CalendarActivityReport.ps1

$TenantId = "xxxxxxxx"
$ClientID = "xxxxxxxxx"
$ClientSecret = "xxxxxxx"

function Get-MSGraphAppToken{
    <#  .SYNOPSIS
        Get an app based authentication token required for interacting with Microsoft Graph API
    .PARAMETER TenantID
        A tenant ID should be provided.
    .PARAMETER ClientID
        Application ID for an Azure AD application. Uses by default the Microsoft Intune PowerShell application ID.
    .PARAMETER ClientSecret
        Web application client secret.
    .EXAMPLE
        # Manually specify username and password to acquire an authentication token:
        Get-MSGraphAppToken -TenantID $TenantID -ClientID $ClientID -ClientSecert = $ClientSecret 
    .NOTES
        Author: Jan Ketil Skanke
        Contact: @JankeSkanke
        Created: 2020-15-03
        Updated: 2020-15-03
        Version history:
        1.0.0 - (2020-03-15) Function created      
    #>[CmdletBinding()]
    param (
        [parameter(Mandatory = $true, HelpMessage = "Your Azure AD Directory ID should be provided")]
        [ValidateNotNullOrEmpty()]
        [string]$TenantID,
        [parameter(Mandatory = $true, HelpMessage = "Application ID for an Azure AD application")]
        [ValidateNotNullOrEmpty()]
        [string]$ClientID,
        [parameter(Mandatory = $true, HelpMessage = "Azure AD Application Client Secret.")]
        [ValidateNotNullOrEmpty()]
        [string]$ClientSecret
        )
Process {
    $ErrorActionPreference = "Stop"
    # Construct URI
    $uri = "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token"
    # Construct Body
    $body = @{
        client_id     = $clientId
        scope         = "https://graph.microsoft.com/.default"
        client_secret = $clientSecret
        grant_type    = "client_credentials"
        }
    try {
        $MyTokenRequest = Invoke-WebRequest -Method Post -Uri $uri -ContentType "application/x-www-form-urlencoded" -Body $body -UseBasicParsing
        $MyToken =($MyTokenRequest.Content | ConvertFrom-Json).access_token
            If(!$MyToken){
                Write-Warning "Failed to get Graph API access token!"
                Exit 1
            }
        $MyHeader = @{"Authorization" = "Bearer $MyToken" }
       }
    catch [System.Exception] {
        Write-Warning "Failed to get Access Token, Error message: $($_.Exception.Message)"; break
    }
    return $MyHeader
    }
}
$Count=0
#Generate Graph API access token
$global:Header = Get-MSGraphAppToken -TenantID $TenantId -ClientID $ClientID -ClientSecret $ClientSecret
$Date = get-date -Format "yyyy-MM-dd"
$currentUriUsers = "https://graph.microsoft.com/v1.0/users?`$select=displayName,mail,userPrincipalName,id,userType,assignedLicenses"
#Get all entries in SharePoint list.
$Users = while (-not [string]::IsNullOrEmpty($currentUriUsers)) {
    # API Call
   # Write-Host "`r`nQuerying $currentUri..." -ForegroundColor Yellow
    $apiCall = Invoke-WebRequest -Method "GET" -Uri $currentUriUsers -ContentType "application/json" -Headers $global:Header -ErrorAction Stop -UseBasicParsing
    $nextLink = $null
    $currentUriUsers = $null
    if ($apiCall.Content) {
        # Check if any data is left
        $nextLink = $apiCall.Content | ConvertFrom-Json | Select-Object '@odata.nextLink'
        $currentUriUser = $nextLink.'@odata.nextLink'
        $apiCall.Content | ConvertFrom-Json
    }
}
$Users = $Users.value | Where-Object{$_.assignedLicenses}
$useractivityList = @()

foreach($user in $users){
$currentUriUser = "https://graph.microsoft.com/v1.0/users/$($user.userprincipalname)/calendar/events?`$filter=start/dateTime ge '$($Date)T00:00:00.00Z'"
#Get all entries in SharePoint list.
$Events = while (-not [string]::IsNullOrEmpty($currentUriUser)) {
    # API Call
   # Write-Host "`r`nQuerying $currentUri..." -ForegroundColor Yellow
    $apiCall = Invoke-WebRequest -Method "GET" -Uri $currentUriUser -ContentType "application/json" -Headers $global:Header -ErrorAction Stop -UseBasicParsing
    $nextLink = $null
    $currentUriUser = $null
    if ($apiCall.Content) {
        # Check if any data is left
        $nextLink = $apiCall.Content | ConvertFrom-Json | Select-Object '@odata.nextLink'
        $currentUriUser = $nextLink.'@odata.nextLink'
        $apiCall.Content | ConvertFrom-Json
    }
}
$Events = $Events.value  | Where-Object{$_.Subject -like "#*"} 


$Monday = @()
$Tuesday = @()
$Wednesday = @()
$Thursday = @()
$Friday = @()

Foreach($Event in $Events){

$DayOfTheWeek = @()
$DayOfTheWeek = (get-date $Event.start.dateTime).DayOfWeek


if($DayOfTheWeek -like "Monday"){If(!$Monday){$Monday += "$($Event.subject)"}Else{$Monday += ", $($Event.subject)"}}
if($DayOfTheWeek -like "Tuesday"){If(!$Tuesday){$Tuesday += "$($Event.subject)"}Else{$Tuesday += ", $($Event.subject)"}}
if($DayOfTheWeek -like "Wednesday"){If(!$Wednesday){$Wednesday += "$($Event.subject)"}Else{$Wednesday += ", $($Event.subject)"}}
if($DayOfTheWeek -like "Thursday"){If(!$Thursday){$Thursday += "$($Event.subject)"}Else{$Thursday += ", $($Event.subject)"}}
if($DayOfTheWeek -like "Friday"){If(!$Friday){$Friday += "$($Event.subject)"}Else{$Friday += ", $($Event.subject)"}}

}

$useractivity = @()
$useractivity = [PSCustomObject]@{
    Name = $User.displayName
    Monday = $($Monday -join "").Replace("#","")
    Tuesday = $($Tuesday -join "").Replace("#","")
    Wednesday = $($Wednesday -join "").Replace("#","")
    Thursday = $($Thursday -join "").Replace("#","")
    Friday = $($Friday -join "").Replace("#","")

}
$useractivityList += $useractivity

}

$useractivityList