using System.Net;
using System.Security.Claims;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;
using Socialize.Api.Data;
using Socialize.Api.Infrastructure.Configuration;
using Socialize.Api.Infrastructure.Emailer.Contracts;
using Socialize.Api.Modules.Identity.Contracts;
using Socialize.Api.Modules.Identity.Data;
using Socialize.Api.Modules.Organizations.Services;
using Socialize.Api.Modules.ReleaseCommunications.Contracts;
using Socialize.Api.Modules.ReleaseCommunications.Data;

namespace Socialize.Api.Modules.ReleaseCommunications.Services;

internal class ReleaseUpdateEmailService(
    AppDbContext dbContext,
    UserManager userManager,
    IEmailSender emailSender,
    IOptionsSnapshot<WebsiteOptions> websiteOptions)
{
    public async Task<ReleaseUpdateEmailSendResultDto> SendManualUpdateEmailAsync(
        ReleaseUpdate update,
        Guid senderUserId,
        bool testMode,
        bool confirmResend,
        CancellationToken ct)
    {
        if (update.Status != ReleaseUpdateStatus.Published)
        {
            throw new InvalidOperationException("Only published release updates can be emailed.");
        }

        if (!testMode && update.ManualEmailSentAt.HasValue && !confirmResend)
        {
            throw new InvalidOperationException("This release update was already emailed. Confirm resend to send it again.");
        }

        IReadOnlyCollection<User> recipients = testMode
            ? await GetTestRecipientsAsync(senderUserId, ct)
            : await GetAudienceRecipientsAsync(update.Audience, ct);

        DateTimeOffset now = DateTimeOffset.UtcNow;
        foreach (User recipient in recipients.Where(recipient => !string.IsNullOrWhiteSpace(recipient.Email)))
        {
            await emailSender.SendEmailAsync(
                recipient.Email!,
                $"What's new in Socialize: {update.Title}",
                BuildSingleUpdateEmail(update));
        }

        if (!testMode)
        {
            update.ManualEmailSentByUserId = senderUserId;
            update.ManualEmailSentAt = now;
            update.ManualEmailAudience = update.Audience.ToString();
            update.ManualEmailRecipientCount = recipients.Count;
            update.UpdatedAt = now;
        }

        return new ReleaseUpdateEmailSendResultDto(recipients.Count, now, testMode);
    }

    public async Task<int> SendDueDigestEmailsAsync(
        TimeSpan inactiveThreshold,
        TimeSpan sendInterval,
        CancellationToken ct)
    {
        DateTimeOffset now = DateTimeOffset.UtcNow;
        DateTimeOffset inactiveBefore = now.Subtract(inactiveThreshold);
        DateTimeOffset lastSentBefore = now.Subtract(sendInterval);

        List<User> ownerUsers = await GetAudienceRecipientsAsync(ReleaseUpdateAudience.OrganizationOwners, ct);
        int sentCount = 0;
        foreach (User user in ownerUsers)
        {
            if (string.IsNullOrWhiteSpace(user.Email) ||
                !ReleaseUpdateEmailRules.IsInactive(user.LastAuthenticatedAt, inactiveBefore))
            {
                continue;
            }

            DateTimeOffset? lastDigestSentAt = await dbContext.ReleaseUpdateEmailDigestReceipts
                .Where(receipt => receipt.UserId == user.Id)
                .OrderByDescending(receipt => receipt.SentAt)
                .Select(receipt => (DateTimeOffset?)receipt.SentAt)
                .FirstOrDefaultAsync(ct);
            if (!ReleaseUpdateEmailRules.CanSendDigest(lastDigestSentAt, lastSentBefore))
            {
                continue;
            }

            ReleaseUpdateAudienceContext audienceContext = await ReleaseUpdateVisibility.GetAudienceContextAsync(
                dbContext,
                new ClaimsPrincipal(new ClaimsIdentity()),
                user.Id,
                ct);

            List<ReleaseUpdate> unreadUpdates = await dbContext.ReleaseUpdates
                .VisibleTo(audienceContext)
                .Where(update => !dbContext.ReleaseUpdateReadReceipts.Any(receipt =>
                    receipt.ReleaseUpdateId == update.Id &&
                    receipt.UserId == user.Id))
                .OrderByDescending(update => update.PublishedAt)
                .Take(10)
                .ToListAsync(ct);

            if (unreadUpdates.Count == 0)
            {
                continue;
            }

            await emailSender.SendEmailAsync(
                user.Email,
                "What's new in Socialize",
                BuildDigestEmail(unreadUpdates));

            dbContext.ReleaseUpdateEmailDigestReceipts.Add(new ReleaseUpdateEmailDigestReceipt
            {
                Id = Guid.NewGuid(),
                UserId = user.Id,
                SentAt = now,
                UpdateCount = unreadUpdates.Count,
            });
            sentCount++;
        }

        await dbContext.SaveChangesAsync(ct);
        return sentCount;
    }

    private async Task<IReadOnlyCollection<User>> GetTestRecipientsAsync(Guid senderUserId, CancellationToken ct)
    {
        User? sender = await userManager.Users.SingleOrDefaultAsync(user => user.Id == senderUserId, ct);
        return sender is null ? [] : [sender];
    }

    private async Task<List<User>> GetAudienceRecipientsAsync(ReleaseUpdateAudience audience, CancellationToken ct)
    {
        IQueryable<User> query = userManager.Users.Where(user => user.EmailConfirmed && user.Email != null);

        if (audience == ReleaseUpdateAudience.Developers)
        {
            IList<User> developers = await userManager.GetUsersInRoleAsync(KnownRoles.Developer);
            return developers.Where(user => user.EmailConfirmed && !string.IsNullOrWhiteSpace(user.Email)).ToList();
        }

        if (audience == ReleaseUpdateAudience.OrganizationOwners)
        {
            Guid[] ownerUserIds = await dbContext.Organizations
                .Select(organization => organization.OwnerUserId)
                .Concat(dbContext.OrganizationMemberships
                    .Where(membership => membership.Role == OrganizationRoles.Owner)
                    .Select(membership => membership.UserId))
                .Distinct()
                .ToArrayAsync(ct);

            query = query.Where(user => ownerUserIds.Contains(user.Id));
        }

        return await query.OrderBy(user => user.Email).ToListAsync(ct);
    }

    private string BuildSingleUpdateEmail(ReleaseUpdate update)
    {
        string updateUrl = $"{websiteOptions.Value.FrontendBaseUrl.TrimEnd('/')}/app/updates?updateId={update.Id}";
        return $"""
            <h1>{HtmlEncode(update.Title)}</h1>
            <p><strong>{HtmlEncode(update.Category.ToString())}</strong></p>
            <p>{HtmlEncode(update.Summary)}</p>
            {FormatBody(update.Body)}
            <p><a href="{HtmlEncode(updateUrl)}">Open What's New</a></p>
            """;
    }

    private string BuildDigestEmail(IReadOnlyCollection<ReleaseUpdate> updates)
    {
        string updateUrl = $"{websiteOptions.Value.FrontendBaseUrl.TrimEnd('/')}/app/updates";
        string listItems = string.Join(
            Environment.NewLine,
            updates.Select(update => $"<li><strong>{HtmlEncode(update.Title)}</strong><br>{HtmlEncode(update.Summary)}</li>"));

        return $"""
            <h1>What's new in Socialize</h1>
            <ul>{listItems}</ul>
            <p><a href="{HtmlEncode(updateUrl)}">Open What's New</a></p>
            """;
    }

    private static string FormatBody(string? body)
    {
        return string.IsNullOrWhiteSpace(body)
            ? string.Empty
            : $"<p>{HtmlEncode(body).Replace(Environment.NewLine, "<br>", StringComparison.Ordinal)}</p>";
    }

    private static string HtmlEncode(string? value)
    {
        return WebUtility.HtmlEncode(value ?? string.Empty);
    }
}