using LightlessSyncServer.Services.Interfaces;
using LightlessSyncShared.Data;
using LightlessSyncShared.Models;
using Microsoft.EntityFrameworkCore;

namespace LightlessSyncServer.Services
{
    public class PruneService(LightlessDbContext dbContext) : IPruneService
    {
        private readonly LightlessDbContext _dbContext = dbContext;

        public async Task<int> CountPrunableUsersAsync(string groupGid, int days, CancellationToken ct)
        {
            var allGroupUsers = await _dbContext.GroupPairs
                .Include(p => p.GroupUser)
                .Include(p => p.Group)
                .Where(g => g.GroupGID == groupGid)
                .ToListAsync(ct).ConfigureAwait(false);

            var inactivitySpan = GetInactivitySpan(days);
            var now = DateTime.UtcNow;

            var usersToPrune = allGroupUsers.Where(p =>
                !p.IsPinned &&
                !p.IsModerator &&
                !string.Equals(p.Group.OwnerUID, p.GroupUserUID, StringComparison.Ordinal) &&
                p.GroupUser.LastLoggedIn < now - inactivitySpan);

            return usersToPrune.Count();
        }

        public async Task<IReadOnlyList<GroupPair>> ExecutePruneAsync(string groupGid, int days, CancellationToken ct)
        {
            var allGroupUsers = await _dbContext.GroupPairs
                .Include(p => p.GroupUser)
                .Include(p => p.Group)
                .Where(g => g.GroupGID == groupGid)
                .ToListAsync(ct).ConfigureAwait(false);

            var inactivitySpan = GetInactivitySpan(days);
            var now = DateTime.UtcNow;

            var usersToPrune = allGroupUsers.Where(p =>
                !p.IsPinned &&
                !p.IsModerator &&
                !string.Equals(p.Group.OwnerUID, p.GroupUserUID, StringComparison.Ordinal) &&
                p.GroupUser.LastLoggedIn < now - inactivitySpan)
                .ToList();

            _dbContext.GroupPairs.RemoveRange(usersToPrune);
            await _dbContext.SaveChangesAsync(ct).ConfigureAwait(false);

            return usersToPrune;
        }

        private static TimeSpan GetInactivitySpan(int days) => days == 0
                ? TimeSpan.FromMinutes(15)
                : TimeSpan.FromDays(days);
    }
}