import { useState, useEffect } from "react";
import { useNavigate, useSearchParams } from "react-router-dom";
import { useAuth } from "../../contexts/AuthContext";
import { useUserProperties } from "../../contexts/UserPropertiesContext";
import {
  createOnboardingCheckout,
  verifyCheckoutSession,
  activateFreeTier,
} from "../../api/stripe";
import Input from "../../components/Input";
import Button from "../../components/Button";
import TierPicker from "../../components/TierPicker";
import "./Subscribe.css";

const STEPS = ["Create Account", "Choose Plan"];

export default function Subscribe() {
  const { currentUser, signup } = useAuth();
  const { state: userProps, dispatch, ACTION_TYPES } = useUserProperties();
  const navigate = useNavigate();
  const [searchParams, setSearchParams] = useSearchParams();

  const hasPaymentReturn = searchParams.get("payment") === "success";
  const [step, setStep] = useState(hasPaymentReturn || currentUser ? 2 : 1);
  const [loading, setLoading] = useState(hasPaymentReturn);
  const [error, setError] = useState("");

  const [data, setData] = useState({
    selectedTier: "",
    email: "",
    password: "",
    confirmPassword: "",
  });

  function set(field, value) {
    setData((prev) => ({ ...prev, [field]: value }));
  }

  // Handle Stripe payment returns
  useEffect(() => {
    const payment = searchParams.get("payment");
    const sessionId = searchParams.get("session_id");
    const signupLockKey = sessionId
      ? `kp_onboard_signup_started_${sessionId}`
      : null;

    if (payment === "cancelled") {
      if (signupLockKey) sessionStorage.removeItem(signupLockKey);
      sessionStorage.removeItem("kp_onboard_email");
      sessionStorage.removeItem("kp_onboard_pw");
      setSearchParams({}, { replace: true });
      setStep(2);
      setError("Payment was cancelled. Please try again.");
      return;
    }

    if (payment !== "success" || !sessionId) return;

    // Phase 1: no account yet — create it. Auth state change remounts the
    // component (App.jsx swaps route trees) and Phase 2 runs on the next mount.
    if (!currentUser) {
      const savedEmail = sessionStorage.getItem("kp_onboard_email");
      const savedPw = sessionStorage.getItem("kp_onboard_pw");
      if (!savedEmail || !savedPw) {
        if (signupLockKey) sessionStorage.removeItem(signupLockKey);
        setSearchParams({}, { replace: true });
        setError("Session expired. Please start the signup process again.");
        setStep(1);
        setLoading(false);
        return;
      }

      // Guard against duplicate signup attempts caused by repeated effects.
      if (signupLockKey && sessionStorage.getItem(signupLockKey) === "1") {
        setLoading(true);
        return;
      }

      setLoading(true);
      if (signupLockKey) sessionStorage.setItem(signupLockKey, "1");
      signup(savedEmail, savedPw).catch((err) => {
        if (signupLockKey) sessionStorage.removeItem(signupLockKey);
        setSearchParams({}, { replace: true });
        setError("Account creation failed: " + err.message);
        setStep(1);
        setLoading(false);
      });
      return;
    }

    // Phase 2: authenticated — verify the checkout and go to the dashboard.
    setSearchParams({}, { replace: true });
    setLoading(true);
    dispatch({ type: ACTION_TYPES.CLEAR_USER_PROPERTIES });

    verifyCheckoutSession(sessionId)
      .then(() => {
        navigate("/addresses", { replace: true });
      })
      .catch((err) => {
        setError("Payment verification failed: " + err.message);
        setStep(2);
      })
      .finally(() => setLoading(false));
  }, [currentUser, searchParams, setSearchParams, signup, navigate, userProps, dispatch, ACTION_TYPES]);

  // ── Step handlers ─────────────────────────────────────────────────────────

  function handleStep1() {
    setError("");
    if (!data.email || !data.password || !data.confirmPassword) {
      setError("Please fill in all fields");
      return;
    }
    if (data.password !== data.confirmPassword) {
      setError("Passwords do not match");
      return;
    }
    if (data.password.length < 6) {
      setError("Password must be at least 6 characters");
      return;
    }
    setStep(2);
  }

  async function handleStep2() {
    setError("");
    if (!data.selectedTier) {
      setError("Please select a plan to continue");
      return;
    }
    try {
      setLoading(true);

      if (data.selectedTier === "free") {
        if (!currentUser) {
          await signup(data.email, data.password);
        }
        await activateFreeTier();
        navigate("/addresses", { replace: true });
        return;
      }

      dispatch({
        type: ACTION_TYPES.SET_USER_PROPERTIES,
        payload: { email: data.email, password: data.password },
      });
      const { url } = await createOnboardingCheckout(
        data.email,
        data.selectedTier,
      );
      window.location.href = url;
    } catch (err) {
      if (err.code === "auth/email-already-in-use") {
        setError("Email already in use. Try logging in instead.");
      } else if (err.code === "auth/invalid-email") {
        setError("Invalid email address");
      } else if (err.code === "auth/weak-password") {
        setError("Password is too weak");
      } else {
        setError("Failed to process plan selection: " + err.message);
      }
    } finally {
      setLoading(false);
    }
  }

  // ── Progress bar ──────────────────────────────────────────────────────────

  function ProgressBar() {
    return (
      <div className="progress-bar">
        {STEPS.map((label, i) => {
          const stepNum = i + 1;
          const done = step > stepNum;
          const active = step === stepNum;
          const dotClass = done
            ? "progress-bar__dot--done"
            : active
              ? "progress-bar__dot--active"
              : "progress-bar__dot--pending";

          return (
            <div key={label} className="progress-bar__step">
              {i > 0 && (
                <div
                  className={`progress-bar__connector ${
                    done || active
                      ? "progress-bar__connector--active"
                      : "progress-bar__connector--inactive"
                  }`}
                />
              )}
              <div>
                <div className={`progress-bar__dot ${dotClass}`}>
                  {done ? "\u2713" : stepNum}
                </div>
                <div
                  className={`progress-bar__label ${
                    active
                      ? "progress-bar__label--active"
                      : "progress-bar__label--inactive"
                  }`}
                >
                  {label}
                </div>
              </div>
            </div>
          );
        })}
      </div>
    );
  }

  // ── Step content ──────────────────────────────────────────────────────────

  function StepCreateAccount() {
    return (
      <>
        <h2 className="mb-lg">Create your account</h2>
        <Input
          label="Email"
          type="email"
          value={data.email}
          onChange={(v) => set("email", v)}
          disabled={loading}
          placeholder="you@example.com"
        />
        <Input
          label="Password"
          type="password"
          value={data.password}
          onChange={(v) => set("password", v)}
          disabled={loading}
          placeholder="At least 6 characters"
        />
        <Input
          label="Confirm Password"
          type="password"
          value={data.confirmPassword}
          onChange={(v) => set("confirmPassword", v)}
          disabled={loading}
          placeholder="Repeat your password"
          className="form-field--last"
        />
      </>
    );
  }

  function StepChoosePlan() {
    return (
      <>
        <h2 className="mb-sm">Choose your monitoring plan</h2>
        <p className="subscribe__subtitle">
          Select the plan that works best for you. You can upgrade anytime.
        </p>
        <TierPicker
          onSelect={(tier) => set("selectedTier", tier)}
          selectedTier={data.selectedTier}
        />
      </>
    );
  }

  // ── Footer navigation ─────────────────────────────────────────────────────

  function Footer() {
    async function handleNext() {
      if (step === 1) handleStep1();
      else if (step === 2) await handleStep2();
    }

    function handleBack() {
      setError("");
      setStep((s) => s - 1);
    }

    const nextLabel =
      step === 1
        ? "Create Account"
        : !data.selectedTier
          ? "Continue"
          : data.selectedTier === "free"
            ? "Start Free Trial"
            : "Subscribe & Continue";

    return (
      <div className="subscribe__footer">
        <div>
          {step === 2 && (
            <Button onClick={handleBack} disabled={loading} variant="ghost">
              ← Back
            </Button>
          )}
        </div>

        <Button
          onClick={handleNext}
          disabled={loading || (step === 2 && !data.selectedTier)}
          className="text-bold"
        >
          {loading ? "Please wait..." : nextLabel}
        </Button>
      </div>
    );
  }

  // ── Render ────────────────────────────────────────────────────────────────

  const stepContent = {
    1: StepCreateAccount(),
    2: StepChoosePlan(),
  };

  return (
    <div className="subscribe">
      <div
        className={`subscribe__container${step === 2 ? " subscribe__container--wide" : ""}`}
      >
        <h1 className="subscribe__title">Koin Ping</h1>

        {ProgressBar()}

        {error && <div className="alert alert--error">{error}</div>}

        <div className="subscribe__card">
          {stepContent[step]}
          {Footer()}
        </div>

        {step === 1 && (
          <p className="subscribe__login-link">
            Already have an account? <a href="/login">Log in here</a>
          </p>
        )}
      </div>
    </div>
  );
}