/* Copyright (c) 2002-2018 Pigeonhole authors, see the included COPYING file
 */

#include "lib.h"
#include "istream.h"
#include "failures.h"

#include "sieve-common.h"
#include "sieve-limits.h"
#include "sieve-script.h"
#include "sieve-lexer.h"
#include "sieve-parser.h"
#include "sieve-error.h"
#include "sieve-ast.h"

/*
 * Forward declarations
 */

static int
sieve_parser_recover(struct sieve_parser *parser,
		     enum sieve_token_type end_token);

/*
 * Parser object
 */

struct sieve_parser {
	pool_t pool;

	bool valid;

	struct sieve_script *script;

	struct sieve_error_handler *ehandler;

	const struct sieve_lexer *lexer;
	struct sieve_ast *ast;
};

struct sieve_parser *
sieve_parser_create(struct sieve_script *script,
		    struct sieve_error_handler *ehandler,
		    enum sieve_error *error_r)
{
	struct sieve_parser *parser;
	const struct sieve_lexer *lexer;

	lexer = sieve_lexer_create(script, ehandler, error_r);
	if (lexer != NULL) {
		pool_t pool = pool_alloconly_create("sieve_parser", 4096);

		parser = p_new(pool, struct sieve_parser, 1);
		parser->pool = pool;
		parser->valid = TRUE;

		parser->ehandler = ehandler;
		sieve_error_handler_ref(ehandler);

		parser->script = script;
		sieve_script_ref(script);

		parser->lexer = lexer;
		parser->ast = NULL;

		return parser;
	}

	return NULL;
}

void sieve_parser_free(struct sieve_parser **parser)
{
	if ((*parser)->ast != NULL)
		sieve_ast_unref(&(*parser)->ast);

	sieve_lexer_free(&(*parser)->lexer);
	sieve_script_unref(&(*parser)->script);

	sieve_error_handler_unref(&(*parser)->ehandler);

	pool_unref(&(*parser)->pool);

	*parser = NULL;
}

/*
 * Internal error handling
 */

inline static void ATTR_FORMAT(4, 5)
sieve_parser_error(struct sieve_parser *parser,
		   const char *csrc_filename, unsigned int csrc_linenum,
		   const char *fmt, ...)
{
	struct sieve_error_params params = {
		.log_type = LOG_TYPE_ERROR,
		.csrc = {
			.filename = csrc_filename,
			.linenum = csrc_linenum,
		},
	};
	va_list args;

	va_start(args, fmt);

	/* Don't report a parse error if the lexer complained already */
	if (sieve_lexer_token_type(parser->lexer) != STT_ERROR) {
		T_BEGIN {
			params.location = sieve_error_script_location(
				parser->script,
				sieve_lexer_token_line(parser->lexer));
			sieve_logv(parser->ehandler, &params, fmt, args);
		} T_END;
	}

	parser->valid = FALSE;

	va_end(args);
}
#define sieve_parser_error(parser, ...) \
	sieve_parser_error(parser, __FILE__, __LINE__, __VA_ARGS__)

/*
 * Sieve grammar parsing
 */

/* sieve_parse_arguments():

   Parses both command arguments and sub-tests:
     arguments = *argument [test / test-list]
     argument = string-list / number / tag
     string = quoted-string / multi-line   [[implicitly handled in lexer]]
     string-list = "[" string *("," string) "]" / string         ;; if
       there is only a single string, the brackets are optional
     test-list = "(" test *("," test) ")"
     test = identifier arguments
 */
static int
sieve_parse_arguments(struct sieve_parser *parser, struct sieve_ast_node *node,
		      unsigned int depth)
{
	const struct sieve_lexer *lexer = parser->lexer;
	struct sieve_ast_node *test = NULL;
	bool test_present = TRUE;
	bool arg_present = TRUE;
	int result = 1; /* Indicates whether the parser is in a defined, not
	                    necessarily error-free state */

	/* Parse arguments */
	while (arg_present && result > 0) {
		struct sieve_ast_argument *arg;

		if (!parser->valid &&
		    !sieve_errors_more_allowed(parser->ehandler)) {
			result = 0;
			break;
		}

		switch (sieve_lexer_token_type(lexer)) {
		/* String list */
		case STT_LSQUARE:
			/* Create stinglist object */
			arg = sieve_ast_argument_stringlist_create(
				node, sieve_lexer_token_line(parser->lexer));
			if (arg == NULL) break;
			sieve_lexer_skip_token(lexer);

			if (sieve_lexer_token_type(lexer) == STT_STRING) {
				bool add_failed = FALSE;

				/* Add the string to the list */
				if (!sieve_ast_stringlist_add(
					arg, sieve_lexer_token_str(lexer),
					sieve_lexer_token_line(parser->lexer)))
					add_failed = TRUE;
				sieve_lexer_skip_token(lexer);

				while (!add_failed &&
				       sieve_lexer_token_type(lexer) == STT_COMMA) {
					sieve_lexer_skip_token(lexer);

					/* Check parser status */
					if (!parser->valid &&
					    !sieve_errors_more_allowed(parser->ehandler)) {
						result = sieve_parser_recover(parser, STT_RSQUARE);
						break;
					}

					if (sieve_lexer_token_type(lexer) == STT_STRING) {
						/* Add the string to the list */
						if (!sieve_ast_stringlist_add(
							arg, sieve_lexer_token_str(lexer),
							sieve_lexer_token_line(parser->lexer)))
							add_failed = TRUE;

						sieve_lexer_skip_token(lexer);
					} else {
						sieve_parser_error(parser,
							"expecting string after ',' in string list, "
							"but found %s",
							sieve_lexer_token_description(lexer));
						result = sieve_parser_recover(parser, STT_RSQUARE);
						break;
					}
				}

				if (add_failed) {
					sieve_parser_error(parser,
						"failed to accept more items in string list");
					return -1;
				}
			} else {
				sieve_parser_error(parser,
					"expecting string after '[' in string list, "
					"but found %s",
					sieve_lexer_token_description(lexer));
				result = sieve_parser_recover(parser, STT_RSQUARE);
			}

			/* Finish the string list */
			if (sieve_lexer_token_type(lexer) == STT_RSQUARE) {
				sieve_lexer_skip_token(lexer);
			} else {
				sieve_parser_error(parser,
					"expecting ',' or end of string list ']', "
					"but found %s",
					sieve_lexer_token_description(lexer));

				if ((result = sieve_parser_recover(parser, STT_RSQUARE)) > 0)
					sieve_lexer_skip_token(lexer);
			}
			break;
		/* Single string */
		case STT_STRING:
			arg = sieve_ast_argument_string_create(
				node, sieve_lexer_token_str(lexer),
				sieve_lexer_token_line(parser->lexer));
			sieve_lexer_skip_token(lexer);
			break;
		/* Number */
		case STT_NUMBER:
			arg = sieve_ast_argument_number_create(
				node, sieve_lexer_token_int(lexer),
				sieve_lexer_token_line(parser->lexer));
			sieve_lexer_skip_token(lexer);
			break;
		/* Tag */
		case STT_TAG:
			arg = sieve_ast_argument_tag_create(
				node, sieve_lexer_token_ident(lexer),
				sieve_lexer_token_line(parser->lexer));
			sieve_lexer_skip_token(lexer);
			break;
		/* End of argument list, continue with tests */
		default:
			arg_present = FALSE;
			break;
		}

		if (arg_present && arg == NULL) {
			sieve_parser_error(parser,
				"failed to accept more arguments for command '%s'",
				node->identifier);
			return -1;
		}

		if (sieve_ast_argument_count(node) > SIEVE_MAX_COMMAND_ARGUMENTS) {
			sieve_parser_error(parser,
				"too many arguments for command '%s'",
				node->identifier);
			return 0;
		}
	}

	if (result <= 0)
		return result; /* Defer recovery to caller */

	/* --> [ test / test-list ]
 	   test-list = "(" test *("," test) ")"
	   test = identifier arguments
	 */
	switch (sieve_lexer_token_type(lexer)) {
	/* Single test */
	case STT_IDENTIFIER:
		if ((depth + 1) > SIEVE_MAX_TEST_NESTING) {
			sieve_parser_error(parser,
				"cannot nest tests deeper than %u levels",
				SIEVE_MAX_TEST_NESTING);
			return 0;
		}

		test = sieve_ast_test_create(
			node, sieve_lexer_token_ident(lexer),
			sieve_lexer_token_line(parser->lexer));
		sieve_lexer_skip_token(lexer);

		/* Theoretically, test can be NULL */
		if (test == NULL)
			break;

		/* Parse test arguments, which may include more tests (recurse) */
		if (sieve_parse_arguments(parser, test, depth + 1) <= 0) {
			return 0; /* Defer recovery to caller */
		}

		break;

	/* Test list */
	case STT_LBRACKET:
		sieve_lexer_skip_token(lexer);

		if (depth+1 > SIEVE_MAX_TEST_NESTING) {
			sieve_parser_error(parser,
				"cannot nest tests deeper than %u levels",
				SIEVE_MAX_TEST_NESTING);
			result = sieve_parser_recover(parser, STT_RBRACKET);

			if (result > 0)
				sieve_lexer_skip_token(lexer);
			return result;
		}

		node->test_list = TRUE;

		/* Test starts with identifier */
		if (sieve_lexer_token_type(lexer) == STT_IDENTIFIER) {
			test = sieve_ast_test_create(
				node, sieve_lexer_token_ident(lexer),
				sieve_lexer_token_line(parser->lexer));
			sieve_lexer_skip_token(lexer);

			if (test == NULL)
				break;

			/* Parse test arguments, which may include more tests (recurse) */
			if ((result = sieve_parse_arguments(parser, test, depth+1)) > 0) {

				/* More tests ? */
				while (sieve_lexer_token_type(lexer) == STT_COMMA) {
					sieve_lexer_skip_token(lexer);

					/* Check parser status */
					if (!parser->valid &&
					    !sieve_errors_more_allowed(parser->ehandler)) {
						result = sieve_parser_recover(parser, STT_RBRACKET);
						break;
					}

					/* Test starts with identifier */
					if (sieve_lexer_token_type(lexer) == STT_IDENTIFIER) {
						test = sieve_ast_test_create(
							node, sieve_lexer_token_ident(lexer),
							sieve_lexer_token_line(parser->lexer));
						sieve_lexer_skip_token(lexer);

						if (test == NULL)
							break;

						/* Parse test arguments, which may include more tests (recurse) */
						if ((result = sieve_parse_arguments(parser, test, depth+1)) <= 0) {
							if (result < 0)
								return result;
							result = sieve_parser_recover(parser, STT_RBRACKET);
							break;
						}
					} else {
						sieve_parser_error(parser,
							"expecting test identifier after ',' in test list, "
							"but found %s",
							sieve_lexer_token_description(lexer));
						result = sieve_parser_recover(parser, STT_RBRACKET);
						break;
					}
				}
				if (test == NULL)
					break;
			} else {
				if (result < 0)
					return result;

				result = sieve_parser_recover(parser, STT_RBRACKET);
			}
		} else {
			sieve_parser_error(parser,
				"expecting test identifier after '(' in test list, "
				"but found %s",
				sieve_lexer_token_description(lexer));

			result = sieve_parser_recover(parser, STT_RBRACKET);
		}

		/* The next token should be a ')', indicating the end of the
		   test list
		     --> previous sieve_parser_recover calls try to restore this
			 situation after parse errors.
		 */
 		if (sieve_lexer_token_type(lexer) == STT_RBRACKET) {
			sieve_lexer_skip_token(lexer);
		} else {
			sieve_parser_error(parser,
				"expecting ',' or end of test list ')', "
				"but found %s",
				sieve_lexer_token_description(lexer));

			/* Recover function tries to make next token equal to
			   ')'. If it succeeds we need to skip it.
			 */
			if ((result = sieve_parser_recover(parser, STT_RBRACKET)) > 0)
				sieve_lexer_skip_token(lexer);
		}
		break;

	default:
		/* Not an error: test / test-list is optional
		     --> any errors are detected by the caller
		 */
		test_present = FALSE;
		break;
	}

	if (test_present && test == NULL) {
		sieve_parser_error(parser,
			"failed to accept more tests for command '%s'",
			node->identifier);
		return -1;
	}

	return result;
}

/* commands = *command
   command = identifier arguments ( ";" / block )
   block = "{" commands "}"
 */
static int
sieve_parse_commands(struct sieve_parser *parser, struct sieve_ast_node *block,
		     unsigned int depth)
{
	const struct sieve_lexer *lexer = parser->lexer;
	int result = 1;

	while (result > 0 &&
	       sieve_lexer_token_type(lexer) == STT_IDENTIFIER) {
		struct sieve_ast_node *command;

		/* Check parser status */
		if (!parser->valid &&
		    !sieve_errors_more_allowed(parser->ehandler)) {
			result = sieve_parser_recover(parser, STT_SEMICOLON);
			break;
		}

		/* Create command node */
		command = sieve_ast_command_create(
			block, sieve_lexer_token_ident(lexer),
			sieve_lexer_token_line(parser->lexer));
		sieve_lexer_skip_token(lexer);

		if (command == NULL) {
			sieve_parser_error(parser,
				"failed to accept more commands inside the block of command '%s'",
				block->identifier);
			return -1;
		}

		result = sieve_parse_arguments(parser, command, 1);

		/* Check whether the command is properly terminated
		   (i.e. with ; or a new block)
		 */
		if (result > 0 &&
		    sieve_lexer_token_type(lexer) != STT_SEMICOLON &&
		    sieve_lexer_token_type(lexer) != STT_LCURLY) {

			sieve_parser_error(parser,
				"expected end of command ';' or the beginning of a compound block '{', "
				"but found %s",
				sieve_lexer_token_description(lexer));
			result = 0;
		}

		/* Try to recover from parse errors to reacquire a defined state
		 */
		if (result == 0)
			result = sieve_parser_recover(parser, STT_SEMICOLON);

		/* Don't bother to continue if we are not in a defined state */
		if (result <= 0)
			return result;

		switch (sieve_lexer_token_type(lexer)) {
		/* End of the command */
		case STT_SEMICOLON:
			sieve_lexer_skip_token(lexer);
			break;
		/* Command has a block {...} */
		case STT_LCURLY:
			sieve_lexer_skip_token(lexer);

			/* Check current depth first */
			if ((depth + 1) > SIEVE_MAX_BLOCK_NESTING) {
				sieve_parser_error(parser,
					"cannot nest command blocks deeper than %u levels",
					SIEVE_MAX_BLOCK_NESTING);
				result = sieve_parser_recover(parser, STT_RCURLY);

				if (result > 0)
					sieve_lexer_skip_token(lexer);
				break;
			}

			command->block = TRUE;

			if ((result = sieve_parse_commands(parser, command, depth + 1)) > 0) {
				if (sieve_lexer_token_type(lexer) != STT_RCURLY) {
					sieve_parser_error(parser,
						"expected end of compound block '}', "
						"but found %s",
						sieve_lexer_token_description(lexer));
					result = sieve_parser_recover(parser, STT_RCURLY);
				} else {
					sieve_lexer_skip_token(lexer);
				}
			} else {
				if (result < 0)
					return result;

				if ((result = sieve_parser_recover(parser, STT_RCURLY)) > 0)
					sieve_lexer_skip_token(lexer);
			}

			break;

		default:
			/* Recovered previously, so this cannot happen */
			i_unreached();
		}
	}

	return result;
}

bool sieve_parser_run(struct sieve_parser *parser, struct sieve_ast **ast)
{
	if (parser->ast != NULL)
		sieve_ast_unref(&parser->ast);

	/* Create AST object if none is provided */
	if (*ast == NULL)
		*ast = sieve_ast_create(parser->script);
	else
		sieve_ast_ref(*ast);

	parser->ast = *ast;

	/* Scan first token */
	sieve_lexer_skip_token(parser->lexer);

	/* Parse */
	if (sieve_parse_commands(parser, sieve_ast_root(parser->ast), 1) > 0 &&
	    parser->valid) {
		/* Parsed right to EOF ? */
		if (sieve_lexer_token_type(parser->lexer) != STT_EOF) {
			sieve_parser_error(parser,
				"unexpected %s found at (the presumed) end of file",
				sieve_lexer_token_description(parser->lexer));
			parser->valid = FALSE;
		}
	} else {
		parser->valid = FALSE;
	}

	/* Clean up AST if parse failed */
	if (!parser->valid) {
		parser->ast = NULL;
		sieve_ast_unref(ast);
	}

	return parser->valid;
}

/* Error recovery:
     To continue parsing after an error it is important to find the next
     parsible item in the stream. The recover function skips over the remaining
     garbage after an error. It tries  to find the end of the failed syntax
     structure and takes nesting of structures into account.
 */

/* Assign useful names to priorities for readability */
enum sieve_grammatical_prio {
	SGP_BLOCK = 3,
	SGP_COMMAND = 2,
	SGP_TEST_LIST = 1,
	SGP_STRING_LIST = 0,

	SGP_OTHER = -1
};

static inline enum sieve_grammatical_prio
__get_token_priority(enum sieve_token_type token)
{
	switch (token) {
	case STT_LCURLY:
	case STT_RCURLY:
		return SGP_BLOCK;
	case STT_SEMICOLON:
		return SGP_COMMAND;
	case STT_LBRACKET:
	case STT_RBRACKET:
		return SGP_TEST_LIST;
	case STT_LSQUARE:
	case STT_RSQUARE:
		return SGP_STRING_LIST;
	default:
		break;
	}

	return SGP_OTHER;
}

static int
sieve_parser_recover(struct sieve_parser *parser,
		     enum sieve_token_type end_token)
{
	/* The tokens that begin/end a specific block/command/list in order
 	   of ascending grammatical priority.
 	 */
 	static const enum sieve_token_type begin_tokens[4] = {
		STT_LSQUARE, STT_LBRACKET, STT_NONE, STT_LCURLY };
	static const enum sieve_token_type end_tokens[4] = {
		STT_RSQUARE, STT_RBRACKET, STT_SEMICOLON, STT_RCURLY};
	const struct sieve_lexer *lexer = parser->lexer;
	int nesting = 1;
	enum sieve_grammatical_prio end_priority =
		__get_token_priority(end_token);

	i_assert(end_priority != SGP_OTHER);

	while (sieve_lexer_token_type(lexer) != STT_EOF &&
	       __get_token_priority(sieve_lexer_token_type(lexer))
		<= end_priority) {
		if (sieve_lexer_token_type(lexer) ==
			begin_tokens[end_priority]) {
			nesting++;
			sieve_lexer_skip_token(lexer);
			continue;
		}
		if (sieve_lexer_token_type(lexer) ==
			end_tokens[end_priority]) {
			nesting--;

			if (nesting == 0) {
				/* Next character is the end */
				return 1;
			}
		}
		sieve_lexer_skip_token(lexer);
	}

	/* Special case: COMMAND */
	if (end_token == STT_SEMICOLON &&
	    sieve_lexer_token_type(lexer) == STT_LCURLY) {
		return 1;
	}

	/* End not found before eof or end of surrounding grammatical structure
	 */
	return 0;
}