#nullable enable
namespace Bts.DataStreamCore;

using BCG;

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

public class BlueRowCollection : IBlueRowCollection {
   readonly ICollection source;
   readonly Func<int, IBlueRow> findRow;
   readonly Func<int, bool> containsKey;

   public BlueRowCollection(ICollection source, IBlueTableSchema schema, Func<int, IBlueRow>? findRow = null, Func<int, bool>? containsKey = null) {
      this.source = source;
      this.schema = schema;
      if (findRow is null || containsKey is null) {
         if (source is IBlueRowCollection brc) {
            findRow ??= id => brc[id];
            containsKey ??= brc.containsID;
         } else if (source is IDictionary dict) {
            findRow ??= id => dict[id] as IBlueRow ?? throw new KeyNotFoundException();
            containsKey ??= id => dict.Contains(id);
         } else if (source is IDictionary<int, IBlueRow> genDict) {
            findRow ??= id => genDict[id];
            containsKey ??= genDict.ContainsKey;
         } else if (source is IReadOnlyDictionary<int, IBlueRow> roGenDict) {
            findRow ??= id => roGenDict[id];
            containsKey = roGenDict.ContainsKey;
         } else {
            var cachedRows = new Lazy<Dictionary<int, IBlueRow>>(() =>
               source.Cast<IBlueRow>().ToDictionary(r => r.Id()));
            findRow ??= id => cachedRows.Value[id];
            // Don't remove this lambda expression. Intellisense may suggest it, but that would
            // instantiate 'cachedRows' immediately and defeat the purpose of using Lazy<T>.
            containsKey ??= id => cachedRows.Value.ContainsKey(id);
         }
      }
      this.findRow = findRow;
      this.containsKey = containsKey;
   }

   public IBlueRow this[int id] => findRow(id);

   public IBlueTableSchema schema { get; }

   public int Count => source.Count;

   public bool containsID(int id) =>
      containsKey(id);

   public IEnumerator GetEnumerator() =>
      source.GetEnumerator();
}