param(
    [string]$ManifestPath = '',
    [string]$AiDirectory = ''
)
$ErrorActionPreference = 'Stop'
$root = [IO.Path]::GetFullPath((Join-Path $PSScriptRoot '../..'))
if (!$ManifestPath) { $ManifestPath = Join-Path $root 'ai/model.json' }
if (!$AiDirectory) { $AiDirectory = Join-Path $root 'ai' }
$lock = $null

function Test-Model([string]$Path, $Manifest) {
    if (!(Test-Path -LiteralPath $Path -PathType Leaf)) { return $false }
    if ((Get-Item -LiteralPath $Path).Length -ne [long]$Manifest.bytes) { return $false }
    return (Get-FileHash -LiteralPath $Path -Algorithm SHA256).Hash -eq $Manifest.sha256
}

try {
    $manifest = Get-Content -LiteralPath $ManifestPath -Raw -Encoding UTF8 | ConvertFrom-Json
    if ([long]$manifest.bytes -le 0 -or $manifest.sha256 -notmatch '^[a-fA-F0-9]{64}$') {
        throw 'Invalid model size or SHA-256 in manifest'
    }
    $ai = [IO.Path]::GetFullPath($AiDirectory).TrimEnd('\', '/') + [IO.Path]::DirectorySeparatorChar
    $model = [IO.Path]::GetFullPath((Join-Path $ai $manifest.file))
    if (!$model.StartsWith($ai, [StringComparison]::OrdinalIgnoreCase)) {
        throw 'Model destination must be inside the ai directory'
    }
    if (Test-Model $model $manifest) {
        Write-Host 'SUCCESS: model already present; size and SHA-256 verified. Nothing to download.'
        exit 0
    }
    $curl = (Get-Command curl.exe -ErrorAction Stop).Source
    New-Item -ItemType Directory -Force -Path ([IO.Path]::GetDirectoryName($model)) | Out-Null
    $lock = [IO.File]::Open("$model.download.lock", [IO.FileMode]::OpenOrCreate,
        [IO.FileAccess]::ReadWrite, [IO.FileShare]::None)
    $part = "$model.part"
    $urls = @($manifest.download_urls)
    if (!$urls.Count -or !$urls[0]) { throw 'No download URLs in model manifest' }
    Write-Host ('Download size: {0:N2} GB. Keep at least 3 GB free.' -f ([long]$manifest.bytes / 1e9))
    Write-Host "Destination: $model"
    foreach ($url in $urls) {
        $uri = [Uri]$url
        if ($uri.Scheme -ne 'https' -and !($uri.Scheme -eq 'http' -and $uri.IsLoopback)) {
            throw 'Model downloads require HTTPS'
        }
        Write-Host "Source: $($uri.Host)"
        if (Test-Path -LiteralPath $part) {
            $length = (Get-Item -LiteralPath $part).Length
            if ($length -eq [long]$manifest.bytes -and (Test-Model $part $manifest)) {
                Move-Item -LiteralPath $part -Destination $model -Force
                Write-Host 'SUCCESS: completed partial file verified and installed.'
                exit 0
            }
            if ($length -ge [long]$manifest.bytes) { Remove-Item -LiteralPath $part }
        }
        # curl validates range responses before appending. Keep partial data on outages.
        $arguments = @('--fail', '--location', '--proto', '=http,https', '--proto-redir', '=http,https',
            '--retry', '2', '--retry-delay', '1', '--connect-timeout', '30',
            '--speed-limit', '1024', '--speed-time', '60', '--continue-at', '-', '--output', $part, $url)
        & $curl @arguments
        $result = $LASTEXITCODE
        if ($result -eq 33 -or $result -eq 36) {
            # Some mirrors ignore Range; retry this source once from the beginning.
            if (Test-Path -LiteralPath $part) { Remove-Item -LiteralPath $part }
            & $curl @arguments
            $result = $LASTEXITCODE
        }
        if ($result -ne 0) {
            Write-Warning "Download interrupted (curl $result). Trying next source; partial data retained."
            continue
        }
        Write-Host 'Verifying downloaded size and SHA-256...'
        if (!(Test-Model $part $manifest)) {
            Write-Warning 'Downloaded file failed integrity verification. Trying next source.'
            if (Test-Path -LiteralPath $part) { Remove-Item -LiteralPath $part }
            continue
        }
        # Never replace an existing destination with unverified data.
        Move-Item -LiteralPath $part -Destination $model -Force
        Write-Host 'SUCCESS: offline model downloaded, verified and installed.'
        exit 0
    }
    throw 'All model sources failed. Run download_fortune_model.bat again to retry/resume.'
} catch {
    Write-Host "ERROR: $($_.Exception.Message)" -ForegroundColor Red
    exit 1
} finally {
    if ($lock) { $lock.Dispose() }
}