#include "database.h"

int findRec(Dbrec *db,dbkeytype key, dbdatatype *data, indextype *idx)
/* Preconditions: The keys of the records are in order.
   Action: Find key in the list of records. Returns whether or not 
           it was found. If found, data is set to the data, (*idx)->it
           points to the record. If not found, (*idx)->it points to the
           record whose key immediately follows key (possibly NULL).
           In either case, (*idx)->prior points to the record before 
           (*idx)->it (possibly NULL). */
{
  Dbrec rec=*db,prior=NULL;
  int cmp;

  while(rec && (cmp=comparedbkey(key,rec->key)) > 0) {
    /* LI: (1) All the keys in the list db up to, but not including rec,
               are less than key.
           (2) prior points to the record before rec in the list. */
    prior = rec;
    rec = rec->next;
  }
  idx->it = rec;
  idx->prior = prior;
  if(rec&&cmp==0) {
    copydbdata(rec->data,*data);
    return 1;
  }
  return 0;
}

int createRec(Dbrec *db,dbkeytype key, dbdatatype data, indextype *idx)
/* Precondition: idx->prior points to the record after which the new
                 record should be inserted. (If NULL, the new record
                 is inserted at the head of the list. idx->it points
                 to the record after idx->prior.
   Action: If the database is not full, adds the record with key key and
           data data, and returns 1. Otherwise, returns 0. */
{
  Dbrec rec;

  rec=(Dbrec)malloc(sizeof(struct dbrec));
  if(rec==NULL)
    return 0;
  copydbkey(key,rec->key);
  copydbdata(data,rec->data);
  rec->next=idx->it;
  if(idx->prior)
    idx->prior->next = rec;
  else
    *db = rec;
  idx->it=rec;
  return 1;
}

int deleteRec(Dbrec *db,indextype idx)
/* Precondition: idx->it points to the record to be deleted.
   idx->prior points to the record before it, or NULL if none before it.
   Postcondition: idx->it is deleted. */
{
  if(idx.prior)
    idx.prior->next = idx.it->next;
  else
    *db = idx.it->next;
  free((void *)idx.it);
}


void initDb(Dbrec *db)
/* Initialize the database *db. */
{
  *db = NULL;
}

void eachRec(Dbrec *db,void (*fn)(dbkeytype,dbdatatype))
/* Apply fn to each record in *db. */
{
  Dbrec rec;

  for(rec=*db;rec;rec=rec->next)
    (*fn)(rec->key,rec->data);
}

void setRec(Dbrec *db,indextype idx, dbdatatype data)
/* Change the data of record idx to become data. */
{
  copydbdata(data,idx.it->data);
}