import React, { useRef, useState, useEffect } from "react";
import { ArrowDown, Check, BookOpen, Layers } from "lucide-react";
import ParallelPerpendicularWidget from "../../../components/lessons/ParallelPerpendicularWidget";
import Quiz from "../../../components/lessons/Quiz";
import { LINEAR_PARALLEL_PERP_QUIZ_DATA } from "../../../utils/constants";
import { Frac } from "../../../components/Math";

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

const LinearParallelPerpendicularLesson: 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="Parallel & Perpendicular"
            icon={Layers}
          />
          <SectionMarker index={1} 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 */}
        <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">
            Parallel & Perpendicular Lines
          </h2>
          <div className="prose prose-slate text-lg text-slate-600 mb-8">
            <p>
              Parallel and perpendicular line questions appear on almost every
              SAT. The core skill is: identify the slope of the given line,
              apply the parallel or perpendicular slope rule, then write the new
              equation through a given point.
            </p>
          </div>

          <div className="bg-blue-50 border border-blue-200 rounded-2xl p-6 mb-8 space-y-5">
            <h3 className="text-lg font-bold text-blue-900">
              The Two Slope Rules
            </h3>

            <div className="grid md:grid-cols-2 gap-4">
              <div className="bg-white rounded-xl p-5 border border-blue-100">
                <p className="font-bold text-blue-900 mb-3 text-lg">
                  Parallel Lines
                </p>
                <div className="bg-blue-50 rounded-lg p-3 text-center mb-3">
                  <p className="font-mono text-blue-800 font-bold text-xl">
                    m₁ = m₂
                  </p>
                  <p className="text-xs text-slate-500 mt-1">
                    Same slope, different y-intercept
                  </p>
                </div>
                <ul className="text-slate-600 text-sm space-y-1 list-disc list-inside">
                  <li>Lines never intersect — they run side by side</li>
                  <li>Same slope guarantees they won't cross</li>
                  <li>
                    If y-intercepts also matched, the lines would be identical
                  </li>
                </ul>
                <div className="mt-3 bg-blue-50 rounded-lg p-2 font-mono text-xs text-slate-600">
                  y = 3x + 1 ∥ y = 3x − 7 (both slope = 3)
                </div>
              </div>
              <div className="bg-white rounded-xl p-5 border border-blue-100">
                <p className="font-bold text-indigo-900 mb-3 text-lg">
                  Perpendicular Lines
                </p>
                <div className="bg-indigo-50 rounded-lg p-3 text-center mb-3">
                  <p className="font-mono text-indigo-800 font-bold text-xl">
                    m₁ × m₂ = −1
                  </p>
                  <p className="text-xs text-slate-500 mt-1">
                    Negative reciprocal slopes
                  </p>
                </div>
                <ul className="text-slate-600 text-sm space-y-1 list-disc list-inside">
                  <li>Lines meet at a 90° angle</li>
                  <li>Rule: flip the fraction and change the sign</li>
                  <li>
                    A horizontal line (slope 0) is ⊥ to a vertical line
                    (undefined slope)
                  </li>
                </ul>
                <div className="mt-3 bg-indigo-50 rounded-lg p-2 font-mono text-xs text-slate-600">
                  y = <Frac n="2" d="3" />x + 1 ⊥ y = <Frac n="−3" d="2" />x + 5
                </div>
              </div>
            </div>

            {/* Negative Reciprocal Examples */}
            <div className="bg-white rounded-xl p-5 border border-blue-100">
              <p className="font-bold text-blue-800 mb-3">
                Finding Perpendicular Slopes: Worked Examples
              </p>
              <div className="overflow-x-auto">
                <table className="w-full text-sm border-collapse">
                  <thead>
                    <tr className="bg-blue-100 text-blue-900">
                      <th className="p-2 text-left font-bold">
                        Original Slope
                      </th>
                      <th className="p-2 text-left font-bold">
                        Step 1: Flip the fraction
                      </th>
                      <th className="p-2 text-left font-bold">
                        Step 2: Negate the sign
                      </th>
                      <th className="p-2 text-left font-bold">
                        Perpendicular Slope
                      </th>
                    </tr>
                  </thead>
                  <tbody className="text-slate-600">
                    <tr className="border-b border-blue-50">
                      <td className="p-2 font-mono">2 (= 2÷1)</td>
                      <td className="p-2">
                        <Frac n="1" d="2" />
                      </td>
                      <td className="p-2">
                        <Frac n="−1" d="2" />
                      </td>
                      <td className="p-2 font-bold text-indigo-700">
                        <Frac n="−1" d="2" />
                      </td>
                    </tr>
                    <tr className="border-b border-blue-50 bg-slate-50">
                      <td className="p-2">
                        <Frac n="−3" d="4" />
                      </td>
                      <td className="p-2">
                        <Frac n="4" d="3" />
                      </td>
                      <td className="p-2">
                        <Frac n="4" d="3" />
                      </td>
                      <td className="p-2 font-bold text-indigo-700">
                        <Frac n="4" d="3" />
                      </td>
                    </tr>
                    <tr className="border-b border-blue-50">
                      <td className="p-2 font-mono">−5</td>
                      <td className="p-2">
                        <Frac n="1" d="5" /> (flip)
                      </td>
                      <td className="p-2">
                        <Frac n="1" d="5" /> (negate negative)
                      </td>
                      <td className="p-2 font-bold text-indigo-700">
                        <Frac n="1" d="5" />
                      </td>
                    </tr>
                    <tr className="bg-slate-50">
                      <td className="p-2 font-mono">0 (horizontal)</td>
                      <td className="p-2 font-mono">—</td>
                      <td className="p-2 font-mono">—</td>
                      <td className="p-2 font-bold text-indigo-700">
                        Undefined (vertical)
                      </td>
                    </tr>
                  </tbody>
                </table>
              </div>
            </div>

            {/* Full Problem Worked Examples */}
            <div className="bg-white rounded-xl p-5 border border-blue-100">
              <p className="font-bold text-blue-800 mb-3">
                Complete Problem: Writing the Equation
              </p>
              <div className="space-y-4">
                <div className="bg-blue-50 rounded-lg p-4 text-sm">
                  <p className="font-semibold text-blue-800 mb-2">
                    Example 1: Find the line parallel to y = 4x − 3 passing
                    through (2, 5)
                  </p>
                  <div className="font-mono space-y-1 text-slate-700">
                    <p>Parallel → same slope: m = 4</p>
                    <p>Use point-slope: y − 5 = 4(x − 2)</p>
                    <p>y − 5 = 4x − 8</p>
                    <p className="text-blue-700 font-bold">
                      y = 4x − 3 &nbsp;← Wait, same as original! Confirm: passes
                      through (2, 5): 5 = 8 − 3 = 5 ✓
                    </p>
                  </div>
                </div>
                <div className="bg-indigo-50 rounded-lg p-4 text-sm">
                  <p className="font-semibold text-indigo-800 mb-2">
                    Example 2: Find the line perpendicular to 2x + 3y = 12
                    passing through (4, 1)
                  </p>
                  <div className="font-mono space-y-1 text-slate-700">
                    <p>
                      First, find slope of 2x + 3y = 12: y ={" "}
                      <Frac n="−2" d="3" />x + 4, so m = <Frac n="−2" d="3" />
                    </p>
                    <p>
                      Perpendicular slope: flip and negate → m ={" "}
                      <Frac n="3" d="2" />
                    </p>
                    <p>
                      Point-slope: y − 1 = <Frac n="3" d="2" />
                      (x − 4)
                    </p>
                    <p>
                      y = <Frac n="3" d="2" />x − 6 + 1
                    </p>
                    <p className="text-indigo-700 font-bold">
                      y = <Frac n="3" d="2" />x − 5
                    </p>
                  </div>
                </div>
              </div>
            </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">
                SAT Trap: Parallel Lines Must Have Different Intercepts
              </p>
              <p className="text-slate-700">
                Parallel lines need the <em>same slope</em> but a{" "}
                <em>different y-intercept</em>. If the intercepts also match,
                the lines are identical — infinitely many intersections, not
                parallel. The SAT sometimes includes a "same slope, same
                intercept" option to trap students.
              </p>
            </div>
          </div>

          <ParallelPerpendicularWidget />

          <button
            onClick={() => scrollToSection(1)}
            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 2: Quiz */}
        <section
          ref={(el) => {
            sectionsRef.current[1] = 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_PARALLEL_PERP_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 LinearParallelPerpendicularLesson;