#include <memdraw.h>

#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>

#define K2 7 /* from -.7 to +.7 inclusive, meaning .2 into each adjacent pixel */
#define NK (2*K2+1)
double K[NK];

double
fac(int L)
{
int i, f;

f = 1;
for(i=L; i>1; --i)
f *= i;
return f;
}

/*
* i0(x) is the modified Bessel function, Σ (x/2)^2L / (L!)²
* There are faster ways to calculate this, but we precompute
* into a table so let's keep it simple.
*/
double
i0(double x)
{
double v;
int L;

v = 1.0;
for(L=1; L<10; L++)
v += pow(x/2., 2*L)/pow(fac(L), 2);
return v;
}

double
kaiser(double x, double τ, double α)
{
if(fabs(x) > τ)
return 0.;
return i0(α*sqrt(1-(x*x/(τ*τ))))/i0(α);
}

void
usage(void)
{
fprint(2, "usage: resample [-x xsize] [-y ysize] [imagefile]\n");
fprint(2, "\twhere size is an integer or a percentage in the form 25%%\n");
exits("usage");
}

int
getint(char *s, int *percent)
{
int n;

if(s == nil)
usage();
n = strtol(s, &s, 0);
*percent = *s == '%';
return n;
}

void
resamplex(uchar *in, int off, int d, int inx, uchar *out, int outx)
{
int i, x, k;
double X, xx, v, rat;

rat = (double)inx/(double)outx;
for(x=0; x<outx; x++){
if(inx == outx){
/* don't resample if size unchanged */
out[off+x*d] = in[off+x*d];
continue;
}
v = 0.0;
X = x*rat;
for(k=-K2; k<=K2; k++){
xx = X + rat*k/10.;
i = xx;
if(i < 0)
i = 0;
if(i >= inx)
i = inx-1;
v += in[off+i*d] * K[K2+k];
}
out[off+x*d] = v;
}
}

void
resampley(uchar **in, int off, int iny, uchar **out, int outy)
{
int y, i, k;
double Y, yy, v, rat;

rat = (double)iny/(double)outy;
for(y=0; y<outy; y++){
if(iny == outy){
/* don't resample if size unchanged */
out[y][off] = in[y][off];
continue;
}
v = 0.0;
Y = y*rat;
for(k=-K2; k<=K2; k++){
yy = Y + rat*k/10.;
i = yy;
if(i < 0)
i = 0;
if(i >= iny)
i = iny-1;
v += in[i][off] * K[K2+k];
}
out[y][off] = v;
}

}

int
max(int a, int b)
{
if(a > b)
return a;
return b;
}

Memimage*
resample(int xsize, int ysize, Memimage *m)
{
int i, j, d, bpl, nchan;
Memimage *new;
uchar **oscan, **nscan;

new = allocmemimage(Rect(0, 0, xsize, ysize), m->chan);
if(new == nil)
sysfatal("can't allocate new image: %r");

oscan = malloc(Dy(m->r)*sizeof(uchar*));
nscan = malloc(max(ysize, Dy(m->r))*sizeof(uchar*));
if(oscan == nil || nscan == nil)
sysfatal("can't allocate: %r");

/* unload original image into scan lines */
bpl = bytesperline(m->r, m->depth);
for(i=0; i<Dy(m->r); i++){
oscan[i] = malloc(bpl);
if(oscan[i] == nil)
sysfatal("can't allocate: %r");
j = unloadmemimage(m, Rect(m->r.min.x, m->r.min.y+i, m->r.max.x, m->r.min.y+i+1), oscan[i], bpl);
if(j != bpl)
sysfatal("unloadmemimage");
}

/* allocate scan lines for destination. we do y first, so need at least Dy(m->r) lines */
bpl = bytesperline(Rect(0, 0, xsize, Dy(m->r)), m->depth);
for(i=0; i<max(ysize, Dy(m->r)); i++){
nscan[i] = malloc(bpl);
if(nscan[i] == nil)
sysfatal("can't allocate: %r");
}

/* resample in X */
nchan = d = m->depth/8;
if(m->chan == XRGB32)
nchan--;
for(i=0; i<Dy(m->r); i++){
for(j=0; j<nchan; j++)
resamplex(oscan[i], j, d, Dx(m->r), nscan[i], xsize);
free(oscan[i]);
oscan[i] = nscan[i];
nscan[i] = malloc(bpl);
if(nscan[i] == nil)
sysfatal("can't allocate: %r");
}

/* resample in Y */
for(i=0; i<xsize; i++)
for(j=0; j<nchan; j++)
resampley(oscan, d*i+j, Dy(m->r), nscan, ysize);

/* pack data into destination */
bpl = bytesperline(new->r, m->depth);
for(i=0; i<ysize; i++){
j = loadmemimage(new, Rect(0, i, xsize, i+1), nscan[i], bpl);
if(j != bpl)
sysfatal("loadmemimage: %r");
}
return new;
}

void
main(int argc, char *argv[])
{
int i, fd, xsize, ysize, xpercent, ypercent;
Rectangle rparam;
Memimage *m, *new, *t1, *t2;
char *file;
ulong tchan;
double v;

for(i=-K2; i<=K2; i++){
K[K2+i] = kaiser(i/10., K2/10., 4.);
// print("%g %g\n", i/10., K[K2+i]);
}

/* normalize */
v = 0.0;
for(i=0; i<NK; i++)
v += K[i];
for(i=0; i<NK; i++)
K[i] /= v;

memimageinit();
memset(&rparam, 0, sizeof rparam);
xsize = ysize = 0;
xpercent = ypercent = 0;

ARGBEGIN{
case 'a': /* compatibility; equivalent to just -x or -y */
if(xsize != 0 || ysize != 0)
usage();
xsize = getint(ARGF(), &xpercent);
if(xsize <= 0)
usage();
ysize = xsize;
ypercent = xpercent;
break;
case 'x':
if(xsize != 0)
usage();
xsize = getint(ARGF(), &xpercent);
if(xsize <= 0)
usage();
break;
case 'y':
if(ysize != 0)
usage();
ysize = getint(ARGF(), &ypercent);
if(ysize <= 0)
usage();
break;
default:
usage();
}ARGEND

if(xsize == 0 && ysize == 0)
usage();

file = "<stdin>";
fd = 0;
if(argc > 1)
usage();
else if(argc == 1){
file = argv[0];
fd = open(file, OREAD);
if(fd < 0)
sysfatal("can't open %s: %r", file);
}

m = readmemimage(fd);
if(m == nil)
sysfatal("can't read %s: %r", file);

if(xpercent)
xsize = Dx(m->r)*xsize/100;
if(ypercent)
ysize = Dy(m->r)*ysize/100;
if(ysize == 0)
ysize = (xsize * Dy(m->r)) / Dx(m->r);
if(xsize == 0)
xsize = (ysize * Dx(m->r)) / Dy(m->r);

switch(m->chan){
default:
for(tchan = m->chan; tchan; tchan >>= 8)
if(TYPE(tchan) == CAlpha){
tchan = RGBA32;
goto Convert;
}
tchan = RGB24;
goto Convert;

case GREY8:
case RGB24:
case RGBA32:
case ARGB32:
case XRGB32:
new = resample(xsize, ysize, m);
break;

case GREY1:
case GREY2:
case GREY4:
tchan = GREY8;
Convert:
/* use library to convert to byte-per-chan form, then convert back */
t1 = allocmemimage(m->r, tchan);
if(t1 == nil)
sysfatal("can't allocate temporary image: %r");
memimagedraw(t1, t1->r, m, m->r.min, nil, ZP, S);
t2 = resample(xsize, ysize, t1);
freememimage(t1);
new = allocmemimage(Rect(0, 0, xsize, ysize), m->chan);
if(new == nil)
sysfatal("can't allocate new image: %r");
/* should do error diffusion here */
memimagedraw(new, new->r, t2, t2->r.min, nil, ZP, S);
freememimage(t2);
break;
}

assert(new);
if(writememimage(1, new) < 0)
sysfatal("write error on output: %r");

exits(nil);
}