Since the URL won't actually be accessed anymore, it's fine to use /dev/null.

set +u
substituteInPlace Cargo.lock \
    --replace "registry+file://$rustRegistry" \
              "registry+file:///dev/null"
set -u
mv Cargo.lock $out/


# Let's replace $indexHash with something more deterministic
mv $out/registry/cache/* $out/registry/cache/HASH

# The registry index changes all the time, so it's not deterministic
# We'll symlink it before running 'cargo build'
rm -rf $out/registry/index/*

# Make git DBs deterministic
# TODO: test with git submodules
[[ ! -d $out/git/checkouts ]] || (cd $out/git/checkouts && for name in *; do
    revs=""
    cd "$out/git/checkouts/$name"
    while read dir; do
        # extract substring: [dir = "./xxx/yyy/.git"] => [branch = "xxx/yyy"]
        branch="${dir:2:$((${#dir}-7))}"

        cd "$out/git/checkouts/$name/$branch"
        rev="$(git rev-parse HEAD)"
        revs="$revs $rev"
    done < <(find . -type d -name .git -print)

    echo "List of revs to keep for git db $name: $revs"

    (
        # The following code was adapted from nix-prefetch-git

        cd "$out/git/db/$name"

        export GIT_DIR=.

        # Remove all remote branches
        git branch -r | while read branch; do
            git branch -rD "$branch" >&2
        done

        # Remove all tags
        git tag | while read tag; do
            git tag -d "$tag" >&2
        done

        # Remove all local branches
        branchrefs=()
        eval "$(git for-each-ref --shell --format='branchrefs+=(%(refname))' refs/heads/)"

        for branchref in "${branchrefs[@]}"; do
            git update-ref -d "$branchref" >&2
        done

        # Create ad-hoc branches for the revs we need
        echo "$revs" | while read rev; do
            echo "Creating git branch b_$rev $rev"
            git branch b_$rev $rev
        done

        # Remove files that have timestamps or otherwise have non-deterministic
        # properties.
        rm -rf logs/ hooks/ index FETCH_HEAD ORIG_HEAD refs/remotes/origin/HEAD config

        # Do a full repack. Must run single-threaded, or else we lose determinism.
        git config pack.threads 1
        git repack -A -d -f
        rm -f config

        # Garbage collect unreferenced objects.
        git gc --prune=all
    )
done)

# Remove unneeded outputs
[[ ! -d $out/registry/src ]] || rm -rf $out/registry/src
[[ ! -d $out/git/checkouts ]] || rm -rf $out/git/checkouts

# XXX: provide some debugging output to see find out why we are seeing
# sporadic hash mismatches
find $out ! -type f
find $out -type f -exec sha256sum {} +