using ZB.MOM.WW.ScadaBridge.Commons.Entities.Templates;

namespace ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests;

public class CycleDetectorTests
{
    // ========================================================================
    // Inheritance cycle detection
    // ========================================================================

    /// <summary>Verifies that self-inheritance is reported as a cycle.</summary>
    [Fact]
    public void DetectInheritanceCycle_SelfInheritance_ReturnsCycle()
    {
        var template = new Template("A") { Id = 1 };
        var all = new List<Template> { template };

        var result = CycleDetector.DetectInheritanceCycle(1, 1, all);

        Assert.NotNull(result);
        Assert.Contains("itself", result);
    }

    /// <summary>Verifies that a direct inheritance cycle is reported.</summary>
    [Fact]
    public void DetectInheritanceCycle_DirectCycle_ReturnsCycle()
    {
        var templateA = new Template("A") { Id = 1, ParentTemplateId = null };
        var templateB = new Template("B") { Id = 2, ParentTemplateId = 1 };
        var all = new List<Template> { templateA, templateB };

        // A tries to inherit from B (B already inherits from A)
        var result = CycleDetector.DetectInheritanceCycle(1, 2, all);

        Assert.NotNull(result);
        Assert.Contains("cycle", result, StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>Verifies that a three-node inheritance cycle is reported.</summary>
    [Fact]
    public void DetectInheritanceCycle_ThreeNodeCycle_ReturnsCycle()
    {
        var templateA = new Template("A") { Id = 1, ParentTemplateId = null };
        var templateB = new Template("B") { Id = 2, ParentTemplateId = 1 };
        var templateC = new Template("C") { Id = 3, ParentTemplateId = 2 };
        var all = new List<Template> { templateA, templateB, templateC };

        // A tries to inherit from C (C -> B -> A creates a cycle)
        var result = CycleDetector.DetectInheritanceCycle(1, 3, all);

        Assert.NotNull(result);
        Assert.Contains("cycle", result, StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>Verifies that an inheritance chain with no cycle returns null.</summary>
    [Fact]
    public void DetectInheritanceCycle_NoCycle_ReturnsNull()
    {
        var templateA = new Template("A") { Id = 1, ParentTemplateId = null };
        var templateB = new Template("B") { Id = 2, ParentTemplateId = null };
        var all = new List<Template> { templateA, templateB };

        var result = CycleDetector.DetectInheritanceCycle(2, 1, all);

        Assert.Null(result);
    }

    // ========================================================================
    // Composition cycle detection
    // ========================================================================

    /// <summary>Verifies that self-composition is reported as a cycle.</summary>
    [Fact]
    public void DetectCompositionCycle_SelfComposition_ReturnsCycle()
    {
        var template = new Template("A") { Id = 1 };
        var all = new List<Template> { template };

        var result = CycleDetector.DetectCompositionCycle(1, 1, all);

        Assert.NotNull(result);
        Assert.Contains("compose itself", result);
    }

    /// <summary>Verifies that a direct composition cycle is reported.</summary>
    [Fact]
    public void DetectCompositionCycle_DirectCycle_ReturnsCycle()
    {
        var templateA = new Template("A") { Id = 1 };
        templateA.Compositions.Add(new TemplateComposition("b1") { Id = 1, TemplateId = 1, ComposedTemplateId = 2 });
        var templateB = new Template("B") { Id = 2 };
        var all = new List<Template> { templateA, templateB };

        // B tries to compose A (A already composes B)
        var result = CycleDetector.DetectCompositionCycle(2, 1, all);

        Assert.NotNull(result);
        Assert.Contains("cycle", result, StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>Verifies that a transitive composition cycle is reported.</summary>
    [Fact]
    public void DetectCompositionCycle_TransitiveCycle_ReturnsCycle()
    {
        var templateA = new Template("A") { Id = 1 };
        templateA.Compositions.Add(new TemplateComposition("b1") { Id = 1, TemplateId = 1, ComposedTemplateId = 2 });
        var templateB = new Template("B") { Id = 2 };
        templateB.Compositions.Add(new TemplateComposition("c1") { Id = 2, TemplateId = 2, ComposedTemplateId = 3 });
        var templateC = new Template("C") { Id = 3 };
        var all = new List<Template> { templateA, templateB, templateC };

        // C tries to compose A => C -> A -> B -> C
        var result = CycleDetector.DetectCompositionCycle(3, 1, all);

        Assert.NotNull(result);
    }

    /// <summary>Verifies that a composition graph with no cycle returns null.</summary>
    [Fact]
    public void DetectCompositionCycle_NoCycle_ReturnsNull()
    {
        var templateA = new Template("A") { Id = 1 };
        var templateB = new Template("B") { Id = 2 };
        var all = new List<Template> { templateA, templateB };

        var result = CycleDetector.DetectCompositionCycle(1, 2, all);

        Assert.Null(result);
    }

    // ========================================================================
    // Cross-graph cycle detection (inheritance + composition)
    // ========================================================================

    /// <summary>Verifies that a cycle spanning inheritance and composition is reported as a cross-graph cycle.</summary>
    [Fact]
    public void DetectCrossGraphCycle_InheritanceCompositionCross_ReturnsCycle()
    {
        // A inherits from B, B composes C. If C tries to set parent = A, that's a cross-graph cycle.
        var templateA = new Template("A") { Id = 1, ParentTemplateId = 2 };
        var templateB = new Template("B") { Id = 2 };
        templateB.Compositions.Add(new TemplateComposition("c1") { Id = 1, TemplateId = 2, ComposedTemplateId = 3 });
        var templateC = new Template("C") { Id = 3 };
        var all = new List<Template> { templateA, templateB, templateC };

        // C tries to add parent = A
        var result = CycleDetector.DetectCrossGraphCycle(3, 1, null, all);

        Assert.NotNull(result);
        Assert.Contains("Cross-graph cycle", result);
    }

    /// <summary>Verifies that a graph with no cross-graph cycle returns null.</summary>
    [Fact]
    public void DetectCrossGraphCycle_NoCycle_ReturnsNull()
    {
        var templateA = new Template("A") { Id = 1 };
        var templateB = new Template("B") { Id = 2 };
        var templateC = new Template("C") { Id = 3 };
        var all = new List<Template> { templateA, templateB, templateC };

        var result = CycleDetector.DetectCrossGraphCycle(3, 1, 2, all);

        Assert.Null(result);
    }

    // ========================================================================
    // Robustness against duplicate Ids and Id 0
    // ========================================================================

    /// <summary>Verifies that duplicate ids in the list do not cause an exception when detecting an inheritance cycle.</summary>
    [Fact]
    public void DetectInheritanceCycle_DuplicateIdsInList_DoesNotThrow()
    {
        // Two not-yet-saved templates both carry Id == 0. ToDictionary(t => t.Id)
        // would throw ArgumentException; the detector must tolerate it.
        var templateA = new Template("A") { Id = 0 };
        var templateB = new Template("B") { Id = 0 };
        var saved = new Template("Saved") { Id = 1 };
        var all = new List<Template> { templateA, templateB, saved };

        var ex = Record.Exception(() => CycleDetector.DetectInheritanceCycle(1, 0, all));

        Assert.Null(ex);
    }

    /// <summary>Verifies that duplicate ids in the list do not cause an exception when detecting a composition cycle.</summary>
    [Fact]
    public void DetectCompositionCycle_DuplicateIdsInList_DoesNotThrow()
    {
        var templateA = new Template("A") { Id = 0 };
        var templateB = new Template("B") { Id = 0 };
        var all = new List<Template> { templateA, templateB };

        var ex = Record.Exception(() => CycleDetector.DetectCompositionCycle(1, 2, all));

        Assert.Null(ex);
    }

    /// <summary>Verifies that duplicate ids in the list do not cause an exception when detecting a cross-graph cycle.</summary>
    [Fact]
    public void DetectCrossGraphCycle_DuplicateIdsInList_DoesNotThrow()
    {
        var templateA = new Template("A") { Id = 0 };
        var templateB = new Template("B") { Id = 0 };
        var all = new List<Template> { templateA, templateB };

        var ex = Record.Exception(() => CycleDetector.DetectCrossGraphCycle(5, 1, 2, all));

        Assert.Null(ex);
    }

    /// <summary>Verifies that an inheritance cycle through a real id of zero is still detected.</summary>
    [Fact]
    public void DetectInheritanceCycle_RealIdZero_StillDetectsCycle()
    {
        // A template legitimately stored with Id 0 (in-memory / test scenario):
        // a self-inheritance attempt must still be detected, not skipped as
        // "no parent" by a 0-as-sentinel overload.
        var template = new Template("Zero") { Id = 0 };
        var all = new List<Template> { template };

        var result = CycleDetector.DetectInheritanceCycle(0, 0, all);

        Assert.NotNull(result);
        Assert.Contains("itself", result);
    }

    /// <summary>Verifies that a parent chain passing through id zero is detected as a cycle.</summary>
    [Fact]
    public void DetectInheritanceCycle_ParentChainThroughIdZero_DetectsCycle()
    {
        // Child(1) -> parent Zero(0) -> parent Child(1): a cycle running through
        // a template whose real Id is 0 must be detected, not silently skipped.
        var zero = new Template("Zero") { Id = 0, ParentTemplateId = 1 };
        var child = new Template("Child") { Id = 1, ParentTemplateId = null };
        var all = new List<Template> { zero, child };

        var result = CycleDetector.DetectInheritanceCycle(1, 0, all);

        Assert.NotNull(result);
        Assert.Contains("cycle", result, StringComparison.OrdinalIgnoreCase);
    }
}