/**
@file     file_contexts.h
@brief    Store the opened file contexts(inode + pid)
@details  Copyright (c) 2023 Acronis International GmbH
@author   Bruce Wang ([email protected])
@since    $Id: $
*/

#pragma once

#include "interval_tree.h"
#include "transport.h"
#include "transport_id.h"
#include "transport_protocol.h"

#define FILE_CONTEXT_MAX_FILE_SIZE (100 * 1024 * 1024)

typedef struct
{
    long long tv_sec;
    long tv_nsec;
} timespec_compat_t;

typedef struct
{
    file_key_t file_key;
    timespec_compat_t i_mtime; /* last modify time */
    timespec_compat_t i_ctime; /* last change time */
} file_context_key_t;

// This struct is stored in msg_t, to keep the necessary information
typedef struct
{
    file_context_key_t key;
    transport_id_t skipped_transport_ids[MAX_TRANSPORT_SIZE];
} file_context_msg_info_t;

// Particular event properties that are being cached.
typedef union
{
    struct
    {
        int flags;
    } open;
    struct
    {
        uint64_t low;
        uint64_t high;
    } rw;
} file_context_params_t;

// This struct used for all request to add to cache from userspace.
typedef struct
{
    // You may pass pid_key==0 to apply per inode instead of per process
    // pid_key could be either unique_pid or pid_version depending on the caching policy.
    // For 'MODIFY+CLOSE' events it is unique_pid, for everything else pid_version
    uint64_t pid_key;
    file_context_params_t params;
    uint32_t ttl_s;
    file_context_key_t key;
} file_context_add_cache_request_t;

// A struct to store the temporary file context information during message creation hence checking.
typedef struct
{
    uint64_t pid_key;
    file_context_params_t params;
    file_context_msg_info_t msg_info;
} file_context_info_t;

// Module is loaded/unloaded functions
/**
 * @brief Initialize the file contexts module.
 * @return 0 on success, negative value on failure.
 */
int file_contexts_init(void);
/**
 * @brief Frees all resources allocated assuming that module start has failed.
 */
void file_contexts_init_fail_free(void);
/**
 * @brief Deinitialize the file contexts module and free all resources.
 */
void file_contexts_deinit(void);

// Internal maintainance function that gets called when inode needs to be removed.
// Usually this happens when node is unlinked/created or on 'inode_free'.
/**
 * @brief Remove all cache entries associated with a given file key (inode).
 * @param file_key Pointer to the file key (inode) to remove from cache.
 */
void remove_common_cache_all(const file_key_t* file_key);

// Reserve context id table from transport allocation/deallocation.
/**
 * @brief Reserve a context ID table entry for a given transport ID.
 * @param id Transport ID to reserve entry for.
 * @return 0 on success, negative value on failure.
 */
int acquire_file_context_entry(transport_id_t id);
/**
 * @brief Release a reserved context ID table entry for a given transport ID.
 * @param id Transport ID to release entry for.
 */
void release_file_context_entry(transport_id_t id);

// Each file context cache has "message" and "client" sides.
// When "message" needs to be generated, "check" functions are used with "file_context_info_t",
// when client decides to cache, "add" functions are used with "file_context_add_cache_request_t".

/* --- OPEN --- */
/**
 * @brief Check if an open event is cached for the given transport IDs and file context info.
 * @param ids Pointer to transport IDs.
 * @param info Pointer to file context info to check.
 * @return true if cached, false otherwise.
 */
bool check_open_cache(const transport_ids_t* ids, file_context_info_t* info);
/**
 * @brief Add an open event to the cache for the given transport ID and request.
 * @param id Transport ID.
 * @param req Pointer to the cache request.
 * @return 0 on success, negative value on failure.
 */
int add_open_cache(transport_id_t id, const file_context_add_cache_request_t* req);

/* --- READ/WRITE --- */
/**
 * @brief Add a read/write event to the cache for the given transport ID, request, and table type.
 * @param id Transport ID.
 * @param req Pointer to the cache request.
 * @param type Table type (read/write).
 * @return 0 on success, negative value on failure.
 */
int add_write_cache(transport_id_t id, const file_context_add_cache_request_t* req);
/**
 * @brief Check and update the read cache for the given transport IDs and file context info.
 * @param ids Pointer to transport IDs.
 * @param info Pointer to file context info to check and update.
 * @return true if cache was updated, false otherwise.
 */
bool check_and_update_read_cache(const transport_ids_t* ids, file_context_info_t *info);
/**
 * @brief Check the write cache for the given transport IDs, file context info, and table type.
 * @param ids Pointer to transport IDs.
 * @param info Pointer to file context info to check.
 * @param type Table type (write).
 * @return true if cached, false otherwise.
 */
bool check_write_cache(const transport_ids_t* ids, file_context_info_t *info);

// Special cache that is for "file modify" events.
// When any modification event happens (fsnotify_modify), an extra node is added in.
// On "close" event is being taken from the cache (check_update) to send file modified flag.
/**
 * @brief Reserve an entry for file modification events in the cache.
 * @return 0 on success, negative value on failure.
 */
int acquire_file_modify_entry(void);
/**
 * @brief Release a reserved entry for file modification events in the cache.
 */
void release_file_modify_entry(void);
/**
 * @brief Add a file modification event to the cache on "MODIFY".
 * @param info Pointer to the cache request.
 * @return true on success, false otherwise.
 */
bool add_file_modify_cache(const file_context_add_cache_request_t *info);
/**
 * @brief Check and update the file modification cache for the given file context info on "CLOSE".
 * @param info Pointer to file context info to check and update.
 * @return true if cache was updated, false otherwise.
 */
bool check_update_file_modify_cache(file_context_info_t *info);

/**
 * @brief Allocate a file context table for the given transport ID and table type.
 * @param id Transport ID.
 * @param type Table type to allocate.
 * @return 0 on success, negative value on failure.
 */
int acquire_file_context_table(transport_id_t id, file_context_table_type_t type);