using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using Dapper;
using GB5Shared.DTO.Framework.Login;
using GB5Shared.QueryExecutor;
using static GB5Shared.QueryExecutor.QueryExecutor;

namespace GB5Shared.ListQuery
{
    // ─────────────────────────────────────────────────────────────────────
    //  SqlListHandler<TQuery, TCriteria, TResult>
    //
    //  Abstract base class for all standard list query handlers.
    //  Owns the boilerplate that would otherwise be repeated in every handler:
    //    • SqlDialectFactory.Get(login.DatabaseType)
    //    • IQueryExecutor.QueryPagedAsync   (HandleAsync — paged result)
    //    • IQueryExecutor.QueryStreamAsync  (StreamAsync — unbounded stream)
    //
    //  Subclass provides ONE override:
    //    • BuildSql(TCriteria criteria, ISqlDialect dialect)
    //        → (string Sql, DynamicParameters Params)
    //
    //  Paging must be embedded in the SQL by SqlClauses.Paging() inside
    //  the QB method. IQueryExecutor.QueryPagedAsync does not accept
    //  separate pageOffset/pageSize parameters.
    //
    //  Generic constraints:
    //    TQuery    : IListQuery<TResult, TCriteria>  — query record with Criteria property
    //    TCriteria : class                           — typed criteria (implements ICriteria)
    //    TResult   : unconstrained                  — the per-row DTO
    //
    //  DI / Scrutor:
    //    This class is abstract → excluded from the Scrutor scan
    //    (.AddClasses(c => c.Where(t => !t.IsAbstract && !t.IsInterface))).
    //    Concrete sealed subclasses are registered automatically. No manual
    //    DI registration is needed.
    //
    //  Usage (the only code a module developer writes):
    //
    //      public sealed class FooListHandler
    //          : SqlListHandler<FooListQuery, FooCriteria, FooListDTO>
    //      {
    //          public FooListHandler(IQueryExecutor qe) : base(qe) { }
    //
    //          protected override (string Sql, DynamicParameters Params) BuildSql(
    //              FooCriteria c, ISqlDialect d)
    //              => FooQB.BuildFooList(c, d);
    //      }
    // ─────────────────────────────────────────────────────────────────────
    public abstract class SqlListHandler<TQuery, TCriteria, TResult>
        : IListHandler<TQuery, TResult>
        where TQuery    : IListQuery<TResult, TCriteria>
        where TCriteria : class
    {
        private readonly IQueryExecutor _qe;

        protected SqlListHandler(IQueryExecutor qe) => _qe = qe;

        // ── The one method subclasses must override ────────────────────────
        /// <summary>
        /// Builds the parameterised SQL for the given criteria and dialect.
        /// Paging (OFFSET/FETCH or LIMIT/OFFSET) must be embedded here via
        /// <c>SqlClauses.Paging()</c>; it is not injected by the executor.
        /// </summary>
        protected abstract (string Sql, DynamicParameters Params) BuildSql(
            TCriteria criteria, ISqlDialect dialect);

        // ── IListHandler<TQuery, TResult> ─────────────────────────────────

        /// <inheritdoc/>
        public async Task<PagedResult<TResult>> HandleAsync(
            TQuery query, LoginDTO login, CancellationToken ct = default)
        {
            var dialect      = SqlDialectFactory.Get(login.DatabaseType);
            var (sql, param) = BuildSql(query.Criteria, dialect);
            // QueryPagedAsync has no CancellationToken overload — paging is in the SQL.
            return await _qe.QueryPagedAsync<TResult>(login, sql, param)
                             .ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async IAsyncEnumerable<TResult> StreamAsync(
            TQuery query, LoginDTO login,
            [EnumeratorCancellation] CancellationToken ct = default)
        {
            var dialect      = SqlDialectFactory.Get(login.DatabaseType);
            var (sql, param) = BuildSql(query.Criteria, dialect);
            // QueryStreamAsync accepts CancellationToken as the 4th positional arg.
            await foreach (var row in _qe.QueryStreamAsync<TResult>(login, sql, param, ct)
                                         .ConfigureAwait(false))
                yield return row;
        }
    }
}