defmodule Textile.Lexer do
  import NimbleParsec
  import Textile.Helpers
  import Textile.MarkupLexer
  import Textile.UrlLexer


  # Structural tags


  # Literals enclosed via [== ==]
  # Will never contain any markup
  bracketed_literal =
    ignore(string("[=="))
    |> repeat(lookahead_not(string("==]")) |> utf8_char([]))
    |> ignore(string("==]"))
    |> reduce({List, :to_string, []})
    |> unwrap_and_tag(:bracketed_literal)

  blockquote_cite =
    lookahead_not(string("\""))
    |> choice([
      bracketed_literal |> reduce(:unwrap),
      utf8_char([])
    ])
    |> repeat()

  # Blockquote opening tag with cite: [bq="the author"]
  # Cite can contain bracketed literals or text
  blockquote_open_cite =
    ignore(string("[bq=\""))
    |> concat(blockquote_cite)
    |> ignore(string("\"]"))
    |> reduce({List, :to_string, []})
    |> unwrap_and_tag(:blockquote_open_cite)

  # Blockquote opening tag
  blockquote_open =
    string("[bq]")
    |> unwrap_and_tag(:blockquote_open)

  # Blockquote closing tag
  blockquote_close =
    string("[/bq]")
    |> unwrap_and_tag(:blockquote_close)

  # Spoiler open tag
  spoiler_open =
    string("[spoiler]")
    |> unwrap_and_tag(:spoiler_open)

  # Spoiler close tag
  spoiler_close =
    string("[/spoiler]")
    |> unwrap_and_tag(:spoiler_close)


  # Images


  image_url_with_title =
    url_ending_in(string("("))
    |> unwrap_and_tag(:image_url)
    |> concat(
      ignore(string("("))
      |> repeat(utf8_char(not: ?)))
      |> ignore(string(")"))
      |> lookahead(string("!"))
      |> reduce({List, :to_string, []})
      |> unwrap_and_tag(:image_title)
    )

  image_url_without_title =
    url_ending_in(string("!"))
    |> unwrap_and_tag(:image_url)

  image_url =
    choice([
      image_url_with_title,
      image_url_without_title
    ])

  bracketed_image_with_link =
    ignore(string("[!"))
    |> concat(image_url)
    |> ignore(string("!:"))
    |> concat(
      url_ending_in(string("]"))
      |> unwrap_and_tag(:image_link_url)
    )

  bracketed_image_without_link =
    ignore(string("[!"))
    |> concat(image_url)
    |> ignore(string("!]"))

  image_with_link =
    ignore(string("!"))
    |> concat(image_url)
    |> ignore(string("!:"))
    |> concat(
      url_ending_in(space())
      |> unwrap_and_tag(:image_link_url)
    )

  image_without_link =
    ignore(string("!"))
    |> concat(image_url)
    |> ignore(string("!"))

  image =
    choice([
      bracketed_image_with_link,
      bracketed_image_without_link,
      image_with_link,
      image_without_link
    ])


  # Links


  {link_markup_start, link_markup_element} = markup_ending_in(string("\""))

  link_url_stop =
    choice([
      string("*"),
      string("_"),
      string("@"),
      string("^"),
      string("~"),
      string("."),
      string("!"),
      string(","),
      string("?") |> concat(choice([space(), eos()]))
    ])

  link_contents_start =
    choice([
      image,
      link_markup_start,
    ])

  link_contents_element =
    choice([
      image,
      link_markup_element
    ])

  link_contents =
    optional(link_contents_start)
    |> repeat(link_contents_element)

  bracketed_link_end =
    string("\":")
    |> unwrap_and_tag(:link_end)
    |> concat(
      url_ending_in(string("]"))
      |> ignore(string("]"))
      |> unwrap_and_tag(:link_url)
    )

  bracketed_link =
    string("[\"")
    |> unwrap_and_tag(:link_start)
    |> concat(link_contents)
    |> concat(bracketed_link_end)

  unbracketed_link_end =
    string("\":")
    |> unwrap_and_tag(:link_end)
    |> concat(
      url_ending_in(link_url_stop)
      |> unwrap_and_tag(:link_url)
    )

  unbracketed_link =
    string("\"")
    |> unwrap_and_tag(:link_start)
    |> concat(link_contents)
    |> concat(unbracketed_link_end)

  link =
    choice([
      bracketed_link,
      unbracketed_link
    ])


  # Textile


  {markup_start, markup_element} = markup_ending_in(eos())

  textile_default =
    choice([
      bracketed_literal,
      blockquote_open_cite,
      blockquote_open,
      blockquote_close,
      spoiler_open,
      spoiler_close,
      link,
      image
    ])

  textile_main =
    choice([
      textile_default,
      markup_element
    ])

  textile_start =
    choice([
      textile_default,
      markup_start
    ])

  textile =
    optional(textile_start)
    |> repeat(textile_main)
    |> eos()


  defparsec :lex, textile
end