package br.cefetrj.sca.dominio;

public final class Isbn {
	final String codigo;

	public Isbn(String id) {
		if (id == null || id.isEmpty()) {
			throw new IllegalArgumentException("Código inválido para ISBN");
		}

		if (!this.validateIsbn13(id)) {
			throw new IllegalArgumentException("Código inválido para ISBN");
		}

		this.codigo = id;
	}

	public String getCodigo() {
		return codigo;
	}

	private boolean validateIsbn13(String isbn) {
		if (isbn == null) {
			return false;
		}

		// remove any hyphens
		isbn = isbn.replaceAll("-", "");

		// must be a 13 digit ISBN
		if (isbn.length() != 13) {
			return false;
		}

		try {
			int tot = 0;
			for (int i = 0; i < 12; i++) {
				int digit = Integer.parseInt(isbn.substring(i, i + 1));
				tot += (i % 2 == 0) ? digit * 1 : digit * 3;
			}

			// checksum must be 0-9. If calculated as 10 then = 0
			int checksum = 10 - (tot % 10);
			if (checksum == 10) {
				checksum = 0;
			}

			return checksum == Integer.parseInt(isbn.substring(12));
		} catch (NumberFormatException nfe) {
			// to catch invalid ISBNs that have non-numeric characters in them
			return false;
		}
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((codigo == null) ? 0 : codigo.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Isbn other = (Isbn) obj;
		if (codigo == null) {
			if (other.codigo != null)
				return false;
		} else if (!codigo.equals(other.codigo))
			return false;
		return true;
	}

	
}