package com.nexussoftware.bibliotech;

public class BiblioTechApp {

    public static void main(String[] args) {

        final String COMPANY_NAME = "Nexus Software";
        final int LOAN_DAYS = 15;
        final double DAILY_RATE = 0.25;

        String employee = "Marta Ruiz";
        String title = "Effective Java";
        String isbn = "978-0000000001";
        int elapsedDays = 27;

        int daysLate = elapsedDays - LOAN_DAYS;
        double fine = daysLate * DAILY_RATE;

        System.out.println("=== BiblioTech - " + COMPANY_NAME + " ===");
        System.out.println("Employee: " + employee);
        System.out.println("Book: " + title);
        System.out.println("ISBN: " + isbn);
        System.out.println("Days late: " + daysLate);
        System.out.println("Fine: " + fine + " EUR");
    }
}

=== BiblioTech - Nexus Software ===
Employee: Marta Ruiz
Book: Effective Java
ISBN: 978-0000000001
Days late: 12
Fine: 3.0 EUR

package com.nexussoftware.bibliotech;

import java.util.Scanner;

public class BiblioTechApp {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        final String COMPANY_NAME = "Nexus Software";
        final int LOAN_DAYS = 15;
        final double DAILY_RATE = 0.25;

        System.out.println("=== BiblioTech - " + COMPANY_NAME + " ===");
        System.out.println("Loan return record");
        System.out.println();

        System.out.print("Employee           : ");
        String employee = input.nextLine();

        System.out.print("Book title         : ");
        String title = input.nextLine();

        System.out.print("ISBN               : ");
        String isbn = input.nextLine();

        System.out.print("Elapsed days       : ");
        int elapsedDays = Integer.parseInt(input.nextLine());

        int daysLate = elapsedDays - LOAN_DAYS;
        double fine = daysLate * DAILY_RATE;

        System.out.println();
        System.out.println("Employee: " + employee);
        System.out.println("Book: " + title);
        System.out.println("ISBN: " + isbn);
        System.out.println("Days late: " + daysLate);
        System.out.println("Fine: " + fine + " EUR");

        input.close();
    }
}

// The delay can never be negative: if it is returned early, it is 0.
int daysLate = elapsedDays > LOAN_DAYS
        ? elapsedDays - LOAN_DAYS
        : 0;

// Breaking down the delay: / gives the whole weeks, % the leftover days.
int weeksLate = daysLate / 7;
int leftoverDays = daysLate % 7;

// Days of term remaining (0 if it has already expired).
int daysRemaining = elapsedDays < LOAN_DAYS
        ? LOAN_DAYS - elapsedDays
        : 0;

double baseFine = daysLate * DAILY_RATE;

// Text labels chosen with ternaries.
String status = daysLate > 0 ? "OVERDUE" : "ON TIME";
String severity = daysLate == 0 ? "-"
                : daysLate <= MINOR_THRESHOLD ? "MINOR"
                : "SEVERE";

// Cap: if the base fine exceeds the maximum, the maximum is charged.
double finalFine = baseFine > MAX_FINE ? MAX_FINE : baseFine;
String capApplied = baseFine > MAX_FINE ? "YES" : "NO";

// Formatted receipt: labels left-aligned in width 22,
// amounts right-aligned with exactly two decimals.
System.out.println("=".repeat(WIDTH));
System.out.printf("%-22s %s%n", "Employee:", employee);
System.out.printf("%-22s %8.2f EUR%n", "FINE TO PAY:", finalFine);

package com.nexussoftware.bibliotech;

import java.util.Scanner;

/**
 * BiblioTechApp - Management system for the internal technical library
 * of Nexus Software.
 *
 * Version 0.1 from module 1: linear record of a loan return, with
 * delay and fine calculation, and printing of a receipt.
 *
 * @author BiblioTech Team - Nexus Software
 * @version 0.1
 */
public class BiblioTechApp {

    public static void main(String[] args) {

        // ---------------------------------------------------------------
        // 1. RESOURCES
        // ---------------------------------------------------------------
        // A single Scanner for the whole application, connected to the
        // keyboard. Closing a Scanner over System.in closes System.in, so
        // we never create more than one.
        Scanner input = new Scanner(System.in);

        // ---------------------------------------------------------------
        // 2. BUSINESS RULES
        // ---------------------------------------------------------------
        // All the constants go together at the top: changing a rate means
        // editing ONE line, not hunting for the number all over the
        // program. 'final' guarantees nobody changes them by accident.
        final String COMPANY_NAME = "Nexus Software";
        final String VERSION = "0.1";
        final int LOAN_DAYS = 15;            // standard loan duration
        final double DAILY_RATE = 0.25;      // euros per day late
        final double MAX_FINE = 20.0;        // absolute cap on the fine
        final int MINOR_THRESHOLD = 7;       // up to 7 days, the delay is minor
        final int DAYS_PER_WEEK = 7;
        final int WIDTH = 52;                // width of the receipt lines

        // ---------------------------------------------------------------
        // 3. WELCOME HEADER
        // ---------------------------------------------------------------
        // "=".repeat(WIDTH) builds the separator line without typing
        // 52 equals signs by hand. repeat() exists since Java 11.
        System.out.println("=".repeat(WIDTH));
        System.out.printf("  BiblioTech v%s - %s%n", VERSION, COMPANY_NAME);
        System.out.println("  Loan return record");
        System.out.println("=".repeat(WIDTH));
        System.out.println();

        // ---------------------------------------------------------------
        // 4. DATA COLLECTION
        // ---------------------------------------------------------------
        // We use print (without ln) so that the cursor stays on the same
        // line as the question.
        // ALL reading is done with nextLine(): that way no line break is
        // ever left pending in the input stream, which is what causes the
        // classic nextInt()-followed-by-nextLine() problem.
        System.out.print("Employee           : ");
        String employee = input.nextLine();

        System.out.print("Book title         : ");
        String title = input.nextLine();

        System.out.print("ISBN               : ");
        String isbn = input.nextLine();

        System.out.print("Elapsed days       : ");
        // The text read is converted to a number with parseInt.
        // If the user types something that is not an integer, the program
        // ends with NumberFormatException (handled in module 6).
        int elapsedDays = Integer.parseInt(input.nextLine());

        // ---------------------------------------------------------------
        // 5. CALCULATIONS
        // ---------------------------------------------------------------

        // Days late clamped to zero. Without the ternary, an early return
        // would give a negative delay and therefore a negative fine:
        // the library paying the employee.
        int daysLate = elapsedDays > LOAN_DAYS
                ? elapsedDays - LOAN_DAYS
                : 0;

        // Days of term remaining. It only makes sense if it has not expired.
        int daysRemaining = elapsedDays < LOAN_DAYS
                ? LOAN_DAYS - elapsedDays
                : 0;

        // Breaking down the delay: integer division gives the whole weeks
        // and the modulo gives the leftover days.
        int weeksLate = daysLate / DAYS_PER_WEEK;
        int leftoverDays = daysLate % DAYS_PER_WEEK;

        // Base fine. daysLate is an int and DAILY_RATE is a double:
        // Java promotes the int to a double before multiplying.
        double baseFine = daysLate * DAILY_RATE;

        // Fine cap. The amount charged never exceeds MAX_FINE.
        double finalFine = baseFine > MAX_FINE ? MAX_FINE : baseFine;
        String capApplied = baseFine > MAX_FINE ? "YES" : "NO";

        // Text labels derived from the calculations.
        String status = daysLate > 0 ? "OVERDUE" : "ON TIME";

        // Nested ternary, read as a ladder from top to bottom.
        String severity = daysLate == 0 ? "-"
                        : daysLate <= MINOR_THRESHOLD ? "MINOR"
                        : "SEVERE";

        // Receipt reference code: the employee's initial in uppercase
        // + the last four digits of the ISBN.
        // charAt(0) takes the first character; substring cuts from the
        // given position to the end.
        String reference = String.format("%c%s-%s",
                employee.charAt(0),
                title.substring(0, 3).toUpperCase(),
                isbn.substring(isbn.length() - 4));

        // ---------------------------------------------------------------
        // 6. RECEIPT
        // ---------------------------------------------------------------
        System.out.println();
        System.out.println("=".repeat(WIDTH));
        System.out.println("  RETURN RECEIPT");
        System.out.println("=".repeat(WIDTH));

        // %-22s aligns the label to the LEFT in width 22, creating a
        // uniform column. %s sticks the value right after it.
        System.out.printf("%-22s %s%n", "Reference:", reference);
        System.out.printf("%-22s %s%n", "Employee:", employee);
        System.out.printf("%-22s %s%n", "Book:", title);
        System.out.printf("%-22s %s%n", "ISBN:", isbn);

        System.out.println("-".repeat(WIDTH));

        // %5d aligns the integers to the RIGHT in width 5, so that the
        // units land in the same column and can be compared at a glance.
        System.out.printf("%-22s %5d days%n", "Standard loan:", LOAN_DAYS);
        System.out.printf("%-22s %5d days%n", "Elapsed:", elapsedDays);
        System.out.printf("%-22s %5d days%n", "Days remaining:", daysRemaining);
        System.out.printf("%-22s %5d days (%d wk. and %d days)%n",
                "Late by:", daysLate, weeksLate, leftoverDays);

        System.out.println("-".repeat(WIDTH));

        // %8.2f: total width 8, exactly 2 decimals. That is what turns a
        // raw 3.0 into a presentable 3.00.
        System.out.printf("%-22s %8.2f EUR%n", "Daily rate:", DAILY_RATE);
        System.out.printf("%-22s %8.2f EUR%n", "Fine calculated:", baseFine);
        System.out.printf("%-22s %8.2f EUR%n", "Maximum fine:", MAX_FINE);
        System.out.printf("%-22s %8s%n", "Cap applied:", capApplied);

        System.out.println("-".repeat(WIDTH));

        System.out.printf("%-22s %8.2f EUR%n", "TOTAL TO PAY:", finalFine);
        System.out.printf("%-22s %s (%s)%n", "Status:", status, severity);

        System.out.println("=".repeat(WIDTH));

        // Warning on the error channel: it is not part of the receipt and
        // can be redirected separately when running the program.
        System.err.println("[warning] Version 0.1: the program does not validate input.");

        // ---------------------------------------------------------------
        // 7. RELEASING RESOURCES
        // ---------------------------------------------------------------
        input.close();
    }
}

bibliotech/
└── src/
    └── main/
        └── java/
            └── com/
                └── nexussoftware/
                    └── bibliotech/
                        └── BiblioTechApp.java

# Compile. You give the PATH of the file, with slashes.
# -d sends the .class files to a separate 'out' folder, away from the source.
javac -d ../../../out com/nexussoftware/bibliotech/BiblioTechApp.java

# Run. You give the qualified CLASS NAME, with dots.
# -cp tells the java command where to look for the compiled classes.
java -cp ../../../out com.nexussoftware.bibliotech.BiblioTechApp

java BiblioTechApp.java

# The receipt is saved to a file; the warning still appears on screen
java -cp ../../../out com.nexussoftware.bibliotech.BiblioTechApp > receipt.txt

====================================================
  BiblioTech v0.1 - Nexus Software
  Loan return record
====================================================

Employee           : Marta Ruiz
Book title         : Effective Java
ISBN               : 978-0000000001
Elapsed days       : 27

====================================================
  RETURN RECEIPT
====================================================
Reference:             MEFF-0001
Employee:              Marta Ruiz
Book:                  Effective Java
ISBN:                  978-0000000001
----------------------------------------------------
Standard loan:            15 days
Elapsed:                  27 days
Days remaining:            0 days
Late by:                  12 days (1 wk. and 5 days)
----------------------------------------------------
Daily rate:                0.25 EUR
Fine calculated:           3.00 EUR
Maximum fine:             20.00 EUR
Cap applied:                    NO
----------------------------------------------------
TOTAL TO PAY:              3.00 EUR
Status:                OVERDUE (SEVERE)
====================================================

====================================================
  BiblioTech v0.1 - Nexus Software
  Loan return record
====================================================

Employee           : Diego Alonso
Book title         : Refactoring
ISBN               : 978-0000000003
Elapsed days       : 9

====================================================
  RETURN RECEIPT
====================================================
Reference:             DREF-0003
Employee:              Diego Alonso
Book:                  Refactoring
ISBN:                  978-0000000003
----------------------------------------------------
Standard loan:            15 days
Elapsed:                   9 days
Days remaining:            6 days
Late by:                   0 days (0 wk. and 0 days)
----------------------------------------------------
Daily rate:                0.25 EUR
Fine calculated:           0.00 EUR
Maximum fine:             20.00 EUR
Cap applied:                    NO
----------------------------------------------------
TOTAL TO PAY:              0.00 EUR
Status:                ON TIME (-)
====================================================

        // --- Additional reading ---
        System.out.print("Book price         : ");
        double bookPrice = Double.parseDouble(input.nextLine());

        // --- Deposit and notice calculations ---
        final double DEPOSIT_PERCENTAGE = 0.10;  // 10 % of the price
        final int NOTICE_THRESHOLD = 3;          // days before warning of expiry

        // The deposit is 10 % of the price: double * double -> double.
        double deposit = bookPrice * DEPOSIT_PERCENTAGE;

        // The fine is deducted, but it can never end up negative:
        // the ternary clamps the result to zero.
        double depositReturned = deposit - finalFine > 0
                ? deposit - finalFine
                : 0.0;

        // The withheld amount is the part of the deposit the library keeps.
        double depositWithheld = deposit - depositReturned;

        // Due notice: a ladder of ternaries.
        // It is evaluated top to bottom and stops at the first true condition.
        String notice = daysLate > 0 ? "OVERDUE"
                      : daysRemaining <= NOTICE_THRESHOLD ? "DUE SOON"
                      : "IN PROGRESS";

        // --- Additional output ---
        System.out.println("-".repeat(WIDTH));
        System.out.printf("%-22s %8.2f EUR%n", "Book price:", bookPrice);
        System.out.printf("%-22s %8.2f EUR%n", "Deposit paid:", deposit);
        System.out.printf("%-22s %8.2f EUR%n", "Deposit withheld:", depositWithheld);
        System.out.printf("%-22s %8.2f EUR%n", "DEPOSIT TO REFUND:", depositReturned);
        System.out.printf("%-22s %s%n", "Notice:", notice);

        // --- Indicators ---
        // Careful: elapsedDays and LOAN_DAYS are ints, so the division
        // would be an INTEGER one. We have to force a double first.
        double termPercentage = (double) elapsedDays / LOAN_DAYS * 100;

        // Average cost per elapsed day. Here finalFine is already a double,
        // so the promotion is automatic and no cast is needed.
        double averageDailyCost = finalFine / elapsedDays;

        // What percentage of the cap the amount charged represents.
        double maxFinePercentage = finalFine / MAX_FINE * 100;

        System.out.println("-".repeat(WIDTH));
        System.out.println("  INDICATORS");
        System.out.println("-".repeat(WIDTH));
        System.out.printf("%-22s %8.2f %%%n", "Term consumed:", termPercentage);
        System.out.printf("%-22s %8.4f EUR/day%n", "Average daily cost:", averageDailyCost);
        System.out.printf("%-22s %8.2f %%%n", "Of maximum fine:", maxFinePercentage);

----------------------------------------------------
  INDICATORS
----------------------------------------------------
Term consumed:           180.00 %
Average daily cost:      0.1111 EUR/day
Of maximum fine:          15.00 %

        // ================= SECOND BOOK =================
        System.out.println();
        System.out.println("--- Second book ---");

        System.out.print("Book title 2       : ");
        String title2 = input.nextLine();

        System.out.print("ISBN 2             : ");
        String isbn2 = input.nextLine();

        System.out.print("Elapsed days 2     : ");
        int elapsedDays2 = Integer.parseInt(input.nextLine());

        // The same calculations as for the first one, duplicated.
        // This duplication is precisely what METHODS (module 3) and
        // LOOPS over collections (module 5) will solve.
        int daysLate2 = elapsedDays2 > LOAN_DAYS
                ? elapsedDays2 - LOAN_DAYS
                : 0;

        double baseFine2 = daysLate2 * DAILY_RATE;

        // Combined total, subject to a single cap for the whole return.
        double grossTotal = baseFine + baseFine2;
        double finalTotal = grossTotal > MAX_FINE ? MAX_FINE : grossTotal;

        // Which one has accrued the greater delay.
        String mostOverdueBook = daysLate >= daysLate2 ? title : title2;
        int highestDelay = daysLate >= daysLate2 ? daysLate : daysLate2;

        // ================= COMBINED RECEIPT =================
        System.out.println();
        System.out.println("=".repeat(WIDTH));
        System.out.println("  COMBINED RETURN RECEIPT");
        System.out.println("=".repeat(WIDTH));
        System.out.printf("%-22s %s%n", "Employee:", employee);
        System.out.println("-".repeat(WIDTH));

        // Table header and two rows with the same format.
        System.out.printf("%-24s %-16s %5s %9s%n", "BOOK", "ISBN", "LATE", "FINE");
        System.out.printf("%-24s %-16s %5d %9.2f%n", title, isbn, daysLate, baseFine);
        System.out.printf("%-24s %-16s %5d %9.2f%n", title2, isbn2, daysLate2, baseFine2);

        System.out.println("-".repeat(WIDTH));
        System.out.printf("%-22s %8.2f EUR%n", "Sum of fines:", grossTotal);
        System.out.printf("%-22s %8.2f EUR%n", "TOTAL TO PAY:", finalTotal);
        System.out.printf("%-22s %s (%d days)%n", "Highest delay:", mostOverdueBook, highestDelay);
        System.out.println("=".repeat(WIDTH));

====================================================
  COMBINED RETURN RECEIPT
====================================================
Employee:              Marta Ruiz
----------------------------------------------------
BOOK                     ISBN              LATE      FINE
Effective Java           978-0000000001      12      3.00
Design Patterns          978-0000000002      25      6.25
----------------------------------------------------
Sum of fines:               9.25 EUR
TOTAL TO PAY:               9.25 EUR
Highest delay:         Design Patterns (25 days)
====================================================