using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using GB5Shared.DTO.Framework.Criteria;

namespace GB5Shared.ListQuery
{
    // ─────────────────────────────────────────────────────────────────────
    //  ICriteria  – universal base for all list criteria
    //
    //  Every criteria class in the system implements this interface.
    //  The four fields (SearchText, OUId, PageSize, PageOffset) are
    //  universal across all list endpoints.
    // ─────────────────────────────────────────────────────────────────────
    public interface ICriteria
    {
        string? SearchText { get; }
        int?    OUId       { get; }
        int     PageSize   { get; }
        int     PageOffset { get; }
    }

    // ─────────────────────────────────────────────────────────────────────
    //  ISortable  – opt-in sort support for list queries
    //
    //  SortBy      : logical column name (validated against QB allowlist)
    //  SortDesc    : true = DESC, false = ASC
    //  SortFields  : compound sort tokens e.g. ["headerdate:desc","partyname:asc"]
    //                When SortFields is non-empty it takes precedence over SortBy.
    // ─────────────────────────────────────────────────────────────────────
    public interface ISortable
    {
        string?   SortBy     { get; }
        bool      SortDesc   { get; }
        string[]? SortFields { get; }
    }

    // ─────────────────────────────────────────────────────────────────────
    //  IPageable  – extends ICriteria with keyset-paging opt-in
    //
    //  CursorId = null → offset paging (default; PageOffset/PageSize apply)
    //  CursorId = N    → keyset paging (infinite-scroll only; no page-jump)
    //  SkipCount = true → omit COUNT(*) OVER() for pure infinite-scroll speed
    //
    //  Keyset guardrail: only suitable when sort is on a stable PK column
    //  and the endpoint is infinite-scroll — never for "jump to page N" UIs.
    // ─────────────────────────────────────────────────────────────────────
    public interface IPageable : ICriteria
    {
        int?  CursorId  { get; }   // null = offset paging; non-null = keyset
        bool  SkipCount { get; }   // true = omit COUNT(*) OVER()
    }

    // ─────────────────────────────────────────────────────────────────────
    //  IListCriteria  – convenience combinator: ICriteria + ISortable + IPageable
    //
    //  Implement this as the base for all standard list query criteria.
    //  The four ICriteria fields plus sort and paging extensions in one interface.
    // ─────────────────────────────────────────────────────────────────────
    public interface IListCriteria : IPageable, ISortable { }

    // ─────────────────────────────────────────────────────────────────────
    //  [CriteriaField]  – maps CriteriaDTO field names to typed properties
    //
    //  Keys      : one or more FieldName values (case-insensitive)
    //  IsFlag    : presence of the key alone = true (no value needed)
    //  Delimiter : for comma-separated array values (default ",")
    // ─────────────────────────────────────────────────────────────────────
    [AttributeUsage(AttributeTargets.Property)]
    public sealed class CriteriaFieldAttribute : Attribute
    {
        public string[] Keys      { get; }
        public bool     IsFlag    { get; init; } = false;
        public string   Delimiter { get; init; } = ",";

        public CriteriaFieldAttribute(params string[] keys) => Keys = keys;
    }

    // ─────────────────────────────────────────────────────────────────────
    //  CriteriaBinder  – generic binder written once for all criteria
    //
    //  Usage:
    //      var c = CriteriaBinder.Bind<PendingMMDocumentCriteria>(criteriaDTO);
    //
    //  Reflection is done once per type T and cached in a ConcurrentDictionary.
    //  All subsequent calls are pure dictionary lookups (~1µs).
    //
    //  Search text resolution:
    //      • Query-param searchText is injected by the router into a synthetic
    //        CriteriaDTO section under the field name "headername" (see
    //        IQueryRouter helpers). When both exist the query-param value wins
    //        because the synthetic section is appended last and the binder
    //        processes sections in order – later values overwrite earlier ones.
    //      • Legacy clients that embed "headername"/"searchtext" inside the
    //        body CriteriaDTO continue to work unchanged when no query param
    //        is supplied.
    // ─────────────────────────────────────────────────────────────────────
    public static class CriteriaBinder
    {
        private static readonly ConcurrentDictionary<Type, IReadOnlyDictionary<string, Action<object, object?>>>
            _cache = new();

        /// <summary>
        /// Binds a <see cref="CriteriaDTO"/> (and an optional user-level criteria DTO)
        /// to a strongly typed criteria instance of type <typeparamref name="T"/>.
        /// </summary>
        public static T Bind<T>(CriteriaDTO dto, CriteriaDTO? userDto = null)
            where T : ICriteria, new()
        {
            var setters  = _cache.GetOrAdd(typeof(T), BuildSetters);
            var instance = new T();

            foreach (var (key, value) in Flatten(dto).Concat(Flatten(userDto)))
                if (setters.TryGetValue(key, out var set))
                    set(instance, value);

            return instance;
        }

        // ── Reflection map (built once per type) ─────────────────────────

        private static IReadOnlyDictionary<string, Action<object, object?>> BuildSetters(Type type)
        {
            var map = new Dictionary<string, Action<object, object?>>(StringComparer.OrdinalIgnoreCase);

            foreach (var prop in type.GetProperties(BindingFlags.Public | BindingFlags.Instance))
            {
                var attr = prop.GetCustomAttribute<CriteriaFieldAttribute>();
                if (attr is null) continue;

                var setter = MakeSetter(prop, attr);
                foreach (var key in attr.Keys)
                    map[key] = setter;
            }

            return map;
        }

        private static Action<object, object?> MakeSetter(PropertyInfo prop, CriteriaFieldAttribute attr)
        {
            var type = Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType;

            return (obj, raw) =>
            {
                if (raw is null && !attr.IsFlag) return;

                object? value = attr.IsFlag ? (object)true : Convert(raw, type, attr.Delimiter);
                try   { prop.SetValue(obj, value); }
                catch { /* skip malformed values gracefully */ }
            };
        }

        private static object? Convert(object? raw, Type type, string delimiter)
        {
            var str = raw?.ToString();
            if (string.IsNullOrWhiteSpace(str)) return null;

            if (type == typeof(int))      return int.Parse(str);
            if (type == typeof(long))     return long.Parse(str);
            if (type == typeof(bool))     return bool.Parse(str);
            if (type == typeof(decimal))  return decimal.Parse(str);
            if (type == typeof(string))   return str;
            if (type == typeof(DateTime)) return DateTime.Parse(str);

            if (type == typeof(int[]))
                return str.Split(delimiter, StringSplitOptions.RemoveEmptyEntries)
                          .Select(x => int.Parse(x.Trim())).ToArray();

            if (type == typeof(string[]))
                return str.Split(delimiter, StringSplitOptions.RemoveEmptyEntries)
                          .Select(x => x.Trim()).ToArray();

            if (type == typeof(short))  return short.Parse(str);
            if (type == typeof(byte))   return byte.Parse(str);
            if (type == typeof(double)) return double.Parse(str);
            if (type == typeof(Guid))   return Guid.Parse(str);

            // Fallback for any other value type (e.g. custom enums): use the already-derived
            // string, not the raw object. `raw` is frequently a System.Text.Json.JsonElement
            // (how CriteriaDTO.FieldValue deserializes from the request body), and JsonElement
            // does not implement IConvertible — passing it to ChangeType throws "Object must
            // implement IConvertible." `str` is a plain string, which does.
            return System.Convert.ChangeType(str, type, System.Globalization.CultureInfo.InvariantCulture);
        }

        // ── Flatten CriteriaDTO to (key, value) pairs ────────────────────

        private static IEnumerable<(string key, object? value)> Flatten(CriteriaDTO? dto)
        {
            if (dto is null) yield break;
            foreach (var s in dto.SectionCriteriaList)
            foreach (var a in s.AttributesCriteriaList)
                yield return (a.FieldName.ToLowerInvariant(), a.FieldValue);
        }
    }

    // ─────────────────────────────────────────────────────────────────────
    //  CriteriaRouterHelper  – helpers for router/endpoint boilerplate
    // ─────────────────────────────────────────────────────────────────────
    public static class CriteriaRouterHelper
    {
        /// <summary>
        /// Injects volatile query-param values (searchText, pageOffset, pageSize) into
        /// a synthetic CriteriaDTO section appended to the existing body criteria.
        ///
        /// Rules:
        ///   • searchTextParam is only injected when non-null (query param supplied).
        ///     If null, the body CriteriaDTO may already contain "headername"/"searchtext"
        ///     from a legacy client — those remain in effect.
        ///   • pageOffset and pageSize are always injected (overriding any body defaults).
        /// </summary>
        public static CriteriaDTO WithSearchAndPaging(
            CriteriaDTO dto,
            string?     searchTextParam,
            int         pageOffset,
            int         pageSize)
        {
            var attrs = new List<AttributesCriteriaDTO>
            {
                new AttributesCriteriaDTO { FieldName = "pageoffset", FieldValue = pageOffset },
                new AttributesCriteriaDTO { FieldName = "pagesize",   FieldValue = pageSize   },
            };

            // Only override search text when the caller explicitly supplied it
            if (searchTextParam is not null)
                attrs.Add(new AttributesCriteriaDTO { FieldName = "headername", FieldValue = searchTextParam });

            var extra = new SectionCriteriaDTO { AttributesCriteriaList = attrs };
            var sections = new List<SectionCriteriaDTO>(dto.SectionCriteriaList) { extra };

            return new CriteriaDTO { SectionCriteriaList = sections };
        }

        /// <summary>
        /// Reads a single integer discriminator field from a flattened criteria dictionary.
        /// </summary>
        public static int GetInt(Dictionary<string, string?> flat, string key, int defaultValue = 0) =>
            flat.TryGetValue(key, out var v) && int.TryParse(v, out var i) ? i : defaultValue;

        /// <summary>
        /// Reads a single string discriminator field from a flattened criteria dictionary.
        /// </summary>
        public static string? GetStr(Dictionary<string, string?> flat, string key) =>
            flat.TryGetValue(key, out var v) ? v : null;

        /// <summary>
        /// Flattens the nested CriteriaDTO structure into a single case-insensitive dictionary.
        /// When a key appears multiple times the last occurrence wins.
        /// </summary>
        public static Dictionary<string, string?> Flatten(CriteriaDTO dto)
        {
            var d = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
            foreach (var s in dto.SectionCriteriaList)
            foreach (var a in s.AttributesCriteriaList)
                d[a.FieldName] = a.FieldValue?.ToString();
            return d;
        }
    }
}