using FastEndpoints;
using System.Security.Cryptography;
using System.Text;

namespace KArtSell.Host.Features.Identity;

/// <summary>
/// VS-01 Backend: Create User Endpoint
/// Accepts: email, password, roles
/// Returns: 201 Created { userId, email, roles, createdAt }
/// Idempotency: IdempotencyKey header
/// </summary>
public sealed class CreateUserRequest
{
    public string Email { get; set; } = "";
    public string Password { get; set; } = "";
    public List<string> Roles { get; set; } = new();
}

public sealed class CreateUserResponse
{
    public Guid UserId { get; set; }
    public string Email { get; set; } = "";
    public List<string> Roles { get; set; } = new();
    public DateTime CreatedAt { get; set; }
}

public sealed class CreateUserEndpoint : Endpoint<CreateUserRequest, CreateUserResponse>
{
    private readonly IIdentityService _identityService;
    private readonly IIdempotencyStore _idempotencyStore;

    public CreateUserEndpoint(IIdentityService identityService, IIdempotencyStore idempotencyStore)
    {
        _identityService = identityService;
        _idempotencyStore = idempotencyStore;
    }

    public override void Configure()
    {
        Post("/api/users");
        Roles("Admin");  // Only Admin can create users
    }

    public override async Task HandleAsync(CreateUserRequest req, CancellationToken ct)
    {
        // Idempotency: Check IdempotencyKey header
        var idempotencyKey = HttpContext.Request.Headers["IdempotencyKey"].ToString();
        if (!string.IsNullOrEmpty(idempotencyKey))
        {
            var existing = await _idempotencyStore.GetAsync(idempotencyKey, ct);
            if (existing != null)
            {
                // Already created, return same response
                Response.StatusCode = StatusCodes.Status201Created;
                await SendAsync(existing, cancellation: ct);
                return;
            }
        }

        // Validation
        if (!IsValidEmail(req.Email))
        {
            ThrowError(r => r.AddError("email", "Invalid email format"));
        }

        if (req.Password.Length < 12)
        {
            ThrowError(r => r.AddError("password", "Password must be at least 12 characters"));
        }

        if (req.Roles.Count == 0)
        {
            ThrowError(r => r.AddError("roles", "User must have at least one role"));
        }

        // Create user (idempotent via email UNIQUE constraint)
        var result = await _identityService.CreateUserAsync(
            req.Email,
            req.Password,
            req.Roles,
            idempotencyKey,
            ct);

        if (!result.IsSuccess)
        {
            if (result.Error.Contains("already exists"))
            {
                ThrowError(StatusCodes.Status409Conflict, r =>
                    r.AddError("email", "User with this email already exists"));
            }
            else
            {
                ThrowError(r => r.AddError("error", result.Error));
            }
        }

        // Store idempotency key
        if (!string.IsNullOrEmpty(idempotencyKey))
        {
            await _idempotencyStore.StoreAsync(idempotencyKey, result.Data, ct);
        }

        Response.StatusCode = StatusCodes.Status201Created;
        await SendAsync(result.Data, cancellation: ct);
    }

    private bool IsValidEmail(string email)
    {
        try
        {
            var addr = new System.Net.Mail.MailAddress(email);
            return addr.Address == email.ToLowerInvariant();
        }
        catch
        {
            return false;
        }
    }

    private void ThrowError(string status, Action<ValidationFailure> configure)
    {
        var failure = new ValidationFailure();
        configure(failure);
        throw new HttpRequestException(failure.ToString());
    }

    private void ThrowError(Action<ValidationFailure> configure)
    {
        ThrowError("400", configure);
    }
}

/// <summary>
/// VS-01 Backend: List Users Endpoint
/// Filters: role, status, page, limit
/// Returns: { items: [User], total, page, limit }
/// </summary>
public sealed class ListUsersRequest
{
    public int Page { get; set; } = 1;
    public int Limit { get; set; } = 20;
    public string? Role { get; set; }
    public string? Status { get; set; }
}

public sealed class UserDto
{
    public Guid Id { get; set; }
    public string Email { get; set; } = "";
    public List<string> Roles { get; set; } = new();
    public string Status { get; set; } = "active";
    public DateTime CreatedAt { get; set; }
}

public sealed class ListUsersResponse
{
    public List<UserDto> Items { get; set; } = new();
    public int Total { get; set; }
    public int Page { get; set; }
    public int Limit { get; set; }
}

public sealed class ListUsersEndpoint : Endpoint<ListUsersRequest, ListUsersResponse>
{
    private readonly IIdentityService _identityService;

    public ListUsersEndpoint(IIdentityService identityService)
    {
        _identityService = identityService;
    }

    public override void Configure()
    {
        Get("/api/users");
        Roles("Admin", "Analyst");  // Visible to Admin and Analyst
    }

    public override async Task HandleAsync(ListUsersRequest req, CancellationToken ct)
    {
        var (items, total) = await _identityService.ListUsersAsync(
            page: req.Page,
            limit: req.Limit,
            roleFilter: req.Role,
            statusFilter: req.Status,
            cancellationToken: ct);

        var response = new ListUsersResponse
        {
            Items = items.Select(u => new UserDto
            {
                Id = u.Id,
                Email = u.Email,
                Roles = u.Roles.ToList(),
                Status = u.Status,
                CreatedAt = u.CreatedAt,
            }).ToList(),
            Total = total,
            Page = req.Page,
            Limit = req.Limit,
        };

        await SendAsync(response, cancellation: ct);
    }
}

/// <summary>
/// VS-01 Backend: Update User Roles Endpoint
/// Body: { roles: ["Analyst", "Viewer"] }
/// Returns: 200 { userId, roles, updatedAt }
/// </summary>
public sealed class UpdateUserRolesRequest
{
    public List<string> Roles { get; set; } = new();
}

public sealed class UpdateUserRolesResponse
{
    public Guid UserId { get; set; }
    public List<string> Roles { get; set; } = new();
    public DateTime UpdatedAt { get; set; }
}

public sealed class UpdateUserRolesEndpoint : Endpoint<UpdateUserRolesRequest, UpdateUserRolesResponse>
{
    private readonly IIdentityService _identityService;

    public UpdateUserRolesEndpoint(IIdentityService identityService)
    {
        _identityService = identityService;
    }

    public override void Configure()
    {
        Patch("/api/users/{id}");
        Roles("Admin");  // Only Admin can modify roles
    }

    public override async Task HandleAsync(UpdateUserRolesRequest req, CancellationToken ct)
    {
        var userId = Route<Guid>("id");

        // Validation
        if (req.Roles.Count == 0)
        {
            ThrowError(r => r.AddError("roles", "User must have at least one role"));
        }

        var validRoles = new[] { "Admin", "Analyst", "Trader", "Viewer" };
        var invalidRoles = req.Roles.Except(validRoles).ToList();
        if (invalidRoles.Count > 0)
        {
            ThrowError(r => r.AddError("roles", $"Invalid roles: {string.Join(", ", invalidRoles)}"));
        }

        // Update roles
        var result = await _identityService.UpdateUserRolesAsync(userId, req.Roles, ct);

        if (!result.IsSuccess)
        {
            if (result.Error.Contains("not found"))
            {
                ThrowError(StatusCodes.Status404NotFound, r =>
                    r.AddError("userId", "User not found"));
            }
            else
            {
                ThrowError(r => r.AddError("error", result.Error));
            }
        }

        await SendAsync(result.Data, cancellation: ct);
    }

    private void ThrowError(Action<ValidationFailure> configure)
    {
        var failure = new ValidationFailure();
        configure(failure);
        throw new HttpRequestException(failure.ToString());
    }

    private void ThrowError(int status, Action<ValidationFailure> configure)
    {
        var failure = new ValidationFailure();
        configure(failure);
        throw new HttpRequestException($"{status}: {failure}");
    }
}

/// <summary>
/// VS-01 Backend: Core Identity Service
/// Handles: User CRUD, Role management, Permission validation
/// Transactional: All operations atomic
/// Idempotent: Replay-safe using email-based dedup
/// </summary>
public interface IIdentityService
{
    Task<OperationResult<CreateUserResponse>> CreateUserAsync(
        string email, string password, List<string> roles, string? idempotencyKey, CancellationToken ct);

    Task<(List<UserModel>, int total)> ListUsersAsync(
        int page, int limit, string? roleFilter, string? statusFilter, CancellationToken ct);

    Task<OperationResult<UpdateUserRolesResponse>> UpdateUserRolesAsync(
        Guid userId, List<string> roles, CancellationToken ct);
}

public class IdentityService : IIdentityService
{
    private readonly NpgsqlDataSource _dataSource;
    private readonly IIdempotencyStore _idempotencyStore;

    public IdentityService(NpgsqlDataSource dataSource, IIdempotencyStore idempotencyStore)
    {
        _dataSource = dataSource;
        _idempotencyStore = idempotencyStore;
    }

    public async Task<OperationResult<CreateUserResponse>> CreateUserAsync(
        string email, string password, List<string> roles, string? idempotencyKey, CancellationToken ct)
    {
        try
        {
            await using var connection = await _dataSource.OpenConnectionAsync(ct);
            await using var transaction = await connection.BeginTransactionAsync(ct);

            var userId = Guid.NewGuid();
            var passwordHash = HashPassword(password);
            var emailNorm = email.ToLowerInvariant();
            var emailHash = ComputeHash(emailNorm);

            const string insertUserSql = """
                INSERT INTO identity.users (id, email, email_hash, password_hash, status, created_at, updated_at, published_at, correlation_id)
                VALUES (@id, @email, @emailHash, @passwordHash, 'active', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP, @correlationId)
                ON CONFLICT(email) DO NOTHING
                RETURNING id, email, status, created_at;
                """;

            await using var cmd = connection.CreateCommand();
            cmd.CommandText = insertUserSql;
            cmd.Parameters.AddWithValue("@id", userId);
            cmd.Parameters.AddWithValue("@email", emailNorm);
            cmd.Parameters.AddWithValue("@emailHash", emailHash);
            cmd.Parameters.AddWithValue("@passwordHash", passwordHash);
            cmd.Parameters.AddWithValue("@correlationId", idempotencyKey ?? Guid.NewGuid().ToString());

            var user = await cmd.ExecuteScalarAsync(ct);
            if (user == null)
            {
                await transaction.RollbackAsync(ct);
                return new OperationResult<CreateUserResponse>
                {
                    IsSuccess = false,
                    Error = "User with this email already exists"
                };
            }

            // Insert roles
            foreach (var role in roles)
            {
                const string insertRoleSql = """
                    INSERT INTO identity.user_roles (user_id, role_id, assigned_at, published_at, correlation_id)
                    SELECT @userId, id, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP, @correlationId
                    FROM identity.roles WHERE name = @roleName;
                    """;

                await using var roleCmd = connection.CreateCommand();
                roleCmd.CommandText = insertRoleSql;
                roleCmd.Parameters.AddWithValue("@userId", userId);
                roleCmd.Parameters.AddWithValue("@roleName", role);
                roleCmd.Parameters.AddWithValue("@correlationId", idempotencyKey ?? Guid.NewGuid().ToString());

                await roleCmd.ExecuteNonQueryAsync(ct);
            }

            await transaction.CommitAsync(ct);

            return new OperationResult<CreateUserResponse>
            {
                IsSuccess = true,
                Data = new CreateUserResponse
                {
                    UserId = userId,
                    Email = emailNorm,
                    Roles = roles,
                    CreatedAt = SystemClock.UtcNow.DateTime,
                }
            };
        }
        catch (Exception ex)
        {
            return new OperationResult<CreateUserResponse>
            {
                IsSuccess = false,
                Error = ex.Message
            };
        }
    }

    public async Task<(List<UserModel>, int total)> ListUsersAsync(
        int page, int limit, string? roleFilter, string? statusFilter, CancellationToken ct)
    {
        await using var connection = await _dataSource.OpenConnectionAsync(ct);

        // Count total
        const string countSql = """
            SELECT COUNT(*) FROM identity.users
            WHERE published_at <= CURRENT_TIMESTAMP
              AND (@status IS NULL OR status = @status)
              AND (@roleFilter IS NULL OR id IN (
                SELECT ur.user_id FROM identity.user_roles ur
                JOIN identity.roles r ON ur.role_id = r.id
                WHERE r.name = @roleFilter AND ur.removed_at IS NULL
              ));
            """;

        await using var countCmd = connection.CreateCommand();
        countCmd.CommandText = countSql;
        countCmd.Parameters.AddWithValue("@status", statusFilter ?? "");
        countCmd.Parameters.AddWithValue("@roleFilter", roleFilter ?? "");

        var total = Convert.ToInt32(await countCmd.ExecuteScalarAsync(ct));

        // Fetch page
        const string selectSql = """
            SELECT u.id, u.email, u.status, u.created_at,
                   array_agg(r.name) FILTER (WHERE r.name IS NOT NULL) as roles
            FROM identity.users u
            LEFT JOIN identity.user_roles ur ON u.id = ur.user_id AND ur.removed_at IS NULL
            LEFT JOIN identity.roles r ON ur.role_id = r.id
            WHERE u.published_at <= CURRENT_TIMESTAMP
              AND (@status IS NULL OR u.status = @status)
            GROUP BY u.id
            ORDER BY u.created_at DESC
            LIMIT @limit OFFSET @offset;
            """;

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = selectSql;
        cmd.Parameters.AddWithValue("@status", statusFilter ?? "");
        cmd.Parameters.AddWithValue("@limit", limit);
        cmd.Parameters.AddWithValue("@offset", (page - 1) * limit);

        var users = new List<UserModel>();
        await using var reader = await cmd.ExecuteReaderAsync(ct);

        while (await reader.ReadAsync(ct))
        {
            users.Add(new UserModel
            {
                Id = reader.GetGuid(0),
                Email = reader.GetString(1),
                Status = reader.GetString(2),
                CreatedAt = reader.GetDateTime(3),
                Roles = reader.IsDBNull(4) ? new List<string>() : ((string[])reader.GetValue(4)).ToList(),
            });
        }

        return (users, total);
    }

    public async Task<OperationResult<UpdateUserRolesResponse>> UpdateUserRolesAsync(
        Guid userId, List<string> roles, CancellationToken ct)
    {
        await using var connection = await _dataSource.OpenConnectionAsync(ct);
        await using var transaction = await connection.BeginTransactionAsync(ct);

        try
        {
            // Verify user exists
            const string verifySql = "SELECT id FROM identity.users WHERE id = @id;";
            await using var verifyCmd = connection.CreateCommand();
            verifyCmd.CommandText = verifySql;
            verifyCmd.Parameters.AddWithValue("@id", userId);

            if (await verifyCmd.ExecuteScalarAsync(ct) == null)
            {
                return new OperationResult<UpdateUserRolesResponse>
                {
                    IsSuccess = false,
                    Error = "User not found"
                };
            }

            // Revoke all current roles
            const string revokeSql = """
                UPDATE identity.user_roles
                SET removed_at = CURRENT_TIMESTAMP
                WHERE user_id = @userId AND removed_at IS NULL;
                """;

            await using var revokeCmd = connection.CreateCommand();
            revokeCmd.CommandText = revokeSql;
            revokeCmd.Parameters.AddWithValue("@userId", userId);
            await revokeCmd.ExecuteNonQueryAsync(ct);

            // Assign new roles
            foreach (var role in roles)
            {
                const string assignSql = """
                    INSERT INTO identity.user_roles (user_id, role_id, assigned_at, published_at, correlation_id)
                    SELECT @userId, id, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP, @correlationId
                    FROM identity.roles WHERE name = @roleName;
                    """;

                await using var assignCmd = connection.CreateCommand();
                assignCmd.CommandText = assignSql;
                assignCmd.Parameters.AddWithValue("@userId", userId);
                assignCmd.Parameters.AddWithValue("@roleName", role);
                assignCmd.Parameters.AddWithValue("@correlationId", Guid.NewGuid().ToString());

                await assignCmd.ExecuteNonQueryAsync(ct);
            }

            await transaction.CommitAsync(ct);

            return new OperationResult<UpdateUserRolesResponse>
            {
                IsSuccess = true,
                Data = new UpdateUserRolesResponse
                {
                    UserId = userId,
                    Roles = roles,
                    UpdatedAt = SystemClock.UtcNow.DateTime,
                }
            };
        }
        catch (Exception ex)
        {
            await transaction.RollbackAsync(ct);
            return new OperationResult<UpdateUserRolesResponse>
            {
                IsSuccess = false,
                Error = ex.Message
            };
        }
    }

    private static string HashPassword(string password)
    {
        // Simplified: use bcrypt in production
        return Convert.ToBase64String(System.Security.Cryptography.SHA256.HashData(Encoding.UTF8.GetBytes(password)));
    }

    private static string ComputeHash(string input)
    {
        return Convert.ToBase64String(System.Security.Cryptography.SHA256.HashData(Encoding.UTF8.GetBytes(input)));
    }
}

public class UserModel
{
    public Guid Id { get; set; }
    public string Email { get; set; } = "";
    public List<string> Roles { get; set; } = new();
    public string Status { get; set; } = "active";
    public DateTime CreatedAt { get; set; }
}

public interface IIdempotencyStore
{
    Task<CreateUserResponse?> GetAsync(string idempotencyKey, CancellationToken ct);
    Task StoreAsync(string idempotencyKey, CreateUserResponse response, CancellationToken ct);
}

public class OperationResult<T>
{
    public bool IsSuccess { get; set; }
    public T? Data { get; set; }
    public string Error { get; set; } = "";
}

public class ValidationFailure
{
    private readonly List<(string field, string message)> _errors = new();

    public void AddError(string field, string message)
    {
        _errors.Add((field, message));
    }

    public override string ToString()
    {
        return string.Join("; ", _errors.Select(e => $"{e.field}: {e.message}"));
    }
}