using GB5Shared.DTO.Report;

namespace GB5Shared.Export
{
    /// <summary>
    /// Recursive multi-level group tree builder, extracted from ReportExport.cs's PDF/HTML render path
    /// so any other export format (e.g. Excel) can reuse the exact same grouping structure instead of
    /// re-implementing it. Node shape is deliberately untyped (Dictionary&lt;string,object&gt;) to match
    /// how PDF/HTML's Handlebars "renderGroupNodes" helper already consumes it via IDictionary/reflection
    /// — kept unchanged here so extraction is behavior-neutral for that path.
    /// </summary>
    public static class GroupTreeBuilder
    {
        /// <summary>
        /// Builds one nesting level per entry in <paramref name="groupColumns"/> (ordered by
        /// DisplaySlNo), starting at <paramref name="levelIndex"/> (callers pass 0). Each node is:
        ///   LevelTitle / LevelValue — this node's group column title + the value all its rows share
        ///   IsLeaf     — true at the innermost (last) level
        ///   Children   — child nodes (non-leaf levels only) — one per distinct value at the NEXT level
        ///   Rows       — the detail rows for this bucket (leaf level only)
        ///   SubTotal   — whatever <paramref name="computeSubTotal"/> returns for this node's rows
        ///                (null when the caller has nothing to subtotal), so a subtotal can render when
        ///                closing any level, not only the leaf.
        /// A single group column produces a tree exactly one level deep.
        /// </summary>
        public static List<object> BuildGroupNodes(
            IEnumerable<Dictionary<string, object>> rows,
            List<ReportViewFieldsDTO> groupColumns,
            int levelIndex,
            Func<List<Dictionary<string, object>>, Dictionary<string, object?>?> computeSubTotal)
        {
            var levelField = groupColumns[levelIndex];
            string levelTitle = levelField.ReportViewFieldsFieldTitle ?? "";
            bool isLeafLevel = levelIndex == groupColumns.Count - 1;

            return rows
                .GroupBy(r => r.ContainsKey(levelTitle) ? r[levelTitle]?.ToString() ?? "" : "")
                .Select(g =>
                {
                    var groupRows = g.ToList();
                    var node = new Dictionary<string, object>
                    {
                        ["LevelTitle"] = levelTitle,
                        ["LevelValue"] = g.Key,
                        ["IsLeaf"] = isLeafLevel,
                        ["SubTotal"] = (object?)computeSubTotal(groupRows)!
                    };
                    if (isLeafLevel)
                        node["Rows"] = groupRows.Cast<object>().ToList();
                    else
                        node["Children"] = BuildGroupNodes(groupRows, groupColumns, levelIndex + 1, computeSubTotal);
                    return (object)node;
                })
                .ToList();
        }
    }
}