class WikiPagesController < ApplicationController
  rescue_from Wiki::Commit::Conflict, with: :render_wiki_conflict

  def index
    title = params[:title].to_s.strip
    descriptions = TagDescription.where(language_code: 'ja')
        .includes(tag: :tag_names)
    pages = unmigrated_wiki_pages.includes(tag_name: :tag)

    if title.present?
      pattern = "%#{ ApplicationRecord.sanitize_sql_like(title) }%"
      descriptions = descriptions.joins(tag: :tag_names)
          .where(tag_names: { language_code: 'ja', primary_flg: true })
          .where('tag_names.name LIKE ?', pattern).limit(20)
      pages = pages.where('tag_names.name LIKE ?', pattern).limit(20)
    end

    json = descriptions.map { |description| WikiPageRepr.tag_description(description) }
    json.concat(WikiPageRepr.base(pages))
    json = json.first(20) if title.present?
    render json:
  end

  def show
    tag_description = TagDescription.find_by(id: params[:id])

    return render_wiki_page_by_tag_description tag_description if tag_description

    page = WikiPage.joins(:tag_name)
                   .includes(tag_name: :tag)
                   .find_by(id: params[:id])

    render_wiki_page_or_404 page
  end

  def show_by_title
    title = params[:title].to_s.strip

    tag_description = tag_description_by_title(title)

    return render_wiki_page_by_tag_description tag_description if tag_description

    page = WikiPage.joins(:tag_name)
                   .includes(tag_name: :tag)
                   .find_by(tag_name: { name: title })

    render_wiki_page_or_404 page
  end

  def exists
    return head :no_content if TagDescription.exists?(id: params[:id])

    head WikiPage.exists?(id: params[:id]) ? :no_content : :not_found
  end

  def exists_by_title
    title = params[:title].to_s.strip
    return head :no_content if tag_description_by_title(title)

    exists = WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
    head exists ? :no_content : :not_found
  end

  def diff
    id = params[:id]
    return render_bad_request('id は必須です．') if id.blank?

    from = params[:from].presence
    to = params[:to].presence

    description = TagDescription.find_by(id:)
    if description
      versions = description_versions(description)
      from_rev = from && versions.find(from)
      to_rev = to ? versions.find(to) : versions.find_by!(version_no: description.version_no)
      resource = WikiPageRepr.tag_description(description)
    else
      page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
      from_rev = from && page.wiki_revisions.find(from)
      to_rev = to ? page.wiki_revisions.find(to) : page.current_revision
      if ((from_rev && !from_rev.content?) || !to_rev&.content?)
        return render_unprocessable_entity('差分を表示できない版です．')
      end
      resource = WikiPageRepr.base(page)
    end

    diffs = Diff::LCS.sdiff(from_rev&.body&.lines || [], to_rev.body.lines)
    diff_json = diffs.map { |change|
      case change.action
      when ?=
        { type: 'context', content: change.old_element }
      when ?!
        [{ type: 'removed', content: change.old_element },
         { type: 'added', content: change.new_element }]
      when ?+
        { type: 'added', content: change.new_element }
      when ?-
        { type: 'removed', content: change.old_element }
      end
    }.flatten.compact

    render json: { wiki_page_id:      resource.fetch('id'),
                   title:             resource.fetch('title'),
                   deprecated_at:     resource.fetch('deprecated_at'),
                   older_revision_id: from_rev&.id,
                   newer_revision_id: to_rev.id,
                   diff:              diff_json }
  end

  def create
    return head :unauthorized unless current_user
    return head :forbidden unless current_user.gte_member?

    title = params[:title].to_s.strip
    body = params[:body].to_s
    message = params[:message].presence

    return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
    return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?

    page = ApplicationRecord.transaction do
      tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
        name.script_code = 'Jpan'
        name.primary_flg = true
        name.auto_generated = false
      end

      Wiki::Commit.create_content!(
          tag_name:, body:, created_by_user: current_user, message:)
    end

    render json: WikiPageRepr.base(page), status: :created
  rescue ActiveRecord::RecordInvalid => e
    render_validation_error e.record
  rescue ActiveRecord::RecordNotUnique
    render_record_not_unique
  end

  def update
    return head :unauthorized unless current_user
    return head :forbidden unless current_user.gte_member?

    title = params[:title]&.strip
    body = params[:body].to_s

    return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
    return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?

    page = WikiPage.find(params[:id])
    base_revision_id = params[:base_revision_id].presence

    ApplicationRecord.transaction do
      page.lock!

      old_title = page.title

      tag = page.tag_name.tag

      if tag && title != old_title
        TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
      end

      page.tag_name.update!(name: title) if title != old_title

      message = params[:message].presence
      Wiki::Commit.content!(page:,
                            body:,
                            created_user: current_user,
                            message:,
                            base_revision_id:)

      if tag && title != old_title
        tag.reload
        TagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
      end
    end

    head :ok
  end

  def changes
    id = params[:id].presence
    description = id && TagDescription.find_by(id:)
    if description
      return render json: description_changes(TagDescription.where(id: description.id))
    end

    pages = id ? WikiPage.where(id:) : unmigrated_wiki_pages
    revisions = WikiRevision.joins(wiki_page: :tag_name)
        .where(wiki_page_id: pages.select(:id))
        .includes(:created_user, wiki_page: { tag_name: :tag })
        .order(id: :desc).limit(200)
    json = revisions.map { |rev|
      { revision_id: rev.id,
        pred: rev.base_revision_id,
        succ: nil,
        wiki_page: { id: rev.wiki_page_id,
                     title: rev.wiki_page.title,
                     deprecated_at: rev.wiki_page.deprecated_at },
        user: rev.created_user && { id: rev.created_user.id, name: rev.created_user.name },
        kind: rev.kind,
        message: rev.message,
        timestamp: rev.created_at }
    }
    unless id
      json.concat(description_changes(TagDescription.where(language_code: 'ja')))
      json.sort_by! { |row| -row[:revision_id] }
    end
    render json: json.first(200)
  end

  private

  def render_wiki_page_or_404 page
    return head :not_found unless page

    rev = find_revision(page)
    return head :not_found unless rev

    if rev.redirect?
      return (
          redirect_to wiki_page_by_title_path(title: rev.redirect_page.title),
                      status: :moved_permanently)
    end

    body = rev.body
    revision_id = rev.id
    pred = page.pred_revision_id(revision_id)
    succ = page.succ_revision_id(revision_id)
    updated_at = rev.created_at

    render json: WikiPageRepr.base(page).merge(body:, revision_id:, pred:, succ:, updated_at:)
  end

  def render_wiki_page_by_tag_description description
    versions = description_versions(description)
    historical = params[:version].present?
    rev = historical ? versions.find_by(id: params[:version]) :
        versions.find_by(version_no: description.version_no)
    return head :not_found unless rev

    pred = versions.find_by(version_no: rev.version_no - 1)&.id
    succ = versions.find_by(version_no: rev.version_no + 1)&.id
    body = historical ? rev.body : description.body
    updated_at = historical ? rev.created_at : description.updated_at
    render json: WikiPageRepr.tag_description(description).merge(
        body:, revision_id: rev.id, pred:, succ:, updated_at:)
  end

  def description_versions description
    TagDescriptionVersion.where(tag_id: description.tag_id,
                                language_code: description.language_code)
  end

  def tag_description_by_title title
    TagDescription.joins(tag: :tag_names)
        .find_by(language_code: 'ja', tag_names: { language_code: 'ja', name: title })
  end

  def unmigrated_wiki_pages
    descriptions = TagDescription.where(language_code: 'ja')
    WikiPage.joins(:tag_name).where.not(id: descriptions.select(:id))
        .where('tag_names.tag_id IS NULL OR tag_names.tag_id NOT IN (?)',
               descriptions.select(:tag_id))
  end

  def description_changes descriptions
    versions = TagDescriptionVersion.where(language_code: 'ja',
                                           tag_id: descriptions.select(:tag_id))
        .order(id: :desc).limit(200).to_a
    return [] if versions.empty?

    by_tag = descriptions.where(tag_id: versions.map(&:tag_id))
        .includes(tag: :tag_names).index_by(&:tag_id)
    users = User.where(id: versions.map(&:created_by_user_id)).index_by(&:id)
    predecessors = TagDescriptionVersion.where(
        language_code: 'ja', tag_id: by_tag.keys,
        version_no: versions.map { |version| version.version_no - 1 })
        .pluck(:tag_id, :version_no, :id)
        .to_h { |tag_id, version_no, id| [[tag_id, version_no], id] }
    versions.map do |version|
      description = by_tag.fetch(version.tag_id)
      user = users[version.created_by_user_id]
      { revision_id: version.id,
        pred: predecessors[[version.tag_id, version.version_no - 1]],
        succ: nil,
        wiki_page: { id: description.id, title: description.tag.name('ja'),
                     deprecated_at: description.tag.deprecated_at },
        user: user && { id: user.id, name: user.name },
        kind: 'content',
        message: nil,
        timestamp: version.created_at }
    end
  end

  def find_revision page
    if params[:version].present?
      page.wiki_revisions.find_by(id: params[:version])
    else
      page.current_revision
    end
  end

  def render_wiki_conflict err
    render json: { error: 'conflict', message: err.message }, status: :conflict
  end
end