/* file name: hashingTableUsingList.c */
/* 雜湊法 : 使用鏈結串列處理碰撞 */

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define MAX_NUM 100  /* 最大資料筆數 */
#define PRIME 97     /* MAX_NUM之質數 */

/* 定義資料結構 */
typedef struct Person {
    long id;
    char name[21];
    struct Person *link;
} Student;

/* 建立雜湊表串列 */
Student *Hashtab[MAX_NUM], *current;

/*函數原型宣告*/
long hashfun(long);
void insert(void);
void del(void);
Student *search(Student *,Student *);
void query(void);
void show(void);
void flushBuffer(void);

int main()
{
    char *menu_prompt =
        "\n=== Hashing Table Program ==\n"
        "  1. Insert\n"
        "  2. Delete\n"
        "  3. Show\n"
        "  4. Search\n"
        "  5. Quit\n"
        "  請輸入選項: ";
    char choice;
    int i;

    /* 起始雜湊串列，將各串列指向 NULL */
    for (i = 0; i< MAX_NUM; i++)
        Hashtab[i] = NULL;

    do {
        printf("%s", menu_prompt);
        choice = toupper(getchar());
        flushBuffer();
        printf("\n");
        switch (choice) {
            case '1':
                insert();
                break;
            case '2':
                del();
                break;
            case '3':
                show();
                break;
            case '4':
                query();
                break;
            case '5':
                puts("Bye Bye ^_^");
                break;
            default:
                puts("錯誤選項!!");
        }
    } while (choice != '5');

    return 0;
}

/* 雜湊函數: */
/* 以除法運算傳求出記錄應儲存的位址 */
long hashfun(long key)
{
    return (key % PRIME);
}

void insert()
{
    Student *newnode;
    long index;

    /*輸入記錄*/
    newnode = (Student *)malloc(sizeof(Student));
    newnode->link = NULL;
    printf("Enter id: ");
    scanf("%ld",&newnode->id);
    printf("Enter Name: ");
    scanf("%s",newnode->name);
    flushBuffer();
    
    /* 利用雜湊函數求得記錄位址 */
    index = hashfun(newnode->id);
    printf("index 為 %ld\n", index);
    /* 判斷該串列是否為空，若為空則建立此鏈結串列 */
    if (Hashtab[index] == NULL) {
        Hashtab[index] = newnode;
        printf("Node insert ok!\n");
    }
    else {
        printf("有碰撞，加入串列中...\n");
        /* 加入於串列中 */
        current = Hashtab[index];
        while (current->link != NULL) {
            current = current->link;
        }
        current->link = newnode;
    }
}

/* 刪除節點函數 */
void del()
{
    Student *node ,*node_parent;
    long index;
    
    node = (Student *)malloc(sizeof(Student));
    printf("Enter ID: ");
    scanf("%ld",&node->id);
    flushBuffer();
    /* 利用雜湊函數轉換記錄位址 */
    index = hashfun(node->id);

    /* 搜尋節點是否存在並傳回指向該節點指標 */
    node = search(Hashtab[index], node);

    if (node == NULL)
        printf("此資料找不到...\n");
    else {
        /* 如節點為串列首，則將串列指向NULL
          否則找到其父節點，並將父節點link向節點後端 */
        printf("ID : %ld   Name : %s\n",node->id,node->name);
    
        if (node == Hashtab[index])
            Hashtab[index] = NULL;
        else {
            node_parent = Hashtab[index];
            while (node_parent->link->id != node->id)
                node_parent = node_parent->link;
            node_parent->link = node->link;
        }
        free(node);
        printf("此筆資料已刪除....\n");
    }
}

/* 搜尋節點函數
   如找到節點則傳回指向該節點之指標
   否則傳回NULL */
Student *search(Student *linklist, Student *Node)
{
    Student *ptr = linklist;
    if (ptr == NULL)
        return NULL;
    while (ptr->id != Node->id && ptr->link != NULL)
        ptr = ptr->link;
    if (ptr == NULL)
        return NULL;
    else
        return ptr;
}

/*查詢節點函數*/
void query()
{
    Student *query_node;
    long index;

    query_node = (Student *)malloc(sizeof(Student));
    printf("Enter ID: ");
    scanf("%ld", &query_node->id);
    flushBuffer();
    index = hashfun(query_node->id);
    /* 搜尋節點 */
    query_node = search(Hashtab[index], query_node);
 
    if (query_node == NULL)
        printf("雜湊表沒有此筆資料...\n");
    else {
        printf("ID: %ld  Name: %s\n",    query_node->id,query_node->name);
    }
}

/* 顯示節點函數，
 從雜湊串列一一尋找是否有節點存在 */
void show()
{
    int i, flag=0;
    Student *ptr;
   
    puts("ID                  NAME");
    puts("------------------------");
    for ( i = 0; i < MAX_NUM; i++ ) {
        if (Hashtab[i] != NULL){
            flag = 1;
            ptr = Hashtab[i];
            /* 串列後面若還有資料，則將整串列顯示出 */
            while (ptr) {
                printf("%-5ld    %15s\n",ptr->id,ptr->name);
                ptr = ptr->link;
            }
        }
     }
     if (flag == 0)
          printf("The Hashing table is empty !!!\n");
}

void flushBuffer()
{
    while (getchar() != '\n')
        continue;
}