using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System.Collections.Concurrent;
using System.Collections.Immutable;

namespace StellaOps.Cli.GitOps;

/// <summary>
/// Controller for GitOps-based release automation.
/// Monitors Git repositories and triggers releases based on Git events.
/// </summary>
public sealed class GitOpsController : BackgroundService
{
    private readonly IGitEventSource _eventSource;
    private readonly IReleaseService _releaseService;
    private readonly IPromotionService _promotionService;
    private readonly TimeProvider _timeProvider;
    private readonly GitOpsConfig _config;
    private readonly ILogger<GitOpsController> _logger;
    private readonly ConcurrentDictionary<string, GitOpsState> _repoStates = new();

    public event EventHandler<GitOpsEventArgs>? ReleaseTriggered;
    public event EventHandler<GitOpsEventArgs>? PromotionTriggered;
    public event EventHandler<GitOpsEventArgs>? ValidationFailed;

    public GitOpsController(
        IGitEventSource eventSource,
        IReleaseService releaseService,
        IPromotionService promotionService,
        TimeProvider timeProvider,
        GitOpsConfig config,
        ILogger<GitOpsController> logger)
    {
        _eventSource = eventSource;
        _releaseService = releaseService;
        _promotionService = promotionService;
        _timeProvider = timeProvider;
        _config = config;
        _logger = logger;

        _eventSource.EventReceived += OnGitEventReceived;
    }

    /// <summary>
    /// Registers a repository for GitOps monitoring.
    /// </summary>
    public async Task<RegistrationResult> RegisterRepositoryAsync(
        GitOpsRepositoryConfig repoConfig,
        CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(repoConfig);

        _logger.LogInformation(
            "Registering repository {RepoUrl} for GitOps",
            repoConfig.RepositoryUrl);

        var state = new GitOpsState
        {
            RepositoryUrl = repoConfig.RepositoryUrl,
            Config = repoConfig,
            Status = GitOpsStatus.Active,
            RegisteredAt = _timeProvider.GetUtcNow()
        };

        _repoStates[repoConfig.RepositoryUrl] = state;

        // Start monitoring
        await _eventSource.SubscribeAsync(repoConfig.RepositoryUrl, repoConfig.Branches, ct);

        return new RegistrationResult
        {
            Success = true,
            RepositoryUrl = repoConfig.RepositoryUrl,
            MonitoredBranches = repoConfig.Branches
        };
    }

    /// <summary>
    /// Unregisters a repository from GitOps monitoring.
    /// </summary>
    public async Task<bool> UnregisterRepositoryAsync(
        string repositoryUrl,
        CancellationToken ct = default)
    {
        if (!_repoStates.TryRemove(repositoryUrl, out _))
        {
            return false;
        }

        await _eventSource.UnsubscribeAsync(repositoryUrl, ct);

        _logger.LogInformation(
            "Unregistered repository {RepoUrl} from GitOps",
            repositoryUrl);

        return true;
    }

    /// <summary>
    /// Manually triggers a release for a commit.
    /// </summary>
    public async Task<TriggerResult> TriggerReleaseAsync(
        ManualTriggerRequest request,
        CancellationToken ct = default)
    {
        _logger.LogInformation(
            "Manually triggering release for {RepoUrl} at {CommitSha}",
            request.RepositoryUrl, request.CommitSha);

        var gitEvent = new GitEvent
        {
            Type = GitEventType.Push,
            RepositoryUrl = request.RepositoryUrl,
            Branch = request.Branch,
            CommitSha = request.CommitSha,
            CommitMessage = request.CommitMessage ?? "Manual trigger",
            Author = request.Author ?? "system",
            Timestamp = _timeProvider.GetUtcNow()
        };

        return await ProcessGitEventAsync(gitEvent, ct);
    }

    /// <summary>
    /// Gets the status of all monitored repositories.
    /// </summary>
    public IReadOnlyList<GitOpsState> GetRepositoryStatuses()
    {
        return _repoStates.Values.ToList();
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("GitOps controller starting");

        await _eventSource.StartAsync(stoppingToken);

        try
        {
            // Keep running until stopped
            await Task.Delay(Timeout.Infinite, stoppingToken);
        }
        catch (OperationCanceledException)
        {
            // Expected on shutdown
        }

        await _eventSource.StopAsync(CancellationToken.None);

        _logger.LogInformation("GitOps controller stopped");
    }

    private async void OnGitEventReceived(object? sender, GitEvent e)
    {
        try
        {
            await ProcessGitEventAsync(e, CancellationToken.None);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex,
                "Error processing Git event for {RepoUrl}",
                e.RepositoryUrl);
        }
    }

    private async Task<TriggerResult> ProcessGitEventAsync(
        GitEvent gitEvent,
        CancellationToken ct)
    {
        if (!_repoStates.TryGetValue(gitEvent.RepositoryUrl, out var state))
        {
            return new TriggerResult
            {
                Success = false,
                Error = "Repository not registered"
            };
        }

        _logger.LogDebug(
            "Processing {EventType} event for {RepoUrl} on {Branch}",
            gitEvent.Type, gitEvent.RepositoryUrl, gitEvent.Branch);

        // Check if branch matches triggers
        var trigger = FindMatchingTrigger(state.Config, gitEvent);
        if (trigger is null)
        {
            _logger.LogDebug(
                "No matching trigger for branch {Branch}",
                gitEvent.Branch);

            return new TriggerResult
            {
                Success = true,
                Skipped = true,
                Reason = "No matching trigger"
            };
        }

        // Validate commit message patterns if configured
        if (!ValidateCommitMessage(gitEvent.CommitMessage, trigger))
        {
            ValidationFailed?.Invoke(this, new GitOpsEventArgs
            {
                Event = gitEvent,
                Reason = "Commit message validation failed"
            });

            return new TriggerResult
            {
                Success = false,
                Error = "Commit message validation failed"
            };
        }

        // Execute trigger action
        return trigger.Action switch
        {
            TriggerAction.CreateRelease => await CreateReleaseAsync(gitEvent, trigger, ct),
            TriggerAction.Promote => await PromoteAsync(gitEvent, trigger, ct),
            TriggerAction.ValidateOnly => await ValidateAsync(gitEvent, trigger, ct),
            _ => new TriggerResult { Success = false, Error = "Unknown action" }
        };
    }

    private GitOpsTrigger? FindMatchingTrigger(GitOpsRepositoryConfig config, GitEvent gitEvent)
    {
        return config.Triggers.FirstOrDefault(t =>
            MatchesBranch(t.BranchPattern, gitEvent.Branch) &&
            (t.EventTypes.Length == 0 || t.EventTypes.Contains(gitEvent.Type)));
    }

    private static bool MatchesBranch(string pattern, string branch)
    {
        if (pattern == "*")
        {
            return true;
        }

        if (pattern.EndsWith("/*"))
        {
            var prefix = pattern[..^2];
            return branch.StartsWith(prefix, StringComparison.OrdinalIgnoreCase);
        }

        return pattern.Equals(branch, StringComparison.OrdinalIgnoreCase);
    }

    private static bool ValidateCommitMessage(string? message, GitOpsTrigger trigger)
    {
        if (string.IsNullOrEmpty(trigger.CommitMessagePattern))
        {
            return true;
        }

        if (string.IsNullOrEmpty(message))
        {
            return false;
        }

        var regex = new System.Text.RegularExpressions.Regex(trigger.CommitMessagePattern);
        return regex.IsMatch(message);
    }

    private async Task<TriggerResult> CreateReleaseAsync(
        GitEvent gitEvent,
        GitOpsTrigger trigger,
        CancellationToken ct)
    {
        _logger.LogInformation(
            "Creating release from {CommitSha} on {Branch}",
            gitEvent.CommitSha, gitEvent.Branch);

        try
        {
            var releaseId = await _releaseService.CreateReleaseAsync(new CreateReleaseRequest
            {
                RepositoryUrl = gitEvent.RepositoryUrl,
                CommitSha = gitEvent.CommitSha,
                Branch = gitEvent.Branch,
                Environment = trigger.TargetEnvironment ?? "development",
                Version = ExtractVersion(gitEvent, trigger),
                AutoPromote = trigger.AutoPromote
            }, ct);

            ReleaseTriggered?.Invoke(this, new GitOpsEventArgs
            {
                Event = gitEvent,
                ReleaseId = releaseId
            });

            return new TriggerResult
            {
                Success = true,
                ReleaseId = releaseId
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex,
                "Failed to create release for {CommitSha}",
                gitEvent.CommitSha);

            return new TriggerResult
            {
                Success = false,
                Error = ex.Message
            };
        }
    }

    private async Task<TriggerResult> PromoteAsync(
        GitEvent gitEvent,
        GitOpsTrigger trigger,
        CancellationToken ct)
    {
        _logger.LogInformation(
            "Promoting from {SourceEnv} to {TargetEnv}",
            trigger.SourceEnvironment, trigger.TargetEnvironment);

        try
        {
            var promotionId = await _promotionService.PromoteAsync(new PromoteRequest
            {
                SourceEnvironment = trigger.SourceEnvironment!,
                TargetEnvironment = trigger.TargetEnvironment!,
                CommitSha = gitEvent.CommitSha,
                AutoApprove = trigger.AutoApprove
            }, ct);

            PromotionTriggered?.Invoke(this, new GitOpsEventArgs
            {
                Event = gitEvent,
                PromotionId = promotionId
            });

            return new TriggerResult
            {
                Success = true,
                PromotionId = promotionId
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to promote");

            return new TriggerResult
            {
                Success = false,
                Error = ex.Message
            };
        }
    }

    private Task<TriggerResult> ValidateAsync(
        GitEvent gitEvent,
        GitOpsTrigger trigger,
        CancellationToken ct)
    {
        _logger.LogInformation(
            "Validating commit {CommitSha}",
            gitEvent.CommitSha);

        // Validation-only mode - no actual release creation
        return Task.FromResult(new TriggerResult
        {
            Success = true,
            ValidationOnly = true
        });
    }

    private static string ExtractVersion(GitEvent gitEvent, GitOpsTrigger trigger)
    {
        // Try to extract version from tag or branch
        if (gitEvent.Type == GitEventType.Tag && gitEvent.Tag is not null)
        {
            var tag = gitEvent.Tag;
            if (tag.StartsWith("v", StringComparison.OrdinalIgnoreCase))
            {
                tag = tag[1..];
            }
            return tag;
        }

        // Use commit SHA prefix as version
        return gitEvent.CommitSha[..8];
    }
}

/// <summary>
/// Configuration for GitOps controller.
/// </summary>
public sealed record GitOpsConfig
{
    public TimeSpan PollInterval { get; init; } = TimeSpan.FromSeconds(30);
    public bool EnableWebhooks { get; init; } = true;
    public int MaxConcurrentEvents { get; init; } = 5;
}

/// <summary>
/// Configuration for a GitOps-monitored repository.
/// </summary>
public sealed record GitOpsRepositoryConfig
{
    public required string RepositoryUrl { get; init; }
    public ImmutableArray<string> Branches { get; init; } = ["main", "release/*"];
    public ImmutableArray<GitOpsTrigger> Triggers { get; init; } = [];
}

/// <summary>
/// A GitOps trigger definition.
/// </summary>
public sealed record GitOpsTrigger
{
    public required string BranchPattern { get; init; }
    public ImmutableArray<GitEventType> EventTypes { get; init; } = [];
    public required TriggerAction Action { get; init; }
    public string? TargetEnvironment { get; init; }
    public string? SourceEnvironment { get; init; }
    public string? CommitMessagePattern { get; init; }
    public bool AutoPromote { get; init; }
    public bool AutoApprove { get; init; }
}

/// <summary>
/// Trigger action types.
/// </summary>
public enum TriggerAction
{
    CreateRelease,
    Promote,
    ValidateOnly
}

/// <summary>
/// State of a monitored repository.
/// </summary>
public sealed record GitOpsState
{
    public required string RepositoryUrl { get; init; }
    public required GitOpsRepositoryConfig Config { get; init; }
    public required GitOpsStatus Status { get; init; }
    public required DateTimeOffset RegisteredAt { get; init; }
    public DateTimeOffset? LastEventAt { get; init; }
    public string? LastCommitSha { get; init; }
}

/// <summary>
/// GitOps status.
/// </summary>
public enum GitOpsStatus
{
    Active,
    Paused,
    Error
}

/// <summary>
/// A Git event.
/// </summary>
public sealed record GitEvent
{
    public required GitEventType Type { get; init; }
    public required string RepositoryUrl { get; init; }
    public required string Branch { get; init; }
    public required string CommitSha { get; init; }
    public string? CommitMessage { get; init; }
    public string? Tag { get; init; }
    public required string Author { get; init; }
    public required DateTimeOffset Timestamp { get; init; }
}

/// <summary>
/// Git event types.
/// </summary>
public enum GitEventType
{
    Push,
    Tag,
    PullRequest,
    Merge
}

/// <summary>
/// Result of repository registration.
/// </summary>
public sealed record RegistrationResult
{
    public required bool Success { get; init; }
    public string? RepositoryUrl { get; init; }
    public ImmutableArray<string> MonitoredBranches { get; init; } = [];
    public string? Error { get; init; }
}

/// <summary>
/// Request to manually trigger.
/// </summary>
public sealed record ManualTriggerRequest
{
    public required string RepositoryUrl { get; init; }
    public required string Branch { get; init; }
    public required string CommitSha { get; init; }
    public string? CommitMessage { get; init; }
    public string? Author { get; init; }
}

/// <summary>
/// Result of a trigger.
/// </summary>
public sealed record TriggerResult
{
    public required bool Success { get; init; }
    public bool Skipped { get; init; }
    public bool ValidationOnly { get; init; }
    public Guid? ReleaseId { get; init; }
    public Guid? PromotionId { get; init; }
    public string? Reason { get; init; }
    public string? Error { get; init; }
}

/// <summary>
/// Event args for GitOps events.
/// </summary>
public sealed class GitOpsEventArgs : EventArgs
{
    public required GitEvent Event { get; init; }
    public Guid? ReleaseId { get; init; }
    public Guid? PromotionId { get; init; }
    public string? Reason { get; init; }
}

/// <summary>
/// Request to create a release.
/// </summary>
public sealed record CreateReleaseRequest
{
    public required string RepositoryUrl { get; init; }
    public required string CommitSha { get; init; }
    public required string Branch { get; init; }
    public required string Environment { get; init; }
    public required string Version { get; init; }
    public bool AutoPromote { get; init; }
}

/// <summary>
/// Request to promote.
/// </summary>
public sealed record PromoteRequest
{
    public required string SourceEnvironment { get; init; }
    public required string TargetEnvironment { get; init; }
    public required string CommitSha { get; init; }
    public bool AutoApprove { get; init; }
}

/// <summary>
/// Interface for Git event source.
/// </summary>
public interface IGitEventSource
{
    event EventHandler<GitEvent>? EventReceived;
    Task StartAsync(CancellationToken ct = default);
    Task StopAsync(CancellationToken ct = default);
    Task SubscribeAsync(string repositoryUrl, ImmutableArray<string> branches, CancellationToken ct = default);
    Task UnsubscribeAsync(string repositoryUrl, CancellationToken ct = default);
}

/// <summary>
/// Interface for release service.
/// </summary>
public interface IReleaseService
{
    Task<Guid> CreateReleaseAsync(CreateReleaseRequest request, CancellationToken ct = default);
}

/// <summary>
/// Interface for promotion service.
/// </summary>
public interface IPromotionService
{
    Task<Guid> PromoteAsync(PromoteRequest request, CancellationToken ct = default);
}