nd-wfc/demos/random_selector_example.cpp

/**
 * @brief Example demonstrating custom random selectors in WFC
 *
 * This example shows how to use different random selection strategies
 * in the Wave Function Collapse algorithm, including:
 * - Default constexpr random selector
 * - Advanced random selector with std::mt19937
 * - Custom lambda-based selectors
 */

#include <iostream>
#include <vector>
#include <array>
#include <random>

#include "../include/nd-wfc/wfc.hpp"

// Simple test world for demonstration
struct SimpleWorld {
    using ValueType = int;
    std::vector<int> data;
    size_t grid_size;

    SimpleWorld(size_t size) : data(size * size, 0), grid_size(size) {}
    size_t size() const { return data.size(); }
    void setValue(size_t id, int value) { data[id] = value; }
    int getValue(size_t id) const { return data[id]; }

    void print() const {
        for (size_t i = 0; i < grid_size; ++i) {
            for (size_t j = 0; j < grid_size; ++j) {
                std::cout << data[i * grid_size + j] << " ";
            }
            std::cout << std::endl;
        }
    }
};

int main() {
    std::cout << "=== WFC Random Selector Examples ===\n\n";

    // Example 1: Using the default constexpr random selector
    std::cout << "1. Default Random Selector (constexpr-friendly):\n";
    {
        WFC::DefaultRandomSelector<int> selector(0x12345678);

        // Test with some sample values
        std::array<int, 4> values = {1, 2, 3, 4};
        std::span<const int> span(values.data(), values.size());

        std::cout << "Possible values: ";
        for (int v : values) std::cout << v << " ";
        std::cout << "\nSelected indices: ";

        for (int i = 0; i < 8; ++i) {
            size_t index = selector(span);
            std::cout << index << "(" << values[index] << ") ";
        }
        std::cout << "\n\n";
    }

    // Example 2: Using the advanced random selector
    std::cout << "2. Advanced Random Selector (std::mt19937):\n";
    {
        std::mt19937 rng(54321);
        WFC::AdvancedRandomSelector<int> selector(rng);

        std::array<int, 5> values = {10, 20, 30, 40, 50};
        std::span<const int> span(values.data(), values.size());

        std::cout << "Possible values: ";
        for (int v : values) std::cout << v << " ";
        std::cout << "\nSelected values: ";

        for (int i = 0; i < 10; ++i) {
            size_t index = selector(span);
            std::cout << values[index] << " ";
        }
        std::cout << "\n\n";
    }

    // Example 3: Custom lambda selector that always picks the first element
    std::cout << "3. Custom Lambda Selector (always first):\n";
    {
        auto firstSelector = [](std::span<const int> values) -> size_t {
            return 0; // Always pick first
        };

        std::array<int, 3> values = {100, 200, 300};
        std::span<const int> span(values.data(), values.size());

        std::cout << "Possible values: ";
        for (int v : values) std::cout << v << " ";
        std::cout << "\nSelected values: ";

        for (int i = 0; i < 5; ++i) {
            size_t index = firstSelector(span);
            std::cout << values[index] << " ";
        }
        std::cout << "\n\n";
    }

    // Example 4: Stateful lambda selector with captured variables
    std::cout << "4. Stateful Lambda Selector (round-robin):\n";
    {
        int callCount = 0;
        auto roundRobinSelector = [&callCount](std::span<const int> values) mutable -> size_t {
            return callCount++ % values.size();
        };

        std::array<int, 3> values = {1, 2, 3};
        std::span<const int> span(values.data(), values.size());

        std::cout << "Possible values: ";
        for (int v : values) std::cout << v << " ";
        std::cout << "\nRound-robin selection: ";

        for (int i = 0; i < 9; ++i) {
            size_t index = roundRobinSelector(span);
            std::cout << values[index] << " ";
        }
        std::cout << "\n\n";
    }

    // Example 5: Custom selector with probability weighting
    std::cout << "5. Weighted Random Selector:\n";
    {
        std::mt19937 rng(99999);
        auto weightedSelector = [&rng](std::span<const int> values) -> size_t {
            // Simple weighted selection - favor earlier indices
            std::vector<double> weights;
            for (size_t i = 0; i < values.size(); ++i) {
                weights.push_back(1.0 / (i + 1.0)); // Higher weight for lower indices
            }

            std::discrete_distribution<size_t> dist(weights.begin(), weights.end());
            return dist(rng);
        };

        std::array<int, 4> values = {1, 2, 3, 4};
        std::span<const int> span(values.data(), values.size());

        std::cout << "Possible values: ";
        for (int v : values) std::cout << v << " ";
        std::cout << "\nWeighted selection ( favors lower values): ";

        for (int i = 0; i < 12; ++i) {
            size_t index = weightedSelector(span);
            std::cout << values[index] << " ";
        }
        std::cout << "\n\n";
    }

    // Example 6: Integration with WFC Builder
    std::cout << "6. WFC Builder Integration:\n";
    {
        // Define a simple WFC setup with custom random selector
        using VariableMap = WFC::VariableIDMap<int, 0, 1, 2, 3>;

        // Using default random selector
        using DefaultWFC = WFC::Builder<SimpleWorld, int, VariableMap>
            ::SetRandomSelector<WFC::DefaultRandomSelector<int>>
            ::Build;

        // Using advanced random selector
        using AdvancedWFC = WFC::Builder<SimpleWorld, int, VariableMap>
            ::SetRandomSelector<WFC::AdvancedRandomSelector<int>>
            ::Build;

        // Note: Lambda types cannot be used directly as template parameters
        // Instead, you would create a custom selector class:
        // class CustomSelector {
        // public:
        //     size_t operator()(std::span<const int> values) const {
        //         return values.size() > 1 ? 1 : 0;
        //     }
        // };
        // using CustomWFC = WFC::Builder<SimpleWorld, int, VariableMap>
        //     ::SetRandomSelector<CustomSelector>
        //     ::Build;

        std::cout << "Successfully created WFC types with different random selectors:\n";
        std::cout << "- DefaultWFC with DefaultRandomSelector\n";
        std::cout << "- AdvancedWFC with AdvancedRandomSelector\n";
        std::cout << "- Custom selector classes can be created for lambda-like behavior\n";
    }

    std::cout << "\n=== Examples completed successfully! ===\n";

    return 0;
}