import { createHmac, timingSafeEqual } from "node:crypto";
import {
  Body,
  Controller,
  Get,
  HttpCode,
  HttpStatus,
  Logger,
  Param,
  Post,
  Query,
  Req,
  Res,
  UnauthorizedException,
  UseGuards,
} from "@nestjs/common";
import { ConfigService } from "@nestjs/config";
import type { Request, Response } from "express";
import { Public } from "../common/decorators/public.decorator";
import { InternalTokenGuard } from "../common/guards/internal-token.guard";
import { ImpersonationService } from "./impersonation.service";

const CONSUME_TOKEN_TTL_SECONDS = 60;

type ConsumePayload = {
  cookieName: string;
  cookieValue: string;
  redirect: string;
  expiresAtMs: number;
  notBeforeMs: number;
};

@Controller()
export class ImpersonationController {
  private readonly logger = new Logger(ImpersonationController.name);

  constructor(
    private impersonation: ImpersonationService,
    private configService: ConfigService,
  ) {}

  // Internal: panel → spoke. Returns a short-lived "consume URL" the panel
  // opens in a new tab. Hand-off via a signed payload avoids cross-site
  // Set-Cookie restrictions (panel domain ≠ sase.tr domain).
  @Post("internal/admin/users/:id/impersonate-readonly")
  @Public()
  @UseGuards(InternalTokenGuard)
  @HttpCode(HttpStatus.OK)
  async impersonateReadonly(
    @Param("id") userId: string,
    @Body() body: { ttlMinutes?: number; reason?: string; founderId?: string },
    @Req() req: Request,
  ) {
    if (!body.founderId) {
      throw new UnauthorizedException("founderId required");
    }
    const reason = (body.reason ?? "").slice(0, 500);
    if (!reason) {
      throw new UnauthorizedException("reason required");
    }

    const { cookieName, cookieValue, expiresAt, sessionId } =
      await this.impersonation.createReadonlySession({
        targetUserId: userId,
        founderId: body.founderId,
        ttlMinutes: body.ttlMinutes ?? 15,
        reason,
        ipAddress: this.getIp(req),
        userAgent:
          typeof req.headers["user-agent"] === "string" ? req.headers["user-agent"] : undefined,
      });

    const baseUrl = this.configService.get<string>("auth.url") ?? "";
    const payload: ConsumePayload = {
      cookieName,
      cookieValue,
      redirect: "/",
      expiresAtMs: expiresAt.getTime(),
      notBeforeMs: Date.now() - 1000,
    };
    const consumeToken = this.signConsumePayload(payload);
    const redirectUrl = `${baseUrl}/api/admin/impersonate/consume?t=${encodeURIComponent(consumeToken)}`;

    return {
      success: true,
      redirectUrl,
      expiresAt: expiresAt.toISOString(),
      sessionIdPrefix: sessionId.slice(0, 8),
    };
  }

  // Public: founder's browser GET. Verifies the signed payload, sets the
  // Better Auth session cookie, redirects to the spoke. One-shot, time-boxed.
  @Get("admin/impersonate/consume")
  @Public()
  async consume(@Query("t") token: string, @Res() res: Response) {
    if (!token) {
      res.status(HttpStatus.BAD_REQUEST).send("missing token");
      return;
    }
    const payload = this.verifyConsumePayload(token);
    if (!payload) {
      res.status(HttpStatus.UNAUTHORIZED).send("invalid or expired consume token");
      return;
    }
    const now = Date.now();
    if (now < payload.notBeforeMs || now > payload.expiresAtMs) {
      res.status(HttpStatus.UNAUTHORIZED).send("consume token outside validity window");
      return;
    }

    const isHttps = (this.configService.get<string>("auth.url") ?? "").startsWith("https://");
    res.cookie(payload.cookieName, payload.cookieValue, {
      httpOnly: true,
      secure: isHttps,
      sameSite: "lax",
      // Path scope: site-wide
      path: "/",
      // maxAge in ms, browser will expire alongside server-side session row
      maxAge: payload.expiresAtMs - now,
    });
    res.redirect(payload.redirect || "/");
  }

  // Sign a JSON payload with HMAC-SHA256(secret) and embed: base64(json).base64(sig)
  private signConsumePayload(payload: ConsumePayload): string {
    const secret = this.consumeSecret();
    const json = JSON.stringify(payload);
    const body = Buffer.from(json, "utf8").toString("base64url");
    const sig = createHmac("sha256", secret).update(body).digest("base64url");
    return `${body}.${sig}`;
  }

  private verifyConsumePayload(token: string): ConsumePayload | null {
    const [body, sig] = token.split(".");
    if (!body || !sig) return null;
    const secret = this.consumeSecret();
    const expected = createHmac("sha256", secret).update(body).digest("base64url");
    const a = Buffer.from(sig);
    const b = Buffer.from(expected);
    if (a.length !== b.length || !timingSafeEqual(a, b)) return null;
    try {
      return JSON.parse(Buffer.from(body, "base64url").toString("utf8"));
    } catch {
      return null;
    }
  }

  private consumeSecret(): string {
    const secret =
      process.env.INTERNAL_IMPERSONATION_SECRET ?? this.configService.get<string>("auth.secret");
    if (!secret) throw new Error("INTERNAL_IMPERSONATION_SECRET or auth.secret required");
    return secret;
  }

  private getIp(req: Request): string | undefined {
    const xff = req.headers["x-forwarded-for"];
    if (typeof xff === "string") return xff.split(",")[0]?.trim();
    if (req.socket?.remoteAddress) return req.socket.remoteAddress;
    return undefined;
  }
}