#=============================================================================
# Copyright 2015-2016 Kitware, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#=============================================================================

set -e

# Disable noise from `pre-commit` when no configuration is present on the
# imported tree.
export PRE_COMMIT_ALLOW_NO_CONFIG=1

########################################################################
# Script for updating third party packages.
#
# This script should be sourced in a project-specific script which sets
# the following variables:
#
#   name
#       The name of the project.
#   ownership
#       A git author name/email for the commits.
#   subtree
#       The location of the third-party package within the main source
#       tree.
#   repo
#       The git repository to use as upstream.
#   tag
#       The tag, branch or commit hash to use for upstream.
#   shortlog
#       Optional.  Set to 'true' to get a shortlog in the commit message.
#   exact_tree_match
#       Optional. Set to 'false' to disable tree-object based matching for
#       previous import commit (required for projects that allow modifying
#       imported trees). In such cases, log-based searching is performed.
#
# Additionally, an "extract_source" function must be defined. It will be
# run within the checkout of the project on the requested tag. It should
# should place the desired tree into $extractdir/$name-reduced. This
# directory will be used as the newest commit for the project.
#
# For convenience, the function may use the "git_archive" function which
# does a standard "git archive" extraction using the (optional) "paths"
# variable to only extract a subset of the source tree.
#
# Dependencies
#
# To update third party packages from git repositories with submodule,
# you will need to install the "git-archive-all" Python package with
#
#   pip install git-archive-all
#
# or install it from https://github.com/Kentzo/git-archive-all.
#
# This package installs a script named "git-archive-all" where pip
# installs executables. If you run pip under your user privileges (i.e.,
# not using "sudo"), this location may be $HOME/.local/bin. Make sure
# that directory is in your path so that git can find the
# "git-archive-all" script.
#
########################################################################

########################################################################
# Utility functions
########################################################################
git_archive () {
    git archive --worktree-attributes --prefix="$name-reduced/" HEAD -- $paths | \
        tar -C "$extractdir" -x
}

confirm_archive_all_exists () {
    which git-archive-all || die "git requires an archive-all command. Please run 'pip install git-archive-all'"
}

git_archive_all () {
    confirm_archive_all_exists
    local tmptarball="temp.tar"
    git archive-all --prefix="" "$tmptarball"
    mkdir -p "$extractdir/$name-reduced"
    tar -C "$extractdir/$name-reduced" -xf "$tmptarball" $paths
    rm -f "$tmptarball"
}

disable_custom_gitattributes() {
    pushd "${extractdir}/${name}-reduced"
    # Git does not allow custom attributes in a subdirectory where we
    # are about to merge the `.gitattributes` file, so disable them.
    sed -i.bak -e '/^\[attr\]/ {s/^/#/;}' .gitattributes
    rm .gitattributes.bak
    popd
}

die () {
    echo >&2 "$@"
    exit 1
}

warn () {
    echo >&2 "warning:" "$@"
}

readonly regex_date='20[0-9][0-9]-[0-9][0-9]-[0-9][0-9]'
readonly basehash_regex="$name $regex_date ([0-9a-f]*)"
toplevel_dir="$( git rev-parse --show-toplevel )"
readonly toplevel_dir

cd "$toplevel_dir"

########################################################################
# Sanity checking
########################################################################
[ -n "$name" ] || \
    die "'name' is empty"
[ -n "$ownership" ] || \
    die "'ownership' is empty"
[ -n "$subtree" ] || \
    die "'subtree' is empty"
[ -n "$repo" ] || \
    die "'repo' is empty"
[ -n "$tag" ] || \
    die "'tag' is empty"
[ -n "$exact_tree_match" ] || \
    exact_tree_match=true

# Check for an empty destination directory on disk.  By checking on disk and
# not in the repo it allows a library to be freshly re-initialized in a single
# commit rather than first deleting the old copy in one commit and adding the
# new copy in a separate commit.
if [ ! -d "$( git rev-parse --show-toplevel )/$subtree" ]; then
    basehash=""
elif $exact_tree_match; then
    # Find the tree object for the current subtree.
    current_tree="$( git rev-parse "HEAD:$subtree" )"
    # Search history for a commit whose subtree matches this tree object.
    basehash=""
    # Limit candidate commits to those with expected import commit messages for efficiency.
    for commit in $( git rev-list --author="$ownership" --grep="$basehash_regex" HEAD ); do
        imported_tree="$( git rev-parse "$commit^{tree}" )"
        # Verify the imported tree is what is currently imported. If so, we
        # have found the desired import commit.
        if [ "$imported_tree" = "$current_tree" ] && [ -n "$imported_tree" ]; then
            basehash="$commit"
            break
        fi
    done
    if [ -z "$basehash" ]; then
        die "No previous import commit found with matching tree object for $subtree. (exact_tree_match enabled)"
    fi
else
    basehash="$( git rev-list --author="$ownership" --grep="$basehash_regex" -n 1 HEAD )"
fi
readonly basehash

[ -n "$basehash" ] || \
    warn "'basehash' is empty; performing initial import"
readonly do_shortlog="${shortlog-false}"

readonly workdir="$PWD/work"
readonly upstreamdir="$workdir/upstream"
readonly extractdir="$workdir/extract"

[ -d "$workdir" ] && \
    die "error: workdir '$workdir' already exists"

trap "rm -rf '$workdir'" EXIT

# Skip LFS downloading; imports should not need LFS data.
export GIT_LFS_SKIP_SMUDGE=1

# Get upstream
git clone --recursive "$repo" "$upstreamdir"

if [ -n "$basehash" ]; then
    # Remove old worktrees
    git worktree prune
    # Use the existing package's history
    git worktree add "$extractdir" "$basehash"
    # Clear out the working tree
    pushd "$extractdir"
    git ls-files -z --recurse-submodules | xargs -0 rm -v
    find . -type d -empty -delete
    popd
else
    # Create a repo to hold this package's history
    mkdir -p "$extractdir"
    git -C "$extractdir" init
fi

# Extract the subset of upstream we care about
pushd "$upstreamdir"
git checkout "$tag"
git submodule sync --recursive
git submodule update --recursive --init
upstream_hash="$( git rev-parse HEAD )"
readonly upstream_hash
upstream_hash_short="$( git rev-parse --short=8 "$upstream_hash" )"
readonly upstream_hash_short
upstream_datetime="$( git rev-list "$upstream_hash" --format='%ci' -n 1 | grep -e "^$regex_date" )"
readonly upstream_datetime
upstream_date="$( echo "$upstream_datetime" | grep -o -e "$regex_date" )"
readonly upstream_date
if $do_shortlog && [ -n "$basehash" ]; then
    upstream_old_short="$( git -C "$toplevel_dir" cat-file commit "$basehash" | sed -n '/'"$basehash_regex"'/ {s/.*(//;s/)//;p;}' | grep -E '^[0-9a-f]+$' )"
    readonly upstream_old_short

    commit_shortlog="

Upstream Shortlog
-----------------

$( git shortlog --no-merges --abbrev=8 --format='%h %s' "$upstream_old_short".."$upstream_hash" )"
else
    commit_shortlog=""
fi
readonly commit_shortlog
extract_source || \
    die "failed to extract source"
popd

[ -d "$extractdir/$name-reduced" ] || \
    die "expected directory to extract does not exist"
readonly commit_summary="$name $upstream_date ($upstream_hash_short)"

# Commit the subset
pushd "$extractdir"
mv -v "$name-reduced/"* .
rmdir "$name-reduced/"
git add -A .
git commit --no-verify --no-post-rewrite --author="$ownership" --date="$upstream_datetime" -F - <<-EOF
$commit_summary

Code extracted from:

    $repo

at commit $upstream_hash ($tag).$commit_shortlog
EOF
git branch -f "upstream-$name"
popd

# Merge the subset into this repository
if [ -n "$basehash" ]; then
    git merge --log -s recursive "-Xsubtree=$subtree/" --no-commit "upstream-$name"
else
    # Note: on Windows 'git merge --help' will open a browser, and the check
    # will fail, so use the flag by default. Apple opens an editor instead;
    # assume the flag is understood there too.
    unrelated_histories_flag=""
    if git --version | grep -q -E 'windows|Apple'; then
        unrelated_histories_flag="--allow-unrelated-histories"
    elif git merge --help | grep -q -e allow-unrelated-histories; then
        unrelated_histories_flag="--allow-unrelated-histories"
    fi
    readonly unrelated_histories_flag

    git fetch "$extractdir" "+upstream-$name:upstream-$name"
    git merge --log -s ours --no-commit $unrelated_histories_flag "upstream-$name"
    git read-tree -u --prefix="$subtree/" "upstream-$name"
fi
git commit --no-edit
git branch -d "upstream-$name"