#include <u.h>
#include <libc.h>
#include <bio.h>

#include "apl9.h"

#define traceprint if(traceeval)print

Rune *errormsg;
int traceeval;

typedef Datum (*evalfn)(Datum, Datum);

Datum strand(Datum, Datum);
Datum monadfun(Datum, Datum);
Datum dyadfun(Datum, Datum);
Datum lpar(Datum, Datum);
Datum rpar(Datum, Datum);
Datum nameis(Datum, Datum);
Datum assign(Datum, Datum);
Datum *lookup(Datum);

int bindingstrengths[15][15] = {
/*	A  F  H  MO DO AF (  )  {  }  [  ]  ←  IS N */
	4, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* A */
	2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* F */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* H */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* MO */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* DO */
	2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* AF */
	5, 5, 5, 5, 5, 5, 0, 6, 5, 5, 5, 5, 5, 5, 5, /* ( */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* ) */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* { */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* } */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* [ */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* ] */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* ← */
	1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* IS */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, /* N */
};

evalfn evalfns[15][15] = {
/*	A  F  H  MO DO AF (  )  {  }  [  ] ← IS N */
	strand, dyadfun, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* A */
	monadfun, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* F */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* H */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* MO */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* DO */
	monadfun, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* AF */
	lpar, lpar, lpar, lpar, lpar, 0, lpar, rpar, lpar, lpar, lpar, lpar, lpar, lpar, lpar, /* ( */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* ) */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* { */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* } */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* [ */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* ] */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* ← */
	assign, assign, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* IS */
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, nameis, 0, 0, /* N */	
};

Datum *
eval(Datum *tokens, int *ntoks)
{
	errormsg = nil;

	/* start by looking up first variable if needed */
	if(*ntoks > 0 && tokens[(*ntoks)-1].tag == NameTag){
		Datum *value = lookup(tokens[(*ntoks)-1]);
		if(value == nil)
			*ntoks = 0;
		else
			tokens[(*ntoks)-1] = *value;
	}

	while(*ntoks > 1){
		int maxlevel = 0;
		int offset;
		evalfn fn = nil;
		traceprint("CURRENT: %S\n", ppdatums(tokens, *ntoks));
		for(offset = (*ntoks)-1; offset >= 0; offset--){
			int level;
retry:
			if(offset == 0)
				level = 0;
			else{
				Datum left = tokens[offset-1];
				Datum right = tokens[offset];
				level = bindingstrengths[left.tag][right.tag];
			}

			if(level == 0 && tokens[offset-1].tag == NameTag){
				Datum *value = lookup(tokens[offset-1]);
				if(value == nil){
					*ntoks = 0;
					return tokens;
				}else{
					tokens[offset-1] = *value;
					goto retry;
				}
			}else if(level < maxlevel){
				Datum left = tokens[offset];
				Datum right = tokens[offset+1];
				fn = evalfns[left.tag][right.tag];
				traceprint("Reducing %S and %S (fn=%p, level=%d, max=%d)\n", ppdatum(left), ppdatum(right), fn, level, maxlevel);
				break;
			}else if(level > maxlevel)
				maxlevel = level;
		}
		if(maxlevel == 0){
			errormsg = L"No reduce rule. Syntax error.";
			*ntoks = 0;
		}else{
			tokens[offset] = fn(tokens[offset],tokens[offset+1]);
			for(int i = offset+1; i < (*ntoks)-1; i++)
				tokens[i] = tokens[i+1];
			(*ntoks)--;
		}
	}
	return tokens;
}

Datum *
lookup(Datum var)
{
	traceprint("VAR LOOKUP %S\n", var.symbol->name);
	if(var.symbol->undefined){
		errormsg = runesmprint("Variable undefined: %S\n", var.symbol->name);
		return nil;
	}else
		return &var.symbol->value;
}

Datum
strand(Datum left, Datum right)
{
	traceprint("Stranding (%d %d)\n", left.array->stranded, right.array->stranded);
	Datum result;
	Array *leftarr = left.array->stranded ? left.array : fnEnclose(left.array);
	Array *rightarr = right.array->stranded ? right.array : fnEnclose(right.array);
	result.tag = ArrayTag;
	result.array = fnCatenateFirst(leftarr, rightarr);
	result.array->stranded = 1;
	return result;
}

Datum
monadfun(Datum left, Datum right)
{
	traceprint("Monadic function application\n");
	Datum result;
	result.tag = ArrayTag;

	/* TODO handle undefined functions here */
	if(left.func.left)
		result.array = dyadfunctiondefs[left.func.code](left.func.left, right.array);
	else
		result.array = monadfunctiondefs[left.func.code](right.array);
	return result;
}

Datum
dyadfun(Datum left, Datum right)
{
	traceprint("Applying left argument to function\n");
	Datum result;
	result.tag = BoundFunctionTag,
	result.func = right.func;
	result.func.left = left.array;
	return result;
}

Datum
lpar(Datum left, Datum right)
{
	/* build up a parthenthesised expression */
	left.expr.ntoks++;
	left.expr.toks = realloc(left.expr.toks, sizeof(Datum) * left.expr.ntoks);
	left.expr.toks[left.expr.ntoks-1] = right;
	traceprint("LPAR: %S\n", ppdatums(left.expr.toks, left.expr.ntoks));
	return left;
}

Datum
rpar(Datum left, Datum right)
{
	/* evaluate a parenthesis expression and return the result */
	USED(right);
	traceprint("RPAR: %S\n", ppdatums(left.expr.toks, left.expr.ntoks));
	Datum *result = eval(left.expr.toks, &left.expr.ntoks);
	result[0].array->stranded = 0;
	return result[0]; /* TODO handle error if ntoks != 1 */
}

Datum
nameis(Datum left, Datum right)
{
	traceprint("NAME SYMBOL %p\n", left.symbol);
	traceprint("NAMEIS %S←\n", left.symbol->name);
	right.tag = AssignmentTag;
	right.symbol = left.symbol;
	return right;
}

Datum
assign(Datum left, Datum right)
{
	left.symbol->value = right; /* TODO think about this*/
	left.symbol->undefined = 0;
	if(left.symbol->value.tag == ArrayTag)
		left.symbol->value.array->stranded = 0;
	return right;
}