`rake schema FOR=Model` as an alternative to `annotate`

schema.rake

require "shellwords"

def terminal_width
  %x(tput cols).chomp.to_i
rescue StandardError
  80
end

def sql_table_command(model_class)
  table_name = model_class.table_name

  case (adapter_name = model_class.connection.adapter_name)
  when "PostgreSQL"
    "\\d #{table_name}"
  when "Mysql2"
    # mariadb doesn't have a terminal command to go into table mode, only a command-line
    # switch, -t.  mySQL does, but it'll error if not supported on the version you're 
    # running.  If you're using mySQL, I'm sure you're used to things working janky, so
    # here you go.
    "DESCRIBE #{table_name};"
  when "SQLite"
    # What's left after spaces between cols and the nn?/pk columns
    full_width = terminal_width
    w = full_width - 13
    col_widths = [(w / 3.0).ceil, (w / 3.0).floor, (w / 3.0).floor, 2, 3]

    <<~"SQL"
      .header on
      .mode column
      .width #{col_widths.join ' '}
      SELECT name as "Column", type as "Type", dflt_value as "Default", pk, "notnull" as "nn?" 
        FROM pragma_table_info(\"#{table_name}\");
      .print "#{col_widths.map { |wx| '-' * wx }.join('  ')}"
      .print
      .schema "#{table_name}"
    SQL
  else
    abort "fatal: don't know table schema command for #{adapter_name}"
  end
end

desc "Display DB schema for model in variable FOR=Model"
task :schema => :environment do
  model = ENV["FOR"]
  abort "fatal: FOR=ModelName required" if model.nil?

  begin
    model_class = model.constantize
    unless model_class.respond_to?(:table_name)
      abort "fatal: #{model_class.name} does not have a table_name"
    end

    exec "echo '#{sql_table_command(model_class)}'" \
         " | #{Shellwords.escape(Rails.root.join('bin/rails'))} dbconsole"
  rescue NameError
    abort "fatal: could not locate model '#{model}'"
  end
end