/*
    SSSD

    LDAP ID backend operation retry logic and connection cache

    Authors:
        Eugene Indenbom <eindenbom@gmail.com>

    Copyright (C) 2008-2010 Red Hat

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "providers/ldap/ldap_common.h"
#include "providers/ldap/sdap_async.h"
#include "providers/ldap/sdap_id_op.h"

/* LDAP async connection cache */
struct sdap_id_conn_cache {
    struct sdap_id_ctx *id_ctx;

    /* list of all open connections */
    struct sdap_id_conn_data *connections;
    /* cached (current) connection */
    struct sdap_id_conn_data *cached_connection;
};

/* LDAP async operation tracker:
 *  - keeps track of connection usage
 *  - keeps track of operation retries */
struct sdap_id_op {
    /* ID backend context */
    struct sdap_id_conn_cache *conn_cache;
    /* double linked list pointers */
    struct sdap_id_op *prev, *next;
    /* current connection */
    struct sdap_id_conn_data *conn_data;
    /* number of reconnects for this operation */
    int reconnect_retry_count;
    /* connection request
     * It is required as we need to know which requests to notify
     * when shared connection request to sdap_handle completes.
     * This member is cleared when sdap_id_op_connect_state
     * associated with request is destroyed */
    struct tevent_req *connect_req;
};

/* LDAP connection cache connection attempt/established connection data */
struct sdap_id_conn_data {
    /* LDAP connection cache */
    struct sdap_id_conn_cache *conn_cache;
    /* double linked list pointers */
    struct sdap_id_conn_data *prev, *next;
    /* sdap handle */
    struct sdap_handle *sh;
    /* connection request */
    struct tevent_req *connect_req;
    /* timer for connection expiration */
    struct tevent_timer *expire_timer;
    /* number of running connection notifies */
    int notify_lock;
    /* list of operations using connect */
    struct sdap_id_op *ops;
};

static void sdap_id_conn_cache_be_offline_cb(void *pvt);

static void sdap_id_release_conn_data(struct sdap_id_conn_data *conn_data);
static int sdap_id_conn_data_destroy(struct sdap_id_conn_data *conn_data);
static bool sdap_is_connection_expired(struct sdap_id_conn_data *conn_data, int timeout);
static bool sdap_can_reuse_connection(struct sdap_id_conn_data *conn_data);
static void sdap_id_conn_data_expire_handler(struct tevent_context *ev,
                                             struct tevent_timer *te,
                                             struct timeval current_time,
                                             void *pvt);
static int sdap_id_conn_data_set_expire_timer(struct sdap_id_conn_data *conn_data);

static void sdap_id_op_hook_conn_data(struct sdap_id_op *op, struct sdap_id_conn_data *conn_data);
static int sdap_id_op_destroy(void *pvt);
static bool sdap_id_op_can_reconnect(struct sdap_id_op *op);

static void sdap_id_op_connect_req_complete(struct sdap_id_op *op, int dp_error, int ret);
static int sdap_id_op_connect_state_destroy(void *pvt);
static int sdap_id_op_connect_step(struct tevent_req *req);
static void sdap_id_op_connect_done(struct tevent_req *subreq);

/* Create a connection cache */
int sdap_id_conn_cache_create(TALLOC_CTX *memctx,
                              struct sdap_id_ctx *id_ctx,
                              struct sdap_id_conn_cache** conn_cache_out)
{
    int ret;
    struct sdap_id_conn_cache *conn_cache = talloc_zero(memctx, struct sdap_id_conn_cache);
    if (!conn_cache) {
        DEBUG(1, ("talloc_zero(struct sdap_id_conn_cache) failed.\n"));
        ret = ENOMEM;
        goto fail;
    }

    conn_cache->id_ctx = id_ctx;

    ret = be_add_offline_cb(conn_cache, id_ctx->be,
                            sdap_id_conn_cache_be_offline_cb, conn_cache,
                            NULL);
    if (ret != EOK) {
        DEBUG(1, ("be_add_offline_cb failed.\n"));
        goto fail;
    }

    *conn_cache_out = conn_cache;
    return EOK;

fail:
    talloc_zfree(conn_cache);
    return ret;
}

/* Callback on BE going offline */
static void sdap_id_conn_cache_be_offline_cb(void *pvt)
{
    struct sdap_id_conn_cache *conn_cache = talloc_get_type(pvt, struct sdap_id_conn_cache);
    struct sdap_id_conn_data *cached_connection = conn_cache->cached_connection;

    /* Release any cached connection on going offline */
    if (cached_connection != NULL) {
        conn_cache->cached_connection = NULL;
        sdap_id_release_conn_data(cached_connection);
    }
}

/* Release sdap_id_conn_data and destroy it if no longer needed */
static void sdap_id_release_conn_data(struct sdap_id_conn_data *conn_data)
{
    struct sdap_id_conn_cache *conn_cache;
    if (!conn_data || conn_data->ops || conn_data->notify_lock) {
        /* connection is in use */
        return;
    }

    conn_cache = conn_data->conn_cache;
    if (conn_data == conn_cache->cached_connection) {
        return;
    }

    DEBUG(9, ("releasing unused connection\n"));

    DLIST_REMOVE(conn_cache->connections, conn_data);
    talloc_zfree(conn_data);
}

/* Destructor for struct sdap_id_conn_data */
static int sdap_id_conn_data_destroy(struct sdap_id_conn_data *conn_data)
{
    struct sdap_id_op *op;

    /* we clean out list of ops to make sure that order of destruction does not matter */
    while ((op = conn_data->ops) != NULL) {
        op->conn_data = NULL;
        DLIST_REMOVE(conn_data->ops, op);
    }

    return 0;
}

/* Check whether connection will expire after timeout seconds */
static bool sdap_is_connection_expired(struct sdap_id_conn_data *conn_data, int timeout)
{
    time_t expire_time;
    if (!conn_data || !conn_data->sh || !conn_data->sh->connected) {
        return true;
    }

    expire_time = conn_data->sh->expire_time;
    if ((expire_time != 0) && (expire_time < time( NULL ) + timeout) ) {
        return true;
    }

    return false;
}

/* Check whether connection can be reused for next LDAP ID operation */
static bool sdap_can_reuse_connection(struct sdap_id_conn_data *conn_data)
{
    int timeout;

    if (!conn_data || !conn_data->sh || !conn_data->sh->connected) {
        return false;
    }

    timeout = dp_opt_get_int(conn_data->conn_cache->id_ctx->opts->basic,
                             SDAP_OPT_TIMEOUT);
    return !sdap_is_connection_expired(conn_data, timeout);
}

/* Set expiration timer for connection if needed */
static int sdap_id_conn_data_set_expire_timer(struct sdap_id_conn_data *conn_data)
{
    int timeout;
    struct timeval tv;

    memset(&tv, 0, sizeof(tv));

    tv.tv_sec = conn_data->sh->expire_time;
    if (tv.tv_sec <= 0) {
        return EOK;
    }

    timeout = dp_opt_get_int(conn_data->conn_cache->id_ctx->opts->basic,
                             SDAP_OPT_TIMEOUT);
    if (timeout > 0) {
        tv.tv_sec -= timeout;
    }

    if (tv.tv_sec <= time(NULL)) {
        return EOK;
    }

    talloc_zfree(conn_data->expire_timer);

    conn_data->expire_timer =
                        tevent_add_timer(conn_data->conn_cache->id_ctx->be->ev,
                                         conn_data, tv,
                                         sdap_id_conn_data_expire_handler,
                                         conn_data);
    if (!conn_data->expire_timer) {
        return ENOMEM;
    }

    return EOK;
}

/* Handler for connection expiration timer */
static void sdap_id_conn_data_expire_handler(struct tevent_context *ev,
                                              struct tevent_timer *te,
                                              struct timeval current_time,
                                              void *pvt)
{
    struct sdap_id_conn_data *conn_data = talloc_get_type(pvt,
                                                          struct sdap_id_conn_data);
    struct sdap_id_conn_cache *conn_cache = conn_data->conn_cache;

    DEBUG(3, ("connection is about to expire, releasing it\n"));

    if (conn_cache->cached_connection == conn_data) {
        conn_cache->cached_connection = NULL;

        sdap_id_release_conn_data(conn_data);
    }
}

/* Create an operation object */
struct sdap_id_op *sdap_id_op_create(TALLOC_CTX *memctx, struct sdap_id_conn_cache *conn_cache)
{
    struct sdap_id_op *op = talloc_zero(memctx, struct sdap_id_op);
    if (!op) {
        return NULL;
    }

    op->conn_cache = conn_cache;

    talloc_set_destructor((void*)op, sdap_id_op_destroy);
    return op;
}

/* Attach/detach connection to sdap_id_op */
static void sdap_id_op_hook_conn_data(struct sdap_id_op *op, struct sdap_id_conn_data *conn_data)
{
    if (!op) {
        DEBUG(0, ("NULL op passed!!!\n"));
        return;
    }

    struct sdap_id_conn_data *current = op->conn_data;
    if (conn_data == current) {
        return;
    }

    if (current) {
        DLIST_REMOVE(current->ops, op);
    }

    op->conn_data = conn_data;

    if (conn_data) {
        DLIST_ADD_END(conn_data->ops, op, struct sdap_id_op*);
    }

    if (current) {
        sdap_id_release_conn_data(current);
    }
}

/* Destructor for sdap_id_op */
static int sdap_id_op_destroy(void *pvt)
{
    struct sdap_id_op *op = talloc_get_type(pvt, struct sdap_id_op);

    if (op->conn_data) {
        DEBUG(9, ("releasing operation connection\n"));
        sdap_id_op_hook_conn_data(op, NULL);
    }

    return 0;
}

/* Check whether retry with reconnect can be performed for the operation */
static bool sdap_id_op_can_reconnect(struct sdap_id_op *op)
{
    /* we allow 2 retries for failover server configured:
     *   - one for connection broken during request execution
     *   - one for the following (probably failed) reconnect attempt */
    int max_retries;
    int count;

    count = be_fo_get_server_count(op->conn_cache->id_ctx->be,
                                   op->conn_cache->id_ctx->service->name);
    max_retries = 2 * count -1;
    if (max_retries < 1) {
        max_retries = 1;
    }

    return op->reconnect_retry_count < max_retries;
}

/* state of connect request */
struct sdap_id_op_connect_state {
    struct sdap_id_ctx *id_ctx;
    struct tevent_context *ev;
    struct sdap_id_op *op;
    int dp_error;
    int result;
};

/* Destructor for operation connection request */
static int sdap_id_op_connect_state_destroy(void *pvt)
{
    struct sdap_id_op_connect_state *state = talloc_get_type(pvt,
                                             struct sdap_id_op_connect_state);
    if (state->op != NULL) {
        /* clear destroyed connection request */
        state->op->connect_req = NULL;
    }

    return 0;
}

/* Begin to connect to LDAP server */
struct tevent_req *sdap_id_op_connect_send(struct sdap_id_op *op,
                                           TALLOC_CTX *memctx,
                                           int *ret_out)
{
    struct tevent_req *req = NULL;
    struct sdap_id_op_connect_state *state;
    int ret = EOK;

    if (!memctx) {
        DEBUG(1, ("Bug: no memory context passed.\n"));
        ret = EINVAL;
        goto done;
    }

    if (op->connect_req) {
        /* Connection already in progress, invalid operation */
        DEBUG(1, ("Bug: connection request is already running or completed and leaked.\n"));
        ret = EINVAL;
        goto done;
    }

    req = tevent_req_create(memctx, &state, struct sdap_id_op_connect_state);
    if (!req) {
        ret = ENOMEM;
        goto done;
    }

    talloc_set_destructor((void*)state, sdap_id_op_connect_state_destroy);

    state->id_ctx = op->conn_cache->id_ctx;
    state->ev = state->id_ctx->be->ev;
    state->op = op;
    op->connect_req = req;

    if (op->conn_data) {
        /* If the operation is already connected,
         * reuse existing connection regardless of its status */
        DEBUG(9, ("reusing operation connection\n"));
        ret = EOK;
        goto done;
    }

    ret = sdap_id_op_connect_step(req);
    if (ret != EOK) {
        goto done;
    }

done:
    if (ret != EOK) {
        talloc_zfree(req);
    } else if (op->conn_data && !op->conn_data->connect_req) {
        /* Connection is already established */
        tevent_req_done(req);
        tevent_req_post(req, state->ev);
    }

    if (ret_out) {
        *ret_out = ret;
    }

    return req;
}

/* Begin a connection retry to LDAP server */
static int sdap_id_op_connect_step(struct tevent_req *req)
{
    struct sdap_id_op_connect_state *state =
                    tevent_req_data(req, struct sdap_id_op_connect_state);
    struct sdap_id_op *op = state->op;
    struct sdap_id_conn_cache *conn_cache = op->conn_cache;

    int ret = EOK;
    struct sdap_id_conn_data *conn_data;
    struct tevent_req *subreq = NULL;

    /* Try to reuse context cached connection */
    conn_data = conn_cache->cached_connection;
    if (conn_data) {
        if (conn_data->connect_req) {
            DEBUG(9, ("waiting for connection to complete\n"));
            sdap_id_op_hook_conn_data(op, conn_data);
            goto done;
        }

        if (sdap_can_reuse_connection(conn_data)) {
            DEBUG(9, ("reusing cached connection\n"));
            sdap_id_op_hook_conn_data(op, conn_data);
            goto done;
        }

        DEBUG(9, ("releasing expired cached connection\n"));
        conn_cache->cached_connection = NULL;
        sdap_id_release_conn_data(conn_data);
    }

    DEBUG(9, ("beginning to connect\n"));

    conn_data = talloc_zero(conn_cache, struct sdap_id_conn_data);
    if (!conn_data) {
        ret = ENOMEM;
        goto done;
    }

    talloc_set_destructor(conn_data, sdap_id_conn_data_destroy);

    conn_data->conn_cache = conn_cache;
    subreq = sdap_cli_connect_send(conn_data, state->ev,
                                   state->id_ctx->opts,
                                   state->id_ctx->be,
                                   state->id_ctx->service, false,
                                   CON_TLS_DFL, false);

    if (!subreq) {
        ret = ENOMEM;
        goto done;
    }

    tevent_req_set_callback(subreq, sdap_id_op_connect_done, conn_data);
    conn_data->connect_req = subreq;

    DLIST_ADD(conn_cache->connections, conn_data);
    conn_cache->cached_connection = conn_data;

    sdap_id_op_hook_conn_data(op, conn_data);

done:
    if (ret != EOK && conn_data) {
        sdap_id_release_conn_data(conn_data);
    }

    if (ret != EOK) {
        talloc_zfree(subreq);
    }

    return ret;
}

/* Subrequest callback for connection completion */
static void sdap_id_op_connect_done(struct tevent_req *subreq)
{
    struct sdap_id_conn_data *conn_data =
                tevent_req_callback_data(subreq, struct sdap_id_conn_data);
    struct sdap_id_conn_cache *conn_cache = conn_data->conn_cache;
    struct sdap_server_opts *srv_opts = NULL;
    struct sdap_server_opts *current_srv_opts = NULL;
    bool can_retry = false;
    bool is_offline = false;
    int ret;

    ret = sdap_cli_connect_recv(subreq, conn_data, &can_retry,
                                &conn_data->sh, &srv_opts);
    conn_data->connect_req = NULL;
    talloc_zfree(subreq);

    conn_data->notify_lock++;

    if (ret == ENOTSUP) {
        DEBUG(0, ("Authentication mechanism not Supported by server\n"));
    }

    if (ret == EOK && (!conn_data->sh || !conn_data->sh->connected)) {
        DEBUG(0, ("sdap_cli_connect_recv returned bogus connection\n"));
        ret = EFAULT;
    }

    if (ret != EOK && !can_retry) {
        /* be is going offline as there is no more servers to try */
        DEBUG(1, ("Failed to connect, going offline (%d [%s])\n",
                  ret, strerror(ret)));
        be_mark_offline(conn_cache->id_ctx->be);
        is_offline = true;
    }

    if (ret == EOK) {
        current_srv_opts = conn_cache->id_ctx->srv_opts;
        if (current_srv_opts) {
            DEBUG(8, ("Old USN: %lu, New USN: %lu\n", current_srv_opts->last_usn, srv_opts->last_usn));

            if (strcmp(srv_opts->server_id, current_srv_opts->server_id) == 0 &&
                srv_opts->supports_usn &&
                current_srv_opts->last_usn > srv_opts->last_usn) {
                DEBUG(5, ("Server was probably re-initialized\n"));

                current_srv_opts->max_user_value = 0;
                current_srv_opts->max_group_value = 0;
                current_srv_opts->max_service_value = 0;
                current_srv_opts->max_sudo_value = 0;
                current_srv_opts->last_usn = srv_opts->last_usn;
            }
        }
        ret = sdap_id_conn_data_set_expire_timer(conn_data);
        sdap_steal_server_opts(conn_cache->id_ctx, &srv_opts);
    }

    if (can_retry) {
        switch (ret) {
            case EOK:
            case ENOTSUP:
            case EACCES:
            case EIO:
            case EFAULT:
            case ETIMEDOUT:
                break;

            default:
                /* do not attempt to retry on errors like ENOMEM */
                can_retry = false;
                is_offline = true;
                be_mark_offline(conn_cache->id_ctx->be);
                break;
        }
    }

    int notify_count = 0;

    /* Notify about connection */
    for(;;) {
        struct sdap_id_op *op;

        if (ret == EOK && !conn_data->sh->connected) {
            DEBUG(9, ("connection was broken after %d notifies\n", notify_count));
        }

        DLIST_FOR_EACH(op, conn_data->ops) {
            if (op->connect_req) {
                break;
            }
        }

        if (!op) {
            break;
        }

        /* another operation to notify */
        notify_count++;

        if (ret != EOK || !conn_data->sh->connected) {
            /* failed to connect or connection got broken during notify */
            bool retry = false;

            /* drop connection from cache now */
            if (conn_cache->cached_connection == conn_data) {
                conn_cache->cached_connection = NULL;
            }

            if (can_retry) {
                /* determining whether retry is possible */
                if (be_is_offline(conn_cache->id_ctx->be)) {
                    /* be is offline, no retry possible */
                    if (ret == EOK) {
                        DEBUG(9, ("skipping automatic retry on op #%d as be is offline\n", notify_count));
                        ret = EIO;
                    }

                    can_retry = false;
                    is_offline = true;
                } else {
                    if (ret == EOK) {
                        DEBUG(9, ("attempting automatic retry on op #%d\n", notify_count));
                        retry = true;
                    } else if (sdap_id_op_can_reconnect(op)) {
                        DEBUG(9, ("attempting failover retry on op #%d\n", notify_count));
                        op->reconnect_retry_count++;
                        retry = true;
                    }
                }
            }

            if (retry && op->connect_req) {
                int retry_ret = sdap_id_op_connect_step(op->connect_req);
                if (retry_ret != EOK) {
                    can_retry = false;
                    sdap_id_op_connect_req_complete(op, DP_ERR_FATAL, retry_ret);
                }

                continue;
            }
        }

        if (ret == EOK) {
            DEBUG(9, ("notify connected to op #%d\n", notify_count));
            sdap_id_op_connect_req_complete(op, DP_ERR_OK, ret);
        } else if (is_offline) {
            DEBUG(9, ("notify offline to op #%d\n", notify_count));
            sdap_id_op_connect_req_complete(op, DP_ERR_OFFLINE, EAGAIN);
        } else {
            DEBUG(9, ("notify error to op #%d: %d [%s]\n", notify_count, ret, strerror(ret)));
            sdap_id_op_connect_req_complete(op, DP_ERR_FATAL, ret);
        }
    }

    /* all operations notified */
    if (conn_data->notify_lock > 0) {
        conn_data->notify_lock--;
    }

    if ((ret == EOK) &&
        conn_data->sh->connected &&
        !be_is_offline(conn_cache->id_ctx->be)) {
        DEBUG(9, ("caching successful connection after %d notifies\n", notify_count));
        conn_cache->cached_connection = conn_data;

        /* Run any post-connection routines */
        be_run_online_cb(conn_cache->id_ctx->be);

    } else {
        if (conn_cache->cached_connection == conn_data) {
            conn_cache->cached_connection = NULL;
        }

        sdap_id_release_conn_data(conn_data);
    }
}

/* Mark operation connection request as complete */
static void sdap_id_op_connect_req_complete(struct sdap_id_op *op, int dp_error, int ret)
{
    struct tevent_req *req = op->connect_req;
    struct sdap_id_op_connect_state *state;

    if (!req) {
        return;
    }

    op->connect_req = NULL;

    state = tevent_req_data(req, struct sdap_id_op_connect_state);
    state->dp_error = dp_error;
    state->result = ret;

    if (ret == EOK) {
        tevent_req_done(req);
    } else {
        sdap_id_op_hook_conn_data(op, NULL);
        tevent_req_error(req, ret);
    }
}

/* Get the result of an asynchronous connect operation on sdap_id_op
 *
 * In dp_error data provider error code is returned:
 *   DP_ERR_OK - connection established
 *   DP_ERR_OFFLINE - backend is offline, operation result is set EAGAIN
 *   DP_ERR_FATAL - operation failed
 */
int sdap_id_op_connect_recv(struct tevent_req *req, int *dp_error)
{
    struct sdap_id_op_connect_state *state = tevent_req_data(req,
                                                             struct sdap_id_op_connect_state);

    *dp_error = state->dp_error;
    return state->result;
}

/* Report completion of LDAP operation and release associated connection.
 * Returns operation result (possible updated) passed in ret parameter.
 *
 * In dp_error data provider error code is returned:
 *   DP_ERR_OK (operation result = EOK) - operation completed
 *   DP_ERR_OK (operation result != EOK) - operation can be retried
 *   DP_ERR_OFFLINE - backend is offline, operation result is set EAGAIN
 *   DP_ERR_FATAL - operation failed */
int sdap_id_op_done(struct sdap_id_op *op, int retval, int *dp_err_out)
{
    bool communication_error;
    switch (retval) {
        case EIO:
        case ETIMEDOUT:
            /* this currently the only possible communication error after connection is established */
            communication_error = true;
            break;

        default:
            communication_error = false;
            break;
    }

    if (communication_error && op->conn_data != 0
            && op->conn_data == op->conn_cache->cached_connection) {
        /* do not reuse failed connection */
        op->conn_cache->cached_connection = NULL;

        DEBUG(5, ("communication error on cached connection, moving to next server\n"));
        be_fo_try_next_server(op->conn_cache->id_ctx->be,
                              op->conn_cache->id_ctx->service->name);
    }

    int dp_err;
    if (retval == EOK) {
        dp_err = DP_ERR_OK;
    } else if (be_is_offline(op->conn_cache->id_ctx->be)) {
        /* if backend is already offline, just report offline, do not duplicate errors */
        dp_err = DP_ERR_OFFLINE;
        retval = EAGAIN;
        DEBUG(9, ("falling back to offline data...\n"));
    } else if (communication_error) {
        /* communication error, can try to reconnect */

        if (!sdap_id_op_can_reconnect(op)) {
            dp_err = DP_ERR_FATAL;
            DEBUG(9, ("too many communication failures, giving up...\n"));
        } else {
            dp_err = DP_ERR_OK;
            retval = EAGAIN;
        }
    } else {
        dp_err = DP_ERR_FATAL;
    }

    if (dp_err == DP_ERR_OK && retval != EOK) {
        /* reconnect retry */
        op->reconnect_retry_count++;
        DEBUG(9, ("advising for connection retry #%i\n", op->reconnect_retry_count));
    } else {
        /* end of request */
        op->reconnect_retry_count = 0;
    }

    if (op->conn_data) {
        DEBUG(9, ("releasing operation connection\n"));
        sdap_id_op_hook_conn_data(op, NULL);
    }

    *dp_err_out = dp_err;
    return retval;
}

/* Get SDAP handle associated with operation by sdap_id_op_connect */
struct sdap_handle *sdap_id_op_handle(struct sdap_id_op *op)
{
    return op && op->conn_data ? op->conn_data->sh : NULL;
}