#! /usr/bin/env bash

set -e -o pipefail

url=
rev=
expHash=
hashType=$NIX_HASH_ALGO
deepClone=$NIX_PREFETCH_GIT_DEEP_CLONE
leaveDotGit=$NIX_PREFETCH_GIT_LEAVE_DOT_GIT
fetchSubmodules=
builder=
branchName=$NIX_PREFETCH_GIT_BRANCH_NAME

# ENV params
out=${out:-}
http_proxy=${http_proxy:-}

# populated by clone_user_rev()
fullRev=
humanReadableRev=
commitDate=
commitDateStrict8601=

if test -n "$deepClone"; then
    deepClone=true
else
    deepClone=false
fi

if test "$leaveDotGit" != 1; then
    leaveDotGit=
else
    leaveDotGit=true
fi

usage(){
    echo  >&2 "syntax: nix-prefetch-git [options] [URL [REVISION [EXPECTED-HASH]]]

Options:
      --out path      Path where the output would be stored.
      --url url       Any url understood by 'git clone'.
      --rev ref       Any sha1 or references (such as refs/heads/master)
      --hash h        Expected hash.
      --branch-name   Branch name to check out into
      --deepClone     Clone the entire repository.
      --no-deepClone  Make a shallow clone of just the required ref.
      --leave-dotGit  Keep the .git directories.
      --fetch-submodules Fetch submodules.
      --builder       Clone as fetchgit does, but url, rev, and out option are mandatory.
      --quiet         Only print the final json summary.
"
    exit 1
}

argi=0
argfun=""
for arg; do
    if test -z "$argfun"; then
        case $arg in
            --out) argfun=set_out;;
            --url) argfun=set_url;;
            --rev) argfun=set_rev;;
            --hash) argfun=set_hashType;;
            --branch-name) argfun=set_branchName;;
            --deepClone) deepClone=true;;
            --quiet) QUIET=true;;
            --no-deepClone) deepClone=false;;
            --leave-dotGit) leaveDotGit=true;;
            --fetch-submodules) fetchSubmodules=true;;
            --builder) builder=true;;
            -h|--help) usage; exit;;
            *)
                : $((++argi))
                case $argi in
                    1) url=$arg;;
                    2) rev=$arg;;
                    3) expHash=$arg;;
                    *) exit 1;;
                esac
                ;;
        esac
    else
        case $argfun in
            set_*)
                var=${argfun#set_}
                eval $var=$arg
                ;;
        esac
        argfun=""
    fi
done

if test -z "$url"; then
    usage
fi


init_remote(){
    local url=$1
    git init
    git remote add origin "$url"
    ( [ -n "$http_proxy" ] && git config http.proxy "$http_proxy" ) || true
}

# Return the reference of an hash if it exists on the remote repository.
ref_from_hash(){
    local hash=$1
    git ls-remote origin | sed -n "\,$hash\t, { s,\(.*\)\t\(.*\),\2,; p; q}"
}

# Return the hash of a reference if it exists on the remote repository.
hash_from_ref(){
    local ref=$1
    git ls-remote origin | sed -n "\,\t$ref, { s,\(.*\)\t\(.*\),\1,; p; q}"
}

# Returns a name based on the url and reference
#
# This function needs to be in sync with nix's fetchgit implementation
# of urlToName() to re-use the same nix store paths.
url_to_name(){
    local url=$1
    local ref=$2
    local base
    base=$(basename "$url" .git | cut -d: -f2)

    if [[ $ref =~ ^[a-z0-9]+$ ]]; then
        echo "$base-${ref:0:7}"
    else
        echo "$base"
    fi
}

# Fetch everything and checkout the right sha1
checkout_hash(){
    local hash="$1"
    local ref="$2"

    if test -z "$hash"; then
        hash=$(hash_from_ref "$ref")
    fi

    git fetch -t ${builder:+--progress} origin || return 1
    git checkout -b "$branchName" "$hash" || return 1
}

# Fetch only a branch/tag and checkout it.
checkout_ref(){
    local hash="$1"
    local ref="$2"

    if "$deepClone"; then
        # The caller explicitly asked for a deep clone.  Deep clones
        # allow "git describe" and similar tools to work.  See
        # https://marc.info/?l=nix-dev&m=139641582514772
        # for a discussion.
        return 1
    fi

    if test -z "$ref"; then
        ref=$(ref_from_hash "$hash")
    fi

    if test -n "$ref"; then
        # --depth option is ignored on http repository.
        git fetch ${builder:+--progress} --depth 1 origin +"$ref" || return 1
        git checkout -b "$branchName" FETCH_HEAD || return 1
    else
        return 1
    fi
}

# Update submodules
init_submodules(){
    # Add urls into .git/config file
    git submodule init

    # list submodule directories and their hashes
    git submodule status |
    while read -r l; do
        local hash
        local dir
        local name
        local url

        # checkout each submodule
        hash=$(echo "$l" | awk '{print $1}' | tr -d '-')
        dir=$(echo "$l" | sed -n 's/^.[0-9a-f]\+ \(.*[^)]*\)\( (.*)\)\?$/\1/p')
        name=$(
            git config -f .gitmodules --get-regexp submodule\..*\.path |
            sed -n "s,^\(.*\)\.path $dir\$,\\1,p")
        url=$(git config --get "${name}.url")

        clone "$dir" "$url" "$hash" ""
    done
}

clone(){
    local top=$PWD
    local dir="$1"
    local url="$2"
    local hash="$3"
    local ref="$4"

    cd "$dir"

    # Initialize the repository.
    init_remote "$url"

    # Download data from the repository.
    checkout_ref "$hash" "$ref" ||
    checkout_hash "$hash" "$ref" || (
        echo 1>&2 "Unable to checkout $hash$ref from $url."
        exit 1
    )

    # Checkout linked sources.
    if test -n "$fetchSubmodules"; then
        init_submodules
    fi

    if [ -z "$builder" ] && [ -f .topdeps ]; then
        if tg help &>/dev/null; then
            echo "populating TopGit branches..."
            tg remote --populate origin
        else
            echo "WARNING: would populate TopGit branches but TopGit is not available" >&2
            echo "WARNING: install TopGit to fix the problem" >&2
        fi
    fi

    cd "$top"
}

# Remove all remote branches, remove tags not reachable from HEAD, do a full
# repack and then garbage collect unreferenced objects.
make_deterministic_repo(){
    local repo="$1"

    # run in sub-shell to not touch current working directory
    (
    cd "$repo"
    # Remove files that contain timestamps or otherwise have non-deterministic
    # properties.
    rm -rf .git/logs/ .git/hooks/ .git/index .git/FETCH_HEAD .git/ORIG_HEAD \
        .git/refs/remotes/origin/HEAD .git/config

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

    # Remove tags not reachable from HEAD. If we're exactly on a tag, don't
    # delete it.
    maybe_tag=$(git tag --points-at HEAD)
    git tag --contains HEAD | while read -r tag; do
        if [ "$tag" != "$maybe_tag" ]; then
            git tag -d "$tag" >&2
        fi
    done

    # 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 .git/config

    # Garbage collect unreferenced objects.
    # Note: --keep-largest-pack prevents non-deterministic ordering of packs
    #   listed in .git/objects/info/packs by only using a single pack
    git gc --prune=all --keep-largest-pack
    )
}


clone_user_rev() {
    local dir="$1"
    local url="$2"
    local rev="${3:-HEAD}"

    # Perform the checkout.
    case "$rev" in
        HEAD|refs/*)
            clone "$dir" "$url" "" "$rev" 1>&2;;
        *)
            if test -z "$(echo "$rev" | tr -d 0123456789abcdef)"; then
                clone "$dir" "$url" "$rev" "" 1>&2
            else
                # if revision is not hexadecimal it might be a tag
                clone "$dir" "$url" "" "refs/tags/$rev" 1>&2
            fi;;
    esac

    pushd "$dir" >/dev/null
    fullRev=$( (git rev-parse "$rev" 2>/dev/null || git rev-parse "refs/heads/$branchName") | tail -n1)
    humanReadableRev=$(git describe "$fullRev" 2> /dev/null || git describe --tags "$fullRev" 2> /dev/null || echo -- none --)
    commitDate=$(git show -1 --no-patch --pretty=%ci "$fullRev")
    commitDateStrict8601=$(git show -1 --no-patch --pretty=%cI "$fullRev")
    popd >/dev/null

    # Allow doing additional processing before .git removal
    eval "$NIX_PREFETCH_GIT_CHECKOUT_HOOK"
    if test -z "$leaveDotGit"; then
        echo "removing \`.git'..." >&2
        find "$dir" -name .git -print0 | xargs -0 rm -rf
    else
        find "$dir" -name .git | while read -r gitdir; do
            make_deterministic_repo "$(readlink -f "$gitdir/..")"
        done
    fi
}

exit_handlers=()

run_exit_handlers() {
    exit_status=$?
    for handler in "${exit_handlers[@]}"; do
        eval "$handler $exit_status"
    done
}

trap run_exit_handlers EXIT

quiet_exit_handler() {
    exec 2>&3 3>&-
    if [ $1 -ne 0 ]; then
        cat "$errfile" >&2
    fi
    rm -f "$errfile"
}

quiet_mode() {
    errfile="$(mktemp "${TMPDIR:-/tmp}/git-checkout-err-XXXXXXXX")"
    exit_handlers+=(quiet_exit_handler)
    exec 3>&2 2>"$errfile"
}

json_escape() {
    local s="$1"
    s="${s//\\/\\\\}" # \
    s="${s//\"/\\\"}" # "
    s="${s//^H/\\\b}" # \b (backspace)
    s="${s//^L/\\\f}" # \f (form feed)
    s="${s//
/\\\n}" # \n (newline)
    s="${s//^M/\\\r}" # \r (carriage return)
    s="${s//   /\\t}" # \t (tab)
    echo "$s"
}

print_results() {
    hash="$1"
    if ! test -n "$QUIET"; then
        echo "" >&2
        echo "git revision is $fullRev" >&2
        if test -n "$finalPath"; then
            echo "path is $finalPath" >&2
        fi
        echo "git human-readable version is $humanReadableRev" >&2
        echo "Commit date is $commitDate" >&2
        if test -n "$hash"; then
            echo "hash is $hash" >&2
        fi
    fi
    if test -n "$hash"; then
        cat <<EOF
{
  "url": "$(json_escape "$url")",
  "rev": "$(json_escape "$fullRev")",
  "date": "$(json_escape "$commitDateStrict8601")",
  "$(json_escape "$hashType")": "$(json_escape "$hash")",
  "fetchSubmodules": $([[ -n "$fetchSubmodules" ]] && echo true || echo false)
}
EOF
    fi
}

remove_tmpPath() {
    rm -rf "$tmpPath"
}

if test -n "$QUIET"; then
    quiet_mode
fi

if test -z "$branchName"; then
    branchName=fetchgit
fi

if test -n "$builder"; then
    test -n "$out" -a -n "$url" -a -n "$rev" || usage
    mkdir -p "$out"
    clone_user_rev "$out" "$url" "$rev"
else
    if test -z "$hashType"; then
        hashType=sha256
    fi

    # If the hash was given, a file with that hash may already be in the
    # store.
    if test -n "$expHash"; then
        finalPath=$(nix-store --print-fixed-path --recursive "$hashType" "$expHash" "$(url_to_name "$url" "$rev")")
        if ! nix-store --check-validity "$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 test -z "$finalPath"; then

        tmpPath="$(mktemp -d "${TMPDIR:-/tmp}/git-checkout-tmp-XXXXXXXX")"
        exit_handlers+=(remove_tmpPath)

        tmpFile="$tmpPath/$(url_to_name "$url" "$rev")"
        mkdir -p "$tmpFile"

        # Perform the checkout.
        clone_user_rev "$tmpFile" "$url" "$rev"

        # Compute the hash.
        hash=$(nix-hash --type $hashType --base32 "$tmpFile")

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

        if test -n "$expHash" -a "$expHash" != "$hash"; then
            echo "hash mismatch for URL \`$url'. Got \`$hash'; expected \`$expHash'." >&2
            exit 1
        fi
    fi

    print_results "$hash"

    if test -n "$PRINT_PATH"; then
        echo "$finalPath"
    fi
fi