git_checkout_latest.zsh

#!/bin/zsh 
# Checks out latest tag into a branch

# Copyright (c) 2025 Maulik Mistry mistry01@gmail.com
# Please share support: https://www.paypal.com/paypalme/m1st0

# 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 included at LICENSE.TXT or
#  
#    http://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.

# Fetch all tags and branches from all remotes
printf "Fetching all tags and branches from all remotes...\n"
git fetch --tags --prune
git fetch --all

# Set the remote to check for updates.
# Tries to guess the user's remote name from the Git config.
# Defaults to 'origin' or 'upstream' if a custom name isn't found.
GIT_USER=$(git config --global user.name 2>/dev/null | tr -d '[:space:]')
if [[ -n "${GIT_USER}" ]] && git remote | grep -q "^${GIT_USER}$"; then
    UPDATE_REMOTE="${GIT_USER}"
elif git remote | grep -q "^upstream$"; then
    UPDATE_REMOTE="upstream"
else
    UPDATE_REMOTE="origin"
fi
printf "Using remote: %s\n" "${UPDATE_REMOTE}"

# Function to safely check out or create a branch
safe_checkout() {
    local branch_name=$1
    local remote_branch=$2
    
    # Check if local branch exists
    if git show-ref --verify --quiet "refs/heads/${branch_name}"; then
        printf "Local branch '${branch_name}' exists. Checking if update needed...\n"
        
        # Switch to the branch first
        git checkout "${branch_name}"
        
        # Check if the local branch is up to date with remote
        local local_commit=$(git rev-parse "${branch_name}")
        local remote_commit=$(git rev-parse "${remote_branch}" 2>/dev/null)
        
        if [[ "${local_commit}" == "${remote_commit}" ]]; then
            printf "Branch '${branch_name}' is already up to date. No changes needed.\n"
            return 0
        else
            printf "Branch '${branch_name}' needs updating...\n"
            # Check for uncommitted changes
            if ! git diff --quiet || ! git diff --cached --quiet; then
                printf "WARNING: You have uncommitted changes. Please commit or stash them first.\n"
                git status --short
                return 1
            fi
            # Safe to update
            git reset --hard "${remote_branch}"
        fi
    else
        printf "Creating new branch '${branch_name}'...\n"
        git checkout -b "${branch_name}" "${remote_branch}"
    fi
}

# Check if user provided a specific tag as argument
if [[ $# -eq 1 ]]; then
    provided_tag="$1"
    # Verify the tag exists
    if git tag | grep -q "^${provided_tag}$"; then
        printf "Found specified tag: ${provided_tag}. Checking it out...\n"
        safe_checkout "${provided_tag}" "tags/${provided_tag}"
        exit 0
    fi
# Otherwise check for a 'release/' branch on the specified remote
elif git branch -r | grep -q "${UPDATE_REMOTE}/release/"; then
    release_branch=$(git branch -r | grep "${UPDATE_REMOTE}/release/" | sort -V | tail -n 1 | xargs)
    release_branch_name=${release_branch#${UPDATE_REMOTE}/}
    printf "Found a release branch on '${UPDATE_REMOTE}': ${release_branch_name}.\n"
    safe_checkout "${release_branch_name}" "${release_branch}"
    
# Otherwise check for the absolute latest tag
elif latest_tag=$(git tag --sort=-v:refname | head -n 1 2>/dev/null); then
    printf "No release branch found. Checking out the latest tag: ${latest_tag}.\n"
    safe_checkout "${latest_tag}" "tags/${latest_tag}"
# Otherwise fall back to the default branch on the specified remote
else
    default_branch=$(git remote show "${UPDATE_REMOTE}" | grep 'HEAD branch' | awk '{print $NF}' | xargs)
    if [[ -n "${default_branch}" ]]; then
        printf "No release branch or tags found. Checking out the default branch from '${UPDATE_REMOTE}': '${default_branch}'.\n"
        safe_checkout "${default_branch}" "${UPDATE_REMOTE}/${default_branch}"
    else
        printf "Could not find a default branch on '${UPDATE_REMOTE}'. Please check the repository manually.\n"
        exit 1
    fi
fi