Saves and loads SerializableGuids and DateTimes to a file on the devices local storage for persistent anchors

AnchorSaveFile.cs

using System;
using System.Collections.Generic;
using System.IO;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using UnityEngine;
using UnityEngine.XR.ARSubsystems;


/// <summary>
/// Saves and loads SerializableGuids and DateTimes to a file on the devices local storage.
/// </summary>
public class AnchorSaveFile
{
    readonly string m_FilePath = Path.Combine(Application.persistentDataPath, "SavedAnchorIds.json");

    bool m_Initialized;
    Awaitable m_InitializeAwaitable;
    Dictionary<SerializableGuid, DateTime> m_SavedAnchorsData = new();

    static AnchorSaveFile s_Instance;
    public static AnchorSaveFile instance
    {
        get
        {
            if (s_Instance != null)
                return s_Instance;

            s_Instance = new AnchorSaveFile();
            return s_Instance;
        }
    }

    AnchorSaveFile()
    {
        m_InitializeAwaitable = PopulateSavedAnchorIdsFromFile();
    }

    public Awaitable SaveAnchorIdAsync(SerializableGuid savedAnchorId)
    {
        return SaveAnchorIdAsync(savedAnchorId, DateTime.Now);
    }

    /// <summary>
    /// Saves a `SerializableGuid` to a file asynchronously, appending to the list of ids already saved.
    /// If no file exists or the file is unreadable, a new file is created.
    /// </summary>
    /// <param name="savedAnchorId">The `SerializableGuid` to save.</param>
    public async Awaitable SaveAnchorIdAsync(SerializableGuid savedAnchorId, DateTime dateTime)
    {
        try
        {
            if (!m_Initialized)
                await m_InitializeAwaitable;

            if (!m_SavedAnchorsData.TryAdd(savedAnchorId, dateTime))
                m_SavedAnchorsData[savedAnchorId] = dateTime;

            await WriteSavedAnchorIdsToFile();
        }
        catch (Exception e)
        {
            Debug.LogException(e);
        }
    }

    public async Awaitable EraseAnchorIdAsync(SerializableGuid savedAnchorId)
    {
        try
        {
            if (!m_Initialized)
                await m_InitializeAwaitable;

            m_SavedAnchorsData.Remove(savedAnchorId);
            await WriteSavedAnchorIdsToFile();
        }
        catch (Exception e)
        {
            Debug.LogException(e);
        }
    }

    /// <summary>
    /// Returns the set of `SerializableGuid`s from the save file.
    /// </summary>
    /// <returns>The set of `SerializableGuid`s that were saved to the file.
    /// If no file exists or the file is unreadable, an an empty set is returned.</returns>
    public async Awaitable<Dictionary<SerializableGuid, DateTime>> GetSavedAnchorsDataAsync()
    {
        if (!m_Initialized)
            await m_InitializeAwaitable;

        return m_SavedAnchorsData;
    }

    async Awaitable PopulateSavedAnchorIdsFromFile()
    {
        try
        {
            m_SavedAnchorsData.Clear();
            if (!File.Exists(m_FilePath))
                return;

            using var streamReader = File.OpenText(m_FilePath);
            using var jsonTextReader = new JsonTextReader(streamReader);

            var kvp = (JObject)await JToken.ReadFromAsync(jsonTextReader);
            foreach (var (idAsString, dateTime) in kvp)
            {
                var tokens = idAsString.Split("-");
                var low = Convert.ToUInt64(tokens[0], 16);
                var high = Convert.ToUInt64(tokens[1], 16);
                var serializableGuid = new SerializableGuid(low, high);
                m_SavedAnchorsData.Add(serializableGuid, (DateTime)dateTime);
            }
        }
        catch (Exception e)
        {
            Debug.LogException(e);
        }
        finally
        {
            m_Initialized = true;
        }
    }

    async Awaitable WriteSavedAnchorIdsToFile()
    {
        var jsonString = JsonConvert.SerializeObject(m_SavedAnchorsData, Formatting.Indented);
        await File.WriteAllTextAsync(m_FilePath, jsonString);
    }
}