Get batches of 10, starting at and including a certain number - ruby-on-rails

Question

I have an action in a controller where I want to generate a batch of 10 consecutive days for each request.
I keep track of where we are in the batch cycle by passing a variable page, for each batch.
The cycle of batches should start with today.
How can I express this in the simplest way?
Right now I have the following mess, which doesn't even work (each batch, except for the first one, start one day too early):
#page_number = (params[:page_number] || 0).to_i + 1
today = Date.today
batch_amount = 10
first_day_of_current_batch = today + (batch_amount * (#page_number - 1))
days = first_day_of_current_batch..(first_day_of_current_batch + batch_amount)

Answer 1

As I didn't understand completely all your requirements, so I will make a few assumptions:
Pages start with 1, nil is assumed as 1
Today is 27th of October, assuming that batch size is 10 and page number 1, the batch should be Sun, 27 Oct 2013..Wed, 05 Nov 2013
Today is 27th of October, assuming that batch size is 10 and page number 2, the batch should be Sun, 06 Oct 2013..Wed, 15 Nov 2013
As You have quite a complex logic there, it will be wise to extract it to separate object.
It's considered a common and good practice, as it decouples Your code and tests.
Custom class:
# app/services/batch_of_days.rb
class Services::BatchOfDays
class << self
def create(page_nr = 1, batch_size = 10, start_from = Date.today)
new(page_nr.to_i, batch_size, start_from).create
end
end
def initialize(page_nr, batch_size, start_from)
#page_nr = page_nr
#batch_size = batch_size
#start_from = start_from
end
def create
first_day..last_day
end
private
def first_day
#first_day ||= #start_from + ( #page_nr - 1 ) * #batch_size
end
def last_day
first_day + #batch_size - 1
end
end
Usage:
irb(main):262:0> BatchOfDays.create
# => Sun, 27 Oct 2013..Tue, 05 Nov 2013
irb(main):262:0> BatchOfDays.create(1)
# => Sun, 27 Oct 2013..Tue, 05 Nov 2013
irb(main):263:0> BatchOfDays.create(2)
# => Wed, 06 Nov 2013..Fri, 15 Nov 2013
irb(main):264:0> BatchOfDays.create(3)
# => Sat, 16 Nov 2013..Mon, 25 Nov 2013

Answer 2

I recommend numbering your pages starting at 0 (i.e. page #0, the first one, begins at Date.today).
You could then use the following:
#page_number = (params[:page_number] || 0).to_i
batch_amount = 10
first = (#page_number * batch_amount).days.from_now.to_date
last = ((#page_number + 1) * batch_amount - 1).days.from_now.to_date
days = (first..last).to_a
the to_date let you specify the range as a range of consecutive days, and the to_a converts the range into an Array of Date objects, one for each day.