require 'mysql2'

module Mysql
  class TableMeta
    MANDATORY_OPTS = [
      :mysql_url, :database, :tables
    ]
    OPTIONAL_OPTS = [
    ]

    GET_TABLE_META_SQL = <<EOT
SELECT
  T.table_name as table_name,
  CCSA.character_set_name as character_set_name
FROM
  information_schema.`TABLES` T,
  information_schema.`COLLATION_CHARACTER_SET_APPLICABILITY` CCSA
WHERE
  CCSA.collation_name = T.table_collation
  AND T.table_schema = '%{database}'
  AND T.table_name in (%{tables});
EOT

    def initialize(opts)
      missing_opts = MANDATORY_OPTS - opts.keys
      raise "Mandatory option(s) are missing: #{missing_opts.join(', ')}" unless (missing_opts.empty?)
      @mysql_url = opts[:mysql_url]
      @database = opts[:database]
      @tables = opts[:tables]
      @table_meta = Hash.new{|h, k| h[k] = {}}
    end

    def update
      conn = Mysql2::Client.new(@mysql_url)
      sql = GET_TABLE_META_SQL % {
        database: @database, tables: @tables.collect{|t| "'#{t}'"}.join(',') }
      columns = conn.query(sql)
      columns.collect do |col|
        @table_meta[col['table_name'].to_sym][:encoding] = get_ruby_charset_name(col['character_set_name'])
      end
    ensure
      conn.close rescue nil if conn
    end

    # Charset naming conversion rule. mysql => ruby
    #
    # mysql
    #   http://dev.mysql.com/doc/refman/5.6/en/charset-charsets.html
    # mysql(supported CJK character sets)
    #   http://dev.mysql.com/doc/refman/5.6/en/faqs-cjk.html#qandaitem-A-11-1-1
    # For ruby, you can see encoding list with "Encoding.list"
    CHARSET_ENCODE_RULE = {
      'ascii' => nil, # 'ASCII-8BIT', (not need to be encoded)
      'utf8' => nil, # 'UTF-8', (not need to be encoded)
      'utf8mb4' => nil, # 'UTF-8', (not need to be encoded)
      'utf16' => 'UTF-16',
      'utf32' => 'UTF-32',
      'latin1' => 'ISO-8859-1',
      'latin2' => 'ISO-8859-2',
      'big5' => 'Big5',
      'cp932' => 'CP932',
      'eucjpms' => 'eucJP-ms',
      'euckr' => 'EUC-KR',
      'gb18030' => 'GB18030',
      'gb2312' => 'GB2312',
      'gbk' => 'GBK',
      'sjis' => 'Shift_JIS',
      'ujis' => 'EUC-JP',
    }

    def get_ruby_charset_name(mysql_charset)
      return nil if mysql_charset.to_s.empty?
      raise "Unsupported charset:#{mysql_charset}." unless CHARSET_ENCODE_RULE.has_key?(mysql_charset)
      charset = CHARSET_ENCODE_RULE[mysql_charset]
      return charset
    end

    # Return table meta
    #   :character_set_name
    def [](table_name)
      @table_meta[table_name.to_sym]
    end
  end
end