package sdb

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"time"
)

type IridiumSDB struct {
	ProtocolRevision byte
	Length           uint16
	Elements         []interface{}
}

type MOHeader struct {
	IEI          byte
	Length       uint16
	CDRReference uint32
	IMEI         [15]byte
	Status       byte
	MOMSN        uint16
	MTMSN        uint16
	TimeSession  uint32
}

func (h MOHeader) SessionTime() time.Time {
	return time.Unix(int64(h.TimeSession), 0)
}

func (h MOHeader) StatusString() string {
	switch h.Status {
	case 0:
		return "The SBD session completed successfully."
	case 1:
		return "The MO message transfer, if any, was successful. The MT message queued at the Iridium Gateway is too large to be transferred within a single SBD session."
	case 2:
		return "The MO message transfer, if any, was successful. The reported location was determined to be of unacceptable quality. This value is only applicable to IMEIs using SBD protocol revision 1."
	case 10:
		return "The SBD session timed out before session completion."
	case 12:
		return "The MO message being transferred by the IMEI is too large to be transferred within a single SBD session."
	case 13:
		return "An RF link loss occurred during the SBD session."
	case 14:
		return "An IMEI protocol anomaly occurred during SBD session."
	case 15:
		return "The IMEI is prohibited from accessing the Iridium Gateway."
	default:
		return ""
	}
}

type MOPayload struct {
	IEI     byte
	Length  uint16
	Payload []byte
}

type MOLocation struct {
	IEI               byte
	Length            uint16
	LocationFlags     byte
	LatitudeDegrees   uint8
	LatitudeTHMinute  uint16
	LongitudeDegrees  uint8
	LongitudeTHMinute uint16
	CEPRadius         uint32
}

type MOConfirmation struct {
	IEI    byte
	Length uint16
	Status byte
}

func ParseSDB(raw []byte) (*IridiumSDB, error) {
	raw_len := len(raw)
	if raw_len < 3 {
		return nil, fmt.Errorf("message structure too short: %d bytes",
			len(raw))
	}

	sdb := IridiumSDB{}
	sdb.ProtocolRevision = raw[0]
	sdb.Length = binary.BigEndian.Uint16(raw[1:3])

	if (int(sdb.Length) + 3) != raw_len {
		return nil, fmt.Errorf("invalid message length (expected %d, got %d)",
			(sdb.Length + 3), raw_len)
	}

	for i := 3; i < raw_len; {
		if (i + 3) > raw_len {
			return nil, fmt.Errorf("invalid element length (at %d)",
				i)
		}
		el_iei := raw[i]
		el_len := binary.BigEndian.Uint16(raw[i+1 : i+3])

		if (i + 3 + int(el_len)) > raw_len {
			return nil, fmt.Errorf("invalid element length (at %d): %d",
				i+1, el_len)
		}

		switch el_iei {
		// MO Header IEI
		case 1:
			buf := bytes.NewReader(raw[i : i+3+int(el_len)])
			moheader := MOHeader{}
			err := binary.Read(buf, binary.BigEndian, &moheader)
			if err != nil {
				return nil, fmt.Errorf("error reading MO header (at %d): %s",
					i, err.Error())
			}
			sdb.Elements = append(sdb.Elements, moheader)

		// MO Payload IEI
		case 2:
			mopayload := MOPayload{}
			mopayload.IEI = el_iei
			mopayload.Length = el_len
			mopayload.Payload = raw[i+3 : i+3+int(el_len)]
			sdb.Elements = append(sdb.Elements, mopayload)

		// MO Location IEI
		case 3:
			buf := bytes.NewReader(raw[i : i+3+int(el_len)])
			molocation := MOLocation{}
			err := binary.Read(buf, binary.BigEndian, &molocation)
			if err != nil {
				return nil, fmt.Errorf("error reading MO location (at %d): %s",
					i, err.Error())
			}
			sdb.Elements = append(sdb.Elements, molocation)

		// MO Confirmation IEI
		case 5:
			moconfirmation := MOConfirmation{}
			moconfirmation.IEI = el_iei
			moconfirmation.Length = el_len
			moconfirmation.Status = raw[i+3]
			sdb.Elements = append(sdb.Elements, moconfirmation)

		default:
			return nil, fmt.Errorf("invalid element IEI (at %d): %d",
				i, el_iei)
		}

		i += (3 + int(el_len))
	}

	return &sdb, nil
}