/*
 *  Parse and validate C declarations.
 *  Copyright © 2011-2012 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 <assert.h>
#include <stdbool.h>

#include "cdecl.h"
#include "typemap.h"
#include "parse.h"
#include "scan.h"
#include "i18n.h"
#include "normalize.h"

/*
 * Verify the declaration specifiers of a declaration.  If top is true, treat
 * this as a top-level declaration.  Otherwise, treat this as a function
 * parameter (which carries additional constraints).
 */
static bool valid_declspecs(struct cdecl *decl, bool top)
{
	struct cdecl_declspec *specs = decl->specifiers;
	struct cdecl_declarator *d   = decl->declarators;
	bool abstract = cdecl_is_abstract(d);
	unsigned num_storage = 0;
	unsigned long typemap;

	typemap = cdecl__build_typemap(specs);
	if (typemap == -1)
		return false;

	for (struct cdecl_declspec *c = specs; c; c = c->next) {
		switch (cdecl_spec_kind(c)) {
		case CDECL_SPEC_TYPE:
			if (c->type == CDECL_TYPE_VOID &&
			    (d->type == CDECL_DECL_IDENT
		             || d->type == CDECL_DECL_ARRAY)) {
				fprintf(stderr, "invalid declaration of type void\n");
				return false;
			}
			continue;
		case CDECL_SPEC_STOR:
			if (top && abstract) {
				fprintf(stderr, "type names cannot have storage-class specifiers\n");
				return false;
			}

			if (!top && c->type != CDECL_STOR_REGISTER) {
				fprintf(stderr, "function parameters may only have register storage\n");
				return false;
			}

			if (++num_storage > 1) {
				fprintf(stderr, "too many storage-class specifiers\n");
				return false;
			}
			break;
		case CDECL_SPEC_QUAL:
			/*
			 * Restrict qualifiers are only valid in the
			 * pointer qualifier list, which isn't checked here.
			 */
			if (c->type == CDECL_QUAL_RESTRICT) {
				fprintf(stderr, "only pointer types can be restrict-qualified.\n");
				return false;
			}
			break;
		case CDECL_SPEC_FUNC:
			if (abstract) {
				fprintf(stderr, "type names cannot have function specifiers\n");
				return false;
			}

			if (!top || d->type != CDECL_DECL_FUNCTION) {
				fprintf(stderr, "only function declarations may have function specifiers.\n");
				return false;
			}
			break;
		default:
			assert(0);
		}
	}

	return true;
}

/*
 * The C grammar leaves ambiguous some cases where parentheses represent a
 * function declarator or just parentheses.  The language uses additional
 * context (whether or not a typedef is in scope, etc.) to resolve these
 * ambiguities, but we don't have access to that kind of information.
 *
 * The cdecl99 parser uses an unambiguous grammar which treats almost
 * everything as a function, and thus considers things like 'int (x)' to
 * be a function type with a single parameter of type 'x' (a typedef name),
 * returning int.  This can result in very complicated types for simple
 * declarations.  Ideally, cdecl99 should try and find the "simplest"
 * explanation for a given declaration.
 *
 * Whether or not it achieves the simplest explanation, we apply a simple rule:
 * if a declarator could be interpreted as something other than a function,
 * do that.
 *
 *   - The function declarator has a null child declarator.
 *   - The function declarator has exactly one parameter, and is not variadic.
 *   - The function parameter has a type specifier, and it is a typedef name.
 *   - The function parameter has no other declaration specifiers.
 *   - The function parameter does not declare an identifier.
 *
 * Since cdecl99 supports things like [*] in any context (in C, such constructs
 * are only valid in function parameter lists), we don't treat them specially
 * here.
 */

static struct cdecl_declarator *reduce_function(struct cdecl *param)
{
	struct cdecl_declspec   *spec = param->specifiers;
	struct cdecl_declarator *decl = param->declarators;
	struct cdecl_declarator *last;

	for (last = decl; last && last->type != CDECL_DECL_NULL;)
		last = last->child;

	if (!last)
		return NULL;

	last->type = CDECL_DECL_IDENT;
	last->u.ident = spec->ident;
	free(param);
	free(spec);

	return decl;
}

static bool function_is_reducible(struct cdecl_declarator *d)
{
	if (d->type != CDECL_DECL_FUNCTION)
		return false;
	if (d->child->type != CDECL_DECL_NULL)
		return false; /* e.g., int (*)(x) */

	if (!d->u.function.parameters)
		return false; /* e.g., int f() */
	if (d->u.function.parameters->next)
		return false; /* e.g., int (x, y) */
	if (d->u.function.variadic)
		return false; /* e.g., int (x, ...) */

	if (d->u.function.parameters->specifiers->type != CDECL_TYPE_IDENT)
		return false; /* e.g. int (int) */
	if (d->u.function.parameters->specifiers->next)
		return false; /* e.g. int (size_t const) */

	return true;
}

static int
simplify_functions(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl_declarator *new;

	if (!function_is_reducible(d))
		return 0;

	new = reduce_function(d->u.function.parameters);
	if (!new)
		return 0; /* e.g. int (foo bar) */
	*p = new;
	free(d->child);
	free(d);

	return 1;
}

/*
 * The parser's bias towards considering things as functions whenever possible
 * makes nested parentheses tricky.  (x) is considered to be part of a function
 * declarator until simplify_functions converts it.  The problem is that
 * (((x))) is not valid as part of a function declarator, but it *is* valid
 * as an identifier enclosed 3 times in parentheses.  This is complicated by
 * the fact that things like (((int))) are not valid anywhere.
 *
 * To avoid ambiguities, the parser actually emits a "function" declarator for
 * every pair of parentheses.  The ones that can't reasonably be functions
 * consist of a single "parameter" with no declaration specifiers (note that
 * every valid function parameter will have at least one type specifier).
 *
 * This pass is to remove these fake functions from the parse tree.  We take
 * care to avoid turning invalid things like ((int)) into valid things like
 * (int) by observing that the only valid function declarators that appear
 * in these "fake" parentheses are those that have a non-null child declarator
 * (for instance, int ((*)(int)) *or* those that will be eliminated by the
 * simplify_functions pass.
 */

static int
reduce_parentheses(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl *param;

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

	param = d->u.function.parameters;
	if (param && param->specifiers == NULL) {
		struct cdecl_declarator *decl;

		assert(!param->next);

		decl = param->declarators;
		if (decl->type == CDECL_DECL_NULL) {
			free(decl);
			free(param);
			d->u.function.parameters = NULL;
			return 0;
		}

		if (d->child->type != CDECL_DECL_NULL) {
			fprintf(stderr, "invalid function parameter\n");
			return -1;
		}

		free(d->child);
		free(param);
		free(d);
		*p = decl;

		/*
		 * We may have replaced d with another fake function which
		 * also needs to be eliminated.
		 */
		if (reduce_parentheses(p, decl) < 0)
			return -1;

		/*
		 * If the remaining declarator is a function, make sure it's
		 * valid by checking its reducibility.
		 */
		decl = *p;
		if (decl->type == CDECL_DECL_FUNCTION
		    && decl->child->type == CDECL_DECL_NULL
		    && !function_is_reducible(decl)) {
			fprintf(stderr, "too many parentheses in function\n");
			return -1;
		}

		return 1;
	}

	return 0;
}

/*
 * Function parameters and return types have a few restrictions that are
 * really easy to check in comparison to the above absurdity.
 */
static int
check_parameters(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl_declspec *spec;
	struct cdecl *param;
	bool has_void = false;

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

	for (param = d->u.function.parameters; param; param = param->next) {
		if (!valid_declspecs(param, false))
			return -1;

		/* Check for "void" function parameters as a special case. */
		for (spec = param->specifiers; spec; spec = spec->next) {
			if (param->declarators->type != CDECL_DECL_NULL)
				continue;
			if (spec->type != CDECL_TYPE_VOID)
				continue;

			if (spec != param->specifiers || spec->next != NULL) {
				fprintf(stderr, "void parameter must not have extra specifiers\n");
				return -1;
			} else if (d->u.function.parameters->next) {
				fprintf(stderr, "a void parameter must stand alone\n");
				return -1;
			} else if (d->u.function.variadic) {
				fprintf(stderr, "variadic functions cannot have a void parameter\n");
				return -1;
			}
		}
	}

	return 0;
}

/*
 * Functions cannot return arrays or functions.  Since the parse tree is
 * "inside-out", we need to look for functions as the child declarator.
 */
static int
check_rettypes(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	if (!d->child || d->child->type != CDECL_DECL_FUNCTION)
		return 0;

	switch (d->type) {
	case CDECL_DECL_FUNCTION:
		fprintf(stderr, "functions cannot return functions\n");
		return -1;
	case CDECL_DECL_ARRAY:
		fprintf(stderr, "functions cannot return arrays\n");
		return -1;
	}

	return 0;
}

static int
check_arrays(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	if (!d->child || d->child->type != CDECL_DECL_ARRAY)
		return 0;

	switch (d->type) {
	case CDECL_DECL_FUNCTION:
		fprintf(stderr, "array members cannot be functions\n");
		return -1;
	}

	return 0;
}

static int
normalize_specs(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl_function *func;
	struct cdecl_pointer *ptr;

	switch (d->type) {
	case CDECL_DECL_POINTER:
		ptr = &d->u.pointer;
		ptr->qualifiers = cdecl__normalize_specs(ptr->qualifiers);
		break;
	case CDECL_DECL_FUNCTION:
		func = &d->u.function;
		for (struct cdecl *i = func->parameters; i; i = i->next)
			i->specifiers = cdecl__normalize_specs(i->specifiers);
		break;
	}

	return 0;
}

static int
check_qualifiers(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl_declspec *spec;
	struct cdecl_pointer *ptr;

	if (!d->child || d->child->type != CDECL_DECL_POINTER)
		return 0;

	ptr = &d->child->u.pointer;
	for (spec = ptr->qualifiers; spec; spec = spec->next) {
		if (spec->type == CDECL_QUAL_RESTRICT
		    && d->type == CDECL_DECL_FUNCTION) {
			fprintf(stderr, "function pointers cannot be restrict-qualified\n");
			return -1;
		}
	}

	return 0;
}

/*
 * Traverse the parse tree, calling a function on every declarator in a
 * depth-first preorder traversal.  The function is given a pointer to the
 * declarator as well as to the pointer which was used to reach that
 * declarator: this can be used to rewrite entire subtrees.
 */
static bool forall_declarators(struct cdecl *decl,
	int f(struct cdecl_declarator **, struct cdecl_declarator *))
{
	struct cdecl_declarator *d, **p;

	for (p = &decl->declarators, d = *p; d; p = &d->child, d = *p) {
		switch (f(p, d)) {
		case 0:
			break;
		case 1:
			d = *p;
			break;
		case -1:
			return false;
		default:
			assert(0);
		}

		if (d->type == CDECL_DECL_FUNCTION) {
			struct cdecl *i;

			for (i = d->u.function.parameters; i; i = i->next) {
				if (!forall_declarators(i, f))
					return false;
			}
		}
	}

	return true;
}

struct cdecl *cdecl_parse_decl(const char *declstr)
{
	struct cdecl_declspec *norm_specs;
	YY_BUFFER_STATE state;
	yyscan_t scanner;
	struct cdecl *decl;
	int rc;

	cdecl__init_i18n();

	rc = cdecl__yylex_init(&scanner);
	if (rc != 0)
		return NULL;

	state = cdecl__yy_scan_string(declstr, scanner);
	rc = cdecl__yyparse(scanner, &decl);
	cdecl__yy_delete_buffer(state, scanner);
	cdecl__yylex_destroy(scanner);

	if (rc != 0)
		return NULL;

	/*
	 * Since the top-level specifiers are shared between each top-level
	 * declarator, we need to normalize them once and then propagate the
	 * new specifier list.
	 */
	norm_specs = cdecl__normalize_specs(decl->specifiers);

	for (struct cdecl *i = decl; i; i = i->next) {
		i->specifiers = norm_specs;

		if (!forall_declarators(i, reduce_parentheses))
			goto err;
		if (!forall_declarators(i, simplify_functions))
			goto err;
		if (!forall_declarators(i, check_parameters))
			goto err;
		if (!forall_declarators(i, check_rettypes))
			goto err;
		if (!forall_declarators(i, check_arrays))
			goto err;
		if (!forall_declarators(i, normalize_specs))
			goto err;
		if (!forall_declarators(i, check_qualifiers))
			goto err;

		if (!valid_declspecs(i, true))
			goto err;

		if (cdecl_is_abstract(i->declarators)
		    && (i != decl || i->next)) {
			fprintf(stderr, "mixing type names and declarations is not allowed\n");
			goto err;
		}
	}

	return decl;
err:
	cdecl__free(decl);
	return NULL;
}

struct cdecl *cdecl_parse_english(const char *english)
{
	YY_BUFFER_STATE state;
	yyscan_t scanner;
	struct cdecl *decl;
	int rc;

	cdecl__init_i18n();

	rc = cdecl__yylex_init_extra(true, &scanner);
	if (rc != 0)
		return NULL;

	state = cdecl__yy_scan_string(english, scanner);
	rc = cdecl__yyparse(scanner, &decl);
	cdecl__yy_delete_buffer(state, scanner);
	cdecl__yylex_destroy(scanner);

	if (rc != 0)
		return NULL;

	for (struct cdecl *i = decl; i; i = i->next) {
		i->specifiers = cdecl__normalize_specs(i->specifiers);

		if (!forall_declarators(i, check_parameters))
			goto err;
		if (!forall_declarators(i, check_rettypes))
			goto err;
		if (!forall_declarators(i, check_arrays))
			goto err;
		if (!forall_declarators(i, normalize_specs))
			goto err;
		if (!forall_declarators(i, check_qualifiers))
			goto err;

		if (!valid_declspecs(i, true))
			goto err;
	}

	return decl;
err:
	cdecl__free(decl);
	return NULL;
}

void cdecl_free(struct cdecl *decl)
{
	cdecl__free(decl);
}