aston-team-project/app/src/main/java/ru/project/datasource/StudentCsvReader.java

package ru.project.datasource;

import ru.project.student.Student;
import ru.project.student.StudentBuilder;

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;

public class StudentCsvReader implements Iterator<Student> {
    private static final String GROUP_NUMBER = "groupNumber";
    private static final String AVERAGE_GRADE = "averageGrade";
    private static final String RECORD_BOOK_NUMBER = "recordBookNumber";

    private final CSVParser parser;
    private final Iterator<CSVRecord> records;

    public StudentCsvReader(String absoluteFilePath) {
        Path path = Paths.get(absoluteFilePath);
        if (!path.isAbsolute()) {
            throw new IllegalArgumentException("File path must be absolute");
        }

        try {
            CSVFormat format = CSVFormat.DEFAULT.builder()
                    .setHeader()
                    .setSkipHeaderRecord(true)
                    .build();
            this.parser = CSVParser.parse(path, StandardCharsets.UTF_8, format);
            validateHeader(parser.getHeaderMap());
            this.records = parser.iterator();
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }

    @Override
    public boolean hasNext() {
        return records.hasNext();
    }

    @Override
    public Student next() {
        if (!records.hasNext()) {
            throw new NoSuchElementException();
        }

        CSVRecord record = records.next();
        if (record.size() != 3) {
            throw new IllegalArgumentException(
                    "Expected 3 columns, but got " + record.size());
        }

        double averageGrade = Double.parseDouble(record.get(AVERAGE_GRADE));
        return new StudentBuilder()
                .setGroupNumber(record.get(GROUP_NUMBER))
                .setAverageGrade(averageGrade)
                .setRecordBookNumber(record.get(RECORD_BOOK_NUMBER))
                .build();
    }

    private static void validateHeader(Map<String, Integer> headerMap) {
        String[] expected = {GROUP_NUMBER, AVERAGE_GRADE, RECORD_BOOK_NUMBER};
        if (headerMap.size() != expected.length
                || !headerMap.keySet().containsAll(Arrays.asList(expected))) {
            throw new IllegalArgumentException("Invalid CSV header");
        }
    }
}