/****************************************************************************
 * drivers/syslog/syslog_device.c
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <sys/types.h>
#include <sys/stat.h>

#include <stdint.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sched.h>
#include <fcntl.h>
#include <errno.h>
#include <assert.h>

#include <nuttx/arch.h>
#include <nuttx/lib/lib.h>
#include <nuttx/fs/fs.h>
#include <nuttx/kmalloc.h>
#include <nuttx/syslog/syslog.h>

#include "syslog.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* Open the device/file write-only, try to create (file) it if it doesn't
 * exist, if the file that already exists, then append the new log data to
 * end of the file.
 */

#define SYSLOG_OFLAGS (O_WRONLY)
#define SYSLOG_OMODE  (S_IROTH | S_IRGRP | S_IRUSR | S_IWUSR)

/****************************************************************************
 * Private Types
 ****************************************************************************/

/* This enumeration represents the state of the SYSLOG device interface */

enum syslog_dev_state
{
  SYSLOG_UNINITIALIZED = 0, /* SYSLOG has not been initialized */
  SYSLOG_INITIALIZING,      /* SYSLOG is being initialized */
  SYSLOG_REOPEN,            /* SYSLOG open failed... try again later */
  SYSLOG_FAILURE,           /* SYSLOG open failed... close and try again */
  SYSLOG_OPENED,            /* SYSLOG device is open and ready to use */
};

/* This structure contains all SYSLOGing state information */

struct syslog_dev_s
{
  syslog_channel_t sl_channel;

  uint8_t      sl_state;    /* See enum syslog_dev_state */
  uint8_t      sl_oflags;   /* Saved open mode (for re-open) */
  uint16_t     sl_mode;     /* Saved open flags (for re-open) */
  struct file  sl_file;     /* The syslog file structure */
  FAR char    *sl_devpath;  /* Full path to the character device */
};

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

static ssize_t syslog_dev_write(FAR syslog_channel_t *channel,
                                FAR const char *buffer, size_t buflen);
static int syslog_dev_putc(FAR syslog_channel_t *channel, int ch);
static int syslog_dev_flush(FAR syslog_channel_t *channel);

/****************************************************************************
 * Private Data
 ****************************************************************************/

/* This structure contains all SYSLOG device operations */

static const struct syslog_channel_ops_s g_syslog_dev_ops =
{
  syslog_dev_putc,
  syslog_dev_putc,
  syslog_dev_flush,
  syslog_dev_write,
  syslog_dev_write,
  syslog_dev_uninitialize
};

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: syslog_dev_open
 *
 * Description:
 *   Opens the SYSLOG character device (or file).
 *
 * Input Parameters:
 *   syslog_dev - Handle to syslog device to be used.
 *   devpath    - The full path to the character device to be used.
 *   oflags     - File open flags.
 *   mode       - File open mode (only if oflags include O_CREAT).
 *
 * Returned Value:
 *   Zero (OK) is returned on success; a negated errno value is returned on
 *   any failure.
 *
 ****************************************************************************/

static int syslog_dev_open(FAR struct syslog_dev_s *syslog_dev,
                           FAR const char *devpath, int oflags, int mode)
{
  int ret;

  /* At this point, the only expected states are SYSLOG_UNINITIALIZED or
   * SYSLOG_REOPEN.  Not SYSLOG_INITIALIZING, SYSLOG_FAILURE, SYSLOG_OPENED.
   */

  DEBUGASSERT(syslog_dev->sl_state == SYSLOG_UNINITIALIZED ||
              syslog_dev->sl_state == SYSLOG_REOPEN);

  /* Save the path to the device in case we have to re-open it.
   * If we get here and sl_devpath is not equal to NULL, that is a clue
   * that we are re-opening the file.
   */

  if (syslog_dev->sl_state == SYSLOG_REOPEN)
    {
      /* Re-opening: Then we should already have a copy of the path to the
       * device. But that may be for a different device if we revert back
       * to old syslog destination after the previous attempt failed.
       */

      DEBUGASSERT(syslog_dev->sl_devpath != NULL);
    }
  else
    {
      /* Initializing. We do not have the device path yet. */

      DEBUGASSERT(syslog_dev->sl_devpath == NULL);
    }

  /* Copy the device path so that we can use it if we
   * have to re-open the file.
   */

  syslog_dev->sl_oflags = oflags;
  syslog_dev->sl_mode = mode;
  if (syslog_dev->sl_devpath != devpath)
    {
      if (syslog_dev->sl_devpath != NULL)
        {
          kmm_free(syslog_dev->sl_devpath);
        }

      syslog_dev->sl_devpath = strdup(devpath);
    }

  DEBUGASSERT(syslog_dev->sl_devpath != NULL);

  syslog_dev->sl_state = SYSLOG_INITIALIZING;

  /* Open the device driver. */

  ret = file_open(&syslog_dev->sl_file, devpath, oflags, mode);
  if (ret < 0)
    {
      /* We failed to open the file. Perhaps it does exist?  Perhaps it
       * exists, but is not ready because it depends on insertion of a
       * removable device?
       *
       * In any case we will attempt to re-open the device repeatedly.
       * The assumption is that the device path is valid but that the
       * driver has not yet been registered or a removable device has
       * not yet been installed.
       */

      syslog_dev->sl_state = SYSLOG_REOPEN;
      return ret;
    }

  /* The SYSLOG device is open and ready for writing. */

  syslog_dev->sl_state = SYSLOG_OPENED;
  return OK;
}

/****************************************************************************
 * Name: syslog_dev_outputready
 *
 * Description:
 * Ignore any output:
 *
 * (1) Before the SYSLOG device has been initialized.  This could happen
 *     from debug output that occurs early in the boot sequence before
 *     syslog_dev_initialize() is called (SYSLOG_UNINITIALIZED).
 * (2) While the device is being initialized.  The case could happen if
 *     debug output is generated while syslog_dev_initialize() executes
 *     (SYSLOG_INITIALIZING).
 * (3) While we are generating SYSLOG output.  The case could happen if
 *     debug output is generated while syslog_dev_putc() executes
 *     (This case is actually handled inside of syslog_lock()).
 * (4) Any debug output generated from interrupt handlers.  A disadvantage
 *     of using the generic character device for the SYSLOG is that it
 *     cannot handle debug output generated from interrupt level handlers.
 * (5) Any debug output generated from the IDLE loop.  The character
 *     driver interface is blocking and the IDLE thread is not permitted
 *     to block.
 * (6) If any failure occurred during output.  In this case, we properly
 *     close the device, and set it for later re-opening.
 *
 * NOTE: That the third case is different.  It applies only to the thread
 * that currently holds the sl_lock.  Other threads should wait.
 * that is why that case is handled in syslog_lock().
 *
 * Input Parameters:
 *   syslog_dev  - Handle to syslog device to be used.
 *
 * Returned Value:
 *   Zero (OK) is returned on success; a negated errno value is returned on
 *   any failure.
 *
 ****************************************************************************/

static int syslog_dev_outputready(FAR struct syslog_dev_s *syslog_dev)
{
  int ret;

  /* We can save checks in the usual case:  That after the SYSLOG device
   * has been successfully opened.
   */

  if (syslog_dev->sl_state != SYSLOG_OPENED)
    {
      if (up_interrupt_context() || sched_idletask())
        {
          return -ENOSYS;
        }

      /* Case (1) and (2) */

      if (syslog_dev->sl_state == SYSLOG_UNINITIALIZED ||
          syslog_dev->sl_state == SYSLOG_INITIALIZING)
        {
          return -EAGAIN; /* Can't access the SYSLOG now... maybe next time? */
        }

      /* Case (6) */

      if (syslog_dev->sl_state == SYSLOG_FAILURE)
        {
          file_close(&syslog_dev->sl_file);

          syslog_dev->sl_state = SYSLOG_REOPEN;
        }

      /* syslog_dev_initialize() is called as soon as enough of the operating
       * system is in place to support the open operation... but it is
       * possible that the SYSLOG device is not yet registered at that time.
       * In this case, we know that the system is sufficiently initialized
       * to support an attempt to re-open the SYSLOG device.
       */

      if (syslog_dev->sl_state == SYSLOG_REOPEN)
        {
          /* Try again to initialize the device.  We may do this repeatedly
           * because the log device might be something that was not ready
           * the first time that syslog_dev_initialize() was called (such as
           * a USB serial device that has not yet been connected or a file in
           * an NFS mounted file system that has not yet been mounted).
           */

          DEBUGASSERT(syslog_dev->sl_devpath != NULL);
          ret = syslog_dev_open(syslog_dev, syslog_dev->sl_devpath,
                                (int)syslog_dev->sl_oflags,
                                (int)syslog_dev->sl_mode);
          if (ret < 0)
            {
              return ret;
            }
        }

      DEBUGASSERT(syslog_dev->sl_state == SYSLOG_OPENED);
    }

  return OK;
}

/****************************************************************************
 * Name: syslog_dev_write
 *
 * Description:
 *   This is the low-level, multiple byte, system logging interface provided
 *   for the character driver interface.
 *
 * Input Parameters:
 *   channel    - Handle to syslog channel to be used.
 *   buffer     - The buffer containing the data to be output.
 *   buflen     - The number of bytes in the buffer.
 *
 * Returned Value:
 *   On success, the character is echoed back to the caller. A negated errno
 *   value is returned on any failure.
 *
 ****************************************************************************/

static ssize_t syslog_dev_write(FAR syslog_channel_t *channel,
                                FAR const char *buffer, size_t buflen)
{
  FAR struct syslog_dev_s *syslog_dev = (FAR struct syslog_dev_s *)channel;
  int ret;

  /* Check if the system is ready to do output operations */

  ret = syslog_dev_outputready(syslog_dev);
  if (ret < 0)
    {
      return ret;
    }

  ret = file_write(&syslog_dev->sl_file, buffer, buflen);
  if (ret < 0)
    {
      syslog_dev->sl_state = SYSLOG_FAILURE;
    }

  return ret;
}

/****************************************************************************
 * Name: syslog_dev_putc
 *
 * Description:
 *   This is the low-level, single character, system logging interface
 *   provided for the character driver interface.
 *
 * Input Parameters:
 *   channel    - Handle to syslog channel to be used.
 *   ch         - The character to add to the SYSLOG (must be positive).
 *
 * Returned Value:
 *   On success, the character is echoed back to the caller. A negated errno
 *   value is returned on any failure.
 *
 ****************************************************************************/

static int syslog_dev_putc(FAR syslog_channel_t *channel, int ch)
{
  FAR struct syslog_dev_s *syslog_dev = (FAR struct syslog_dev_s *)channel;
  ssize_t nbytes;
  uint8_t uch;
  int ret;

  /* Check if the system is ready to do output operations */

  ret = syslog_dev_outputready(syslog_dev);
  if (ret < 0)
    {
      return ret;
    }

  uch = (uint8_t)ch;
  nbytes = file_write(&syslog_dev->sl_file, &uch, 1);
  if (nbytes < 0)
    {
      syslog_dev->sl_state = SYSLOG_FAILURE;
    }

  return nbytes;
}

/****************************************************************************
 * Name: syslog_dev_flush
 *
 * Description:
 *   Flush any buffer data in the file system to media.
 *
 * Input Parameters:
 *   channel    - Handle to syslog channel to be used.
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno value is returned on any failure.
 *
 ****************************************************************************/

static int syslog_dev_flush(FAR syslog_channel_t *channel)
{
#if defined(CONFIG_SYSLOG_FILE) && !defined(CONFIG_DISABLE_MOUNTPOINT)
  FAR struct syslog_dev_s *syslog_dev = (FAR struct syslog_dev_s *)channel;

  /* Ignore return value, always return success.  file_fsync() could fail
   * because the file is not open, the inode is not a mountpoint, or the
   * mountpoint does not support the sync() method.
   */

  file_fsync(&syslog_dev->sl_file);
#else
  UNUSED(channel);
#endif

  return OK;
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: syslog_dev_initialize
 *
 * Description:
 *   Initialize to use the character device (or file) at
 *   CONFIG_SYSLOG_DEVPATH as the SYSLOG sink.
 *
 *   On power up, the SYSLOG facility is non-existent or limited to very
 *   low-level output.  This function may be called later in the
 *   initialization sequence after full driver support has been initialized.
 *   (via syslog_initialize())  It installs the configured SYSLOG drivers
 *   and enables full SYSLOGing capability.
 *
 *   NOTE that this implementation excludes using a network connection as
 *   SYSLOG device.  That would be a good extension.
 *
 * Input Parameters:
 *   devpath - The full path to the character device to be used.
 *   oflags  - File open flags.
 *   mode    - File open mode (only if oflags include O_CREAT).
 *
 * Returned Value:
 *   Returns a newly created SYSLOG channel, or NULL in case of any failure.
 *
 ****************************************************************************/

FAR syslog_channel_t *syslog_dev_initialize(FAR const char *devpath,
                                            int oflags, int mode)
{
  FAR struct syslog_dev_s *syslog_dev;

  syslog_dev = kmm_zalloc(sizeof(struct syslog_dev_s));

  if (syslog_dev == NULL)
    {
      return NULL;
    }

  syslog_dev_open(syslog_dev, devpath, oflags, mode);

  syslog_dev->sl_channel.sc_ops = &g_syslog_dev_ops;

  return (FAR syslog_channel_t *)syslog_dev;
}

/****************************************************************************
 * Name: syslog_dev_uninitialize
 *
 * Description:
 *   Disable the last device/file channel in preparation to use a different
 *   SYSLOG device. Currently only used for CONFIG_SYSLOG_FILE.
 *
 * Input Parameters:
 *   channel    - Handle to syslog channel to be used.
 *
 * Returned Value:
 *   Zero (OK) is returned on success; a negated errno value is returned on
 *   any failure.
 *
 * Assumptions:
 *   The caller has already switched the SYSLOG source to some safe channel
 *   (the default channel).
 *
 ****************************************************************************/

void syslog_dev_uninitialize(FAR syslog_channel_t *channel)
{
  FAR struct syslog_dev_s *syslog_dev = (FAR struct syslog_dev_s *)channel;

  /* Uninitializing a SYSLOG device should not take place within
   * interrupt context.
   */

  if (up_interrupt_context() || sched_idletask())
    {
      DEBUGASSERT(!up_interrupt_context() && !sched_idletask());
      return;
    }

  /* The device cannot be uninitialized while it is being
   * initialized simultaneously.
   */

  DEBUGASSERT(syslog_dev->sl_state != SYSLOG_UNINITIALIZED &&
              syslog_dev->sl_state != SYSLOG_INITIALIZING);

  /* Attempt to flush any buffered data. */

  syslog_dev_flush(channel);

  /* Close the detached file instance. */

  if (syslog_dev->sl_state == SYSLOG_OPENED ||
      syslog_dev->sl_state == SYSLOG_FAILURE)
    {
      file_close(&syslog_dev->sl_file);
    }

  /* Set the device in UNINITIALIZED state. */

  syslog_dev->sl_state = SYSLOG_UNINITIALIZED;

  /* Free the device path */

  if (syslog_dev->sl_devpath != NULL)
    {
      lib_free(syslog_dev->sl_devpath);
    }

  /* Free the channel structure */

  kmm_free(syslog_dev);
}

/****************************************************************************
 * Name: syslog_dev_channel
 *
 * Description:
 *   Configure to use the character device at CONFIG_SYSLOG_DEVPATH as the
 *   SYSLOG channel.
 *
 *   This tiny function is simply a wrapper around syslog_dev_initialize()
 *   and syslog_channel_register().  It calls syslog_dev_initialize() to
 *   configure the character device at CONFIG_SYSLOG_DEVPATH then calls
 *   syslog_channel_register() to use that device as the SYSLOG output
 *   channel.
 *
 *   NOTE interrupt level SYSLOG output will be lost in this case unless
 *   the interrupt buffer is used.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   A pointer to the new SYSLOG channel; NULL is returned on any failure.
 *
 ****************************************************************************/

FAR syslog_channel_t *syslog_dev_channel(FAR const char *devpath)
{
  FAR syslog_channel_t *dev_channel;

  /* Initialize the character driver interface */

  dev_channel = syslog_dev_initialize(devpath, SYSLOG_OFLAGS, SYSLOG_OMODE);
  if (dev_channel == NULL)
    {
      return NULL;
    }

  /* Use the character driver as the SYSLOG channel */

  if (syslog_channel_register(dev_channel) != OK)
    {
      syslog_dev_uninitialize(dev_channel);
      dev_channel = NULL;
    }

  return dev_channel;
}