AI Wrapper on Next.js 16 (App Router), MySQL 8 and Better Auth

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";

// ponytail: single module-level pool; the runtime + mysql2's pool handle concurrency,
// so no globalThis singleton dance needed.
const pool = mysql.createPool(process.env.DATABASE_URL!);

export const db = drizzle({ client: pool });

import { boolean, mysqlTable, text, timestamp, varchar } from "drizzle-orm/mysql-core";

export const user = mysqlTable("user", {
  id: varchar("id", { length: 255 }).primaryKey(),
  name: text("name").notNull(),
  email: varchar("email", { length: 255 }).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 = mysqlTable("session", {
  id: varchar("id", { length: 255 }).primaryKey(),
  expiresAt: timestamp("expires_at").notNull(),
  token: varchar("token", { length: 255 }).notNull().unique(),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull(),
  ipAddress: text("ip_address"),
  userAgent: text("user_agent"),
  userId: varchar("user_id", { length: 255 })
    .notNull()
    .references(() => user.id, { onDelete: "cascade" }),
});

export const account = mysqlTable("account", {
  id: varchar("id", { length: 255 }).primaryKey(),
  accountId: text("account_id").notNull(),
  providerId: text("provider_id").notNull(),
  userId: varchar("user_id", { length: 255 })
    .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 = mysqlTable("verification", {
  id: varchar("id", { length: 255 }).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: "mysql", 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,
  int,
  json,
  mysqlTable,
  text,
  timestamp,
  varchar,
} from "drizzle-orm/mysql-core";
// Better Auth owns identity; we only reference its `user` table by id.
import { user } from "./auth-schema";

export type CallStatus = "ok" | "error" | "filtered";

/** One profile per Better Auth user — extends identity with AI-app preferences
 *  and the soft monthly token budget the metering layer enforces. */
export const userProfiles = mysqlTable(
  "user_profiles",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    // Better Auth's user.id is text — match it as varchar(255). One profile per
    // user, so the FK itself is unique (this is the 1:1 extension of `user`).
    userId: varchar("user_id", { length: 255 })
      .notNull()
      .unique()
      .references(() => user.id, { onDelete: "cascade" }),
    displayName: text("display_name"),
    // Default model this user's requests fall back to (e.g. gpt-4o-mini).
    defaultModel: varchar("default_model", { length: 255 }).notNull().default("gpt-4o-mini"),
    // Soft cap the metering layer checks token_usage against per calendar month.
    monthlyTokenBudget: bigint("monthly_token_budget", { mode: "number" })
      .notNull()
      .default(0),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [index("idx_profile_model").on(t.defaultModel)],
);

/** Append-only token meter: one row per upstream LLM call. Roll up by
 *  user + window for budget enforcement and cost reporting. */
export const tokenUsage = mysqlTable(
  "token_usage",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    userId: varchar("user_id", { length: 255 })
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    // Which upstream model was billed (provider model id, opaque to us).
    model: varchar("model", { length: 255 }).notNull(),
    promptTokens: int("prompt_tokens").notNull().default(0),
    completionTokens: int("completion_tokens").notNull().default(0),
    // ponytail: store cost in micro-cents as an integer — no float money, and
    // fine-grained enough for sub-cent per-token pricing without a numeric type.
    costMicrocents: bigint("cost_microcents", { mode: "number" })
      .notNull()
      .default(0),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [
    // Drives the "tokens used this month" rollup + budget check.
    index("idx_usage_user_time").on(t.userId, t.createdAt),
    index("idx_usage_model").on(t.model),
  ],
);

/** Append-only prompt/completion history — the auditable record of every
 *  exchange (prompt in, completion out, model, token split, outcome). */
export const promptLogs = mysqlTable(
  "prompt_logs",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    userId: varchar("user_id", { length: 255 })
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    model: varchar("model", { length: 255 }).notNull(),
    prompt: text("prompt").notNull(),
    // Null while a streamed completion is still in flight.
    completion: text("completion"),
    promptTokens: int("prompt_tokens").notNull().default(0),
    completionTokens: int("completion_tokens").notNull().default(0),
    latencyMs: int("latency_ms"),
    status: varchar("status", { length: 32 }).$type<CallStatus>().notNull().default("ok"),
    // ponytail: opaque per-call metadata (tool calls, finish_reason, etc.) —
    // json bag beats a column-per-provider-field churn.
    metadata: json("metadata"),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [
    // Drives the per-user history feed (most-recent-first).
    index("idx_log_user_time").on(t.userId, t.createdAt),
    check(
      "prompt_logs_status_check",
      sql`${t.status} in ('ok','error','filtered')`,
    ),
  ],
);

export const userProfilesRelations = relations(userProfiles, ({ one }) => ({
  user: one(user, {
    fields: [userProfiles.userId],
    references: [user.id],
  }),
}));

export const tokenUsageRelations = relations(tokenUsage, ({ one }) => ({
  user: one(user, { fields: [tokenUsage.userId], references: [user.id] }),
}));

export const promptLogsRelations = relations(promptLogs, ({ one }) => ({
  user: one(user, { fields: [promptLogs.userId], references: [user.id] }),
}));

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";

// Serverless: a small pool per short-lived instance — many instances × a big pool exhausts MySQL.
export const pool = mysql.createPool({ uri: process.env.DATABASE_URL!, connectionLimit: 2 });
export const db = drizzle({ client: pool });

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";

// Long-running process: a real, reused pool (mysql2 manages idle recycling).
export const pool = mysql.createPool({ uri: process.env.DATABASE_URL!, connectionLimit: 10 });
export const db = drizzle({ client: pool });

import { drizzle } from "drizzle-orm/planetscale-serverless";
import { Client } from "@planetscale/database";

// Edge/Workers have NO TCP sockets, so mysql2 cannot run here. PlanetScale's HTTP driver
// speaks MySQL over fetch — the client that works on Workers (the MySQL analog of Neon's HTTP driver).
const client = new Client({ url: process.env.DATABASE_URL! });
export const db = drizzle({ client });