import { create } from "zustand";

import {
  generateVariableParenthesisSession,
  gradeVariableParenthesisAnswer,
} from "@/lib/engine/variable-parenthesis";
import type { VariableParenthesisTermCount } from "@/lib/engine/variable-parenthesis";
import type {
  VariableGradeResult,
  VariableParenthesisProblem,
  VariableUserAnswer,
} from "@/lib/engine/variable-types";

export interface VariableGameSession {
  problems: VariableParenthesisProblem[];
  currentIndex: number;
  results: (VariableGradeResult | null)[];
  termCount: VariableParenthesisTermCount;
}

export type VariableProblemCount = 5 | 10;
export type VariableMaxTermCount = VariableParenthesisTermCount;

interface VariableGameState {
  session: VariableGameSession | null;
  selectedProblemCount: VariableProblemCount;
  selectedMaxTermCount: VariableMaxTermCount;
  setProblemCount: (count: VariableProblemCount) => void;
  setMaxTermCount: (count: VariableMaxTermCount) => void;
  initSession: (
    count?: VariableProblemCount,
    maxTermCount?: VariableMaxTermCount,
  ) => void;
  submitAnswer: (answer: VariableUserAnswer) => void;
  nextProblem: () => void;
  resetSession: () => void;
}

const DEFAULT_SESSION_COUNT: VariableProblemCount = 10;
const DEFAULT_MAX_TERM_COUNT: VariableMaxTermCount = 2;

function createSession(
  count: VariableProblemCount = DEFAULT_SESSION_COUNT,
  maxTermCount: VariableMaxTermCount = DEFAULT_MAX_TERM_COUNT,
): VariableGameSession {
  const problems = generateVariableParenthesisSession(count, maxTermCount);

  return {
    problems,
    currentIndex: 0,
    results: problems.map(() => null),
    termCount: maxTermCount,
  };
}

export const useVariableGameStore = create<VariableGameState>((set, get) => ({
  session: null,
  selectedProblemCount: DEFAULT_SESSION_COUNT,
  selectedMaxTermCount: DEFAULT_MAX_TERM_COUNT,
  setProblemCount: (count) => {
    set({ selectedProblemCount: count });
  },
  setMaxTermCount: (count) => {
    set({ selectedMaxTermCount: count });
  },
  initSession: (count, maxTermCount) => {
    const selectedProblemCount = count ?? get().selectedProblemCount;
    const selectedMaxTermCount = maxTermCount ?? get().selectedMaxTermCount;

    set({ session: createSession(selectedProblemCount, selectedMaxTermCount) });
  },
  submitAnswer: (answer) => {
    const { session } = get();

    if (!session || session.currentIndex >= session.problems.length) return;
    if (session.results[session.currentIndex] !== null) return;

    const problem = session.problems[session.currentIndex];
    const result = gradeVariableParenthesisAnswer(problem, answer);
    const results = [...session.results];
    results[session.currentIndex] = result;

    set({
      session: {
        ...session,
        results,
      },
    });
  },
  nextProblem: () => {
    const { session } = get();

    if (!session || session.currentIndex >= session.problems.length) return;
    if (session.results[session.currentIndex] === null) return;

    set({
      session: {
        ...session,
        currentIndex: session.currentIndex + 1,
      },
    });
  },
  resetSession: () => {
    set({
      session: createSession(
        get().selectedProblemCount,
        get().selectedMaxTermCount,
      ),
    });
  },
}));