Fintech ledger on Next.js 16 (App Router), Postgres (Neon) and Better Auth

import { drizzle } from "drizzle-orm/postgres-js";
import postgres from "postgres";

// Neon pooled endpoint = PgBouncer transaction mode → prepared statements off.
// ponytail: single module-level client; the serverless runtime + PgBouncer do
// the pooling, so no custom pool/globalThis singleton dance needed.
const client = postgres(process.env.DATABASE_URL!, { prepare: false });

export const db = drizzle({ client });

import { boolean, pgTable, text, timestamp } from "drizzle-orm/pg-core";

export const user = pgTable("user", {
  id: text("id").primaryKey(),
  name: text("name").notNull(),
  email: text("email").notNull().unique(),
  emailVerified: boolean("email_verified").notNull().default(false),
  image: text("image"),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull().defaultNow(),
});

export const session = pgTable("session", {
  id: text("id").primaryKey(),
  expiresAt: timestamp("expires_at").notNull(),
  token: text("token").notNull().unique(),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull(),
  ipAddress: text("ip_address"),
  userAgent: text("user_agent"),
  userId: text("user_id")
    .notNull()
    .references(() => user.id, { onDelete: "cascade" }),
});

export const account = pgTable("account", {
  id: text("id").primaryKey(),
  accountId: text("account_id").notNull(),
  providerId: text("provider_id").notNull(),
  userId: text("user_id")
    .notNull()
    .references(() => user.id, { onDelete: "cascade" }),
  accessToken: text("access_token"),
  refreshToken: text("refresh_token"),
  idToken: text("id_token"),
  accessTokenExpiresAt: timestamp("access_token_expires_at"),
  refreshTokenExpiresAt: timestamp("refresh_token_expires_at"),
  scope: text("scope"),
  password: text("password"),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull(),
});

export const verification = pgTable("verification", {
  id: text("id").primaryKey(),
  identifier: text("identifier").notNull(),
  value: text("value").notNull(),
  expiresAt: timestamp("expires_at").notNull(),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull().defaultNow(),
});

// Better Auth instance (self-hosted, Next.js 16 (App Router)).
import { betterAuth } from "better-auth";
import { drizzleAdapter } from "better-auth/adapters/drizzle";
// Reuse the SAME postgres-js/Drizzle client the db slice exported in
// src/lib/db.ts — Better Auth shares the pooled `DATABASE_URL` connection.
import { db } from "./db";
import * as authSchema from "@/db/auth-schema";

export const auth = betterAuth({
  // Drizzle adapter over the shared client. The schema is passed HERE (not into
  // drizzle()) — it is the only consumer that needs it, so the db client stays
  // schema-less. ponytail: do NOT enable experimental.joins; it is the one option
  // that would make the adapter reach into db._.fullSchema.
  // ponytail: usePlural stays false (the default) — with it true Better Auth would
  // look for `sessions`/`accounts` and could bind to the analytics/ledger app-type tables.
  database: drizzleAdapter(db, { provider: "pg", schema: authSchema }),
  // ponytail: email+password is the shortest real auth that works out of
  // the box — add socialProviders / plugins here when the app needs them.
  emailAndPassword: { enabled: true },
  secret: process.env.BETTER_AUTH_SECRET,
  baseURL: process.env.BETTER_AUTH_URL,
});

export type Session = typeof auth.$Infer.Session;

// Mount Better Auth on Next's route layer.
import { toNextJsHandler } from "better-auth/next-js";
import { auth } from "@/lib/auth";

export const { GET, POST } = toNextJsHandler(auth);

// Session-protection proxy for Next.js 16 (App Router) (Next 16 renamed middleware.ts → proxy.ts).
// ponytail: getSessionCookie only checks the cookie EXISTS (no DB hit at
// the Edge runtime) — do the real auth.api.getSession() check inside
// protected Server Components / route handlers. This just bounces
// logged-out users before render.
import { NextResponse, type NextRequest } from "next/server";
import { getSessionCookie } from "better-auth/cookies";

export function proxy(request: NextRequest) {
  const sessionCookie = getSessionCookie(request);
  if (!sessionCookie) {
    return NextResponse.redirect(new URL("/sign-in", request.url));
  }
  return NextResponse.next();
}

export const config = {
  // ponytail: guard the SaaS app surface; widen the matcher per app-type.
  matcher: ["/dashboard/:path*", "/settings/:path*"],
};

// === file: src/db/schema.ts ===
import { relations, sql } from "drizzle-orm";
import {
  bigint,
  check,
  index,
  pgTable,
  text,
  timestamp,
  uuid,
} from "drizzle-orm/pg-core";
// Better Auth owns identity; we only reference its `user` table by id.
import { user } from "./auth-schema";

export const accounts = pgTable(
  "accounts",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    ownerId: text("owner_id").notNull().references(() => user.id, { onDelete: "cascade" }),
    name: text("name").notNull(),
    type: text("type").notNull(),
    currency: text("currency").notNull().default("USD"),
    createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
  },
  (t) => [
    index("idx_account_owner").on(t.ownerId),
    check("accounts_type_check", sql`${t.type} in ('asset','liability','equity','revenue','expense')`),
  ],
);

export const journalEntries = pgTable(
  "journal_entries",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    creatorId: text("creator_id").notNull().references(() => user.id, { onDelete: "cascade" }),
    description: text("description").notNull(),
    postedAt: timestamp("posted_at", { withTimezone: true }).notNull().defaultNow(),
  },
  (t) => [index("idx_entry_posted").on(t.postedAt)],
);

// Double-entry: each entry has >= 2 lines; debits must equal credits (enforced in app).
export const journalLines = pgTable(
  "journal_lines",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    entryId: uuid("entry_id").notNull().references(() => journalEntries.id, { onDelete: "cascade" }),
    accountId: uuid("account_id").notNull().references(() => accounts.id, { onDelete: "cascade" }),
    direction: text("direction").notNull(),
    amountCents: bigint("amount_cents", { mode: "number" }).notNull(),
  },
  (t) => [
    index("idx_line_account").on(t.accountId),
    index("idx_line_entry").on(t.entryId),
    check("journal_lines_direction_check", sql`${t.direction} in ('debit','credit')`),
  ],
);

export const accountsRelations = relations(accounts, ({ one, many }) => ({
  owner: one(user, { fields: [accounts.ownerId], references: [user.id] }),
  lines: many(journalLines),
}));
export const journalEntriesRelations = relations(journalEntries, ({ one, many }) => ({
  creator: one(user, { fields: [journalEntries.creatorId], references: [user.id] }),
  lines: many(journalLines),
}));
export const journalLinesRelations = relations(journalLines, ({ one }) => ({
  entry: one(journalEntries, { fields: [journalLines.entryId], references: [journalEntries.id] }),
  account: one(accounts, { fields: [journalLines.accountId], references: [accounts.id] }),
}));

import { drizzle } from "drizzle-orm/postgres-js";
import postgres from "postgres";

// Serverless: one connection per (short-lived) instance; Neon's pooler multiplexes.
export const sql = postgres(process.env.DATABASE_URL!, { prepare: false, max: 1 });
export const db = drizzle(sql);

import { drizzle } from "drizzle-orm/postgres-js";
import postgres from "postgres";

// Long-running process: a real, reused pool. Still prepare:false on the pooled endpoint.
export const sql = postgres(process.env.DATABASE_URL!, { prepare: false, max: 10, idle_timeout: 20 });
export const db = drizzle(sql);

import { neon } from "@neondatabase/serverless";
import { drizzle } from "drizzle-orm/neon-http";

// Edge/Workers have NO TCP sockets, so postgres-js cannot run here. Neon's HTTP
// driver speaks Postgres over fetch — the only client that works on Workers.
export const sql = neon(process.env.DATABASE_URL!);
export const db = drizzle(sql);