#include "ps_graph.h"
#include <math.h>
#include <stdio.h>

#define TEMP_BUF_SIZE  128

/* rozměry grafu */
#define GRAPH_SIZE 400
#define HALF_GRAPH_SIZE (GRAPH_SIZE / 2)

#define GRAPH_CENTER_X 306
#define GRAPH_CENTER_Y 500

/* písmo */
#define FONT "Helvetica"
#define FONT_SIZE_HEADER    15
#define FONT_SIZE_LABEL     12
#define FONT_SIZE_VALUE     9

#define GRID_STEP (GRAPH_SIZE / 10)

/* posuny popisků */
#define HEADER_OFFSET_Y (10)

#define X_VAL_OFFSET_X (0)
#define X_VAL_OFFSET_Y (-13)

#define Y_VAL_OFFSET_X (-5)
#define Y_VAL_OFFSET_Y (-3)

#define X_LABEL_OFFSET_X (0)
#define X_LABEL_OFFSET_Y (-30)

#define Y_LABEL_OFFSET_X (-40)
#define Y_LABEL_OFFSET_Y (-3)

/* počet částí grafu funkce */
#define FUNCTION_SEGMENTS 1000

/* koeficienty pro zarovnání textu */
#define ALIGN_CENTER    (-0.5)
#define ALIGN_RIGHT     (-1.0)

static void generate_text_align(FILE *file, int x, int y, double alignment, const char *str) {
    fprintf(file,
        "newpath\n"
        /* posun na cílovou pozici */
        "%d %d moveto\n"
        /* vložení dvou řetězců s popiskem */
        "(%s) dup\n"
        /* zjištění šířky a výšky řetežce, odstranění výšky ze zásobníku (nezajímá) */
        "stringwidth pop\n"
        /* koeficient pro zarovnání */
        "%f mul\n"
        /* posun o šířku doleva */
        "0 rmoveto\n"
        /* zobrazení řetězce */
        "show\n"
        "\n",
        x, y, str, alignment
    );
}

static void set_font(FILE *file, const char *font, int size) {
    fprintf(file,
        "/%s findfont\n"
        "%d scalefont\n"
        "setfont\n",
        font, size
    );
}

static void generate_grid(FILE *file, const struct graph_range *range) {
    int i;
    fprintf(file,
        "2 setlinewidth\n"
        "/gridline {\n"
        "   .5 setlinewidth\n"
        "   .5 setgray\n"
        "   [3 3] 0 setdash\n"
        "   newpath\n"
        "   moveto\n"
        "   rlineto\n"
        "   stroke\n"
        "} def\n"
        "\n"
    );

    for (i = -HALF_GRAPH_SIZE + GRID_STEP; i < HALF_GRAPH_SIZE; i += GRID_STEP) {
        fprintf(file, "%5d     0 %5d %5d gridline\n", GRAPH_SIZE, -HALF_GRAPH_SIZE, i);
        fprintf(file, "    0 %5d %5d %5d gridline\n", GRAPH_SIZE, i, -HALF_GRAPH_SIZE);
    }

    set_font(file, FONT, FONT_SIZE_VALUE);

    /* hodnoty */
    for (i = -HALF_GRAPH_SIZE; i <= HALF_GRAPH_SIZE; i += GRID_STEP) {
        double inorm = (double)i / (double)GRAPH_SIZE + 0.5;
        double xval = range->xmax * inorm + range->xmin * (1.0 - inorm); 
        double yval = range->ymax * inorm + range->ymin * (1.0 - inorm); 
        char buf[TEMP_BUF_SIZE];

        /* hodnota osy y */
        snprintf(buf, TEMP_BUF_SIZE, "%.2f", yval);
        generate_text_align(file, -HALF_GRAPH_SIZE + Y_VAL_OFFSET_X, i + Y_VAL_OFFSET_Y, ALIGN_RIGHT, buf);

        /* hodnota osy x */
        snprintf(buf, TEMP_BUF_SIZE, "%.2f", xval);
        generate_text_align(file, i + X_VAL_OFFSET_X, -HALF_GRAPH_SIZE + X_VAL_OFFSET_Y, ALIGN_CENTER, buf);

    }

    /* popisky os */
    set_font(file, FONT, FONT_SIZE_LABEL);
    generate_text_align(file, -HALF_GRAPH_SIZE + Y_LABEL_OFFSET_X, Y_LABEL_OFFSET_Y, ALIGN_RIGHT, "y");
    generate_text_align(file, X_LABEL_OFFSET_X, -HALF_GRAPH_SIZE + X_LABEL_OFFSET_Y, ALIGN_CENTER, "x");
}

static void generate_function(FILE *file, const struct expr_node *node, const struct graph_range *range) {
    int i;
    int first = 1;

    fprintf(file,
        "2 setlinewidth\n"
        "0 .3 .7 setrgbcolor\n"
        "newpath\n"
    );

    for (i = 0; i < FUNCTION_SEGMENTS; ++i) {
        const char *cmd = "lineto";
        double xpos, ypos;
        double x, y;
       
        x = range->xmin + (range->xmax - range->xmin) * (double)i / (double)FUNCTION_SEGMENTS;

        /* funkce není definována */
        if (node_eval(node, x, &y) != EVAL_OK) {
            first = 1;
            continue;
        }

        xpos = (double)(-HALF_GRAPH_SIZE) + (x - range->xmin) / (range->xmax - range->xmin) * (double)GRAPH_SIZE;
        ypos = (double)(-HALF_GRAPH_SIZE) + (y - range->ymin) / (range->ymax - range->ymin) * (double)GRAPH_SIZE;
        
        if (first) {
            cmd = "moveto";
            first = 0;
        }
        fprintf(file, "%.2f %.2f %s\n", xpos, ypos, cmd);

    }

    fprintf(file,
        "stroke\n"
    );
}

void ps_generate_graph(FILE *file, const struct expr_node *node, const struct graph_range *range, const char *function) {
    char buf[TEMP_BUF_SIZE];
    
    /* posun na střed */
    fprintf(file, "%d %d translate\n", GRAPH_CENTER_X, GRAPH_CENTER_Y);

    /* hlavička */
    if (function) {
        set_font(file, FONT, FONT_SIZE_HEADER);
        snprintf(buf, TEMP_BUF_SIZE, "y = %s", function);
        generate_text_align(file, 0, HALF_GRAPH_SIZE + HEADER_OFFSET_Y, ALIGN_CENTER, buf);
    }

    generate_grid(file, range);

    /* ořezová oblast pro graf */
    fprintf(file,
        "[] 0 setdash\n"
        "newpath\n"
        "%d %d moveto\n"
        "%d 0 rlineto\n"
        "0 %d rlineto\n"
        "%d 0 rlineto\n"
        "closepath\n"
        "gsave\n"
        "clip\n",
        -HALF_GRAPH_SIZE, -HALF_GRAPH_SIZE, GRAPH_SIZE, GRAPH_SIZE, -GRAPH_SIZE 
    );

    /* samotný graf */
    generate_function(file, node, range);

    /* rámeček */
    fprintf(file,
        "grestore\n"
        "2 setlinewidth\n"
        "0 0 0 setrgbcolor\n"
        "stroke\n"
    );
}