Add linked suggestions with synced voting

Endpoints/AdminEndpoints.cs

@@ -3,6 +3,7 @@ using GameList.Domain;
 using GameList.Contracts;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.EntityFrameworkCore;
+using System.Collections.Generic;
 
 namespace GameList.Endpoints;
 
@@ -51,6 +52,78 @@ public static class AdminEndpoints
             return Results.Ok(new { voters, ready, waiting });
         });
 
+        admin.MapPost("/link-suggestions", async ([FromBody] LinkSuggestionsRequest request, HttpContext ctx, AppDbContext db, IConfiguration config) =>
+        {
+            var player = await EndpointHelpers.GetAuthenticatedPlayer(ctx, db);
+            if (player is null || !await EndpointHelpers.IsAdmin(ctx, db, config)) return Results.Unauthorized();
+
+            var phase = await EndpointHelpers.GetPhase(db, player.Id);
+            if (phase != Phase.Vote)
+                return EndpointHelpers.PhaseMismatch(Phase.Vote, phase);
+
+            if (request.SourceSuggestionId == request.TargetSuggestionId)
+                return Results.BadRequest(new { error = "Pick two different games to link." });
+
+            var suggestions = await db.Suggestions.ToListAsync();
+            var source = suggestions.FirstOrDefault(s => s.Id == request.SourceSuggestionId);
+            var target = suggestions.FirstOrDefault(s => s.Id == request.TargetSuggestionId);
+            if (source is null || target is null)
+                return Results.NotFound(new { error = "Suggestion not found." });
+
+            var rootIndex = EndpointHelpers.BuildLinkRoots(suggestions.Select(s => (s.Id, s.ParentSuggestionId)));
+            if (!rootIndex.TryGetValue(source.Id, out var sourceRoot) || !rootIndex.TryGetValue(target.Id, out var targetRoot))
+                return Results.NotFound(new { error = "Suggestion not found." });
+
+            if (sourceRoot == targetRoot)
+                return Results.BadRequest(new { error = "These games are already linked." });
+
+            var affectedRootIds = new HashSet<int> { sourceRoot, targetRoot };
+            var affectedIds = rootIndex
+                .Where(kv => affectedRootIds.Contains(kv.Value))
+                .Select(kv => kv.Key)
+                .ToList();
+
+            await using var tx = await db.Database.BeginTransactionAsync();
+
+            foreach (var suggestion in suggestions)
+            {
+                var root = rootIndex.GetValueOrDefault(suggestion.Id);
+                if (root == targetRoot)
+                {
+                    suggestion.ParentSuggestionId = suggestion.Id == targetRoot ? null : targetRoot;
+                }
+                else if (root == sourceRoot)
+                {
+                    suggestion.ParentSuggestionId = targetRoot;
+                }
+            }
+
+            await db.SaveChangesAsync();
+
+            var affectedPlayerIds = await db.Votes
+                .Where(v => affectedIds.Contains(v.SuggestionId))
+                .Select(v => v.PlayerId)
+                .Distinct()
+                .ToListAsync();
+
+            await db.Votes.Where(v => affectedIds.Contains(v.SuggestionId)).ExecuteDeleteAsync();
+
+            if (affectedPlayerIds.Count > 0)
+            {
+                await db.Players.Where(p => affectedPlayerIds.Contains(p.Id))
+                    .ExecuteUpdateAsync(p => p.SetProperty(x => x.VotesFinal, false));
+            }
+
+            await tx.CommitAsync();
+
+            return Results.Ok(new
+            {
+                RootId = targetRoot,
+                LinkedSuggestionIds = affectedIds,
+                UnfinalizedPlayers = affectedPlayerIds.Count
+            });
+        });
+
         admin.MapPost("/reset", async (HttpContext ctx, AppDbContext db, IConfiguration config) =>
         {
             if (!await EndpointHelpers.IsAdmin(ctx, db, config)) return Results.Unauthorized();