social-media/backend/src/Socialize.Api/Modules/CalendarIntegrations/Handlers/UserCalendarExportFeed.cs

using FastEndpoints;
using Microsoft.EntityFrameworkCore;
using Socialize.Api.Data;
using Socialize.Api.Infrastructure.Security;
using Socialize.Api.Modules.CalendarIntegrations.Data;
using Socialize.Api.Modules.CalendarIntegrations.Services;
using Socialize.Api.Modules.Identity.Data;

namespace Socialize.Api.Modules.CalendarIntegrations.Handlers;

public record UserCalendarExportFeedDto(
    bool IsEnabled,
    string? FeedUrl,
    DateTimeOffset? CreatedAt,
    DateTimeOffset? UpdatedAt,
    DateTimeOffset? RevokedAt);

public class GetUserCalendarExportFeedHandler(AppDbContext dbContext)
    : EndpointWithoutRequest<UserCalendarExportFeedDto>
{
    public override void Configure()
    {
        Get("/api/calendar-integrations/export-feed");
        Options(o => o.WithTags("Calendar Integrations"));
    }

    public override async Task HandleAsync(CancellationToken ct)
    {
        UserCalendarExportFeed? feed = await dbContext.UserCalendarExportFeeds
            .SingleOrDefaultAsync(candidate => candidate.UserId == User.GetUserId(), ct);

        await SendAsync(UserCalendarExportFeedMapper.ToDto(feed, UserCalendarExportFeedMapper.BuildFeedUrl(feed)), cancellation: ct);
    }
}

public class EnableUserCalendarExportFeedHandler(AppDbContext dbContext)
    : EndpointWithoutRequest<UserCalendarExportFeedDto>
{
    public override void Configure()
    {
        Post("/api/calendar-integrations/export-feed/enable");
        Options(o => o.WithTags("Calendar Integrations"));
    }

    public override async Task HandleAsync(CancellationToken ct)
    {
        Guid userId = User.GetUserId();
        string token = CalendarExportFeedTokenService.GenerateToken();
        string tokenHash = CalendarExportFeedTokenService.HashToken(token);
        DateTimeOffset now = DateTimeOffset.UtcNow;

        UserCalendarExportFeed? feed = await dbContext.UserCalendarExportFeeds
            .SingleOrDefaultAsync(candidate => candidate.UserId == userId, ct);

        if (feed is null)
        {
            feed = new UserCalendarExportFeed
            {
                Id = Guid.NewGuid(),
                UserId = userId,
                Token = token,
                TokenHash = tokenHash,
                UpdatedAt = now,
            };
            dbContext.UserCalendarExportFeeds.Add(feed);
        }
        else if (feed.TokenHash is null || feed.RevokedAt.HasValue)
        {
            feed.Token = token;
            feed.TokenHash = tokenHash;
            feed.RevokedAt = null;
            feed.UpdatedAt = now;
        }
        else
        {
            token = string.Empty;
        }

        await dbContext.SaveChangesAsync(ct);
        await SendAsync(UserCalendarExportFeedMapper.ToDto(feed, UserCalendarExportFeedMapper.BuildFeedUrl(feed, token)), cancellation: ct);
    }
}

public class RegenerateUserCalendarExportFeedHandler(AppDbContext dbContext)
    : EndpointWithoutRequest<UserCalendarExportFeedDto>
{
    public override void Configure()
    {
        Post("/api/calendar-integrations/export-feed/regenerate");
        Options(o => o.WithTags("Calendar Integrations"));
    }

    public override async Task HandleAsync(CancellationToken ct)
    {
        Guid userId = User.GetUserId();
        string token = CalendarExportFeedTokenService.GenerateToken();
        DateTimeOffset now = DateTimeOffset.UtcNow;

        UserCalendarExportFeed? feed = await dbContext.UserCalendarExportFeeds
            .SingleOrDefaultAsync(candidate => candidate.UserId == userId, ct);

        if (feed is null)
        {
            feed = new UserCalendarExportFeed
            {
                Id = Guid.NewGuid(),
                UserId = userId,
                UpdatedAt = now,
            };
            dbContext.UserCalendarExportFeeds.Add(feed);
        }

        feed.TokenHash = CalendarExportFeedTokenService.HashToken(token);
        feed.Token = token;
        feed.RevokedAt = null;
        feed.UpdatedAt = now;

        await dbContext.SaveChangesAsync(ct);
        await SendAsync(UserCalendarExportFeedMapper.ToDto(feed, UserCalendarExportFeedMapper.BuildFeedUrl(feed, token)), cancellation: ct);
    }
}

public class RevokeUserCalendarExportFeedHandler(AppDbContext dbContext)
    : EndpointWithoutRequest<UserCalendarExportFeedDto>
{
    public override void Configure()
    {
        Delete("/api/calendar-integrations/export-feed");
        Options(o => o.WithTags("Calendar Integrations"));
    }

    public override async Task HandleAsync(CancellationToken ct)
    {
        UserCalendarExportFeed? feed = await dbContext.UserCalendarExportFeeds
            .SingleOrDefaultAsync(candidate => candidate.UserId == User.GetUserId(), ct);

        if (feed is not null)
        {
            feed.TokenHash = null;
            feed.Token = null;
            feed.RevokedAt = DateTimeOffset.UtcNow;
            feed.UpdatedAt = feed.RevokedAt.Value;
            await dbContext.SaveChangesAsync(ct);
        }

        await SendAsync(UserCalendarExportFeedMapper.ToDto(feed, null), cancellation: ct);
    }
}

public class GetUserCalendarExportFeedIcsHandler(
    AppDbContext dbContext,
    CalendarExportFeedService feedService)
    : EndpointWithoutRequest
{
    public override void Configure()
    {
        AllowAnonymous();
        Get("/api/calendar-integrations/export-feed/{token}.ics");
        Options(o => o.WithTags("Calendar Integrations"));
    }

    public override async Task HandleAsync(CancellationToken ct)
    {
        string? token = Route<string?>("token");
        if (string.IsNullOrWhiteSpace(token))
        {
            await SendNotFoundAsync(ct);
            return;
        }

        string tokenHash = CalendarExportFeedTokenService.HashToken(token);

        UserCalendarExportFeed? feed = await dbContext.UserCalendarExportFeeds
            .SingleOrDefaultAsync(candidate =>
                candidate.TokenHash == tokenHash &&
                !candidate.RevokedAt.HasValue,
                ct);

        if (feed is null)
        {
            await SendNotFoundAsync(ct);
            return;
        }

        User? user = await dbContext.Users.SingleOrDefaultAsync(candidate => candidate.Id == feed.UserId, ct);
        if (user is null)
        {
            await SendNotFoundAsync(ct);
            return;
        }

        string appBaseUrl = $"{HttpContext.Request.Scheme}://{HttpContext.Request.Host}";
        string ics = await feedService.BuildUserFeedAsync(feed.UserId, user.Email, appBaseUrl, ct);

        HttpContext.Response.ContentType = "text/calendar; charset=utf-8";
        await HttpContext.Response.WriteAsync(ics, ct);
    }
}

file static class UserCalendarExportFeedMapper
{
    public static UserCalendarExportFeedDto ToDto(UserCalendarExportFeed? feed, string? feedUrl)
    {
        return new UserCalendarExportFeedDto(
            feed?.TokenHash is not null && !feed.RevokedAt.HasValue,
            feedUrl,
            feed?.CreatedAt,
            feed?.UpdatedAt,
            feed?.RevokedAt);
    }

    public static string? BuildFeedUrl(UserCalendarExportFeed? feed, string? token = null)
    {
        if (feed?.TokenHash is null || feed.RevokedAt.HasValue)
        {
            return null;
        }

        string effectiveToken = string.IsNullOrWhiteSpace(token) ? feed.Token ?? string.Empty : token;
        return string.IsNullOrWhiteSpace(effectiveToken)
            ? null
            : $"/api/calendar-integrations/export-feed/{effectiveToken}.ics";
    }
}