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

    [Parameter(Mandatory=$true)]
    [string]
    $UserId,

    [Parameter(Mandatory=$true)]
    [securestring]
    $AccessToken
)

$account_data_type_prefix = 'de.lubiland.pingposh.'
$account_data_types = @{
    next_batch = $account_data_type_prefix+'next_batch'
}


function Send-MatrixEvent {
    param (
        [Parameter(Mandatory=$true)]
        [string]
        $RoomId,

        [Parameter(Mandatory=$true)]
        [string]
        $Event,

        [Parameter(Mandatory=$true)]
        [string]
        $EventType
    )

    #txn_id should be unique per client, so we use timestamp+random
    $txn_id = '{0}{1}' -f (Get-Date -UFormat '%s'),(Get-Random)

    $uri = '{0}/_matrix/client/r0/rooms/{1}/send/{2}/{3}' -f $HomeServer,$RoomId,$EventType,$txn_id

    $header_splat = @{
        Authentication = 'Bearer'
        Token = $AccessToken
        ContentType = 'application/json'
    }
    $http_splat = @{
        Uri = $uri
        Method = 'Put'
        Body = $Event
    }

    $response = Invoke-RestMethod @header_splat @http_splat
    if($response.event_id) {
        Write-Host ('Event {0} sent to room {1}' -f $response.event_id,$RoomId)
    }
}
function Send-Pong {
    param (
        [Parameter(Mandatory=$true)]
        [string]
        $RoomId,

        [Parameter(Mandatory=$true)]
        [string]
        $Body,

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

        [Parameter(Mandatory=$true)]
        [string]
        $OriginHomeServer,

        [Parameter(Mandatory=$true)]
        [int]
        $Duration,
        
        [Parameter(Mandatory=$true)]
        [string]
        $PingEventId
    )

    $event = @{
        msgtype = 'm.notice'
        body = $Body
        pong = @{
            from = $OriginHomeServer
            ms = $Duration
            ping = $PingEventId
        }
    }

    if($FormattedBody) {
        $event += @{
            format = 'org.matrix.custom.html'
            formatted_body = $FormattedBody
        }
    }

    $event_json = $event | ConvertTo-Json -Compress

    Send-MatrixEvent -RoomId $RoomId -Event $event_json -EventType 'm.room.message'
}
function Compare-Timestamps {
    param (
        [Parameter(Mandatory=$true)]
        [Int64]
        $OriginServerTs
    )

    $current_time = (Get-Date).ToUniversalTime()

    #$OriginServerTs is milliseconds since 1970-01-01 (epoch time in milliseconds)
    $original_time = Get-Date -Date ((Get-Date -Date '1970-01-01') + [timespan]::FromMilliseconds($OriginServerTs))

    #return the difference
    Write-Output ($current_time - $original_time)
}
function ConvertTo-HumanReadableTimespan {
    param (
        [parameter(Mandatory=$true)]
        [timespan]
        $TimeSpan
    )

    switch($TimeSpan) {
        Default {
            $output = '{0} days' -f [System.Math]::Round($TimeSpan.TotalDays, 2)
        }
        {$PSItem.TotalHours -lt 24} {
            $output = '{0} h' -f [System.Math]::Round($TimeSpan.TotalHours, 2)
        }
        {$PSItem.TotalMinutes -lt 120} {
            $output = '{0} min' -f [System.Math]::Round($TimeSpan.TotalMinutes, 2)
        }
        {$PSItem.TotalSeconds -lt 120} {
            $output = '{0} s' -f [System.Math]::Round($TimeSpan.TotalSeconds, 2)
        }
        {$PSItem.TotalMilliseconds -lt 10000} {
            $output = '{0} ms' -f [System.Math]::Round($TimeSpan.TotalMilliseconds, 0)
        }
    }

    Write-Output $output
}
function Join-Pong {
    param (
        [Parameter(Mandatory=$true)]
        [string]
        $RoomId,

        [Parameter(Mandatory=$true)]
        [string]
        $PingEventId,

        [Parameter(Mandatory=$true)]
        [string]
        $SenderMxId,

        [Parameter(Mandatory=$true)]
        [string]
        $ReadableTimespan,

        [Parameter(Mandatory=$false)]
        [string]
        $Ball
    )

    if($Ball) {
        $padded_ball = $Ball+' '
    }

    $body = '{0}: Pong! (ping {1}took {2} to arrive)' -f $SenderMxId,$padded_ball,$ReadableTimespan
    $formatted_body  = '<a href=''https://matrix.to/#/{0}''>{0}</a>: Pong! ' -f $SenderMxId
    $formatted_body += '(<a href="https://matrix.to/#/{0}/{1}">ping</a> {2}took {3} to arrive)' -f $RoomId,$PingEventId,$padded_ball,$ReadableTimespan

    return @{
        Body = $body
        FormattedBody = $formatted_body
    }
}
function Open-Event {
    param (
        [Parameter(Mandatory=$true)]
        $Event,

        [Parameter(Mandatory=$true)]
        $RoomId
    )

    #the "ball" is a string returned by the bot
    if($Event.content.msgtype -eq 'm.text' -and $Event.content.body -match '!ping( (?<ball>.*))?') {
        $difference = Compare-Timestamps -OriginServerTs $Event.origin_server_ts
        $readable_timespan = ConvertTo-HumanReadableTimespan -TimeSpan $difference

        #$bodies contains a hashtable with keys Body and FormattedBody
        $bodies = Join-Pong -RoomId $RoomId -PingEventId $Event.event_id -SenderMxId $Event.sender -ReadableTimespan $readable_timespan -Ball $Matches.ball

        $origin_homeserver = $Event.sender.Split(':')[1]
        Send-Pong -RoomId $RoomId @bodies -OriginHomeServer $origin_homeserver -Duration $difference.TotalMilliseconds -PingEventId $Event.event_id
    }
}
function Get-MatrixAccountData {
    param (
        [Parameter(Mandatory=$true)]
        [string]
        $Type
    )

    $uri = '{0}/_matrix/client/r0/user/{1}/account_data/{2}' -f $HomeServer,$UserId,$Type

    $header_splat = @{
        Authentication = 'Bearer'
        Token = $AccessToken
        ContentType = 'application/json'
    }
    $http_splat = @{
        Uri = $uri
        Method = 'Get'
    }

    $response = Invoke-RestMethod @header_splat @http_splat
    return $response
}
function Set-MatrixAccountData {
    param (
        [Parameter(Mandatory=$true)]
        [string]
        $Type,

        [Parameter(Mandatory=$true)]
        [System.Object]
        $Content
    )

    $uri = '{0}/_matrix/client/r0/user/{1}/account_data/{2}' -f $HomeServer,$UserId,$Type

    $header_splat = @{
        Authentication = 'Bearer'
        Token = $AccessToken
        ContentType = 'application/json'
    }
    $http_splat = @{
        Uri = $uri
        Method = 'Put'
        Body = $Content | ConvertTo-Json -Compress
    }

    Invoke-RestMethod @header_splat @http_splat | Out-Null
}
function Get-NextBatchToken {
    $account_data = Get-MatrixAccountData -Type $account_data_types.next_batch
    return $account_data.next_batch
}
function Set-NextBatchToken {
    param (
        [Parameter(Mandatory=$true)]
        [string]
        $Token
    )

    Set-MatrixAccountData -Type $account_data_types.next_batch -Content @{next_batch = $Token}
}
function Invoke-MatrixSync {
    param (
        [string]
        $Token,

        [string]
        $FilterId,

        [int]
        $Timeout = 30000
    )

    $uri = '{0}/_matrix/client/r0/sync?timeout={1}' -f $HomeServer,$Timeout
    if($Token) {
        $uri += '&since={0}' -f $Token
    }
    if($FilterId) {
        $uri += '&filter={0}' -f $FilterId
    }

    $header_splat = @{
        Authentication = 'Bearer'
        Token = $AccessToken
        ContentType = 'application/json'
    }
    $http_splat = @{
        Uri = $uri
    }

    $response = Invoke-RestMethod @header_splat @http_splat

    #.PSObject.Properties because the rooms under .join are [NoteProperty]
    $room_ids = $response.rooms.join.PSObject.Properties.Name
    foreach($room_id in $room_ids) {
        $events = $response.rooms.join.$room_id.timeline.events
        foreach($event in $events) {
            Open-Event -Event $event -RoomId $room_id
        }
    }

    return $response.next_batch
}
function Get-MatrixFilterId {
    param (
        [System.Object]
        $Filter
    )

    $uri = '{0}/_matrix/client/r0/user/{1}/filter' -f $HomeServer,$UserId

    $header_splat = @{
        Authentication = 'Bearer'
        Token = $AccessToken
        ContentType = 'application/json'
    }
    $http_splat = @{
        Uri = $uri
        Method = 'Post'
        #a filter can be up to 3 layers deep according to spec
        #https://matrix.org/docs/spec/client_server/r0.6.0#filtering
        Body = $Filter | ConvertTo-Json -Compress -Depth 3
    }

    $response = Invoke-RestMethod @header_splat @http_splat

    return $response.filter_id
}
function Get-FilterId {
    $filter = @{
        event_fields = @(
            #all fields used in Open-Event
            'event_id'
            'sender'
            'origin_server_ts'
            'content.msgtype'
            'content.body'
        )
        presence = @{
            #we don't use presence information
            types = @('invalid')
        }
        account_data = @{
            #we only retrieve account_data via the account_data api endpoint
            types = @('invalid')
        }
        room = @{
            ephemeral = @{
                #we don't use ephemeral events like typing or read receipts
                types = @('invalid')
            }
            state = @{
                #we don't use room state
                types = @('invalid')
            }
            timeline = @{
                #exclude ourself
                not_senders = @(
                    $UserId
                )
                types = @(
                    #to receive !ping commands
                    'm.room.message'
                )
            }
            account_data = @{
                #we don't use room specific account_data
                types = @('invalid')
            }
        }
    }

    $filter_id = Get-MatrixFilterId -Filter $filter
    return $filter_id
}
function Start-MatrixSync {
    #get last used next_batch from account_data
    $token = Get-NextBatchToken

    #get /sync filter
    $filter_id = Get-FilterId

    Try {
        #try first sync with the old token
        $token = Invoke-MatrixSync -Token $token -FilterId $filter_id
    } Catch {
        #if it fails start a fresh sync reset $token
        $token = $null
    }

    while($true) {
        #use $token of the previous sync
        Set-NextBatchToken -Token $token
        $token = Invoke-MatrixSync -Token $token -FilterId $filter_id
    }
}


Start-MatrixSync