using InboxIntel.Application.Abstractions;
using InboxIntel.Domain.Common;
using InboxIntel.Domain.Entities;
using Microsoft.EntityFrameworkCore;
using System.Reflection;

namespace InboxIntel.Infrastructure.Persistence;

public class AppDbContext : DbContext, IAppDbContext
{
    private readonly ICurrentUser? _currentUser;

    public AppDbContext(DbContextOptions<AppDbContext> options, ICurrentUser? currentUser = null) : base(options)
        => _currentUser = currentUser;

    /// <summary>
    /// Tenant id used by the global query filters below. Resolves to the
    /// authenticated user during an HTTP request. It is <see cref="Guid.Empty"/>
    /// when there is no current user (background workers, design-time tooling,
    /// startup migration) — in which case filtering is DISABLED, because those
    /// paths are trusted server code that already scope their own queries by a
    /// userId passed in explicitly. The security value is on the HTTP attack
    /// surface: a forgotten manual <c>WHERE UserId ==</c> can no longer leak
    /// another tenant's rows, since the filter restricts to the caller.
    /// </summary>
    public Guid CurrentUserId => _currentUser?.UserId ?? Guid.Empty;

    public DbSet<User> Users => Set<User>();
    public DbSet<Email> Emails => Set<Email>();
    public DbSet<MailThread> Threads => Set<MailThread>();
    public DbSet<Sender> Senders => Set<Sender>();
    public DbSet<MailDomain> Domains => Set<MailDomain>();
    public DbSet<Attachment> Attachments => Set<Attachment>();
    public DbSet<Label> Labels => Set<Label>();
    public DbSet<EmailLabel> EmailLabels => Set<EmailLabel>();
    public DbSet<SyncState> SyncStates => Set<SyncState>();
    public DbSet<AnalyticsAggregate> AnalyticsAggregates => Set<AnalyticsAggregate>();
    public DbSet<WidgetLayout> WidgetLayouts => Set<WidgetLayout>();
    public DbSet<UnsubscribeItem> UnsubscribeItems => Set<UnsubscribeItem>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(Assembly.GetExecutingAssembly());

        // Defense-in-depth tenant isolation (systemic IDOR safeguard). Every
        // user-owned entity is filtered to the current user so a query that forgets
        // its manual `WHERE UserId ==` clause cannot leak across tenants. Applied
        // uniformly to all user-scoped entities so EF sees no filtered/unfiltered
        // navigation mismatch. Bypassed when CurrentUserId is Guid.Empty (workers).
        modelBuilder.Entity<Email>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<Sender>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<MailThread>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<MailDomain>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<Attachment>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<Label>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        // AUDIT M-6: EmailLabel is the required end of a relationship with the filtered Email
        // entity; without a matching filter EF warns on boot and joins could surface rows whose
        // parent is filtered out. Filter via the Email navigation so the pair is consistent.
        modelBuilder.Entity<EmailLabel>().HasQueryFilter(el => CurrentUserId == Guid.Empty || el.Email!.UserId == CurrentUserId);
        modelBuilder.Entity<SyncState>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<AnalyticsAggregate>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<WidgetLayout>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);
        modelBuilder.Entity<UnsubscribeItem>().HasQueryFilter(e => CurrentUserId == Guid.Empty || e.UserId == CurrentUserId);

        // PostgreSQL full-text search: generated tsvector over subject + body with a
        // GIN index, maintained by the DB and read-only in code. Subject is weighted 'A'
        // and body 'B' so ts_rank_cd ranks a subject match above a body-only mention. The
        // tsvector type is Npgsql-only, so map it only for relational providers and ignore
        // it otherwise (e.g. the InMemory provider used by tests).
        if (Database.IsRelational())
        {
            // pg_trgm powers the fuzzy/typo fallback in SearchService (word_similarity).
            modelBuilder.HasPostgresExtension("pg_trgm");

            modelBuilder.Entity<Email>().Property(e => e.SearchVector)
                .HasColumnType("tsvector")
                .HasComputedColumnSql(
                    "setweight(to_tsvector('english', coalesce(\"Subject\",'')), 'A') || " +
                    "setweight(to_tsvector('english', coalesce(\"BodyText\",'')), 'B')",
                    stored: true);
            modelBuilder.Entity<Email>().HasIndex(e => e.SearchVector).HasMethod("GIN");

            // Trigram GIN indexes so the sender/domain `.Contains()` filters in SearchService
            // (which translate to `LIKE '%x%'`, non-sargable on a btree) become index-accelerated.
            // Needs pg_trgm (enabled by the EnablePgTrgm migration).
            modelBuilder.Entity<Sender>().HasIndex(s => s.Address)
                .HasMethod("gin").HasOperators("gin_trgm_ops");
            modelBuilder.Entity<Sender>().HasIndex(s => s.DisplayName)
                .HasMethod("gin").HasOperators("gin_trgm_ops");
            modelBuilder.Entity<MailDomain>().HasIndex(d => d.Name)
                .HasMethod("gin").HasOperators("gin_trgm_ops");

            // pgvector: 768-dim embedding for semantic search, with an HNSW cosine index.
            // Populated by the embedding backfill worker when AI is enabled; null otherwise.
            modelBuilder.HasPostgresExtension("vector");
            modelBuilder.Entity<Email>().Property(e => e.Embedding).HasColumnType("vector(768)");
            modelBuilder.Entity<Email>().HasIndex(e => e.Embedding)
                .HasMethod("hnsw").HasOperators("vector_cosine_ops");
        }
        else
        {
            modelBuilder.Entity<Email>().Ignore(e => e.SearchVector);
            modelBuilder.Entity<Email>().Ignore(e => e.Embedding);
        }

        base.OnModelCreating(modelBuilder);
    }

    public override Task<int> SaveChangesAsync(CancellationToken ct = default)
    {
        foreach (var entry in ChangeTracker.Entries<AuditableEntity>())
        {
            if (entry.State == EntityState.Modified)
                entry.Entity.UpdatedAtUtc = DateTimeOffset.UtcNow;
        }
        return base.SaveChangesAsync(ct);
    }
}