Need PHP function to generate PDU.

I am currently sending SMS with AT commands in Text mode. In order to better support concatenated SMS, line breaks, and encodings, I want to switch to PDU mode. I need a PHP function that will generate PDU to be sent by Asterisk. Output need to be a JSON array with the PDU generated and part number, and total number of parts. Maxumum parts is 10. If more than 10 parts, error needs to be returned. If a mandatory parameter is missing or if parameter has wrong format, error needs to be returned. Parameters sent: *Destination number in international format (ie: 14152470402) *Message – SMS content Validity Period - in hours (if empty, Default is 72 hours) Status Report Request - 0 or 1 (if empty, Default is 1) Response expected: Status - ok (success) / ok (error with code) Number of parts - parts in total Order - order number of each part PDU (ie: 07912160130300F411000A8158888700890000aa27D3E614D42CCEE7E17319342FBBE920B3FCDD0605A9A0E1) if status is OK Error reply { "status":"error", "id":3 } Success reply (1 part) { "status":"ok", "total":1, "parts": [ { "order":1, "pdu":"007100099121436587F90008FF8C05000329030100370033621030EC306E30E9306D662F8868308562266A29306630554EF656F330605B9A590930C430C1629E96C530A85D0E00390038524D30CF51FA5B503053305E3050653F969B7A81307C52367F8E3075305F696D514330A666F8712130EA3073540C7C7330B330DF30BD30E94ED8829D5EA78D85308B307F30B9305C30025DE830D530EC" }, ] } Success reply (3 parts) { "status":"ok", "total":3, "parts": [ { "order":1, "pdu":"007100099121436587F90008FF8C05000329030100370033621030EC306E30E9306D662F8868308562266A29306630554EF656F330605B9A590930C430C1629E96C530A85D0E00390038524D30CF51FA5B503053305E3050653F969B7A81307C52367F8E3075305F696D514330A666F8712130EA3073540C7C7330B330DF30BD30E94ED8829D5EA78D85308B307F30B9305C30025DE830D530EC" }, { "order":2, "pdu":"007100099121436587F90008FF8C05000329030230AF65AD82B830A230B530BD53168F2930CC30A230B78EE25C3130B330EF66428A664E2630EA30BD30CF30ED66F84EAC30443081304A80055CA1663C306D30B950AC7D4430AA65B05C5E30FC308F306B304D65995C0630FC72695EB75EFA62D8304B307330B9304830028A6630D830BD30CF30CA5CA179D26B62305A3060307030444E880038" }, { "order":3, "pdu":"007100099121436587F90008FF5E05000329030300317AF630AD4F7352DD30AF304882B8003375B530C3305C308230508FD1529B304E3084524D97003076305F306430885FF500350031822A30E130A676845171304A8EE299AC30EA30C459D35EA66210520652DF305E3002" } ] } Function needs to check the message encoding for the DCS. It can be alphabet (GSM 7bit) or languages such as Chinese, Korean, Japanese, Arabic... (UCS2 (16bit)) (*) Mandatory fields Expected: - The PHP function - PHP script calling the function with parameters and displaying result. - List of error codes - List of tests done