/*
 *  Render C declarations as English.
 *  Copyright © 2011, 2021, 2023 Nick Bowler
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <stdio.h>
#include <inttypes.h>
#include <assert.h>

#include "cdecl.h"
#include "cdecl-internal.h"

#define PRE_SPECS (CDECL_SPEC_FUNC|CDECL_SPEC_STOR)
#define POST_SPECS (CDECL_SPEC_QUAL|CDECL_SPEC_TYPE)

static size_t explain_specs(struct output_state *dst, struct cdecl_declspec *s, unsigned mask)
{
	size_t ret;

	ret = cdecl__emit_specs(dst, s, mask);
	return ret + cdecl__emit(dst, " " + !ret);
}

static size_t
explain_specs_post(struct output_state *dst, struct cdecl_declspec *s)
{
	return cdecl__emit_specs(dst, s, POST_SPECS);
}

/*
 * If declarator declares an identifier foo, then emit "foo as "; otherwise
 * emit nothing.
 */
static size_t
explain_name(struct output_state *dst, struct cdecl_declarator *d)
{
	size_t ret;

	while (d->child)
		d = d->child;

	if (d->type != CDECL_DECL_IDENT)
		return 0;

	ret = cdecl__emit(dst, d->u.ident);
	return ret + cdecl__emit(dst, " as ");
}

/*
 * For a pointer declarator, emit "[QUAL ]pointer to ", where
 * QUAL is the (possibly empty) list of qualifiers.
 */
static size_t
explain_pointer(struct output_state *dst, struct cdecl_pointer *p)
{
	size_t ret;

	ret = explain_specs(dst, p->qualifiers, -1);
	return ret + cdecl__emit(dst, "pointer to ");
}

/*
 * For an array declarator, emit "[variable-length ]array [X ]of ", where
 * for a variable-length array X is the (possibly omitted) identifier name,
 * and for normal arrays X is the (possibly omitted) length.
 */
static size_t
explain_array(struct output_state *dst, struct cdecl_array *a)
{
	size_t ret = 0, rc = 0;

	if (a->vla)
		ret += cdecl__emit(dst, "variable-length ");
	ret += cdecl__emit(dst, "array ");

	if (a->vla) {
		rc = cdecl__emit(dst, a->vla);
		ret += rc;
	} else {
		rc = snprintf(dst->dst, dst->dstlen, "%.0" PRIuMAX, a->length);
		ret += cdecl__advance(dst, rc);
	}

	return ret + cdecl__emit(dst, " of " + !rc);
}

static size_t
explain_declarators(struct output_state *dst, struct cdecl_declarator *decl);

static size_t explain_decl(struct output_state *dst, struct cdecl *decl)
{
	size_t ret;

	ret  = explain_name(dst, decl->declarators);
	ret += explain_specs(dst, decl->specifiers, PRE_SPECS);
	ret += explain_declarators(dst, decl->declarators);
	ret += explain_specs_post(dst, decl->specifiers);

	return ret;
}

/*
 * For a function declarator, emit "function [PARAM ]returning ", where
 * PARAM is the (omitted in the case of an empty non-prototype identifier
 * list) parameter or identifier lists enclosed in parentheses.
 */
static size_t
explain_function(struct output_state *dst, struct cdecl_function *f)
{
	size_t ret = 0;

	ret += cdecl__emit(dst, "function ");

	if (f->parameters) {
		struct cdecl *p;

		ret += cdecl__emit(dst, "(");

		for (p = f->parameters; p; p = p->next) {
			ret += explain_decl(dst, p);
			if (p->next)
				ret += cdecl__emit(dst, ", ");
		}

		if (f->variadic)
			ret += cdecl__emit(dst, ", ...) ");
		else
			ret += cdecl__emit(dst, ") ");
	}

	return ret + cdecl__emit(dst, "returning ");
}

static size_t
explain_declarators(struct output_state *dst, struct cdecl_declarator *d)
{
	size_t ret;

	if (d->type == CDECL_DECL_IDENT || d->type == CDECL_DECL_NULL)
		return 0;

	ret = explain_declarators(dst, d->child);

	switch (d->type) {
	case CDECL_DECL_POINTER:
		return ret + explain_pointer(dst, &d->u.pointer);
	case CDECL_DECL_ARRAY:
		return ret + explain_array(dst, &d->u.array);
	case CDECL_DECL_FUNCTION:
		return ret + explain_function(dst, &d->u.function);
	default:
		assert(0);
	}
}

size_t cdecl_explain(char *buf, size_t n, struct cdecl *decl)
{
	struct output_state dst = { buf, n };
	size_t ret;

	if (cdecl_is_abstract(decl->declarators))
		ret = cdecl__emit(&dst, "type ");
	else
		ret = cdecl__emit(&dst, "declare ");

	return ret + explain_decl(&dst, decl);
}