defmodule Dt do
	@moduledoc """
	DateTime utiity.
	"""

	# https://hexdocs.pm/timex/Timex.Format.DateTime.Formatters.Strftime.html

	def now_ym(),  do: Timex.now |> to_ym_string
	def now_ymd(), do: Timex.now |> to_ymd_string

	def diff_ymd_string( to, from, units ), do: Timex.diff( Dt.to_datetime( to ), to_datetime( from ), units )

	def add_days( dt, days ), do: to_datetime( dt ) |> Timex.add( Timex.Duration.from_days( days ) ) |> to_ymd_string

	def list_ymd( to, from ), do: if to < from, do: [], else: 0..diff_ymd_string( to, from, :days ) |> Enum.map( &( add_days( to, -&1 ) ) )

	@doc """
	Datetime to string

	## Examples
		iex> Dt.to_string( ~N[2018-01-02 23:44:09.005], "%Y/%m/%d %H:%M:%S" )
		"2018/01/02 23:44:09"
		iex> Dt.to_string( ~N[2018-01-02 23:44:09.005], "%Y/%m/%d %H:%M:%S.%L" )
		"2018/01/02 23:44:09.005"
		iex> Dt.to_string( ~N[2018-01-02 23:44:09.005], "%Y/%m/%d %H:%M:%S", :with_status )
		{ :ok, "2018/01/02 23:44:09" }
	"""
	def to_string( dt, format_str, with_status \\ :no_status ) do
		ms_treated_format_str = if String.contains?( format_str, "%L" ) do
			ms = dt |> Timex.format( "{ss}" ) |> Tpl.ok |> String.replace( ".", "" )
			format_str |> String.replace( "%L", ms )
		else
			format_str
		end
		result = Timex.format( dt, ms_treated_format_str, :strftime )
		if with_status == :no_status do
			{ :ok, return } = result
			return
		else
			result
		end
	end
	@doc """
	Datetime from string

	## Examples
		iex> Dt.from_string( "2018/01/02 23:44:09", "%Y/%m/%d %H:%M:%S" )
		~N[2018-01-02 23:44:09]
		iex> Dt.from_string( "2018/01/02 23:44:09", "%Y/%m/%d %H:%M:%S", :with_status )
		{ :ok, ~N[2018-01-02 23:44:09] }
	"""
	def from_string( dt_str, format_str, with_status \\ :no_status ) do
		result = Timex.parse( dt_str, format_str, :strftime )
		if with_status == :no_status do
			{ :ok, return } = result
			return
		else
			result
		end
	end

	@doc """
	Get datetime from string/tuple

	## Examples
		iex> Dt.to_datetime( "2018/1" )
		~N[2018-01-01 00:00:00]
		iex> Dt.to_datetime( "2018/ 1" )
		~N[2018-01-01 00:00:00]
		iex> Dt.to_datetime( "2018/01" )
		~N[2018-01-01 00:00:00]
		iex> Dt.to_datetime( "2018/1/2" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "2018/1/2 3:4" )
		~N[2018-01-02 03:04:00]
		iex> Dt.to_datetime( "2018/1/2 3:4:5" )
		~N[2018-01-02 03:04:05]
		iex> Dt.to_datetime( "2018/1/2 03:04" )
		~N[2018-01-02 03:04:00]
		iex> Dt.to_datetime( "2018/1/2 03:04:05" )
		~N[2018-01-02 03:04:05]
		iex> Dt.to_datetime( "2018/ 1/ 2" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "2018/1/ 2" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "2018/01/ 2" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "2018/01/02" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "2018/01/02 23:44" )
		~N[2018-01-02 23:44:00]
		iex> Dt.to_datetime( "2018/01/02 23:44:09" )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( "2018/01/02 23:44:09.005" )
		~N[2018-01-02 23:44:09.005]
		iex> Dt.to_datetime( "2018-01-02" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "2018-01-02 23:44" )
		~N[2018-01-02 23:44:00]
		iex> Dt.to_datetime( "2018-01-02 23:44:09" )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( "2018-01-02 23:44:09.005" )
		~N[2018-01-02 23:44:09.005]
		iex> Dt.to_datetime( "Jan-02-2018" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "Jan-02-2018 23:44" )
		~N[2018-01-02 23:44:00]
		iex> Dt.to_datetime( "Jan-02-2018 23:44:09" )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( "Jan-02-2018 23:44:09.005" )
		~N[2018-01-02 23:44:09.005]
		iex> Dt.to_datetime( "Jan-02-18" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "Jan-02-18 23:44" )
		~N[2018-01-02 23:44:00]
		iex> Dt.to_datetime( "Jan-02-18 23:44:09" )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( "Jan-02-18 23:44:09.005" )
		~N[2018-01-02 23:44:09.005]
		#iex> Dt.to_datetime( "Jan-02-98" )
		#~N[1998-01-02 00:00:00]
		#iex> Dt.to_datetime( "Jan-02-98 23:44" )
		#~N[1998-01-02 23:44:00]
		#iex> Dt.to_datetime( "Jan-02-98 23:44:09" )
		#~N[1998-01-02 23:44:09]
		#iex> Dt.to_datetime( "Jan-02-98 23:44:09.005" )
		#~N[1998-01-02 23:44:09.005]
		iex> Dt.to_datetime( "January-02-2018" )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( "January-02-2018 23:44" )
		~N[2018-01-02 23:44:00]
		iex> Dt.to_datetime( "January-02-2018 23:44:09" )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( "January-02-2018 23:44:09.005" )
		~N[2018-01-02 23:44:09.005]
		iex> Dt.to_datetime( "2018-01-02 23:44:09Z" )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( "2018-01-02T23:44:09Z" )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( { 2018, 1, 2 } )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( { { 2018, 1, 2 }, { 23, 44, 9 } } )
		~N[2018-01-02 23:44:09]
		iex> Dt.to_datetime( ~D[2018-01-02] )
		~N[2018-01-02 00:00:00]
		iex> Dt.to_datetime( ~N[2018-01-02 23:10:07] )
		~N[2018-01-02 23:10:07]
	"""
	def to_datetime( str ) when is_binary( str ) do
		[
			"%Y/%_m", 
			"%Y/%_m/%_d", 
			"%Y/%_m/%_d %_H:%_M", 
			"%Y/%_m/%_d %_H:%_M:%_S", 
			"%Y/%_m/%_d %_H:%_M:%_S.%_L", 
			"%Y-%_m-%_d", 
			"%Y-%_m-%_d %_H:%_M", 
			"%Y-%_m-%_d %_H:%_M:%_S", 
			"%Y-%_m-%_d %_H:%_M:%_S.%_L", 
			"%b-%_d-%Y", 
			"%b-%_d-%Y %_H:%_M", 
			"%b-%_d-%Y %_H:%_M:%_S", 
			"%b-%_d-%Y %_H:%_M:%_S.%_L", 
			"%b-%_d-%y", 
			"%b-%_d-%y %_H:%_M", 
			"%b-%_d-%y %_H:%_M:%_S", 
			"%b-%_d-%y %_H:%_M:%_S.%_L", 
			"%B-%_d-%Y", 
			"%B-%_d-%Y %_H:%_M", 
			"%B-%_d-%Y %_H:%_M:%_S", 
			"%B-%_d-%Y %_H:%_M:%_S.%_L", 
			"%Y-%_m-%_d %_H:%_M:%_SZ", 
			"%Y-%_m-%_d %_H:%_M:%_S.%_LZ", 
			"%Y-%_m-%_dT%_H:%_M:%_SZ", 
			"%Y-%_m-%_dT%_H:%_M:%_S.%_LZ", 
		]
		|> Enum.map( &( str |> from_string( &1, :with_status ) ) )
		|> Enum.filter( &elem( &1, 0 ) == :ok )
		|> List.first
		|> Tpl.ok
	end
	def to_datetime( value ) do
		value
		|> Timex.to_datetime
		|> DateTime.to_string
		|> to_datetime
	end

	@doc """
	To JST string from UTC

	## Examples
		iex> Dt.to_jst( "2018/1/2 10:23:45" )
		"2018/01/02 19:23"
		iex> Dt.to_jst( "2018/1/2 15:23:45" )
		"2018/01/03 00:23"
	"""
	def to_jst( utc, cut_second \\ :cut_second ) do
		utc
		|> to_datetime
		|> Timex.Timezone.convert( "Asia/Tokyo" )
		|> DateTime.to_string
		|> String.replace( "+09:00 JST Asia/Tokyo", "" )
		|> hyphen_to_slash
		|> cut_second( cut_second )
	end

	@doc """
	To yyyy/mm string

	## Examples
		iex> Dt.to_ym_string( ~N[2018-01-02 03:04:05] )
		"2018/01"
	"""
	def to_ym_string( dt ),  do: dt |> to_string( "%Y/%0m" )

	@doc """
	To yyyy/mm/dd string

	## Examples
		iex> Dt.to_ymd_string( ~N[2018-01-02 03:04:05] )
		"2018/01/02"
	"""
	def to_ymd_string( dt ), do: dt |> to_string( "%Y/%0m/%0d" )

	@doc """
	To yyyy/mm/dd string

	## Examples
		iex> Dt.to_ymd_string( ~N[2018-01-02 03:04:05] )
		"2018/01/02"
	"""
	def to_ymdhmsl( dt ), do: dt |> to_string( "%Y/%0m/%0d" )

	@doc """
	Hyphen to slash

	## Examples
		iex> Dt.hyphen_to_slash( "2018-01-02 03:04:05" )
		"2018/01/02 03:04:05"
		iex> Dt.hyphen_to_slash( "2018/01/02 03:04:05" )
		"2018/01/02 03:04:05"
	"""
	def hyphen_to_slash( str ), do: str |> String.replace( "-", "/" )

	@doc """
	Slash to hyphen

	## Examples
		iex> Dt.slash_to_hyphen( "2018/01/02 03:04:05" )
		"2018-01-02 03:04:05"
		iex> Dt.slash_to_hyphen( "2018-01-02 03:04:05" )
		"2018-01-02 03:04:05"
	"""
	def slash_to_hyphen( str ), do: str |> String.replace( "/", "-" )

	def cut_second( str, cut_second \\ :cut_second ), do: if cut_second == :cut_second, do: str |> String.slice( 0, 16 ), else: str
end