Program.cs

using Dat;
using Microsoft.EntityFrameworkCore;
using OpenLoco.Common;
using OpenLoco.Dat.FileParsing;
using OpenLoco.Definitions;
using OpenLoco.Definitions.Database;
using OpenLoco.Definitions.SourceData;
using System.Text.Json;
using System.Text.Json.Serialization;

using var db = Seed();

Console.WriteLine("done");
Console.ReadLine();

static LocoDb Seed()
{
	var builder = new DbContextOptionsBuilder<LocoDb>();
	const string connectionString = "Data Source=Q:\\Games\\Locomotion\\Server\\loco-dev.db";
	_ = builder.UseSqlite(connectionString);
	var db = new LocoDb(builder.Options);

	// Note: The database must exist before this script works
	Console.WriteLine($"Database path: {connectionString}");

	const bool seed = true;
	const bool DeleteExisting = true;

	if (seed)
	{
		SeedDb(db, DeleteExisting);
	}

	return db;
}

static void SeedDb(LocoDb db, bool deleteExisting)
{
	if (deleteExisting)
	{
		Console.WriteLine("Clearing database");
		_ = db.Users.ExecuteDelete();
		_ = db.Roles.ExecuteDelete();
		_ = db.Objects.ExecuteDelete();
		_ = db.Tags.ExecuteDelete();
		_ = db.Modpacks.ExecuteDelete();
		_ = db.Authors.ExecuteDelete();
		_ = db.Licences.ExecuteDelete();
		_ = db.SaveChanges(); // not necessary since ExecuteDelete auto-saves
	}

	const string ObjDirectory = "Q:\\Games\\Locomotion\\Server\\Objects";
	var allDatFiles = SawyerStreamUtils.GetDatFilesInDirectory(ObjDirectory);

	Console.WriteLine("Seeding");

	var jsonOptions = new JsonSerializerOptions() { WriteIndented = true, Converters = { new JsonStringEnumConverter() }, };

	// ...

	if (!db.Roles.Any())
	{
		Console.WriteLine("Seeding Roles");

		var roles = JsonSerializer.Deserialize<IEnumerable<string>>(File.ReadAllText("Q:\\Games\\Locomotion\\Server\\roles.json"), jsonOptions);
		if (roles != null)
		{
			db.AddRange(roles.Select(x => new TblRole() { Name = x }));
			_ = db.SaveChanges();
		}
	}

	// ...

	Console.WriteLine("Seeding Users");

	var users = JsonSerializer.Deserialize<IEnumerable<UserJsonRecord>>(File.ReadAllText("Q:\\Games\\Locomotion\\Server\\users.json"), jsonOptions);
	if (users != null)
	{
		db.AddRange(users.Select(x => new TblUser()
		{
			Name = x.Name,
			DisplayName = x.DisplayName,
			Author = db.Authors.SingleOrDefault(a => a.Name == x.Author),
			Roles = [.. db.Roles.Where(r => x.Roles.Contains(r.Name))],
			PasswordHashed = x.PasswordHashed,
			PasswordSalt = x.PasswordSalt
		}));
		_ = db.SaveChanges();
	}

	// ...

	if (!db.Authors.Any())
	{

		Console.WriteLine("Seeding Authors");

		var authors = JsonSerializer.Deserialize<IEnumerable<string>>(File.ReadAllText("Q:\\Games\\Locomotion\\Server\\authors.json"), jsonOptions);
		if (authors != null)
		{
			db.AddRange(authors.Select(x => new TblUser() { Name = x }));
			_ = db.SaveChanges();
		}
	}

	// ...

	if (!db.Tags.Any())
	{
		Console.WriteLine("Seeding Tags");

		var tags = JsonSerializer.Deserialize<IEnumerable<string>>(File.ReadAllText("Q:\\Games\\Locomotion\\Server\\tags.json"), jsonOptions);
		if (tags != null)
		{
			db.AddRange(tags.Select(x => new TblTag() { Name = x }));
			_ = db.SaveChanges();
		}
	}

	// ...

	if (!db.Licences.Any())
	{
		Console.WriteLine("Seeding Licences");

		var licences = JsonSerializer.Deserialize<IEnumerable<LicenceJsonRecord>>(File.ReadAllText("Q:\\Games\\Locomotion\\Server\\licences.json"), jsonOptions);
		if (licences != null)
		{
			db.AddRange(licences.Select(x => new TblLicence() { Name = x.Name, Text = x.Text }));
			_ = db.SaveChanges();
		}
	}

	// ...

	if (!db.Modpacks.Any())
	{
		Console.WriteLine("Seeding Modpacks");

		var modpacks = JsonSerializer.Deserialize<IEnumerable<ModpackJsonRecord>>(File.ReadAllText("Q:\\Games\\Locomotion\\Server\\modpacks.json"), jsonOptions);
		if (modpacks != null)
		{
			db.AddRange(modpacks.Select(x => new TblModpack() { Name = x.Name, Author = x.Author == null ? null : db.Authors.Single(a => a.Name == x.Author) }));
			_ = db.SaveChanges();
		}
	}

	// ...

	if (!db.Objects.Any())
	{
		var fileArr = allDatFiles.ToArray();
		Console.WriteLine($"Seeding {fileArr.Length} Objects");

		var progress = new Progress<float>();
		var index = ObjectIndex.LoadOrCreateIndex(ObjDirectory);

		var objectMetadata = JsonSerializer.Deserialize<IEnumerable<ObjectMetadata>>(File.ReadAllText("Q:\\Games\\Locomotion\\Server\\objectMetadata.json"), jsonOptions);
		var objectMetadataDict = objectMetadata!.ToDictionary(x => (x.ObjectName, x.Checksum), x => x);

		var gameReleaseDate = new DateTimeOffset(2004, 09, 07, 0, 0, 0, TimeSpan.Zero);

		foreach (var objIndex in index.Objects.DistinctBy(x => (x.ObjectName, x.Checksum)))
		{
			var metadataKey = (objIndex.ObjectName, objIndex.Checksum);
			if (!objectMetadataDict.TryGetValue(metadataKey, out var meta))
			{ }

			var fullPath = Path.Combine(ObjDirectory, objIndex.Filename);
			var creationTime = objIndex.IsVanilla ? gameReleaseDate : File.GetLastWriteTimeUtc(fullPath); // this is the "Modified" time as shown in Windows

			var authors = meta?.Authors == null ? null : db.Authors.Where(x => meta.Authors.Contains(x.Name)).ToList();
			var tags = meta?.Tags == null ? null : db.Tags.Where(x => meta.Tags.Contains(x.Name)).ToList();
			var modpacks = meta?.Modpacks == null ? null : db.Modpacks.Where(x => meta.Modpacks.Contains(x.Name)).ToList();
			var licence = meta?.Licence == null ? null : db.Licences.Where(x => x.Name == meta.Licence).First();

			var tblLocoObject = new TblLocoObject()
			{
				Name = $"{objIndex.ObjectName}_{objIndex.Checksum}",  // same as server upload name
				PathOnDisk = objIndex.Filename.Replace('\\', '/'), // make the path linux-compatible
				OriginalName = objIndex.ObjectName,
				OriginalChecksum = objIndex.Checksum,
				IsVanilla = objIndex.IsVanilla,
				ObjectType = objIndex.ObjectType,
				VehicleType = objIndex.VehicleType,
				Description = meta?.Description,
				Authors = authors ?? [],
				CreationDate = creationTime,
				LastEditDate = null,
				UploadDate = DateTimeOffset.Now,
				Tags = tags ?? [],
				Modpacks = modpacks ?? [],
				Availability = ObjectAvailability.NewGames,
				Licence = licence,
			};

			_ = db.Add(tblLocoObject);
		}

		_ = db.SaveChanges();
	}

	Console.WriteLine("Finished seeding");
}

static Dictionary<(string ObjectName, string Checksum), GlenDbData2> LoadMetadata(string metadataFile)
{
	if (!File.Exists(metadataFile))
	{
		return [];
	}

	var text = File.ReadAllText(metadataFile);
	var metadata = JsonSerializer.Deserialize<GlenDBSchema2>(text).data;
	var kvList = metadata.GroupBy(x => (x.ObjectName, uint32_t_LittleToBigEndian(x.Checksum)));
	return kvList.ToDictionary(x => x.Key, x => x.First());
}

static string? uint32_t_LittleToBigEndian(string input)
{
	var r = new string(input.Chunk(2).Reverse().SelectMany(x => x).ToArray());
	return Convert.ToUInt32(r, 16).ToString();
}