// @ts-check
"use strict";

/** @typedef {{t: "identity", roomId: string}} IdentityMessage
 *
 * The first message sent by the server, gives your room ID and client ID in the message itself
 */

/** @typedef {{t: "sdp", sdp: {type: RTCSdpType, sdp: string}}} SdpMessage
 *
 * Message sent by a party in webrtc negotiation
 */

/** @typedef {{t: "ice", ice: RTCIceCandidateInit}} IceMessage
 *
 * Message sent by a party in webrtc negotiation
 */

/** @typedef {{t: "partyJoins"}} PartyJoinsMessage
 *
 * When sent by the server to the hosting party: signals that a new party
 * joined to room to watch your stream.
 */

/** @typedef {{t: "joinRoom", roomId: string}} JoinRoomMessage
 *
 * When sent by the party to the server: signals wanting to leave the current
 * room and join another.
 */

/** @typedef {{t: "leaveRoom"}} LeaveRoomMessage
 *
 * Indicates that the other end has closed the connection: either a watcher
 * left, or a host closed the stream.
 */

/** @typedef {{t: "joinRoom", status: "success" | "404"}} JoinRoomResponse
 */

/**
 * @typedef {Object} ServerMessage
 * @property {string} senderId
 * @property {IdentityMessage | SdpMessage | IceMessage | PartyJoinsMessage | JoinRoomResponse  | LeaveRoomMessage} body
 */

/**
 * @typedef {Object} ClientMessage
 * @property {string | null} targetId
 * @property {SdpMessage | IceMessage | JoinRoomMessage} body
 */


/**
 * @param {unknown} x
 * @returns {x is object}
 */
export const isObj = x => typeof x === "object" || x != null;
/**
 * @param {unknown} x
 * @returns {x is string}
 */
export const isString = x => typeof x === "string" || x instanceof String;
/**
 * @param {unknown} x
 * @returns {x is array}
 */
export const isArray = Array.isArray
/**
 * @param {unknown} x
 * @returns {x is RTCSdpType}
 */
export const isRtcSdptype = x => x === "answer" || x === "offer" || x === "pranswer" || x === "rollback";
/**
 * @param {unknown} x
 * @returns {x is RTCIceCandidateInit}
 *
 * This is stupid, but according to the api all the fields are optional. I
 * might check that if the field is present it's set to a string..
 */
export const isRtcIceCandidateInit = isObj;

/**
 * @param {string} jsonStr
 * @returns {ServerMessage | null}
 */
export function decodeServerMessage(jsonStr) {
    /** @type {unknown} */
    const json = JSON.parse(jsonStr);
    if (!isObj(json)) {
        return null;
    }
    if (!("senderId" in json && isString(json.senderId))) {
        return null;
    }
    if (!("body" in json && typeof json.body === "object" && json.body != null)) {
        return null;
    }
    if (!("t" in json.body)) {
        return null;
    }
    if (json.body.t === "sdp"
        && "sdp" in json.body && isObj(json.body.sdp)
        && "type" in json.body.sdp && isRtcSdptype(json.body.sdp.type)
        && "sdp" in json.body.sdp && isString(json.body.sdp.sdp)
    ) {
        return {
            senderId: json.senderId,
            body: {
                t: json.body.t,
                sdp: {
                    type: json.body.sdp.type,
                    sdp: json.body.sdp.sdp,
                },
            },
        };
    } else if (json.body.t === "ice"
        && "ice" in json.body && isRtcIceCandidateInit(json.body.ice)
    ) {
        return {
            senderId: json.senderId,
            body: {
                t: json.body.t,
                ice: json.body.ice,
            },
        };
    } else if (json.body.t === "identity"
        && "roomId" in json.body && isString(json.body.roomId)
    ) {
        return {
            senderId: json.senderId,
            body: {
                t: json.body.t,
                roomId: json.body.roomId,
            },
        };
    } else if (json.body.t === "partyJoins") {
        return {
            senderId: json.senderId,
            body: {
                t: json.body.t,
            },
        };
    } else if (json.body.t === "joinRoom"
    && "status" in json.body && (json.body.status === "success" || json.body.status === "404")
    ) {
        return {
            senderId: json.senderId,
            body: {
                t: json.body.t,
                status: json.body.status,
            },
        };
    } else if (json.body.t === "leaveRoom") {
        return {
            senderId: json.senderId,
            body: {
                t: json.body.t,
            },
        };
    } else {
        return null;
    }
}
/**
 * @param {ClientMessage} msg
 * @returns {string}
 */
export function encodeServerMessage(msg) {
    return JSON.stringify(msg);
}