using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.Json;
using System.Text.Json.Serialization;
using FluentAssertions;
using StellaOps.Signals.Models;
using StellaOps.Signals.Parsing;
using Xunit;

namespace StellaOps.Signals.Reachability.Tests;

/// <summary>
/// Determinism tests for the stella.callgraph.v1 schema.
/// These tests validate:
/// - Round-trip serialization produces identical output
/// - Schema migration from legacy formats
/// - Enum values serialize as expected strings
/// - Arrays maintain stable ordering
/// </summary>
public sealed class CallgraphSchemaV1DeterminismTests
{
    private static readonly string RepoRoot = LocateRepoRoot();
    private static readonly string FixtureRoot = Path.Combine(RepoRoot, "tests", "reachability", "fixtures", "callgraph-schema-v1");

    private static readonly JsonSerializerOptions DeterministicOptions = new()
    {
        WriteIndented = true,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
        Converters = { new JsonStringEnumConverter(JsonNamingPolicy.CamelCase) }
    };

    public static IEnumerable<object[]> GoldenFixtures()
    {
        if (!Directory.Exists(FixtureRoot))
        {
            yield break;
        }

        foreach (var file in Directory.GetFiles(FixtureRoot, "*.json").OrderBy(f => f, StringComparer.Ordinal))
        {
            yield return new object[] { Path.GetFileNameWithoutExtension(file) };
        }
    }

    [Theory]
    [MemberData(nameof(GoldenFixtures))]
    public void GoldenFixture_DeserializesWithoutError(string fixtureName)
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, $"{fixtureName}.json"));

        var document = JsonSerializer.Deserialize<CallgraphDocument>(json);

        document.Should().NotBeNull();
        document!.Id.Should().NotBeNullOrEmpty();
    }

    [Theory]
    [MemberData(nameof(GoldenFixtures))]
    public void GoldenFixture_NodesHaveRequiredFields(string fixtureName)
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, $"{fixtureName}.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        foreach (var node in document.Nodes)
        {
            node.Id.Should().NotBeNullOrEmpty($"Node in {fixtureName} must have Id");
            node.Name.Should().NotBeNullOrEmpty($"Node {node.Id} in {fixtureName} must have Name");
        }
    }

    [Theory]
    [MemberData(nameof(GoldenFixtures))]
    public void GoldenFixture_EdgesReferenceValidNodes(string fixtureName)
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, $"{fixtureName}.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var nodeIds = document.Nodes.Select(n => n.Id).ToHashSet(StringComparer.Ordinal);

        foreach (var edge in document.Edges)
        {
            nodeIds.Should().Contain(edge.SourceId, $"Edge source {edge.SourceId} in {fixtureName} must reference existing node");
            nodeIds.Should().Contain(edge.TargetId, $"Edge target {edge.TargetId} in {fixtureName} must reference existing node");
        }
    }

    [Theory]
    [MemberData(nameof(GoldenFixtures))]
    public void GoldenFixture_EntrypointsReferenceValidNodes(string fixtureName)
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, $"{fixtureName}.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var nodeIds = document.Nodes.Select(n => n.Id).ToHashSet(StringComparer.Ordinal);

        foreach (var entrypoint in document.Entrypoints)
        {
            nodeIds.Should().Contain(entrypoint.NodeId, $"Entrypoint {entrypoint.NodeId} in {fixtureName} must reference existing node");
        }
    }

    [Fact]
    public void DotNetFixture_HasCorrectLanguageEnum()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "dotnet-aspnetcore-minimal.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.LanguageType.Should().Be(CallgraphLanguage.DotNet);
    }

    [Fact]
    public void JavaFixture_HasCorrectLanguageEnum()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "java-spring-boot.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.LanguageType.Should().Be(CallgraphLanguage.Java);
    }

    [Fact]
    public void NodeFixture_HasCorrectLanguageEnum()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "node-express-api.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.LanguageType.Should().Be(CallgraphLanguage.Node);
    }

    [Fact]
    public void GoFixture_HasCorrectLanguageEnum()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "go-gin-api.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.LanguageType.Should().Be(CallgraphLanguage.Go);
    }

    [Fact]
    public void AllEdgeReasonsFixture_ContainsAllEdgeReasons()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "all-edge-reasons.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var expectedReasons = Enum.GetValues<EdgeReason>();
        var actualReasons = document.Edges.Select(e => e.Reason).Distinct().ToHashSet();

        foreach (var expected in expectedReasons)
        {
            actualReasons.Should().Contain(expected, $"EdgeReason.{expected} should be covered by fixture");
        }
    }

    [Fact]
    public void AllEdgeReasonsFixture_ContainsAllEdgeKinds()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "all-edge-reasons.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var expectedKinds = Enum.GetValues<EdgeKind>();
        var actualKinds = document.Edges.Select(e => e.Kind).Distinct().ToHashSet();

        foreach (var expected in expectedKinds)
        {
            actualKinds.Should().Contain(expected, $"EdgeKind.{expected} should be covered by fixture");
        }
    }

    [Fact]
    public void AllVisibilityFixture_ContainsAllVisibilityLevels()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "all-visibility-levels.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var expectedVisibilities = Enum.GetValues<SymbolVisibility>();
        var actualVisibilities = document.Nodes.Select(n => n.Visibility).Distinct().ToHashSet();

        foreach (var expected in expectedVisibilities)
        {
            actualVisibilities.Should().Contain(expected, $"SymbolVisibility.{expected} should be covered by fixture");
        }
    }

    [Fact]
    public void LegacyFixture_HasNoSchemaField()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "legacy-no-schema.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        // Legacy fixture should deserialize but have default schema (v1) due to property default
        document.Schema.Should().Be(CallgraphSchemaVersions.V1);
    }

    [Fact]
    public void LegacyFixture_MigratesToV1Schema()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "legacy-no-schema.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var migrated = CallgraphSchemaMigrator.EnsureV1(document);

        migrated.Schema.Should().Be(CallgraphSchemaVersions.V1);
        // Verify that nodes have visibility inferred (may be Unknown for some cases)
        migrated.Nodes.Should().AllSatisfy(n => Enum.IsDefined(n.Visibility).Should().BeTrue());
        // Verify that edges have reason inferred (defaults to DirectCall for legacy 'call' type)
        migrated.Edges.Should().AllSatisfy(e => Enum.IsDefined(e.Reason).Should().BeTrue());
    }

    [Theory]
    [InlineData("dotnet-aspnetcore-minimal")]
    [InlineData("java-spring-boot")]
    [InlineData("node-express-api")]
    [InlineData("go-gin-api")]
    public void V1Fixture_MigrationIsIdempotent(string fixtureName)
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, $"{fixtureName}.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var migrated1 = CallgraphSchemaMigrator.EnsureV1(document);
        var migrated2 = CallgraphSchemaMigrator.EnsureV1(migrated1);

        migrated2.Schema.Should().Be(migrated1.Schema);
        migrated2.Nodes.Should().HaveCount(migrated1.Nodes.Count);
        migrated2.Edges.Should().HaveCount(migrated1.Edges.Count);
        migrated2.Entrypoints.Should().HaveCount(migrated1.Entrypoints.Count);
    }

    [Fact]
    public void EdgeReason_SerializesAsCamelCaseString()
    {
        var edge = new CallgraphEdge
        {
            SourceId = "s1",
            TargetId = "t1",
            Type = "call",
            Reason = EdgeReason.DirectCall
        };

        var json = JsonSerializer.Serialize(edge, DeterministicOptions);

        json.Should().Contain("\"reason\": \"directCall\"");
    }

    [Fact]
    public void SymbolVisibility_SerializesAsCamelCaseString()
    {
        var node = new CallgraphNode
        {
            Id = "n1",
            Name = "Test",
            Kind = "method",
            Visibility = SymbolVisibility.Public
        };

        var json = JsonSerializer.Serialize(node, DeterministicOptions);

        json.Should().Contain("\"visibility\": \"public\"");
    }

    [Fact]
    public void EntrypointKind_SerializesAsCamelCaseString()
    {
        var entrypoint = new CallgraphEntrypoint
        {
            NodeId = "n1",
            Kind = EntrypointKind.Http,
            Framework = EntrypointFramework.AspNetCore
        };

        var json = JsonSerializer.Serialize(entrypoint, DeterministicOptions);

        json.Should().Contain("\"kind\": \"http\"");
        json.Should().Contain("\"framework\": \"aspNetCore\"");
    }

    [Theory]
    [MemberData(nameof(GoldenFixtures))]
    public void GoldenFixture_NodesSortedById(string fixtureName)
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, $"{fixtureName}.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var nodeIds = document.Nodes.Select(n => n.Id).ToList();
        var sortedIds = nodeIds.OrderBy(id => id, StringComparer.Ordinal).ToList();

        nodeIds.Should().Equal(sortedIds, $"Nodes in {fixtureName} should be sorted by Id for determinism");
    }

    [Theory]
    [MemberData(nameof(GoldenFixtures))]
    public void GoldenFixture_EntrypointsSortedByOrder(string fixtureName)
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, $"{fixtureName}.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var orders = document.Entrypoints.Select(e => e.Order).ToList();
        var sortedOrders = orders.OrderBy(o => o).ToList();

        orders.Should().Equal(sortedOrders, $"Entrypoints in {fixtureName} should be sorted by Order for determinism");
    }

    [Fact]
    public void DotNetFixture_HasCorrectAspNetCoreEntrypoints()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "dotnet-aspnetcore-minimal.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.Entrypoints.Should().Contain(e => e.Kind == EntrypointKind.Main && e.Framework == EntrypointFramework.AspNetCore);
        document.Entrypoints.Should().Contain(e => e.Kind == EntrypointKind.Http && e.Route == "/weatherforecast");
    }

    [Fact]
    public void JavaFixture_HasCorrectSpringEntrypoints()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "java-spring-boot.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.Entrypoints.Should().Contain(e => e.Kind == EntrypointKind.Main && e.Framework == EntrypointFramework.SpringBoot);
        document.Entrypoints.Should().Contain(e => e.Kind == EntrypointKind.Http && e.Route == "/owners/{ownerId}");
    }

    [Fact]
    public void GoFixture_HasModuleInitEntrypoint()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "go-gin-api.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.Entrypoints.Should().Contain(e => e.Kind == EntrypointKind.ModuleInit && e.Phase == EntrypointPhase.ModuleInit);
    }

    [Fact]
    public void AllEdgeReasonsFixture_ReflectionEdgeIsUnresolved()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "all-edge-reasons.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var reflectionEdge = document.Edges.Single(e => e.Reason == EdgeReason.ReflectionString);
        reflectionEdge.IsResolved.Should().BeFalse("Reflection edges are typically unresolved");
        reflectionEdge.Weight.Should().BeLessThan(1.0, "Reflection edges should have lower confidence");
    }

    [Fact]
    public void AllEdgeReasonsFixture_DiBindingHasProvenance()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "all-edge-reasons.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        var diEdge = document.Edges.Single(e => e.Reason == EdgeReason.DiBinding);
        diEdge.Provenance.Should().NotBeNullOrEmpty("DI binding edges should include provenance");
    }

    [Fact]
    public void Artifacts_HaveRequiredFields()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "dotnet-aspnetcore-minimal.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.Artifacts.Should().NotBeEmpty();
        foreach (var artifact in document.Artifacts)
        {
            artifact.ArtifactKey.Should().NotBeNullOrEmpty();
            artifact.Kind.Should().NotBeNullOrEmpty();
            artifact.Sha256.Should().NotBeNullOrEmpty().And.HaveLength(64);
        }
    }

    [Fact]
    public void Metadata_HasRequiredToolInfo()
    {
        var json = File.ReadAllText(Path.Combine(FixtureRoot, "dotnet-aspnetcore-minimal.json"));
        var document = JsonSerializer.Deserialize<CallgraphDocument>(json)!;

        document.GraphMetadata.Should().NotBeNull();
        document.GraphMetadata!.ToolId.Should().NotBeNullOrEmpty();
        document.GraphMetadata!.ToolVersion.Should().NotBeNullOrEmpty();
        document.GraphMetadata!.AnalysisTimestamp.Should().NotBe(default);
    }

    private static string LocateRepoRoot()
    {
        var current = new DirectoryInfo(AppContext.BaseDirectory);
        while (current != null)
        {
            if (File.Exists(Path.Combine(current.FullName, "Directory.Build.props")))
            {
                return current.FullName;
            }

            current = current.Parent;
        }

        throw new InvalidOperationException("Cannot locate repository root (missing Directory.Build.props).");
    }
}