# * George Moschovitis  <gm@navel.gr>
# (c) 2004-2005 Navel, all rights reserved.
# $Id: pager.rb 254 2005-02-10 12:44:05Z gmosx $

require 'nitro/uri'

module N; module UI

# Displays a collection of entitities in multiple pages.
#
# === Design
#
# The new version is carefully designed for scaleability. It stores 
# only the items for one page. The name parameter is needed, multiple 
# pagers can coexist in a single page. Unlike older pagers this 
# pager leverages the SQL LIMIT option to optimize database interaction.
#
# === Example
#
#	@pager = N::UI::Pager.new('entries', @request, 5)
#	@entries = N::BlogEntry.all("ORDER BY oid #{@pager.sql_limit}")
#	@pager.set(N::BlogEntry.count)
#
# default navigation (customize with css):
#	<div class="pager">#{@pager.navigation}</div>
#
# custom navigation:
#
# <table cellspacing="0" width="100%" border="1">
#		<tr>
#			<td width="64"><x:pager-prev>Previous</x:pager-prev></td>
#			<td width="100%"></td>
#			<td width="64"><x:pager-next>Next</x:pager-next></td>
#		</tr>
# </table>
#--
# INVESTIGATE:
# mysql> SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name
#    -> WHERE id > 100 LIMIT 10;
#	mysql> SELECT FOUND_ROWS();
#++

class Pager < Array
	
	attr_accessor :name, :idx, :page, :page_count 
	
	# Total count of items
	attr_accessor :total_count
	
	# Page items
	attr_accessor :page_items
	
	# Read needed variables from the request.
	attr_accessor :request
	
	def initialize(name, request, items_per_page = 10, items = nil)
		raise "items_per_page should be > 0" unless items_per_page > 0
	
		@request, @name = request, name
		@page = request.query.fetch("__pg#{@name}", 1).to_i
		@items_per_page = items_per_page
		@start_idx = (@page - 1) * items_per_page
		
		if items
			set(items.size())			
			# gmosx, FIXME: not exactly what i want!
			items.slice!(@start_idx, @items_per_page)
		end
	end
	
	def set(total_count)
		@total_count = total_count
		@page_count = (@total_count.to_f() / @items_per_page).ceil()
	end
	
	def first_page
		return 1
	end
	
	def last_page 
		return @page_count
	end
	
	def previous_page
		return [@page - 1, 1].max()
	end
	
	def next_page
		return [@page + 1, @page_count].min()
	end
	
	# Iterator
	
	def each(&block)
		@page_items.each(&block)
	end
	
	# Iterator
	# Returns 1-based index.
	
	def each_with_index
		idx = @start_idx
		for item in @page_items
			yield(idx + 1, item)
			idx += 1
		end
	end
	
	def empty?
		return @items.empty?
	end
	
	def size
		return @items.size()
	end
	
	# Returns the range of the current page.
	
	def page_range
		s = @idx
		e = [@idx + @items_per_page - 1, all_total_count].min
		
		return [s, e]
	end
	
	# Override if needed.
	
	def nav_range
		# effective range = 10 pages.
		s = [@page - 5, 1].max()
		e = [@page + 9, @page_count].min()
		
		d = 9 - (e - s)
		e += d if d < 0
		
		return (s..e)
	end
	
	# Override this method in your application
	# if needed.
	# TODO: better markup.
	
	def navigation
		nav = ""
		
		unless @page == first_page()
			nav << %{
				<div class="first"><a href="#{target_uri(first_page())}">First</a></div>
				<div class="previous"><a href="#{target_uri(previous_page())}">Previous</a></div>
			}
		end
		
		unless @page == last_page()
			nav << %{
				<div class="last"><a href="#{target_uri(last_page())}">Last</a></div>
				<div class="next"><a href="#{target_uri(next_page())}">Next</a></div>
			}
		end

		nav << %{<ul>}
		
		for i in nav_range()
			if i == @page
				nav << %{
					<li class="active">#{i}</li>
				}
			else
				nav << %{
					<li><a href="#{target_uri(i)}">#{i}</a></li>
				}			
			end
		end
		
		nav << %{</ul>}
		
		return nav
	end

	# Create an appropriate SQL limit clause.
	# Returns postgres/mysql compatible limit.
	
	def sql_limit
		if @start_idx > 0
			return "LIMIT #{@items_per_page} OFFSET #{@start_idx}"
		else
			# gmosx: perhaps this is optimized ? naaaaaah...
			return "LIMIT #{@items_per_page}"
		end
	end
	
	# Returns the current offset. The offset is zero-based.
	
	def offset
		(@page-1) * @items_per_page
	end
	
	# Generate the target URI.
	# 
	def target_uri(page)
		params = {"__pg#{@name}" => page}
		return N::UriUtils.update_query_string(@request.uri.to_s, params)
	end

end

end; end