class MicroSql::PgAdapter < MicroSql
  def initialize(url)
    require 'pg'

    uri = URI.parse(url)
    
    @impl = PG.connect :host     => uri.host, 
                       :port     => uri.port || 5433, 
                       :user     => uri.user, 
                       :password => uri.password, 
                       :dbname   => uri.path[1..-1]

    @impl.set_notice_receiver { |result| MicroSql.logger.info(result.error_message) }
  end

  TRANSACTION_STATUSES = %w(PQTRANS_IDLE PQTRANS_ACTIVE PQTRANS_INTRANS PQTRANS_INERROR PQTRANS_UNKNOWN)

  def connection
    @impl
  end
  
  def transaction_status
    TRANSACTION_STATUSES[@impl.transaction_status]
  end

  def transaction?
    status = @impl.transaction_status
    status == PG::Connection::PQTRANS_INTRANS || status == PG::Connection::PQTRANS_INERROR
  end
  
  def transaction(&block)
    return savepoint_transaction(&block) if transaction?

    begin
      r = nil
      @impl.transaction do
        r = yield
      end
      r
    rescue RollbackException
      nil
    end
  end
  
  private

  def savepoint_transaction(&block)
    savepoint_name = "sqdb_#{object_id}"

    exec! "SAVEPOINT #{savepoint_name}"
    r = yield
    exec! "RELEASE SAVEPOINT #{savepoint_name}"
    r
  rescue RollbackException
    exec! "ROLLBACK TO SAVEPOINT #{savepoint_name}"
    nil
  end

  public
  
  def tables
    exec("SELECT tablename FROM pg_tables WHERE tablename NOT LIKE 'pg_%' AND tablename NOT LIKE 'sql_%'").map(&:first)
  end
  
  def primary_keys(table)
    sql = <<-SQL
    SELECT  pg_attribute.attname
    FROM    pg_index, pg_class, pg_attribute 
    WHERE 
      pg_class.oid = ?::regclass AND
      indrelid = pg_class.oid AND
      pg_attribute.attrelid = pg_class.oid AND 
      pg_attribute.attnum = any(pg_index.indkey) AND 
      indisprimary
    SQL
    
    exec(sql, table).map(&:first)
  end
  
  def primary_key(table)
    keys = primary_keys(table)
    raise(Error, "No support for primary key (in table #{table})") if keys.length > 1
    keys.first || raise(Error, "No primary key in table #{table}")
  end

  private

  def insert_sql(table_name, *args)
    "#{super} RETURNING #{table(table_name).primary_key}"
  end
  
  public
  
  def execute_batch(sql)
    sql.split(";").each { |part|
      exec!(part) 
    }
  end
  
  private

  def execute(flag, sql, *args)
    execute_(flag, sql, *args)
  rescue PG::Error
    raise Error, $!.message
  end
  
  def execute_(flag, sql, *args)
    adjusted_sql = replace_placeholders(sql)

    result = if adjusted_sql && (flag == :prepare || flag == :ask) && prepared_statement = prepare(adjusted_sql) 
      @impl.exec_prepared(prepared_statement, args)
    else
      @impl.exec(adjusted_sql || sql, args)
    end

    case sql
    when /^\s*UPDATE\b/
      return result.cmd_tuples
    when /^\s*DELETE\b/
      return result.cmd_tuples
    when /^\s*INSERT\b/
      # postgresql has a different way of returning newly inserted ids; e.g.
      #   "INSERT ... RETURNING id"
      # The returned id value is returned to the pg driver the same as
      # a SELECT would be. We therefore evaluate only the first record.
      flag = :insert
      records = result.values
    else
      records = result.values
      records = records[0,1] if flag == :ask
    end

    result = convert_records result, records
  
    flag == :insert ? format_results_for_ask(result) : result
  end

  module Conversion
    extend self
    
    def nop; end
    
    def string(s);  s; end
    def unknown(s); s; end
    def integer(s); s.to_i; end
    def bytea(s);   PG::Connection.unescape_bytea(s); end
  end

  def conversion_for(ftype, fmod)
    sym = case ftype
    when 16                 then :boolean
    when 17                 then :bytea
    when 19                 then :nop
    when 20, 21, 22, 23, 26 then :integer
    when 25                 then :nop           # "text"
    when 700, 701           then :float
    when 790, 1700          then :big_decimal
    when 1083, 1266         then :string_to_time
    end
  
    return sym if sym && Conversion.respond_to?(sym)
    raise "Unsupported conversion #{sym.inspect}" if sym
    
    typename = @impl.exec( "SELECT format_type($1,$2)", [ftype, fmod] ).getvalue( 0, 0 )
    
    return :nop if typename == "unknown"
    raise "Unsupported format_type #{typename.inspect} (ftype, fmod: #{ftype}, #{fmod})"
  end
  
  def convert_records(result, records)
    # Get the type of the result columns
    converters = (0 ... result.num_fields).map do |i| 
      conversion = conversion_for result.ftype(i), result.fmod(i)
      [ conversion, i ] unless conversion == :nop
    end.compact

    records.map do |record|
      converters.each do |type, idx|
        record[idx] = Conversion.send type, record[idx]
      end
      record
    end
  end

  def replace_placeholders(sql)
    idx = 0
    query = sql.gsub("?") do 
      idx += 1
      "$#{idx}" 
    end
    
    idx == 0 ? nil : query
  end
  
  def prepare_query(key, sql)
    @impl.prepare(key, sql)
    key
  end
end