# Copyright 2011, 2012, 2013, 2014, 2015, 2016 Kevin Ryde

# This file is part of Math-PlanePath.
#
# Math-PlanePath is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 3, or (at your option) any later
# version.
#
# Math-PlanePath is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License along
# with Math-PlanePath.  If not, see <http://www.gnu.org/licenses/>.


package Math::PlanePath::KochPeaks;
use 5.004;
use strict;
#use List::Util 'max';
*max = \&Math::PlanePath::_max;

use vars '$VERSION', '@ISA';
$VERSION = 123;
use Math::PlanePath;
@ISA = ('Math::PlanePath');

use Math::PlanePath::Base::Generic
  'is_infinite',
  'round_nearest';
use Math::PlanePath::Base::Digits
  'round_down_pow';
use Math::PlanePath::KochCurve;
*_divrem_mutate = \&Math::PlanePath::_divrem_mutate;

# uncomment this to run the ### lines
#use Devel::Comments;


use constant class_y_negative => 0;
use constant n_frac_discontinuity => .5;
use constant x_negative_at_n => 1;
use constant sumabsxy_minimum  => 1; # minimum X=1,Y=0
use constant absdiffxy_minimum => 1; # X=Y never occurs
use constant rsquared_minimum  => 1; # minimum X=1,Y=0

use constant dx_maximum => 2;
use constant dy_minimum => -1;
use constant dy_maximum => 1;
use constant absdx_minimum => 1; # never vertical
use constant dsumxy_maximum => 2; # diagonal NE
use constant ddiffxy_maximum => 2; # diagonal NW
use constant dir_maximum_dxdy => (1,-1); # South-East
use constant turn_any_straight => 0; # never straight


#------------------------------------------------------------------------------

# N=1 to 3      3 of, level=0
# N=4 to 12     9 of, level=1
# N=13 to 45   33 of, level=2
#
# N=0.5 to 3.49     diff=3
# N=3.39 to 12.49   diff=9
# N=12.5 to 45.5    diff=33
#
# each length = 2*4^level + 1
#
#     Nstart = 1 + 2*4^0 + 1 + 2*4^1 + 1 + ... + 2*4^(level-1) + 1
#            = 1 + level + 2*[ 4^0 + 4^1 + ... + 4^(level-1) ]
#            = level+1 + 2*[ (4^level - 1)/3 ]
#            = level+1 + (2*4^level - 2)/3
#            = level + (2*4^level - 2 + 3)/3
#            = level + (2*4^level + 1)/3
#
#     3*n = 2*4^level + 1
#     3*n-1 = 2*4^level
#     (3*n-1)/2 = 4^level
#
# Nbase = 0.5 + 2*4^0 + 1 + 2*4^1 + 1 + ... + 2*4^(level-1) + 1
#       = level + (2*4^level + 1)/3 - 1/2
#       = level + 2/3*4^level + 1/3 - 1/2
#       = level + 2/3*4^level - 1/6
#       = level + 4/6*4^level - 1/6
#       = level + (4*4^level - 1)/6
#       = level + (4^(level+1) - 1)/6
#
#     6*N = 4^(level+1) - 1
#     6*N + 1 = 4^(level+1)
#     level+1 = log4(6*N + 1)
#     level = log4(6*N + 1) - 1
#
### loop 1: (2*4**1 + 1)/3
### loop 2: (2*4**2 + 1)/3
### loop 3: (2*4**3 + 1)/3

# sub _n_to_level {
#   my ($n) = @_;
#   my ($side, $level) = round_down_pow(6*$n + 1, 4);
#   my $base = $level + (2*$side + 1)/3 - .5;
#   ### $level
#   ### $base
#   if ($base > $n) {
#     $level--;
#     $side /= 4;
#     $base = $level + (2*$side + 1)/3 - .5;
#     ### $level
#     ### $base
#   }
#   return ($level, $base, $side + .5);
# }
# sub _level_to_base {
#   my ($level) = @_;
#   return $level + (2*$side + 1)/3 - .5;
# }

sub _n_to_side_level_base {
  my ($n) = @_;
  my ($side, $level) = round_down_pow((3*$n-1)/2, 4);
  my $base = $level + (2*$side + 1)/3;
  ### $level
  ### $base
  if (2*$n+1 < 2*$base) {
    $level--;
    $side /= 4;
    $base = $level + (2*$side + 1)/3;
    ### $level
    ### $base
  }
  return ($side, $level, $base);
}

sub n_to_xy {
  my ($self, $n) = @_;
  ### KochPeaks n_to_xy(): $n

  # $n<0.5 no good for Math::BigInt circa Perl 5.12, compare in integers
  return if 2*$n < 1;

  if (is_infinite($n)) { return ($n,$n); }

  my ($side, $level, $base) = _n_to_side_level_base($n);

  my $rem = $n - $base;
  my $frac;
  if ($rem < 0) {
    ### neg frac
    $frac = $rem;
    $rem = 0;
  } elsif ($rem > 2*$side) {
    ### excess frac
    $frac = $rem - 2*$side;
    $rem -= $frac;
  } else {
    ### no frac
    $frac = 0;
  }
  ### $frac
  ### $rem
  ### $n

  ### next base would be: ($level+1) + (2*4**($level+1) + 1)/3
  ### assert: $n-$frac >= $base
  ### assert: $n-$frac < ($level+1) + (2*4**($level+1) + 1)/3

  ### assert: $rem>=0
  ### assert: $rem < 2 * 4 ** $level + 1
  ### assert: $rem <= 2*$side+1

  my $pos = 3**$level;
  if ($rem < $side) {
    my ($x, $y) = Math::PlanePath::KochCurve->n_to_xy($rem);
    ### left side: $rem
    ### flat: "$x,$y"
    $x += 2*$frac;
    return (($x-3*$y)/2 - $pos,    # rotate +60
            ($x+$y)/2);
  } else {
    my ($x, $y) = Math::PlanePath::KochCurve->n_to_xy($rem-$side);
    ### right side: $rem-$side
    ### flat: "$x,$y"
    $x += 2*$frac;
    return (($x+3*$y)/2,           # rotate -60
            ($y-$x)/2 + $pos);
  }
}

sub xy_to_n {
  my ($self, $x, $y) = @_;
  ### KochPeaks xy_to_n(): "$x, $y"

  $x = round_nearest ($x);
  $y = round_nearest ($y);

  if ($y < 0 || ! (($x ^ $y) & 1)) {
    ### neg y or parity...
    return undef;
  }
  my ($len,$level) = round_down_pow ($y+abs($x), 3);
  ### $level
  ### $len
  if (is_infinite($level)) {
    return $level;
  }

  my $n;
  if ($x < 0) {
    $x += $len;
    ($x,$y) = (($x+3*$y)/2,   # rotate -60
               ($y-$x)/2);
    $n = 0;
    ### left rotate -60 to: "x=$x,y=$y   n=$n"
  } else {
    $y -= $len;
    ($x,$y) = (($x-3*$y)/2,   # rotate +60
               ($x+$y)/2);
    $n = 1;
    ### right rotate +60 to: "x=$x,y=$y   n=$n"
  }

  foreach (1 .. $level) {
    $n *= 4;
    ### at: "level=$level len=$len   x=$x,y=$y  n=$n"
    if ($x < $len) {
      $len /= 3;
      my $rel = 2*$len;
      if ($x < $rel) {
        ### digit 0
      } else {
        ### digit 1 sub: "$rel to x=".($x-$rel)
        $x -= $rel;
        ($x,$y) = (($x+3*$y)/2,   # rotate -60
                   ($y-$x)/2);
        $n += 1;
      }
    } else {
      $len /= 3;
      $x -= 4*$len;
      if ($x < $y) {   # before diagonal
        ### digit 2...
        ($x,$y) = (($x-3*$y)/2 + 2*$len,     # rotate +60
                   ($x+$y)/2);
        $n += 2;
      } else {
        #### digit 3...
        $n += 3;
      }
    }
  }
  ### end at: "x=$x,y=$y   n=$n"
  if ($x) {
    ### endmost point
    $n += 1;
    $x -= 2;
  }
  if ($x != 0 || $y != 0) {
    return undef;
  }
  return $n + $level + (2*4**$level + 1)/3 + ($x == 2);
}


# level extends to x= +/- 3^level
#                  y= 0 to 3^level
#
# diagonal X=Y or Y=-X is lowest in a level, so round down abs(X)+Y to pow 3
#
# end of level is 1 before base of level+1
#     basenext = (level+1) + (2*4^(level+1) + 1)/3
#     basenext-1 = level + (2*4^(level+1) + 1)/3
#                = level + (8*4^level + 1)/3

# not exact
sub rect_to_n_range {
  my ($self, $x1,$y1, $x2,$y2) = @_;
  ### KochPeaks rect_to_n_range(): "$x1,$y1  $x2,$y2"

  $x1 = round_nearest ($x1);
  $y1 = round_nearest ($y1);
  $x2 = round_nearest ($x2);
  $y2 = round_nearest ($y2);
  ### rounded: "$x1,$y1  $x2,$y2"

  if ($y1 < 0 && $y2 < 0) {
    return (1,0);
  }

  # can't make use of the len=3**$level returned by round_down_pow()
  my ($len, $level) = round_down_pow (max(abs($x1),abs($x2))
                                      + max($y1, $y2),
                                      3);
  ### $level
  return (1, $level + (8 * 4**$level + 1)/3);
}

# peak Y is at N = Nstart + (count-1)/2
#                = level + (2*4^level + 1)/3 + (2*4^level + 1 - 1)/2
#                = level + (2*4^level + 1)/3 + (2*4^level)/2
#                = level + (2*4^level + 1)/3 + 4^level
#                = level + (2*4^level + 1 + 3*4^level)/3
#                = level + (5*4^level + 1)/3

#------------------------------------------------------------------------------

sub level_to_n_range {
  my ($self, $level) = @_;
  my $pow = 4**$level;
  return ((2*$pow + 1)/3 + $level,
          (8*$pow + 1)/3 + $level);
}
sub n_to_level {
  my ($self, $n) = @_;
  if ($n < 1) { return undef; }
  if (is_infinite($n)) { return $n; }
  $n = round_nearest($n);
  my ($side, $level, $base) = _n_to_side_level_base($n);
  return $level;
}

#------------------------------------------------------------------------------
1;
__END__

=for stopwords eg Ryde Math-PlanePath Nlast Xlo Xhi Xlo=-9 Xhi=+9 Ypeak Xlo,Xhi

=head1 NAME

Math::PlanePath::KochPeaks -- Koch curve peaks

=head1 SYNOPSIS

 use Math::PlanePath::KochPeaks;
 my $path = Math::PlanePath::KochPeaks->new;
 my ($x, $y) = $path->n_to_xy (123);

=head1 DESCRIPTION

This path traces out concentric peaks made from integer versions of the
self-similar C<KochCurve> at successively greater replication levels.

                               29                                 9
                              /  \
                      27----28    30----31                        8
                        \              /
             23          26          32          35               7
            /  \        /              \        /  \
    21----22    24----25                33----34    36----37      6
      \                                                  /
       20                                              38         5
      /                                                  \
    19----18                                        40----39      4
            \                                      /
             17                 8                41               3
            /                 /  \                 \
    15----16           6---- 7     9----10          42----43      2
      \                 \              /                 /
       14                 5     2    11                44         1
      /                 /     /  \     \                 \
    13                 4     1    3     12                45  <- Y=0

                                ^
    -9 -8 -7 -6 -5 -4 -3 -2 -1 X=0 1  2  3  4  5  6  7  8  9 ...

The initial figure is the peak N=1,2,3 then for the next level each straight
side expands to 3x longer with a notch in the middle like N=4 through N=8,

                                  *
                                 / \
      *---*     becomes     *---*   *---*

The angle is maintained in each replacement so

                                  *
                                 /
                            *---*
                             \
        *                     *
       /        becomes      /
      *                     *

For example the segment N=1 to N=2 becomes N=4 to N=8, or in the next level
N=5 to N=6 becomes N=17 to N=21.

The X,Y coordinates are arranged as integers on a square grid.  The result
is flattened triangular segments with diagonals at a 45 degree angle.

Unlike other triangular grid paths C<KochPeaks> uses the "odd" squares, with
one of X,Y odd and the other even.  This means the rotation formulas etc
described in L<Math::PlanePath/Triangular Lattice> don't apply directly.

=head2 Level Ranges

Counting the innermost N=1 to N=3 peak as level 0, each peak is

    Nstart = level + (2*4^level + 1)/3
    Nend   = level + (8*4^level + 1)/3
    points = Nend-Nstart+1 = 2*4^level + 1

=for GP-DEFINE  Nstart(k) = k + (2*4^k + 1)/3

=for GP-DEFINE  Nend(k) = k + (8*4^k + 1)/3

=for GP-DEFINE  points(k) = 2*4^k + 1

=for GP-Test  vector(20,k,my(k=k-1); Nend(k)-Nstart(k)+1) == vector(20,k,my(k=k-1); points(k))

=for GP-Test  2+(2*4^2+1)/3 == 13

=for GP-Test  Nstart(0) == 1

=for GP-Test  Nend(0) == 3

=for GP-Test  Nstart(2) == 13

=for GP-Test  2+(8*4^2+1)/3 == 45

=for GP-Test  Nend(2) == 45

=for GP-Test  points(2) == 33

=for GP-Test  2*4^2+1 == 33

=for GP-Test  45-13+1 == 33

For example the outer peak shown above is level 2 starting at
Nstart=2+(2*4^2+1)/3=13 through to Nend=2+(8*4^2+1)/3=45 with
points=2*4^2+1=33 inclusive (45-13+1=33).  The X width at a given level is
the endpoints at

    Xlo = -(3^level)
    Xhi = +(3^level)

For example the level 2 above runs from Xlo=-9 to Xhi=+9.  The highest Y is
the centre peak half-way through the level at

    Ypeak = 3^level
    Npeak = level + (5*4^level + 1)/3

=for GP-DEFINE  Npeak(k) = k + (5*4^k + 1)/3

=for GP-Test  vector(20,k,my(k=k-1); (Nstart(k) + Nend(k))/2) == vector(20,k,my(k=k-1); Npeak(k))

=for GP-Test  2+(5*4^2+1)/3 == 29

=for GP-Test  Npeak(2) == 29

For example the level 2 outer peak above is Ypeak=3^2=9 at
N=2+(5*4^2+1)/3=29.  For each level the Xlo,Xhi and Ypeak extents grow by a
factor of 3.

The triangular notches in each segment are not big enough to go past the Xlo
and Xhi end points.  The new triangular part can equal the ends, such as N=6
or N=19, but not go beyond.

In general a segment like N=5 to N=6 which is at the Xlo end will expand to
give two such segments and two points at the limit in the next level, as for
example N=5 to N=6 expands to N=19,20 and N=20,21.  So the count of points
at Xlo doubles each time,

    CountLo = 2^level
    CountHi = 2^level      same at Xhi

=head1 FUNCTIONS

See L<Math::PlanePath/FUNCTIONS> for behaviour common to all path classes.

=over 4

=item C<$path = Math::PlanePath::KochPeaks-E<gt>new ()>

Create and return a new path object.

=item C<($x,$y) = $path-E<gt>n_to_xy ($n)>

Return the X,Y coordinates of point number C<$n> on the path.  Points begin
at 0 and if C<$n E<lt> 0> then the return is an empty list.

Fractional C<$n> gives an X,Y position along a straight line between the
integer positions.

=back

=head2 Level Methods

=over

=item C<($n_lo, $n_hi) = $path-E<gt>level_to_n_range($level)>

Return per L</Level Ranges> above,

    ((2 * 4**$level + 1)/3 + $level,
     (8 * 4**$level + 1)/3 + $level)

=back

=head1 FORMULAS

=head2 Rectangle to N Range

The baseline for a given level is along a diagonal X+Y=3^level or
-X+Y=3^level.  The containing level can thus be found as

    level = floor(log3( Xmax + Ymax ))
    with Xmax as maximum absolute value, max(abs(X))

The endpoint in a level is simply 1 before the start of the next, so

     Nlast = Nstart(level+1) - 1
           = (level+1) + (2*4^(level+1) + 1)/3 - 1
           = level + (8*4^level + 1)/3

Using this Nlast is an over-estimate of the N range needed, but an easy
calculation.

It's not too difficult to work down for an exact range, by considering which
parts of the curve might intersect a rectangle.  But some backtracking and
level descending is necessary because a rectangle might extend into the
empty part of a notch and so be past its baseline but not intersect any.
There's plenty of room for a rectangle to intersect nothing at all too.

=head1 SEE ALSO

L<Math::PlanePath>,
L<Math::PlanePath::KochCurve>,
L<Math::PlanePath::KochSnowflakes>,
L<Math::PlanePath::PeanoCurve>,
L<Math::PlanePath::HilbertCurve>

=head1 HOME PAGE

L<http://user42.tuxfamily.org/math-planepath/index.html>

=head1 LICENSE

Copyright 2011, 2012, 2013, 2014, 2015, 2016 Kevin Ryde

Math-PlanePath is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

Math-PlanePath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
more details.

You should have received a copy of the GNU General Public License along with
Math-PlanePath.  If not, see <http://www.gnu.org/licenses/>.

=cut
