#
# migrate.rb
# ==========
#
# Migrate an I2 Wiki to Instiki. There must be only one 'book' in I2. A default
# 'Web' is created in Instiki for this, with a system password of "changeme",
# configured for Textile with CamelCase Wiki words disabled - only the
# '[[foo]]' syntax is allowed.
#
# Run this script using "script/runner" inside the target Instiki installation.
#

# Create a base class which establishes the alternative database connection.
# Update the connection details as required to read the source Wiki data.

class I2Database < ActiveRecord::Base
  establish_connection(
    "adapter"=>"postgresql",
    "host"=>"/home/rool/postgres/",
    "database"=>"i2",
    "username"=>"rool",
    "password"=>"set-password-here"
  )
end

# We're going to use namespaced models to avoid name clashes below. This
# provokes problems with ActiveRecord; see:
#
# https://rails.lighthouseapp.com/projects/8994/tickets/2283-unnecessary-exception-raised-in-asdependenciesload_missing_constant
#
# The ugly but effective monkey patch given in the above ticket is applied
# below. More structural changes were eventually considered, but this is
# sufficient for our needs here.

module ActiveSupport
  module Dependencies
    extend self

    #def load_missing_constant(from_mod, const_name)

    def forgiving_load_missing_constant( from_mod, const_name )
      begin
        old_load_missing_constant(from_mod, const_name)
      rescue ArgumentError => arg_err
        if arg_err.message == "#{from_mod} is not missing constant #{const_name}!"
          return from_mod.const_get(const_name)
        else
          raise
        end
      end
    end
    alias :old_load_missing_constant :load_missing_constant
    alias :load_missing_constant :forgiving_load_missing_constant
  end
end

# Create a module to avoid namespace clashes (with 'Page' in particular) -
# use "I2::Page" for an I2 page model, c.f. just "Page" for an Instiki model.

module I2
  class Page < I2Database
    set_table_name 'pages'

    has_many :versions
  end

  class Version < I2Database
    set_table_name 'versions'

    belongs_to :author
    belongs_to :page
  end

  class Author < I2Database
    set_table_name 'authors'

    has_many :versions
    has_many :pages,   :through => :versions
  end
end

# Create the basic System and Web objects.

system               = System.new
system.password      = "changeme"
system.save!

web                  = Web.new
web.name             = "Documentation"
web.address          = "documentation"
web.additional_style = ""
web.allow_uploads    = 1
web.published        = 0
web.count_pages      = 0
web.markup           = "textile"
web.color            = "008B26"
web.max_upload_size  = 100
web.safe_mode        = 0
web.brackets_only    = 1
web.save!

# Given an I2::Version instance, return body text suitable for Instiki.
#
def process_body( i2version )

  # Complications:
  #
  # I2 allowed a nil revision body for some of its Versions. Instiki fails
  # if you have that, so make sure at least an empty string is present.

  content = ( i2version.body ) || ''

  # New RedCloth versions don't like it if you try to use an ID/anchor with
  # capital letters, so use a rather permissive gsub to fix these - it
  # risks catching other "#foo" cases than just anchor/IDs in links or
  # definitions, but (at least in ROOL's case) that seems to be very rare
  # (visual examination of about 1700 matches didn't spot any). We also
  # need to change "+"s to "%20" - see the next complication for why.

  content.gsub!(/\#[A-Za-z\-\+_]+/) { | str | str.downcase.gsub('+', '%20') }

  # # Textilised references of the form "a+b+c" were interpreted as "a b c"
  # # under I2 (i.e. "+" mapped to " ") but this is not the case under
  # # Instiki. Replacing the "+"s with "%20" solves the problem albeit in an
  # # ugly fashion - but it's less trouble than patching Instiki and having
  # # difficulty with upgrades later.
  #
  # 2011-03-13 (ADH): Commented out as changes to the Page model within
  #                   Instiki handle this case via a different method.
  #
  # content.gsub!(/((\"\:)|(\]))[A-Za-z0-9_\-\%]+\+([A-Za-z0-9_\-\%]+(\+)?)+/) { | str | str.gsub('+', '%20') }

  # A common vertical spacing hack in the ROOL wiki to separate tables was
  # to use <br> just above the table definition, but in new Textile any
  # block element must have a blank line above it else the block text is
  # rendered 'raw'. CSS improvements for the new Wiki make sure that such
  # blocks don't vertically abut so the line breaks are useless - remove,
  # but keep the line feed to make sure we don't let Textile block markup
  # touch without an intervening blank line, provoking the problem we're
  # trying to solve.

  return content.gsub(/\n\<br\ ?\/?\>/, "\n")
end

# Set the ID of the Web all pages are to be placed into here; set the ID of the
# I2 Book to copy over here as well.

target_instiki_web    = Web.first
target_instiki_web_id = target_instiki_web.id
source_i2_book_id     = 1 # Get this e.g. from observation of SQL.

#Web.transaction do
begin

  # Pages
  # =====
  #
  # Instiki Page maps to I2 Page
  #
  #   I2 field       Instiki field
  #   ======================================
  #   title          name
  #   created_at     created_at
  #   updated_at     updated_at
  #   book_id        1 (well, Web.first.id)
  #                  locked_by and locked_at => nil or empty or whatever
  #
  # Revisons
  # ========
  #
  # Instiki Version maps to I2 Revision
  #
  #   I2 field       Instiki field
  #   ======================================
  #   page_id        mapped equivalent "page_id"
  #   author_id      get author and write name to "author"
  #   created_at     created_at
  #   body           content
  #   book_id        N/A (redundant; Revision has Web through Page)
  #                  updated_at => copy created_at
  #                  revised_at => copy created_at
  #                  ip => Make up (e.g. 127.0.0.1)

  page_count    = 0
  page_total    = I2::Page.count
  version_count = 0
  version_total = I2::Version.count

  wiki          = Wiki.new

  app           = ActionController::Integration::Session.new
  app.host      = "www.riscosopen.org"
  app.https!

  PageRenderer.setup_url_generator( UrlGenerator.new( app ) )

  I2::Page.all( :order => 'id ASC' ).each do | i2page |
    next unless i2page.book_id == source_i2_book_id

    # Create and save the equivalent Instiki page and revisions. I2 has a very
    # shaky use of 

    i2versions = i2page.versions.find( :all, :order => 'created_at ASC' )
    i2version  = i2versions.try( :shift )

    if ( i2version.nil? )
      puts "WARNING: No versions found for page '#{ i2page.title }' (#{ i2page.id }) - skipping"
      next
    end

    # Instiki assumes a name of "HomePage" for the default starting page in
    # any given 'Web'.

    name = i2page.title
    name = "HomePage" if ( name == "Home Page" )

    # I2 on the ROOL site has had one or two nasty hiccups wherein a page with
    # a duplicate title was created. We can't handle that. Instiki just adds
    # a new revision to whatever existing page has a matching title, even if
    # you use its "write_page" call (see below). The best solution based on
    # observation of the data at hand is to simply skip the duplicate page; the
    # original page of a given title always takes precedence and any later
    # same-name copies are ignored.

    next unless ( Page.find_by_name( name ).nil? )

    # Create the page and associated first revision.

    begin
      page_count    += 1
      version_count += 1

      puts "Page #{ page_count } of #{ page_total } ('#{ name }')..."

      wiki.write_page(
        target_instiki_web.address,
        name,
        process_body( i2version ),
        i2page.created_at,
        Author.new( i2version.author.name, '127.0.0.1' ),
        PageRenderer.new
      )

    rescue => e
      puts "WARNING: Could not save I2 page ID #{ i2page.id }:"
      puts e.message
      next # Must not try to process other revisions since we have no page

    end

    # Now handle any other revisions.

    i2versions.each do | i2version |

      begin
        version_count += 1

        puts "version #{ version_count } of #{ version_total } done..."

        wiki.revise_page(
          target_instiki_web.address,
          name,
          name,
          process_body( i2version ),
          i2version.created_at,
          Author.new( i2version.author.name, '127.0.0.1' ),
          PageRenderer.new
        )

      rescue => e
        puts "WARNING: Could not save I2 version ID #{ i2version.id }:"
        puts e.message

      end
    end
  end

  puts "Finished"

end

# Done!