#include <stdlib.h>
#include <stdio.h>

/* matrices of open squares, and of visible squares */
int open[200][200];
int seen[200][200];

/* current map dimensions, and player coords */
int height, width;
int px, py;

/* call this to read a map from a textfile and initialize the globals */
void init_map(char *path) {
    FILE *fp = fopen(path, "r");

    char c;
    int y = 0;
    int x = 0;
    while(666) {
        c = fgetc(fp);
        if(c == EOF)
            break;
        else if(c == '\n') {
            if(y == 0)
                width = x;
            else if(x != width) {
                printf("row %d has invalid width: %d (%d)", y, x, width);
                exit(1);
            }
            x = 0;
            y++;
        } else {
            if(c == '@') {
                px = x;
                py = y;
                open[y][x] = 1;
            } else if(c == '.')
                open[y][x] = 1;
            else if(c == '#')
                open[y][x] = 0;
            else {
                printf("invalid char %c (%hho) at row %d, col %d", c, c, y, x);
                exit(1);
            }
            x++;
        }
    }
    height = y;

    fclose(fp);
}

/* output the map and los data in ASCII */
void draw_map(void) {
    int y, x;

    printf("+");
    for(x = 0; x < width; x++) printf("-");
    printf("+\n");

    for(y = 0; y < height; y++) {
        printf("|");
        for(x = 0; x < width; x++) {
            if(y == py && x == px)
                printf("@");
            else if(seen[y][x] && open[y][x])
                printf(".");
            else if(seen[y][x])
                printf("#");
            else if(open[y][x])
                printf(" ");
            else
                printf("+");
        }
        printf("|\n");
    }
    printf("+");
    for(x = 0; x < width; x++) printf("-");
    printf("+\n\n");
}

/* calculate all squares the player can see, using get_los() */
void mark_all_los(void) {
    int x, y;
    for(y=0; y < height; y++) for(x=0; x < width; x++)
        seen[y][x] = get_los(px, py, x, y);
}

/* determine if (x1, y1) can see (x2, y2) */
int get_los(x1, y1, x2, y2) {
    int dx = x2 - x1;
    int dy = y2 - y1;
    int ax = abs(dx);
    int ay = abs(dy);
    int ix = dx > 0 ? 1 : -1;
    int iy = dy > 0 ? 1 : -1;

    int i;
    int xoff = 0;
    int yoff = 0;

    /* horizontal line case */
    if(ay == 0) {
        for(i = 1; i < ax; i++) {
            x1 += ix;
            if(!open[y1][x1]) return 0;
        }
        return 1;
    }

    /* vertical line case */
    if(ax == 0) {
        for(i = 1; i < ay; i++) {
            y1 += iy;
            if(!open[y1][x1]) return 0;
        }
        return 1;
    }

    /* more horizontal movement case */
    if(ax > ay) {
        for(i = 1; i < ax; i++) {
            xoff += ix;
            yoff = (xoff * dy) / dx;
            if(yoff * dx % dy == 0)
                if(!open[y1 + yoff][x1 + xoff]) return 0;
            else
                if(!open[y1 + yoff][x1 + xoff] && !open[y1 + yoff + iy][x1 + xoff]) return 0;
        }
        return 1;
    }

    /* more vertical movement case */
    if(ay > ax) {
        for(i = 1; i < ay; i++) {
            yoff += iy;
            xoff = (yoff * dx) / dy;
            if(yoff * dx % dy == 0)
                if(!open[y1 + yoff][x1 + xoff]) return 0;
            else
                if(!open[y1 + yoff][x1 + xoff] && !open[y1 + yoff][x1 + xoff + ix]) return 0;
        }
        return 1;
    }

    /* exact diagonal movement case */
    if(ay == ax) {
        for(i = 1; i < ax; i++) {
            x1 += ix;
            y1 += iy;
            if(!open[y1][x1]) return 0;
        }
        return 1;
    }
}

int main(int argc, char **argv) {
    int i;
    if(argc == 1) {
        printf("usage: %s map1 [map2 ...]\n\n", argv[0]);
        printf("maps are text files in the following style:\n");
        printf("#####.\n#...#.\n#..@#.\n#.....\n#####.\n");
        exit(0);
    }

    for(i = 1; i < argc; i++) {
        init_map(argv[i]);
        mark_all_los();
        draw_map();
    }
}