diff --git a/Rotationator/GambitStageInfo.cs b/Rotationator/GambitStageInfo.cs
new file mode 100644
index 0000000..a4044cd
--- /dev/null
+++ b/Rotationator/GambitStageInfo.cs
@@ -0,0 +1,37 @@
+namespace Rotationator;
+
+public class GambitStageInfo
+{
+    public VersusRule Rule
+    {
+        get;
+        set;
+    }
+
+    public List<int> Stages
+    {
+        get;
+        set;
+    }
+
+    public GambitStageInfo()
+    {
+        Rule = VersusRule.None;
+        Stages = new List<int>();
+    }
+
+    public dynamic ToByamlStagesList()
+    {
+        List<dynamic> byamlStages = new List<dynamic>();
+        
+        foreach (int id in Stages)
+        {
+            byamlStages.Add(new Dictionary<string, dynamic>()
+            {
+                { "MapID", id }
+            });
+        }
+
+        return byamlStages;
+    }
+}
\ No newline at end of file
diff --git a/Rotationator/GambitVersusPhase.cs b/Rotationator/GambitVersusPhase.cs
new file mode 100644
index 0000000..e1c2b1d
--- /dev/null
+++ b/Rotationator/GambitVersusPhase.cs
@@ -0,0 +1,73 @@
+namespace Rotationator;
+
+public class GambitVersusPhase
+{
+    public int Length
+    {
+        get;
+        set;
+    }
+
+    public GambitStageInfo RegularInfo
+    {
+        get;
+        set;
+    }
+
+    public GambitStageInfo GachiInfo
+    {
+        get;
+        set;
+    }
+    
+    public GambitVersusPhase()
+    {
+        Length = 0;
+        RegularInfo = new GambitStageInfo();
+        GachiInfo = new GambitStageInfo();
+    }
+
+    public GambitVersusPhase(dynamic byamlPhase)
+    {
+        Length = byamlPhase["Time"];
+        
+        dynamic byamlRegularStages = byamlPhase["RegularStages"];
+
+        RegularInfo = new GambitStageInfo()
+        {
+            Rule = VersusRuleUtil.FromEnumString(byamlPhase["RegularRule"]),
+            Stages = new List<int>()
+            {
+                byamlRegularStages[0]["MapID"],
+                byamlRegularStages[1]["MapID"]
+            }
+        };
+        
+        dynamic byamlGachiStages = byamlPhase["GachiStages"];
+
+        GachiInfo = new GambitStageInfo()
+        {
+            Rule = VersusRuleUtil.FromEnumString(byamlPhase["GachiRule"]),
+            Stages = new List<int>()
+            {
+                byamlGachiStages[0]["MapID"],
+                byamlGachiStages[1]["MapID"]
+            }
+        };
+    }
+    
+    public dynamic ToByamlPhase()
+    {
+        dynamic byamlPhase = new Dictionary<string, dynamic>();
+
+        byamlPhase["Time"] = Length;
+
+        byamlPhase["GachiRule"] = GachiInfo.Rule.ToEnumString();
+        byamlPhase["GachiStages"] = GachiInfo.ToByamlStagesList();
+        
+        byamlPhase["RegularRule"] = RegularInfo.Rule.ToEnumString();
+        byamlPhase["RegularStages"] = RegularInfo.ToByamlStagesList();
+
+        return byamlPhase;
+    }
+}
\ No newline at end of file
diff --git a/Rotationator/Program.cs b/Rotationator/Program.cs
index e5dff12..9520f2b 100644
--- a/Rotationator/Program.cs
+++ b/Rotationator/Program.cs
@@ -1,3 +1,273 @@
-// See https://aka.ms/new-console-template for more information
+using System.CommandLine;
+using System.Text.Json;
+using OatmealDome.BinaryData;
+using OatmealDome.NinLib.Byaml;
+using OatmealDome.NinLib.Byaml.Dynamic;
+using Rotationator;
 
-Console.WriteLine("Hello, World!");
\ No newline at end of file
+//
+// Constants
+//
+
+const int maximumPhases = 192; // TODO correct?
+
+Dictionary<VersusRule, List<int>> bannedStages = new Dictionary<VersusRule, List<int>>()
+{
+    {
+        VersusRule.Paint,
+        new List<int>() // nothing banned
+    },
+    {
+        VersusRule.Goal,
+        new List<int>()
+        {
+            2, // Saltspray Rig
+            4, // Blackbelly Skatepark
+            14 // Piranha Pit
+        }
+    },
+    {
+        VersusRule.Area,
+        new List<int>() // nothing banned
+    },
+    {
+        VersusRule.Lift,
+        new List<int>()
+        {
+            2, // Saltspray Rig
+            6, // Port Mackerel
+        }
+    }
+};
+
+List<int> defaultStagePool = new List<int>()
+{
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
+};
+
+List<VersusRule> defaultGachiRulePool = new List<VersusRule>()
+{
+    VersusRule.Goal,
+    VersusRule.Area,
+    VersusRule.Lift
+};
+
+Random random = new Random();
+
+//
+// Command handling
+//
+
+Argument<string> lastByamlArg = new Argument<string>("lastByaml", "The last VSSetting BYAML file.");
+
+Argument<string> outputByamlArg = new Argument<string>("lastByaml", "The output VSSetting BYAML file.");
+
+Command command = new RootCommand("Generates a new VSSetting BYAMl file.")
+{
+    lastByamlArg,
+    outputByamlArg
+};
+
+command.SetHandler((lastPath, outPath) => Run(lastPath, outPath), lastByamlArg, outputByamlArg);
+
+command.Invoke(args);
+
+//
+// Entrypoint
+//
+
+void Run(string lastByamlPath, string outputByamlPath)
+{
+    Console.WriteLine("run");
+    
+    dynamic lastByaml = ByamlFile.Load(lastByamlPath);
+    
+    DateTime lastBaseTime = DateTime.Parse(lastByaml["DateTime"]).ToUniversalTime();
+    List<dynamic> lastPhases = lastByaml["Phases"];
+    
+    //
+    // Find phase start point
+    //
+    
+    DateTime loopTime = lastBaseTime;
+    DateTime referenceNow = DateTime.UtcNow;
+
+    int lastPhasesStartIdx = -1;
+
+    for (int i = 0; i < lastPhases.Count; i++)
+    {
+        Dictionary<string, dynamic> phase = lastPhases[i];
+
+        DateTime phaseEndTime = loopTime.AddHours((int)phase["Time"]);
+
+        if (referenceNow >= loopTime && phaseEndTime > referenceNow)
+        {
+            lastPhasesStartIdx = i;
+            break;
+        }
+
+        loopTime = phaseEndTime;
+    }
+
+    DateTime baseTime;
+    List<GambitVersusPhase> currentPhases;
+
+    if (lastPhasesStartIdx != -1)
+    {
+        baseTime = loopTime;
+        currentPhases = lastPhases.Skip(lastPhasesStartIdx).Select(p => new GambitVersusPhase(p)).ToList();
+    }
+    else
+    {
+        throw new NotImplementedException("not supported yet");
+    }
+
+    // The last phase is set to 10 years, so correct this to the correct phase length.
+    currentPhases.Last().Length = 4;
+    
+    //
+    // Generate new phases to fill out the schedule
+    //
+
+    List<VersusRule> gachiRulePool = new List<VersusRule>();
+    Dictionary<VersusRule, List<int>> stagePools = new Dictionary<VersusRule, List<int>>()
+    {
+        { VersusRule.Paint, new List<int>() },
+        { VersusRule.Goal, new List<int>() },
+        { VersusRule.Area, new List<int>() },
+        { VersusRule.Lift, new List<int>() }
+    };
+
+    for (int i = currentPhases.Count; i < maximumPhases; i++)
+    {
+        GambitVersusPhase currentPhase = new GambitVersusPhase();
+        GambitVersusPhase lastPhase = i != 0 ? currentPhases[i - 1] : new GambitVersusPhase();
+        
+        VersusRule gachiRule = PickGachiRule(currentPhase.GachiInfo, lastPhase.GachiInfo, gachiRulePool);
+
+        currentPhase.RegularInfo.Rule = VersusRule.Paint;
+        currentPhase.RegularInfo.Stages.Add(PickStage(currentPhase, lastPhase, VersusRule.Paint,
+            stagePools[VersusRule.Paint]));
+        currentPhase.RegularInfo.Stages.Add(PickStage(currentPhase, lastPhase, VersusRule.Paint,
+            stagePools[VersusRule.Paint]));
+        currentPhase.RegularInfo.Stages.Sort();
+        
+        currentPhase.GachiInfo.Rule = gachiRule;
+        currentPhase.GachiInfo.Stages.Add(PickStage(currentPhase, lastPhase, gachiRule, stagePools[gachiRule]));
+        currentPhase.GachiInfo.Stages.Add(PickStage(currentPhase, lastPhase, gachiRule, stagePools[gachiRule]));
+        currentPhase.GachiInfo.Stages.Sort();
+        
+        currentPhase.Length = 4;
+        
+        currentPhases.Add(currentPhase);
+    }
+    
+    //
+    // Write BYAML
+    //
+    
+    // As a fallback in case the schedule isn't updated in time, make the last phase 10 years long.
+    currentPhases.Last().Length = 24 * 365 * 10;
+
+    // Set the new base DateTime (this is usually in the JST time zone, but it accepts UTC time as well).
+    lastByaml["DateTime"] = baseTime.ToString("yyyy-MM-dd'T'HH:mm:ssK");
+
+    // Set the new phases.
+    lastByaml["Phases"] = currentPhases.Select(p => p.ToByamlPhase());
+    
+    // Add some metadata about this BYAML file and how it was built.
+    lastByaml["ByamlInfo"] = new Dictionary<string, dynamic>()
+    {
+        { "Generator", "Rotationator 1" },
+        { "GenerationTime", referenceNow.ToString("O") },
+        { "BaseByamlStartTime", baseTime.ToString("O") },
+    };
+    
+    ByamlFile.Save(outputByamlPath, lastByaml, new ByamlSerializerSettings()
+    {
+        ByteOrder = ByteOrder.BigEndian,
+        SupportsBinaryData = false,
+        Version = ByamlVersion.One
+    });
+
+    File.WriteAllText(outputByamlPath + ".json", JsonSerializer.Serialize(lastByaml, new JsonSerializerOptions()
+    {
+        WriteIndented = true
+    }));
+}
+
+//
+// Utility function to pick a random element from a pool.
+//
+
+T GetRandomElementFromPool<T>(List<T> pool, Func<T, bool> validityChecker)
+{
+    T element;
+    
+    do
+    {
+        element = pool[random.Next(0, pool.Count)];
+    } while (!validityChecker(element));
+    
+    pool.Remove(element);
+
+    return element;
+}
+
+//
+// Random stage + rule pickers.
+//
+
+VersusRule PickGachiRule(GambitStageInfo stageInfo, GambitStageInfo lastStageInfo, List<VersusRule> pool)
+{
+    if (pool.Count == 0)
+    {
+        pool.AddRange(defaultGachiRulePool);
+    }
+
+    return GetRandomElementFromPool(pool, rule => rule != lastStageInfo.Rule);
+}
+
+int PickStage(GambitVersusPhase phase, GambitVersusPhase lastPhase, VersusRule rule, List<int> pool)
+{
+    List<int> bannedStagesForRule = bannedStages[rule];
+
+    if (pool.Count == 0)
+    {
+        pool.AddRange(defaultStagePool.Except(bannedStagesForRule));
+    }
+
+    bool IsStageValid(int stageId)
+    {
+        // Don't pick this stage if it's already used in this phase.
+        if (phase.RegularInfo.Stages.Contains(stageId) || phase.GachiInfo.Stages.Contains(stageId))
+        {
+            return false;
+        }
+
+        // Don't pick this stage if it's present in the last phase.
+        if (lastPhase.RegularInfo.Stages.Contains(stageId) || lastPhase.GachiInfo.Stages.Contains(stageId))
+        {
+            return false;
+        }
+
+        return true;
+    }
+
+    // Check if all of our options are invalid.
+    if (pool.All(i => !IsStageValid(i)))
+    {
+        // If so, pick a random stage from the default pool, excluding:
+        // - the current phase's stages (in both Regular and Gachi)
+        // - the last phase's stages (in both Regular and Gachi)
+        // - all banned stages for this rule
+        pool = defaultStagePool.Except(phase.RegularInfo.Stages)
+            .Except(phase.GachiInfo.Stages)
+            .Except(lastPhase.RegularInfo.Stages)
+            .Except(lastPhase.GachiInfo.Stages)
+            .Except(bannedStagesForRule)
+            .ToList();
+    }
+
+    return GetRandomElementFromPool(pool, IsStageValid);
+}
\ No newline at end of file
diff --git a/Rotationator/VersusRule.cs b/Rotationator/VersusRule.cs
new file mode 100644
index 0000000..f574560
--- /dev/null
+++ b/Rotationator/VersusRule.cs
@@ -0,0 +1,26 @@
+namespace Rotationator;
+
+public enum VersusRule
+{
+    None,
+    
+    /// <summary>
+    /// Turf War
+    /// </summary>
+    Paint,
+    
+    /// <summary>
+    /// Rainmaker
+    /// </summary>
+    Goal,
+    
+    /// <summary>
+    /// Splat Zones
+    /// </summary>
+    Area,
+    
+    /// <summary>
+    /// Tower Control
+    /// </summary>
+    Lift
+}
\ No newline at end of file
diff --git a/Rotationator/VersusRuleUtil.cs b/Rotationator/VersusRuleUtil.cs
new file mode 100644
index 0000000..718be5d
--- /dev/null
+++ b/Rotationator/VersusRuleUtil.cs
@@ -0,0 +1,40 @@
+namespace Rotationator;
+
+public static class VersusRuleUtil
+{
+    public static VersusRule FromEnumString(string str)
+    {
+        switch (str)
+        {
+            case "cPnt":
+                return VersusRule.Paint;
+            case "cVgl":
+                return VersusRule.Goal;
+            case "cVar":
+                return VersusRule.Area;
+            case "cVlf":
+                return VersusRule.Lift;
+            default: // "cNone"
+                return VersusRule.None;
+        }
+    }
+
+    public static string ToEnumString(this VersusRule rule)
+    {
+        switch (rule)
+        {
+            case VersusRule.None:
+                return "cNone";
+            case VersusRule.Paint:
+                return "cPnt";
+            case VersusRule.Goal:
+                return "cVgl";
+            case VersusRule.Area:
+                return "cVar";
+            case VersusRule.Lift:
+                return "cVlf";
+            default:
+                throw new ArgumentOutOfRangeException(nameof(rule), "VersusRule not supported");
+        }
+    }
+}
\ No newline at end of file