using System.Net;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.TestHost;
using Microsoft.Extensions.Diagnostics.HealthChecks;
using Microsoft.Extensions.DependencyInjection;
using ZB.MOM.WW.Health;

namespace ZB.MOM.WW.Health.Tests;

/// <summary>
/// Verifies the three-tier <see cref="ZbHealthEndpointExtensions.MapZbHealth"/> convention:
/// each endpoint runs only the checks tagged for its tier, /healthz runs nothing, and the
/// standard ASP.NET HealthChecks status-to-HTTP mapping (Healthy/Degraded → 200, Unhealthy → 503)
/// holds per tier.
/// </summary>
public sealed class TierMappingTests
{
    /// <summary>
    /// An <see cref="IHealthCheck"/> test double that records each invocation and returns a
    /// configurable result, so tests can assert which checks actually ran per tier.
    /// </summary>
    private sealed class RecordingHealthCheck : IHealthCheck
    {
        private readonly HealthStatus _status;
        private int _invocations;

        public RecordingHealthCheck(HealthStatus status) => _status = status;

        public int Invocations => Volatile.Read(ref _invocations);

        public Task<HealthCheckResult> CheckHealthAsync(
            HealthCheckContext context,
            CancellationToken cancellationToken = default)
        {
            Interlocked.Increment(ref _invocations);
            return Task.FromResult(new HealthCheckResult(_status));
        }
    }

    private static async Task<(HttpResponseMessage Response, RecordingHealthCheck Ready, RecordingHealthCheck Active)>
        RunAsync(string path, HealthStatus readyStatus = HealthStatus.Healthy, HealthStatus activeStatus = HealthStatus.Healthy)
    {
        var ready = new RecordingHealthCheck(readyStatus);
        var active = new RecordingHealthCheck(activeStatus);

        var builder = WebApplication.CreateBuilder();
        builder.WebHost.UseTestServer();

        builder.Services.AddHealthChecks()
            .AddCheck("ready-check", ready, tags: new[] { ZbHealthTags.Ready })
            .AddCheck("active-check", active, tags: new[] { ZbHealthTags.Active });

        await using var app = builder.Build();
        app.MapZbHealth();
        await app.StartAsync();

        var client = app.GetTestClient();
        var response = await client.GetAsync(path);
        return (response, ready, active);
    }

    [Fact]
    public async Task ReadyEndpoint_RunsOnlyReadyCheck()
    {
        var (response, ready, active) = await RunAsync("/health/ready");

        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
        Assert.Equal(1, ready.Invocations);
        Assert.Equal(0, active.Invocations);
    }

    [Fact]
    public async Task ActiveEndpoint_RunsOnlyActiveCheck()
    {
        var (response, ready, active) = await RunAsync("/health/active");

        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
        Assert.Equal(0, ready.Invocations);
        Assert.Equal(1, active.Invocations);
    }

    [Fact]
    public async Task LivenessEndpoint_RunsNoChecks_AndReturns200()
    {
        var (response, ready, active) = await RunAsync("/healthz");

        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
        Assert.Equal(0, ready.Invocations);
        Assert.Equal(0, active.Invocations);
    }

    [Fact]
    public async Task ReadyEndpoint_Healthy_Returns200()
    {
        var (response, _, _) = await RunAsync("/health/ready", readyStatus: HealthStatus.Healthy);

        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
    }

    [Fact]
    public async Task ReadyEndpoint_Unhealthy_Returns503()
    {
        var (response, _, _) = await RunAsync("/health/ready", readyStatus: HealthStatus.Unhealthy);

        Assert.Equal(HttpStatusCode.ServiceUnavailable, response.StatusCode);
    }

    [Fact]
    public async Task ActiveEndpoint_Unhealthy_Returns503()
    {
        var (response, _, _) = await RunAsync("/health/active", activeStatus: HealthStatus.Unhealthy);

        Assert.Equal(HttpStatusCode.ServiceUnavailable, response.StatusCode);
    }

    [Fact]
    public async Task LivenessEndpoint_UnaffectedByUnhealthyChecks()
    {
        // Even though every registered check is Unhealthy, /healthz runs none of them
        // (predicate _ => false) and stays 200 as long as the process is up.
        var (response, ready, active) = await RunAsync(
            "/healthz", readyStatus: HealthStatus.Unhealthy, activeStatus: HealthStatus.Unhealthy);

        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
        Assert.Equal(0, ready.Invocations);
        Assert.Equal(0, active.Invocations);
    }

    [Fact]
    public async Task Options_OverrideRoutePaths()
    {
        var ready = new RecordingHealthCheck(HealthStatus.Healthy);
        var active = new RecordingHealthCheck(HealthStatus.Healthy);

        var builder = WebApplication.CreateBuilder();
        builder.WebHost.UseTestServer();
        builder.Services.AddHealthChecks()
            .AddCheck("ready-check", ready, tags: new[] { ZbHealthTags.Ready })
            .AddCheck("active-check", active, tags: new[] { ZbHealthTags.Active });

        await using var app = builder.Build();
        app.MapZbHealth(new ZbHealthEndpointOptions
        {
            ReadyPath = "/custom/ready",
            ActivePath = "/custom/active",
            LivePath = "/custom/live",
        });
        await app.StartAsync();

        var client = app.GetTestClient();

        var readyResponse = await client.GetAsync("/custom/ready");
        Assert.Equal(HttpStatusCode.OK, readyResponse.StatusCode);
        Assert.Equal(1, ready.Invocations);
        Assert.Equal(0, active.Invocations);

        var liveResponse = await client.GetAsync("/custom/live");
        Assert.Equal(HttpStatusCode.OK, liveResponse.StatusCode);

        // The default paths must no longer be mapped when overridden.
        var defaultReady = await client.GetAsync("/health/ready");
        Assert.Equal(HttpStatusCode.NotFound, defaultReady.StatusCode);
    }
}