/// \file
/// POM configuration parser for C.
///
/// ## Thread-safety
///
/// Of course, you should not free or \ref pom_conf_merge into
/// a configuration while another thread is using it.
///
/// Otherwise, libpom is fully thread-safe
/// provided that C11 atomics are available
/// (`__STDC_VERSION__ >= 201112L && !defined(__STDC_NO_ATOMICS__)`).
/// But beware of race conditions when using \ref pom_conf_next_unread_key
/// — this will not lead to UB but you may get unexpected results —
/// ensure there is synchronization so that all threads
/// have certainly read their keys before calling it.
///
/// If C11 atomics are not available, you can almost certainly still get away
/// with sharing configurations across threads, as long as you use proper
/// synchronization for \ref pom_conf_next_unread_key.
/// (Essentially, libpom may end up writing the same value to the same address
///  from separate threads, which is *technically* undefined behaviour, but will
///  likely never be an issue on any real machine.)
/// Even if you are extremely paranoid, you can still use
/// distinct configurations in different threads without worry.
///
/// ## Notes
///
/// Every libpom function may change the value of `errno` arbitrarily
/// (its value after any libpom call should be ignored).

/// \mainpage libpom doxygen documentation
///
/// See \ref pom.h for all types/functions.
#ifndef POM__H_
#define POM__H_

#ifndef POM_NO_STDIO
#include <stdio.h>
#endif
#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>

#ifdef __cplusplus
extern "C" {
#endif

#ifndef POM__MUST_USE_L
	#if _MSC_VER >= 1700 // supposedly was added in VS2012
		#define POM__MUST_USE_L _Check_return_
	#else
		#define POM__MUST_USE_L
	#endif
#endif
#ifndef POM__MUST_USE_R
	#if __GNUC__ >= 4
		#define POM__MUST_USE_R __attribute__((warn_unused_result))
	#else
		#define POM__MUST_USE_R
	#endif
#endif

/// A POM configuration
typedef struct pom_conf pom_conf;

/// A POM-related error
typedef struct pom_error pom_error;

/// An opaque iterator produced by \ref pom_conf_next_unread_key.
typedef struct pom_unread_key_iter pom_unread_key_iter;

/// An opaque iterator produced by \ref pom_conf_next_item.
typedef struct pom_item_iter pom_item_iter;

/// An opaque iterator produced by \ref pom_conf_next_key.
typedef struct pom_key_iter pom_key_iter;

/// Item returned by \ref pom_conf_next_item
typedef struct pom_item {
	/// The key.
	///
	/// This pointer is valid until \ref pom_conf_free is called.
	const char *key;
	/// The value of the key.
	///
	/// This pointer is valid until \ref pom_conf_free is called.
	const char *value;
	/// The file where the key was defined.
	///
	/// This pointer is valid until \ref pom_conf_free is called.
	const char *file;
	/// The line number where the key was defined.
	uint64_t line;
} pom_item;

/// Settings for libpom.
///
/// Start by initializing this to zero,
/// then fill out only the fields you need.
typedef struct pom_settings {
	/// Data to pass to allocation functions.
	void *allocator_udata;
	/// calloc function to use for all purposes, or `NULL` to use libc `calloc`.
	void *(*calloc)(void *udata, size_t nmemb, size_t sz);
	/// realloc function to use for all purposes, or `NULL` to use libc `realloc`.
	void *(*realloc)(void *udata, void *ptr, size_t new_sz);
	/// free function to use for all purposes, or `NULL` to use libc `free`.
	void (*free)(void *udata, void *ptr);
	/// Language for error messages.
	///
	/// Should be an IETF-style language tag.
	/// Closest-matching implemented language will be used (e.g. `"fr-CA"` will use `"fr"`),
	/// or else `"en"` if there are no matches.
	///
	/// Current supported languages: `en`, `fr`.
	char error_lang[16];
	/// Reserved for future use. Must be set to 0.
	void *reserved[4];
} pom_settings;

/// Load a configuration using a `read`-like function.
///
/// Most of the time, you won't need this function:
/// use \ref pom_load_file to load from a `FILE *`,
/// \ref pom_load_path to load from a path,
/// and \ref pom_load_string to load from a string.
///
/// `settings` can be `NULL`, in which case the default settings are used.
///
/// On success, a configuration is returned and `*error` is set to `NULL`
/// if `error` is not `NULL`.
///
/// On failure, `NULL` is returned, and `*error` is filled out if `error` is not `NULL`,
/// in which case it must be freed with `free`.
/// In the extremely rare case that `error` is not `NULL` and
/// there isn’t even enough memory for an out-of-memory
/// error, `NULL` is returned and `*error` is set to `NULL`.
///
/// `read_func` will be passed the `userdata` pointer passed to this function,
/// a buffer, and the length of that buffer (which will be nonzero).
/// It returns the number of bytes read, or 0 if the end of the file was reached.
/// It can fill out as much or as little of the buffer as it wants —
/// a short read count is not interpreted as the end of the file.
/// `read_func` will not be called excessively/with lots of tiny reads—it's
/// okay to do unbuffered reads in it.
///
/// `filename` is only used for errors.
POM__MUST_USE_L
pom_conf *
pom_load(const pom_settings *settings, const char *filename,
	size_t (*read_func)(void *userdata, char *buf, size_t len),
	void *userdata, pom_error **error)
POM__MUST_USE_R;

#ifndef POM_NO_STDIO
/// Load configuration from a `FILE *` opened in read-binary mode.
///
/// On success, a configuration is returned and `*error` is set to `NULL`
/// if `error` is not `NULL`.
///
/// On failure, `NULL` is returned, and `*error` is filled out if `error` is not `NULL`
/// (or set to `NULL` if no memory is available),
/// in which case it must be freed with `free`.
///
/// `filename` is only used for errors.
POM__MUST_USE_L
pom_conf *
pom_load_file(const pom_settings *settings, const char *filename, FILE *file, pom_error **error)
POM__MUST_USE_R;

/// Load configuration from a file path.
///
/// On success, a configuration is returned and `*error` is set to `NULL`
/// if `error` is not `NULL`.
///
/// On failure, `NULL` is returned, and `*error` is filled out if `error` is not `NULL`
/// (or set to `NULL` if no memory is available),
/// in which case it must be freed with `free`.
POM__MUST_USE_L
pom_conf *
pom_load_path(const pom_settings *settings, const char *path, pom_error **error)
POM__MUST_USE_R;
#endif

/// Load configuration from a string.
///
/// On success, a configuration is returned and `*error` is set to `NULL`
/// if `error` is not `NULL`.
///
/// On failure, `NULL` is returned, and `*error` is filled out if `error` is not `NULL`,
/// in which case it must be freed with `free`.
///
/// `filename` is only used for errors.
POM__MUST_USE_L
pom_conf *
pom_load_string(const pom_settings *settings, const char *filename, const char *string, pom_error **error)
POM__MUST_USE_R;

/// Get the message of this error.
///
/// This will be a string such as `"Duplicate key: foo.bar"`
///
/// Error messages may change arbitrarily in future versions.
///
/// The returned pointer is valid until the error is freed.
///
/// See also \ref pom_error_print and \ref pom_error_to_string, which
/// are probably actually what you want in most cases.
const char *
pom_error_message(const pom_error *error);

/// Get the name of the file where this error occured.
///
/// The returned pointer is valid until the error is freed.
const char *
pom_error_file(const pom_error *error);

/// Get line number where this error occured.
uint64_t
pom_error_line(const pom_error *error);

/// Get next error in error list, or `NULL` if this is the last error.
///
/// You can only call \ref pom_error_message, \ref pom_error_file, and \ref pom_error_line
/// on the returned error, not \ref pom_error_print or \ref pom_error_to_string.
/// (This is enforced with `const`-ness.)
const pom_error *
pom_error_next(const pom_error *error);

#ifndef POM_NO_STDIO
/// Print error to `stderr`.
///
/// Includes every error in an error list (see \ref pom_error_next).
void
pom_error_print(pom_error *error);
#endif

/// Convert error to string. Return value is valid until `error` is `free()`’d.
///
/// Includes every error in an error list (see \ref pom_error_next).
const char *
pom_error_to_string(pom_error *error);

/// Returns `true` if `key` is present in `conf`, `false` otherwise.
bool
pom_conf_has(const pom_conf *conf, const char *key);

/// Get location where `key` was defined in `conf`.
///
/// Returns `true` and sets `*file` and `*line` if the `key` is present.
/// The pointer which `*file` is set to is valid until \ref pom_conf_free is called.
///
/// Returns `false` and sets `*file = NULL`, `*line = 0` if `key` is not present.
///
/// Either of `file`, `line` may be `NULL`, in which case it is not set.
bool
pom_conf_location(const pom_conf *conf, const char *key, const char **file, uint64_t *line);

/// Get value of `key` in configuration, or `NULL` if key is not present.
///
/// The returned pointer is valid until \ref pom_conf_free is called.
const char *
pom_conf_get(const pom_conf *conf, const char *key);

/// Get value of `key` in configuration, or use `dflt` if not present.
///
/// The returned pointer is valid until \ref pom_conf_free is called.
const char *
pom_conf_get_or_default(const pom_conf *conf, const char *key, const char *dflt);

/// Get signed integer value of `key`.
///
/// Returns `NULL` on success, putting the integer value in `*value`.
///
/// If `key` is not set or is not a valid integer
/// (decimal or `0x`/`0X`-prefixed hexadecimal, absolute value less than 2<sup>53</sup>),
/// returns an error.
/// `*value` is set to 0 in these cases.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_int(const pom_conf *conf, const char *key, int64_t *value)
POM__MUST_USE_R;

/// Get signed integer value of `key`, or `dflt` if not present.
///
/// Returns `NULL` on success, putting the integer value in `*value`.
///
/// If `key` is set but not a valid integer
/// (decimal or `0x`/`0X`-prefixed hexadecimal, absolute value less than 2<sup>53</sup>),
/// returns an error.
/// `*value` is still set to `dflt` in this case.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_int_or_default(const pom_conf *conf, const char *key, int64_t *value, int64_t dflt)
POM__MUST_USE_R;

/// Get unsigned integer value of `key`.
///
/// Returns `NULL` on success, putting the unsigned integer value in `*value`.
///
/// If `key` is not set or is not a valid unsigned integer
/// (decimal or `0x`/`0X`-prefixed hexadecimal, less than 2<sup>53</sup>),
/// returns an error.
/// `*value` is set to 0 in these case cases.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_uint(const pom_conf *conf, const char *key, uint64_t *value)
POM__MUST_USE_R;

/// Get unsigned integer value of `key`, or `dflt` if not present.
///
/// Returns `NULL` on success, putting the unsigned integer value in `*value`.
///
/// If `key` is set but not a valid unsigned integer
/// (decimal or `0x`/`0X`-prefixed hexadecimal, less than 2<sup>53</sup>),
/// returns an error.
/// `*value` is set to 0 in this case.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_uint_or_default(const pom_conf *conf, const char *key, uint64_t *value, uint64_t dflt)
POM__MUST_USE_R;

/// Get floating-point value of `key`.
///
/// Returns `NULL` on success, putting the floating-point value in `*value`.
///
/// If `key` is not set or is set but not a valid floating-point number,
/// returns an error.
/// `*value` is set to 0.0 in this case.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_float(const pom_conf *conf, const char *key, double *value)
POM__MUST_USE_R;

/// Get floating-point value of `key`, or `dflt` if not present.
///
/// Returns `NULL` on success, putting the floating-point value in `*value`.
///
/// If `key` is set but not a valid floating-point number,
/// returns an error.
/// `*value` is still set to `dflt` in this case.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_float_or_default(const pom_conf *conf, const char *key, double *value, double dflt)
POM__MUST_USE_R;

/// Get boolean value of `key`.
///
/// Returns `NULL` on success, putting the boolean value in `*value`.
///
/// If `key` is not set or is set but not a valid boolean
/// (`off`/`false`/`no`/`on`/`true`/`yes`),
/// returns an error.
/// `*value` is set to `false` in this case.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_bool(const pom_conf *conf, const char *key, bool *value)
POM__MUST_USE_R;

/// Get boolean value of `key`, or `dflt` if not present.
///
/// Returns `NULL` on success, putting the boolean value in `*value`.
///
/// If `key` is set but not a valid boolean
/// (`off`/`false`/`no`/`on`/`true`/`yes`),
/// returns an error.
/// `*value` is still set to `dflt` in this case.
///
/// The returned error must be `free()`d.
POM__MUST_USE_L
pom_error *
pom_conf_get_bool_or_default(const pom_conf *conf, const char *key, bool *value, bool dflt)
POM__MUST_USE_R;

/// Get comma-separated list value of `key`, or `NULL` if not present. The return value must be freed with `free`.
///
/// The list is `NULL`-terminated.
///
/// Commas can be escaped in list entries using `\,`.
///
/// (`free`ing the list also frees the entries thanks to a "hack" where list entries are stored
///  inline after the entry pointers.)
POM__MUST_USE_L
char **
pom_conf_get_list(const pom_conf *conf, const char *key)
POM__MUST_USE_R;

/// Extract section out of POM configuration.
///
/// Specifically, this returns the configuration consisting of all keys
/// prefixed by `section.`, with that prefix removed, and their corresponding
/// values.
///
/// The returned section doesn't need to be freed, and is valid until
/// \ref pom_conf_free is called on the original configuration.
const pom_conf *
pom_conf_section(const pom_conf *conf, const char *section);

/// Get all ‘direct’ keys in `conf` (i.e. all first components of defined keys).
///
/// The first call to this function should be with `*iter = NULL`.
/// Each time it is called with the same `iter`, it returns the next
/// direct key in the `conf`.
/// After all direct keys have been returned (or if an out-of-memory error occurs),
/// `NULL` is returned, any memory
/// associated with the iterator is freed, and `*iter` is set to `NULL`.
/// This function may modify `*iter` arbitrarily — do not attempt
/// to copy `*iter` or compare it with other iterators.
/// The keys are returned in an arbitrary order that may change in future versions.
/// If you decide to stop iterating halfway through,
/// you should still call this function repeatedly until you get `NULL`;
/// otherwise memory associated with the iterator may be leaked.
///
/// The correct usage for this function is:
///
/// ```C
/// pom_key_iter *iter = NULL;
/// const char *key;
/// while ((key = pom_conf_next_key(conf, &iter))) {
///     printf("Key: %s\n", key);
/// }
/// ```
const char *
pom_conf_next_key(const pom_conf *conf, pom_key_iter **iter);

/// Get all key-value pairs in `conf`.
///
/// The first call to this function should be with `*iter = NULL`.
/// Each time it is called with the same `conf` and `iter`, it returns the next
/// key-value pair in `conf`.
/// After all items have been returned (or if an out-of-memory error occurs),
/// `NULL` is returned, any memory
/// associated with the iterator is freed, and `*iter` is set to `NULL`.
/// This function may modify `*iter` arbitrarily — do not attempt
/// to copy `*iter` or compare it with other iterators.
/// The items are returned in an arbitrary order that may change in future versions.
/// If you decide to stop iterating halfway through,
/// you should still call this function repeatedly until you get `NULL`;
/// otherwise memory associated with the iterator may be leaked.
///
/// The returned pointer is only valid until the next call to \ref pom_conf_next_item.
///
/// The correct usage for this function is:
///
/// ```C
/// pom_item_iter *iter = NULL;
/// const pom_item *item;
/// while ((item = pom_conf_next_item(conf, &iter))) {
///     printf("Key: %s, Value: %s\n", item->key, item->value);
/// }
/// ```
const pom_item *
pom_conf_next_item(const pom_conf *conf, pom_item_iter **iter);

/// Create a copy of `conf`.
///
/// The copy must be freed with \ref pom_conf_free.
///
/// Returns `NULL` on out-of-memory.
///
/// The copy is entirely independent from `conf` — it can be passed to a separate
/// thread without worry.
POM__MUST_USE_L
pom_conf *
pom_conf_copy(const pom_conf *conf)
POM__MUST_USE_R;

/// Merge keys from `other` into `conf`, preferring keys in `other`.
///
/// Sections obtained from \ref pom_conf_section and iterators
/// (\ref pom_conf_next_unread_key, \ref pom_conf_next_item, \ref pom_conf_next_key)
/// will still point to the old configuration.
/// For this reason, the old configuration is kept in memory until \ref pom_conf_free
/// is called, so if you are repeatedly calling this function (unlikely, but who knows),
/// you should make a copy of `conf` after each call (with \ref pom_conf_copy),
/// then free the old value of `conf`.
///
/// Returns `false` on out-of-memory, in which case `conf` is unchanged.
bool
pom_conf_merge(pom_conf *conf, const pom_conf *other);

/// Get all unread keys in `conf`.
///
/// The first call to this function should be with `*iter = NULL`.
/// Each time it is called with the same `iter`, it returns the next
/// key in the `conf` that has not been accessed with a `pom_conf_get*` function.
/// After all such keys have been returned (or if an out-of-memory error occurs),
/// `NULL` is returned, any memory
/// associated with the iterator is freed, and `*iter` is set to `NULL`.
/// This function may modify `*iter` arbitrarily — do not attempt
/// to copy `*iter` or compare it with other iterators.
/// The keys are returned in an arbitrary order that may change in future versions.
/// If you decide to stop iterating halfway through,
/// you should still call this function repeatedly until you get `NULL`;
/// otherwise memory associated with the iterator may be leaked.
///
/// The correct usage for this function is:
///
/// ```C
/// pom_unread_key_iter *iter = NULL;
/// const char *key;
/// while ((key = pom_conf_next_unread_key(conf, &iter))) {
///     printf("Unknown key: %s\n", key);
/// }
/// ```
const char *
pom_conf_next_unread_key(const pom_conf *conf, pom_unread_key_iter **iter);

#ifndef POM_NO_STDIO
/// Print `key: value` for each `key` in `conf` to `stdout`.
void
pom_conf_print(const pom_conf *conf);
#endif
/// Free a POM configuration.
void
pom_conf_free(pom_conf *conf);

#ifdef __cplusplus
} // extern "C"
#endif

#endif // POM__H_