<#
.SYNOPSIS
    Interactive mailbox message counter for Microsoft 365 (Graph).

.DESCRIPTION
    Prompts the user to choose "my mailbox" or "another/shared mailbox", gathers the target mailbox,
    start date, and end date, then connects to Microsoft Graph with the appropriate delegated scope
    and returns a count of RECEIVED messages (excluding drafts and self-sent) within the specified
    local time window. It searches ALL folders (Inbox, subfolders, Junk, Deleted Items, etc.) so
    post-delivery moves don't matter.

    Time boundaries are created using the specified Windows time zone (default: "Eastern Standard Time"
    for Toronto). The script computes the correct UTC offset for the provided dates (including DST)
    and generates ISO 8601 timestamps with offsets (e.g., 2025-01-01T00:00:00-05:00).

.REQUIREMENTS
    - PowerShell 5.1+ (Windows) or PowerShell 7+
    - Microsoft.Graph PowerShell SDK (will auto-install for CurrentUser if missing)
    - For "another/shared mailbox":
        * Your signed-in account must have Full Access to that mailbox in Exchange Online.

.PARAMETERS (prompted)
    - Scope mode: "1 = My mailbox" or "2 = Another/shared mailbox"
    - Mailbox SMTP address (e.g., user@domain.com)
    - Start date (YYYY-MM-DD), inclusive
    - End date   (YYYY-MM-DD), exclusive

.OUTPUTS
    Prints a single integer count and a short summary of inputs.

.NOTES
    Example month window:
      Start: 2025-01-01
      End:   2025-02-01
    These will be interpreted at 00:00 local time of the configured time zone.

    (c) 2025 Robbie Ferguson. All rights reserved.
#>

# --------------------------- User-editable settings ---------------------------
# Windows Time Zone ID (use `tzutil /l` to list). "Eastern Standard Time" covers Toronto with DST.
$TimeZoneId = 'Eastern Standard Time'
# -----------------------------------------------------------------------------

# Helper: ensure Microsoft Graph SDK is available
function Ensure-GraphModule {
    $moduleName = 'Microsoft.Graph'
    if (-not (Get-Module -ListAvailable -Name $moduleName)) {
        Write-Host "Microsoft.Graph module not found. Installing for CurrentUser..."
        try {
            Set-PSRepository PSGallery -InstallationPolicy Trusted -ErrorAction SilentlyContinue
            Install-Module $moduleName -Scope CurrentUser -Force -ErrorAction Stop
        } catch {
            Write-Error "Failed to install Microsoft.Graph: $($_.Exception.Message)"
            Read-Host "Press Enter to exit"
            exit 1
        }
    }
    Import-Module $moduleName -ErrorAction Stop
}

# Helper: get TimeZoneInfo safely
function Get-TimeZoneInfoSafe {
    param([string]$Id)
    try {
        return [System.TimeZoneInfo]::FindSystemTimeZoneById($Id)
    } catch {
        Write-Error "Time zone '$Id' not found. Edit `$TimeZoneId at the top (Windows TZ IDs, e.g., 'Eastern Standard Time')."
        Read-Host "Press Enter to exit"
        exit 1
    }
}

# Helper: build ISO timestamp with correct offset for a date at 00:00 local time
function Get-ISOStartOfDayWithOffset {
    param(
        [datetime]$DateOnly,
        [System.TimeZoneInfo]$Tz
    )
    # Local 00:00 in the TZ
    $local = Get-Date -Date "$($DateOnly.ToString('yyyy-MM-dd')) 00:00:00"
    $offset = $Tz.GetUtcOffset($local)
    $sign = if ($offset -lt [TimeSpan]::Zero) { '-' } else { '+' }
    $hh = [math]::Abs($offset.Hours).ToString('00')
    $mm = [math]::Abs($offset.Minutes).ToString('00')
    $offStr = "$sign$hh`:$mm"
    return "{0}T00:00:00{1}" -f $local.ToString('yyyy-MM-dd'), $offStr
}

# Helper: connect to Graph with appropriate scope
function Connect-GraphWithScope {
    param([string]$Scope)
    try {
        Disconnect-MgGraph -ErrorAction SilentlyContinue | Out-Null
    } catch {}
    try {
        Connect-MgGraph -Scopes $Scope -ErrorAction Stop | Out-Null
    } catch {
        Write-Error "Failed to connect to Microsoft Graph with scope '$Scope': $($_.Exception.Message)"
        Read-Host "Press Enter to exit"
        exit 1
    }
}

# Helper: validate date input (YYYY-MM-DD)
function Read-DateStrict {
    param([string]$Prompt,[datetime]$Default)
    while ($true) {
        $in = Read-Host "$Prompt (YYYY-MM-DD) [Enter for $($Default.ToString('yyyy-MM-dd'))]"
        if ([string]::IsNullOrWhiteSpace($in)) { return $Default.Date }
        if ([datetime]::TryParseExact($in, 'yyyy-MM-dd', $null, 'None', [ref]([datetime]$out))) {
            return $out.Date
        }
        Write-Host "Invalid date. Please use YYYY-MM-DD." -ForegroundColor Yellow
    }
}

# Start
Write-Host "=== M365 Mailbox Message Counter ===" -ForegroundColor Cyan
Ensure-GraphModule

# 1) Which mailbox type?
Write-Host "Select mailbox type:" -ForegroundColor Cyan
Write-Host "  1) My mailbox" 
Write-Host "  2) Another/shared mailbox (requires delegation with Full Access)"
$mode = Read-Host "Enter 1 or 2"
if ($mode -notin @('1','2')) {
    Write-Error "Invalid selection."
    Read-Host "Press Enter to exit"
    exit 1
}

# 2) Target mailbox SMTP
$Mailbox = Read-Host "Enter the mailbox SMTP address to check (e.g., user@domain.com)"
if ([string]::IsNullOrWhiteSpace($Mailbox) -or ($Mailbox -notmatch '^[^@\s]+@[^@\s]+\.[^@\s]+$')) {
    Write-Error "Invalid email address."
    Read-Host "Press Enter to exit"
    exit 1
}

# 3) Date range (inclusive start, exclusive end)
# Defaults to January 2025 for convenience; change as needed
$defaultStart = Get-Date '2025-01-01'
$defaultEnd   = Get-Date '2025-02-01'
$StartDate = Read-DateStrict -Prompt "Start date (inclusive)" -Default $defaultStart
$EndDate   = Read-DateStrict -Prompt "End date (exclusive)"  -Default $defaultEnd
if ($EndDate -le $StartDate) {
    Write-Error "End date must be AFTER start date."
    Read-Host "Press Enter to exit"
    exit 1
}

# Prepare TZ and ISO strings with correct offsets for each boundary date
$tz = Get-TimeZoneInfoSafe -Id $TimeZoneId
$startISO = Get-ISOStartOfDayWithOffset -DateOnly $StartDate -Tz $tz
$endISO   = Get-ISOStartOfDayWithOffset -DateOnly $EndDate   -Tz $tz

# 4) Connect with proper scope
$scope = if ($mode -eq '1') { 'Mail.Read' } else { 'Mail.Read.Shared' }
Connect-GraphWithScope -Scope $scope

# Show who is signed in (helpful for multi-tenant admins)
try {
    $ctx = Get-MgContext
    if ($ctx) { Write-Host "Connected as: $($ctx.Account)  |  Tenant: $($ctx.TenantId)  |  Scope(s): $($ctx.Scopes -join ', ')" -ForegroundColor DarkGray }
} catch {}

# 5) Perform count
try {
    $count = 0
    # Exclude drafts and self-sent (from == mailbox) to count RECEIVED mail
    $filter = "receivedDateTime ge $startISO and receivedDateTime lt $endISO and isDraft eq false and (from/emailAddress/address ne '$Mailbox')"
    # Ask Graph for a count; we don't need to page through items (PageSize 1 trick)
    Get-MgUserMessage -UserId $Mailbox -Filter $filter -CountVariable count -PageSize 1 | Out-Null

    Write-Host ""
    Write-Host "Mailbox: $Mailbox" -ForegroundColor Green
    Write-Host "Window:  $($StartDate.ToString('yyyy-MM-dd'))  to  $($EndDate.ToString('yyyy-MM-dd'))  ($TimeZoneId)" -ForegroundColor Green
    Write-Host "Count of RECEIVED messages (all folders, excluding drafts & self-sent):" -ForegroundColor Green
    Write-Host $count -ForegroundColor Cyan
} catch {
    Write-Host ""
    Write-Error "Query failed: $($_.Exception.Message)"

    # Common guidance
    if ($mode -eq '2') {
        Write-Host "If this is another/shared mailbox, ensure:" -ForegroundColor Yellow
        Write-Host "  - Your account has Full Access to $Mailbox in Exchange Online (Mailbox Delegation)." -ForegroundColor Yellow
    } else {
        Write-Host "If this is your own mailbox and it still fails, try reconnecting and consenting the scope." -ForegroundColor Yellow
    }
}

Write-Host ""
Read-Host "Press Enter to exit"