run/RunPlus/SessionMessage.swift

import Foundation

struct SyncPlayPayload: Codable {
    let trackID: String
    let startUptime: TimeInterval
    let startPosition: TimeInterval
}

struct TrackInfoPayload: Codable {
    let trackID: String
    let displayName: String
}

enum SessionMessage: Codable {
    case hello
    case libraryRequest
    case trackInfo(TrackInfoPayload)
    case trackRequest(String)
    case play(SyncPlayPayload)
    case pause
    case seek(TimeInterval)
    case syncRequest(TimeInterval)
    case syncResponse(hostUptime: TimeInterval, peerUptime: TimeInterval)
    case driftCorrection(position: TimeInterval, hostUptime: TimeInterval)

    private enum CodingKeys: String, CodingKey {
        case type
        case payload
        case position
        case hostUptime
        case peerUptime
        case trackID
        case displayName
    }

    private enum MessageType: String, Codable {
        case hello
        case libraryRequest
        case trackInfo
        case trackRequest
        case play
        case pause
        case seek
        case syncRequest
        case syncResponse
        case driftCorrection
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let type = try container.decode(MessageType.self, forKey: .type)
        switch type {
        case .hello:
            self = .hello
        case .libraryRequest:
            self = .libraryRequest
        case .trackInfo:
            let payload = try container.decode(TrackInfoPayload.self, forKey: .payload)
            self = .trackInfo(payload)
        case .trackRequest:
            let trackID = try container.decode(String.self, forKey: .trackID)
            self = .trackRequest(trackID)
        case .play:
            let payload = try container.decode(SyncPlayPayload.self, forKey: .payload)
            self = .play(payload)
        case .pause:
            self = .pause
        case .seek:
            let position = try container.decode(TimeInterval.self, forKey: .position)
            self = .seek(position)
        case .syncRequest:
            let hostUptime = try container.decode(TimeInterval.self, forKey: .hostUptime)
            self = .syncRequest(hostUptime)
        case .syncResponse:
            let hostUptime = try container.decode(TimeInterval.self, forKey: .hostUptime)
            let peerUptime = try container.decode(TimeInterval.self, forKey: .peerUptime)
            self = .syncResponse(hostUptime: hostUptime, peerUptime: peerUptime)
        case .driftCorrection:
            let position = try container.decode(TimeInterval.self, forKey: .position)
            let hostUptime = try container.decode(TimeInterval.self, forKey: .hostUptime)
            self = .driftCorrection(position: position, hostUptime: hostUptime)
        }
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        switch self {
        case .hello:
            try container.encode(MessageType.hello, forKey: .type)
        case .libraryRequest:
            try container.encode(MessageType.libraryRequest, forKey: .type)
        case .trackInfo(let payload):
            try container.encode(MessageType.trackInfo, forKey: .type)
            try container.encode(payload, forKey: .payload)
        case .trackRequest(let trackID):
            try container.encode(MessageType.trackRequest, forKey: .type)
            try container.encode(trackID, forKey: .trackID)
        case .play(let payload):
            try container.encode(MessageType.play, forKey: .type)
            try container.encode(payload, forKey: .payload)
        case .pause:
            try container.encode(MessageType.pause, forKey: .type)
        case .seek(let position):
            try container.encode(MessageType.seek, forKey: .type)
            try container.encode(position, forKey: .position)
        case .syncRequest(let hostUptime):
            try container.encode(MessageType.syncRequest, forKey: .type)
            try container.encode(hostUptime, forKey: .hostUptime)
        case .syncResponse(let hostUptime, let peerUptime):
            try container.encode(MessageType.syncResponse, forKey: .type)
            try container.encode(hostUptime, forKey: .hostUptime)
            try container.encode(peerUptime, forKey: .peerUptime)
        case .driftCorrection(let position, let hostUptime):
            try container.encode(MessageType.driftCorrection, forKey: .type)
            try container.encode(position, forKey: .position)
            try container.encode(hostUptime, forKey: .hostUptime)
        }
    }
}