<#
.SYNOPSIS
    Bootstrap script to deploy and start the Autopilot Monitor agent.

.DESCRIPTION
    This script is designed to be deployed via Intune as a PowerShell Script during Autopilot.
    It runs VERY EARLY in the enrollment process (first Intune action) and:
    1. Creates a unique session ID for this enrollment
    2. Downloads the monitoring agent binaries
    3. Verifies integrity via SHA-256 hash from version.json
    4. Installs agent binaries (agent uses built-in backend URL or CLI override)
    5. Registers agent as Scheduled Task (runs on computer startup)
    6. Agent self-destructs when enrollment completes

    INTEGRITY VERIFICATION:
    The script downloads version.json from the same blob container as the agent ZIP.
    If version.json contains a "sha256" field, the downloaded ZIP is verified against it
    using SHA-256. This prevents tampering during download (MITM) and detects corrupted
    downloads. If the hash does not match, installation is aborted.

    For backward compatibility: if version.json does not contain a "sha256" field (older
    builds), the script falls back to the legacy Content-MD5 header check.

.PARAMETER AgentDownloadUrl
    URL to download the agent binaries from (ZIP file)

.EXAMPLE
    .\Install-AutopilotMonitor.ps1
    (Uses built-in backend URL from the agent)

.NOTES
    - Agent is temporary and auto-removes after enrollment
    - Everything in C:\ProgramData\AutopilotMonitor (easy cleanup)
    - No Registry entries (clean machine after removal)
    - Scheduled Task survives reboots during enrollment
    - SHA-256 integrity verification since v1.0.706+
    - IMPORTANT: This script MUST remain pure ASCII (no Unicode/UTF-8 special chars).
      PowerShell 5.1 (IME) reads scripts without BOM as ANSI, corrupting multi-byte chars.

.CHANGELOG
    2026-03-30  Fixed non-ASCII characters (em-dashes, Unicode symbols) that broke
                script parsing under PowerShell 5.1 / IME AgentExecutor
    2026-03-29  Hardened integrity check: SHA-256 verification via version.json
    2026-02-16  Extended OS age default threshold
    2026-02-13  Simplified bootstrapper, introduced --install parameter for agent
    2026-02-12  More robust download with integrity check (Content-MD5)
    2026-02-12  Enhanced pre-flight checks, boot time support
    2026-02-12  Added pre-flight check: skip if agent already installed
    2026-02-05  Initial version
#>

[CmdletBinding()]
param(
    [Parameter(Mandatory = $false)]
    [string]$AgentDownloadUrl = "https://autopilotmonitor.blob.core.windows.net/agent/AutopilotMonitor-Agent.zip",
    
    [Parameter(Mandatory = $false)]
    [int]$MaxOsAgeMinutes = 120
)

# Configuration - Everything in ProgramData for easy cleanup
$AgentBasePath = "$env:ProgramData\AutopilotMonitor"
$AgentBinPath = "$AgentBasePath\Agent"
$AgentLogPath = "$AgentBasePath\Logs"
$LogFile = "$AgentLogPath\bootstrap_agent.log"

# Ensure directories exist
New-Item -Path $AgentBasePath -ItemType Directory -Force -ErrorAction SilentlyContinue | Out-Null
New-Item -Path $AgentBinPath -ItemType Directory -Force -ErrorAction SilentlyContinue | Out-Null
New-Item -Path $AgentLogPath -ItemType Directory -Force -ErrorAction SilentlyContinue | Out-Null

function Write-Log {
    param([string]$Message)
    $timestamp = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
    $logMessage = "[$timestamp] $Message"
    Write-Output $logMessage
    Add-Content -Path $LogFile -Value $logMessage -ErrorAction SilentlyContinue
}

function Get-FileMd5Base64 {
    param(
        [Parameter(Mandatory = $true)]
        [string]$Path
    )

    $md5 = [System.Security.Cryptography.MD5]::Create()
    try {
        $stream = [System.IO.File]::OpenRead($Path)
        try {
            $hashBytes = $md5.ComputeHash($stream)
        }
        finally {
            $stream.Dispose()
        }

        return [Convert]::ToBase64String($hashBytes)
    }
    finally {
        $md5.Dispose()
    }
}

try {
    Write-Log "===== Autopilot Monitor Bootstrap Started ====="

    # -- Pre-flight: Skip installation on already-enrolled devices --

    # Check 1: OS install date must be within threshold (fresh device)
    # TODO: issue is the OS might got installed a long time ago but the OOBE just started now (e.g. old image, or re-flash).
    # Ideally we want to detect the OOBE start time... need to investigate if there's a reliable way to get that (event log? registry? WMI?). 
    # For now we just check OS install date as a proxy, which should work in most cases except for old images or re-flashed devices.
    $osInstallDate = (Get-CimInstance Win32_OperatingSystem).InstallDate
    $osAge = (Get-Date) - $osInstallDate
    $osAgeMinutesRounded = [int][Math]::Round($osAge.TotalMinutes)
    Write-Log "OS install date: $osInstallDate (age: ${osAgeMinutesRounded}m)"

    if ($osAge.TotalMinutes -gt $MaxOsAgeMinutes) {
        Write-Log "SKIP: OS was installed ${osAgeMinutesRounded}m ago (threshold: ${MaxOsAgeMinutes}m). Device is not freshly provisioned."
        exit 0
    }

    # Check 2: MDM enrollment must not be completed yet
    $enrollmentPath = "HKLM:\SOFTWARE\Microsoft\Enrollments"
    $mdmEnrolled = $false

    if (Test-Path $enrollmentPath) {
        $enrollmentEntries = Get-ChildItem -Path $enrollmentPath -ErrorAction SilentlyContinue |
            Where-Object { $_.PSChildName -match '^[0-9A-Fa-f\-]{36}$' }

        foreach ($entry in $enrollmentEntries) {
            $providerID = (Get-ItemProperty -Path $entry.PSPath -Name "ProviderID" -ErrorAction SilentlyContinue).ProviderID
            if ($providerID) {
                $mdmEnrolled = $true
                Write-Log "Found MDM enrollment: ProviderID=$providerID (EnrollmentID=$($entry.PSChildName))"
                break
            }
        }
    }

    if ($mdmEnrolled) {
        # Double-check: Is enrollment status tracking showing completed?
        $espPath = "HKLM:\SOFTWARE\Microsoft\Windows\Autopilot\EnrollmentStatusTracking\Device\Setup"
        $hasCompleted = (Get-ItemProperty -Path $espPath -Name "HasProvisioningCompleted" -ErrorAction SilentlyContinue).HasProvisioningCompleted

        if ($hasCompleted -eq 1) {
            Write-Log "SKIP: Autopilot enrollment already completed (HasProvisioningCompleted=1). Device is already enrolled."
            exit 0
        }
    }

    # Check 3: Is the agent already installed? (leftover from previous run)
    if (Test-Path $AgentBinPath) {
        $existingAgent = Get-ChildItem -Path $AgentBinPath -Filter "AutopilotMonitor.Agent.exe" -ErrorAction SilentlyContinue
        if ($existingAgent) {
            Write-Log "SKIP: Agent already installed at $($existingAgent.FullName). Previous enrollment may have been in progress. Please check if enrollment completed or clean up C:\ProgramData\AutopilotMonitor before re-running."
            exit 0
        }
    }

    Write-Log "Pre-flight checks passed - device is freshly provisioned and enrollment in progress"

    # Download and extract agent binaries
    $agentExePath = Join-Path $AgentBinPath "AutopilotMonitor.Agent.exe"

    if (Test-Path $agentExePath) {
        Write-Log "Agent already installed at $agentExePath"
    }
    else {
        Write-Log "Downloading agent from $AgentDownloadUrl..."

        try {
            # Derive version.json URL from the agent download URL (same blob container)
            $versionJsonUrl = $AgentDownloadUrl -replace '[^/]+$', 'version.json'
            $expectedSha256 = $null

            # Download version.json for SHA-256 integrity verification
            try {
                Write-Log "Fetching version.json from $versionJsonUrl for integrity verification..."
                $versionJsonResponse = Invoke-RestMethod -Uri $versionJsonUrl -UseBasicParsing -TimeoutSec 5 -ErrorAction Stop
                if ($versionJsonResponse.sha256) {
                    $expectedSha256 = $versionJsonResponse.sha256.ToLowerInvariant()
                    Write-Log "SHA-256 hash from version.json: $expectedSha256 (version: $($versionJsonResponse.version))"
                } else {
                    Write-Log "version.json has no sha256 field - falling back to legacy MD5 check (older build)"
                }
            }
            catch {
                Write-Log "WARNING: Could not fetch version.json - falling back to legacy MD5 check: $($_.Exception.Message)"
            }

            # Download agent ZIP
            $zipPath = Join-Path $env:TEMP "AutopilotMonitor-Agent.zip"
            $maxDownloadAttempts = 3
            $downloadAttempt = 0
            $downloadResponse = $null

            do {
                $downloadAttempt++
                try {
                    Write-Log "Download attempt ${downloadAttempt}/${maxDownloadAttempts}"
                    $downloadResponse = Invoke-WebRequest `
                        -Uri $AgentDownloadUrl `
                        -OutFile $zipPath `
                        -UseBasicParsing `
                        -TimeoutSec 30 `
                        -ErrorAction Stop `
                        -PassThru
                    Write-Log "Downloaded agent to $zipPath"
                    break
                }
                catch {
                    if ($downloadAttempt -ge $maxDownloadAttempts) {
                        throw
                    }

                    $retryDelaysInSeconds = @(2, 4, 8)
                    $retryDelaySeconds = $retryDelaysInSeconds[$downloadAttempt - 1]
                    Write-Log "Download failed (attempt $downloadAttempt): $($_.Exception.Message). Retrying in ${retryDelaySeconds}s..."
                    Start-Sleep -Seconds $retryDelaySeconds
                }
            } while ($downloadAttempt -lt $maxDownloadAttempts)

            # Integrity check: SHA-256 (preferred) or legacy Content-MD5 (fallback)
            if ($expectedSha256) {
                $actualSha256 = (Get-FileHash $zipPath -Algorithm SHA256).Hash.ToLowerInvariant()
                Write-Log "Validating SHA-256 hash against version.json"
                if ($actualSha256 -ne $expectedSha256) {
                    throw "SHA-256 integrity check FAILED. Expected='$expectedSha256', Actual='$actualSha256'. Download may be tampered or corrupted."
                }
                Write-Log "SHA-256 integrity check passed"
            }
            else {
                # Legacy fallback: Content-MD5 header check
                $expectedMd5Header = $downloadResponse.Headers["Content-MD5"]
                $expectedMd5 = if ($expectedMd5Header -is [System.Array]) { "$($expectedMd5Header[0])".Trim() } else { "$expectedMd5Header".Trim() }
                if ($expectedMd5 -notmatch '\S') {
                    Write-Log "WARNING: No SHA-256 and no Content-MD5 header - skipping integrity validation"
                }
                else {
                    $actualMd5 = Get-FileMd5Base64 -Path $zipPath
                    Write-Log "Validating Content-MD5 header against downloaded ZIP"
                    if ($actualMd5 -ne $expectedMd5) {
                        throw "MD5 integrity check failed. Expected (Content-MD5)='$expectedMd5', Actual='$actualMd5'"
                    }
                    Write-Log "MD5 integrity check passed"
                }
            }

            # Extract to agent bin path
            Expand-Archive -Path $zipPath -DestinationPath $AgentBinPath -Force
            Write-Log "Extracted agent to $AgentBinPath"

            # Cleanup
            Remove-Item $zipPath -Force -ErrorAction SilentlyContinue
            Write-Log "Cleaned up temporary files"

            # Verify extraction
            if (-not (Test-Path $agentExePath)) {
                throw "Agent executable not found after extraction at $agentExePath"
            }

            Write-Log "Agent installation completed successfully"
        }
        catch {
            Write-Log "ERROR downloading/extracting agent: $($_.Exception.Message)"
            throw
        }
    }

    # Let the agent install/deploy itself and manage its own Scheduled Task
    Write-Log "Calling agent install mode (--install)..."
    & $agentExePath --install
    $installExitCode = $LASTEXITCODE
    if ($installExitCode -ne 0) {
        throw "Agent install failed with exit code $installExitCode"
    }
    Write-Log "Agent install mode completed successfully"

    Write-Log "===== Bootstrap Completed Successfully ====="
    Write-Log "Agent Path: $AgentBasePath"
    Write-Log "Scheduled Task: managed by agent (--install)"
    Write-Log "Agent will monitor enrollment and auto-remove when complete"
    Write-Log "Bootstrap log: $LogFile"
    Write-Log ""
    Write-Log "IMPORTANT: Agent runs as Scheduled Task and will:"
    Write-Log "  - Generate unique session ID on startup"
    Write-Log "  - Survive reboots during enrollment"
    Write-Log "  - Monitor enrollment phases in real-time"
    Write-Log "  - Upload events to built-in backend URL"
    Write-Log "  - Self-destruct when enrollment completes"

    exit 0
}
catch {
    Write-Log "===== Bootstrap FAILED ====="
    Write-Log "ERROR: $($_.Exception.Message)"
    Write-Log "Stack trace: $($_.ScriptStackTrace)"
    Write-Log "Please check log file: $LogFile"
    exit 1
}