using System.Reflection;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using Microsoft.Extensions.Configuration;
using w4c_workflows.Services.Execution;
using Xunit;

namespace w4c_workflows.Tests;

public class CSharpScriptExecutorTests
{
    private readonly CSharpScriptExecutor _executor = new();

    [Fact]
    public async Task Executes_program_with_string_input()
    {
        using var dir = new TempDir();
        dir.Write("Program.cs", """
            using System.Text.Json;
            public static class Program
            {
                public static object Main(string input)
                {
                    using var doc = JsonDocument.Parse(input);
                    var n = doc.RootElement.GetProperty("n").GetInt32();
                    return new { squared = n * n };
                }
            }
            """);

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Program.cs", "{\"n\":5}", dir.Path), default);

        Assert.True(result.Success, result.Error);
        Assert.NotNull(result.Output);
        using var output = JsonDocument.Parse(result.Output!);
        Assert.Equal(25, output.RootElement.GetProperty("squared").GetInt32());
    }

    [Fact]
    public async Task Compiles_only_entry_file_not_other_cs_files()
    {
        // Only the entry file (Program.cs) is compiled. Helper.cs exists in the
        // directory but is NOT included, so referencing Helper.Add causes a
        // compilation error. This prevents duplicate-type errors when multiple
        // tasks each define their own Program class in the same workflow directory.
        using var dir = new TempDir();
        dir.Write("Helper.cs", """
            public static class Helper
            {
                public static int Add(int a, int b) => a + b;
            }
            """);
        dir.Write("Program.cs", """
            using System.Text.Json;
            public static class Program
            {
                public static object Main(string input)
                {
                    using var doc = JsonDocument.Parse(input);
                    var a = doc.RootElement.GetProperty("a").GetInt32();
                    var b = doc.RootElement.GetProperty("b").GetInt32();
                    return new { sum = Helper.Add(a, b) };
                }
            }
            """);

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Program.cs", "{\"a\":2,\"b\":3}", dir.Path), default);

        Assert.False(result.Success);
        Assert.Contains("compilation failed", result.Error, StringComparison.OrdinalIgnoreCase);
    }

    [Fact]
    public async Task Supports_custom_entry_function_name()
    {
        using var dir = new TempDir();
        dir.Write("Program.cs", """
            public static class Program
            {
                public static object Transform(string input) => new { echo = input };
            }
            """);

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Program.cs", "{\"x\":1}", dir.Path, entryFunction: "Transform"), default);

        Assert.True(result.Success, result.Error);
        using var output = JsonDocument.Parse(result.Output!);
        Assert.Equal("{\"x\":1}", output.RootElement.GetProperty("echo").GetString());
    }

    [Fact]
    public async Task Supports_async_entry()
    {
        using var dir = new TempDir();
        dir.Write("Program.cs", """
            using System.Threading.Tasks;
            public static class Program
            {
                public static async Task<object> Main(string input)
                {
                    await Task.Yield();
                    return new { ok = true };
                }
            }
            """);

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Program.cs", "{}", dir.Path), default);

        Assert.True(result.Success, result.Error);
        Assert.Contains("\"ok\":true", result.Output);
    }

    [Fact]
    public async Task Fails_with_compile_error()
    {
        using var dir = new TempDir();
        dir.Write("Program.cs", "public static class Program { public static object Main(string input) { return ; } }");

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Program.cs", "{}", dir.Path), default);

        Assert.False(result.Success);
        Assert.Contains("compilation failed", result.Error, StringComparison.OrdinalIgnoreCase);
    }

    [Fact]
    public async Task Fails_when_entry_method_missing()
    {
        using var dir = new TempDir();
        dir.Write("Program.cs", "public static class Program { public static int NotTheEntry() => 1; }");

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Program.cs", "{}", dir.Path), default);

        Assert.False(result.Success);
        Assert.Contains("no static entry method", result.Error);
    }

    [Fact]
    public async Task Runs_program_with_dynamic_input()
    {
        // Frontend stubs generate `dynamic input` (compiles to `object`), but the
        // executor used to only match `string` params — so a valid stub compiled
        // yet was never found at invoke time.
        using var dir = new TempDir();
        dir.Write("Main.cs", """
            public static class Program
            {
                public static object Main(dynamic input)
                {
                    return new
                    {
                        ok = true,
                        input = input
                    };
                }
            }
            """);

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Main.cs", "{\"x\":1}", dir.Path), default);

        Assert.True(result.Success, result.Error);
        using var output = JsonDocument.Parse(result.Output!);
        Assert.True(output.RootElement.GetProperty("ok").GetBoolean());
        Assert.Equal("{\"x\":1}", output.RootElement.GetProperty("input").GetString());
    }

    [Fact]
    public async Task Reports_expression_body_followed_by_block_as_compile_error()
    {
        // Regression: an LLM/agent edit turned the stub body into `=> { ... }`,
        // which is invalid C#. This is exactly the reported failure
        // "Main.cs(5,48): error CS1525: Invalid expression term '{'".
        using var dir = new TempDir();
        dir.Write("Main.cs", """
            public static class Program
            {
                public static object Main(dynamic input) =>
                {
                    return new
                    {
                        ok = true,
                        input = input
                    };
                }
            }
            """);

        var result = await _executor.ExecuteAsync(
            Invocation.For("csharp", "Main.cs", "{}", dir.Path), default);

        Assert.False(result.Success);
        Assert.Contains("compilation failed", result.Error, StringComparison.OrdinalIgnoreCase);
        Assert.Contains("CS1525", result.Error, StringComparison.OrdinalIgnoreCase);
    }

    // ------------------------------------------------------- P0-6 hardening

    [Fact]
    public async Task Compiled_assembly_is_cached_by_source_hash()
    {
        using var dir = new TempDir();
        // Unique source so the cache key is unique to this test.
        var marker = Guid.NewGuid().ToString("N");
        dir.Write("Program.cs", $$"""
            public static class Program
            {
                public static object Main(string input) => new { marker = "{{marker}}" };
            }
            """);

        var source = File.ReadAllText(Path.Combine(dir.Path, "Program.cs"));
        var key = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(source)));

        Assert.False(CacheContains(key));

        var invocation = Invocation.For("csharp", "Program.cs", "{}", dir.Path);
        var first = await _executor.ExecuteAsync(invocation, default);
        Assert.True(first.Success, first.Error);
        Assert.True(CacheContains(key));

        // Second run is a cache hit; it must succeed and the image is reused.
        var second = await _executor.ExecuteAsync(invocation, default);
        Assert.True(second.Success, second.Error);
        Assert.Contains(marker, second.Output);
    }

    [Fact]
    public async Task Times_out_when_the_entry_exceeds_the_deadline()
    {
        var config = new ConfigurationBuilder()
            .AddInMemoryCollection(new Dictionary<string, string?> { ["Workflows:CSharpTimeoutSeconds"] = "1" })
            .Build();
        var executor = new CSharpScriptExecutor(config);

        using var dir = new TempDir();
        dir.Write("Program.cs", """
            using System.Threading.Tasks;
            public static class Program
            {
                public static async Task<object> Main(string input)
                {
                    await Task.Delay(10000);
                    return new { ok = true };
                }
            }
            """);

        var result = await executor.ExecuteAsync(
            Invocation.For("csharp", "Program.cs", "{}", dir.Path), default);

        Assert.False(result.Success);
        Assert.Contains("timed out", result.Error, StringComparison.OrdinalIgnoreCase);
    }

    [Fact]
    public async Task Cancellation_is_propagated_not_swallowed()
    {
        using var dir = new TempDir();
        dir.Write("Program.cs", """
            using System.Threading.Tasks;
            public static class Program
            {
                public static async Task<object> Main(string input)
                {
                    await Task.Delay(10000);
                    return new { ok = true };
                }
            }
            """);

        using var cts = new CancellationTokenSource();
        cts.Cancel();

        await Assert.ThrowsAnyAsync<OperationCanceledException>(
            () => _executor.ExecuteAsync(Invocation.For("csharp", "Program.cs", "{}", dir.Path), cts.Token));
    }

    private static bool CacheContains(string key)
    {
        var field = typeof(CSharpScriptExecutor).GetField(
            "AssemblyCache", BindingFlags.NonPublic | BindingFlags.Static)!;
        var cache = field.GetValue(null)!;
        return (bool)cache.GetType().GetMethod("ContainsKey")!.Invoke(cache, new object[] { key })!;
    }
}