refactor: introduce IConceptsMapReadRepository and SegmentIdParser to improve data access and domain logic encapsulation.

src/NexusReader.Infrastructure/Persistence/ConceptsMapReadRepository.cs

@@ -0,0 +1,48 @@
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Application.Abstractions.Persistence;
+using NexusReader.Data.Persistence;
+using NexusReader.Domain.Entities;
+
+namespace NexusReader.Infrastructure.Persistence;
+
+/// <summary>
+/// EF Core implementation of <see cref="IConceptsMapReadRepository"/>.
+/// Uses <see cref="IDbContextFactory{TContext}"/> for Blazor-safe scoped context creation.
+/// </summary>
+internal sealed class ConceptsMapReadRepository : IConceptsMapReadRepository
+{
+    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
+
+    public ConceptsMapReadRepository(IDbContextFactory<AppDbContext> dbContextFactory)
+    {
+        _dbContextFactory = dbContextFactory;
+    }
+
+    /// <inheritdoc />
+    public async Task<string?> GetLastReadPageIdAsync(string userId, CancellationToken cancellationToken = default)
+    {
+        await using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+
+        var user = await dbContext.Users
+            .Where(u => u.Id == userId)
+            .Select(u => new { u.LastReadPageId })
+            .FirstOrDefaultAsync(cancellationToken);
+
+        return user?.LastReadPageId;
+    }
+
+    /// <inheritdoc />
+    public async Task<List<KnowledgeUnit>> GetKnowledgeUnitsForBookAsync(
+        Guid bookId,
+        string tenantId,
+        CancellationToken cancellationToken = default)
+    {
+        await using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+
+        return await dbContext.KnowledgeUnits
+            .Where(k => k.EbookId == bookId &&
+                        (k.TenantId == tenantId || k.TenantId == "global" || string.IsNullOrEmpty(k.TenantId)))
+            .OrderBy(k => k.CreatedAt)
+            .ToListAsync(cancellationToken);
+    }
+}