An mbtiles wrapper in ruby

mbtiles.rb

require 'sqlite3'

# https://github.com/mapbox/mbtiles-spec/blob/master/1.1/spec.md
class Mbtiles
  attr_reader :tile_format, :db_file_name

  def initialize(db_file_name, format=:png)
    @db_file_name = db_file_name
    load_database(db_file_name)

    @tile_format = read_tile_format
  end

  def close
    @db.close
  end

  def has_tile?(z, x, y)
    @db.get_first_value(SQL_MATCHING_TILE_COUNT, z, x, y) != 0
  end

  def tile(z, x, y)
    @db.get_first_value(SQL_READ_TILE, z, x, y)
  end

  def save(z, x, y, data)
    @db.execute(SQL_INSERT_TILE, z, x, y, data)
  end

  def delete(z, x, y)
    @db.execute(SQL_DELETE_TILE, z, x, y)
  end

  def metadata
    rows = @db.execute(SQL_READ_METADATA)
    rows.each.with_object({}) { |row, hash| hash[row[0]] = row[1] }
  end

  private

  def load_database(db_file_name)
    db_exists = File.exists?(db_file_name)
    @db = SQLite3::Database.new(db_file_name)

    if !db_exists
      @db.execute(SQL_CREATE_TILES_TABLE)
      @db.execute(SQL_CREATE_METADATA_TABLE)

      @db.execute(SQL_INSERT_METADATA, "format", format.to_s)
    end
  end

  def read_tile_format
    @db.get_first_value(SQL_READ_TILE_FORMAT)
  end

  SQL_CREATE_TILES_TABLE = "CREATE TABLE IF NOT EXISTS tiles (zoom_level integer, tile_column integer, tile_row integer, tile_data blob)"
  SQL_INSERT_TILE = "INSERT INTO tiles (zoom_level, tile_column, tile_row, tile_data) VALUES(?, ?, ?, ?)"
  SQL_READ_TILE = "SELECT tile_data FROM tiles WHERE zoom_level=? and tile_column=? and tile_row=?"
  SQL_DELETE_TILE = "DELETE FROM tiles WHERE zoom_level=? and tile_column=? and tile_row=?"
  SQL_CREATE_METADATA_TABLE = "CREATE TABLE IF NOT EXISTS metadata (name text, value text)"
  SQL_INSERT_METADATA = "INSERT INTO metadata (name, value) VALUES (?, ?)"
  SQL_READ_METADATA = "SELECT name, value FROM metadata"
  SQL_READ_TILE_FORMAT = "SELECT value FROM metadata where name = 'format'"
  SQL_MATCHING_TILE_COUNT = "SELECT COUNT(*) FROM tiles WHERE zoom_level=? and tile_column=? and tile_row=?"
end