/*
 * Function-plotting program.  Has five functions (identity, odd, square,
 * cubic, sine) and you can plot them at different scales.
 * I put in the 'help' facility in all full glory as an example.
 */

#include <stdio.h>
#include "plot.h"
#include "functions.h"

struct {
    char *name;
    double (*function)(double);
    char *description;
} functions[] = {
    { "identity", identity, "the identity function" },
    { "odd", odd, "shows which values are odd" },
    { "square", square, "y**2" },
    { "cubic", cubic, "y**3 - 2y + 1" },
    { "sine", sine, "sine function (actually 3sin(y) to look better)" },
};


enum parsestatus {
    valid,  /* valid input, proceed to plot */
    blank,  /* blank line, ignore */
    syntax, /* syntax error */
    nosuch  /* syntax is ok but there is no such function */
};


int main()
{
    extern enum parsestatus parse(char *s, double (**fp)(double), double *scale);
    char buf[80];
    double (*f)(double);
    double scale;

    while (fgets(buf, sizeof buf, stdin)) {
        switch (parse(buf, &f, &scale)) {
        case valid:
            plot(f, scale);
            break;
        case blank:
            break;
        case syntax:
            printf("syntax error -- type 'help' for help\n");
            break;
        case nosuch:
            printf("no such function -- type 'help' for a list\n");
            break;
        }
    }

    return 0;
}


enum parsestatus parse(char *s, double (**fp)(double), double *scale)
{
    char name[80];
    int i;
    extern void help();

    switch (sscanf(s, "%79s%lg", name, scale)) {
    case 1:
        *scale = 10;
        break;
    case 2:
        break;
    default:
        return (s[0] == '\n') ? blank : syntax;
    }
    if (strcmp(name, "quit") == 0)
        exit(0);
    if (strcmp(name, "help") == 0) {
        help();
        return blank;
    }
    for (i = 0; i < sizeof functions / sizeof functions[0]; i++) {
        if (strcmp(name, functions[i].name) == 0) {
            *fp = functions[i].function;
            return valid;
        }
    }
    return nosuch;
}


void help()
{
    int i;

    printf("Type a function name, followed by an optional scaling factor.\n");
    printf("(Separate the function name from the scale with a space.)\n");
    printf("The default scale is 10.  The functions are:\n");
    for (i = 0; i < sizeof functions / sizeof functions[0]; i++)
        printf("    %s - %s\n", functions[i].name, functions[i].description);
    printf("Type quit to quit.\n");
}