database.c

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

#define COLUMN_USERNAME_SIZE 32
#define COLUMN_EMAIL_SIZE 255

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

#define TABLE_MAX_PAGES 100 // arbitrary limit to allocate

typedef enum {
    NODE_INTERNAL,
    NODE_LEAF
} NodeType;

typedef struct {
    uint32_t id;
    char username[COLUMN_USERNAME_SIZE];
    char email[COLUMN_EMAIL_SIZE];
} Row;

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;

/*
 * 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;
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;
                        
/*
 *  Even distribution between two nodes to keep tree balanced 
 */

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;
                        
                        
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);
}

typedef enum {
    EXECUTE_SUCCESS,
    EXECUTE_TABLE_FULL,
    EXECUTE_DUPLICATE_KEY
} ExecuteResult;

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

typedef enum {
    META_COMMAND_SUCCESS,
    META_COMMAND_UNRECOGNIZED_COMMAND
} MetaCommandResult;

typedef enum {
    PREPARE_SUCCESS,
    PREPARE_SYNTAX_ERROR,
    PREPARE_UNRECOGNIZED_STATEMENT
} PrepareResult;

typedef enum {
    STATEMENT_INSERT,
    STATEMENT_SELECT
} StatementType;

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

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

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

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

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

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

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

void initialize_leaf_node(void* node);
void set_node_root(void* node, bool is_root);

Pager* pager_open(const char* filename){
    int file_desc = 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 (file_desc == -1) {
        printf("unable to open\n");
        exit(EXIT_FAILURE);
    }
    
    off_t file_length = lseek(file_desc, 0, SEEK_END);
    
    Pager* pager = malloc(sizeof(Pager));
    pager->file_descriptor = file_desc;
    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;
}

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 it 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];
}


Table* database_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 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 close_input_buffer(InputBuffer* input_buffer) {
    free(input_buffer->buffer);
    free(input_buffer);
}

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

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

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

void* leaf_node_cell(void* node, uint32_t cell_num) {
    return node + LEAF_NODE_HEADER_SIZE + cell_num * LEAF_NODE_NUM_CELLS_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* leaf_node_next_leaf(void* node) {
    return node + LEAF_NODE_NEXT_LEAF_OFFSET;
}

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 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;
}

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;
}

Cursor* leaf_node_find(Table* table, uint32_t page_num, uint32_t key);

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);
    }

}

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 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(child, 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;
    }
}

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

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;
}

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; // No sibling at right
}


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;
    
    //Perform binary search of leaf node
    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;
}

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 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 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) {
        //Making 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));
}

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;
    }
}

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

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

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 database_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);
    free(table);
}

MetaCommandResult do_meta_command(InputBuffer* input_buffer, Table* table) {
    if (strcmp(input_buffer->buffer, ".exit") == 0) {
        database_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:");
        print_constants();
        return META_COMMAND_SUCCESS;
    } else {
        return META_COMMAND_UNRECOGNIZED_COMMAND;
    }
}


PrepareResult prepare_statement(InputBuffer* input_buffer,
                                Statement* statement) {
  if (strncmp(input_buffer->buffer, "insert", 6) == 0) {
    statement->type = STATEMENT_INSERT;
    int args_assigned = sscanf(
        input_buffer->buffer, "insert %d %s %s", 
        &(statement->row_to_insert.id),
        statement->row_to_insert.username,
        statement->row_to_insert.email);
    if (args_assigned < 3) {
        return PREPARE_SYNTAX_ERROR;
    }
    return PREPARE_SUCCESS;
  }
  if (strcmp(input_buffer->buffer, "select") == 0) {
    statement->type = STATEMENT_SELECT;
    return PREPARE_SUCCESS;
  }

  return PREPARE_UNRECOGNIZED_STATEMENT;
}


ExecuteResult execute_insert(Statement* statement, Table* table) {
    void* node = get_page(table->pager, table->root_page_num);
    uint32_t num_cells = (*leaf_node_num_cells(node));
    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);
    
    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 = database_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_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;
        }
    }
}