db.c

#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

struct InputBuffer_t {
  char* buffer;
  size_t buffer_length;
  ssize_t input_length;
};
typedef struct InputBuffer_t InputBuffer;

enum ExecuteResult_t {
  EXECUTE_SUCCESS,
  EXECUTE_DUPLICATE_KEY,
  EXECUTE_TABLE_FULL
};
typedef enum ExecuteResult_t ExecuteResult;

enum MetaCommandResult_t {
  META_COMMAND_SUCCESS,
  META_COMMAND_UNRECOGNIZED_COMMAND
};
typedef enum MetaCommandResult_t MetaCommandResult;

enum PrepareResult_t {
  PREPARE_SUCCESS,
  PREPARE_NEGATIVE_ID,
  PREPARE_STRING_TOO_LONG,
  PREPARE_SYNTAX_ERROR,
  PREPARE_UNRECOGNIZED_STATEMENT
};
typedef enum PrepareResult_t PrepareResult;

enum StatementType_t { STATEMENT_INSERT, STATEMENT_SELECT };
typedef enum StatementType_t StatementType;

const uint32_t COLUMN_USERNAME_SIZE = 32;
const uint32_t COLUMN_EMAIL_SIZE = 255;
struct Row_t {
  uint32_t id;
  char username[COLUMN_USERNAME_SIZE + 1];
  char email[COLUMN_EMAIL_SIZE + 1];
};
typedef struct Row_t Row;

struct Statement_t {
  StatementType type;
  Row row_to_insert;  // only used by insert statement
};
typedef struct Statement_t Statement;

#define size_of_attribute(Struct, Attribute) sizeof(((Struct*)0)->Attribute)

const uint32_t ID_SIZE = size_of_attribute(Row, id);
const uint32_t USERNAME_SIZE = size_of_attribute(Row, username);
const uint32_t EMAIL_SIZE = size_of_attribute(Row, email);
const uint32_t ID_OFFSET = 0;
const uint32_t USERNAME_OFFSET = ID_OFFSET + ID_SIZE;
const uint32_t EMAIL_OFFSET = USERNAME_OFFSET + USERNAME_SIZE;
const uint32_t ROW_SIZE = ID_SIZE + USERNAME_SIZE + EMAIL_SIZE;

const uint32_t PAGE_SIZE = 4096;
const uint32_t TABLE_MAX_PAGES = 100;

struct Pager_t {
  int file_descriptor;
  uint32_t file_length;
  uint32_t num_pages;
  void* pages[TABLE_MAX_PAGES];
};
typedef struct Pager_t Pager;

struct Table_t {
  Pager* pager;
  uint32_t root_page_num;
};
typedef struct Table_t Table;

struct Cursor_t {
  Table* table;
  uint32_t page_num;
  uint32_t cell_num;
  bool end_of_table;  // Indicates a position one past the last element
};
typedef struct Cursor_t Cursor;

void print_row(Row* row) {
  printf("(%d, %s, %s)\n", row->id, row->username, row->email);
}

enum NodeType_t { NODE_INTERNAL, NODE_LEAF };
typedef enum NodeType_t NodeType;

/*
 * Common Node Header Layout
 */
const uint32_t NODE_TYPE_SIZE = sizeof(uint8_t);
const uint32_t NODE_TYPE_OFFSET = 0;
const uint32_t IS_ROOT_SIZE = sizeof(uint8_t);
const uint32_t IS_ROOT_OFFSET = NODE_TYPE_SIZE;
const uint32_t PARENT_POINTER_SIZE = sizeof(uint32_t);
const uint32_t PARENT_POINTER_OFFSET = IS_ROOT_OFFSET + IS_ROOT_SIZE;
const uint8_t COMMON_NODE_HEADER_SIZE =
    NODE_TYPE_SIZE + IS_ROOT_SIZE + PARENT_POINTER_SIZE;

/*
 * Internal Node Header Layout
 */
const uint32_t INTERNAL_NODE_NUM_KEYS_SIZE = sizeof(uint32_t);
const uint32_t INTERNAL_NODE_NUM_KEYS_OFFSET = COMMON_NODE_HEADER_SIZE;
const uint32_t INTERNAL_NODE_RIGHT_CHILD_SIZE = sizeof(uint32_t);
const uint32_t INTERNAL_NODE_RIGHT_CHILD_OFFSET =
    INTERNAL_NODE_NUM_KEYS_OFFSET + INTERNAL_NODE_NUM_KEYS_SIZE;
const uint32_t INTERNAL_NODE_HEADER_SIZE = COMMON_NODE_HEADER_SIZE +
                                           INTERNAL_NODE_NUM_KEYS_SIZE +
                                           INTERNAL_NODE_RIGHT_CHILD_SIZE;

/*
 * Internal Node Body Layout
 */
const uint32_t INTERNAL_NODE_KEY_SIZE = sizeof(uint32_t);
const uint32_t INTERNAL_NODE_CHILD_SIZE = sizeof(uint32_t);
const uint32_t INTERNAL_NODE_CELL_SIZE =
    INTERNAL_NODE_CHILD_SIZE + INTERNAL_NODE_KEY_SIZE;
/* Keep this small for testing */
const uint32_t INTERNAL_NODE_MAX_CELLS = 3;

/*
 * Leaf Node Header Layout
 */
const uint32_t LEAF_NODE_NUM_CELLS_SIZE = sizeof(uint32_t);
const uint32_t LEAF_NODE_NUM_CELLS_OFFSET = COMMON_NODE_HEADER_SIZE;
const uint32_t LEAF_NODE_NEXT_LEAF_SIZE = sizeof(uint32_t);
const uint32_t LEAF_NODE_NEXT_LEAF_OFFSET =
    LEAF_NODE_NUM_CELLS_OFFSET + LEAF_NODE_NUM_CELLS_SIZE;
const uint32_t LEAF_NODE_HEADER_SIZE = COMMON_NODE_HEADER_SIZE +
                                       LEAF_NODE_NUM_CELLS_SIZE +
                                       LEAF_NODE_NEXT_LEAF_SIZE;

/*
 * Leaf Node Body Layout
 */
const uint32_t LEAF_NODE_KEY_SIZE = sizeof(uint32_t);
const uint32_t LEAF_NODE_KEY_OFFSET = 0;
const uint32_t LEAF_NODE_VALUE_SIZE = ROW_SIZE;
const uint32_t LEAF_NODE_VALUE_OFFSET =
    LEAF_NODE_KEY_OFFSET + LEAF_NODE_KEY_SIZE;
const uint32_t LEAF_NODE_CELL_SIZE = LEAF_NODE_KEY_SIZE + LEAF_NODE_VALUE_SIZE;
const uint32_t LEAF_NODE_SPACE_FOR_CELLS = PAGE_SIZE - LEAF_NODE_HEADER_SIZE;
const uint32_t LEAF_NODE_MAX_CELLS =
    LEAF_NODE_SPACE_FOR_CELLS / LEAF_NODE_CELL_SIZE;
const uint32_t LEAF_NODE_RIGHT_SPLIT_COUNT = (LEAF_NODE_MAX_CELLS + 1) / 2;
const uint32_t LEAF_NODE_LEFT_SPLIT_COUNT =
    (LEAF_NODE_MAX_CELLS + 1) - LEAF_NODE_RIGHT_SPLIT_COUNT;

NodeType get_node_type(void* node) {
  uint8_t value = *((uint8_t*)(node + NODE_TYPE_OFFSET));
  return (NodeType)value;
}

void set_node_type(void* node, NodeType type) {
  uint8_t value = type;
  *((uint8_t*)(node + NODE_TYPE_OFFSET)) = value;
}

bool is_node_root(void* node) {
  uint8_t value = *((uint8_t*)(node + IS_ROOT_OFFSET));
  return (bool)value;
}

void set_node_root(void* node, bool is_root) {
  uint8_t value = is_root;
  *((uint8_t*)(node + IS_ROOT_OFFSET)) = value;
}

uint32_t* node_parent(void* node) { return node + PARENT_POINTER_OFFSET; }

uint32_t* internal_node_num_keys(void* node) {
  return node + INTERNAL_NODE_NUM_KEYS_OFFSET;
}

uint32_t* internal_node_right_child(void* node) {
  return node + INTERNAL_NODE_RIGHT_CHILD_OFFSET;
}

uint32_t* internal_node_cell(void* node, uint32_t cell_num) {
  return node + INTERNAL_NODE_HEADER_SIZE + cell_num * INTERNAL_NODE_CELL_SIZE;
}

uint32_t* internal_node_child(void* node, uint32_t child_num) {
  uint32_t num_keys = *internal_node_num_keys(node);
  if (child_num > num_keys) {
    printf("Tried to access child_num %d > num_keys %d\n", child_num, num_keys);
    exit(EXIT_FAILURE);
  } else if (child_num == num_keys) {
    return internal_node_right_child(node);
  } else {
    return internal_node_cell(node, child_num);
  }
}

uint32_t* internal_node_key(void* node, uint32_t key_num) {
  return (void*)internal_node_cell(node, key_num) + INTERNAL_NODE_CHILD_SIZE;
}

uint32_t* leaf_node_num_cells(void* node) {
  return node + LEAF_NODE_NUM_CELLS_OFFSET;
}

uint32_t* leaf_node_next_leaf(void* node) {
  return node + LEAF_NODE_NEXT_LEAF_OFFSET;
}

void* leaf_node_cell(void* node, uint32_t cell_num) {
  return node + LEAF_NODE_HEADER_SIZE + cell_num * LEAF_NODE_CELL_SIZE;
}

uint32_t* leaf_node_key(void* node, uint32_t cell_num) {
  return leaf_node_cell(node, cell_num);
}

void* leaf_node_value(void* node, uint32_t cell_num) {
  return leaf_node_cell(node, cell_num) + LEAF_NODE_KEY_SIZE;
}

uint32_t get_node_max_key(void* node) {
  switch (get_node_type(node)) {
    case NODE_INTERNAL:
      return *internal_node_key(node, *internal_node_num_keys(node) - 1);
    case NODE_LEAF:
      return *leaf_node_key(node, *leaf_node_num_cells(node) - 1);
  }
}

void print_constants() {
  printf("ROW_SIZE: %d\n", ROW_SIZE);
  printf("COMMON_NODE_HEADER_SIZE: %d\n", COMMON_NODE_HEADER_SIZE);
  printf("LEAF_NODE_HEADER_SIZE: %d\n", LEAF_NODE_HEADER_SIZE);
  printf("LEAF_NODE_CELL_SIZE: %d\n", LEAF_NODE_CELL_SIZE);
  printf("LEAF_NODE_SPACE_FOR_CELLS: %d\n", LEAF_NODE_SPACE_FOR_CELLS);
  printf("LEAF_NODE_MAX_CELLS: %d\n", LEAF_NODE_MAX_CELLS);
}

void* get_page(Pager* pager, uint32_t page_num) {
  if (page_num > TABLE_MAX_PAGES) {
    printf("Tried to fetch page number out of bounds. %d > %d\n", page_num,
           TABLE_MAX_PAGES);
    exit(EXIT_FAILURE);
  }

  if (pager->pages[page_num] == NULL) {
    // Cache miss. Allocate memory and load from file.
    void* page = malloc(PAGE_SIZE);
    uint32_t num_pages = pager->file_length / PAGE_SIZE;

    // We might save a partial page at the end of the file
    if (pager->file_length % PAGE_SIZE) {
      num_pages += 1;
    }

    if (page_num <= num_pages) {
      lseek(pager->file_descriptor, page_num * PAGE_SIZE, SEEK_SET);
      ssize_t bytes_read = read(pager->file_descriptor, page, PAGE_SIZE);
      if (bytes_read == -1) {
        printf("Error reading file: %d\n", errno);
        exit(EXIT_FAILURE);
      }
    }

    pager->pages[page_num] = page;

    if (page_num >= pager->num_pages) {
      pager->num_pages = page_num + 1;
    }
  }

  return pager->pages[page_num];
}

void indent(uint32_t level) {
  for (uint32_t i = 0; i < level; i++) {
    printf("  ");
  }
}

void print_tree(Pager* pager, uint32_t page_num, uint32_t indentation_level) {
  void* node = get_page(pager, page_num);
  uint32_t num_keys, child;

  switch (get_node_type(node)) {
    case (NODE_LEAF):
      num_keys = *leaf_node_num_cells(node);
      indent(indentation_level);
      printf("- leaf (size %d)\n", num_keys);
      for (uint32_t i = 0; i < num_keys; i++) {
        indent(indentation_level + 1);
        printf("- %d\n", *leaf_node_key(node, i));
      }
      break;
    case (NODE_INTERNAL):
      num_keys = *internal_node_num_keys(node);
      indent(indentation_level);
      printf("- internal (size %d)\n", num_keys);
      for (uint32_t i = 0; i < num_keys; i++) {
        child = *internal_node_child(node, i);
        print_tree(pager, child, indentation_level + 1);

        indent(indentation_level + 1);
        printf("- key %d\n", *internal_node_key(node, i));
      }
      child = *internal_node_right_child(node);
      print_tree(pager, child, indentation_level + 1);
      break;
  }
}

void serialize_row(Row* source, void* destination) {
  memcpy(destination + ID_OFFSET, &(source->id), ID_SIZE);
  memcpy(destination + USERNAME_OFFSET, &(source->username), USERNAME_SIZE);
  memcpy(destination + EMAIL_OFFSET, &(source->email), EMAIL_SIZE);
}

void deserialize_row(void* source, Row* destination) {
  memcpy(&(destination->id), source + ID_OFFSET, ID_SIZE);
  memcpy(&(destination->username), source + USERNAME_OFFSET, USERNAME_SIZE);
  memcpy(&(destination->email), source + EMAIL_OFFSET, EMAIL_SIZE);
}

void initialize_leaf_node(void* node) {
  set_node_type(node, NODE_LEAF);
  set_node_root(node, false);
  *leaf_node_num_cells(node) = 0;
  *leaf_node_next_leaf(node) = 0;  // 0 represents no sibling
}

void initialize_internal_node(void* node) {
  set_node_type(node, NODE_INTERNAL);
  set_node_root(node, false);
  *internal_node_num_keys(node) = 0;
}

Cursor* leaf_node_find(Table* table, uint32_t page_num, uint32_t key) {
  void* node = get_page(table->pager, page_num);
  uint32_t num_cells = *leaf_node_num_cells(node);

  Cursor* cursor = malloc(sizeof(Cursor));
  cursor->table = table;
  cursor->page_num = page_num;
  cursor->end_of_table = false;

  // Binary search
  uint32_t min_index = 0;
  uint32_t one_past_max_index = num_cells;
  while (one_past_max_index != min_index) {
    uint32_t index = (min_index + one_past_max_index) / 2;
    uint32_t key_at_index = *leaf_node_key(node, index);
    if (key == key_at_index) {
      cursor->cell_num = index;
      return cursor;
    }
    if (key < key_at_index) {
      one_past_max_index = index;
    } else {
      min_index = index + 1;
    }
  }

  cursor->cell_num = min_index;
  return cursor;
}

uint32_t internal_node_find_child(void* node, uint32_t key) {
  /*
  Return the index of the child which should contain
  the given key.
  */

  uint32_t num_keys = *internal_node_num_keys(node);

  /* Binary search */
  uint32_t min_index = 0;
  uint32_t max_index = num_keys; /* there is one more child than key */

  while (min_index != max_index) {
    uint32_t index = (min_index + max_index) / 2;
    uint32_t key_to_right = *internal_node_key(node, index);
    if (key_to_right >= key) {
      max_index = index;
    } else {
      min_index = index + 1;
    }
  }

  return min_index;
}

Cursor* internal_node_find(Table* table, uint32_t page_num, uint32_t key) {
  void* node = get_page(table->pager, page_num);

  uint32_t child_index = internal_node_find_child(node, key);
  uint32_t child_num = *internal_node_child(node, child_index);
  void* child = get_page(table->pager, child_num);
  switch (get_node_type(child)) {
    case NODE_LEAF:
      return leaf_node_find(table, child_num, key);
    case NODE_INTERNAL:
      return internal_node_find(table, child_num, key);
  }
}

/*
Return the position of the given key.
If the key is not present, return the position
where it should be inserted
*/
Cursor* table_find(Table* table, uint32_t key) {
  uint32_t root_page_num = table->root_page_num;
  void* root_node = get_page(table->pager, root_page_num);

  if (get_node_type(root_node) == NODE_LEAF) {
    return leaf_node_find(table, root_page_num, key);
  } else {
    return internal_node_find(table, root_page_num, key);
  }
}

Cursor* table_start(Table* table) {
  Cursor* cursor = table_find(table, 0);

  void* node = get_page(table->pager, cursor->page_num);
  uint32_t num_cells = *leaf_node_num_cells(node);
  cursor->end_of_table = (num_cells == 0);

  return cursor;
}

void* cursor_value(Cursor* cursor) {
  uint32_t page_num = cursor->page_num;
  void* page = get_page(cursor->table->pager, page_num);
  return leaf_node_value(page, cursor->cell_num);
}

void cursor_advance(Cursor* cursor) {
  uint32_t page_num = cursor->page_num;
  void* node = get_page(cursor->table->pager, page_num);

  cursor->cell_num += 1;
  if (cursor->cell_num >= (*leaf_node_num_cells(node))) {
    /* Advance to next leaf node */
    uint32_t next_page_num = *leaf_node_next_leaf(node);
    if (next_page_num == 0) {
      /* This was rightmost leaf */
      cursor->end_of_table = true;
    } else {
      cursor->page_num = next_page_num;
      cursor->cell_num = 0;
    }
  }
}

Pager* pager_open(const char* filename) {
  int fd = open(filename,
                O_RDWR |      // Read/Write mode
                    O_CREAT,  // Create file if it does not exist
                S_IWUSR |     // User write permission
                    S_IRUSR   // User read permission
                );

  if (fd == -1) {
    printf("Unable to open file\n");
    exit(EXIT_FAILURE);
  }

  off_t file_length = lseek(fd, 0, SEEK_END);

  Pager* pager = malloc(sizeof(Pager));
  pager->file_descriptor = fd;
  pager->file_length = file_length;
  pager->num_pages = (file_length / PAGE_SIZE);

  if (file_length % PAGE_SIZE != 0) {
    printf("Db file is not a whole number of pages. Corrupt file.\n");
    exit(EXIT_FAILURE);
  }

  for (uint32_t i = 0; i < TABLE_MAX_PAGES; i++) {
    pager->pages[i] = NULL;
  }

  return pager;
}

Table* db_open(const char* filename) {
  Pager* pager = pager_open(filename);

  Table* table = malloc(sizeof(Table));
  table->pager = pager;
  table->root_page_num = 0;

  if (pager->num_pages == 0) {
    // New database file. Initialize page 0 as leaf node.
    void* root_node = get_page(pager, 0);
    initialize_leaf_node(root_node);
    set_node_root(root_node, true);
  }

  return table;
}

InputBuffer* new_input_buffer() {
  InputBuffer* input_buffer = malloc(sizeof(InputBuffer));
  input_buffer->buffer = NULL;
  input_buffer->buffer_length = 0;
  input_buffer->input_length = 0;

  return input_buffer;
}

void print_prompt() { printf("db > "); }

void read_input(InputBuffer* input_buffer) {
  ssize_t bytes_read =
      getline(&(input_buffer->buffer), &(input_buffer->buffer_length), stdin);

  if (bytes_read <= 0) {
    printf("Error reading input\n");
    exit(EXIT_FAILURE);
  }

  // Ignore trailing newline
  input_buffer->input_length = bytes_read - 1;
  input_buffer->buffer[bytes_read - 1] = 0;
}

void pager_flush(Pager* pager, uint32_t page_num) {
  if (pager->pages[page_num] == NULL) {
    printf("Tried to flush null page\n");
    exit(EXIT_FAILURE);
  }

  off_t offset = lseek(pager->file_descriptor, page_num * PAGE_SIZE, SEEK_SET);

  if (offset == -1) {
    printf("Error seeking: %d\n", errno);
    exit(EXIT_FAILURE);
  }

  ssize_t bytes_written =
      write(pager->file_descriptor, pager->pages[page_num], PAGE_SIZE);

  if (bytes_written == -1) {
    printf("Error writing: %d\n", errno);
    exit(EXIT_FAILURE);
  }
}

void db_close(Table* table) {
  Pager* pager = table->pager;

  for (uint32_t i = 0; i < pager->num_pages; i++) {
    if (pager->pages[i] == NULL) {
      continue;
    }
    pager_flush(pager, i);
    free(pager->pages[i]);
    pager->pages[i] = NULL;
  }

  int result = close(pager->file_descriptor);
  if (result == -1) {
    printf("Error closing db file.\n");
    exit(EXIT_FAILURE);
  }
  for (uint32_t i = 0; i < TABLE_MAX_PAGES; i++) {
    void* page = pager->pages[i];
    if (page) {
      free(page);
      pager->pages[i] = NULL;
    }
  }
  free(pager);
}

MetaCommandResult do_meta_command(InputBuffer* input_buffer, Table* table) {
  if (strcmp(input_buffer->buffer, ".exit") == 0) {
    db_close(table);
    exit(EXIT_SUCCESS);
  } else if (strcmp(input_buffer->buffer, ".btree") == 0) {
    printf("Tree:\n");
    print_tree(table->pager, 0, 0);
    return META_COMMAND_SUCCESS;
  } else if (strcmp(input_buffer->buffer, ".constants") == 0) {
    printf("Constants:\n");
    print_constants();
    return META_COMMAND_SUCCESS;
  } else {
    return META_COMMAND_UNRECOGNIZED_COMMAND;
  }
}

PrepareResult prepare_insert(InputBuffer* input_buffer, Statement* statement) {
  statement->type = STATEMENT_INSERT;

  char* keyword = strtok(input_buffer->buffer, " ");
  char* id_string = strtok(NULL, " ");
  char* username = strtok(NULL, " ");
  char* email = strtok(NULL, " ");

  if (id_string == NULL || username == NULL || email == NULL) {
    return PREPARE_SYNTAX_ERROR;
  }

  int id = atoi(id_string);
  if (id < 0) {
    return PREPARE_NEGATIVE_ID;
  }
  if (strlen(username) > COLUMN_USERNAME_SIZE) {
    return PREPARE_STRING_TOO_LONG;
  }
  if (strlen(email) > COLUMN_EMAIL_SIZE) {
    return PREPARE_STRING_TOO_LONG;
  }

  statement->row_to_insert.id = id;
  strcpy(statement->row_to_insert.username, username);
  strcpy(statement->row_to_insert.email, email);

  return PREPARE_SUCCESS;
}

PrepareResult prepare_statement(InputBuffer* input_buffer,
                                Statement* statement) {
  if (strncmp(input_buffer->buffer, "insert", 6) == 0) {
    return prepare_insert(input_buffer, statement);
  }
  if (strcmp(input_buffer->buffer, "select") == 0) {
    statement->type = STATEMENT_SELECT;
    return PREPARE_SUCCESS;
  }

  return PREPARE_UNRECOGNIZED_STATEMENT;
}

/*
Until we start recycling free pages, new pages will always
go onto the end of the database file
*/
uint32_t get_unused_page_num(Pager* pager) { return pager->num_pages; }

void create_new_root(Table* table, uint32_t right_child_page_num) {
  /*
  Handle splitting the root.
  Old root copied to new page, becomes left child.
  Address of right child passed in.
  Re-initialize root page to contain the new root node.
  New root node points to two children.
  */

  void* root = get_page(table->pager, table->root_page_num);
  void* right_child = get_page(table->pager, right_child_page_num);
  uint32_t left_child_page_num = get_unused_page_num(table->pager);
  void* left_child = get_page(table->pager, left_child_page_num);

  /* Left child has data copied from old root */
  memcpy(left_child, root, PAGE_SIZE);
  set_node_root(left_child, false);

  /* Root node is a new internal node with one key and two children */
  initialize_internal_node(root);
  set_node_root(root, true);
  *internal_node_num_keys(root) = 1;
  *internal_node_child(root, 0) = left_child_page_num;
  uint32_t left_child_max_key = get_node_max_key(left_child);
  *internal_node_key(root, 0) = left_child_max_key;
  *internal_node_right_child(root) = right_child_page_num;
  *node_parent(left_child) = table->root_page_num;
  *node_parent(right_child) = table->root_page_num;
}

void internal_node_insert(Table* table, uint32_t parent_page_num,
                          uint32_t child_page_num) {
  /*
  Add a new child/key pair to parent that corresponds to child
  */

  void* parent = get_page(table->pager, parent_page_num);
  void* child = get_page(table->pager, child_page_num);
  uint32_t child_max_key = get_node_max_key(child);
  uint32_t index = internal_node_find_child(parent, child_max_key);

  uint32_t original_num_keys = *internal_node_num_keys(parent);
  *internal_node_num_keys(parent) = original_num_keys + 1;

  if (original_num_keys >= INTERNAL_NODE_MAX_CELLS) {
    printf("Need to implement splitting internal node\n");
    exit(EXIT_FAILURE);
  }

  uint32_t right_child_page_num = *internal_node_right_child(parent);
  void* right_child = get_page(table->pager, right_child_page_num);

  if (child_max_key > get_node_max_key(right_child)) {
    /* Replace right child */
    *internal_node_child(parent, original_num_keys) = right_child_page_num;
    *internal_node_key(parent, original_num_keys) =
        get_node_max_key(right_child);
    *internal_node_right_child(parent) = child_page_num;
  } else {
    /* Make room for the new cell */
    for (uint32_t i = original_num_keys; i > index; i--) {
      void* destination = internal_node_cell(parent, i);
      void* source = internal_node_cell(parent, i - 1);
      memcpy(destination, source, INTERNAL_NODE_CELL_SIZE);
    }
    *internal_node_child(parent, index) = child_page_num;
    *internal_node_key(parent, index) = child_max_key;
  }
}

void update_internal_node_key(void* node, uint32_t old_key, uint32_t new_key) {
  uint32_t old_child_index = internal_node_find_child(node, old_key);
  *internal_node_key(node, old_child_index) = new_key;
}

void leaf_node_split_and_insert(Cursor* cursor, uint32_t key, Row* value) {
  /*
  Create a new node and move half the cells over.
  Insert the new value in one of the two nodes.
  Update parent or create a new parent.
  */

  void* old_node = get_page(cursor->table->pager, cursor->page_num);
  uint32_t old_max = get_node_max_key(old_node);
  uint32_t new_page_num = get_unused_page_num(cursor->table->pager);
  void* new_node = get_page(cursor->table->pager, new_page_num);
  initialize_leaf_node(new_node);
  *node_parent(new_node) = *node_parent(old_node);
  *leaf_node_next_leaf(new_node) = *leaf_node_next_leaf(old_node);
  *leaf_node_next_leaf(old_node) = new_page_num;

  /*
  All existing keys plus new key should should be divided
  evenly between old (left) and new (right) nodes.
  Starting from the right, move each key to correct position.
  */
  for (int32_t i = LEAF_NODE_MAX_CELLS; i >= 0; i--) {
    void* destination_node;
    if (i >= LEAF_NODE_LEFT_SPLIT_COUNT) {
      destination_node = new_node;
    } else {
      destination_node = old_node;
    }
    uint32_t index_within_node = i % LEAF_NODE_LEFT_SPLIT_COUNT;
    void* destination = leaf_node_cell(destination_node, index_within_node);

    if (i == cursor->cell_num) {
      serialize_row(value,
                    leaf_node_value(destination_node, index_within_node));
      *leaf_node_key(destination_node, index_within_node) = key;
    } else if (i > cursor->cell_num) {
      memcpy(destination, leaf_node_cell(old_node, i - 1), LEAF_NODE_CELL_SIZE);
    } else {
      memcpy(destination, leaf_node_cell(old_node, i), LEAF_NODE_CELL_SIZE);
    }
  }

  /* Update cell count on both leaf nodes */
  *(leaf_node_num_cells(old_node)) = LEAF_NODE_LEFT_SPLIT_COUNT;
  *(leaf_node_num_cells(new_node)) = LEAF_NODE_RIGHT_SPLIT_COUNT;

  if (is_node_root(old_node)) {
    return create_new_root(cursor->table, new_page_num);
  } else {
    uint32_t parent_page_num = *node_parent(old_node);
    uint32_t new_max = get_node_max_key(old_node);
    void* parent = get_page(cursor->table->pager, parent_page_num);

    update_internal_node_key(parent, old_max, new_max);
    internal_node_insert(cursor->table, parent_page_num, new_page_num);
    return;
  }
}

void leaf_node_insert(Cursor* cursor, uint32_t key, Row* value) {
  void* node = get_page(cursor->table->pager, cursor->page_num);

  uint32_t num_cells = *leaf_node_num_cells(node);
  if (num_cells >= LEAF_NODE_MAX_CELLS) {
    // Node full
    leaf_node_split_and_insert(cursor, key, value);
    return;
  }

  if (cursor->cell_num < num_cells) {
    // Make room for new cell
    for (uint32_t i = num_cells; i > cursor->cell_num; i--) {
      memcpy(leaf_node_cell(node, i), leaf_node_cell(node, i - 1),
             LEAF_NODE_CELL_SIZE);
    }
  }

  *(leaf_node_num_cells(node)) += 1;
  *(leaf_node_key(node, cursor->cell_num)) = key;
  serialize_row(value, leaf_node_value(node, cursor->cell_num));
}

ExecuteResult execute_insert(Statement* statement, Table* table) {
  Row* row_to_insert = &(statement->row_to_insert);
  uint32_t key_to_insert = row_to_insert->id;
  Cursor* cursor = table_find(table, key_to_insert);

  void *node = get_page(table->pager, cursor->page_num);
  uint32_t num_cells = *leaf_node_num_cells(node);

  if (cursor->cell_num < num_cells) {
    uint32_t key_at_index = *leaf_node_key(node, cursor->cell_num);
    if (key_at_index == key_to_insert) {
      return EXECUTE_DUPLICATE_KEY;
    }
  }

  leaf_node_insert(cursor, row_to_insert->id, row_to_insert);

  free(cursor);

  return EXECUTE_SUCCESS;
}

ExecuteResult execute_select(Statement* statement, Table* table) {
  Cursor* cursor = table_start(table);

  Row row;
  while (!(cursor->end_of_table)) {
    deserialize_row(cursor_value(cursor), &row);
    print_row(&row);
    cursor_advance(cursor);
  }

  free(cursor);

  return EXECUTE_SUCCESS;
}

ExecuteResult execute_statement(Statement* statement, Table* table) {
  switch (statement->type) {
    case (STATEMENT_INSERT):
      return execute_insert(statement, table);
    case (STATEMENT_SELECT):
      return execute_select(statement, table);
  }
}

int main(int argc, char* argv[]) {
  if (argc < 2) {
    printf("Must supply a database filename.\n");
    exit(EXIT_FAILURE);
  }

  char* filename = argv[1];
  Table* table = db_open(filename);

  InputBuffer* input_buffer = new_input_buffer();
  while (true) {
    print_prompt();
    read_input(input_buffer);

    if (input_buffer->buffer[0] == '.') {
      switch (do_meta_command(input_buffer, table)) {
        case (META_COMMAND_SUCCESS):
          continue;
        case (META_COMMAND_UNRECOGNIZED_COMMAND):
          printf("Unrecognized command '%s'\n", input_buffer->buffer);
          continue;
      }
    }

    Statement statement;
    switch (prepare_statement(input_buffer, &statement)) {
      case (PREPARE_SUCCESS):
        break;
      case (PREPARE_NEGATIVE_ID):
        printf("ID must be positive.\n");
        continue;
      case (PREPARE_STRING_TOO_LONG):
        printf("String is too long.\n");
        continue;
      case (PREPARE_SYNTAX_ERROR):
        printf("Syntax error. Could not parse statement.\n");
        continue;
      case (PREPARE_UNRECOGNIZED_STATEMENT):
        printf("Unrecognized keyword at start of '%s'.\n",
               input_buffer->buffer);
        continue;
    }

    switch (execute_statement(&statement, table)) {
      case (EXECUTE_SUCCESS):
        printf("Executed.\n");
        break;
      case (EXECUTE_DUPLICATE_KEY):
        printf("Error: Duplicate key.\n");
        break;
      case (EXECUTE_TABLE_FULL):
        printf("Error: Table full.\n");
        break;
    }
  }
}