/* SPDX-License-Identifier: GPL-2.0 */

/**
 * \file mp.h Internal mood parser API (backend).
 *
 * This header is included from the lexer, the parser, and from \ref mp.c, but
 * not from \ref mood.c, the only user of the mood parser front end. It
 * contains structures and function prototypes which are considered
 * implementation details.
 *
 * There is one function for each keyword in the context-free grammar of the
 * parser. These functions return the semantic value of the keyword.
 *
 * The functions declared here are defined either in mp.c or in mp.y.
 */

/** Opaque, only known to mp.c. Passed to the generated mp_yyparse(). */
struct mp_context;

/**
 * Since we use a reentrant lexer, all functions generated by flex(1)
 * receive an additional argument of this type.
 */
typedef void *mp_yyscan_t;

/** Parsed regex pattern. */
struct mp_re_pattern {
	regex_t preg; /**< Pre-compiled regex. **/
	unsigned flags; /**< Subset of the cflags described in regex(3). */
};

/** Parsed wildcard pattern. */
struct mp_wc_pattern {
	char *pat; /**< Unescaped C string (without quotes and flags). */
	unsigned flags; /**< For modifying matching behaviour. */
};

/**
 * The possible values of a node in the abstract syntax tree (AST).
 *
 * Constant semantic values (string literals, numeric constants, wildcard and
 * regex patterns which are part of the mood definition) are determined during
 * \ref mp_init() while values which depend on the audio file (path, bitrate,
 * etc.) are determined during mp_eval_row().
 *
 * This union, and the \ref mp_ast_node structure below are used extensively in
 * mp.y. However, both need to be public because the lexer must be able to
 * create AST nodes for the constant semantic values.
 */
union mp_semantic_value {
	bool boolval; /**< Comparators, =~ and =|. */
	char *strval; /**< String literals, tags, path. */
	int64_t intval; /**< Constants, bitrate, frequency, etc. */
	struct mp_wc_pattern wc_pattern; /**< Right-hand side operand of =|. */
	struct mp_re_pattern re_pattern; /**< Right-hand side operand of =~. */
};

/**
 * Describes one node of the abstract syntax tree.
 *
 * A node is either interior or a leaf node. Interior nodes have at least one
 * child while leaf nodes have a semantic value and no children.
 *
 * Examples: (a) STRING_LITERAL has a semantic value (the unescaped string
 * literal) and no children, (b) NEG (unary minus) has no semantic value but
 * one child (the numeric expression that is to be negated), (c) LESS_OR_EQUAL
 * has no semantic value and two children (the two numeric expressions being
 * compared).
 */
struct mp_ast_node {
	/** Corresponds to a token type, for example LESS_OR_EQUAL. */
	int id;
	union {
		/** Pointers to the child nodes (interior nodes only). */
		struct mp_ast_node **children;
		/** Leaf nodes only. */
		union mp_semantic_value sv;
	};
	/**
	 * The number of children is implicitly given by the id, but we include
	 * it here to avoid having to maintain a lookup table. The AST is
	 * usually small, so we can afford to waste a byte per node.
	 */
	uint8_t num_children;
};

/* Called from both the lexer and the parser. */
__printf_3_4 void mp_parse_error(int line, struct mp_context *ctx,
		const char *fmt, ...);

/* Helper functions for the lexer. */
unsigned parse_quoted_string(const char *src, const char quote_chars[2],
		char **result);
int mp_parse_regex_pattern(const char *src, struct mp_re_pattern *result);
void mp_parse_wildcard_pattern(const char *src, struct mp_wc_pattern *result);

/*
 * The functions below are implemented in mp.y. They are documented here
 * because mp.y is not doxyfied.
 */

/**
 * Allocate a new leaf node for the abstract syntax tree.
 *
 * \param id Initial value for the ->id field of the new node
 *
 * \return Pointer to a node whose ->num_children field is initialized to zero.
 * The caller is expected to initialize the ->sv field.
 */
struct mp_ast_node *mp_new_ast_leaf_node(int id);

/**
 * Evaluate an abstract syntax tree, starting at the root node.
 *
 * \param root As returned from \ref mp_init() via the context pointer.
 * \param ctx Contains the aft row to evaluate.
 *
 * \return True if the AST evaluates to true, a non-empty string, or a
 * non-zero number. False otherwise.
 *
 * \sa mp_eval_row().
 */
bool mp_eval_ast(struct mp_ast_node *root, struct mp_context *ctx);

/**
 * Deallocate an abstract syntax tree.
 *
 * This frees the memory occupied by the nodes of the AST, the child pointers
 * of the internal nodes and the (constant) semantic values of the leaf nodes
 * (string literals, unescaped wildcard patterns and pre-compiled regular
 * expressions).
 *
 * \param root It's OK to pass NULL here.
 */
void mp_free_ast(struct mp_ast_node *root);

/* Helper functions for the parser. */
bool mp_is_set(const char *attr, struct mp_context *ctx);
char *mp_path(struct mp_context *ctx);
int64_t mp_year(struct mp_context *ctx);
int64_t mp_num_attributes_set(struct mp_context *ctx);
int64_t mp_duration(struct mp_context *ctx);

/* Generated with MP_AFSI() */
/** \cond MP_AFSI */
int64_t mp_num_played(struct mp_context *ctx);
int64_t mp_image_id(struct mp_context *ctx);
int64_t mp_lyrics_id(struct mp_context *ctx);
/** \endcond */

/* Generated with MP_AFHI() */
/** \cond MP_AFHI */
int64_t mp_bitrate(struct mp_context *ctx);
int64_t mp_frequency(struct mp_context *ctx);
int64_t mp_channels(struct mp_context *ctx);
/** \endcond */

/* Generated with MP_TAG() */
/** \cond MP_TAG */
char *mp_artist(struct mp_context *ctx);
char *mp_title(struct mp_context *ctx);
char *mp_album(struct mp_context *ctx);
char *mp_comment(struct mp_context *ctx);
/** \endcond */