school_compare/nextjs-app/hooks/useComparison.ts

/**
 * Custom hook for managing school comparison state
 */

'use client';

import { useState, useEffect, useCallback } from 'react';
import useSWR from 'swr';
import { fetcher } from '@/lib/api';
import { getFromLocalStorage, setToLocalStorage } from '@/lib/utils';
import type { School, ComparisonResponse } from '@/lib/types';

const STORAGE_KEY = 'selectedSchools';
const MAX_SCHOOLS = 5;

export function useComparison() {
  const [selectedSchools, setSelectedSchools] = useState<School[]>([]);
  const [isInitialized, setIsInitialized] = useState(false);

  // Load from localStorage on mount
  useEffect(() => {
    const stored = getFromLocalStorage<School[]>(STORAGE_KEY, []);
    setSelectedSchools(stored);
    setIsInitialized(true);
  }, []);

  // Save to localStorage when schools change
  useEffect(() => {
    if (isInitialized) {
      setToLocalStorage(STORAGE_KEY, selectedSchools);
    }
  }, [selectedSchools, isInitialized]);

  // Fetch comparison data for selected schools
  const urns = selectedSchools.map((s) => s.urn).join(',');
  const { data, error, isLoading, mutate } = useSWR<ComparisonResponse>(
    selectedSchools.length > 0 ? `/compare?urns=${urns}` : null,
    fetcher,
    {
      revalidateOnFocus: false,
      dedupingInterval: 10000, // 10 seconds
    }
  );

  const addSchool = useCallback((school: School) => {
    setSelectedSchools((prev) => {
      // Check if already selected
      if (prev.some((s) => s.urn === school.urn)) {
        return prev;
      }

      // Check max limit
      if (prev.length >= MAX_SCHOOLS) {
        alert(`Maximum ${MAX_SCHOOLS} schools can be compared`);
        return prev;
      }

      return [...prev, school];
    });
  }, []);

  const removeSchool = useCallback((urn: number) => {
    setSelectedSchools((prev) => prev.filter((s) => s.urn !== urn));
  }, []);

  const clearAll = useCallback(() => {
    setSelectedSchools([]);
  }, []);

  const isSelected = useCallback(
    (urn: number) => selectedSchools.some((s) => s.urn === urn),
    [selectedSchools]
  );

  return {
    selectedSchools,
    comparisonData: data?.comparison,
    isLoading,
    error,
    addSchool,
    removeSchool,
    clearAll,
    isSelected,
    canAddMore: selectedSchools.length < MAX_SCHOOLS,
    mutate,
  };
}