using GameList.Contracts;
using GameList.Data;
using GameList.Domain;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.ChangeTracking;

namespace GameList.Endpoints;

internal sealed class VoteWorkflowService(AppDbContext db)
{
    public async Task<ServiceResult<IReadOnlyList<VoteRecordDto>>> GetMineAsync(Guid playerId)
    {
        var phase = await EndpointHelpers.GetCurrentPhaseAsync(db, playerId);
        if (phase != Phase.Vote)
            return ServiceResult<IReadOnlyList<VoteRecordDto>>.Failure(ServiceError.PhaseMismatch(Phase.Vote, phase));

        IReadOnlyList<VoteRecordDto> votes = await db.Votes
            .AsNoTracking()
            .Where(v => v.PlayerId == playerId)
            .Select(v => new VoteRecordDto(v.SuggestionId, v.Score))
            .ToListAsync();

        return ServiceResult<IReadOnlyList<VoteRecordDto>>.Success(votes);
    }

    public async Task<ServiceResult<VoteUpsertResponse>> UpsertAsync(Guid playerId, int suggestionId, int score)
    {
        if (score is < 0 or > 10)
            return ServiceResult<VoteUpsertResponse>.Failure(ServiceError.BadRequest("Score must be between 0 and 10."));

        var playerState = await db.Players
            .AsNoTracking()
            .Where(p => p.Id == playerId)
            .Select(p => new
            {
                p.VotesFinal,
                p.DisplayName
            })
            .FirstAsync();

        if (playerState.VotesFinal)
            return ServiceResult<VoteUpsertResponse>.Failure(ServiceError.BadRequest("Votes are finalized. Unfinalize before changing scores."));

        var phase = await EndpointHelpers.GetCurrentPhaseAsync(db, playerId);
        if (phase != Phase.Vote)
            return ServiceResult<VoteUpsertResponse>.Failure(ServiceError.PhaseMismatch(Phase.Vote, phase));

        if (string.IsNullOrWhiteSpace(playerState.DisplayName))
            return ServiceResult<VoteUpsertResponse>.Failure(ServiceError.BadRequest("Set a display name before voting."));

        var linkMap = await db.Suggestions
            .AsNoTracking()
            .Select(s => new
            {
                s.Id,
                s.ParentSuggestionId
            })
            .ToListAsync();
        var rootIndex = EndpointHelpers.BuildLinkRoots(linkMap.Select(s => (s.Id, s.ParentSuggestionId)));
        if (!rootIndex.ContainsKey(suggestionId))
            return ServiceResult<VoteUpsertResponse>.Failure(ServiceError.BadRequest("Suggestion not found."));

        var linkedIds = EndpointHelpers.LinkedIdsFor(suggestionId, rootIndex);
        if (linkedIds.Count == 0)
            linkedIds.Add(suggestionId);

        var existingVotes = await db.Votes
            .Where(v => v.PlayerId == playerId && linkedIds.Contains(v.SuggestionId))
            .ToListAsync();

        for (var attempt = 0; attempt < 2; attempt++)
        {
            foreach (var linkedSuggestionId in linkedIds)
            {
                var vote = existingVotes.FirstOrDefault(v => v.SuggestionId == linkedSuggestionId);
                if (vote == null)
                {
                    db.Votes.Add(new Vote
                    {
                        PlayerId = playerId,
                        SuggestionId = linkedSuggestionId,
                        Score = score
                    });
                }
                else
                {
                    vote.Score = score;
                }
            }

            try
            {
                await db.SaveChangesAsync();
                return ServiceResult<VoteUpsertResponse>.Success(new VoteUpsertResponse(linkedIds, score));
            }
            catch (DbUpdateException ex) when (attempt == 0 && EndpointHelpers.IsSqliteConstraintViolation(ex))
            {
                DetachAddedVotes(db.ChangeTracker.Entries<Vote>());

                await db.Votes
                    .Where(v => v.PlayerId == playerId && linkedIds.Contains(v.SuggestionId))
                    .ExecuteUpdateAsync(v => v.SetProperty(x => x.Score, score));

                existingVotes = await db.Votes
                    .Where(v => v.PlayerId == playerId && linkedIds.Contains(v.SuggestionId))
                    .ToListAsync();
            }
        }

        return ServiceResult<VoteUpsertResponse>.Failure(ServiceError.Conflict("Vote update conflict. Please retry."));
    }

    public async Task<ServiceResult<VoteFinalizeResponse>> SetFinalizeAsync(Guid playerId, bool final)
    {
        var phase = await EndpointHelpers.GetCurrentPhaseAsync(db, playerId);
        if (phase != Phase.Vote)
            return ServiceResult<VoteFinalizeResponse>.Failure(ServiceError.PhaseMismatch(Phase.Vote, phase));

        var player = await db.Players.FirstAsync(p => p.Id == playerId);

        player.VotesFinal = final;
        await db.SaveChangesAsync();
        return ServiceResult<VoteFinalizeResponse>.Success(new VoteFinalizeResponse(player.VotesFinal));
    }

    private static void DetachAddedVotes(IEnumerable<EntityEntry<Vote>> voteEntries)
    {
        foreach (var entry in voteEntries)
        {
            if (entry.State == EntityState.Added)
                entry.State = EntityState.Detached;
        }
    }
}