require 'fileutils'

start_time = Time.now


SOURCE_DB = {
  :name => 'db_name',
  :user => 'db_user',
  :password => 'db_pass',
  :host => 'localhost'
}
TARGET_DB = {
  :name => 'db_name',
  :user => 'db_user',
  :password => 'db_pass',
  :host => 'foo.abcdef.us-east-1.rds.amazonaws.com'
}

DUMP_DIR  = '/mnt/db_dump'


# These tables can be moved beforehand, and the diff later
INSERT_ONLY_TABLES = %w[click_tracking logs]


def benchmark(label = nil)
  puts label unless label.nil?
  before = Time.now
  yield
  after = Time.now
  puts "Took %.3fs" % (after - before)
end

def host_user_password(db)
  "--host='#{db[:host]}' --user='#{db[:user]}' --password='#{db[:password]}'"
end

def show_tables(db)
  `mysql --execute='SHOW TABLES' --silent #{host_user_password(db)} #{db[:name]}`.split("\n")
end

def dump_db_tables(db, tables, dir, where = nil)
  FileUtils.mkdir_p(dir, :mode => 0777)
  where_arg = where.nil? ? '' : %(--where="#{where}")

  benchmark("Dumping tables [#{tables.join(', ')}] to #{dir} #{where_arg}") do
    system "mysqldump --verbose #{host_user_password(db)} --tab=#{dir} #{where_arg} #{LOCK_ARG} #{db[:name]} #{tables.join(' ')}"
  end
end

def dump_db_before(db, migrate_before = [])
  dir = "#{DUMP_DIR}/#{db[:name]}/before"
  dump_db_tables(db, migrate_before, dir)
end

def dump_db_hot(db, migrate_before = [])
  dir = "#{DUMP_DIR}/#{db[:name]}/hot"
  tables = show_tables(db) - migrate_before
  dump_db_tables(db, tables, dir)
end

def dump_db_diff(source, target, migrate_before = [])
  dir = "#{DUMP_DIR}/#{source[:name]}/diff"

  migrate_before.each do |table|
    last_max_id = `mysql --execute='SELECT MAX(id) FROM #{table}' --silent #{host_user_password(target)} #{target[:name]}`.strip
    dump_db_tables(source, [table], dir, "id > #{last_max_id}")
  end
end

def dump_db_structure(db)
  dump_file = "#{DUMP_DIR}/#{db[:name]}_structure.sql"
  FileUtils.mkdir_p(DUMP_DIR, :mode => 0777)

  benchmark("Dumping structure of #{db[:name]} to #{dump_file}") do
    system "mysqldump --verbose #{host_user_password(db)} --no-data #{db[:name]} > #{dump_file}"
  end
end

def import_db_structure(source, target)
  dump_file = "#{DUMP_DIR}/#{source[:name]}_structure.sql"

  benchmark("Importing structure of #{source[:name]} from #{dump_file}") do
    system "mysql #{host_user_password(target)} #{target[:name]} < #{dump_file}"
  end
end

def import_db_tables(target, tables, dir)
  benchmark("Importing tables from #{dir}") do
    dump_files = tables.map { |table| File.join(dir, "#{table}.txt") }
    system "mysqlimport --local --compress --verbose #{host_user_password(target)} #{target[:name]} #{dump_files.join(' ')}"
  end
end

def import_db_before(source, target, migrate_before = [])
  dir = "#{DUMP_DIR}/#{source[:name]}/before"
  import_db_tables(target, migrate_before, dir)
end

def import_db_hot(source, target, migrate_before = [])
  dir = "#{DUMP_DIR}/#{source[:name]}/hot"
  tables = show_tables(source) - migrate_before
  import_db_tables(target, tables, dir)
end

def import_db_diff(source, target, migrate_before = [])
  dir = "#{DUMP_DIR}/#{source[:name]}/diff"
  import_db_tables(target, migrate_before, dir)
end


if ARGV.include?('--before')
  # Don't lock tables while the site is still up
  LOCK_ARG = "--skip-lock-tables"
  # Run these before
  dump_db_structure(SOURCE_DB)
  dump_db_before(SOURCE_DB, INSERT_ONLY_TABLES)
  import_db_structure(SOURCE_DB, TARGET_DB)
  import_db_before(SOURCE_DB, TARGET_DB, INSERT_ONLY_TABLES)
else
  LOCK_ARG = ""
  # Run these when the site is offline
  dump_db_hot(SOURCE_DB, INSERT_ONLY_TABLES)
  dump_db_diff(SOURCE_DB, TARGET_DB, INSERT_ONLY_TABLES)
  import_db_hot(SOURCE_DB, TARGET_DB, INSERT_ONLY_TABLES)
  import_db_diff(SOURCE_DB, TARGET_DB, INSERT_ONLY_TABLES)
end

puts "Script ran for: %.3fs" % (Time.now - start_time)