1 files changed, 39 insertions, 0 deletions
diff --git a/src/Godosa.Core/Runs/RunFlags.cs b/src/Godosa.Core/Runs/RunFlags.cs
new file mode 100644
index 0000000..1eca433
--- /dev/null
+++ b/src/Godosa.Core/Runs/RunFlags.cs
@@ -0,0 +1,39 @@
+using System.Globalization;
+
+namespace Godosa.Core.Runs;
+
+/// <summary>Shared run flags: <c>--deterministic [seed]</c> (fixed step, seeded streams), <c>--digest [every=N]</c>
+/// (state hash lines), <c>--headless</c> (no window; implies deterministic). <see cref="Seed"/> null = the game's default.</summary>
+public sealed record RunFlags(bool Deterministic = false, ulong? Seed = null, bool Digest = false, int DigestEvery = 0, bool Headless = false)
+{
+    public ulong SeedOr(ulong fallback) => Seed ?? fallback;
+
+    /// <summary>Consumes the run flag at <paramref name="i"/> (and its optional value, advancing <paramref name="i"/>);
+    /// false when <c>args[i]</c> is no run flag.</summary>
+    public static bool TryTake(IReadOnlyList<string> args, ref int i, ref RunFlags flags)
+    {
+        string? next = i + 1 < args.Count ? args[i + 1] : null;
+        switch (args[i])
+        {
+            case "--deterministic":
+                flags = flags with { Deterministic = true };
+                if (next != null && ulong.TryParse(next, NumberStyles.None, CultureInfo.InvariantCulture, out var seed))
+                    (flags, i) = (flags with { Seed = seed }, i + 1);
+                return true;
+            case "--digest":
+                flags = flags with { Digest = true };
+                if (next != null && next.StartsWith("every=", StringComparison.Ordinal))
+                {
+                    if (!int.TryParse(next.AsSpan(6), NumberStyles.None, CultureInfo.InvariantCulture, out var every) || every < 1)
+                        throw new ArgumentException($"--digest {next}: every=N needs N ≥ 1");
+                    (flags, i) = (flags with { DigestEvery = every }, i + 1);
+                }
+                return true;
+            case "--headless":
+                flags = flags with { Headless = true, Deterministic = true };
+                return true;
+            default:
+                return false;
+        }
+    }
+}