package JWebmail::Plugin::Paginate;

use Mojo::Base Mojolicious::Plugin;

use List::Util qw(any max);
use POSIX 'ceil';


sub _clamp {
    my ($x, $y, $z) = @_;

    die '!($x <= $z)' unless $x <= $z;

    if ($x <= $y && $y <= $z) {
        return $y;
    }

    return $x if ($y < $x);
    return $z if ($z < $y);
}

sub _paginate {
    my %args = @_;

    my $first_item  = $args{first_item};
    my $page_size   = $args{page_size};
    my $total_items = $args{total_items};

    my $current_page = ceil($first_item/$page_size);
    my $total_pages  = ceil($total_items/$page_size);

    my $page = sub {
        my $page_ = shift;
        return [0, 0] unless $total_items;
        $page_ = _clamp(0, $page_, $total_pages-1);
        [_clamp(0, $page_*$page_size, $total_items-1), _clamp(0, ($page_+1)*$page_size, $total_items)]
    };

    my $ret = {
        total_items => $total_items,
        page_size   => $page_size,

        total_pages  => $total_pages,
        current_page => $current_page,

        first_page => $page->(0),
        prev_page  => $page->($current_page-1),
        this_page  => $page->($current_page),
        next_page  => $page->($current_page+1),
        last_page  => $page->($total_pages-1),
    };

    if ($total_items) {
        $ret->{first_item} = $first_item;
        $ret->{last_item} = _clamp($first_item, $first_item+$page_size-1, $total_items-1);
    }

    return $ret;
}

sub paginate {
    my $c = shift;
    my ($count) = @_;

    my $v = $c->validation;
    my $start = $v->optional('start')->num(0, undef)->param // 0;
    my $psize = $v->optional('page_size')->num(1, undef)->param // 50;

    $start = _clamp(0, $start, max($count-1, 0));
    my $end = _clamp($start, $start+$psize, max($count, 0));

    $c->stash(pgn => _paginate(
        first_item  => int($start/$psize)*$psize,
        page_size   => $psize,
        total_items => $count,
    ));

    return $start, $end;
}

sub make_link {
    my ($c, $txt, $to) = @_;

    return $c->link_to(
        $txt => $c->url_with->query({start => $c->stash('pgn')->{$to}[0]}),
        class => ($c->param('start')//0) == $c->stash('pgn')->{$to}[0] ? 'disabled' : '',
    );
}

sub register {
    my ($self, $app, $conf) = @_;
    $conf //= {};

    $app->helper(paginate => \&paginate);
    $app->helper('_paginate.make_link' => \&make_link);
}


1

__END__

=encoding utf-8

=head1 NAME

JWebmail::Plugin::Paginate

=head1 SYNOPSIS

  sub my_route {
    my ($c) = @_;

    $c->stash($c->paginate(1234));
  }

=head1 DESCRIPTION

L<JWebmail::Helper> provides useful helper functions and validator cheks and filter for
L<JWebmail::Controller::All> and various templates.

=head1 HELPERS

=head2 paginate

A helper for calculating page bounds.

Takes the total number of items as argument.

Reads in 'start' and 'page_size' query arguments.
start is 0 based.

Returns the calculated start and end points as 0 based inclusive range.

Sets the stash values (all 1 based inclusive):

  first_item
  last_item
  total_items
  page_size
  total_pages
  current_page
  first_page
  prev_page
  next_page
  last_page

=head1 SEE ALSO

L<JWebmail>

=head1 NOTICE

This package is part of JWebmail.