class PostImportPreviewer
  FIELDS = [
    'title',
    'thumbnail_base',
    'original_created_from',
    'original_created_before',
    'duration',
    'tags',
    'parent_post_ids',
  ].freeze
  def initialize existing: 'skip'
    @existing = existing == 'error' ? 'error' : 'skip'
  end

  def preview_rows rows:, fetch_metadata: true, metadata_cache: { }
    urls = {}
    rows.map { |row|
      preview_row(row, urls:, fetch_metadata:, metadata_cache:)
    }
  end

  def normalised_url value
    PostUrlNormaliser.normalise(value)
  end

  private

  def preview_row row, urls:, fetch_metadata:, metadata_cache:
    row = row.symbolize_keys
    attributes = initial_attributes(row)
    provenance = initial_provenance(row)
    tag_sources = initial_tag_sources(row, attributes, provenance)
    url = row[:url].to_s.strip
    provenance['url'] = 'manual'
    normal_url = normalised_url(url)
    url_for_metadata = normal_url || url
    existing_post = normal_url.present? && Post.exists?(url: normal_url)

    validation_warnings = []
    validation_errors = {}
    validation_errors[:url] = ['URL が不正です．'] if normal_url.blank?
    validation_errors[:url] = ['URL が重複しています．'] if normal_url.present? && urls.key?(normal_url)
    urls[normal_url] = true if normal_url.present?
    if normal_url.present? && existing_post
      if @existing == 'error'
        validation_errors[:url] = ['既存投稿です．']
      else
        validation_warnings << '既存投稿のためスキップします．'
      end
    end

    if row[:metadata_url].present? && row[:metadata_url] != url_for_metadata
      clear_automatic_values!(attributes, provenance, tag_sources)
    end

    fetch_warnings = Array(row[:fetch_warnings]).dup
    should_fetch = should_fetch_metadata?(fetch_metadata, row[:source_row].to_i)
    if should_fetch && !(existing_post && @existing == 'skip')
      metadata, fetch_warnings =
        metadata_for(url_for_metadata, metadata_cache, fetch_warnings)
      apply_metadata!(attributes, provenance, tag_sources, metadata)
    end

    attributes['url'] = url
    validate_basic_data(attributes, validation_errors)
    validate_preview_tags(
      merged_tags(tag_sources, provenance['tags']),
      validation_errors,
      validation_warnings,
    )
    validate_parents(attributes['parent_post_ids'], validation_errors)
    attributes.delete('url')
    attributes['tags'] = merged_tags(tag_sources, provenance['tags'])

    {
      source_row: row[:source_row],
      url: normal_url || url,
      attributes:,
      provenance:,
      tag_sources:,
      metadata_url: url_for_metadata,
      fetch_warnings:,
      validation_warnings:,
      warnings: fetch_warnings + validation_warnings,
      validation_errors:,
      status: validation_errors.present? \
                ? 'error' \
                : ((fetch_warnings + validation_warnings).present? ? 'warning' : 'ready'),
      existing: existing_post,
    }
  end

  def should_fetch_metadata? fetch_metadata, source_row
    case fetch_metadata
    when true then true
    when Integer then fetch_metadata == source_row
    when false, nil then false
    else raise ArgumentError, 'メタデータ取得対象が不正です．'
    end
  end

  def initial_attributes row
    attributes = row[:attributes]&.stringify_keys || {}
    FIELDS.to_h { |field| [field, attributes[field].to_s] }
  end

  def initial_provenance row
    provenance = row[:provenance]&.stringify_keys || {}
    FIELDS.to_h { |field| [field, provenance[field].presence || 'automatic'] }
      .merge('url' => 'manual')
  end

  def initial_tag_sources row, attributes, provenance
    sources = row[:tag_sources]&.stringify_keys || { 'automatic' => '', 'manual' => '' }
    sources['automatic'] = sources['automatic'].to_s
    sources['manual'] =
      provenance['tags'] == 'manual' ? attributes['tags'].to_s : sources['manual'].to_s
    sources
  end

  def clear_automatic_values! attributes, provenance, tag_sources
    ['title', 'thumbnail_base', 'original_created_from',
     'original_created_before', 'duration'].each do |field|
      attributes[field] = '' if provenance[field] == 'automatic'
    end
    tag_sources['automatic'] = ''
    attributes['tags'] = merged_tags(tag_sources, provenance['tags'])
  end

  def metadata_for url, cache, previous_warnings
    cache[url] ||= fetch_metadata(url)
  end

  def fetch_metadata url
    return [{}, ['URL が空です．']] if url.blank?

    data = PostMetadataFetcher.fetch(url).stringify_keys
    warnings = []
    warnings << 'タイトルを取得できませんでした．' if data['title'].blank?
    warnings << 'サムネールを取得できませんでした．' if data['thumbnail_base'].blank?
    [data.compact, warnings]
  rescue Preview::UrlSafety::UnsafeUrl,
         Preview::HttpFetcher::FetchFailed,
         Preview::HttpFetcher::ResponseTooLarge => e
    Rails.logger.info(
      "post_import_metadata_fetch_failure "\
      "#{ { error: e.class.name, message: e.message }.to_json }",
    )
    [{}, ['メタデータを取得できませんでした．']]
  end

  def apply_metadata! attributes, provenance, tag_sources, metadata
    metadata.each do |field, value|
      if field == 'tags'
        next if provenance['tags'] == 'manual'

        tag_sources['automatic'] = value.to_s
        attributes['tags'] = merged_tags(tag_sources)
        next
      end
      next unless provenance[field] == 'automatic' || attributes[field].blank?

      attributes[field] = value
      provenance[field] = 'automatic'
    end
  end

  def merged_tags sources, origin = nil
    return sources['manual'].to_s if origin == 'manual'

    sources['automatic'].to_s
  end

  def validate_preview_tags raw, errors, warnings
    names = raw.to_s.split
    return if names.empty?
    if names.any? { _1.downcase.start_with?('nico:') }
      errors[:tags] = ['ニコニコ・タグは直接指定できません．']
      return
    end

    parsed = names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
    existing = Tag.joins(:tag_name).where(tag_names: { name: parsed }).includes(:tag_name).to_a
    deprecated = existing.select(&:deprecated?).map(&:name)
    errors[:tags] = ["廃止済みタグがあります: #{ deprecated.join(' ') }"] if deprecated.present?
    known = existing.reject(&:deprecated?).map(&:name)
    new_tags = parsed.uniq - known
    warnings << "新規タグを作成します: #{ new_tags.join(' ') }" if new_tags.present?
  rescue Tag::SectionLiteralParseError
    errors[:tags] = ['タグ区間の記法が不正です．']
  end

  def validate_basic_data attributes, errors
    post = Post.new(title: attributes['title'].presence,
                    url: attributes['url'],
                    thumbnail_base: attributes['thumbnail_base'].presence,
                    original_created_from: attributes['original_created_from'].presence,
                    original_created_before: attributes['original_created_before'].presence,
                    video_ms: parse_duration(attributes['duration'], errors))
    post.valid?
    post.errors.each do |error|
      next if error.attribute == :url && error.type == :taken

      (errors[error.attribute] ||= []) << error.message
    end
  end

  def parse_duration value, errors
    return nil if value.blank?

    value.is_a?(Numeric) ? value.to_i : Tag.time_to_ms!(value.to_s, tag_name: '動画時間')
  rescue Tag::SectionLiteralParseError
    errors[:video_ms] = ['動画時間の記法が不正です．']
    nil
  end

  def validate_parents raw, errors
    ids = raw.to_s.split.map { Integer(_1, exception: false) }
    return if ids.compact.empty? && raw.to_s.blank?

    errors[:parent_post_ids] = ['親投稿 Id. が不正です．'] and return if ids.any? { _1.nil? || _1 <= 0 }
    if Post.where(id: ids).count != ids.uniq.length
      errors[:parent_post_ids] = ['存在しない親投稿 Id. があります．']
    end
  end
end