git-pullff-main.ps1

# * カレントブランチのままで (= ローカル main ブランチを checkout せずに)
#   fast forward 可能な場合のみ ローカル main ブランチを origin/main ブランチに更新
#   - `git fetch origin main:main` だと fast forward 不可能な場合も上書き更新されるため
# * カレントブランチがローカル main ブランチの場合は何もせず終了 (detached HEAD を避けるため)

$localMain = "main"
$remote = "origin"
$remoteMain = "main"



#-----------------------------------------------------------------------------------------
# カレントブランチが $localMain の場合は処理を中止 ($localMain が進むと detatched HEAD になるため)
$currentBranch = (git branch --show-current).Trim()
if ($LASTEXITCODE -ne 0) {
    Write-Error "Failed to get current branch"
    exit 1
}

if ($currentBranch -eq $localMain) {
    Write-Host "Current branch is already '$localMain'. Skipping update to avoid detached HEAD state."
    exit 0
}

# リモートから fetch
git fetch $remote
if ($LASTEXITCODE -ne 0) {
    Write-Error "Failed to fetch from $remote"
    exit 1
}

# $localMain が $remote/$remoteMain と等しければ処理を終了
$localMainCommit = git rev-parse "$localMain"
if ($LASTEXITCODE -ne 0) {
    Write-Error "Failed to get commit hash of $localMain"
    exit 1
}
$remoteMainCommit = git rev-parse "$remote/$remoteMain"
if ($LASTEXITCODE -ne 0) {
    Write-Error "Failed to get commit hash of $remote/$remoteMain"
    exit 1
}
if ($localMainCommit -eq $remoteMainCommit) {
    Write-Host "$localMain is already up to date with $remote/$remoteMain"
    exit 0
}


# fast forward 可能か確認
git merge-base --is-ancestor "$localMain" "$remote/$remoteMain"
$isMainConflict = $LASTEXITCODE # 0: fast forward 可能, 1: conflict, それ以外: エラー
if ($isMainConflict -ne 0 -and $isMainConflict -ne 1) {
    Write-Error "Failed to check merge-base"
    exit 1
}

if ($isMainConflict -eq 0) {
    # fast forward 可能な場合進める
    git update-ref "refs/heads/$localMain" "refs/remotes/$remote/$remoteMain"
    if ($LASTEXITCODE -eq 0) {
        Write-Host "$localMain branch updated to $remote/$remoteMain"
    } else {
        Write-Error "Failed to update $localMain branch"
        exit 1
    }
} else {
    # fast forward 不可能な場合、警告を表示して終了
    Write-Host "Warning: $localMain has unpushed commits. Check with 'git log $localMain..$remote/$remoteMain'"
    exit 1
}