import React, { useRef, useState, useEffect } from "react";
import {
  ArrowDown,
  Check,
  BookOpen,
  Scale,
  ArrowRight,
  RotateCcw,
} from "lucide-react";
import LinearSolutionsWidget from "../../../components/lessons/LinearSolutionsWidget";
import Quiz from "../../../components/lessons/Quiz";
import { LINEAR_EQ_QUIZ_DATA } from "../../../utils/constants";
import { Frac } from "../../../components/Math";

interface LessonProps {
  onFinish?: () => void;
}

const BalanceScaleWidget = () => {
  const [left, setLeft] = useState(15);
  const [right, setRight] = useState(15);
  const [tilt, setTilt] = useState(0);
  const [message, setMessage] = useState("Balanced");

  const apply = (val: number, side: "both" | "left" | "right") => {
    let newLeft = left;
    let newRight = right;
    if (side === "left" || side === "both") newLeft += val;
    if (side === "right" || side === "both") newRight += val;
    setLeft(newLeft);
    setRight(newRight);
    if (newLeft === newRight) {
      setTilt(0);
      setMessage("Perfectly Balanced! ✅");
    } else if (newLeft > newRight) {
      setTilt(-15);
      setMessage("Unbalanced! Left side is heavier. ❌");
    } else {
      setTilt(15);
      setMessage("Unbalanced! Right side is heavier. ❌");
    }
  };

  const reset = () => {
    setLeft(15);
    setRight(15);
    setTilt(0);
    setMessage("Balanced");
  };

  return (
    <div className="bg-white p-6 rounded-xl shadow-lg border border-slate-200">
      <div className="flex justify-between items-center mb-8">
        <h3 className="font-bold text-slate-700">Algebra Balance Scale</h3>
        <button onClick={reset} className="text-slate-400 hover:text-slate-600">
          <RotateCcw className="w-4 h-4" />
        </button>
      </div>
      <div className="relative h-40 w-full mb-8 flex justify-center items-end">
        <div className="absolute bottom-0 w-0 h-0 border-l-[20px] border-l-transparent border-r-[20px] border-r-transparent border-b-[40px] border-b-slate-800"></div>
        <div
          className="w-64 h-2 bg-slate-600 absolute bottom-[40px] transition-transform duration-700"
          style={{ transform: `rotate(${tilt}deg)` }}
        >
          <div
            className="absolute left-0 top-0 flex flex-col items-center"
            style={{ transform: `translateY(0px) rotate(${-tilt}deg)` }}
          >
            <div className="w-20 h-20 border-b-4 border-l-2 border-r-2 border-slate-400 rounded-b-xl bg-slate-50 flex items-center justify-center shadow-inner relative top-2">
              <span className="font-bold text-blue-600 text-lg">{left} kg</span>
            </div>
            <div className="w-0.5 h-16 bg-slate-400 absolute -top-16"></div>
          </div>
          <div
            className="absolute right-0 top-0 flex flex-col items-center"
            style={{ transform: `translateY(0px) rotate(${-tilt}deg)` }}
          >
            <div className="w-20 h-20 border-b-4 border-l-2 border-r-2 border-slate-400 rounded-b-xl bg-slate-50 flex items-center justify-center shadow-inner relative top-2">
              <span className="font-bold text-emerald-600 text-lg">
                {right} kg
              </span>
            </div>
            <div className="w-0.5 h-16 bg-slate-400 absolute -top-16"></div>
          </div>
        </div>
      </div>
      <div
        className={`text-center font-bold mb-6 ${tilt === 0 ? "text-green-600" : "text-rose-600"}`}
      >
        {message}
      </div>
      <div className="grid grid-cols-2 gap-4">
        <button
          onClick={() => apply(-5, "left")}
          className="p-3 rounded-lg border-2 border-slate-200 hover:border-rose-300 hover:bg-rose-50 text-slate-600 text-sm font-bold transition-all"
        >
          Subtract 5 from Left ONLY
        </button>
        <button
          onClick={() => apply(-5, "both")}
          className="p-3 rounded-lg border-2 border-blue-500 bg-blue-50 hover:bg-blue-100 text-blue-700 text-sm font-bold transition-all shadow-sm"
        >
          Subtract 5 from BOTH sides
        </button>
      </div>
      <p className="text-xs text-center text-slate-400 mt-4">
        Goal: Keep the scale balanced while isolating the variable.
      </p>
    </div>
  );
};

const LinearEquationsLesson: React.FC<LessonProps> = ({ onFinish }) => {
  const [activeSection, setActiveSection] = useState(0);
  const sectionsRef = useRef<(HTMLElement | null)[]>([]);

  const scrollToSection = (index: number) => {
    setActiveSection(index);
    sectionsRef.current[index]?.scrollIntoView({
      behavior: "smooth",
      block: "start",
    });
  };

  useEffect(() => {
    const observer = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => {
          if (entry.isIntersecting) {
            const index = sectionsRef.current.indexOf(
              entry.target as HTMLElement,
            );
            if (index !== -1) setActiveSection(index);
          }
        });
      },
      { rootMargin: "-20% 0px -60% 0px" },
    );
    sectionsRef.current.forEach((section) => {
      if (section) observer.observe(section);
    });
    return () => observer.disconnect();
  }, []);

  const SectionMarker = ({
    index,
    title,
    icon: Icon,
  }: {
    index: number;
    title: string;
    icon: any;
  }) => {
    const isActive = activeSection === index;
    const isPast = activeSection > index;
    return (
      <button
        onClick={() => scrollToSection(index)}
        className={`flex items-center gap-3 p-3 w-full rounded-lg transition-all ${isActive ? "bg-white shadow-md border border-blue-100" : "hover:bg-slate-100"}`}
      >
        <div
          className={`w-8 h-8 rounded-full flex items-center justify-center shrink-0 ${isActive ? "bg-blue-600 text-white" : isPast ? "bg-blue-400 text-white" : "bg-slate-200 text-slate-500"}`}
        >
          {isPast ? (
            <Check className="w-4 h-4" />
          ) : (
            <Icon className="w-4 h-4" />
          )}
        </div>
        <div className="text-left">
          <p
            className={`text-sm font-bold ${isActive ? "text-blue-900" : "text-slate-600"}`}
          >
            {title}
          </p>
        </div>
      </button>
    );
  };

  return (
    <div className="flex flex-col lg:flex-row min-h-screen">
      <aside className="w-full lg:w-64 lg:fixed lg:top-20 lg:bottom-0 lg:overflow-y-auto p-4 border-r border-slate-200 bg-slate-50 z-0 hidden lg:block">
        <nav className="space-y-2">
          <SectionMarker index={0} title="The Balance Principle" icon={Scale} />
          <SectionMarker
            index={1}
            title="Number of Solutions"
            icon={ArrowRight}
          />
          <SectionMarker index={2} title="Practice" icon={BookOpen} />
        </nav>
      </aside>

      <div className="flex-1 lg:ml-64 p-6 md:p-12 max-w-4xl mx-auto">
        {/* Section 1: Balance Principle */}
        <section
          ref={(el) => {
            sectionsRef.current[0] = el;
          }}
          className="min-h-screen flex flex-col justify-center mb-24 pt-20 lg:pt-0"
        >
          <h2 className="text-4xl font-extrabold text-slate-900 mb-6">
            The Balance Principle
          </h2>
          <div className="prose prose-slate text-lg text-slate-600 mb-6">
            <p>
              Linear equations are like a balance scale. Whatever you do to one
              side, you <strong>must</strong> do to the other. The goal is
              always to <strong>isolate the variable</strong> — get x by itself
              on one side with a number on the other.
            </p>
          </div>

          <BalanceScaleWidget />

          {/* 4-Step Process */}
          <div className="mt-8 bg-blue-50 border border-blue-200 rounded-2xl p-6 space-y-4">
            <h3 className="font-bold text-blue-900 text-lg">
              The 4-Step Solve Process
            </h3>
            <div className="space-y-3">
              {[
                {
                  step: "1",
                  title: "Distribute",
                  desc: "Expand parentheses and clear fractions by multiplying through by the LCD (lowest common denominator).",
                },
                {
                  step: "2",
                  title: "Combine Like Terms",
                  desc: "Simplify each side of the equation separately — add/subtract terms with the same variable.",
                },
                {
                  step: "3",
                  title: "Move",
                  desc: "Get all variable terms on one side, all constant terms on the other, using addition or subtraction.",
                },
                {
                  step: "4",
                  title: "Divide",
                  desc: "Divide both sides by the coefficient of the variable to solve.",
                },
              ].map((item) => (
                <div
                  key={item.step}
                  className="flex gap-4 bg-white rounded-xl p-4 border border-blue-100"
                >
                  <div className="w-8 h-8 bg-blue-600 text-white rounded-full flex items-center justify-center font-bold shrink-0">
                    {item.step}
                  </div>
                  <div>
                    <p className="font-bold text-slate-800">{item.title}</p>
                    <p className="text-slate-600 text-sm">{item.desc}</p>
                  </div>
                </div>
              ))}
            </div>
          </div>

          {/* Three Worked Examples */}
          <div className="mt-8 space-y-4">
            <div className="bg-emerald-50 border border-emerald-200 rounded-xl p-6">
              <p className="font-bold text-emerald-800 mb-3">
                Example 1: Basic (no fractions)
              </p>
              <div className="font-mono text-sm space-y-1 text-slate-700">
                <p>Solve: 3(2x − 4) = 2x + 8</p>
                <p className="text-slate-500">
                  Step 1 (Distribute): 6x − 12 = 2x + 8
                </p>
                <p className="text-slate-500">Step 3 (Move): 4x = 20</p>
                <p className="text-slate-500">
                  Step 4 (Divide by 4):{" "}
                  <strong className="text-emerald-700">x = 5</strong>
                </p>
              </div>
            </div>
            <div className="bg-emerald-50 border border-emerald-200 rounded-xl p-6">
              <p className="font-bold text-emerald-800 mb-3">
                Example 2: With fractions — clear them first!
              </p>
              <div className="font-mono text-sm space-y-1 text-slate-700">
                <p>
                  Solve: <Frac n="x" d="3" /> + 2 = <Frac n="x" d="2" /> − 1
                </p>
                <p className="text-slate-500">
                  Multiply every term by 6 (LCD of 3 and 2):
                </p>
                <p className="text-slate-500">2x + 12 = 3x − 6</p>
                <p className="text-slate-500">12 + 6 = 3x − 2x</p>
                <p className="text-slate-500">
                  <strong className="text-emerald-700">x = 18</strong>
                </p>
              </div>
            </div>
            <div className="bg-emerald-50 border border-emerald-200 rounded-xl p-6">
              <p className="font-bold text-emerald-800 mb-3">
                Example 3: Literal equations (isolating a variable)
              </p>
              <div className="font-mono text-sm space-y-1 text-slate-700">
                <p>Solve for r: A = P(1 + rt)</p>
                <p className="text-slate-500">
                  Divide both sides by P: <Frac n="A" d="P" /> = 1 + rt
                </p>
                <p className="text-slate-500">
                  Subtract 1: <Frac n="A" d="P" /> − 1 = rt
                </p>
                <p className="text-slate-500">
                  Divide by t:{" "}
                  <strong className="text-emerald-700">
                    r ={" "}
                    <Frac
                      n={
                        <>
                          <Frac n="A" d="P" /> − 1
                        </>
                      }
                      d="t"
                    />
                  </strong>
                </p>
              </div>
            </div>
          </div>

          <div className="mt-6 bg-red-50 border border-red-200 rounded-xl p-4 text-sm">
            <p className="font-bold text-red-800 mb-1">
              Common SAT Mistake: Distributing a Negative
            </p>
            <p className="text-slate-700">
              When distributing a negative sign: −3(x − 4) = −3x + 12, NOT −3x −
              12. The negative multiplies EVERY term inside the parentheses.
            </p>
          </div>

          <button
            onClick={() => scrollToSection(1)}
            className="mt-8 group flex items-center text-blue-600 font-bold hover:text-blue-800 transition-colors"
          >
            Next: Number of Solutions{" "}
            <ArrowDown className="ml-2 w-5 h-5 group-hover:translate-y-1 transition-transform" />
          </button>
        </section>

        {/* Section 2: Number of Solutions */}
        <section
          ref={(el) => {
            sectionsRef.current[1] = el;
          }}
          className="min-h-screen flex flex-col justify-center mb-24"
        >
          <h2 className="text-4xl font-extrabold text-slate-900 mb-6">
            One, None, or Infinite Solutions?
          </h2>
          <div className="prose prose-slate text-lg text-slate-600 mb-8">
            <p>
              Not all equations have exactly one answer. After simplifying, look
              at what's left. The SAT frequently asks for a value of <em>k</em>{" "}
              that makes an equation have no solution or infinitely many
              solutions — this is a critical concept to master.
            </p>
          </div>

          <div className="bg-blue-50 border border-blue-200 rounded-2xl p-6 mb-8 space-y-4">
            <h3 className="text-lg font-bold text-blue-900">
              The Three Outcomes
            </h3>
            <div className="grid grid-cols-1 md:grid-cols-3 gap-4">
              <div className="bg-blue-100 rounded-xl p-4 text-center">
                <div className="font-bold text-blue-900 text-base mb-2">
                  One Solution
                </div>
                <div className="font-mono text-sm text-blue-700 bg-white rounded p-2 mb-2">
                  2x + 1 = x + 5
                </div>
                <div className="text-xs text-blue-700">
                  Variable survives after simplification → unique answer:{" "}
                  <strong>x = 4</strong>
                </div>
              </div>
              <div className="bg-red-50 border border-red-200 rounded-xl p-4 text-center">
                <div className="font-bold text-red-900 text-base mb-2">
                  No Solution
                </div>
                <div className="font-mono text-sm text-red-700 bg-white rounded p-2 mb-2">
                  2x + 3 = 2x + 5
                </div>
                <div className="text-xs text-red-700">
                  Variables cancel → <strong>3 = 5</strong> (false statement —
                  impossible)
                </div>
              </div>
              <div className="bg-emerald-50 border border-emerald-200 rounded-xl p-4 text-center">
                <div className="font-bold text-emerald-900 text-base mb-2">
                  Infinite Solutions
                </div>
                <div className="font-mono text-sm text-emerald-700 bg-white rounded p-2 mb-2">
                  2x + 3 = 2x + 3
                </div>
                <div className="text-xs text-emerald-700">
                  Variables cancel → <strong>3 = 3</strong> (always true — every
                  x works)
                </div>
              </div>
            </div>
          </div>

          {/* Finding k */}
          <div className="bg-blue-50 border border-blue-200 rounded-2xl p-6 mb-8 space-y-4">
            <h3 className="text-lg font-bold text-blue-900">
              SAT Focus: Finding the Value of k
            </h3>

            <div className="bg-white rounded-xl p-5 border border-blue-100">
              <p className="font-bold text-blue-800 mb-3">
                Example: For what value of k does 4x + k = 4x − 2 have no
                solution?
              </p>
              <div className="font-mono text-sm text-slate-700 space-y-1">
                <p>After subtracting 4x from both sides: k = −2</p>
                <p>
                  If k = −2: −2 = −2 (always true) → infinite solutions, not no
                  solution!
                </p>
                <p className="text-blue-700 font-bold">
                  For no solution: k ≠ −2 (any other value gives a false
                  statement like k = −2 being false)
                </p>
              </div>
              <p className="text-slate-500 text-xs mt-2">
                The equation has no solution for any value of k EXCEPT −2. For
                infinite solutions, set k = −2.
              </p>
            </div>

            <div className="bg-white rounded-xl p-5 border border-blue-100">
              <p className="font-bold text-blue-800 mb-3">
                Example: For what value of k does 3(x + k) = 3x + 12 have
                infinite solutions?
              </p>
              <div className="font-mono text-sm text-slate-700 space-y-1">
                <p>Distribute: 3x + 3k = 3x + 12</p>
                <p>Subtract 3x: 3k = 12</p>
                <p className="text-blue-700 font-bold">k = 4</p>
              </div>
              <p className="text-slate-500 text-xs mt-2">
                For k = 4: 12 = 12 (always true) → infinite solutions. ✓
              </p>
            </div>

            <div className="bg-red-50 border border-red-200 rounded-xl p-4 text-sm">
              <p className="font-bold text-red-800 mb-1">The Key Rule</p>
              <p className="text-slate-700">
                <strong>No solution</strong>: same variable coefficients,
                different constants (parallel lines).
                <br />
                <strong>Infinite solutions</strong>: same variable coefficients
                AND same constants (identical lines).
              </p>
            </div>
          </div>

          <LinearSolutionsWidget />
          <button
            onClick={() => scrollToSection(2)}
            className="mt-12 group flex items-center text-blue-600 font-bold hover:text-blue-800 transition-colors"
          >
            Next: Practice Quiz{" "}
            <ArrowDown className="ml-2 w-5 h-5 group-hover:translate-y-1 transition-transform" />
          </button>
        </section>

        {/* Section 3: Quiz */}
        <section
          ref={(el) => {
            sectionsRef.current[2] = el;
          }}
          className="min-h-screen flex flex-col justify-center"
        >
          <h2 className="text-4xl font-extrabold text-slate-900 mb-8">
            Practice Time
          </h2>
          {LINEAR_EQ_QUIZ_DATA.map((quiz, idx) => (
            <div key={quiz.id} className="mb-12">
              <Quiz data={quiz} />
            </div>
          ))}
          <div className="p-8 bg-blue-900 rounded-2xl text-white text-center mt-12">
            <h3 className="text-2xl font-bold mb-4">Topic Mastered!</h3>
            <button
              onClick={onFinish}
              className="px-6 py-3 bg-white text-blue-900 font-bold rounded-full hover:bg-blue-50 transition-colors"
            >
              Finish Lesson ✓
            </button>
          </div>
        </section>
      </div>
    </div>
  );
};

export default LinearEquationsLesson;
