syntax = "proto3";

option java_package = "com.geeksville.mesh";

option optimize_for = LITE_RUNTIME;
option go_package = "github.com/meshtastic/gomeshproto";

option java_outer_classname = "ChannelProtos";

/*
 * Full settings (center freq, spread factor, pre-shared secret key etc...)
 * needed to configure a radio for speaking on a particular channel This
 * information can be encoded as a QRcode/url so that other users can configure
 * their radio to join the same channel.
 * A note about how channel names are shown to users: channelname-Xy
 * poundsymbol is a prefix used to indicate this is a channel name (idea from @professr).
 * Where X is a letter from A-Z (base 26) representing a hash of the PSK for this
 * channel - so that if the user changes anything about the channel (which does
 * force a new PSK) this letter will also change. Thus preventing user confusion if
 * two friends try to type in a channel name of "BobsChan" and then can't talk
 * because their PSKs will be different.
 * The PSK is hashed into this letter by "0x41 + [xor all bytes of the psk ] modulo 26"
 * This also allows the option of someday if people have the PSK off (zero), the
 * users COULD type in a channel name and be able to talk.
 * Y is a lower case letter from a-z that represents the channel 'speed' settings
 * (for some future definition of speed)
 * FIXME: Add description of multi-channel support and how primary vs secondary channels are used.
 * FIXME: explain how apps use channels for security.
 * explain how remote settings and remote gpio are managed as an example
 */
message ChannelSettings {

  /*
   * If zero then, use default max legal continuous power (ie. something that won't
   * burn out the radio hardware)
   * In most cases you should use zero here.
   * Units are in dBm.
   */
  int32 tx_power = 1;

  /*
   * Standard predefined channel settings
   * Note: these mappings must match ModemConfigChoice in the device code.
   */
  enum ModemConfig {

    /*
     * TODO: REPLACE
     */
    VLongSlow = 0;

    /*
     * TODO: REPLACE
     */
    LongSlow = 1;

    /*
     * TODO: REPLACE
     */
    LongFast = 2;

    /*
     * TODO: REPLACE
     */
    MidSlow = 3;

    /*
     * TODO: REPLACE
     */
    MidFast = 4;

    /*
     * TODO: REPLACE
     */
    ShortSlow = 5;

    /*
     * TODO: REPLACE
     */
    ShortFast = 6;
  }

  /*
   * Note: This is the 'old' mechanism for specifying channel parameters.
   * Either modem_config or bandwidth/spreading/coding will be specified - NOT BOTH.
   * As a heuristic: If bandwidth is specified, do not use modem_config.
   * Because protobufs take ZERO space when the value is zero this works out nicely.
   * This value is replaced by bandwidth/spread_factor/coding_rate.
   * If you'd like to experiment with other options add them to MeshRadio.cpp in the device code.
   */
  ModemConfig modem_config = 3;

  /*
   * Bandwidth in MHz
   * Certain bandwidth numbers are 'special' and will be converted to the
   * appropriate floating point value: 31 -> 31.25MHz
   */
  uint32 bandwidth = 6;

  /*
   * A number from 7 to 12.
   * Indicates number of chirps per symbol as 1<<spread_factor.
   */
  uint32 spread_factor = 7;

  /*
   * The denominator of the coding rate.
   * ie for 4/8, the value is 8. 5/8 the value is 5.
   */
  uint32 coding_rate = 8;

  /*
   * NOTE: this field is _independent_ and unrelated to the concepts in channel.proto.
   * this is controlling the actual hardware frequency the radio is transmitting on.
   * In a perfect world we would have called it something else (band?) but I forgot to make this change during the big 1.2 renaming.
   * Most users should never need to be exposed to this field/concept.
   * A channel number between 1 and 13 (or whatever the max is in the current
   * region). If ZERO then the rule is "use the old channel name hash based
   * algorithm to derive the channel number")
   * If using the hash algorithm the channel number will be: hash(channel_name) %
   * NUM_CHANNELS (Where num channels depends on the regulatory region).
   * NUM_CHANNELS_US is 13, for other values see MeshRadio.h in the device code.
   * hash a string into an integer - djb2 by Dan Bernstein. -
   * http://www.cse.yorku.ca/~oz/hash.html
   * unsigned long hash(char *str) {
   *   unsigned long hash = 5381; int c;
   *   while ((c = *str++) != 0)
   *     hash = ((hash << 5) + hash) + (unsigned char) c;
   *   return hash;
   * }
   */
  uint32 channel_num = 9;

  /*
   * A simple pre-shared key for now for crypto.
   * Must be either 0 bytes (no crypto), 16 bytes (AES128), or 32 bytes (AES256).
   * A special shorthand is used for 1 byte long psks.
   * These psks should be treated as only minimally secure,
   * because they are listed in this source code.
   * Those bytes are mapped using the following scheme:
   * `0` = No crypto
   * `1` = The special "default" channel key: {0xd4, 0xf1, 0xbb, 0x3a, 0x20, 0x29, 0x07, 0x59, 0xf0, 0xbc, 0xff, 0xab, 0xcf, 0x4e, 0x69, 0xbf}
   * `2` through 10 = The default channel key, except with 1 through 9 added to the last byte.
   * Shown to user as simple1 through 10
   */
  bytes psk = 4;

  /*
   * A SHORT name that will be packed into the URL.
   * Less than 12 bytes.
   * Something for end users to call the channel
   * If this is the empty string it is assumed that this channel
   * is the special (minimally secure) "Default"channel.
   * In user interfaces it should be rendered as a local language translation of "X".
   * For channel_num hashing empty string will be treated as "X".
   * Where "X" is selected based on the English words listed above for ModemConfig
   */
  string name = 5;

  /*
   * Used to construct a globally unique channel ID.
   * The full globally unique ID will be: "name.id" where ID is shown as base36.
   * Assuming that the number of meshtastic users is below 20K (true for a long time)
   * the chance of this 64 bit random number colliding with anyone else is super low.
   * And the penalty for collision is low as well, it just means that anyone trying to decrypt channel messages might need to
   * try multiple candidate channels.
   * Any time a non wire compatible change is made to a channel, this field should be regenerated.
   * There are a small number of 'special' globally known (and fairly) insecure standard channels.
   * Those channels do not have a numeric id included in the settings, but instead it is pulled from
   * a table of well known IDs.
   * (see Well Known Channels FIXME)
   */
  fixed32 id = 10;

  /*
   * If true, messages on the mesh will be sent to the *public* internet by any gateway ndoe
   */
  bool uplink_enabled = 16;

  /*
   * If true, messages seen on the internet will be forwarded to the local mesh.
   */
  bool downlink_enabled = 17;
}

/*
 * A pair of a channel number, mode and the (sharable) settings for that channel
 */
message Channel {

  /*
   * How this channel is being used (or not).
   * Note: this field is an enum to give us options for the future.
   * In particular, someday we might make a 'SCANNING' option.
   * SCANNING channels could have different frequencies and the radio would
   * occasionally check that freq to see if anything is being transmitted.
   * For devices that have multiple physical radios attached, we could keep multiple PRIMARY/SCANNING channels active at once to allow
   * cross band routing as needed.
   * If a device has only a single radio (the common case) only one channel can be PRIMARY at a time
   * (but any number of SECONDARY channels can't be sent received on that common frequency)
   */
  enum Role {

    /*
     * This channel is not in use right now
     */
    DISABLED = 0;

    /*
     * This channel is used to set the frequency for the radio - all other enabled channels must be SECONDARY
     */
    PRIMARY = 1;

    /*
     * Secondary channels are only used for encryption/decryption/authentication purposes.
     * Their radio settings (freq etc) are ignored, only psk is used.
     */
    SECONDARY = 2;
  }

  /*
   * The index of this channel in the channel table (from 0 to MAX_NUM_CHANNELS-1)
   * (Someday - not currently implemented) An index of -1 could be used to mean "set by name",
   * in which case the target node will find and set the channel by settings.name.
   */
  int32 index = 1;

  /*
   * The new settings, or NULL to disable that channel
   */
  ChannelSettings settings = 2;

  /*
   * TODO: REPLACE
   */
  Role role = 3;
}