#include <math.h>
#include <stddef.h>
#include "studio/bitmap.h"
#include "studio/geometry.h"
#include "studio/random.h"

struct bitmap *plot(struct bitmap *image, vector coordinate, const colour ink, const double pressure)
{
    assert(image);
    assert(image->depth == grey8);
    const double nib[6][6] = {
        {0.01, 0.03, 0.06, 0.06, 0.03, 0.01},
        {0.03, 0.10, 0.30, 0.30, 0.10, 0.03},
        {0.06, 0.30, 1.00, 1.00, 0.30, 0.06},
        {0.06, 0.30, 1.00, 1.00, 0.30, 0.06},
        {0.03, 0.10, 0.30, 0.30, 0.10, 0.03},
        {0.01, 0.03, 0.06, 0.06, 0.03, 0.01}
    };
    coordinate = subtract(scalar(2.5), coordinate);
    coordinate = (vector){.x = round(coordinate.x), .y = round(coordinate.y)};
    for (size_t x = 0; x < sizeof nib / sizeof *nib; ++x) {
        for (size_t y = 0; y < sizeof nib[x] / sizeof *nib[x]; ++y) {
            const vector position = add(coordinate, (vector){.x = x, .y = y});
            const double mark = getbitmap(image, position.x, position.y).grey[level] - (
                (image->clear.grey[level] - ink.grey[level]) * nib[x][y] * pressure
            );
            image = setbitmap(image, position.x, position.y, (colour){
                .grey[level] = round(mark > 0.0 ? (mark <= 255.0 ? mark : 255.0) : 0.0)
            });
        }
    }
    return image;
}

struct bitmap *line(struct bitmap *image, const vector from, const vector to, const colour ink, double pressure)
{
    const vector length = subtract(from, to);
    double steps = fabs(length.x) >= fabs(length.y) ? fabs(length.x) : fabs(length.y);
    const vector increment = divide(length, scalar(steps));
    const double lift = (pressure * (any(500) / 1000.0)) / steps;
    for (vector point = from; steps > 0.0; --steps, point = add(increment, point))
        image = plot(image, point, ink, pressure -= lift);
    image = plot(image, to, ink, pressure);
    return image;
}