/**
 * TaskChampion
 *
 * This file defines the C interface to libtaskchampion.  This is a thin
 * wrapper around the Rust `taskchampion` crate.  Refer to the documentation
 * for that crate at https://docs.rs/taskchampion/latest/taskchampion/ for API
 * details.  The comments in this file focus mostly on the low-level details of
 * passing values to and from TaskChampion.
 *
 * # Overview
 *
 * This library defines two major types used to interact with the API, that map directly
 * to Rust types.
 *
 *  * TCReplica - see https://docs.rs/taskchampion/latest/taskchampion/struct.Replica.html
 *  * TCTask - see https://docs.rs/taskchampion/latest/taskchampion/struct.Task.html
 *  * TCServer - see https://docs.rs/taskchampion/latest/taskchampion/trait.Server.html
 *  * TCWorkingSet - see https://docs.rs/taskchampion/latest/taskchampion/struct.WorkingSet.html
 *
 * It also defines a few utility types:
 *
 *  * TCString - a wrapper around both C (NUL-terminated) and Rust (always utf-8) strings.
 *  * TC…List - a list of objects represented as a C array
 *  * see below for the remainder
 *
 * # Safety
 *
 * Each type contains specific instructions to ensure memory safety.
 * The general rules are as follows.
 *
 * No types in this library are threadsafe.  All values should be used in only
 * one thread for their entire lifetime.  It is safe to use unrelated values in
 * different threads (for example, different threads may use different
 * TCReplica values concurrently).
 *
 * ## Pass by Pointer
 *
 * Several types such as TCReplica and TCString are "opaque" types and always
 * handled as pointers in C. The bytes these pointers address are private to
 * the Rust implemetation and must not be accessed from C.
 *
 * Pass-by-pointer values have exactly one owner, and that owner is responsible
 * for freeing the value (using a `tc_…_free` function), or transferring
 * ownership elsewhere.  Except where documented otherwise, when a value is
 * passed to C, ownership passes to C as well.  When a value is passed to Rust,
 * ownership stays with the C code.  The exception is TCString, ownership of
 * which passes to Rust when it is used as a function argument.
 *
 * The limited circumstances where one value must not outlive another, due to
 * pointer references between them, are documented below.
 *
 * ## Pass by Value
 *
 * Types such as TCUuid and TC…List are passed by value, and contain fields
 * that are accessible from C.  C code is free to access the content of these
 * types in a _read_only_ fashion.
 *
 * Pass-by-value values that contain pointers also have exactly one owner,
 * responsible for freeing the value or transferring ownership.  The tc_…_free
 * functions for these types will replace the pointers with NULL to guard
 * against use-after-free errors.  The interior pointers in such values should
 * never be freed directly (for example, `tc_string_free(tcuda.value)` is an
 * error).
 *
 * TCUuid is a special case, because it does not contain pointers.  It can be
 * freely copied and need not be freed.
 *
 * ## Lists
 *
 * Lists are a special kind of pass-by-value type.  Each contains `len` and
 * `items`, where `items` is an array of length `len`.  Lists, and the values
 * in the `items` array, must be treated as read-only.  On return from an API
 * function, a list's ownership is with the C caller, which must eventually
 * free the list.  List data must be freed with the `tc_…_list_free` function.
 * It is an error to free any value in the `items` array of a list.
 */


#ifndef TASKCHAMPION_H
#define TASKCHAMPION_H

#include <stdbool.h>
#include <stdint.h>
#include <time.h>

/**
 * Length, in bytes, of the string representation of a UUID (without NUL terminator)
 */
#define TC_UUID_STRING_BYTES 36

/**
 * A result from a TC operation.  Typically if this value is TC_RESULT_ERROR,
 * the associated object's `tc_.._error` method will return an error message.
 */
enum TCResult
#ifdef __cplusplus
  : int32_t
#endif // __cplusplus
 {
  TC_RESULT_ERROR = -1,
  TC_RESULT_OK = 0,
};
#ifndef __cplusplus
typedef int32_t TCResult;
#endif // __cplusplus

/**
 * The status of a task, as defined by the task data model.
 */
typedef enum TCStatus {
  TC_STATUS_PENDING,
  TC_STATUS_COMPLETED,
  TC_STATUS_DELETED,
  TC_STATUS_RECURRING,
  /**
   * Unknown signifies a status in the task DB that was not
   * recognized.
   */
  TC_STATUS_UNKNOWN,
} TCStatus;

/**
 * A replica represents an instance of a user's task data, providing an easy interface
 * for querying and modifying that data.
 *
 * # Error Handling
 *
 * When a `tc_replica_..` function that returns a TCResult returns TC_RESULT_ERROR, then
 * `tc_replica_error` will return the error message.
 *
 * # Safety
 *
 * The `*TCReplica` returned from `tc_replica_new…` functions is owned by the caller and
 * must later be freed to avoid a memory leak.
 *
 * Any function taking a `*TCReplica` requires:
 *  - the pointer must not be NUL;
 *  - the pointer must be one previously returned from a tc_… function;
 *  - the memory referenced by the pointer must never be modified by C code; and
 *  - except for `tc_replica_free`, ownership of a `*TCReplica` remains with the caller.
 *
 * Once passed to `tc_replica_free`, a `*TCReplica` becomes invalid and must not be used again.
 *
 * TCReplicas are not threadsafe.
 */
typedef struct TCReplica TCReplica;

/**
 * TCServer represents an interface to a sync server.  Aside from new and free, a server
 * has no C-accessible API, but is designed to be passed to `tc_replica_sync`.
 *
 * ## Safety
 *
 * TCServer are not threadsafe, and must not be used with multiple replicas simultaneously.
 */
typedef struct TCServer TCServer;

/**
 * A task, as publicly exposed by this library.
 *
 * A task begins in "immutable" mode.  It must be converted to "mutable" mode
 * to make any changes, and doing so requires exclusive access to the replica
 * until the task is freed or converted back to immutable mode.
 *
 * An immutable task carries no reference to the replica that created it, and can be used until it
 * is freed or converted to a TaskMut.  A mutable task carries a reference to the replica and
 * must be freed or made immutable before the replica is freed.
 *
 * All `tc_task_..` functions taking a task as an argument require that it not be NULL.
 *
 * When a `tc_task_..` function that returns a TCResult returns TC_RESULT_ERROR, then
 * `tc_task_error` will return the error message.
 *
 * # Safety
 *
 * A task is an owned object, and must be freed with tc_task_free (or, if part of a list,
 * with tc_task_list_free).
 *
 * Any function taking a `*TCTask` requires:
 *  - the pointer must not be NUL;
 *  - the pointer must be one previously returned from a tc_… function;
 *  - the memory referenced by the pointer must never be modified by C code; and
 *  - except for `tc_{task,task_list}_free`, ownership of a `*TCTask` remains with the caller.
 *
 * Once passed to tc_task_free, a `*TCTask` becomes  invalid and must not be used again.
 *
 * TCTasks are not threadsafe.
 */
typedef struct TCTask TCTask;

/**
 * A TCWorkingSet represents a snapshot of the working set for a replica.  It is not automatically
 * updated based on changes in the replica.  Its lifetime is independent of the replica and it can
 * be freed at any time.
 *
 * To iterate over a working set, search indexes 1 through largest_index.
 *
 * # Safety
 *
 * The `*TCWorkingSet` returned from `tc_replica_working_set` is owned by the caller and
 * must later be freed to avoid a memory leak.  Its lifetime is independent of the replica
 * from which it was generated.
 *
 * Any function taking a `*TCWorkingSet` requires:
 *  - the pointer must not be NUL;
 *  - the pointer must be one previously returned from `tc_replica_working_set`
 *  - the memory referenced by the pointer must never be accessed by C code; and
 *  - except for `tc_replica_free`, ownership of a `*TCWorkingSet` remains with the caller.
 *
 * Once passed to `tc_replica_free`, a `*TCWorkingSet` becomes invalid and must not be used again.
 *
 * TCWorkingSet is not threadsafe.
 */
typedef struct TCWorkingSet TCWorkingSet;

/**
 * TCString supports passing strings into and out of the TaskChampion API.
 *
 * # Rust Strings and C Strings
 *
 * A Rust string can contain embedded NUL characters, while C considers such a character to mark
 * the end of a string.  Strings containing embedded NULs cannot be represented as a "C string"
 * and must be accessed using `tc_string_content_and_len` and `tc_string_clone_with_len`.  In
 * general, these two functions should be used for handling arbitrary data, while more convenient
 * forms may be used where embedded NUL characters are impossible, such as in static strings.
 *
 * # UTF-8
 *
 * TaskChampion expects all strings to be valid UTF-8. `tc_string_…` functions will fail if given
 * a `*TCString` containing invalid UTF-8.
 *
 * # Safety
 *
 * The `ptr` field may be checked for NULL, where documentation indicates this is possible.  All
 * other fields in a TCString are private and must not be used from C.  They exist in the struct
 * to ensure proper allocation and alignment.
 *
 * When a `TCString` appears as a return value or output argument, ownership is passed to the
 * caller.  The caller must pass that ownership back to another function or free the string.
 *
 * Any function taking a `TCString` requires:
 *  - the pointer must not be NUL;
 *  - the pointer must be one previously returned from a tc_… function; and
 *  - the memory referenced by the pointer must never be modified by C code.
 *
 * Unless specified otherwise, TaskChampion functions take ownership of a `TCString` when it is
 * given as a function argument, and the caller must not use or free TCStrings after passing them
 * to such API functions.
 *
 * A TCString with a NULL `ptr` field need not be freed, although tc_free_string will not fail
 * for such a value.
 *
 * TCString is not threadsafe.
 */
typedef struct TCString {
  void *ptr;
  size_t _u1;
  size_t _u2;
  uint8_t _u3;
} TCString;

/**
 * TCAnnotation contains the details of an annotation.
 *
 * # Safety
 *
 * An annotation must be initialized from a tc_.. function, and later freed
 * with `tc_annotation_free` or `tc_annotation_list_free`.
 *
 * Any function taking a `*TCAnnotation` requires:
 *  - the pointer must not be NUL;
 *  - the pointer must be one previously returned from a tc_… function;
 *  - the memory referenced by the pointer must never be modified by C code; and
 *  - ownership transfers to the called function, and the value must not be used
 *    after the call returns.  In fact, the value will be zeroed out to ensure this.
 *
 * TCAnnotations are not threadsafe.
 */
typedef struct TCAnnotation {
  /**
   * Time the annotation was made.  Must be nonzero.
   */
  time_t entry;
  /**
   * Content of the annotation.  Must not be NULL.
   */
  struct TCString description;
} TCAnnotation;

/**
 * TCAnnotationList represents a list of annotations.
 *
 * The content of this struct must be treated as read-only.
 */
typedef struct TCAnnotationList {
  /**
   * number of annotations in items
   */
  size_t len;
  /**
   * total size of items (internal use only)
   */
  size_t _capacity;
  /**
   * array of annotations. these remain owned by the TCAnnotationList instance and will be freed by
   * tc_annotation_list_free.  This pointer is never NULL for a valid TCAnnotationList.
   */
  struct TCAnnotation *items;
} TCAnnotationList;

/**
 * TCKV contains a key/value pair that is part of a task.
 *
 * Neither key nor value are ever NULL.  They remain owned by the TCKV and
 * will be freed when it is freed with tc_kv_list_free.
 */
typedef struct TCKV {
  struct TCString key;
  struct TCString value;
} TCKV;

/**
 * TCKVList represents a list of key/value pairs.
 *
 * The content of this struct must be treated as read-only.
 */
typedef struct TCKVList {
  /**
   * number of key/value pairs in items
   */
  size_t len;
  /**
   * total size of items (internal use only)
   */
  size_t _capacity;
  /**
   * array of TCKV's. these remain owned by the TCKVList instance and will be freed by
   * tc_kv_list_free.  This pointer is never NULL for a valid TCKVList.
   */
  struct TCKV *items;
} TCKVList;

/**
 * TCTaskList represents a list of tasks.
 *
 * The content of this struct must be treated as read-only: no fields or anything they reference
 * should be modified directly by C code.
 *
 * When an item is taken from this list, its pointer in `items` is set to NULL.
 */
typedef struct TCTaskList {
  /**
   * number of tasks in items
   */
  size_t len;
  /**
   * total size of items (internal use only)
   */
  size_t _capacity;
  /**
   * array of pointers representing each task. these remain owned by the TCTaskList instance and
   * will be freed by tc_task_list_free.  This pointer is never NULL for a valid TCTaskList,
   * and the *TCTaskList at indexes 0..len-1 are not NULL.
   */
  struct TCTask **items;
} TCTaskList;

/**
 * TCUuid is used as a task identifier.  Uuids do not contain any pointers and need not be freed.
 * Uuids are typically treated as opaque, but the bytes are available in big-endian format.
 *
 */
typedef struct TCUuid {
  uint8_t bytes[16];
} TCUuid;

/**
 * TCUuidList represents a list of uuids.
 *
 * The content of this struct must be treated as read-only.
 */
typedef struct TCUuidList {
  /**
   * number of uuids in items
   */
  size_t len;
  /**
   * total size of items (internal use only)
   */
  size_t _capacity;
  /**
   * array of uuids. these remain owned by the TCUuidList instance and will be freed by
   * tc_uuid_list_free.  This pointer is never NULL for a valid TCUuidList.
   */
  struct TCUuid *items;
} TCUuidList;

/**
 * TCStringList represents a list of strings.
 *
 * The content of this struct must be treated as read-only.
 */
typedef struct TCStringList {
  /**
   * number of strings in items
   */
  size_t len;
  /**
   * total size of items (internal use only)
   */
  size_t _capacity;
  /**
   * TCStringList representing each string. these remain owned by the TCStringList instance and will
   * be freed by tc_string_list_free.  This pointer is never NULL for a valid TCStringList, and the
   * *TCStringList at indexes 0..len-1 are not NULL.
   */
  struct TCString *items;
} TCStringList;

/**
 * TCUda contains the details of a UDA.
 */
typedef struct TCUda {
  /**
   * Namespace of the UDA.  For legacy UDAs, this may have a NULL ptr field.
   */
  struct TCString ns;
  /**
   * UDA key.  Must not be NULL.
   */
  struct TCString key;
  /**
   * Content of the UDA.  Must not be NULL.
   */
  struct TCString value;
} TCUda;

/**
 * TCUdaList represents a list of UDAs.
 *
 * The content of this struct must be treated as read-only.
 */
typedef struct TCUdaList {
  /**
   * number of UDAs in items
   */
  size_t len;
  /**
   * total size of items (internal use only)
   */
  size_t _capacity;
  /**
   * array of UDAs. These remain owned by the TCUdaList instance and will be freed by
   * tc_uda_list_free.  This pointer is never NULL for a valid TCUdaList.
   */
  struct TCUda *items;
} TCUdaList;

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

/**
 * Free a TCAnnotation instance.  The instance, and the TCString it contains, must not be used
 * after this call.
 */
void tc_annotation_free(struct TCAnnotation *tcann);

/**
 * Free a TCAnnotationList instance.  The instance, and all TCAnnotations it contains, must not be used after
 * this call.
 *
 * When this call returns, the `items` pointer will be NULL, signalling an invalid TCAnnotationList.
 */
void tc_annotation_list_free(struct TCAnnotationList *tcanns);

/**
 * Free a TCKVList instance.  The instance, and all TCKVs it contains, must not be used after
 * this call.
 *
 * When this call returns, the `items` pointer will be NULL, signalling an invalid TCKVList.
 */
void tc_kv_list_free(struct TCKVList *tckvs);

/**
 * Create a new TCReplica with an in-memory database.  The contents of the database will be
 * lost when it is freed with tc_replica_free.
 */
struct TCReplica *tc_replica_new_in_memory(void);

/**
 * Create a new TCReplica with an on-disk database having the given filename.  On error, a string
 * is written to the error_out parameter (if it is not NULL) and NULL is returned.  The caller
 * must free this string.
 */
struct TCReplica *tc_replica_new_on_disk(struct TCString path,
                                         bool create_if_missing,
                                         struct TCString *error_out);

/**
 * Get a list of all tasks in the replica.
 *
 * Returns a TCTaskList with a NULL items field on error.
 */
struct TCTaskList tc_replica_all_tasks(struct TCReplica *rep);

/**
 * Get a list of all uuids for tasks in the replica.
 *
 * Returns a TCUuidList with a NULL items field on error.
 *
 * The caller must free the UUID list with `tc_uuid_list_free`.
 */
struct TCUuidList tc_replica_all_task_uuids(struct TCReplica *rep);

/**
 * Get the current working set for this replica.  The resulting value must be freed
 * with tc_working_set_free.
 *
 * Returns NULL on error.
 */
struct TCWorkingSet *tc_replica_working_set(struct TCReplica *rep);

/**
 * Get an existing task by its UUID.
 *
 * Returns NULL when the task does not exist, and on error.  Consult tc_replica_error
 * to distinguish the two conditions.
 */
struct TCTask *tc_replica_get_task(struct TCReplica *rep, struct TCUuid tcuuid);

/**
 * Create a new task.  The task must not already exist.
 *
 * Returns the task, or NULL on error.
 */
struct TCTask *tc_replica_new_task(struct TCReplica *rep,
                                   enum TCStatus status,
                                   struct TCString description);

/**
 * Create a new task.  The task must not already exist.
 *
 * Returns the task, or NULL on error.
 */
struct TCTask *tc_replica_import_task_with_uuid(struct TCReplica *rep, struct TCUuid tcuuid);

/**
 * Synchronize this replica with a server.
 *
 * The `server` argument remains owned by the caller, and must be freed explicitly.
 */
TCResult tc_replica_sync(struct TCReplica *rep, struct TCServer *server, bool avoid_snapshots);

/**
 * Undo local operations until the most recent UndoPoint.
 *
 * If undone_out is not NULL, then on success it is set to 1 if operations were undone, or 0 if
 * there are no operations that can be done.
 */
TCResult tc_replica_undo(struct TCReplica *rep, int32_t *undone_out);

/**
 * Get the number of local, un-synchronized operations (not including undo points), or -1 on
 * error.
 */
int64_t tc_replica_num_local_operations(struct TCReplica *rep);

/**
 * Get the number of undo points (number of undo calls possible), or -1 on error.
 */
int64_t tc_replica_num_undo_points(struct TCReplica *rep);

/**
 * Add an UndoPoint, if one has not already been added by this Replica.  This occurs automatically
 * when a change is made.  The `force` flag allows forcing a new UndoPoint even if one has already
 * been created by this Replica, and may be useful when a Replica instance is held for a long time
 * and used to apply more than one user-visible change.
 */
TCResult tc_replica_add_undo_point(struct TCReplica *rep, bool force);

/**
 * Rebuild this replica's working set, based on whether tasks are pending or not.  If `renumber`
 * is true, then existing tasks may be moved to new working-set indices; in any case, on
 * completion all pending tasks are in the working set and all non- pending tasks are not.
 */
TCResult tc_replica_rebuild_working_set(struct TCReplica *rep, bool renumber);

/**
 * Get the latest error for a replica, or a string with NULL ptr if no error exists.  Subsequent
 * calls to this function will return NULL.  The rep pointer must not be NULL.  The caller must
 * free the returned string.
 */
struct TCString tc_replica_error(struct TCReplica *rep);

/**
 * Free a replica.  The replica may not be used after this function returns and must not be freed
 * more than once.
 */
void tc_replica_free(struct TCReplica *rep);

/**
 * Create a new TCServer that operates locally (on-disk).  See the TaskChampion docs for the
 * description of the arguments.
 *
 * On error, a string is written to the error_out parameter (if it is not NULL) and NULL is
 * returned.  The caller must free this string.
 *
 * The server must be freed after it is used - tc_replica_sync does not automatically free it.
 */
struct TCServer *tc_server_new_local(struct TCString server_dir, struct TCString *error_out);

/**
 * Create a new TCServer that connects to a remote server.  See the TaskChampion docs for the
 * description of the arguments.
 *
 * On error, a string is written to the error_out parameter (if it is not NULL) and NULL is
 * returned.  The caller must free this string.
 *
 * The server must be freed after it is used - tc_replica_sync does not automatically free it.
 */
struct TCServer *tc_server_new_remote(struct TCString origin,
                                      struct TCUuid client_key,
                                      struct TCString encryption_secret,
                                      struct TCString *error_out);

/**
 * Free a server.  The server may not be used after this function returns and must not be freed
 * more than once.
 */
void tc_server_free(struct TCServer *server);

/**
 * Create a new TCString referencing the given C string.  The C string must remain valid and
 * unchanged until after the TCString is freed.  It's typically easiest to ensure this by using a
 * static string.
 *
 * NOTE: this function does _not_ take responsibility for freeing the given C string.  The
 * given string can be freed once the TCString referencing it has been freed.
 *
 * For example:
 *
 * ```text
 * char *url = get_item_url(..); // dynamically allocate C string
 * tc_task_annotate(task, tc_string_borrow(url)); // TCString created, passed, and freed
 * free(url); // string is no longer referenced and can be freed
 * ```
 */
struct TCString tc_string_borrow(const char *cstr);

/**
 * Create a new TCString by cloning the content of the given C string.  The resulting TCString
 * is independent of the given string, which can be freed or overwritten immediately.
 */
struct TCString tc_string_clone(const char *cstr);

/**
 * Create a new TCString containing the given string with the given length. This allows creation
 * of strings containing embedded NUL characters.  As with `tc_string_clone`, the resulting
 * TCString is independent of the passed buffer, which may be reused or freed immediately.
 *
 * The length should _not_ include any trailing NUL.
 *
 * The given length must be less than half the maximum value of usize.
 */
struct TCString tc_string_clone_with_len(const char *buf, size_t len);

/**
 * Get the content of the string as a regular C string.  The given string must be valid.  The
 * returned value is NULL if the string contains NUL bytes or (in some cases) invalid UTF-8.  The
 * returned C string is valid until the TCString is freed or passed to another TC API function.
 *
 * In general, prefer [`tc_string_content_with_len`] except when it's certain that the string is
 * valid and NUL-free.
 *
 * This function takes the TCString by pointer because it may be modified in-place to add a NUL
 * terminator.  The pointer must not be NULL.
 *
 * This function does _not_ take ownership of the TCString.
 */
const char *tc_string_content(const struct TCString *tcstring);

/**
 * Get the content of the string as a pointer and length.  The given string must not be NULL.
 * This function can return any string, even one including NUL bytes or invalid UTF-8.  The
 * returned buffer is valid until the TCString is freed or passed to another TaskChampio
 * function.
 *
 * This function takes the TCString by pointer because it may be modified in-place to add a NUL
 * terminator.  The pointer must not be NULL.
 *
 * This function does _not_ take ownership of the TCString.
 */
const char *tc_string_content_with_len(const struct TCString *tcstring, size_t *len_out);

/**
 * Free a TCString.  The given string must not be NULL.  The string must not be used
 * after this function returns, and must not be freed more than once.
 */
void tc_string_free(struct TCString *tcstring);

/**
 * Free a TCStringList instance.  The instance, and all TCStringList it contains, must not be used after
 * this call.
 *
 * When this call returns, the `items` pointer will be NULL, signalling an invalid TCStringList.
 */
void tc_string_list_free(struct TCStringList *tcstrings);

/**
 * Convert an immutable task into a mutable task.
 *
 * The task must not be NULL. It is modified in-place, and becomes mutable.
 *
 * The replica must not be NULL. After this function returns, the replica _cannot be used at all_
 * until this task is made immutable again.  This implies that it is not allowed for more than one
 * task associated with a replica to be mutable at any time.
 *
 * Typical mutation of tasks is bracketed with `tc_task_to_mut` and `tc_task_to_immut`:
 *
 * ```c
 * tc_task_to_mut(task, rep);
 * success = tc_task_done(task);
 * tc_task_to_immut(task, rep);
 * if (!success) { ... }
 * ```
 */
void tc_task_to_mut(struct TCTask *task, struct TCReplica *tcreplica);

/**
 * Convert a mutable task into an immutable task.
 *
 * The task must not be NULL.  It is modified in-place, and becomes immutable.
 *
 * The replica passed to `tc_task_to_mut` may be used freely after this call.
 */
void tc_task_to_immut(struct TCTask *task);

/**
 * Get a task's UUID.
 */
struct TCUuid tc_task_get_uuid(struct TCTask *task);

/**
 * Get a task's status.
 */
enum TCStatus tc_task_get_status(struct TCTask *task);

/**
 * Get the underlying key/value pairs for this task.  The returned TCKVList is
 * a "snapshot" of the task and will not be updated if the task is subsequently
 * modified.  It is the caller's responsibility to free the TCKVList.
 */
struct TCKVList tc_task_get_taskmap(struct TCTask *task);

/**
 * Get a task's description.
 */
struct TCString tc_task_get_description(struct TCTask *task);

/**
 * Get a task property's value, or NULL if the task has no such property, (including if the
 * property name is not valid utf-8).
 */
struct TCString tc_task_get_value(struct TCTask *task, struct TCString property);

/**
 * Get the entry timestamp for a task (when it was created), or 0 if not set.
 */
time_t tc_task_get_entry(struct TCTask *task);

/**
 * Get the wait timestamp for a task, or 0 if not set.
 */
time_t tc_task_get_wait(struct TCTask *task);

/**
 * Get the modified timestamp for a task, or 0 if not set.
 */
time_t tc_task_get_modified(struct TCTask *task);

/**
 * Check if a task is waiting.
 */
bool tc_task_is_waiting(struct TCTask *task);

/**
 * Check if a task is active (started and not stopped).
 */
bool tc_task_is_active(struct TCTask *task);

/**
 * Check if a task is blocked (depends on at least one other task).
 */
bool tc_task_is_blocked(struct TCTask *task);

/**
 * Check if a task is blocking (at least one other task depends on it).
 */
bool tc_task_is_blocking(struct TCTask *task);

/**
 * Check if a task has the given tag.  If the tag is invalid, this function will return false, as
 * that (invalid) tag is not present. No error will be reported via `tc_task_error`.
 */
bool tc_task_has_tag(struct TCTask *task, struct TCString tag);

/**
 * Get the tags for the task.
 *
 * The caller must free the returned TCStringList instance.  The TCStringList instance does not
 * reference the task and the two may be freed in any order.
 */
struct TCStringList tc_task_get_tags(struct TCTask *task);

/**
 * Get the annotations for the task.
 *
 * The caller must free the returned TCAnnotationList instance.  The TCStringList instance does not
 * reference the task and the two may be freed in any order.
 */
struct TCAnnotationList tc_task_get_annotations(struct TCTask *task);

/**
 * Get the named UDA from the task.
 *
 * Returns a TCString with NULL ptr field if the UDA does not exist.
 */
struct TCString tc_task_get_uda(struct TCTask *task, struct TCString ns, struct TCString key);

/**
 * Get the named legacy UDA from the task.
 *
 * Returns NULL if the UDA does not exist.
 */
struct TCString tc_task_get_legacy_uda(struct TCTask *task, struct TCString key);

/**
 * Get all UDAs for this task.
 *
 * Legacy UDAs are represented with an empty string in the ns field.
 */
struct TCUdaList tc_task_get_udas(struct TCTask *task);

/**
 * Get all UDAs for this task.
 *
 * All TCUdas in this list have a NULL ns field.  The entire UDA key is
 * included in the key field.  The caller must free the returned list.
 */
struct TCUdaList tc_task_get_legacy_udas(struct TCTask *task);

/**
 * Set a mutable task's status.
 */
TCResult tc_task_set_status(struct TCTask *task, enum TCStatus status);

/**
 * Set a mutable task's property value by name.  If value.ptr is NULL, the property is removed.
 */
TCResult tc_task_set_value(struct TCTask *task, struct TCString property, struct TCString value);

/**
 * Set a mutable task's description.
 */
TCResult tc_task_set_description(struct TCTask *task, struct TCString description);

/**
 * Set a mutable task's entry (creation time).  Pass entry=0 to unset
 * the entry field.
 */
TCResult tc_task_set_entry(struct TCTask *task, time_t entry);

/**
 * Set a mutable task's wait timestamp.  Pass wait=0 to unset the wait field.
 */
TCResult tc_task_set_wait(struct TCTask *task, time_t wait);

/**
 * Set a mutable task's modified timestamp.  The value cannot be zero.
 */
TCResult tc_task_set_modified(struct TCTask *task, time_t modified);

/**
 * Start a task.
 */
TCResult tc_task_start(struct TCTask *task);

/**
 * Stop a task.
 */
TCResult tc_task_stop(struct TCTask *task);

/**
 * Mark a task as done.
 */
TCResult tc_task_done(struct TCTask *task);

/**
 * Mark a task as deleted.
 */
TCResult tc_task_delete(struct TCTask *task);

/**
 * Add a tag to a mutable task.
 */
TCResult tc_task_add_tag(struct TCTask *task, struct TCString tag);

/**
 * Remove a tag from a mutable task.
 */
TCResult tc_task_remove_tag(struct TCTask *task, struct TCString tag);

/**
 * Add an annotation to a mutable task.  This call takes ownership of the
 * passed annotation, which must not be used after the call returns.
 */
TCResult tc_task_add_annotation(struct TCTask *task, struct TCAnnotation *annotation);

/**
 * Remove an annotation from a mutable task.
 */
TCResult tc_task_remove_annotation(struct TCTask *task, int64_t entry);

/**
 * Set a UDA on a mutable task.
 */
TCResult tc_task_set_uda(struct TCTask *task,
                         struct TCString ns,
                         struct TCString key,
                         struct TCString value);

/**
 * Remove a UDA fraom a mutable task.
 */
TCResult tc_task_remove_uda(struct TCTask *task, struct TCString ns, struct TCString key);

/**
 * Set a legacy UDA on a mutable task.
 */
TCResult tc_task_set_legacy_uda(struct TCTask *task, struct TCString key, struct TCString value);

/**
 * Remove a UDA fraom a mutable task.
 */
TCResult tc_task_remove_legacy_uda(struct TCTask *task, struct TCString key);

/**
 * Get all dependencies for a task.
 */
struct TCUuidList tc_task_get_dependencies(struct TCTask *task);

/**
 * Add a dependency.
 */
TCResult tc_task_add_dependency(struct TCTask *task, struct TCUuid dep);

/**
 * Remove a dependency.
 */
TCResult tc_task_remove_dependency(struct TCTask *task, struct TCUuid dep);

/**
 * Get the latest error for a task, or a string NULL ptr field if the last operation succeeded.
 * Subsequent calls to this function will return NULL.  The task pointer must not be NULL.  The
 * caller must free the returned string.
 */
struct TCString tc_task_error(struct TCTask *task);

/**
 * Free a task.  The given task must not be NULL.  The task must not be used after this function
 * returns, and must not be freed more than once.
 *
 * If the task is currently mutable, it will first be made immutable.
 */
void tc_task_free(struct TCTask *task);

/**
 * Take an item from a TCTaskList.  After this call, the indexed item is no longer associated
 * with the list and becomes the caller's responsibility, just as if it had been returned from
 * `tc_replica_get_task`.
 *
 * The corresponding element in the `items` array will be set to NULL.  If that field is already
 * NULL (that is, if the item has already been taken), this function will return NULL.  If the
 * index is out of bounds, this function will also return NULL.
 *
 * The passed TCTaskList remains owned by the caller.
 */
struct TCTask *tc_task_list_take(struct TCTaskList *tasks, size_t index);

/**
 * Free a TCTaskList instance.  The instance, and all TCTaskList it contains, must not be used after
 * this call.
 *
 * When this call returns, the `items` pointer will be NULL, signalling an invalid TCTaskList.
 */
void tc_task_list_free(struct TCTaskList *tasks);

/**
 * Free a TCUda instance.  The instance, and the TCStrings it contains, must not be used
 * after this call.
 */
void tc_uda_free(struct TCUda *tcuda);

/**
 * Free a TCUdaList instance.  The instance, and all TCUdas it contains, must not be used after
 * this call.
 *
 * When this call returns, the `items` pointer will be NULL, signalling an invalid TCUdaList.
 */
void tc_uda_list_free(struct TCUdaList *tcudas);

/**
 * Create a new, randomly-generated UUID.
 */
struct TCUuid tc_uuid_new_v4(void);

/**
 * Create a new UUID with the nil value.
 */
struct TCUuid tc_uuid_nil(void);

/**
 * Write the string representation of a TCUuid into the given buffer, which must be
 * at least TC_UUID_STRING_BYTES long.  No NUL terminator is added.
 */
void tc_uuid_to_buf(struct TCUuid tcuuid, char *buf);

/**
 * Return the hyphenated string representation of a TCUuid.  The returned string
 * must be freed with tc_string_free.
 */
struct TCString tc_uuid_to_str(struct TCUuid tcuuid);

/**
 * Parse the given string as a UUID.  Returns TC_RESULT_ERROR on parse failure or if the given
 * string is not valid.
 */
TCResult tc_uuid_from_str(struct TCString s, struct TCUuid *uuid_out);

/**
 * Free a TCUuidList instance.  The instance, and all TCUuids it contains, must not be used after
 * this call.
 *
 * When this call returns, the `items` pointer will be NULL, signalling an invalid TCUuidList.
 */
void tc_uuid_list_free(struct TCUuidList *tcuuids);

/**
 * Get the working set's length, or the number of UUIDs it contains.
 */
size_t tc_working_set_len(struct TCWorkingSet *ws);

/**
 * Get the working set's largest index.
 */
size_t tc_working_set_largest_index(struct TCWorkingSet *ws);

/**
 * Get the UUID for the task at the given index.  Returns true if the UUID exists in the working
 * set.  If not, returns false and does not change uuid_out.
 */
bool tc_working_set_by_index(struct TCWorkingSet *ws, size_t index, struct TCUuid *uuid_out);

/**
 * Get the working set index for the task with the given UUID.  Returns 0 if the task is not in
 * the working set.
 */
size_t tc_working_set_by_uuid(struct TCWorkingSet *ws, struct TCUuid uuid);

/**
 * Free a TCWorkingSet.  The given value must not be NULL.  The value must not be used after this
 * function returns, and must not be freed more than once.
 */
void tc_working_set_free(struct TCWorkingSet *ws);

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

#endif /* TASKCHAMPION_H */