/*
 * Copyright (c) 2016 MariaDB Corporation Ab
 *
 * Use of this software is governed by the Business Source License included
 * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
 *
 * Change Date: 2019-07-01
 *
 * On the date above, in accordance with the Business Source License, use
 * of this software will be governed by version 2 or later of the General
 * Public License.
 */

/**
 * @file monitor.c  - The monitor module management routines
 *
 * @verbatim
 * Revision History
 *
 * Date         Who                     Description
 * 08/07/13     Mark Riddoch            Initial implementation
 * 23/05/14     Massimiliano Pinto      Addition of monitor_interval parameter
 *                                      and monitor id
 * 30/10/14     Massimiliano Pinto      Addition of disable_master_failback parameter
 * 07/11/14     Massimiliano Pinto      Addition of monitor network timeouts
 * 08/05/15     Markus Makela           Moved common monitor variables to MONITOR struct
 *
 * @endverbatim
 */
#include <maxscale/monitor.h>

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <maxscale/alloc.h>
#include <mysqld_error.h>
#include <maxscale/paths.h>
#include <maxscale/log_manager.h>
#include <maxscale/mysql_utils.h>
#include <maxscale/pcre2.h>
#include <maxscale/secrets.h>
#include <maxscale/spinlock.h>

#include "maxscale/config.h"
#include "maxscale/externcmd.h"
#include "maxscale/monitor.h"
#include "maxscale/modules.h"

static MXS_MONITOR  *allMonitors = NULL;
static SPINLOCK monLock = SPINLOCK_INIT;

static void monitor_server_free_all(MXS_MONITOR_SERVERS *servers);

/** Server type specific bits */
static unsigned int server_type_bits = SERVER_MASTER | SERVER_SLAVE |
                                       SERVER_JOINED | SERVER_NDB;

/** All server bits */
static unsigned int all_server_bits = SERVER_RUNNING |  SERVER_MAINT |
                                      SERVER_MASTER | SERVER_SLAVE |
                                      SERVER_JOINED | SERVER_NDB;

/**
 * Allocate a new monitor, load the associated module for the monitor
 * and start execution on the monitor.
 *
 * @param name          The name of the monitor module to load
 * @param module        The module to load
 * @return      The newly created monitor
 */
MXS_MONITOR *
monitor_alloc(char *name, char *module)
{
    name = MXS_STRDUP(name);
    char *my_module = MXS_STRDUP(module);

    MXS_MONITOR *mon = (MXS_MONITOR *)MXS_MALLOC(sizeof(MXS_MONITOR));

    if (!name || !mon || !my_module)
    {
        MXS_FREE(name);
        MXS_FREE(mon);
        MXS_FREE(my_module);
        return NULL;
    }

    if ((mon->module = load_module(module, MODULE_MONITOR)) == NULL)
    {
        MXS_ERROR("Unable to load monitor module '%s'.", name);
        MXS_FREE(name);
        MXS_FREE(mon);
        return NULL;
    }
    mon->state = MONITOR_STATE_ALLOC;
    mon->name = name;
    mon->module_name = my_module;
    mon->handle = NULL;
    mon->databases = NULL;
    *mon->password = '\0';
    *mon->user = '\0';
    mon->read_timeout = DEFAULT_READ_TIMEOUT;
    mon->write_timeout = DEFAULT_WRITE_TIMEOUT;
    mon->connect_timeout = DEFAULT_CONNECT_TIMEOUT;
    mon->interval = MONITOR_DEFAULT_INTERVAL;
    mon->parameters = NULL;
    mon->created_online = false;
    mon->server_pending_changes = false;
    spinlock_init(&mon->lock);
    spinlock_acquire(&monLock);
    mon->next = allMonitors;
    allMonitors = mon;
    spinlock_release(&monLock);

    return mon;
}

/**
 * Free a monitor, first stop the monitor and then remove the monitor from
 * the chain of monitors and free the memory.
 *
 * @param mon   The monitor to free
 */
void
monitor_free(MXS_MONITOR *mon)
{
    MXS_MONITOR *ptr;

    mon->module->stopMonitor(mon);
    mon->state = MONITOR_STATE_FREED;
    spinlock_acquire(&monLock);
    if (allMonitors == mon)
    {
        allMonitors = mon->next;
    }
    else
    {
        ptr = allMonitors;
        while (ptr->next && ptr->next != mon)
        {
            ptr = ptr->next;
        }
        if (ptr->next)
        {
            ptr->next = mon->next;
        }
    }
    spinlock_release(&monLock);
    config_parameter_free(mon->parameters);
    monitor_server_free_all(mon->databases);
    MXS_FREE(mon->name);
    MXS_FREE(mon->module_name);
    MXS_FREE(mon);
}


/**
 * Start an individual monitor that has previously been stopped.
 *
 * @param monitor The Monitor that should be started
 */
void
monitorStart(MXS_MONITOR *monitor, void* params)
{
    spinlock_acquire(&monitor->lock);

    if ((monitor->handle = (*monitor->module->startMonitor)(monitor, params)))
    {
        monitor->state = MONITOR_STATE_RUNNING;
    }
    else
    {
        MXS_ERROR("Failed to start monitor '%s'.", monitor->name);
    }

    spinlock_release(&monitor->lock);
}

/**
 * Start all monitors
 */
void monitorStartAll()
{
    MXS_MONITOR *ptr;

    spinlock_acquire(&monLock);
    ptr = allMonitors;
    while (ptr)
    {
        monitorStart(ptr, ptr->parameters);
        ptr = ptr->next;
    }
    spinlock_release(&monLock);
}

/**
 * Stop a given monitor
 *
 * @param monitor       The monitor to stop
 */
void
monitorStop(MXS_MONITOR *monitor)
{
    spinlock_acquire(&monitor->lock);

    /** Only stop the monitor if it is running */
    if (monitor->state == MONITOR_STATE_RUNNING)
    {
        monitor->state = MONITOR_STATE_STOPPING;
        monitor->module->stopMonitor(monitor);
        monitor->state = MONITOR_STATE_STOPPED;

        MXS_MONITOR_SERVERS* db = monitor->databases;
        while (db)
        {
            // TODO: Create a generic entry point for this or move it inside stopMonitor
            mysql_close(db->con);
            db->con = NULL;
            db = db->next;
        }
    }

    spinlock_release(&monitor->lock);
}

/**
 * Shutdown all running monitors
 */
void
monitorStopAll()
{
    MXS_MONITOR *ptr;

    spinlock_acquire(&monLock);
    ptr = allMonitors;
    while (ptr)
    {
        monitorStop(ptr);
        ptr = ptr->next;
    }
    spinlock_release(&monLock);
}

/**
 * Add a server to a monitor. Simply register the server that needs to be
 * monitored to the running monitor module.
 *
 * @param mon           The Monitor instance
 * @param server        The Server to add to the monitoring
 */
bool monitorAddServer(MXS_MONITOR *mon, SERVER *server)
{
    bool rval = false;

    if (monitor_server_in_use(server))
    {
        MXS_ERROR("Server '%s' is already monitored.", server->unique_name);
    }
    else
    {
        rval = true;
        MXS_MONITOR_SERVERS *db = (MXS_MONITOR_SERVERS *)MXS_MALLOC(sizeof(MXS_MONITOR_SERVERS));
        MXS_ABORT_IF_NULL(db);

        db->server = server;
        db->con = NULL;
        db->next = NULL;
        db->mon_err_count = 0;
        db->log_version_err = true;
        /** Server status is uninitialized */
        db->mon_prev_status = -1;
        /* pending status is updated by get_replication_tree */
        db->pending_status = 0;

        monitor_state_t old_state = mon->state;

        if (old_state == MONITOR_STATE_RUNNING)
        {
            monitorStop(mon);
        }

        spinlock_acquire(&mon->lock);

        if (mon->databases == NULL)
        {
            mon->databases = db;
        }
        else
        {
            MXS_MONITOR_SERVERS *ptr = mon->databases;
            while (ptr->next != NULL)
            {
                ptr = ptr->next;
            }
            ptr->next = db;
        }
        spinlock_release(&mon->lock);

        if (old_state == MONITOR_STATE_RUNNING)
        {
            monitorStart(mon, mon->parameters);
        }
    }

    return rval;
}

static void monitor_server_free(MXS_MONITOR_SERVERS *tofree)
{
    if (tofree)
    {
        if (tofree->con)
        {
            mysql_close(tofree->con);
        }
        MXS_FREE(tofree);
    }
}

/**
 * Free monitor server list
 * @param servers Servers to free
 */
static void monitor_server_free_all(MXS_MONITOR_SERVERS *servers)
{
    while (servers)
    {
        MXS_MONITOR_SERVERS *tofree = servers;
        servers = servers->next;
        monitor_server_free(tofree);
    }
}

/**
 * Remove a server from a monitor.
 *
 * @param mon           The Monitor instance
 * @param server        The Server to remove
 */
void monitorRemoveServer(MXS_MONITOR *mon, SERVER *server)
{
    monitor_state_t old_state = mon->state;

    if (old_state == MONITOR_STATE_RUNNING)
    {
        monitorStop(mon);
    }

    spinlock_acquire(&mon->lock);

    MXS_MONITOR_SERVERS *ptr = mon->databases;

    if (ptr && ptr->server == server)
    {
        mon->databases = mon->databases->next;
    }
    else
    {
        MXS_MONITOR_SERVERS *prev = ptr;

        while (ptr)
        {
            if (ptr->server == server)
            {
                prev->next = ptr->next;
                break;
            }
            prev = ptr;
            ptr = ptr->next;
        }
    }
    spinlock_release(&mon->lock);

    if (ptr)
    {
        monitor_server_free(ptr);
    }

    if (old_state == MONITOR_STATE_RUNNING)
    {
        monitorStart(mon, mon->parameters);
    }
}

/**
 * Add a default user to the monitor. This user is used to connect to the
 * monitored databases but may be overriden on a per server basis.
 *
 * @param mon           The monitor instance
 * @param user          The default username to use when connecting
 * @param passwd        The default password associated to the default user.
 */
void
monitorAddUser(MXS_MONITOR *mon, char *user, char *passwd)
{
    if (user != mon->user)
    {
        snprintf(mon->user, sizeof(mon->user), "%s", user);
    }

    if (passwd != mon->password)
    {
        snprintf(mon->password, sizeof(mon->password), "%s", passwd);
    }
}

/**
 * Show all monitors
 *
 * @param dcb   DCB for printing output
 */
void
monitorShowAll(DCB *dcb)
{
    MXS_MONITOR *ptr;

    spinlock_acquire(&monLock);
    ptr = allMonitors;
    while (ptr)
    {
        monitorShow(dcb, ptr);
        ptr = ptr->next;
    }
    spinlock_release(&monLock);
}

/**
 * Show a single monitor
 *
 * @param dcb   DCB for printing output
 */
void
monitorShow(DCB *dcb, MXS_MONITOR *monitor)
{
    const char *state;

    switch (monitor->state)
    {
    case MONITOR_STATE_RUNNING:
        state = "Running";
        break;
    case MONITOR_STATE_STOPPING:
        state = "Stopping";
        break;
    case MONITOR_STATE_STOPPED:
        state = "Stopped";
        break;
    case MONITOR_STATE_ALLOC:
        state = "Allocated";
        break;
    default:
        state = "Unknown";
        break;
    }

    dcb_printf(dcb, "Monitor:           %p\n", monitor);
    dcb_printf(dcb, "Name:              %s\n", monitor->name);
    dcb_printf(dcb, "State:             %s\n", state);
    dcb_printf(dcb, "Sampling interval: %lu milliseconds\n", monitor->interval);
    dcb_printf(dcb, "Connect Timeout:   %i seconds\n", monitor->connect_timeout);
    dcb_printf(dcb, "Read Timeout:      %i seconds\n", monitor->read_timeout);
    dcb_printf(dcb, "Write Timeout:     %i seconds\n", monitor->write_timeout);
    dcb_printf(dcb, "Monitored servers: ");

    const char *sep = "";

    for (MXS_MONITOR_SERVERS *db = monitor->databases; db; db = db->next)
    {
        dcb_printf(dcb, "%s%s:%d", sep, db->server->name, db->server->port);
        sep = ", ";
    }

    dcb_printf(dcb, "\n");

    if (monitor->handle)
    {
        if (monitor->module->diagnostics)
        {
            monitor->module->diagnostics(dcb, monitor);
        }
        else
        {
            dcb_printf(dcb, "\t(no diagnostics)\n");
        }
    }
    else
    {
        dcb_printf(dcb, "\tMonitor failed\n");
    }
    dcb_printf(dcb, "\n");
}

/**
 * List all the monitors
 *
 * @param dcb   DCB for printing output
 */
void
monitorList(DCB *dcb)
{
    MXS_MONITOR *ptr;

    spinlock_acquire(&monLock);
    ptr = allMonitors;
    dcb_printf(dcb, "---------------------+---------------------\n");
    dcb_printf(dcb, "%-20s | Status\n", "Monitor");
    dcb_printf(dcb, "---------------------+---------------------\n");
    while (ptr)
    {
        dcb_printf(dcb, "%-20s | %s\n", ptr->name,
                   ptr->state & MONITOR_STATE_RUNNING
                   ? "Running" : "Stopped");
        ptr = ptr->next;
    }
    dcb_printf(dcb, "---------------------+---------------------\n");
    spinlock_release(&monLock);
}

/**
 * Find a monitor by name
 *
 * @param       name    The name of the monitor
 * @return      Pointer to the monitor or NULL
 */
MXS_MONITOR *
monitor_find(const char *name)
{
    MXS_MONITOR *ptr;

    spinlock_acquire(&monLock);
    ptr = allMonitors;
    while (ptr)
    {
        if (!strcmp(ptr->name, name))
        {
            break;
        }
        ptr = ptr->next;
    }
    spinlock_release(&monLock);
    return ptr;
}

/**
 * Set the monitor sampling interval.
 *
 * @param mon           The monitor instance
 * @param interval      The sampling interval in milliseconds
 */
void
monitorSetInterval(MXS_MONITOR *mon, unsigned long interval)
{
    mon->interval = interval;
}

/**
 * Set Monitor timeouts for connect/read/write
 *
 * @param mon           The monitor instance
 * @param type          The timeout handling type
 * @param value         The timeout to set
 */
bool
monitorSetNetworkTimeout(MXS_MONITOR *mon, int type, int value)
{
    bool rval = true;

    if (value > 0)
    {
        switch (type)
        {
        case MONITOR_CONNECT_TIMEOUT:
            mon->connect_timeout = value;
            break;

        case MONITOR_READ_TIMEOUT:
            mon->read_timeout = value;
            break;

        case MONITOR_WRITE_TIMEOUT:
            mon->write_timeout = value;
            break;

        default:
            MXS_ERROR("Monitor setNetworkTimeout received an unsupported action type %i", type);
            rval = false;
            break;
        }
    }
    else
    {
        MXS_ERROR("Negative value for monitor timeout.");
        rval = false;
    }
    return rval;
}

/**
 * Provide a row to the result set that defines the set of monitors
 *
 * @param set   The result set
 * @param data  The index of the row to send
 * @return The next row or NULL
 */
static RESULT_ROW *
monitorRowCallback(RESULTSET *set, void *data)
{
    int *rowno = (int *)data;
    int i = 0;;
    char buf[20];
    RESULT_ROW *row;
    MXS_MONITOR *ptr;

    spinlock_acquire(&monLock);
    ptr = allMonitors;
    while (i < *rowno && ptr)
    {
        i++;
        ptr = ptr->next;
    }
    if (ptr == NULL)
    {
        spinlock_release(&monLock);
        MXS_FREE(data);
        return NULL;
    }
    (*rowno)++;
    row = resultset_make_row(set);
    resultset_row_set(row, 0, ptr->name);
    resultset_row_set(row, 1, ptr->state & MONITOR_STATE_RUNNING
                      ? "Running" : "Stopped");
    spinlock_release(&monLock);
    return row;
}

/**
 * Return a resultset that has the current set of monitors in it
 *
 * @return A Result set
 */
RESULTSET *
monitorGetList()
{
    RESULTSET *set;
    int *data;

    if ((data = (int *)MXS_MALLOC(sizeof(int))) == NULL)
    {
        return NULL;
    }
    *data = 0;
    if ((set = resultset_create(monitorRowCallback, data)) == NULL)
    {
        MXS_FREE(data);
        return NULL;
    }
    resultset_add_column(set, "Monitor", 20, COL_TYPE_VARCHAR);
    resultset_add_column(set, "Status", 10, COL_TYPE_VARCHAR);

    return set;
}

/**
 * @brief Check if the monitor user has all required permissions to operate properly.
 *
 * @param service Monitor to inspect
 * @param query Query to execute
 * @return True on success, false if monitor credentials lack permissions
 */
bool check_monitor_permissions(MXS_MONITOR* monitor, const char* query)
{
    if (monitor->databases == NULL || // No servers to check
        config_get_global_options()->skip_permission_checks)
    {
        return true;
    }

    char *user = monitor->user;
    char *dpasswd = decrypt_password(monitor->password);
    MXS_CONFIG* cnf = config_get_global_options();
    bool rval = false;

    for (MXS_MONITOR_SERVERS *mondb = monitor->databases; mondb; mondb = mondb->next)
    {
        if (mon_connect_to_db(monitor, mondb) != MONITOR_CONN_OK)
        {
            MXS_ERROR("[%s] Failed to connect to server '%s' (%s:%d) when"
                      " checking monitor user credentials and permissions: %s",
                      monitor->name, mondb->server->unique_name, mondb->server->name,
                      mondb->server->port, mysql_error(mondb->con));
            switch (mysql_errno(mondb->con))
            {
            case ER_ACCESS_DENIED_ERROR:
            case ER_DBACCESS_DENIED_ERROR:
            case ER_ACCESS_DENIED_NO_PASSWORD_ERROR:
                break;
            default:
                rval = true;
                break;
            }
        }
        else if (mysql_query(mondb->con, query) != 0)
        {
            switch (mysql_errno(mondb->con))
            {
            case ER_TABLEACCESS_DENIED_ERROR:
            case ER_COLUMNACCESS_DENIED_ERROR:
            case ER_SPECIFIC_ACCESS_DENIED_ERROR:
            case ER_PROCACCESS_DENIED_ERROR:
            case ER_KILL_DENIED_ERROR:
                rval = false;
                break;

            default:
                rval = true;
                break;
            }

            MXS_ERROR("[%s] Failed to execute query '%s' with user '%s'. MySQL error message: %s",
                      monitor->name, query, user, mysql_error(mondb->con));
        }
        else
        {
            rval = true;
            MYSQL_RES *res = mysql_use_result(mondb->con);
            if (res == NULL)
            {
                MXS_ERROR("[%s] Result retrieval failed when checking monitor permissions: %s",
                          monitor->name, mysql_error(mondb->con));
            }
            else
            {
                mysql_free_result(res);
            }
        }
    }

    MXS_FREE(dpasswd);
    return rval;
}

/**
 * Add parameters to the monitor
 * @param monitor Monitor
 * @param params Config parameters
 */
void monitorAddParameters(MXS_MONITOR *monitor, MXS_CONFIG_PARAMETER *params)
{
    while (params)
    {
        MXS_CONFIG_PARAMETER* clone = config_clone_param(params);
        if (clone)
        {
            clone->next = monitor->parameters;
            monitor->parameters = clone;
        }
        params = params->next;
    }
}

bool monitorRemoveParameter(MXS_MONITOR *monitor, const char *key)
{
    MXS_CONFIG_PARAMETER *prev = NULL;

    for (MXS_CONFIG_PARAMETER *p = monitor->parameters; p; p = p->next)
    {
        if (strcmp(p->name, key) == 0)
        {
            if (p == monitor->parameters)
            {
                monitor->parameters = monitor->parameters->next;
                p->next = NULL;
            }
            else
            {
                prev->next = p->next;
                p->next = NULL;
            }
            config_parameter_free(p);
            return true;
        }
        prev = p;
    }
    return false;
}

/**
 * Set a pending status bit in the monitor server
 *
 * @param server        The server to update
 * @param bit           The bit to clear for the server
 */
void
monitor_set_pending_status(MXS_MONITOR_SERVERS *ptr, int bit)
{
    ptr->pending_status |= bit;
}

/**
 * Clear a pending status bit in the monitor server
 *
 * @param server        The server to update
 * @param bit           The bit to clear for the server
 */
void
monitor_clear_pending_status(MXS_MONITOR_SERVERS *ptr, int bit)
{
    ptr->pending_status &= ~bit;
}

/*
 * Determine a monitor event, defined by the difference between the old
 * status of a server and the new status.
 *
 * @param   node                The monitor server data for a particular server
 * @result  monitor_event_t     A monitor event (enum)
 */
static mxs_monitor_event_t mon_get_event_type(MXS_MONITOR_SERVERS* node)
{
    typedef enum
    {
        DOWN_EVENT,
        UP_EVENT,
        LOSS_EVENT,
        NEW_EVENT,
        UNSUPPORTED_EVENT
    } general_event_type;

    general_event_type event_type = UNSUPPORTED_EVENT;

    unsigned int prev = node->mon_prev_status & all_server_bits;
    unsigned int present = node->server->status & all_server_bits;

    if (prev == present)
    {
        /* This should never happen */
        ss_dassert(false);
        return UNDEFINED_EVENT;
    }

    if ((prev & SERVER_RUNNING) == 0)
    {
        /* The server was not running previously */
        if ((present & SERVER_RUNNING) != 0)
        {
            event_type = UP_EVENT;
        }
        else
        {
            /* Otherwise, was not running and still is not running. This should never happen. */
            ss_dassert(false);
        }
    }
    else
    {
        /* Previous state must have been running */
        if ((present & SERVER_RUNNING) == 0)
        {
            event_type = DOWN_EVENT;
        }
        else
        {
            /** These are used to detect whether we actually lost something or
             * just transitioned from one state to another */
            unsigned int prev_bits = prev & (SERVER_MASTER | SERVER_SLAVE);
            unsigned int present_bits = present & (SERVER_MASTER | SERVER_SLAVE);

            /* Was running and still is */
            if ((!prev_bits || !present_bits || prev_bits == present_bits) &&
                (prev & server_type_bits))
            {
                /* We used to know what kind of server it was */
                event_type = LOSS_EVENT;
            }
            else
            {
                /* We didn't know what kind of server it was, now we do*/
                event_type = NEW_EVENT;
            }
        }
    }

    mxs_monitor_event_t rval = UNDEFINED_EVENT;

    switch (event_type)
    {
    case UP_EVENT:
        rval = (present & SERVER_MASTER) ? MASTER_UP_EVENT :
               (present & SERVER_SLAVE) ? SLAVE_UP_EVENT :
               (present & SERVER_JOINED) ? SYNCED_UP_EVENT :
               (present & SERVER_NDB) ? NDB_UP_EVENT :
               SERVER_UP_EVENT;
        break;

    case DOWN_EVENT:
        rval = (prev & SERVER_MASTER) ? MASTER_DOWN_EVENT :
               (prev & SERVER_SLAVE) ? SLAVE_DOWN_EVENT :
               (prev & SERVER_JOINED) ? SYNCED_DOWN_EVENT :
               (prev & SERVER_NDB) ? NDB_DOWN_EVENT :
               SERVER_DOWN_EVENT;
        break;

    case LOSS_EVENT:
        rval = (prev & SERVER_MASTER) ? LOST_MASTER_EVENT :
               (prev & SERVER_SLAVE) ? LOST_SLAVE_EVENT :
               (prev & SERVER_JOINED) ? LOST_SYNCED_EVENT :
               (prev & SERVER_NDB) ? LOST_NDB_EVENT :
               UNDEFINED_EVENT;
        break;

    case NEW_EVENT:
        rval = (present & SERVER_MASTER) ? NEW_MASTER_EVENT :
               (present & SERVER_SLAVE) ? NEW_SLAVE_EVENT :
               (present & SERVER_JOINED) ? NEW_SYNCED_EVENT :
               (present & SERVER_NDB) ? NEW_NDB_EVENT :
               UNDEFINED_EVENT;
        break;

    default:
        /* This should never happen */
        ss_dassert(false);
        break;
    }

    ss_dassert(rval != UNDEFINED_EVENT);
    return rval;
}

/*
 * Given a monitor event (enum) provide a text string equivalent
 * @param   node    The monitor server data whose event is wanted
 * @result  string  The name of the monitor event for the server
 */
static const char* mon_get_event_name(MXS_MONITOR_SERVERS* node)
{
    mxs_monitor_event_t event = mon_get_event_type(node);

    for (int i = 0; mxs_monitor_event_enum_values[i].name; i++)
    {
        if (mxs_monitor_event_enum_values[i].enum_value & event)
        {
            return mxs_monitor_event_enum_values[i].name;
        }
    }

    ss_dassert(false);
    return "undefined_event";
}

/**
 * Create a list of running servers
 *
 * @param servers Monitored servers
 * @param dest Destination where the string is appended, must be null terminated
 * @param len Length of @c dest
 */
static void mon_append_node_names(MXS_MONITOR_SERVERS* servers, char* dest, int len, int status)
{
    char *separator = "";
    char arr[MAX_SERVER_NAME_LEN + 64]; // Some extra space for port and separator
    dest[0] = '\0';

    while (servers && len)
    {
        if (status == 0 || servers->server->status & status)
        {
            snprintf(arr, sizeof(arr), "%s%s:%d", separator, servers->server->name,
                     servers->server->port);
            separator = ",";
            int arrlen = strlen(arr);

            if (arrlen < len)
            {
                strcat(dest, arr);
                len -= arrlen;
            }
        }
        servers = servers->next;
    }
}

/**
 * Check if current monitored server status has changed
 *
 * @param mon_srv       The monitored server
 * @return              true if status has changed or false
 */
bool mon_status_changed(MXS_MONITOR_SERVERS* mon_srv)
{
    bool rval = false;

    /* Previous status is -1 if not yet set */
    if (mon_srv->mon_prev_status != -1)
    {

        unsigned int old_status = mon_srv->mon_prev_status & all_server_bits;
        unsigned int new_status = mon_srv->server->status & all_server_bits;

        /**
         * The state has changed if the relevant state bits are not the same,
         * the server is either running, stopping or starting and the server is
         * not going into maintenance or coming out of it
         */
        if (old_status != new_status &&
            ((old_status | new_status) & SERVER_MAINT) == 0 &&
            ((old_status | new_status) & SERVER_RUNNING) == SERVER_RUNNING)
        {
            rval = true;
        }
    }

    return rval;
}

/**
 * Check if current monitored server has a loggable failure status
 *
 * @param mon_srv       The monitored server
 * @return              true if failed status can be logged or false
 */
bool
mon_print_fail_status(MXS_MONITOR_SERVERS* mon_srv)
{
    return (SERVER_IS_DOWN(mon_srv->server) && mon_srv->mon_err_count == 0);
}

/**
 * Launch a script
 * @param mon Owning monitor
 * @param ptr The server which has changed state
 * @param script Script to execute
 */
void
monitor_launch_script(MXS_MONITOR* mon, MXS_MONITOR_SERVERS* ptr, const char* script)
{
    char arg[strlen(script) + 1];
    strcpy(arg, script);

    EXTERNCMD* cmd = externcmd_allocate(arg);

    if (cmd == NULL)
    {
        MXS_ERROR("Failed to initialize script '%s'. See previous errors for the "
                  "cause of this failure.", script);
        return;
    }

    if (externcmd_matches(cmd, "$INITIATOR"))
    {
        char initiator[strlen(ptr->server->name) + 24]; // Extra space for port
        snprintf(initiator, sizeof(initiator), "%s:%d", ptr->server->name, ptr->server->port);
        externcmd_substitute_arg(cmd, "[$]INITIATOR", initiator);
    }

    if (externcmd_matches(cmd, "$EVENT"))
    {
        externcmd_substitute_arg(cmd, "[$]EVENT", mon_get_event_name(ptr));
    }

    char nodelist[PATH_MAX + MON_ARG_MAX + 1] = {'\0'};

    if (externcmd_matches(cmd, "$NODELIST"))
    {
        mon_append_node_names(mon->databases, nodelist, sizeof(nodelist), SERVER_RUNNING);
        externcmd_substitute_arg(cmd, "[$]NODELIST", nodelist);
    }

    if (externcmd_matches(cmd, "$LIST"))
    {
        mon_append_node_names(mon->databases, nodelist, sizeof(nodelist), 0);
        externcmd_substitute_arg(cmd, "[$]LIST", nodelist);
    }

    if (externcmd_matches(cmd, "$MASTERLIST"))
    {
        mon_append_node_names(mon->databases, nodelist, sizeof(nodelist), SERVER_MASTER);
        externcmd_substitute_arg(cmd, "[$]MASTERLIST", nodelist);
    }

    if (externcmd_matches(cmd, "$SLAVELIST"))
    {
        mon_append_node_names(mon->databases, nodelist, sizeof(nodelist), SERVER_SLAVE);
        externcmd_substitute_arg(cmd, "[$]SLAVELIST", nodelist);
    }

    if (externcmd_matches(cmd, "$SYNCEDLIST"))
    {
        mon_append_node_names(mon->databases, nodelist, sizeof(nodelist), SERVER_JOINED);
        externcmd_substitute_arg(cmd, "[$]SYNCEDLIST", nodelist);
    }

    if (externcmd_execute(cmd))
    {
        MXS_ERROR("Failed to execute script '%s' on server state change event '%s'.",
                  script, mon_get_event_name(ptr));
    }
    else
    {
        ss_dassert(cmd->argv != NULL && cmd->argv[0] != NULL);
        // Construct a string with the script + arguments
        char *scriptStr = NULL;
        int totalStrLen = 0;
        bool memError = false;
        for (int i = 0; cmd->argv[i]; i++)
        {
            totalStrLen += strlen(cmd->argv[i]) + 1; // +1 for space and one \0
        }
        int spaceRemaining = totalStrLen;
        if ((scriptStr = MXS_CALLOC(totalStrLen, sizeof(char))) != NULL)
        {
            char *currentPos = scriptStr;
            // The script name should not begin with a space
            int len = snprintf(currentPos, spaceRemaining, "%s", cmd->argv[0]);
            currentPos += len;
            spaceRemaining -= len;

            for (int i = 1; cmd->argv[i]; i++)
            {
                if ((cmd->argv[i])[0] == '\0')
                {
                    continue; // Empty argument, print nothing
                }
                len = snprintf(currentPos, spaceRemaining, " %s", cmd->argv[i]);
                currentPos += len;
                spaceRemaining -= len;
            }
            ss_dassert(spaceRemaining > 0);
            *currentPos = '\0';
        }
        else
        {
            memError = true;
            scriptStr = cmd->argv[0]; // print at least something
        }
        MXS_NOTICE("Executed monitor script '%s' on event '%s'.",
                   scriptStr, mon_get_event_name(ptr));
        if (!memError)
        {
            MXS_FREE(scriptStr);
        }
    }

    externcmd_free(cmd);
}

/**
 * Connect to a database. This will always leave a valid database handle in the
 * database->con pointer. This allows the user to call MySQL C API functions to
 * find out the reason of the failure.
 * @param mon Monitor
 * @param database Monitored database
 * @return MONITOR_CONN_OK if the connection is OK else the reason for the failure
 */
mxs_connect_result_t
mon_connect_to_db(MXS_MONITOR* mon, MXS_MONITOR_SERVERS *database)
{
    mxs_connect_result_t rval = MONITOR_CONN_OK;

    /** Return if the connection is OK */
    if (database->con && mysql_ping(database->con) == 0)
    {
        return rval;
    }

    if (database->con)
    {
        mysql_close(database->con);
    }

    if ((database->con = mysql_init(NULL)))
    {
        char *uname = mon->user;
        char *passwd = mon->password;

        if (database->server->monuser[0] && database->server->monpw[0])
        {
            uname = database->server->monuser;
            passwd = database->server->monpw;
        }

        char *dpwd = decrypt_password(passwd);

        mysql_optionsv(database->con, MYSQL_OPT_CONNECT_TIMEOUT, (void *) &mon->connect_timeout);
        mysql_optionsv(database->con, MYSQL_OPT_READ_TIMEOUT, (void *) &mon->read_timeout);
        mysql_optionsv(database->con, MYSQL_OPT_WRITE_TIMEOUT, (void *) &mon->write_timeout);
        mysql_optionsv(database->con, MYSQL_PLUGIN_DIR, get_connector_plugindir());
        time_t start = time(NULL);
        bool result = (mxs_mysql_real_connect(database->con, database->server, uname, dpwd) != NULL);
        time_t end = time(NULL);

        if (!result)
        {
            if ((int) difftime(end, start) >= mon->connect_timeout)
            {
                rval = MONITOR_CONN_TIMEOUT;
            }
            else
            {
                rval = MONITOR_CONN_REFUSED;
            }
        }

        MXS_FREE(dpwd);
    }
    else
    {
        rval = MONITOR_CONN_REFUSED;
    }

    return rval;
}

/**
 * Log an error about the failure to connect to a backend server
 * and why it happened.
 * @param database Backend database
 * @param rval Return value of mon_connect_to_db
 */
void
mon_log_connect_error(MXS_MONITOR_SERVERS* database, mxs_connect_result_t rval)
{
    MXS_ERROR(rval == MONITOR_CONN_TIMEOUT ?
              "Monitor timed out when connecting to server %s:%d : \"%s\"" :
              "Monitor was unable to connect to server %s:%d : \"%s\"",
              database->server->name, database->server->port,
              mysql_error(database->con));
}

static void mon_log_state_change(MXS_MONITOR_SERVERS *ptr)
{
    SERVER srv;
    srv.status = ptr->mon_prev_status;
    char *prev = server_status(&srv);
    char *next = server_status(ptr->server);
    MXS_NOTICE("Server changed state: %s[%s:%u]: %s. [%s] -> [%s]",
               ptr->server->unique_name, ptr->server->name, ptr->server->port,
               mon_get_event_name(ptr), prev, next);
    MXS_FREE(prev);
    MXS_FREE(next);
}

MXS_MONITOR* monitor_server_in_use(const SERVER *server)
{
    MXS_MONITOR *rval = NULL;

    spinlock_acquire(&monLock);

    for (MXS_MONITOR *mon = allMonitors; mon && !rval; mon = mon->next)
    {
        spinlock_acquire(&mon->lock);

        for (MXS_MONITOR_SERVERS *db = mon->databases; db && !rval; db = db->next)
        {
            if (db->server == server)
            {
                rval = mon;
            }
        }

        spinlock_release(&mon->lock);
    }

    spinlock_release(&monLock);

    return rval;
}

/**
 * Creates a monitor configuration at the location pointed by @c filename
 *
 * @param monitor Monitor to serialize into a configuration
 * @param filename Filename where configuration is written
 * @return True on success, false on error
 */
static bool create_monitor_server_config(const MXS_MONITOR *monitor, const char *filename)
{
    int file = open(filename, O_EXCL | O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);

    if (file == -1)
    {
        char errbuf[MXS_STRERROR_BUFLEN];
        MXS_ERROR("Failed to open file '%s' when serializing monitor '%s': %d, %s",
                  filename, monitor->name, errno, strerror_r(errno, errbuf, sizeof(errbuf)));
        return false;
    }

    /**
     * Only additional parameters are added to the configuration. This prevents
     * duplication or addition of parameters that don't support it.
     *
     * TODO: Check for return values on all of the dprintf calls
     */
    dprintf(file, "[%s]\n", monitor->name);

    if (monitor->databases)
    {
        dprintf(file, "servers=");
        for (MXS_MONITOR_SERVERS *db = monitor->databases; db; db = db->next)
        {
            if (db != monitor->databases)
            {
                dprintf(file, ",");
            }
            dprintf(file, "%s", db->server->unique_name);
        }
        dprintf(file, "\n");
    }

    close(file);

    return true;
}

static bool create_monitor_config(const MXS_MONITOR *monitor, const char *filename)
{
    int file = open(filename, O_EXCL | O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);

    if (file == -1)
    {
        char errbuf[MXS_STRERROR_BUFLEN];
        MXS_ERROR("Failed to open file '%s' when serializing monitor '%s': %d, %s",
                  filename, monitor->name, errno, strerror_r(errno, errbuf, sizeof(errbuf)));
        return false;
    }

    /**
     * Only additional parameters are added to the configuration. This prevents
     * duplication or addition of parameters that don't support it.
     *
     * TODO: Check for return values on all of the dprintf calls
     */
    dprintf(file, "[%s]\n", monitor->name);
    dprintf(file, "type=monitor\n");
    dprintf(file, "module=%s\n", monitor->module_name);
    dprintf(file, "user=%s\n", monitor->user);
    dprintf(file, "password=%s\n", monitor->password);
    dprintf(file, "monitor_interval=%lu\n", monitor->interval);
    dprintf(file, "backend_connect_timeout=%d\n", monitor->connect_timeout);
    dprintf(file, "backend_write_timeout=%d\n", monitor->write_timeout);
    dprintf(file, "backend_read_timeout=%d\n", monitor->read_timeout);
    close(file);

    return true;
}

bool monitor_serialize_servers(const MXS_MONITOR *monitor)
{
    bool rval = false;
    char filename[PATH_MAX];
    snprintf(filename, sizeof(filename), "%s/%s.cnf.tmp", get_config_persistdir(),
             monitor->name);

    if (unlink(filename) == -1 && errno != ENOENT)
    {
        char err[MXS_STRERROR_BUFLEN];
        MXS_ERROR("Failed to remove temporary monitor configuration at '%s': %d, %s",
                  filename, errno, strerror_r(errno, err, sizeof(err)));
    }
    else if (create_monitor_server_config(monitor, filename))
    {
        char final_filename[PATH_MAX];
        strcpy(final_filename, filename);

        char *dot = strrchr(final_filename, '.');
        ss_dassert(dot);
        *dot = '\0';

        if (rename(filename, final_filename) == 0)
        {
            rval = true;
        }
        else
        {
            char err[MXS_STRERROR_BUFLEN];
            MXS_ERROR("Failed to rename temporary monitor configuration at '%s': %d, %s",
                      filename, errno, strerror_r(errno, err, sizeof(err)));
        }
    }

    return rval;
}

bool monitor_serialize(const MXS_MONITOR *monitor)
{
    bool rval = false;
    char filename[PATH_MAX];
    snprintf(filename, sizeof(filename), "%s/%s.cnf.tmp", get_config_persistdir(),
             monitor->name);

    if (unlink(filename) == -1 && errno != ENOENT)
    {
        char err[MXS_STRERROR_BUFLEN];
        MXS_ERROR("Failed to remove temporary monitor configuration at '%s': %d, %s",
                  filename, errno, strerror_r(errno, err, sizeof(err)));
    }
    else if (create_monitor_config(monitor, filename))
    {
        char final_filename[PATH_MAX];
        strcpy(final_filename, filename);

        char *dot = strrchr(final_filename, '.');
        ss_dassert(dot);
        *dot = '\0';

        if (rename(filename, final_filename) == 0)
        {
            rval = true;
        }
        else
        {
            char err[MXS_STRERROR_BUFLEN];
            MXS_ERROR("Failed to rename temporary monitor configuration at '%s': %d, %s",
                      filename, errno, strerror_r(errno, err, sizeof(err)));
        }
    }

    return rval;
}

void mon_hangup_failed_servers(MXS_MONITOR *monitor)
{
    for (MXS_MONITOR_SERVERS *ptr = monitor->databases; ptr; ptr = ptr->next)
    {
        if (mon_status_changed(ptr) &&
            (!(SERVER_IS_RUNNING(ptr->server)) ||
             !(SERVER_IS_IN_CLUSTER(ptr->server))))
        {
            dcb_hangup_foreach(ptr->server);
        }
    }
}
/**
  * Acquire locks on all servers monitored by this monitor. There should
  * only be max 1 monitor per server.
  * @param monitor The target monitor
  */
void lock_monitor_servers(MXS_MONITOR *monitor)
{
    MXS_MONITOR_SERVERS *ptr = monitor->databases;
    while (ptr)
    {
        spinlock_acquire(&ptr->server->lock);
        ptr = ptr->next;
    }
}
/**
  * Release locks on all servers monitored by this monitor. There should
  * only be max 1 monitor per server.
  * @param monitor The target monitor
  */
void release_monitor_servers(MXS_MONITOR *monitor)
{
    MXS_MONITOR_SERVERS *ptr = monitor->databases;
    while (ptr)
    {
        spinlock_release(&ptr->server->lock);
        ptr = ptr->next;
    }
}
/**
  * Sets the current status of all servers monitored by this monitor to
  * the pending status. This should only be called at the beginning of
  * a monitor loop, after the servers are locked.
  * @param monitor The target monitor
  */
void servers_status_pending_to_current(MXS_MONITOR *monitor)
{
    MXS_MONITOR_SERVERS *ptr = monitor->databases;
    while (ptr)
    {
        ptr->server->status = ptr->server->status_pending;
        ptr = ptr->next;
    }
    monitor->server_pending_changes = false;
}
/**
  *  Sets the pending status of all servers monitored by this monitor to
  *  the current status. This should only be called at the end of
  *  a monitor loop, before the servers are released.
  *  @param monitor The target monitor
  */
void servers_status_current_to_pending(MXS_MONITOR *monitor)
{
    MXS_MONITOR_SERVERS *ptr = monitor->databases;
    while (ptr)
    {
        ptr->server->status_pending = ptr->server->status;
        ptr = ptr->next;
    }
}

void mon_process_state_changes(MXS_MONITOR *monitor, const char *script, uint64_t events)
{
    for (MXS_MONITOR_SERVERS *ptr = monitor->databases; ptr; ptr = ptr->next)
    {
        if (mon_status_changed(ptr))
        {
            mon_log_state_change(ptr);

            if (script && (events & mon_get_event_type(ptr)))
            {
                monitor_launch_script(monitor, ptr, script);
            }
        }
    }
}