From 4f762c2e55ea55dc67406b54809b2fa62ef6c961 Mon Sep 17 00:00:00 2001
From: Kristóf Marussy <kristof@marussy.com>
Date: Thu, 28 Jan 2021 17:27:40 +0100
Subject: Initial commit

---
 gitmirror.sh | 148 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100755 gitmirror.sh

diff --git a/gitmirror.sh b/gitmirror.sh
new file mode 100755
index 0000000..29503d9
--- /dev/null
+++ b/gitmirror.sh
@@ -0,0 +1,148 @@
+#!/usr/bin/env bash
+set -Eeuo pipefail
+
+msg() {
+    echo "==> $1"
+}
+
+read_branches() {
+    local prefix="refs/$1/"
+    local -n read_branches_target="$2"
+    local refname
+    local objname
+    local -i name_length
+    local -i max_length=0
+    while IFS=$'\t' read -r refname objname; do
+        local branch_name="${refname#"${prefix}"}"
+        read_branches_target["${branch_name}"]="${objname}"
+        name_length=${#branch_name}
+        if (( name_length > max_length )); then
+            max_length=$name_length
+        fi
+    done < <(git for-each-ref "${prefix}**" \
+        --format=$'%(refname)\t%(objectname)' \
+        --color=never)
+    for branch_name in "${!read_branches_target[@]}"; do
+        printf "    %*s = %s\n" \
+            $((-max_length)) \
+            "${branch_name}" \
+            "${read_branches_target["${branch_name}"]}"
+    done
+}
+
+get_or_empty() {
+    local -n get_or_empty_array="$1"
+    local key="$2"
+    local -n get_or_empty_target="$3"
+    if [[ -v get_or_empty_array["${key}"] ]]; then
+        get_or_empty_target="${get_or_empty_array["${key}"]}"
+    else
+        # shellcheck disable=SC2034
+        get_or_empty_target=''
+    fi
+}
+
+archive_if_needed() {
+    local archive_prefix="$1"
+    local branch_name="$2"
+    local old_tip="$3"
+    local new_tip="$4"
+    if ! git merge-base --is-ancestor "${old_tip}" "${new_tip}"; then
+        local archive_name="${archive_prefix}${branch_name}"
+        msg "Refusing to clobber ${branch_name}, archiving as ${archive_name}"
+        git tag -a -m "Archive before synchronization" "${archive_name}" "${old_tip}"
+    fi
+}
+
+sync_mirror() {
+    if (( $# == 0 || $# > 2 )); then
+        echo "Usage: $0 REPOSITORY [REMOTE]" >&2
+        exit 1
+    fi
+
+    local repository="$1"
+    local remote
+    if (( $# == 1 )); then
+        remote="origin"
+    else
+        remote="$2"
+    fi
+    local archive_prefix
+    archive_prefix="$(TZ='UTC' printf 'archives/%(%Y%m%dT%H%M%S)TZ/')"
+
+    msg "Synchronizing ${repository} with ${remote}"
+    pushd "${repository}" > /dev/null
+
+    msg "Remote tracking branches before fetch"
+    # shellcheck disable=SC2034
+    local -A old_tracking
+    read_branches "remotes/${remote}" old_tracking
+
+    msg "Local branches"
+    # shellcheck disable=SC2034
+    local -A local_branches
+    read_branches "heads" local_branches
+
+    msg "Fetch from ${remote}"
+    git fetch --tags "${remote}"
+
+    msg "Remote tracking branches after fetch"
+    local -A new_tracking
+    read_branches "remotes/${remote}" new_tracking
+
+    local -a to_patch=()
+
+    local branch_name
+
+    for branch_name in "${!new_tracking[@]}"; do
+        local new_tip="${new_tracking["${branch_name}"]}"
+        local old_tip
+        get_or_empty old_tracking "${branch_name}" old_tip
+        local local_tip
+        get_or_empty local_branches "${branch_name}" local_tip
+        local patch_tip
+        get_or_empty local_branches "patch-for/${branch_name}" patch_tip
+
+        if [[ -n "${old_tip}" ]]; then
+            archive_if_needed "${archive_prefix}" "${remote}/${branch_name}" \
+                "${old_tip}" "${new_tip}"
+        fi
+
+        if [[ -z "${local_tip}" ]]; then
+            msg "Create local branch ${branch_name} at ${new_tip}"
+            git branch --no-track "${branch_name}" "${patch_tip:-"${new_tip}"}"
+            git branch --set-upstream-to="${remote}/${branch_name}" "${branch_name}"
+            if [[ -n "${patch_tip}" ]]; then
+                msg "Will patch newly created local branch ${branch_name}"
+                to_patch+=("${branch_name}")
+            fi
+        else
+            if [[ -z "${patch_tip}" ]]; then
+                if [[ "${local_tip}" != "${new_tip}" ]]; then
+                    archive_if_needed "${archive_prefix}" "${branch_name}" \
+                        "${local_tip}" "${old_tip:-"${new_tip}"}"
+                    msg "Update local branch ${branch_name} to ${new_tip}"
+                    git update-ref "refs/heads/${branch_name}" "${new_tip}" "${local_tip}"
+                fi
+            else
+                if ! git merge-base --is-ancestor "${new_tip}" "${local_tip}"; then
+                    msg "Will update local branch ${branch_name} to ${new_tip} by patching"
+                    to_patch+=("${branch_name}")
+                fi
+            fi
+        fi
+    done
+
+    local job_name="${repository}-apply-patch"
+
+    for branch_name in "${to_patch[@]}"; do
+        msg "Triggering Jenkings job ${job_name} for branch ${branch_name}"
+        # TODO
+    done
+
+    popd > /dev/null
+}
+
+if [[ "$0" == "${BASH_SOURCE[0]}" ]]; then
+    sync_mirror "$@"
+fi
-- 
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