/*
 * Ex. No. 6: IMPLEMENTATION OF DOUBLY LINKED LIST
 * Library Borrowed Book Record System using a doubly linked list
 * Supports: INSERT (beginning/end/position), DELETE (beginning/end/position/by ID),
 *           SEARCH by Book ID, DISPLAY (forward/reverse)
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define TITLE_LEN 60
#define AUTHOR_LEN 50

struct Node {
    int bookId;
    char title[TITLE_LEN];
    char author[AUTHOR_LEN];
    struct Node *prev;
    struct Node *next;
};

struct Node *head = NULL;

/* Count nodes in list */
int countNodes(void) {
    int count = 0;
    struct Node *cur = head;
    while (cur != NULL) {
        count++;
        cur = cur->next;
    }
    return count;
}

/* Return the last node, or NULL if the list is empty */
struct Node *lastNode(void) {
    struct Node *cur = head;
    if (cur == NULL) {
        return NULL;
    }
    while (cur->next != NULL) {
        cur = cur->next;
    }
    return cur;
}

struct Node *makeNode(int bookId, const char *title, const char *author) {
    struct Node *node = (struct Node *)malloc(sizeof(struct Node));
    if (node == NULL) {
        printf("Memory allocation failed.\n");
        exit(1);
    }
    node->bookId = bookId;
    strcpy(node->title, title);
    strcpy(node->author, author);
    node->prev = NULL;
    node->next = NULL;
    return node;
}

/* i) Insert at beginning */
void insertBeginning(int bookId, const char *title, const char *author) {
    struct Node *node = makeNode(bookId, title, author);
    node->next = head;
    if (head != NULL) {
        head->prev = node;
    }
    head = node;
    printf("Record inserted at beginning.\n");
}

/* ii) Insert at end */
void insertEnd(int bookId, const char *title, const char *author) {
    struct Node *node = makeNode(bookId, title, author);
    struct Node *last = lastNode();
    if (last == NULL) {
        head = node;
    } else {
        last->next = node;
        node->prev = last;
    }
    printf("Record inserted at end.\n");
}

/* iii) Insert at a given position (1-based) */
void insertAtPosition(int pos, int bookId, const char *title, const char *author) {
    int size = countNodes();
    if (pos < 1 || pos > size + 1) {
        printf("Invalid position. Valid range is 1 to %d.\n", size + 1);
        return;
    }
    if (pos == 1) {
        insertBeginning(bookId, title, author);
        return;
    }

    struct Node *prev = head;
    int i;
    for (i = 1; i < pos - 1; i++) {
        prev = prev->next;
    }

    struct Node *node = makeNode(bookId, title, author);
    node->next = prev->next;
    node->prev = prev;
    if (prev->next != NULL) {
        prev->next->prev = node;
    }
    prev->next = node;
    printf("Record inserted at position %d.\n", pos);
}

/* iv) Delete from beginning */
void deleteBeginning(void) {
    if (head == NULL) {
        printf("List is empty. Nothing to delete.\n");
        return;
    }
    struct Node *doomed = head;
    head = head->next;
    if (head != NULL) {
        head->prev = NULL;
    }
    printf("Deleted record: BookID=%d, Title=%s\n", doomed->bookId, doomed->title);
    free(doomed);
}

/* v) Delete from end */
void deleteEnd(void) {
    if (head == NULL) {
        printf("List is empty. Nothing to delete.\n");
        return;
    }
    struct Node *doomed = lastNode();
    if (doomed->prev == NULL) {
        head = NULL;
    } else {
        doomed->prev->next = NULL;
    }
    printf("Deleted record: BookID=%d, Title=%s\n", doomed->bookId, doomed->title);
    free(doomed);
}

/* vi) Delete from a given position (1-based) */
void deleteAtPosition(int pos) {
    int size = countNodes();
    if (head == NULL) {
        printf("List is empty. Nothing to delete.\n");
        return;
    }
    if (pos < 1 || pos > size) {
        printf("Invalid position. Valid range is 1 to %d.\n", size);
        return;
    }
    if (pos == 1) {
        deleteBeginning();
        return;
    }

    struct Node *doomed = head;
    int i;
    for (i = 1; i < pos; i++) {
        doomed = doomed->next;
    }

    doomed->prev->next = doomed->next;
    if (doomed->next != NULL) {
        doomed->next->prev = doomed->prev;
    }
    printf("Deleted record: BookID=%d, Title=%s\n", doomed->bookId, doomed->title);
    free(doomed);
}

/* vii) Delete a record by its Book ID */
void deleteById(int bookId) {
    struct Node *cur = head;
    while (cur != NULL && cur->bookId != bookId) {
        cur = cur->next;
    }
    if (cur == NULL) {
        printf("Book ID %d not found.\n", bookId);
        return;
    }

    if (cur->prev == NULL) {
        head = cur->next;
    } else {
        cur->prev->next = cur->next;
    }
    if (cur->next != NULL) {
        cur->next->prev = cur->prev;
    }
    printf("Deleted record: BookID=%d, Title=%s\n", cur->bookId, cur->title);
    free(cur);
}

/* viii) Search by Book ID */
void search(int bookId) {
    struct Node *cur = head;
    int pos = 1;
    while (cur != NULL) {
        if (cur->bookId == bookId) {
            printf("Found at position %d: BookID=%d, Title=%s, Author=%s\n",
                   pos, cur->bookId, cur->title, cur->author);
            return;
        }
        cur = cur->next;
        pos++;
    }
    printf("Book ID %d not found.\n", bookId);
}

/* ix) Display all records in forward order */
void displayForward(void) {
    if (head == NULL) {
        printf("List is empty.\n");
        return;
    }
    struct Node *cur = head;
    int pos = 1;
    printf("--- Borrowed Book Records (Forward) ---\n");
    while (cur != NULL) {
        printf("%d) BookID=%d, Title=%s, Author=%s\n", pos, cur->bookId, cur->title, cur->author);
        cur = cur->next;
        pos++;
    }
}

/* x) Display all records in reverse order */
void displayReverse(void) {
    if (head == NULL) {
        printf("List is empty.\n");
        return;
    }
    struct Node *cur = lastNode();
    int pos = countNodes();
    printf("--- Borrowed Book Records (Reverse) ---\n");
    while (cur != NULL) {
        printf("%d) BookID=%d, Title=%s, Author=%s\n", pos, cur->bookId, cur->title, cur->author);
        cur = cur->prev;
        pos--;
    }
}

/* Free all remaining nodes before exit */
void freeList(void) {
    struct Node *cur = head;
    while (cur != NULL) {
        struct Node *next = cur->next;
        free(cur);
        cur = next;
    }
    head = NULL;
}

void readBook(int *bookId, char *title, char *author) {
    printf("Enter book ID: ");
    scanf("%d", bookId);
    printf("Enter book title: ");
    scanf(" %59[^\n]", title);
    printf("Enter author name: ");
    scanf(" %49[^\n]", author);
}

int main(void) {
    int choice, bookId, pos;
    char title[TITLE_LEN];
    char author[AUTHOR_LEN];

    do {
        printf("\n===== Library Borrowed Book Record System =====\n");
        printf("1. Insert at Beginning\n");
        printf("2. Insert at End\n");
        printf("3. Insert at a Given Position\n");
        printf("4. Delete from Beginning\n");
        printf("5. Delete from End\n");
        printf("6. Delete from a Given Position\n");
        printf("7. Delete by Book ID\n");
        printf("8. Search by Book ID\n");
        printf("9. Display Forward\n");
        printf("10. Display Reverse\n");
        printf("11. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                readBook(&bookId, title, author);
                insertBeginning(bookId, title, author);
                break;
            case 2:
                readBook(&bookId, title, author);
                insertEnd(bookId, title, author);
                break;
            case 3:
                printf("Enter position: ");
                scanf("%d", &pos);
                readBook(&bookId, title, author);
                insertAtPosition(pos, bookId, title, author);
                break;
            case 4:
                deleteBeginning();
                break;
            case 5:
                deleteEnd();
                break;
            case 6:
                printf("Enter position: ");
                scanf("%d", &pos);
                deleteAtPosition(pos);
                break;
            case 7:
                printf("Enter book ID to delete: ");
                scanf("%d", &bookId);
                deleteById(bookId);
                break;
            case 8:
                printf("Enter book ID to search: ");
                scanf("%d", &bookId);
                search(bookId);
                break;
            case 9:
                displayForward();
                break;
            case 10:
                displayReverse();
                break;
            case 11:
                printf("Exiting...\n");
                break;
            default:
                printf("Invalid choice.\n");
        }
    } while (choice != 11);

    freeList();
    return 0;
}