module.exports = create

var classifyCharacter = require('micromark/dist/util/classify-character')
var chunkedSplice = require('micromark/dist/util/chunked-splice')
var resolveAll = require('micromark/dist/util/resolve-all')
var shallow = require('micromark/dist/util/shallow')

function create(options) {
  var settings = options || {}
  var single = settings.singleTilde
  var tokenizer = {
    tokenize: tokenizeStrikethrough,
    resolveAll: resolveAllStrikethrough
  }

  if (single === null || single === undefined) {
    single = true
  }

  return {text: {126: tokenizer}, insideSpan: {null: tokenizer}}

  // Take events and resolve strikethrough.
  function resolveAllStrikethrough(events, context) {
    var index = -1
    var strikethrough
    var text
    var open
    var nextEvents

    // Walk through all events.
    while (++index < events.length) {
      // Find a token that can close.
      if (
        events[index][0] === 'enter' &&
        events[index][1].type === 'strikethroughSequenceTemporary' &&
        events[index][1]._close
      ) {
        open = index

        // Now walk back to find an opener.
        while (open--) {
          // Find a token that can open the closer.
          if (
            events[open][0] === 'exit' &&
            events[open][1].type === 'strikethroughSequenceTemporary' &&
            events[open][1]._open &&
            // If the sizes are the same:
            events[index][1].end.offset - events[index][1].start.offset ===
              events[open][1].end.offset - events[open][1].start.offset
          ) {
            events[index][1].type = 'strikethroughSequence'
            events[open][1].type = 'strikethroughSequence'

            strikethrough = {
              type: 'strikethrough',
              start: shallow(events[open][1].start),
              end: shallow(events[index][1].end)
            }

            text = {
              type: 'strikethroughText',
              start: shallow(events[open][1].end),
              end: shallow(events[index][1].start)
            }

            // Opening.
            nextEvents = [
              ['enter', strikethrough, context],
              ['enter', events[open][1], context],
              ['exit', events[open][1], context],
              ['enter', text, context]
            ]

            // Between.
            chunkedSplice(
              nextEvents,
              nextEvents.length,
              0,
              resolveAll(
                context.parser.constructs.insideSpan.null,
                events.slice(open + 1, index),
                context
              )
            )

            // Closing.
            chunkedSplice(nextEvents, nextEvents.length, 0, [
              ['exit', text, context],
              ['enter', events[index][1], context],
              ['exit', events[index][1], context],
              ['exit', strikethrough, context]
            ])

            chunkedSplice(events, open - 1, index - open + 3, nextEvents)

            index = open + nextEvents.length - 2
            break
          }
        }
      }
    }

    return removeRemainingSequences(events)
  }

  function removeRemainingSequences(events) {
    var index = -1
    var length = events.length

    while (++index < length) {
      if (events[index][1].type === 'strikethroughSequenceTemporary') {
        events[index][1].type = 'data'
      }
    }

    return events
  }

  function tokenizeStrikethrough(effects, ok, nok) {
    var previous = this.previous
    var events = this.events
    var size = 0

    return start

    function start(code) {
      if (
        code !== 126 ||
        (previous === 126 &&
          events[events.length - 1][1].type !== 'characterEscape')
      ) {
        return nok(code)
      }

      effects.enter('strikethroughSequenceTemporary')
      return more(code)
    }

    function more(code) {
      var before = classifyCharacter(previous)
      var token
      var after

      if (code === 126) {
        // If this is the third marker, exit.
        if (size > 1) return nok(code)
        effects.consume(code)
        size++
        return more
      }

      if (size < 2 && !single) return nok(code)
      token = effects.exit('strikethroughSequenceTemporary')
      after = classifyCharacter(code)
      token._open = !after || (after === 2 && before)
      token._close = !before || (before === 2 && after)
      return ok(code)
    }
  }
}