discourse-legacy_links/plugin.rb

# plugins/discourse-legacy_links/plugin.rb

# frozen_string_literal: true

# name: discourse-legacy_links
# about: A plugin to handle legacy Gossamer Forums URLs
# version: 0.4
# authors: saint@federated.computer
# url: https://gitea.federated.computer/saint/discourse-legacy_links.git

# require 'digest'

# enabled_site_setting :discourse_legacy_routing_enabled

# after_initialize do
after_initialize do
  module ::DiscourseLegacyLinks
    class Engine < ::Rails::Engine
      engine_name "discourse_legacy_links"
      isolate_namespace DiscourseLegacyLinks
    end

    # Define the custom controller
    class CustomPostController < ::ApplicationController
      # Match URLs that include a post_id at the end or query parameter
      # Main action triggered when the route is matched.
      def index
        post_id = extract_post_id_from_request

        if post_id
          logger.info "[DEBUG] Processing request for post_id: #{post_id}"
          post = find_post_by_custom_field(post_id)
          
          if post
            # Redirect to the post URL if found
            logger.info "[DEBUG] Redirecting to post with ID: #{post.id}"
            redirect_to post_url(post)
          else
            # Return 404 if the post is not found
            logger.error "[ERROR] Post with original_gossamer_id #{post_id} not found"
            render plain: 'Post not found', status: 404
          end
        else
          # Handle cases where the post_id cannot be extracted
          logger.error "[ERROR] Could not extract post_id from the request"
          render plain: 'Invalid URL', status: 400
        end
      end

      private

      # Extracts the post ID from the request URL or query string.
      # Supports various formats of legacy forum URLs.
      # @return [Integer, nil] The extracted post ID or nil if not found
      def extract_post_id_from_request
        # Check if post_id is passed as a query parameter (?post=post_id)
        if params[:post_id]
          post_id = params[:post_id].to_i
          logger.info "[DEBUG] Extracted post_id from query param: #{post_id}"
          return post_id
        end

        # Check for post_id in the URL path (e.g., /forum/.../P12345/)
        if match = request.path.match(%r{/forum/[^/]+/P(\d+)/?})
          post_id = match[1].to_i
          logger.info "[DEBUG] Extracted post_id from URL path: #{post_id}"
          return post_id
        end

        # Check for post_id in the query string (e.g., ?post=12345)
        if match = request.query_string.match(/post=(\d+)/)
          post_id = match[1].to_i
          logger.info "[DEBUG] Extracted post_id from query string (?post=): #{post_id}"
          return post_id
        end

        # Check for parent_post_id in the query string (e.g., ?parent_post_id=12345)
        if match = request.query_string.match(/parent_post_id=(\d+)/)
          post_id = match[1].to_i
          logger.info "[DEBUG] Extracted parent_post_id from query string: #{post_id}"
          return post_id
        end

        # If no post_id was found in any format
        logger.warn "[DEBUG] Could not extract post_id from request"
        nil
      end

      # Finds the Discourse post that has the specified custom field value.
      # The custom field used is 'original_gossamer_id'.
      # @param post_id [Integer] The extracted Gossamer forum post ID
      # @return [Post, nil] The corresponding Discourse post or nil if not found
      def find_post_by_custom_field(post_id)
        logger.info "[DEBUG] Searching for post with custom field 'original_gossamer_id' and value #{post_id}"

        # Use ActiveRecord query to find the post by the custom field value
        post = Post.joins(:topic_custom_fields)
                   .where(topic_custom_fields: { name: 'original_gossamer_id', value: post_id.to_s })
                   .first

        if post
          logger.info "[DEBUG] Found post with ID: #{post.id} for original_gossamer_id: #{post_id}"
        else
          logger.warn "[DEBUG] No post found for original_gossamer_id: #{post_id}"
        end

        post
      end

      # Redirects to the specified Discourse post.
      # @param post [Post] The Discourse post to redirect to
      def redirect_to_post(post)
        topic_url = "#{Discourse.base_url}/t/#{post.topic_id}/#{post.post_number}"
        logger.info "[DEBUG] Redirecting to topic URL: #{topic_url}"
        redirect topic_url
      end
    end

    # Register custom routes to handle legacy URLs
    Discourse::Application.routes.append do
      get '/forum/*path' => 'custom_post#index'
    end
  end
end