diff --git a/src/game/Puzzle.cpp b/src/game/Puzzle.cpp
new file mode 100644
index 0000000..28a9a23
--- /dev/null
+++ b/src/game/Puzzle.cpp
@@ -0,0 +1,112 @@
+#include "Puzzle.h"
+#include <cassert>
+
+namespace
+{
+    static constexpr Puzzle::PuzPos Dirs[4]{
+        {-1, 0},
+        {0, -1},
+        {0, 1},
+        {1, 0},
+    };
+}
+
+namespace Puzzle
+{
+    bool PuzzleNode::HasElement(PuzzleElementType search) const
+    {
+        for (int32_t i = 0; i < Config::MaxElementsPerTile; ++i)
+        {
+            if (PlacedTypes[i] == search) return true;
+        }
+        return false;
+    }
+
+    bool PuzzleNode::IsEmpty() const
+    {
+        for (int32_t i = 0; i < Config::MaxElementsPerTile; ++i)
+        {
+            if (PlacedTypes[i] != PuzzleElementType::None) return false;
+        }
+        return true;
+    }
+
+    uint8_t PuzzleCardStack::GetRemainingCount()
+    {
+        assert(MaxAvailableCount >= UsedCount);
+        return MaxAvailableCount - UsedCount;
+    }
+
+    bool PuzzleSolver::IsPuzzleSolved(const PuzzleData& puzzle)
+    {
+        bool IsSolved = true;
+        for (uint32_t i = 0; i < puzzle.GoalPositionCount; ++i)
+        {
+        }
+        return IsSolved;
+    }
+
+    bool PuzzleSolver::IsExitSatisfied(const PuzzleData& puzzle, ElemPos pos)
+    {
+        const PuzzleNode& goalNode = puzzle.GetNodeAt(pos.Position);
+        PuzzleElementType goalType = puzzle.GetElementAt(pos);
+
+        uint32_t currentPositionQueueIdx = 0;
+        uint32_t positionQueueCount = 0;
+        PuzPos positionQueue[Config::MaxTilesInPuzzle];
+
+        positionQueue[0] = pos.Position;
+        positionQueueCount++;
+        while (positionQueueCount > 0)
+        {
+            assert(currentPositionQueueIdx < Config::MaxTilesInPuzzle);
+            PuzPos currentPos = positionQueue[currentPositionQueueIdx];
+            for (PuzPos dir : Dirs)
+            {
+                PuzPos nextPos = currentPos + dir;
+                if (IsValidGoalConnection(puzzle, nextPos, currentPos, goalType))
+                {
+                    const PuzzleNode& node = puzzle.GetNodeAt(nextPos);
+                    for (PuzzleElementType e : node.PlacedTypes)
+                    {
+                        if (IsValidSource(e, goalType))
+                        {
+                            return true;
+                        }
+                    }
+                    positionQueue[positionQueueCount] = nextPos;
+                    positionQueueCount++;
+                }
+            }
+            currentPositionQueueIdx++;
+        }
+        return false;
+    }
+
+    bool PuzzleSolver::IsValidGoalConnection(const PuzzleData& puzzle,
+                                             PuzPos flowFrom,
+                                             PuzPos flowTo,
+                                             PuzzleElementType goalType)
+    {
+        const PuzzleNode& from = puzzle.GetNodeAt(flowFrom);
+        const PuzzleNode& to = puzzle.GetNodeAt(flowTo);
+
+        if (goalType == PuzzleElementType::WaterGoal)
+        {
+            return from.HasElement(PuzzleElementType::WaterIn) || from.HasElement(PuzzleElementType::WaterChannel) ||
+                   from.HasElement(PuzzleElementType::WaterGoal);
+        }
+        else if (goalType == PuzzleElementType::ElectricGoal)
+        {
+            return from.HasElement(PuzzleElementType::ElectricIn) || from.HasElement(PuzzleElementType::ElectricGoal) ||
+                   from.IsEmpty();
+        }
+        assert(false);
+        return false;
+    }
+    bool PuzzleSolver::IsValidSource(PuzzleElementType sourceType, PuzzleElementType goalType)
+    {
+        return (sourceType == PuzzleElementType::WaterIn && goalType == PuzzleElementType::WaterGoal) ||
+               (sourceType == PuzzleElementType::ElectricIn && goalType == PuzzleElementType::ElectricGoal);
+    }
+} // namespace Puzzle
diff --git a/src/game/Puzzle.h b/src/game/Puzzle.h
new file mode 100644
index 0000000..31e8087
--- /dev/null
+++ b/src/game/Puzzle.h
@@ -0,0 +1,120 @@
+#pragma once
+#include <cstdint>
+
+namespace Puzzle
+{
+    struct Config
+    {
+        static constexpr uint32_t CardSize = 2;
+        static constexpr uint32_t NodesPerCard = CardSize * CardSize;
+        static constexpr uint32_t MaxElementsPerTile = 4;
+        static constexpr uint32_t MaxPuzzleSizeCards = 16;
+        static constexpr uint32_t MaxCardsInPuzzle = MaxPuzzleSizeCards * MaxPuzzleSizeCards;
+        static constexpr uint32_t MaxPuzzleSizeTiles = 16 * CardSize;
+        static constexpr uint32_t MaxTilesInPuzzle = MaxPuzzleSizeTiles * MaxPuzzleSizeTiles;
+        static constexpr uint32_t MaxAvailableStacks = 16;
+        static constexpr uint32_t MaxGoalPositions = 16;
+    };
+
+    struct PuzPos
+    {
+        int8_t X = 0;
+        int8_t Y = 0;
+
+        PuzPos& operator+=(const PuzPos& rhs)
+        {
+            X += rhs.X;
+            Y += rhs.Y;
+            return *this;
+        }
+
+        friend PuzPos operator+(PuzPos lhs, const PuzPos& rhs)
+        {
+            lhs += rhs;
+            return lhs;
+        }
+    };
+
+    struct ElemPos
+    {
+        PuzPos Position;
+        uint8_t ElemIdx = 0;
+    };
+
+    enum class PuzzleElementType : uint8_t
+    {
+        None,
+        WaterIn,
+        WaterGoal,
+        WaterChannel,
+        ElectricIn,
+        ElectricGoal,
+        Blocked,
+        Bridge,
+    };
+
+    struct PuzzleNode
+    {
+        PuzzleElementType PlacedTypes[Config::MaxElementsPerTile]{PuzzleElementType::None};
+
+        bool HasElement(PuzzleElementType search) const;
+        bool IsEmpty() const;
+    };
+
+    struct StaticPuzzleCard
+    {
+        PuzzleNode Nodes[Config::NodesPerCard];
+    };
+
+    struct StaticPuzzleCardHandle
+    {
+        uint16_t Idx = UINT16_MAX;
+    };
+
+    struct PlacedPuzzleCard
+    {
+        StaticPuzzleCardHandle RefCard;
+        PuzPos Position;
+        uint8_t Rotation = 0;
+        bool IsLocked = false;
+    };
+
+    struct PuzzleCardStack
+    {
+        StaticPuzzleCardHandle RefCard;
+        uint8_t MaxAvailableCount = 0;
+        uint8_t UsedCount = 0;
+
+        uint8_t GetRemainingCount();
+    };
+
+    struct PuzzleData
+    {
+        uint32_t AvailableCardCount = 0;
+        PuzzleCardStack AvailableCards[Config::MaxAvailableStacks];
+        uint32_t PlacedCardCount = 0;
+        PlacedPuzzleCard PlacedCards[Config::MaxCardsInPuzzle];
+
+        // Indexed by board position
+        PuzzleNode PlacedNodes[Config::MaxTilesInPuzzle];
+
+        uint32_t GoalPositionCount = 0;
+        ElemPos GoalPositions[Config::MaxGoalPositions];
+
+        const PuzzleNode& GetNodeAt(PuzPos pos) const;
+        PuzzleElementType GetElementAt(ElemPos pos) const;
+    };
+
+    struct PuzzleSolver
+    {
+        bool IsPuzzleSolved(const PuzzleData& puzzle);
+        bool IsExitSatisfied(const PuzzleData& puzzle, ElemPos pos);
+
+        // This assumes flowFrom is already verified to be connected.
+        bool IsValidGoalConnection(const PuzzleData& puzzle,
+                                   PuzPos flowFrom,
+                                   PuzPos flowTo,
+                                   PuzzleElementType goalType);
+        bool IsValidSource(PuzzleElementType sourceType, PuzzleElementType goalType);
+    };
+} // namespace Puzzle