using System.ComponentModel.DataAnnotations;
using Jiaowu.Api.Domain.Academic;
using Jiaowu.Api.Domain.Identity;
using Jiaowu.Api.Infrastructure.Auth;
using Jiaowu.Api.Infrastructure.Persistence;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;

namespace Jiaowu.Api.Controllers;

[ApiController]
[Authorize]
[Route("api/notifications")]
public sealed class NotificationsController(
    AppDbContext db,
    ICurrentUserDataScope currentUserDataScope) : ControllerBase
{
    private const string Senders =
        SystemRoles.SuperAdmin + "," +
        SystemRoles.AcademicAdmin + "," +
        SystemRoles.CollegeAdmin + "," +
        SystemRoles.Counselor + "," +
        SystemRoles.Teacher;

    [HttpGet]
    public async Task<ActionResult> GetNotifications(
        bool? unreadOnly,
        NotificationCategory? category,
        string? keyword,
        int page = 1,
        int pageSize = 20,
        CancellationToken cancellationToken = default)
    {
        page = Math.Max(1, page);
        pageSize = Math.Clamp(pageSize, 1, 100);
        var userId = currentUserDataScope.Current.UserId;
        var source = db.Notifications.AsNoTracking()
            .Where(x => x.UserId == userId);
        if (unreadOnly == true)
            source = source.Where(x => !x.IsRead);
        if (category.HasValue)
            source = source.Where(x => x.Category == category);
        if (!string.IsNullOrWhiteSpace(keyword))
        {
            var value = keyword.Trim();
            source = source.Where(x =>
                x.Title.Contains(value) ||
                x.Content.Contains(value));
        }

        var total = await source.CountAsync(cancellationToken);
        var items = await source
            .OrderByDescending(x => x.CreatedAt)
            .Skip((page - 1) * pageSize)
            .Take(pageSize)
            .Select(x => new
            {
                x.Id,
                x.Title,
                x.Content,
                x.Category,
                x.IsRead,
                x.LinkUrl,
                SenderName = x.MessageDispatch == null
                    ? "教务系统"
                    : x.MessageDispatch.SenderName,
                AudienceName = x.MessageDispatch == null
                    ? null
                    : x.MessageDispatch.AudienceName,
                IsManual = x.MessageDispatchId != null,
                x.CreatedAt
            })
            .ToListAsync(cancellationToken);

        var unreadCount = await db.Notifications
            .CountAsync(x => x.UserId == userId && !x.IsRead, cancellationToken);
        var unreadByCategory = await db.Notifications.AsNoTracking()
            .Where(x => x.UserId == userId && !x.IsRead)
            .GroupBy(x => x.Category)
            .Select(x => new { Category = x.Key, Count = x.Count() })
            .ToListAsync(cancellationToken);

        return Ok(new
        {
            Items = items,
            Total = total,
            UnreadCount = unreadCount,
            UnreadByCategory = unreadByCategory
        });
    }

    [HttpGet("unread-count")]
    public async Task<ActionResult> GetUnreadCount(CancellationToken cancellationToken)
    {
        var userId = currentUserDataScope.Current.UserId;
        var count = await db.Notifications
            .CountAsync(x => x.UserId == userId && !x.IsRead, cancellationToken);
        return Ok(new { Count = count });
    }

    [HttpGet("composer")]
    [Authorize(Roles = Senders)]
    public async Task<ActionResult> GetComposer(CancellationToken cancellationToken)
    {
        var scope = currentUserDataScope.Current;
        if (IsSchoolAdministrator(scope))
        {
            var recipientCount = await db.Users.AsNoTracking()
                .CountAsync(
                    x => x.IsEnabled && x.Id != scope.UserId,
                    cancellationToken);
            return Ok(new
            {
                AudienceType = MessageAudienceType.School,
                AudienceName = "全校已启用账号",
                RecipientCount = recipientCount,
                TeachingTasks = Array.Empty<object>()
            });
        }

        if (scope.IsInRole(SystemRoles.CollegeAdmin) ||
            scope.IsInRole(SystemRoles.Counselor))
        {
            var collegeId = await ResolveSenderCollegeIdAsync(
                scope,
                cancellationToken);
            if (!collegeId.HasValue)
            {
                return ConflictProblem(
                    "当前账号未关联学院，暂时无法确定发信范围。");
            }

            var college = await db.Colleges.AsNoTracking()
                .Where(x => x.Id == collegeId.Value)
                .Select(x => x.Name)
                .FirstOrDefaultAsync(cancellationToken);
            if (college is null)
                return ConflictProblem("当前账号关联的学院不存在。");

            var recipientCount = await db.Users.AsNoTracking()
                .CountAsync(
                    x => x.IsEnabled &&
                         x.Id != scope.UserId &&
                         x.CollegeId == collegeId.Value,
                    cancellationToken);
            return Ok(new
            {
                AudienceType = MessageAudienceType.College,
                AudienceName = $"{college}全院成员",
                RecipientCount = recipientCount,
                TeachingTasks = Array.Empty<object>()
            });
        }

        if (scope.IsInRole(SystemRoles.Teacher))
        {
            var tasks = await db.TeachingTasks.AsNoTracking()
                .Where(task =>
                    task.Status != TeachingTaskStatus.Draft &&
                    task.Teachers.Any(item =>
                        item.Teacher!.UserId == scope.UserId))
                .OrderByDescending(task => task.AcademicTerm!.IsCurrent)
                .ThenByDescending(task => task.AcademicTerm!.StartDate)
                .ThenBy(task => task.TaskNumber)
                .Select(task => new
                {
                    task.Id,
                    task.TaskNumber,
                    CourseName = task.Course!.Name,
                    TermName = task.AcademicTerm!.Name,
                    RecipientCount = db.Students.Count(student =>
                        student.Status == StudentStatus.Active &&
                        student.UserId != null &&
                        (task.Classes.Any(item =>
                             item.AdministrativeClassId ==
                             student.AdministrativeClassId) ||
                         db.CourseEnrollments.Any(enrollment =>
                             enrollment.StudentId == student.Id &&
                             enrollment.Status ==
                             CourseEnrollmentStatus.Enrolled &&
                             enrollment.CourseSelectionOffering!
                                 .TeachingTaskId == task.Id)))
                })
                .ToListAsync(cancellationToken);
            return Ok(new
            {
                AudienceType = MessageAudienceType.TeachingTask,
                AudienceName = "所带教学班",
                RecipientCount = 0,
                TeachingTasks = tasks
            });
        }

        return Forbid();
    }

    [HttpPost("send")]
    [Authorize(Roles = Senders)]
    public async Task<ActionResult> Send(
        SendMessageRequest request,
        CancellationToken cancellationToken)
    {
        var title = request.Title.Trim();
        var content = request.Content.Trim();
        if (title.Length == 0)
            return ValidationProblem("请填写消息标题。");
        if (content.Length == 0)
            return ValidationProblem("请填写消息正文。");
        var scope = currentUserDataScope.Current;
        MessageAudienceType audienceType;
        Guid? audienceId = null;
        string audienceName;
        List<Guid> recipientIds;

        if (IsSchoolAdministrator(scope))
        {
            audienceType = MessageAudienceType.School;
            audienceName = "全校已启用账号";
            recipientIds = await db.Users.AsNoTracking()
                .Where(x => x.IsEnabled && x.Id != scope.UserId)
                .Select(x => x.Id)
                .ToListAsync(cancellationToken);
        }
        else if (scope.IsInRole(SystemRoles.CollegeAdmin) ||
                 scope.IsInRole(SystemRoles.Counselor))
        {
            var collegeId = await ResolveSenderCollegeIdAsync(
                scope,
                cancellationToken);
            if (!collegeId.HasValue)
            {
                return ConflictProblem(
                    "当前账号未关联学院，暂时无法确定发信范围。");
            }

            var collegeName = await db.Colleges.AsNoTracking()
                .Where(x => x.Id == collegeId.Value)
                .Select(x => x.Name)
                .FirstOrDefaultAsync(cancellationToken);
            if (collegeName is null)
                return ConflictProblem("当前账号关联的学院不存在。");

            audienceType = MessageAudienceType.College;
            audienceId = collegeId.Value;
            audienceName = $"{collegeName}全院成员";
            recipientIds = await db.Users.AsNoTracking()
                .Where(x =>
                    x.IsEnabled &&
                    x.Id != scope.UserId &&
                    x.CollegeId == collegeId.Value)
                .Select(x => x.Id)
                .ToListAsync(cancellationToken);
        }
        else if (scope.IsInRole(SystemRoles.Teacher))
        {
            if (!request.TeachingTaskId.HasValue)
                return ValidationProblem("请选择接收消息的教学班。");

            var task = await db.TeachingTasks.AsNoTracking()
                .Where(x =>
                    x.Id == request.TeachingTaskId.Value &&
                    x.Status != TeachingTaskStatus.Draft &&
                    x.Teachers.Any(item =>
                        item.Teacher!.UserId == scope.UserId))
                .Select(x => new
                {
                    x.Id,
                    x.TaskNumber,
                    CourseName = x.Course!.Name
                })
                .FirstOrDefaultAsync(cancellationToken);
            if (task is null)
            {
                return ConflictProblem(
                    "只能向自己所带且已发布的教学班发信。");
            }

            audienceType = MessageAudienceType.TeachingTask;
            audienceId = task.Id;
            audienceName = $"{task.TaskNumber} · {task.CourseName}";
            recipientIds = await GetTeachingTaskRecipientIdsAsync(
                task.Id,
                cancellationToken);
        }
        else
        {
            return Forbid();
        }

        recipientIds = recipientIds.Distinct().ToList();
        if (recipientIds.Count == 0)
            return ConflictProblem("当前发信范围内没有可接收消息的已启用账号。");

        var dispatch = new MessageDispatch
        {
            SenderUserId = scope.UserId,
            SenderName = scope.DisplayName ?? "教务用户",
            Title = title,
            Content = content,
            Category = NotificationCategory.General,
            AudienceType = audienceType,
            AudienceId = audienceId,
            AudienceName = audienceName,
            RecipientCount = recipientIds.Count,
            LinkUrl = null
        };
        dispatch.Notifications = recipientIds.Select(userId => new Notification
        {
            UserId = userId,
            Title = title,
            Content = content,
            Category = NotificationCategory.General,
            LinkUrl = null
        }).ToList();

        db.MessageDispatches.Add(dispatch);
        await db.SaveChangesAsync(cancellationToken);
        return Ok(new
        {
            dispatch.Id,
            dispatch.AudienceName,
            dispatch.RecipientCount,
            dispatch.CreatedAt
        });
    }

    [HttpGet("sent")]
    [Authorize(Roles = Senders)]
    public async Task<ActionResult> GetSent(
        int page = 1,
        int pageSize = 20,
        CancellationToken cancellationToken = default)
    {
        page = Math.Max(1, page);
        pageSize = Math.Clamp(pageSize, 1, 100);
        var userId = currentUserDataScope.Current.UserId;
        var source = db.MessageDispatches.AsNoTracking()
            .Where(x => x.SenderUserId == userId);
        var total = await source.CountAsync(cancellationToken);
        var items = await source
            .OrderByDescending(x => x.CreatedAt)
            .Skip((page - 1) * pageSize)
            .Take(pageSize)
            .Select(x => new
            {
                x.Id,
                x.Title,
                x.Content,
                x.Category,
                x.AudienceType,
                x.AudienceName,
                x.RecipientCount,
                x.CreatedAt
            })
            .ToListAsync(cancellationToken);
        return Ok(new { Items = items, Total = total });
    }

    [HttpPost("{id:guid}/read")]
    public async Task<ActionResult> MarkRead(
        Guid id,
        CancellationToken cancellationToken)
    {
        var userId = currentUserDataScope.Current.UserId;
        var notification = await db.Notifications
            .FirstOrDefaultAsync(
                x => x.Id == id && x.UserId == userId,
                cancellationToken);
        if (notification is null) return NotFound();
        notification.IsRead = true;
        await db.SaveChangesAsync(cancellationToken);
        return NoContent();
    }

    [HttpPost("read-all")]
    public async Task<ActionResult> MarkAllRead(
        CancellationToken cancellationToken)
    {
        var userId = currentUserDataScope.Current.UserId;
        await db.Notifications
            .Where(x => x.UserId == userId && !x.IsRead)
            .ExecuteUpdateAsync(
                updates => updates.SetProperty(x => x.IsRead, true),
                cancellationToken);
        return NoContent();
    }

    private async Task<List<Guid>> GetTeachingTaskRecipientIdsAsync(
        Guid teachingTaskId,
        CancellationToken cancellationToken)
    {
        return await db.Students.AsNoTracking()
            .Where(student =>
                student.Status == StudentStatus.Active &&
                student.UserId != null &&
                db.Users.Any(user =>
                    user.Id == student.UserId &&
                    user.IsEnabled) &&
                (db.TeachingTaskClasses.Any(item =>
                     item.TeachingTaskId == teachingTaskId &&
                     item.AdministrativeClassId ==
                     student.AdministrativeClassId) ||
                 db.CourseEnrollments.Any(enrollment =>
                     enrollment.StudentId == student.Id &&
                     enrollment.Status == CourseEnrollmentStatus.Enrolled &&
                     enrollment.CourseSelectionOffering!.TeachingTaskId ==
                     teachingTaskId)))
            .Select(x => x.UserId!.Value)
            .Distinct()
            .ToListAsync(cancellationToken);
    }

    private async Task<Guid?> ResolveSenderCollegeIdAsync(
        CurrentUserScope scope,
        CancellationToken cancellationToken)
    {
        if (scope.CollegeId.HasValue)
            return scope.CollegeId;
        if (!scope.IsInRole(SystemRoles.Counselor))
            return null;

        var collegeIds = await db.AdministrativeClasses.AsNoTracking()
            .Where(x => x.CounselorUserId == scope.UserId)
            .Select(x => x.Major!.CollegeId)
            .Distinct()
            .Take(2)
            .ToListAsync(cancellationToken);
        return collegeIds.Count == 1 ? collegeIds[0] : null;
    }

    private static bool IsSchoolAdministrator(CurrentUserScope scope) =>
        scope.IsInRole(SystemRoles.SuperAdmin) ||
        scope.IsInRole(SystemRoles.AcademicAdmin);

    private ActionResult ConflictProblem(string detail) =>
        Conflict(new ProblemDetails
        {
            Title = "无法发送消息",
            Detail = detail,
            Status = StatusCodes.Status409Conflict
        });

    private ActionResult ValidationProblem(string detail) =>
        BadRequest(new ProblemDetails
        {
            Title = "消息内容不完整",
            Detail = detail,
            Status = StatusCodes.Status400BadRequest
        });
}

public sealed record SendMessageRequest(
    [property: Required, StringLength(200)] string Title,
    [property: Required, StringLength(1000)] string Content,
    Guid? TeachingTaskId = null);

/// <summary>
/// Centralized helper to send notifications across the app.
/// </summary>
public static class NotificationService
{
    public static async Task SendAsync(
        AppDbContext db,
        Guid userId,
        string title,
        string content,
        string? linkUrl = null,
        CancellationToken cancellationToken = default,
        NotificationCategory category = NotificationCategory.General)
    {
        db.Notifications.Add(new Notification
        {
            UserId = userId,
            Title = title,
            Content = content,
            Category = category,
            LinkUrl = linkUrl
        });
        await db.SaveChangesAsync(cancellationToken);
    }

    public static async Task SendToRoleAsync(
        AppDbContext db,
        string roleName,
        string title,
        string content,
        Guid? collegeId = null,
        string? linkUrl = null,
        CancellationToken cancellationToken = default,
        NotificationCategory category = NotificationCategory.General)
    {
        var query = db.Users
            .Join(
                db.UserRoles,
                user => user.Id,
                userRole => userRole.UserId,
                (user, userRole) => new
                {
                    user.Id,
                    user.IsEnabled,
                    user.CollegeId,
                    userRole.RoleId
                })
            .Join(
                db.Roles,
                item => item.RoleId,
                role => role.Id,
                (item, role) => new
                {
                    item.Id,
                    item.IsEnabled,
                    item.CollegeId,
                    RoleName = role.Name!
                });

        var userIds = query.Where(x =>
            x.RoleName == roleName &&
            x.IsEnabled);

        if (collegeId.HasValue)
        {
            userIds = userIds.Where(x => x.CollegeId == collegeId.Value);
        }

        var ids = await userIds
            .Select(x => x.Id)
            .Distinct()
            .ToListAsync(cancellationToken);
        foreach (var id in ids)
        {
            db.Notifications.Add(new Notification
            {
                UserId = id,
                Title = title,
                Content = content,
                Category = category,
                LinkUrl = linkUrl
            });
        }
        await db.SaveChangesAsync(cancellationToken);
    }

    public static async Task SendToUserIdsAsync(
        AppDbContext db,
        IEnumerable<Guid> userIds,
        string title,
        string content,
        string? linkUrl = null,
        CancellationToken cancellationToken = default,
        NotificationCategory category = NotificationCategory.General)
    {
        foreach (var userId in userIds.Distinct())
        {
            db.Notifications.Add(new Notification
            {
                UserId = userId,
                Title = title,
                Content = content,
                Category = category,
                LinkUrl = linkUrl
            });
        }
        await db.SaveChangesAsync(cancellationToken);
    }
}