using System;
using System.Collections.Concurrent;
using System.Reflection;
using GB5Shared.DTO.Framework.Login;

namespace GB5Shared.ListQuery
{
    // ─────────────────────────────────────────────────────────────────────
    //  IQueryGuard<TQuery>
    //
    //  Optional per-query validation executed BEFORE the QB builds SQL.
    //  Use to enforce domain-specific mandatory-filter rules (e.g. date range
    //  required, minimum criteria supplied, OUId mandatory for heavy queries).
    //
    //  Register as IQueryGuard<TQuery> — Scrutor / AddListInfrastructure() scans
    //  module assemblies automatically. Multiple guards per query are supported;
    //  all run in registration order. GenericListHandler requests them via
    //  IEnumerable<IQueryGuard<TQuery>> — empty enumerable = permissive (no guard).
    //
    //  Rules:
    //    • Throw ArgumentException (or a domain-specific exception) to reject.
    //    • Do NOT perform DB calls inside a guard — guards are sync and fast.
    //    • Guards run before dialect resolution and QB — no SQL is built on reject.
    // ─────────────────────────────────────────────────────────────────────
    public interface IQueryGuard<in TQuery>
    {
        void Validate(TQuery query, LoginDTO login);
    }

    // ─────────────────────────────────────────────────────────────────────
    //  QueryIntent  – marks the intended execution target of a query
    //
    //  Used by IQueryExecutor (Phase 2) to route to main DB vs read replica.
    //  Default is Transactional (main DB). Override with [QuerySource] only
    //  where the semantic difference matters.
    //
    //  Rules:
    //    • Transactional: short OLTP queries that need fresh data.
    //    • Reporting: heavier reads acceptable on read replica (seconds stale).
    //    • Analytics: cross-period aggregations — data warehouse only.
    //    • Never mark as Reporting/Analytics if the result affects a workflow
    //      decision that requires up-to-the-second accuracy.
    // ─────────────────────────────────────────────────────────────────────
    public enum QueryIntent
    {
        Transactional = 0,  // main DB — OLTP queries, must be current
        Reporting     = 1,  // read replica — heavier reads, seconds stale is fine
        Analytics     = 2,  // data warehouse — cross-period aggregations
    }

    // ─────────────────────────────────────────────────────────────────────
    //  [QuerySource]  – decorate a query record to declare its intent
    //
    //  GenericListHandler reads this once per TQuery type at startup (cached).
    //  If absent, defaults to QueryIntent.Transactional.
    //
    //  Example:
    //      [QuerySource(QueryIntent.Reporting)]
    //      public sealed record PendingMMDocumentsQuery(PendingMMDocumentCriteria Criteria)
    //          : IListQuery<PendingAllocationListDTO, PendingMMDocumentCriteria>;
    // ─────────────────────────────────────────────────────────────────────
    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
    public sealed class QuerySourceAttribute : Attribute
    {
        public QueryIntent Intent { get; }
        public QuerySourceAttribute(QueryIntent intent) => Intent = intent;
    }

    // ─────────────────────────────────────────────────────────────────────
    //  QueryIntentResolver  – cached, one read per TQuery type
    //
    //  Called once per type by GenericListHandler's static initialiser.
    //  The result is cached in a ConcurrentDictionary — zero runtime overhead
    //  after the first call for each query type.
    // ─────────────────────────────────────────────────────────────────────
    internal static class QueryIntentResolver
    {
        private static readonly ConcurrentDictionary<Type, QueryIntent> _cache = new();

        public static QueryIntent Get(Type queryType) =>
            _cache.GetOrAdd(queryType, t =>
                t.GetCustomAttribute<QuerySourceAttribute>()?.Intent
                ?? QueryIntent.Transactional);
    }
}