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=head1 DESCRIPTION

This backoff algorithm calculates the next delay using Fibonacci sequence. For
example, if the two initial numbers are 2 and 3:

 2, 3, 5, 8, 13, 21, ...

C<initial_delay1> and C<initial_delay2> are required. The other attributes are
optional.

There are limits on the number of attempts (`max_attempts`) and total duration
(`max_actual_duration`).

It is recommended to add a jitter factor, e.g. 0.25 to add some randomness to
avoid "thundering herd problem".

=head1 METHODS


=head2 new

Usage:

 new(%args) -> obj

This function is not exported.

Arguments ('*' denotes required arguments):

=over 4

=item * B<consider_actual_delay> => I<bool> (default: 0)

Whether to consider actual delay.

If set to true, will take into account the actual delay (timestamp difference).
For example, when using the Constant strategy of delay=2, you log failure()
again right after the previous failure() (i.e. specify the same timestamp).
failure() will then return ~2+2 = 4 seconds. On the other hand, if you waited 2
seconds before calling failure() again (i.e. specify the timestamp that is 2
seconds larger than the previous timestamp), failure() will return 2 seconds.
And if you waited 4 seconds or more, failure() will return 0.

=item * B<delay_on_success> => I<ufloat> (default: 0)

Number of seconds to wait after a success.

=item * B<initial_delay1>* => I<ufloat>

Initial delay for the first attempt after failure, in seconds.

=item * B<initial_delay2>* => I<ufloat>

Initial delay for the second attempt after failure, in seconds.

=item * B<jitter_factor> => I<float>

How much to add randomness.

If you set this to a value larger than 0, the actual delay will be between a
random number between original_delay * (1-jitter_factor) and original_delay *
(1+jitter_factor). Jitters are usually added to avoid so-called "thundering
herd" problem.

The jitter will be applied to delay on failure as well as on success.

=item * B<max_actual_duration> => I<ufloat> (default: 0)

Maximum number of seconds for all of the attempts (0 means unlimited).

If set to a positive number, will limit the number of seconds for all of the
attempts. This setting is used to limit the amount of time you are willing to
spend on a task. For example, when using the Exponential strategy of
initial_delay=3 and max_attempts=10, the delays will be 3, 6, 12, 24, ... If
failures are logged according to the suggested delays, and max_actual_duration
is set to 21 seconds, then the third failure() will return -1 instead of 24
because 3+6+12 >= 21, even though max_attempts has not been exceeded.

=item * B<max_attempts> => I<uint> (default: 0)

Maximum number consecutive failures before giving up.

0 means to retry endlessly without ever giving up. 1 means to give up after a
single failure (i.e. no retry attempts). 2 means to retry once after a failure.
Note that after a success, the number of attempts is reset (as expected). So if
max_attempts is 3, and if you fail twice then succeed, then on the next failure
the algorithm will retry again for a maximum of 3 times.

=item * B<max_delay> => I<ufloat>

Maximum delay time, in seconds.

=item * B<min_delay> => I<ufloat> (default: 0)

Maximum delay time, in seconds.


=back

Return value:  (obj)

=head1 HOMEPAGE

Please visit the project's homepage at L<https://metacpan.org/release/Algorithm-Backoff>.

=head1 SOURCE

Source repository is at L<https://github.com/perlancar/perl-Algorithm-Backoff>.

=head1 SEE ALSO

L<https://en.wikipedia.org/wiki/Fibonacci_number>

L<Algorithm::Backoff>

Other C<Algorithm::Backoff::*> classes.

=head1 AUTHOR

perlancar <perlancar@cpan.org>