namespace YY.Admin.Core.Helper;

/// <summary>MES 只读数据：远端列表与本地缓存按 Id 对比合并</summary>
public static class MesReadOnlyCacheMergeHelper
{
    public sealed record MergeResult(int Added, int Updated, int Removed)
    {
        public bool HasChanges => Added > 0 || Updated > 0 || Removed > 0;
    }

    /// <summary>
    /// 对比远端与本地，返回合并后的列表及变更统计。
    /// 内容相同则保留本地副本；<paramref name="mergeUpdated"/> 可定制变更行的合并策略（如保留本地子表）。
    /// </summary>
    public static (List<T> Merged, MergeResult Stats) Merge<T>(
        IReadOnlyList<T> local,
        IReadOnlyList<T> remote,
        Func<T, string?> getId,
        Func<T, T, bool> isContentEqual,
        Func<T, T> clone,
        Func<T, T, T>? mergeUpdated = null)
    {
        var localById = new Dictionary<string, T>(StringComparer.OrdinalIgnoreCase);
        foreach (var item in local)
        {
            var id = getId(item);
            if (!string.IsNullOrWhiteSpace(id))
                localById[id] = item;
        }

        var remoteIds = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        var merged = new List<T>(remote.Count);
        int added = 0, updated = 0;

        foreach (var remoteItem in remote)
        {
            var id = getId(remoteItem);
            if (string.IsNullOrWhiteSpace(id))
            {
                merged.Add(clone(remoteItem));
                added++;
                continue;
            }

            remoteIds.Add(id);

            if (!localById.TryGetValue(id, out var localItem))
            {
                merged.Add(clone(remoteItem));
                added++;
            }
            else if (!isContentEqual(localItem, remoteItem))
            {
                merged.Add(mergeUpdated != null ? mergeUpdated(localItem, remoteItem) : clone(remoteItem));
                updated++;
            }
            else
            {
                merged.Add(clone(localItem));
            }
        }

        int removed = localById.Keys.Count(id => !remoteIds.Contains(id));
        return (merged, new MergeResult(added, updated, removed));
    }
}