#pragma once

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


// This is a fairly low-level client library for the tomsg protocol. No state
// is kept; the API just allows for sending commands and receiving responses
// and push messages from the server.
// Use tomsg_connect() to connect, then wait for messages by poll(2)'ing on the
// file descriptor returned by tomsg_poll_fd(). To send a command, use
// functions like tomsg_register(), tomsg_send(), etc.


struct tomsg_client;

enum tomsg_retval {
	// Successful result
	TOMSG_OK = 0,

	// Error codes
	TOMSG_ERR_CONNECT,    // Server refused connection
	TOMSG_ERR_CLOSED,     // Server connection unexpectedly closed
	TOMSG_ERR_VERSION,    // Server protocol version incompatible
	TOMSG_ERR_TRANSPORT,  // Error in the underlying SSH transport
	TOMSG_ERR_SPACE,      // Argument contained space or LF, while it could not
	TOMSG_ERR_AGAIN,      // (tomsg_next_event) no events for now, poll(2) and try again
	TOMSG_ERR_PARSE,      // (tomsg_next_event) could not parse line from server, line ignored
	TOMSG_ERR_MEMORY,     // Error allocating memory
};

// Should return 'true' if the key is trusted, 'false' otherwise. The hash is
// sha256 in byte form, not yet encoded in hexadecimal or similar. The
// 'userdata' pointer comes from the 'tomsg_connect' invocation.
typedef bool (*tomsg_hostkey_checker_t)(
	const unsigned char *hash, size_t length, void *userdata);

// Convenience function to convert a hash to a human-readable form. Returns a
// reference to an internal static buffer.
const char* tomsg_print_hash(const unsigned char *hash, size_t length);

// Returns reference to internal static buffer.
const char* tomsg_strerror(enum tomsg_retval code);

// If successful, stores a new connection structure in 'client' and returns
// TOMSG_OK. On error, stores NULL in 'client' and returns an error code.
enum tomsg_retval tomsg_connect(
	const char *hostname, int port,
	tomsg_hostkey_checker_t checker,
	void *userdata,  // for checker
	struct tomsg_client **client  // output
);

// Close the connection. This also frees the client structure. Note that even
// in case of an error, you must still call this function to prevent a memory
// leak.
void tomsg_close(struct tomsg_client *client);

// Returns a file descriptor that can be listened for read-ready events (using
// e.g. select(2) or poll(2)). Whenever it becomes ready for reading, you
// should call tomsg_next_event(). If the connection was already closed
// internally due to an error, returns -1.
int tomsg_poll_fd(const struct tomsg_client *client);

enum tomsg_event_type {
	// Data in union fields indicated (but check 'error' first)
	TOMSG_EV_REGISTER,      // login
	TOMSG_EV_LOGIN,         // login
	TOMSG_EV_LOGOUT,        // -
	TOMSG_EV_LIST_ROOMS,    // list_rooms
	TOMSG_EV_LIST_MEMBERS,  // list_members
	TOMSG_EV_CREATE_ROOM,   // create_room
	TOMSG_EV_INVITE,        // join
	TOMSG_EV_SEND,          // send
	TOMSG_EV_HISTORY,       // history
	TOMSG_EV_PING,          // -
	TOMSG_EV_IS_ONLINE,     // is_online
	TOMSG_EV_USER_ACTIVE,   // user_active
	TOMSG_EV_PUSH_ONLINE,   // is_online
	TOMSG_EV_PUSH_MESSAGE,  // push_message
	TOMSG_EV_PUSH_INVITE,   // push_invite
	TOMSG_EV_PUSH_JOIN,     // join
};

struct history_message {
	char *username;
	int64_t timestamp;
	int64_t msgid;
	char *message;
};

struct tomsg_event {
	enum tomsg_event_type type;
	// If the server returned an error, 'error' is non-NULL; otherwise it is
	// NULL, and the union fields describe the server's response.
	// Actually, if 'error' is non-NULL, the union fields that can be
	// filled with request data will already be filled.
	char *error;

	union {
		struct {
			char *username;
		} login;
		struct {
			int64_t count;
			char **rooms;
		} list_rooms;
		struct {
			char *room_name;
			int64_t count;
			char **members;
		} list_members;
		struct {
			char *room_name;
		} create_room;
		struct {
			char *room_name;
			char *username;
		} join;
		struct {
			int64_t tag;  // the tag of the send request, returned by tomsg_send()
			int64_t msgid;
		} send;
		struct {
			char *room_name;
			int64_t count;
			struct history_message *messages;
		} history;
		struct {
			char *username;
			int64_t online_count;
		} is_online;
		struct {
			bool active;
		} user_active;
		struct {
			char *room_name;
			struct history_message message;
		} push_message;
		struct {
			char *room_name;
			char *inviter;
		} push_invite;
	};
};

// Free the fields in the event structure corresponding to the event type set.
// The structure memory may be re-used for a different event afterwards. Note
// that, despite the name, the fields are not actually set to NULL -- they
// couldn't be, since the structure is passed by value (to indicate ownership
// transfer).
void tomsg_event_nullify(struct tomsg_event event);

// Will return TOMSG_ERR_AGAIN if no events are available at present. In that
// case, use poll(2) on the file descriptor from tomsg_poll_fd().
// NOTE: when calling this function, you must call it as long as it gives
// TOMSG_OK, because there might be multiple messages in one batch.
enum tomsg_retval tomsg_next_event(
	struct tomsg_client *client,
	struct tomsg_event *event  // output
);

// Send a register command to the server.
enum tomsg_retval tomsg_register(
	struct tomsg_client *client,
	const char *username, const char *password
);

// Send a login command to the server.
enum tomsg_retval tomsg_login(
	struct tomsg_client *client,
	const char *username, const char *password
);

// Send a logout command to the server.
enum tomsg_retval tomsg_logout(struct tomsg_client *client);

// Send a list_rooms command to the server.
enum tomsg_retval tomsg_list_rooms(struct tomsg_client *client);

// Send a list_members command to the server.
enum tomsg_retval tomsg_list_members(struct tomsg_client *client, const char *room_name);

// Send a create_room command to the server.
enum tomsg_retval tomsg_create_room(struct tomsg_client *client);

// Send an invite command to the server.
enum tomsg_retval tomsg_invite(
	struct tomsg_client *client, const char *room_name, const char *username);

// Send a send command to the server.
// If 'tag' is not NULL, will write the message request tag to the referenced
// location. This tag will also be given in the TOMSG_EV_SEND response, so that
// the response can be linked to the original message.
enum tomsg_retval tomsg_send(
	struct tomsg_client *client, const char *room_name, const char *message,
	int64_t *tag  // output
);

// Send a history command to the server.
// Pass -1 to 'before_msgid' to return the latest 'count' instead messages
// before that id.
enum tomsg_retval tomsg_history(
	struct tomsg_client *client, const char *room_name,
	int64_t count, int64_t before_msgid);

// Send a ping command to the server.
enum tomsg_retval tomsg_ping(struct tomsg_client *client);

// Send an is_online command to the server.
enum tomsg_retval tomsg_is_online(struct tomsg_client *client, const char *username);

// Send a user_active command to the server.
enum tomsg_retval tomsg_user_active(struct tomsg_client *client, bool active);