main.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include "models.c"

InputBuffer *new_input_buffer() {
    InputBuffer *input_buffer = (InputBuffer *) 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 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);
}

Table *new_table() {
    Table *table = (Table *) malloc(sizeof(Table));
    table->num_rows = 0;
    for (uint32_t i = 0; i < TABLE_MAX_PAGES; i++) {
        table->pages[i] = NULL;
    }
    return table;
}

void free_table(Table *table) {
    for (int i = 0; table->pages[i]; i++) {
        free(table->pages[i]);
    }
    free(table);
}

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

MetaCommandResult do_meta_command(InputBuffer *input_buffer, Table *table) {
    if (strcmp(input_buffer->buffer, ".exit") == 0) {
        close_input_buffer(input_buffer);
        free_table(table);
        exit(EXIT_SUCCESS);
    } else {
        return META_COMMAND_UNRECOGNIZED_COMMAND;
    }
}

void *row_slot(Table *table, uint32_t row_num) {
    uint32_t page_num = row_num / ROWS_PER_PAGE;
    void *page = table->pages[page_num];
    if (page == NULL) {
        page = table->pages[page_num] = malloc(PAGE_SIZE);
    }
    uint32_t row_offset = row_num % ROWS_PER_PAGE;
    uint32_t byte_offset = row_offset * ROW_SIZE;
    return page + byte_offset;
}

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;
}

ExecuteResult execute_insert(Statement *statement, Table *table) {
    if (table->num_rows >= TABLE_MAX_ROWS) {
        return EXECUTE_TABLE_FULL;
    }

    Row *row_to_insert = &(statement->row_to_insert);

    serialize_row(row_to_insert, row_slot(table, table->num_rows));
    table->num_rows += 1;

    return EXECUTE_SUCCESS;
}

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

ExecuteResult execute_select(Statement *statement, Table *table) {
    Row row;
    for (uint32_t i = 0; i < table->num_rows; i++) {
        deserialize_row(row_slot(table, i), &row);
        print_row(&row);
    }
    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[]) {
    Table *table = new_table();
    InputBuffer *input_buffer = new_input_buffer();
    while (1) {
        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_TABLE_FULL):
                printf("Error: Table full.\n");
                break;
        }
    }
}