Get Office365 Calendar Events

function Get-O365CalendarEvent
{
<#
    .SYNOPSIS
        Function to gather Calendar Events between two specific dates

    .DESCRIPTION
        Function to gather Calendar Events between two specific dates
        It is using the REST API available against Office365

    .PARAMETER EmailAddress
        Specifies the mailbox email address to query.
        Default is the current user
        Example: info@lazywinadmin.com

    .PARAMETER StartDateTime
        Specifies the Start Date Time
        The UTC date and time when the event starts. (datetimeoffset)
        Default is now.

    .PARAMETER EndDateTime
        Specifies the End Date Time
        The UTC date and time when the event ends. (datetimeoffset)
        Default is next week (7 days).

    .PARAMETER Credential
        Specifies alternative credentials
        By default it will use the current user.

    .PARAMETER PageResult
        Specifies the number of items to return. Max is 50.

    .EXAMPLE
        PS C:\> Get-O365CalendarEvent

        Get the calendar Events of the next coming week for the current user.

    .EXAMPLE
        PS C:\> Get-O365CalendarEvent -EmailAddress info@lazywinadmin.com -Credential (Get-Credential) | Select-Object -Property Subject, StartTimeZone, Start, End, @{L="Attendees";E={$psitem.attendees.emailaddress | Select-Object -Property name -Unique|Sort}}

        Get the calendar Events Subject, StartTimeZone,Start, End, Attendees for the last 7 days

    .EXAMPLE
        Get-O365CalendarEvent -EmailAddress info@lazywinadmin.com -Credential $cred -StartDateTime $((Get-Date).adddays(-50)) -PageResult 15

    .NOTES
        Francois-Xavier Cat
        www.lazywinadmin.com
        @lazywinadm
        github.com/lazywinadmin

        # More about the Calendar operations
        https://msdn.microsoft.com/office/office365/api/calendar-rest-operations

        # Filter/Sorting/Top/Order
        https://msdn.microsoft.com/office/office365/APi/complex-types-for-mail-contacts-calendar#UseODataqueryparametersPageresults

    .HISTORY

        Stephane van Gulick - PowerShellDistrict.com: Added Headers Property
        'timeZone' to fit the display gap that could happen between an actual
        event an the current timeZone.
#>
    [CmdletBinding()]
    param
    (
        [String]$EmailAddress,
        [datetime]$StartDateTime = (Get-Date),
        [datetime]$EndDateTime = ((Get-Date).adddays(7)),
        [System.Management.Automation.Credential()]
        $Credential = [System.Management.Automation.PSCredential]::Empty,
        [ValidateNotNullOrEmpty()]
        [ValidateRange(1, 50)]
        $PageResult = '10',
        [ValidateSet(
            'Romance Standard Time',
            'Atlantic Standard Time'
        )]
        $Timezone #complete list available here https://technet.microsoft.com/en-us/library/cc749073(v=ws.10).aspx
    )

    PROCESS
    {
        $Splatting = @{
            Credential = $Credential
            Uri = "https://outlook.office365.com/api/v1.0/users/$EmailAddress/calendarview?startDateTime=$StartDateTime&endDateTime=$($EndDateTime)&`$top=$PageResult"

        }

        if ($TimeZone){
            $headers = New-Object 'System.Collections.Generic.Dictionary[[String],[String]]'
            $headers.Add('Prefer', "outlook.timezone=`"$TimeZone`"")
            $Splatting.Add('Headers',$headers)
        }
        if (-not $PSBoundParameters['EmailAddress'])
        {
            #Query the current User
            $Splatting.Uri = "https://outlook.office365.com/api/v1.0/me/calendarview?startDateTime=$StartDateTime&endDateTime=$($EndDateTime)&`$top=$PageResult"
        }

        Invoke-RestMethod @Splatting  | Select-Object -ExpandProperty Value
    }
}