import type { FriendMessage } from '../events';
import type { MsgPushContext } from '../msg-push/context';
import { decodeDatalineMsgBody, elementsFromDatalineBody } from './codec';
import { DATALINE_SELF_TER_TYPE, findDatalineDeviceByTerType } from './device-contacts';

/**
 * Incoming my-device chats reuse the private-file push type but carry a
 * different body. Rewrite the conversation peer onto the matching device
 * contact — both sides of the wire use the logged-in account number.
 */
export function tryDecodeDatalineFriendMessage(ctx: MsgPushContext): FriendMessage | null {
    if (ctx.head.msgType !== 529 || ctx.head.subType !== 7) {
        return null;
    }

    const raw = ctx.body?.msgContent;

    if (!raw || raw.length === 0) {
        return null;
    }

    const body = decodeDatalineMsgBody(raw);

    if (!body) {
        return null;
    }

    if (
        body.subCmd == null &&
        !body.header &&
        !body.generic &&
        !(body.ftn && body.ftn.length > 0)
    ) {
        return null;
    }

    const elements = elementsFromDatalineBody(body);
    const srcTer = body.header?.srcTerType ?? 0;
    const dstTer = body.header?.dstTerType ?? 0;
    const sentBySelf = srcTer === DATALINE_SELF_TER_TYPE;
    const peerTer = peerTerType(srcTer, dstTer);
    const peer = findDatalineDeviceByTerType(peerTer);
    const sequenceAuthoritative = ctx.head.ntMsgSeq > 0;

    return {
        kind: 'friend_message',
        time: ctx.head.timestamp,
        selfUin: ctx.selfUin,
        senderUin: sentBySelf ? ctx.selfUin : (peer?.uin ?? ctx.fromUin),
        senderUid: sentBySelf ? ctx.fromUid : (peer?.uid ?? ctx.fromUid),
        ...(peer ? { peerUin: peer.uin } : {}),
        msgSeq: ctx.head.sequence,
        ntMsgSeq: ctx.head.ntMsgSeq,
        clientSeq: ctx.head.sequence,
        sequenceAuthoritative,
        msgId: ctx.head.msgId & 0x7fffffff,
        elements,
        senderNick: sentBySelf ? '' : (peer?.name ?? ''),
    };
}

function peerTerType(srcTer: number, dstTer: number): number {
    if (srcTer !== DATALINE_SELF_TER_TYPE && srcTer > 0) {
        return srcTer;
    }

    if (dstTer !== DATALINE_SELF_TER_TYPE && dstTer > 0) {
        return dstTer;
    }

    return dstTer || srcTer || DATALINE_SELF_TER_TYPE;
}