defmodule Gallery do
  @unsplash_url "https://images.unsplash.com"
	
  @ids [
    "photo-1562971179-4ad6903a7ed6",
    "photo-1552673597-e3cd6747a996",
    "photo-1561133036-61a7ed56b424",
    "photo-1530717449302-271006cdc1bf"
  ]

  def thumb_url(id), do: image_url(id, %{w: 100, h: 100, fit: "crop"})
  def large_url(id), do: image_url(id, %{h: 500, fit: "crop"})

  def image_ids(), do: @ids
	
	def first_id(ids \\ @ids) do
		List.first(ids)
	end


	def prev_image_id(ids\\@ids, id) do
		Enum.at(ids, prev_index(ids, id))
	end
  
  def prev_index(ids, id) do
		ids
		|> Enum.find_index(& &1 == id)
		|> Kernel.-(1)
  end

	def next_image_id(ids\\@ids, id) do
		Enum.at(ids, next_index(ids, id), first_id(ids))
	end
  
  def next_index(ids, id) do
  	ids
  	|> Enum.find_index(& &1 == id)
		|> Kernel.+(1)
  end

	def image_url(image_id, params) do
		URI.parse(@unsplash_url)
		|> URI.merge(image_id)
		|> Map.put(:query, URI.encode_query(params))
		|> URI.to_string()
	end
end