using MongoDB.Bson;
using MongoDB.Driver;
using QuestionsApi.Models;

namespace QuestionsApi.Services;

public static class Step3SystemBackfillCommand
{
    public const string Confirmation = "BACKFILL_STEP3_SYSTEMS";

    public static async Task<int> RunAsync(IConfiguration configuration, string[] args, TextWriter output)
    {
        var apply = args.Contains("--apply", StringComparer.Ordinal);
        var confirmIndex = Array.IndexOf(args, "--confirm");
        var confirmation = confirmIndex >= 0 && confirmIndex + 1 < args.Length ? args[confirmIndex + 1] : "";
        var database = new MongoDatabaseProvider(configuration).Database;
        var questions = database.GetCollection<Question>("Questions");
        var all = await questions.Find(FilterDefinition<Question>.Empty).ToListAsync();
        var classified = all.Select(question => (Question: question, System: Step3SystemCatalog.Derive(question) ?? "")).ToList();
        var changes = classified.Where(item => item.System.Length > 0 && item.Question.Step3System != item.System).ToList();
        var unmapped = classified.Count(item => item.System.Length == 0);
        await output.WriteLineAsync($"Questions requiring Step3System backfill: {changes.Count}; unmapped: {unmapped}.");
        foreach (var group in classified.Where(item => item.System.Length == 0)
                     .GroupBy(item => $"{item.Question.System} | {item.Question.PerformanceCategory} | {item.Question.Discipline}")
                     .OrderByDescending(group => group.Count()).ThenBy(group => group.Key, StringComparer.Ordinal))
            await output.WriteLineAsync($"Unmapped ({group.Count()}): {group.Key}; ids: {string.Join(", ", group.Select(item => item.Question.ExternalId).Take(10))}");
        if (!apply)
        {
            await output.WriteLineAsync($"Dry run only. Re-run with --apply --confirm {Confirmation}.");
            return 0;
        }
        if (confirmation != Confirmation)
        {
            await output.WriteLineAsync($"Refusing migration: --confirm {Confirmation} is required.");
            return 2;
        }
        if (changes.Count > 0)
        {
            var writes = changes.Select(item => new UpdateOneModel<Question>(
                Builders<Question>.Filter.Eq(question => question.Id, item.Question.Id),
                Builders<Question>.Update.Set(question => question.Step3System, item.System))).ToList();
            await questions.BulkWriteAsync(writes, new BulkWriteOptions { IsOrdered = false });
        }
        var remaining = await questions.CountDocumentsAsync(new BsonDocumentFilterDefinition<Question>(
            new BsonDocument("$or", new BsonArray
            {
                new BsonDocument(nameof(Question.Step3System), new BsonDocument("$exists", false)),
                new BsonDocument(nameof(Question.Step3System), "")
            })));
        await output.WriteLineAsync($"Backfilled {changes.Count}; unmapped or empty Step3System: {remaining}.");
        return 0;
    }
}