#include <u.h>
#include <libc.h>
#include <ctype.h>
#include <draw.h>
#include <event.h>

typedef struct Op Op;
typedef struct Operator Operator;
typedef struct Token Token;
typedef struct Constant Constant;
typedef struct Code Code;

enum {
	ONONE,
	ONUMBER,
	OVAR,
	OUNARY,
	OBINARY,
};

struct Op {
	int type;
	union {
		void (*f)(void);
		double val;
	};
};

enum {
	TNONE,
	TNUMBER,
	TVAR,
	TOP,
	TPARENL,
	TPARENR,
};

struct Token {
	int type;
	union {
		Operator *op;
		double val;
	};
	Token *next;
};

double *stack, *sp;
void add(void) { sp--; *sp += *(sp+1); }
void sub(void) { sp--; *sp -= *(sp+1); }
void mul(void) { sp--; *sp *= *(sp+1); }
void div(void) { sp--; *sp /= *(sp+1); }
void pot(void) { sp--; *sp = pow(*sp, *(sp+1)); }
void osin(void) { *sp = sin(*sp); }
void ocos(void) { *sp = cos(*sp); }
void otan(void) { *sp = tan(*sp); }
void oasin(void) { *sp = asin(*sp); }
void oacos(void) { *sp = acos(*sp); }
void oatan(void) { *sp = atan(*sp); }
void osqrt(void) { *sp = sqrt(*sp); }
void olog(void) { *sp = log10(*sp); }
void oln(void) { *sp = log(*sp); }

struct Operator {
	char *s;
	char type;
	char rassoc;
	short prec;
	void (*f)(void);
} ops[] = {
	"+",	OBINARY,	0,	0,	add,
	"-",	OBINARY,	0,	0,	sub,
	"*",	OBINARY,	0,	100,	mul,
	"/",	OBINARY,	0,	100,	div,
	"^",	OBINARY,	1,	200,	pot,
	"sin",	OUNARY,		0,	50,	osin,
	"cos",	OUNARY,		0,	50,	ocos,
	"tan",	OUNARY,		0,	50,	otan,
	"asin",	OUNARY,		0,	50,	oasin,
	"acos",	OUNARY,		0,	50,	oacos,
	"atan",	OUNARY,		0,	50,	oatan,
	"sqrt",	OUNARY,		0,	50,	osqrt,
	"log",	OUNARY,		0,	50,	olog,
	"ln",	OUNARY,		0,	50,	oln,
};

struct Constant {
	char *s;
	double val;
} consts[] = {
	"pi",	3.14159265359,
	"π",	3.14159265359,
	"e",	2.71828182846,
};

struct Code {
	Op* p;
	int len, cap;
} *fns;
int nfns;

Token *opstackbot;
double xmin = -10, xmax = 10;
double ymin = -10, ymax = 10;

void *
emalloc(int size)
{
	void *v;
	
	v = mallocz(size, 1);
	if(v == nil)
		sysfatal("emalloc: %r");
	setmalloctag(v, getcallerpc(&size));
	return v;
}

void
addop(Code *c, Op o)
{
	if(c->len >= c->cap) {
		c->cap += 32;
		c->p = realloc(c->p, sizeof(Op) * c->cap);
		if(c->p == nil)
			sysfatal("realloc: %r");
	}
	c->p[c->len++] = o;
}

void
push(Token *t)
{
	t->next = opstackbot;
	opstackbot = t;
}

void
pop(Code *c)
{
	Token *t;
	Op o;
	
	t = opstackbot;
	if(t == nil)
		sysfatal("stack underflow");
	opstackbot = t->next;
	if(t->type != TOP)
		sysfatal("non-operator pop");
	o.type = t->op->type;
	o.f = t->op->f;
	addop(c, o);
	free(t);
}

void
popdel(void)
{
	Token *t;
	
	t = opstackbot;
	opstackbot = t->next;
	free(t);
}

Token *
lex(char **s)
{
	Token *t;
	Operator *o;
	Constant *c;

	while(isspace(**s))
		(*s)++;
	if(**s == 0)
		return nil;
	
	t = emalloc(sizeof(*t));
	if(isdigit(**s)) {
		t->type = TNUMBER;
		t->val = strtod(*s, s);
		return t;
	}
	if(**s == '(') {
		t->type = TPARENL;
		(*s)++;
		return t;
	}
	if(**s == ')') {
		t->type = TPARENR;
		(*s)++;
		return t;
	}
	if(**s == 'x') {
		t->type = TVAR;
		(*s)++;
		return t;
	}
	for(o = ops; o < ops + nelem(ops); o++)
		if(strncmp(*s, o->s, strlen(o->s)) == 0) {
			t->type = TOP;
			t->op = o;
			*s += strlen(o->s);
			return t;
		}
	for(c = consts; c < consts + nelem(consts); c++)
		if(strncmp(*s, c->s, strlen(c->s)) == 0) {
			t->type = TNUMBER;
			t->val = c->val;
			*s += strlen(c->s);
			return t;
		}
	sysfatal("syntax error at %s", *s);
	return nil;
}

void
parse(Code *c, char *s)
{
	Token *t;
	Op o;
	
	while(t = lex(&s)) {
		switch(t->type) {
		case TNUMBER:
			o.type = ONUMBER;
			o.val = t->val;
			addop(c, o);
			free(t);
			break;
		case TVAR:
			o.type = OVAR;
			addop(c, o);
			free(t);
			break;
		case TOP:
			if(t->op->type == OBINARY)
				while(opstackbot != nil && opstackbot->type == TOP &&
					(opstackbot->op->prec > t->op->prec ||
					t->op->rassoc && opstackbot->op->prec == t->op->prec))
					pop(c);
			push(t);
			break;
		case TPARENL:
			push(t);
			break;
		case TPARENR:
			while(opstackbot != nil && opstackbot->type == TOP)
				pop(c);
			if(opstackbot == nil)
				sysfatal("mismatched parentheses");
			popdel();
			free(t);
			break;
		default:
			sysfatal("unknown token type %d", t->type);
		}
	}
	while(opstackbot != nil)
		switch(opstackbot->type) {
		case TOP:
			pop(c);
			break;
		case TPARENL:
			sysfatal("mismatched parentheses");
		default:
			sysfatal("syntax error");
		}
}

int
calcstack(Code *c)
{
	int cur, max;
	Op *o;
	
	cur = 0;
	max = 0;
	for(o = c->p; o < c->p + c->len; o++)
		switch(o->type) {
		case ONUMBER: case OVAR:
			if(++cur > max)
				max = cur;
			break;
		case OUNARY:
			if(cur == 0)
				sysfatal("syntax error");
			break;
		case OBINARY:
			if(cur <= 1)
				sysfatal("syntax error");
			cur--;
			break;
		}

	if(cur != 1)
		sysfatal("syntax error");
	return max;
}

double
calc(Code *c, double x)
{
	Op *o;
	
	sp = stack - 1;
	for(o = c->p; o < c->p + c->len; o++)
		switch(o->type) {
		case ONUMBER:
			*++sp = o->val;
			break;
		case OVAR:
			*++sp = x;
			break;
		case OUNARY: case OBINARY:
			o->f();
		}
	return *sp;
}

double
convx(Image *i, int x)
{
	return (xmax - xmin) * (x - i->r.min.x) / (i->r.max.x - i->r.min.x) + xmin;
}

int
deconvx(Image *i, double dx)
{
	return (dx - xmin) * (i->r.max.x - i->r.min.x) / (xmax - xmin) + i->r.min.x + 0.5;
}

double
convy(Image *i, int y)
{
	return (ymax - ymin) * (i->r.max.y - y) / (i->r.max.y - i->r.min.y) + ymin;
}

int
deconvy(Image *i, double dy)
{
	return (ymax - dy) * (i->r.max.y - i->r.min.y) / (ymax - ymin) + i->r.min.y + 0.5;
}

void
drawinter(Code *co, Image *i, Image *c, double x1, double x2, int n)
{
	double y1, y2;
	int iy1, iy2;
	int ix1, ix2;

	ix1 = deconvx(i, x1);
	ix2 = deconvx(i, x2);
	iy1 = iy2 = 0;
	y1 = calc(co, x1);
	if(!isNaN(y1)) {
		iy1 = deconvy(i, y1);
		draw(i, Rect(ix1, iy1, ix1 + 1, iy1 + 1), c, nil, ZP);
	}
	y2 = calc(co, x2);
	if(!isNaN(y2)) {
		iy2 = deconvy(i, y2);
		draw(i, Rect(ix2, iy2, ix2 + 1, iy2 + 1), c, nil, ZP);
	}
	if(!isNaN(y1) && !isNaN(y2) && (iy2 < iy1 - 1 || iy2 > iy1 + 1) && n < 10) {
		drawinter(co, i, c, x1, (x1 + x2) / 2, n + 1);
		drawinter(co, i, c, (x1 + x2) / 2, x2, n + 1);
	}
}

void
drawgraph(Code *co, Image *i, Image *c)
{
	int x;
	
	for(x = i->r.min.x; x < i->r.max.x; x++)
		drawinter(co, i, c, convx(i, x), convx(i, x + 1), 0);
}

void
drawgraphs(void)
{
	int i;
	
	for(i = 0; i < nfns; i++)
		drawgraph(&fns[i], screen, display->black);
	flushimage(display, 1);
}

void
usage(void)
{
	fprint(2, "usage: fplot function\n");
	exits("usage");
}

void
zoom(void)
{
	Mouse m;
	Rectangle r;
	double xmin_, xmax_, ymin_, ymax_;
	
	m.buttons = 7;
	r = egetrect(1, &m);
	if(r.min.x == 0 && r.min.y == 0 && r.max.x == 0 && r.max.y == 0)
		return;
	xmin_ = convx(screen, r.min.x);
	xmax_ = convx(screen, r.max.x);
	ymin_ = convy(screen, r.max.y);
	ymax_ = convy(screen, r.min.y);
	xmin = xmin_;
	xmax = xmax_;
	ymin = ymin_;
	ymax = ymax_;
	draw(screen, screen->r, display->white, nil, ZP);
	drawgraphs();
}

void
parsefns(int n, char **s)
{
	int i, max, cur;

	max = 0;
	nfns = n;
	fns = emalloc(sizeof(*fns) * n);
	for(i = 0; i < nfns; i++) {
		parse(&fns[i], s[i]);
		cur = calcstack(&fns[i]);
		if(cur > max)
			max = cur;
	}
	stack = emalloc(sizeof(*stack) * max);
}

void
main(int argc, char **argv)
{
	Event e;

	if(argc < 2)
		usage();
	setfcr(getfcr() & ~(FPZDIV | FPINVAL));
	parsefns(argc - 1, argv + 1);
	if(initdraw(nil, nil, "fplot") < 0)
		sysfatal("initdraw: %r");
	einit(Emouse | Ekeyboard);
	drawgraphs();
	for(;;) {
		switch(event(&e)) {
		case Ekeyboard:
			switch(e.kbdc) {
			case 'q': exits(nil);
			case 'z': zoom();
			}
		}
	}
}

void
eresized(int new)
{
	if(new) {
		if(getwindow(display, Refnone) < 0)
			sysfatal("getwindow: %r");
		drawgraphs();
	}
}