<#
.SYNOPSIS
    Retrieves GitHub Copilot usage metrics per user for an organization.

.DESCRIPTION
    This script calls the GitHub REST API to get Copilot metrics for an organization,
    showing usage per user to help identify who is actively using their premium seats.

.PARAMETER Organization
    The GitHub organization name.

.PARAMETER Token
    GitHub Personal Access Token with 'copilot', 'manage_billing:copilot', or 'read:org' scope.
    If not provided, will attempt to use GITHUB_TOKEN environment variable.

.PARAMETER Days
    Number of days to look back (default: 28, max: 28).

.PARAMETER ExportToExcel
    Optional path to export results to Excel file (e.g., "copilot-usage.xlsx").

.PARAMETER IncludeUserSeats
    Include individual user seat information (who has access and when they last used it).

.EXAMPLE
    .\Get-CopilotUsage.ps1 -Organization "myorg" -Token "ghp_xxxxx"

.EXAMPLE
    .\Get-CopilotUsage.ps1 -Organization "myorg" -Days 7 -ExportToExcel "copilot-usage.xlsx"

.EXAMPLE
    .\Get-CopilotUsage.ps1 -Organization "myorg" -IncludeUserSeats -ExportToExcel "copilot-usage.xlsx"

.NOTES
    API Documentation: https://docs.github.com/en/rest/copilot/copilot-metrics
    Required Token Scopes: 'copilot', 'manage_billing:copilot', or 'read:org'
    This script requires the ImportExcel module. Install it with: Install-Module -Name ImportExcel
#>

[CmdletBinding()]
param(
    [Parameter(Mandatory = $true)]
    [string]$Organization,

    [Parameter(Mandatory = $false)]
    [string]$Token,

    [Parameter(Mandatory = $false)]
    [ValidateRange(1, 28)]
    [int]$Days = 28,

    [Parameter(Mandatory = $false)]
    [string]$ExportToExcel,

    [Parameter(Mandatory = $false)]
    [switch]$IncludeUserSeats
)

# Check if ImportExcel module is available when export is requested
if (-not [string]::IsNullOrEmpty($ExportToExcel)) {
    if (-not (Get-Module -ListAvailable -Name ImportExcel)) {
        Write-Warning "ImportExcel module is not installed. Installing it now..."
        try {
            Install-Module -Name ImportExcel -Scope CurrentUser -Force -AllowClobber
            Write-Host "ImportExcel module installed successfully." -ForegroundColor Green
        } catch {
            Write-Error "Failed to install ImportExcel module. Please install it manually: Install-Module -Name ImportExcel"
            Write-Host "Continuing without Excel export..." -ForegroundColor Yellow
            $ExportToExcel = ""
        }
    }
    if (-not [string]::IsNullOrEmpty($ExportToExcel)) {
        Import-Module ImportExcel
    }
}

# Use environment variable if token not provided
if ([string]::IsNullOrEmpty($Token)) {
    $Token = $env:GITHUB_TOKEN
    if ([string]::IsNullOrEmpty($Token)) {
        Write-Error "GitHub token not provided. Use -Token parameter or set GITHUB_TOKEN environment variable."
        exit 1
    }
}

# API endpoint
$apiUrl = "https://api.github.com/orgs/$Organization/copilot/metrics"

# Headers for authentication
$headers = @{
    "Accept"               = "application/vnd.github+json"
    "Authorization"        = "Bearer $Token"
    "X-GitHub-Api-Version" = "2022-11-28"
}

Write-Host "Fetching Copilot usage metrics for organization: $Organization" -ForegroundColor Cyan
Write-Host "Time period: Last $Days days" -ForegroundColor Cyan
Write-Host ""

# Variables to store data
$dailySummary = @()
$languageSummary = @()
$editorSummary = @()
$overallSummary = $null
$userSeats = @()

try {
    # Calculate date range
    $since = (Get-Date).AddDays(-$Days).ToString("yyyy-MM-dd")
    $until = (Get-Date).ToString("yyyy-MM-dd")

    # Add query parameters
    $uri = "$apiUrl`?since=$since&until=$until"

    # Make API request
    $response = Invoke-RestMethod -Uri $uri -Headers $headers -Method Get

    if ($null -eq $response -or $response.Count -eq 0) {
        Write-Warning "No usage data found for the specified period."
        exit 0
    }

    # Process and display results
    $userMetrics = @()

    foreach ($dayMetric in $response) {
        $date = $dayMetric.date

        if ($null -ne $dayMetric.copilot_ide_code_completions) {
            foreach ($editor in $dayMetric.copilot_ide_code_completions.editors) {
                foreach ($model in $editor.models) {
                    foreach ($language in $model.languages) {
                        $userMetrics += [PSCustomObject]@{
                            Date                      = $date
                            Editor                    = $editor.name
                            Model                     = $model.name
                            Language                  = $language.name
                            TotalEngagedUsers         = $language.total_engaged_users
                            SuggestionsCount          = $language.total_code_suggestions
                            AcceptancesCount          = $language.total_code_acceptances
                            LinesAccepted             = $language.total_code_lines_accepted
                            LinesSuggested            = $language.total_code_lines_suggested
                            ActiveUsers               = $language.total_engaged_users
                        }
                    }
                }
            }
        }
    }

    # Aggregate by user activity
    Write-Host "=== COPILOT USAGE SUMMARY ===" -ForegroundColor Green
    Write-Host ""

    if ($userMetrics.Count -eq 0) {
        Write-Warning "No detailed metrics available for this period."
    } else {
        # Group by date and calculate totals
        $dailySummary = $userMetrics | Group-Object Date | ForEach-Object {
            $dayData = $_.Group
            [PSCustomObject]@{
                Date              = $_.Name
                TotalEngagedUsers = ($dayData | Measure-Object -Property TotalEngagedUsers -Maximum).Maximum
                TotalSuggestions  = ($dayData | Measure-Object -Property SuggestionsCount -Sum).Sum
                TotalAcceptances  = ($dayData | Measure-Object -Property AcceptancesCount -Sum).Sum
                TotalLinesAccepted = ($dayData | Measure-Object -Property LinesAccepted -Sum).Sum
                AcceptanceRate    = if (($dayData | Measure-Object -Property SuggestionsCount -Sum).Sum -gt 0) {
                    [math]::Round((($dayData | Measure-Object -Property AcceptancesCount -Sum).Sum /
                    ($dayData | Measure-Object -Property SuggestionsCount -Sum).Sum) * 100, 2)
                } else { 0 }
            }
        } | Sort-Object Date -Descending

        # Display daily summary
        Write-Host "Daily Summary:" -ForegroundColor Yellow
        $dailySummary | Format-Table -AutoSize

        # Calculate overall statistics
        $totalUsers = ($dailySummary | Measure-Object -Property TotalEngagedUsers -Maximum).Maximum
        $totalSuggestions = ($dailySummary | Measure-Object -Property TotalSuggestions -Sum).Sum
        $totalAcceptances = ($dailySummary | Measure-Object -Property TotalAcceptances -Sum).Sum
        $overallAcceptanceRate = if ($totalSuggestions -gt 0) {
            [math]::Round(($totalAcceptances / $totalSuggestions) * 100, 2)
        } else { 0 }

        Write-Host ""
        Write-Host "=== OVERALL STATISTICS ===" -ForegroundColor Green
        Write-Host "Peak Engaged Users: $totalUsers" -ForegroundColor White
        Write-Host "Total Suggestions: $totalSuggestions" -ForegroundColor White
        Write-Host "Total Acceptances: $totalAcceptances" -ForegroundColor White
        Write-Host "Overall Acceptance Rate: $overallAcceptanceRate%" -ForegroundColor White
        Write-Host ""

        # Language breakdown
        $languageSummary = $userMetrics | Group-Object Language | ForEach-Object {
            $langData = $_.Group
            [PSCustomObject]@{
                Language          = $_.Name
                TotalSuggestions  = ($langData | Measure-Object -Property SuggestionsCount -Sum).Sum
                TotalAcceptances  = ($langData | Measure-Object -Property AcceptancesCount -Sum).Sum
                AcceptanceRate    = if (($langData | Measure-Object -Property SuggestionsCount -Sum).Sum -gt 0) {
                    [math]::Round((($langData | Measure-Object -Property AcceptancesCount -Sum).Sum /
                    ($langData | Measure-Object -Property SuggestionsCount -Sum).Sum) * 100, 2)
                } else { 0 }
            }
        } | Sort-Object TotalAcceptances -Descending

        Write-Host "Language Breakdown:" -ForegroundColor Yellow
        $languageSummary | Format-Table -AutoSize

        # Editor breakdown
        $editorSummary = $userMetrics | Group-Object Editor | ForEach-Object {
            $editorData = $_.Group
            [PSCustomObject]@{
                Editor            = $_.Name
                TotalSuggestions  = ($editorData | Measure-Object -Property SuggestionsCount -Sum).Sum
                TotalAcceptances  = ($editorData | Measure-Object -Property AcceptancesCount -Sum).Sum
            }
        } | Sort-Object TotalAcceptances -Descending

        Write-Host "Editor Breakdown:" -ForegroundColor Yellow
        $editorSummary | Format-Table -AutoSize

        # Create overall summary object for Excel
        $overallSummary = [PSCustomObject]@{
            Organization          = $Organization
            DateRange             = "$since to $until"
            PeakEngagedUsers      = $totalUsers
            TotalSuggestions      = $totalSuggestions
            TotalAcceptances      = $totalAcceptances
            OverallAcceptanceRate = "$overallAcceptanceRate%"
            ReportGeneratedDate   = (Get-Date).ToString("yyyy-MM-dd HH:mm:ss")
        }
    }

    # Fetch individual user seat information if requested
    if ($IncludeUserSeats) {
        Write-Host ""
        Write-Host "=== FETCHING USER SEAT INFORMATION ===" -ForegroundColor Green
        Write-Host ""

        try {
            # First, get the seat assignments
            $seatsUrl = "https://api.github.com/orgs/$Organization/copilot/billing/seats"
            $page = 1
            $perPage = 100
            $allSeats = @()

            do {
                $seatsUri = "$seatsUrl`?per_page=$perPage&page=$page"
                $seatsResponse = Invoke-RestMethod -Uri $seatsUri -Headers $headers -Method Get

                if ($null -ne $seatsResponse.seats) {
                    $allSeats += $seatsResponse.seats
                }

                $page++
            } while ($seatsResponse.seats.Count -eq $perPage)

            Write-Host "Found $($allSeats.Count) user seats" -ForegroundColor Cyan
            Write-Host ""
            Write-Host "NOTE: GitHub does not provide per-user 'credit usage' via API." -ForegroundColor Yellow
            Write-Host "Credit calculation is based on billing model: 1 seat = 300 credits/month" -ForegroundColor Yellow
            Write-Host "'Wasting credits' means: seat assigned but user inactive >30 days" -ForegroundColor Yellow
            Write-Host ""

            # Calculate credits consumed per user
            # GitHub Copilot Business/Enterprise charges per seat regardless of usage
            # If a user has a seat assigned, they consume the full month's credits
            # The "last_activity_at" tells us if they're actually using it
            $creditsPerMonth = 300
            $daysInMonth = [DateTime]::DaysInMonth((Get-Date).Year, (Get-Date).Month)
            $currentDay = (Get-Date).Day

            # Calculate how many days have passed in the current month
            $daysElapsedInMonth = $currentDay

            if ($allSeats.Count -eq 0) {
                Write-Warning "No user seats found."
            } else {
                $userSeats = $allSeats | ForEach-Object {
                    $username = $_.assignee.login

                    $lastActivityDate = if ($_.last_activity_at) {
                        try {
                            # Try parsing as DateTime - handles multiple formats
                            if ($_.last_activity_at -is [DateTime]) {
                                $_.last_activity_at
                            } else {
                                [DateTime]::Parse($_.last_activity_at, [System.Globalization.CultureInfo]::InvariantCulture, [System.Globalization.DateTimeStyles]::None)
                            }
                        } catch {
                            # Fallback: try different parsing methods
                            try {
                                [DateTime]::ParseExact($_.last_activity_at, "MM/dd/yyyy HH:mm:ss", [System.Globalization.CultureInfo]::InvariantCulture)
                            } catch {
                                try {
                                    # ISO 8601 format
                                    [DateTime]::Parse($_.last_activity_at)
                                } catch {
                                    Write-Verbose "Could not parse date: $($_.last_activity_at) for user $username"
                                    $null
                                }
                            }
                        }
                    } else {
                        $null
                    }

                    $daysSinceLastActivity = if ($lastActivityDate) {
                        [math]::Round(((Get-Date) - $lastActivityDate).TotalDays)
                    } else {
                        $null
                    }

                    $isActive = if ($daysSinceLastActivity -ne $null) {
                        $daysSinceLastActivity -le 30
                    } else {
                        $false
                    }

                    $assignedDate = if ($_.created_at) {
                        try {
                            if ($_.created_at -is [DateTime]) {
                                $_.created_at
                            } else {
                                $parsedDate = [DateTime]::Parse($_.created_at, [System.Globalization.CultureInfo]::InvariantCulture, [System.Globalization.DateTimeStyles]::None)
                                $parsedDate
                            }
                        } catch {
                            try {
                                [DateTime]::ParseExact($_.created_at, "MM/dd/yyyy HH:mm:ss", [System.Globalization.CultureInfo]::InvariantCulture)
                            } catch {
                                $null
                            }
                        }
                    } else {
                        $null
                    }

                    # Calculate credits consumed
                    # GitHub Copilot billing model: Charges per seat per month
                    # Once a seat is assigned, the FULL monthly cost applies
                    # Credits don't depend on usage - they're consumed just by having the seat

                    # Check if the seat is currently assigned (not pending cancellation)
                    $isPendingCancellation = ![string]::IsNullOrEmpty($_.pending_cancellation_date)

                    if ($isPendingCancellation) {
                        # Seat is being cancelled - no credits for full month
                        $creditsConsumed = 0
                    } elseif ($assignedDate -and $assignedDate.Year -eq (Get-Date).Year -and $assignedDate.Month -eq (Get-Date).Month) {
                        # Assigned THIS month - pro-rate based on days from assignment to end of month
                        $daysAssignedThisMonth = $currentDay - $assignedDate.Day + 1
                        $creditsConsumed = [math]::Round(($daysAssignedThisMonth / $daysInMonth) * $creditsPerMonth, 2)
                    } else {
                        # Assigned before this month - FULL month charge
                        $creditsConsumed = $creditsPerMonth
                    }

                    $creditsRemaining = [math]::Round($creditsPerMonth - $creditsConsumed, 2)
                    $creditsUsagePercent = if ($creditsPerMonth -gt 0) {
                        [math]::Round(($creditsConsumed / $creditsPerMonth) * 100, 2)
                    } else {
                        0
                    }

                    # Determine if credits are being wasted (assigned but not actively using)
                    $isWastingCredits = ($creditsConsumed -gt 0) -and ($daysSinceLastActivity -eq $null -or $daysSinceLastActivity -gt 30)

                    [PSCustomObject]@{
                        Username              = $username
                        DisplayName           = $_.assignee.name
                        Email                 = $_.assignee.email
                        AssignedAt            = $assignedDateFormatted
                        LastActivityAt        = if ($lastActivityDate) { $lastActivityDate.ToString("yyyy-MM-dd HH:mm:ss") } else { "Never" }
                        DaysSinceLastActivity = if ($daysSinceLastActivity -ne $null) { $daysSinceLastActivity } else { "N/A" }
                        IsActive30Days        = $isActive
                        IsWastingCredits      = $isWastingCredits
                        DaysAssignedThisMonth = if ($assignedDate) { $daysAssignedThisMonth } else { $currentDay }
                        CreditsAllocated      = $creditsPerMonth
                        CreditsConsumed       = $creditsConsumed
                        CreditsRemaining      = $creditsRemaining
                        CreditsUsagePercent   = $creditsUsagePercent
                        PendingCancellationDate = if ($_.pending_cancellation_date) { $_.pending_cancellation_date } else { "" }
                        Editor                = $_.last_activity_editor
                        AssigningTeam         = if ($_.assigning_team) { $_.assigning_team.name } else { "" }
                    }
                } | Sort-Object CreditsConsumed -Descending

                Write-Host "Total Seats Assigned: $($userSeats.Count)" -ForegroundColor Cyan
                $activeUsers = ($userSeats | Where-Object { $_.IsActive30Days -eq $true }).Count
                $inactiveUsers = ($userSeats | Where-Object { $_.IsActive30Days -eq $false }).Count
                $wastingCredits = ($userSeats | Where-Object { $_.IsWastingCredits -eq $true }).Count

                Write-Host "Active Users (last 30 days): $activeUsers" -ForegroundColor Green
                Write-Host "Inactive Users: $inactiveUsers" -ForegroundColor Yellow
                Write-Host "Users Wasting Credits: $wastingCredits" -ForegroundColor Red
                Write-Host ""

                # Show top users by credit consumption
                Write-Host "All Users by Credit Consumption (Month of $(Get-Date -Format 'MMMM yyyy')):" -ForegroundColor Yellow
                $userSeats | Select-Object -First 50 |
                    Format-Table Username, DaysAssignedThisMonth, CreditsConsumed, CreditsUsagePercent, LastActivityAt, IsWastingCredits, Editor -AutoSize

                # Show users wasting credits
                Write-Host ""
                Write-Host "Users WASTING Credits (assigned but inactive >30 days):" -ForegroundColor Red
                $userSeats | Where-Object { $_.IsWastingCredits -eq $true } |
                    Select-Object -First 50 |
                    Format-Table Username, CreditsConsumed, DaysSinceLastActivity, LastActivityAt, AssignedAt -AutoSize

                # Credit usage summary
                $totalCreditsAllocated = $userSeats.Count * $creditsPerMonth
                $totalCreditsConsumed = ($userSeats | Measure-Object -Property CreditsConsumed -Sum).Sum
                $totalCreditsWasted = ($userSeats | Where-Object { $_.IsWastingCredits -eq $true } | Measure-Object -Property CreditsConsumed -Sum).Sum
                $creditEfficiency = if ($totalCreditsAllocated -gt 0) {
                    [math]::Round(($totalCreditsConsumed / $totalCreditsAllocated) * 100, 2)
                } else { 0 }

                Write-Host ""
                Write-Host "=== CREDIT USAGE ANALYSIS (Month of $(Get-Date -Format 'MMMM yyyy')) ===" -ForegroundColor Green
                Write-Host "Credits per User per Month: $creditsPerMonth" -ForegroundColor White
                Write-Host "Total Seats: $($userSeats.Count)" -ForegroundColor White
                Write-Host "Total Credits Allocated (Full Month): $totalCreditsAllocated ($($userSeats.Count) users x $creditsPerMonth)" -ForegroundColor White
                Write-Host "Total Credits Consumed (Month-to-Date): $([math]::Round($totalCreditsConsumed, 2))" -ForegroundColor Cyan
                Write-Host "Total Credits on WASTED Seats: $([math]::Round($totalCreditsWasted, 2))" -ForegroundColor Red
                Write-Host "Potential Monthly Savings (remove inactive): $([math]::Round(($wastingCredits * $creditsPerMonth), 2)) credits" -ForegroundColor Yellow
                Write-Host ""
                Write-Host "Days Elapsed in Month: $currentDay of $daysInMonth" -ForegroundColor White
                Write-Host "Credit Utilization: $creditEfficiency% (of full-month allocation)" -ForegroundColor $(if ($creditEfficiency -lt 50) { "Red" } elseif ($creditEfficiency -lt 75) { "Yellow" } else { "Green" })
                Write-Host ""

                # Recommendations
                if ($wastingCredits -gt 0) {
                    Write-Host "💡 RECOMMENDATIONS:" -ForegroundColor Cyan
                    Write-Host "  → Remove $wastingCredits inactive user(s) to save ~$([math]::Round(($wastingCredits * $creditsPerMonth), 2)) credits/month" -ForegroundColor Yellow
                    Write-Host "  → That's approximately `$$([math]::Round(($wastingCredits * 19), 2))/month in wasted costs (at ~`$19/seat)" -ForegroundColor Yellow
                }
            }
        } catch {
            Write-Warning "Failed to retrieve user seat information: $_"
            Write-Host "You may need 'manage_billing:copilot' scope to access seat details." -ForegroundColor Yellow
        }
    }
} catch {
    Write-Error "An error occurred: $_"
    exit 1
}

# Export to Excel if requested
if (-not [string]::IsNullOrEmpty($ExportToExcel)) {
    Write-Host ""
    Write-Host "Exporting to Excel: $ExportToExcel" -ForegroundColor Cyan

    try {
        # Remove existing file if it exists
        if (Test-Path $ExportToExcel) {
            Remove-Item $ExportToExcel -Force
        }

        # Export to multiple worksheets
        $excelParams = @{
            Path          = $ExportToExcel
            AutoSize      = $true
            FreezeTopRow  = $true
            BoldTopRow    = $true
        }

        $sheetCount = 1

        # Sheet 1: Overall Summary
        if ($null -ne $overallSummary) {
            $overallSummary | Export-Excel @excelParams -WorksheetName "Overall Summary" -TableName "OverallSummary"
            $sheetCount++
        }

        # Sheet 2: Daily Summary
        if ($dailySummary.Count -gt 0) {
            $dailySummary | Export-Excel @excelParams -WorksheetName "Daily Summary" -TableName "DailySummary"
            $sheetCount++
        }

        # Sheet 3: Language Breakdown
        if ($languageSummary.Count -gt 0) {
            $languageSummary | Export-Excel @excelParams -WorksheetName "Language Breakdown" -TableName "LanguageBreakdown"
            $sheetCount++
        }

        # Sheet 4: Editor Breakdown
        if ($editorSummary.Count -gt 0) {
            $editorSummary | Export-Excel @excelParams -WorksheetName "Editor Breakdown" -TableName "EditorBreakdown"
            $sheetCount++
        }

        # Sheet 5: Detailed Metrics
        if ($userMetrics.Count -gt 0) {
            $userMetrics | Sort-Object Date -Descending |
                Export-Excel @excelParams -WorksheetName "Detailed Metrics" -TableName "DetailedMetrics"
            $sheetCount++
        }

        # Sheet 6: User Seats (if included)
        if ($userSeats.Count -gt 0) {
            $userSeats | Export-Excel @excelParams -WorksheetName "User Seats" -TableName "UserSeats"
            $sheetCount++
        }

        Write-Host "Results exported to: $ExportToExcel" -ForegroundColor Green
        Write-Host "Excel file contains multiple worksheets:" -ForegroundColor Green
        Write-Host "  - Overall Summary" -ForegroundColor White
        Write-Host "  - Daily Summary" -ForegroundColor White
        Write-Host "  - Language Breakdown" -ForegroundColor White
        Write-Host "  - Editor Breakdown" -ForegroundColor White
        Write-Host "  - Detailed Metrics" -ForegroundColor White
        if ($userSeats.Count -gt 0) {
            Write-Host "  - User Seats (per-user credit information)" -ForegroundColor White
        }
    } catch {
        Write-Error "Failed to export to Excel: $_"
    }
}

Write-Host ""
Write-Host "Note: For individual user seat management in browser, visit:" -ForegroundColor Cyan
Write-Host "https://github.com/organizations/$Organization/settings/copilot/seat_management" -ForegroundColor Cyan

Write-Host ""
Write-Host "Script completed." -ForegroundColor Green