class PostImportPreviewer
  FIELDS = %w[title thumbnail_base original_created_from original_created_before duration tags parent_post_ids].freeze

  def initialize parsed:, url_column:, mappings: { }, existing: 'skip'
    @parsed = parsed
    @url_column = url_column.to_i
    @mappings = mappings.to_h.stringify_keys
    @existing = existing == 'error' ? 'error' : 'skip'
  end

  def preview
    preview_rows(rows: @parsed[:rows])
  end

  def preview_rows rows:, fetch_metadata: true, metadata_cache: { }
    urls = { }
    rows.map do |row|
      row = row.symbolize_keys
      values = row[:values] || []
      attributes = row[:attributes]&.stringify_keys || FIELDS.to_h { |field| [field, mapped_value(field, values)] }
      provenance = row[:provenance]&.stringify_keys || mapped_provenance(attributes)
      url = row[:url].presence || values[@url_column].to_s.strip
      provenance['url'] ||= row[:url].present? ? 'manual' : 'mapped'
      attributes['url'] = url
      fetch_warnings = Array(row[:fetch_warnings]).dup
      should_fetch = fetch_metadata == true || fetch_metadata.to_i == row[:source_row].to_i
      metadata, fetch_warnings = metadata_for(url, should_fetch, metadata_cache, fetch_warnings)
      metadata.each do |field, value|
        next unless provenance[field] == 'automatic' || attributes[field].blank?

        attributes[field] = value
        provenance[field] = 'automatic'
      end
      post = Post.new(url:)
      post.valid?
      normal_url = post.url
      errors = post.errors.to_hash.transform_values(&:dup)
      validation_warnings = []
      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? && Post.exists?(url: normal_url)
        @existing == 'error' ? errors[:url] = ['既存投稿です．'] : validation_warnings << '既存投稿のためスキップします．'
      end
      validate_basic_data(attributes, errors)
      validate_preview_tags(attributes['tags'], errors, validation_warnings)
      validate_parents(attributes['parent_post_ids'], errors)
      attributes.delete('url')
      { source_row: row[:source_row], url: normal_url || url, attributes:, provenance:,
        fetch_warnings:, validation_warnings:, warnings: fetch_warnings + validation_warnings, errors:,
        status: errors.present? ? 'error' : ((fetch_warnings + validation_warnings).present? ? 'warning' : 'ready'),
        existing: normal_url.present? && Post.exists?(url: normal_url) }
    end
  end

  def metadata_for url, fetch_metadata, cache, previous_warnings
    return [{ }, previous_warnings] unless fetch_metadata

    cache[url] ||= fetch_metadata(url)
  end

  private

  def mapped_value field, values
    mapping = @mappings[field]
    return '' if mapping.blank?
    return mapping['value'].to_s if mapping['kind'] == 'fixed'

    Array(mapping['columns']).filter_map { |index| values[index.to_i].to_s.presence }.join(field == 'tags' ? ' ' : '')
  end

  def mapped_provenance attributes
    attributes.to_h.to_h { |field, value|
      mapping = @mappings[field.to_s]
      origin =
          if value.present? && mapping&.[]('kind') == 'fixed'
            'fixed'
          elsif value.present?
            'mapped'
          else
            'automatic'
          end
      [field.to_s, origin]
    }
  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
    [{ }, ["メタデータを取得できませんでした: #{ e.message }"]]
  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 { |error| (errors[error.attribute] ||= []) << error.message }
  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 }
    errors[:parent_post_ids] = ['存在しない親投稿 Id. があります．'] if Post.where(id: ids).count != ids.uniq.length
  end
end