param(
    [string]$Remote = "gitea",
    [string]$MainBranch = "main"
)

$ErrorActionPreference = "Stop"

# Verify remote exists.
$remotes = git remote
if ($remotes -notcontains $Remote) {
    throw "Git remote '$Remote' does not exist. Available remotes: $($remotes -join ', ')"
}

Write-Host "Using remote: $Remote"
Write-Host "Canonical branch: $MainBranch"

# Update remote references.
git fetch $Remote --prune

# Update local main from the selected remote.
git switch $MainBranch
git pull --ff-only $Remote $MainBranch

# Get all branches on this specific remote.
$remotePrefix = "$Remote/"

$branches = git for-each-ref `
    --format="%(refname:short)" `
    "refs/remotes/$Remote" |
    Where-Object {
        $_ -ne "$Remote/$MainBranch" -and
        $_ -ne "$Remote/HEAD"
    }

foreach ($remoteBranch in $branches) {
    # Remove "<remote>/" prefix while preserving branch names such as
    # agent/foo/bar.
    $branch = $remoteBranch.Substring($remotePrefix.Length)

    Write-Host ""
    Write-Host "Updating $branch..."

    # Check whether the local branch already exists.
    git show-ref --verify --quiet "refs/heads/$branch"

    if ($LASTEXITCODE -eq 0) {
        git switch $branch

        # Make sure the local branch reflects the latest remote branch
        # before modifying the instruction files.
        git pull --ff-only $Remote $branch
    }
    else {
        git switch --track -c $branch "$Remote/$branch"
    }

    # Force these files to exactly match canonical main.
    git restore `
        --source "$MainBranch" `
        -- AGENTS.md PROJECT_GOAL.md

    git add AGENTS.md PROJECT_GOAL.md

    # Commit only when one of the files actually changed.
    git diff --cached --quiet

    if ($LASTEXITCODE -ne 0) {
        git commit -m "Sync agent instructions from $MainBranch"
        git push $Remote $branch
    }
    else {
        Write-Host "Already up to date."
    }
}

git switch $MainBranch

Write-Host ""
Write-Host "Finished synchronizing AGENTS.md and PROJECT_GOAL.md."