factorio-calc/tests/FactorioCalc.Tests/SolverBugFixTests.cs

using FactorioCalc.Domain;
using FactorioCalc.Solver;
using Xunit;

namespace FactorioCalc.Tests;

/// <summary>
/// Regression tests for critical bugs fixed in ProductionSolver.
/// </summary>
public class SolverBugFixTests
{
    // --- Bug #1: mainProduct should filter by target resourceId, not .First() ---

    [Fact]
    public void Solve_MultiProductRecipe_UsesCorrectProduct()
    {
        // Simulate a recipe that produces multiple products (like oil refining)
        var resources = new Dictionary<int, Resource>
        {
            { 1, new Resource(1, "Crude Oil") },
            { 2, new Resource(2, "Light Oil") },
            { 3, new Resource(3, "Heavy Oil") },
        };
        var machines = new Dictionary<int, Machine>
        {
            { 1, new Machine(1, "Chemical Plant", 0.5, 6.0, 4, new[] { "advanced-crafting" }) },
        };

        // One recipe produces BOTH Light Oil and Heavy Oil
        var recipes = new Dictionary<int, Recipe>
        {
            {
                1, new Recipe(1, "Oil Refining", "advanced-crafting", 4.0, "advanced-crafting",
                    new[] { new Ingredient(1, 1) },
                    new[] { new Product(3, 1), new Product(2, 1) })  // Heavy Oil first, Light Oil second
            },
        };

        var repo = new TestRepository(recipes, resources, machines, new Dictionary<int, Module>());
        var solver = new ProductionSolver(repo);

        // Target Light Oil (resourceId=2) — it's the SECOND product in the list
        var targets = new[] { new ProductionTarget(2, 10) };
        var result = solver.Solve(targets);

        Assert.Single(result.Executions);
        // Should not throw — the solver correctly finds the matching product
    }

    // --- Bug #2: DFS visited should not block recalculation for double targets ---

    [Fact]
    public void Solve_DoubleTargetsForResource_AggregatesDemand()
    {
        var resources = new Dictionary<int, Resource>
        {
            { 1, new Resource(1, "Iron Ore") },
            { 7, new Resource(7, "Iron Plate") },
            { 9, new Resource(9, "Steel Plate") },
            { 5, new Resource(5, "Coal") },
        };
        var machines = new Dictionary<int, Machine>
        {
            { 3, new Machine(3, "Smelter", 0.5, 3.0, 2, new[] { "smelting" }) },
        };
        var recipes = new Dictionary<int, Recipe>
        {
            {
                1, new Recipe(1, "Iron Plate", "smelting", 3.0, "smelting",
                    new[] { new Ingredient(1, 1) },
                    new[] { new Product(7, 1) })
            },
            {
                2, new Recipe(2, "Steel Plate", "smelting", 5.0, "smelting",
                    new[] { new Ingredient(7, 2), new Ingredient(5, 1) },
                    new[] { new Product(9, 1) })
            },
        };

        var repo = new TestRepository(recipes, resources, machines, new Dictionary<int, Module>());
        var solver = new ProductionSolver(repo);

        // Two targets that both need Iron Plate: Steel Plate (needs 2/sec × 2 iron plate) + direct 5/sec
        var targets = new[]
        {
            new ProductionTarget(9, 2),  // Steel Plate → needs 4 Iron Plate/sec
            new ProductionTarget(7, 5),  // Iron Plate direct → needs 5 more/sec
        };
        var result = solver.Solve(targets);

        // Should have both Steel Plate and Iron Plate executions
        Assert.Equal(2, result.Executions.Count);

        var ironPlateExec = result.Executions.First(e => e.RecipeId == 1);
        // Iron Plate should account for BOTH demands (4 from steel + 5 direct = 9 total)
        Assert.True(ironPlateExec.MachineCount >= 9,
            $"Expected at least 9 machines for Iron Plate (demand=9/sec), got {ironPlateExec.MachineCount}");
    }

    // --- Bug #3: effectiveSpeed should not go to zero with heavy productivity modules ---

    [Fact]
    public void Solve_HeavyProductivityModules_DoesNotDivideByZero()
    {
        var resources = new Dictionary<int, Resource>
        {
            { 1, new Resource(1, "Iron Ore") },
            { 7, new Resource(7, "Iron Plate") },
        };
        var machines = new Dictionary<int, Machine>
        {
            { 3, new Machine(3, "Smelter", 0.5, 3.0, 2, new[] { "smelting" }) },
        };
        var recipes = new Dictionary<int, Recipe>
        {
            {
                1, new Recipe(1, "Iron Plate", "smelting", 3.0, "smelting",
                    new[] { new Ingredient(1, 1) },
                    new[] { new Product(7, 1) })
            },
        };

        // Extreme productivity modules: -20% speed × 4 slots = -80% total speed
        var extremeModules = new[]
        {
            new Module(1, "Prod Mod 3", ModuleType.Productivity, -0.20, 0.30, -0.15),
            new Module(2, "Prod Mod 3", ModuleType.Productivity, -0.20, 0.30, -0.15),
            new Module(3, "Prod Mod 3", ModuleType.Productivity, -0.20, 0.30, -0.15),
            new Module(4, "Prod Mod 3", ModuleType.Productivity, -0.20, 0.30, -0.15),
        };

        var moduleDict = new Dictionary<int, Module>();
        for (var i = 0; i < extremeModules.Length; i++)
            moduleDict[i + 1] = extremeModules[i];
        var repo = new TestRepository(recipes, resources, machines, moduleDict);
        var solver = new ProductionSolver(repo);

        var targets = new[] { new ProductionTarget(7, 10) };

        // Should NOT throw DivideByZeroException
        var result = solver.SolveWithModules(targets, extremeModules);

        Assert.Single(result.Executions);
        var exec = result.Executions.First();
        // Speed should be clamped to minimum (0.05), not negative or zero
        Assert.True(exec.EffectiveSpeed >= 0.05, $"EffectiveSpeed {exec.EffectiveSpeed} below minimum");
        Assert.True(exec.MachineCount > 0 && exec.MachineCount < int.MaxValue,
            $"MachineCount {exec.MachineCount} is unreasonable");
    }

    [Fact]
    public void Solve_ProductivityModules_IncreasesOutput()
    {
        var resources = new Dictionary<int, Resource>
        {
            { 1, new Resource(1, "Iron Ore") },
            { 7, new Resource(7, "Iron Plate") },
        };
        var machines = new Dictionary<int, Machine>
        {
            { 3, new Machine(3, "Smelter", 0.5, 3.0, 2, new[] { "smelting" }) },
        };
        var recipes = new Dictionary<int, Recipe>
        {
            {
                1, new Recipe(1, "Iron Plate", "smelting", 3.0, "smelting",
                    new[] { new Ingredient(1, 1) },
                    new[] { new Product(7, 1) })
            },
        };

        var prodModule = new Module(1, "Prod Mod 1", ModuleType.Productivity, -0.10, 0.10, -0.05);

        var repo = new TestRepository(recipes, resources, machines, new Dictionary<int, Module> { { 1, prodModule } });
        var solver = new ProductionSolver(repo);

        var targets = new[] { new ProductionTarget(7, 10) };

        var resultNoModules = solver.Solve(targets);
        var resultWithModules = solver.SolveWithModules(targets, new[] { prodModule });

        var execNoModules = resultNoModules.Executions.First();
        var execWithModules = resultWithModules.Executions.First();

        // With productivity, we need fewer machines because output per cycle is higher
        // (even though speed is lower, the +10% output compensates)
        Assert.True(execWithModules.EffectiveProductivity > 0, "Productivity bonus should be positive");
    }
}