/**
 * Module dependencies
 */

var util = require('util');
var _ = require('@sailshq/lodash');

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Lodash methods in use:
//
// • Basic things:
//   ° _.isString, _.isObject, _.isArray, _.isError, _.isFunction, _.isNumber
// • Node <=5 compat. things:
//   ° _.extend
// • Stranger things:
//   ° _.matches   (for .taste())
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

/**
 * flaverr()
 *
 * Flavor an Error instance with the specified error code string or dictionary of customizations.
 *
 * Specifically, this modifies the provided Error instance either:
 * (A) by attaching a `code` property and setting it to the specified value (e.g. "E_USAGE"), or
 * (B) merging the specified dictionary of stuff into the Error
 *
 * If a `message` or `name` is provided, the Error instance's `stack` will be recalculated accordingly.
 * This can be used to consume an omen -- i.e. giving this Error instance's stack trace "hindsight",
 * and keeping it from getting "cliffed-out" on the wrong side of asynchronous callbacks.
 *
 * Besides improving the quality of your everyday errors and allowing for exception-based switching,
 * you can also use flaverr to build an _omen_, an Error instance defined ahead of time in order to
 * grab a stack trace. (used for providing a better experience when viewing the stack trace of errors
 * that come from one or more asynchronous ticks down the line; e.g. uniqueness errors.)
 *
 * > The "omen" approach is inspired by the implementation originally devised for Waterline:
 * > https://github.com/balderdashy/waterline/blob/6b1f65e77697c36561a0edd06dff537307986cb7/lib/waterline/utils/query/build-omen.js
 *
 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 * @param {String|Dictionary} codeOrCustomizations
 *           e.g. `"E_USAGE"`
 *                    -OR-
 *                `{ name: 'UsageError', code: 'E_UHOH', machineInstance: foo, errors: [], misc: 'etc' }`
 *
 * @param {Error?} err
 *           If `undefined`, a new Error will be instantiated instead.
 *           e.g. `new Error('Invalid usage: That is not where the quarter is supposed to go.')`
 *
 * @param {Function?} caller
 *        An optional function to use for context (useful for building omens)
 *        The stack trace of the omen will be snipped based on the instruction where
 *        this "caller" function was invoked.
 *
 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 * @returns {Error}
 *          An Error instance.
 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 */

function flaverr (codeOrCustomizations, err, caller){

  // Parse error (e.g. tolerate bluebird/stripe look-alikes)
  if (err !== undefined) {
    err = flaverr.parseError(err) || err;
    if (!_.isError(err)) {
      throw new Error('Unexpected usage.  If specified, expected 2nd argument to be an Error instance (but instead got `'+util.inspect(err, {depth: null})+'`)');
    }
  }//ﬁ

  if (caller !== undefined && typeof caller !== 'function') {
    throw new Error('Unexpected usage.  If specified, expected 3rd argument should be a function that will be used as a stack trace context (but instead got `'+util.inspect(caller, {depth: null})+'`)');
  }


  if (_.isString(codeOrCustomizations)) {
    if (!err) {
      err = new Error();
      err.code = codeOrCustomizations;
    } else {
      err.code = codeOrCustomizations;
    }
  }
  else if (_.isObject(codeOrCustomizations) && !_.isArray(codeOrCustomizations) && typeof codeOrCustomizations !== 'function') {
    if (codeOrCustomizations.stack) { throw new Error('Unexpected usage.  Customizations (dictionary provided as 1st arg) are not allowed to contain a `stack`.  Instead, use `newErr = flaverr({ name: original.name, message: original.message }, omen)`'); }
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    // FUTURE: (maybe?  see traceFrom notes below)
    // if (codeOrCustomizations.stack) { throw new Error('Unexpected usage of `flaverr()`.  Customizations (dictionary provided as 1st arg) are not allowed to contain a `stack`.  Instead, use `flaverr.traceFrom(omen, err)`'); }
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    if (!err){

      if (codeOrCustomizations.message !== undefined) {
        err = new Error(codeOrCustomizations.message);
      }
      else if (Object.keys(codeOrCustomizations).length === 0) {
        err = new Error();
      }
      else {
        err = new Error(util.inspect(codeOrCustomizations, {depth: 5}));
      }

    } else {

      if (codeOrCustomizations.name || codeOrCustomizations.message) {

        if (codeOrCustomizations.name === undefined) {
          codeOrCustomizations.name = err.name;
        }
        if (codeOrCustomizations.message === undefined) {
          codeOrCustomizations.message = err.message;
        }

        var numCharsToShift;
        if (err.message.length > 0) {
          // e.g. stack `FooBar: Blah blah blah\n  at skdfgjagsd…`
          numCharsToShift = err.name.length + 2 + err.message.length;
        } else {
          // e.g. stack `FooBar\n  at dudgjkadgsj…`
          numCharsToShift = err.name.length;
        }

        if (codeOrCustomizations.message.length > 0) {
          // e.g. stack `BazBot: Blurge blurge blurge\n  at dudgjkadgsj…`
          err.stack = codeOrCustomizations.name + ': '+ codeOrCustomizations.message + err.stack.slice(numCharsToShift);
        } else {
          // e.g. stack `BazBot\n  at dudgjkadgsj…`
          err.stack = codeOrCustomizations.name + err.stack.slice(numCharsToShift);
        }
        // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        // FUTURE: Explore a fancier strategy like this (maybe):
        // ```
        // if (omen && omen._traceReference && Error.captureStackTrace) {
        //   var omen2 = new Error(message);
        //   Error.captureStackTrace(omen2, omen._traceReference);
        //   omen2.name = name;
        //   return omen;
        // }
        // ```
        // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      }//ﬁ

    }//ﬁ

    // Always merge in the customizations, whether this is an existing error or a new one.
    _.extend(err, codeOrCustomizations);

  }
  else {
    throw new Error('Unexpected usage.  Expected 1st argument to be either a string error code or a dictionary of customizations (but instead got `'+util.inspect(codeOrCustomizations, {depth: null})+'`)');
  }


  // If a `caller` reference was provided, then use it to adjust the stack trace.
  // (Note that we silently skip this step if the `Error.captureStackTrace` is missing
  // on the currently-running platform)
  if (caller && Error.captureStackTrace) {
    Error.captureStackTrace(err, caller);
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    // FUTURE: maybe do something fancier here, or where this is called, to keep track of the omen so
    // that it can support both sorts of usages (Deferred and explicit callback.)
    //
    // This way, it could do an even better job of reporting exactly where the error came from in
    // userland code as the very first entry in the stack trace.  e.g.
    // ```
    // Error.captureStackTrace(omen, Deferred.prototype.exec);
    // // ^^ but would need to pass through the original omen or something
    // ```
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  }//ﬁ

  return err;
}//ƒ


// Export flaverr.
module.exports = flaverr;



/**
 * flaverr.getBareTrace()
 *
 * Return the bare stack trace of an Error, with the identifying `name`/colon/space/`message`
 * preamble trimmed off, leaving only the info about stack frames.
 *
 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 * Note:
 * While this function may have other uses, it was designed as a simple way of including
 * a stack trace in console warning messages.
 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 *
 * @param  {Error?|Function?} errOrCaller
 *         If an Error is provided, its bare stack trace will be used.
 *         Otherwise, a new Error will be instantiated on the fly and
 *         its stack trace will be used.  If a function is provided
 *         instead of an Error, it is understood to be the caller and,
 *         used for improving the trace of the newly instantiated Error
 *         instance.
 *
 * @param {Number?} framesToKeep         (««« YOU PROBABLY SHOULDN'T USE THIS!!)
 *        The number of frames from the top of the call stack to retain
 *        in the output trace.  If omitted, all frames will be included.
 *        |  WARNING:
 *        |  It is almost NEVER a good idea to pass this argument in!!!
 *        |  Making programmatic assumptions about the call stack is
 *        |  notoriously difficult (and usually ill-advised), since it
 *        |  is something that can be impacted by many unexpected factors:
 *        |  from refactoring within your code base, interference from
 *        |  your dependencies, or even other runtime aspects or your
 *        |  users' environments that are completely out of your control.
 *        |  This warning applies both to app-level code AND for modules!
 *        |  In fact, the only reason this feature is even included in
 *        |  `flaverr` is for use during debugging, as well as (much more
 *        |  rarely) use cases for certain kinds of developer tooling.
 *        |  Proceed at your own risk.  You have been warned!
 *
 * @returns {String}
 */

module.exports.getBareTrace = function getBareTrace(errOrCaller, framesToKeep){
  var err;
  if (_.isError(errOrCaller)) {
    err = errOrCaller;
  } else if (_.isFunction(errOrCaller) || errOrCaller === undefined) {
    err = flaverr.buildOmen(errOrCaller||getBareTrace);
  } else {
    throw new Error('Unexpected usage of `.getBareTrace()`.  If an argument is supplied, it must be an Error instance or function (the caller to use when generating a new trace).  But instead, got: '+util.inspect(errOrCaller, {depth: 5}));
  }

  var numCharsToShift;
  if (err.message.length > 0) {
    // e.g. stack `FooBar: Blah blah blah\n  at skdfgjagsd…`
    numCharsToShift = err.name.length + 2 + err.message.length;
  } else {
    // e.g. stack `FooBar\n  at dudgjkadgsj…`
    numCharsToShift = err.name.length;
  }

  var bareTrace = err.stack;
  bareTrace = bareTrace.slice(numCharsToShift);
  bareTrace = bareTrace.replace(/^[\n]+/g,'');

  if (framesToKeep !== undefined) {
    if (!_.isNumber(framesToKeep) || framesToKeep < 1 || Math.floor(framesToKeep) !== framesToKeep) { throw new Error('Unexpected usage of `.getBareTrace()`.  If a 2nd argument is supplied, it must be a positive whole integer (the # of stack frames to keep from the top of the call stack).  But instead, got: '+util.inspect(framesToKeep, {depth: 5})); }
    // throw new Error('Unexpected usage of `getBareTrace()`.  The 2nd argument is experimental and not yet supported for external use.');
    bareTrace = bareTrace.split(/\n/g).slice(0, framesToKeep).join('\n');
  }

  return bareTrace;
};




/**
 * buildOmen()
 *
 * Return a new Error instance for use as an omen.
 *
 * > Note: This isn't particularly slow, but it isn't speedy either.
 * > For VERY hot code paths, it's a good idea to skip this in production unless debugging.
 * > The standard way to do that is a userland check like:
 * > ```
 * > var omen = (process.env.NODE_ENV !== 'production' || process.env.DEBUG)?
 * >   flaverr.buildOmen(theUserlandFunctionIAmInsideOf)
 * >   :
 * >   undefined;
 * > ```
 * >
 * > Then `.omen()` method (see below) is a shortcut for this.
 *
 * @param {Function?} caller
 *        An optional function to use for context (useful for further improving stack traces)
 *        The stack trace of the omen will be snipped based on the instruction where
 *        this "caller" function was invoked.  Otherwise, if omitted, `.buildOmen()` itself
 *        will be considered the caller.
 *
 * @returns {Error}
 */
module.exports.buildOmen = function buildOmen(caller) {
  if (caller !== undefined && !_.isFunction(caller)){ throw new Error('Unexpected usage:  If an argument is supplied, it must be a function (the "caller", used for adjusting the stack trace).  Instead, got: '+util.inspect(caller, {depth: 5})); }
  var omen = flaverr({}, new Error('omen'), caller||buildOmen);
  if (caller !== undefined && !omen.stack.match(/\n/)) {
    throw new Error('Unexpected behavior:  When constructing omen using the specified "caller", the resulting Error\'s stack trace does not contain any newline characters.  This usually means the provided "caller" isn\'t actually the caller at all (or at least it wasn\'t this time).  Thus `Error.captureStackTrace()` failed to determine a trace.  To resolve this, pass in a valid "caller" or if that\'s not possible, omit the "caller" argument altogether.');
  }
  return omen;
};



/**
 * omen()
 *
 * Do exactly the same thing as `.buildOmen()`, but instead of ALWAYS returning a new
 * Error instance, sometimes return `undefined` instead.  (Useful for performance reasons.)
 *
 * @param {Function?} caller
 *        (See `buildOmen()` for details.)
 *
 * @returns {Error?}
 *          Error instance is returned UNLESS:
 *            (A) the `NODE_ENV` system environment is set to "production", and
 *            (B) the `DEBUG` system environment variable has not been set, or is falsey.
 *          Otherwise, this returns `undefined`.
 */

module.exports.omen = function omen(caller){
  return (process.env.NODE_ENV !== 'production' || process.env.DEBUG)?
    flaverr.buildOmen(caller||omen)
    :
    undefined;
};



/**
 * flaverr.parseError()
 *
 * Investigate the provided value and return a canonical Error instance,
 * if it is one itself, or if is is a recognized wrapper that contains one.
 *
 * > • If the provided value is a canonical Error instance already, then
 * >   this just returns it as-is.
 * >
 * > • Otherwise, it attempts to tease out a canonical Error using a few
 * >   different heuristics, including support for parsing special
 * >   not-quite-Errors from bluebird.
 * >
 * > • If no existing Error instance can be squeezed out, then return `undefined`.
 * >   (The `.parseError()` function **NEVER** constructs Error instances.)
 *
 * @param  {Ref}  err
 *
 * @returns {Error?}
 */

module.exports.parseError = function(err) {

  if (_.isError(err)) {
    // > ok as-is
    return err;
  } else if (_.isObject(err) && err.cause && _.isError(err.cause)) {
    // Bluebird "errors"
    //
    // > async+await errors from bluebird are not necessarily "true" Error instances,
    // > as per _.isError() anyway (see https://github.com/node-machine/machine/commits/6b9d9590794e33307df1f7ba91e328dd236446a9).
    // > So to be reasonable, we have to be a bit more relaxed here and tolerate these
    // > sorts of "errors" directly as well (by tweezing out the `cause`, which is
    // > where the underlying Error instance actually lives.)
    return err.cause;
  } else if (_.isObject(err) && _.isString(err.type) && _.isString(err.message) && _.isString(err.stack)) {
    // Stripe SDK "errors"
    //
    // > The Stripe SDK likes to throw some not-quite-Error-instances.
    // > But they're close enough to use once you factor in a little integration
    // > code to adapt them.  (Note that we have to remove the `stack`-- but we
    // > alias it separately as `_originalStack`.)
    var stripeErrorProps = _.omit(err, ['stack']);
    return flaverr(_.extend(stripeErrorProps, {
      name: err.type,
      _originalStack: err.stack
    }));
  } else {
    return undefined;
  }

};



/**
 * flaverr.parseOrBuildError()
 *
 * Investigate the provided value and attempt to parse out a canonical Error instance
 * using `flaverr.parseError()`.  If that fails, construct a new Error instance (or
 * consume the omen, if one was provided) using the provided data as a basis for the
 * message, and then return that.
 *
 * > • If no canonical Error can be obtained, this function constructs a new
 * >   Error instance, maintaining the provided value as `.raw` and making a
 * >   simple, best-effort guess at an appropriate error message.
 *
 * @param  {Ref}  err
 * @param  {Error?}  omenForNewError
 *         If `parseOrBuildError()` determines that it must construct a new Error instance,
 *         then, if specified, this omen will be consumed instead of generating a new
 *         Error.
 *
 * @returns {Error}
 *
 *
 * e.g.
 * ```
 *   flaverr.unwrap('E_NON_ERROR', flaverr.parseOrBuildError('bleh'))
 *   // => 'bleh'
 * ```
 */

module.exports.parseOrBuildError = function(err, omenForNewError) {

  var parsedErr = flaverr.parseError(err);

  if (parsedErr) {
    return parsedErr;
  }
  else {
    // > build a new error, pretty-printing the original value as the `message`,
    // > or using it verbatim if it's a string.  Note that we still attach the
    // > original value as `.raw` as well)
    return flaverr.wrap('E_NON_ERROR', err, omenForNewError||undefined);
  }

};


// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// FUTURE: (see note in .wrap() for reasoning)
// (+ maybe we can come up with a snappier, but also non-ambiguous, name for this?
// Basically this is for handling completely unknown/untrusted things that have been
// sent back through a callback, rejected, or thrown from somewhere else.)
//
//     (Maybe `.insulate()`?  And its inverse)
//
// ```
// module.exports.parseOrBuildThenWrapAndRetrace = function parseOrBuildThenWrapAndRetrace(raw, caller){
//   // Note that it's important for us to build an omen here, rather than accepting one as an argument!
//   // (Remember: This function is not intended for low-level use!)
//
//   var omen = caller? flaverr.omen(caller) : flaverr.omen(parseOrBuildThenWrapAndRetrace);
//   var err = flaverr.parseError(raw);
//   if (err){
//     // If it's already a parseable Error, wrap it.
//     return flaverr.wrap('E_FROM_WITHIN', err, omen||undefined);
//   } else {
//     // Otherwise, it's some random thing so still wrap it, but use the special code
//     // for non-errors (i.e. just like in `parseOrBuildError()`)
//     return flaverr.wrap('E_NON_ERROR', raw, omen||undefined);
//   }
// };
// ```
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


/**
 * flaverr.wrap()
 *
 * Build & return a new Envelope (Error instance), stuffing the provided data into its
 * `raw` property and flavoring the new envelope error with the provided customizations.
 *
 * > Note: Any Envelope is easily reversed back into its raw state (see `flaverr.unwrap()`).
 *
 * > WARNING: THIS IS DESIGNED FOR LOW-LEVEL USE IN FLOW CONTROL TOOLS LIKE PARLEY/MACHINE/ETC!
 * > (See .insulate() above for a simpler utility designed for more common, everyday tasks in userland.)
 *
 * ----------------------------------------------------------------------------------------------------
 * A few common envelope patterns come with recommended/conventional error codes:
 *
 * • E_ESCAPE_HATCH   -- (Wraps an underlying Error instance in an easily-reversible fashion.)
 *       Useful as a special Error for escaping from an outer `try` block.
 *
 * • E_NON_ERROR      -- (Wraps some value other than an Error instance in an easily-reversible fashion.)
 *       Useful as simple mechanism for encasing some value that is **not an Error instance** inside
 *       a new Error instance.
 *
 * • E_FROM_WITHIN    -- (Wraps something thrown/rejected/throwbacked from untrusted code)
 *       Useful as a wrapper around some value that was thrown from untrusted code, and thus might
 *       have properties (`.code`, `.name`, etc) that could conflict with programmatic error negotiation
 *       elsewhere, or that would be otherwise confusing if unleashed on userland as-is. (This is
 *       particularly useful for wrapping errors thrown from invocations of your procedural params;
 *       e.g. in the `catch` block where you handle any error thrown by invoking a custom, user-specified
 *       iteratee function.)
 *
 * Anything else can be generally assumed to be some mysterious internal error from a 3rd party
 * module/etc -- an error which may or may not be directly relevant to your users.  In fact, it
 * may or may not even necessarily be an Error instance!  (Regardless, it is accessible in `.raw`.)
 *
 * ----------------------------------------------------------------------------------------------------
 *
 * @param  {String|Dictionary} codeOrCustomizations
 *         Customizations for the Envelope.  (Use `{}` to indicate no customizations.)
 *
 * @param  {Ref} raw
 *         The thing to wrap.
 *
 * @param  {Error?} omen
 *         An optional Error instance to consume instead of building a new Error instance.
 *
 * ----------------------------------------------------------------------------------------------------
 * @returns {Error}
 *          The Envelope (either a new Error instance, or the modified version of the provided omen)
 */
module.exports.wrap = function(codeOrCustomizations, raw, omen){

  // Note: This method always requires customizations, and is very careful to put `raw`
  // **untouched** into the new Envelope's `.raw` property.  Similarly, `.unwrap()` helps
  // you retrieve this property from an Envelope untouched, through careful ducktyping.
  // This is good for low-level utilities that need to verify correctness, but not super
  // beautiful to use.  See `.insulate()` above for a simpler, everyday utility.

  if (raw === undefined) { throw new Error('The 2nd argument to `flaverr.wrap()` (the raw thing to wrap) is mandatory.'); }
  if (omen !== undefined && !_.isError(omen)) { throw new Error('If provided, `omen` must be an Error instance to be used for improving stack traces.'); }

  var customizations;
  if (_.isString(codeOrCustomizations)) {
    customizations = {
      code: codeOrCustomizations
    };
  }
  else if (!_.isError(codeOrCustomizations) && _.isObject(codeOrCustomizations) && !_.isArray(codeOrCustomizations) && typeof codeOrCustomizations !== 'function') {
    customizations = codeOrCustomizations;
    if (customizations.name) {
      throw new Error('Invalid 1st argument to `flaverr.wrap()`: No need to provide a custom `name` for the Envelope-- the `.name` for errors returned by flaverr.wrap() is set in stone ("Envelope") and always attached automatically.');
    }
  }
  else {
    throw new Error('1st argument to `flaverr.wrap()` must be either a valid string to indicate the `.code` for the Envelope, or a dictionary of customizations to fold in (never an Error instance though!)  But instead of one of those, got: '+util.inspect(codeOrCustomizations, {depth:5}));
  }

  return flaverr(_.extend({
    name: 'Envelope',
    message: _.isError(raw) ? raw.message : _.isString(raw) ? raw : util.inspect(raw, {depth: 5}),
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    // ^ FUTURE: Better error message for the non-error case?
    // (see the `exits.error` impl in the machine runner for comparison,
    // and be sure to try any changes out by hand to experience the message
    // before deciding.  It's definitely not cut and dry whether there should
    // even be a custom message in this case, or if just displaying the output
    // as the `message` -- like we currently do -- is more appropriate)
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    raw: raw
  }, customizations), omen||undefined);
};





/**
 * flaverr.unwrap()
 *
 * Unwrap the provided Envelope, grabbing its "raw" property.
 *
 * Or, in some cases, just return the original 2nd argument as-is, if it is:
 * • a non-error
 * • an Error without `.name === 'Envelope'`
 * • an Error that doesn't match the provided negotiation rule
 *
 * @param  {String|Dictionary} negotiationRule
 *         A negotiation rule (e.g. like you'd use with flaverr.taste() or parley/bluebird's .catch() )
 *
 * @param  {Ref?} envelopeOrSomething
 *         The thing to try and potentially unwrap.
 *
 * @returns {Ref?}
 *          EITHER the original, untouched `envelopeOrSomething` (if it wasn't an Envelope or wasn't a match)
 *          OR the `.raw` stuff from inside of it (assuming it was an Envelop and it was a match)
 *
 * e.g.
 * ```
 *  flaverr.unwrap('E_NON_ERROR', flaverr.parseOrBuildError(3))
 *  // => 3
 *
 *  flaverr.unwrap('E_NON_ERROR', 3)
 *  // => 3
 *
 *  flaverr.unwrap({}, flaverr.parseOrBuildError(3))
 *  // => 3
 *
 *  flaverr.unwrap({}, flaverr.wrap({}, 3))
 *  // => 3
 *
 *  flaverr.unwrap({code:'E_ESCAPE_HATCH', traceRef: self}, err)
 *  // => …(the wrapped error)…
 *
 *  flaverr.unwrap('E_NON_ERROR', flaverr.wrap('E_NON_ERROR', Infinity))
 *  // => Infinity
 * ```
 */
module.exports.unwrap = function(negotiationRule, envelopeOrSomething){
  if (negotiationRule === undefined) { throw new Error('Unexpected usage of `.unwrap()`.  1st argument (the negotiation rule, or "unwrap", to be check for) is mandatory.'); }
  if (!_.isString(negotiationRule) && (!_.isObject(negotiationRule) || _.isArray(negotiationRule) || _.isError(negotiationRule))) { throw new Error('Unexpected usage of `.unwrap()`.  1st argument (the negotiation rule, or "unwrap", to check for) must be a string or dictionary (aka plain JS object), like the kind you\'d use for a similar purpose in Lodash or bluebird.  But instead, got: '+util.inspect(negotiationRule, {depth: 5})); }

  // First normalize (in case there are weird bluebird errors)
  var thingToUnwrap = flaverr.parseError(envelopeOrSomething) || envelopeOrSomething;

  if (!_.isError(thingToUnwrap) || thingToUnwrap.name !== 'Envelope' || !flaverr.taste(negotiationRule, thingToUnwrap)) {
    return thingToUnwrap;
  }
  else {
    return thingToUnwrap.raw;
  }
};





/**
 * flaverr.taste()
 *
 * Return whether the specified Error matches the given "taste" (aka negotiation rule).
 *
 * > (Uses _.matches() for dictionary comparison.)
 * > https://lodash.com/docs/3.10.1#matches
 *
 * @param  {String|Dictionary} negotiationRule
 * @param  {Ref} err
 * @return {Boolean}
 *
 * --
 *
 * > e.g.
 * > ```
 * > if (flaverr.taste('E_UNIQUE', 3822)){
 * >   //…
 * > }
 * >
 * > if (flaverr.taste('E_UNIQUE', err)){
 * >   //…
 * > }
 * >
 * > if (flaverr.taste({name:'AdapterError', code: 'E_UNIQUE'}, err)) {
 * >   //…
 * > }
 * > ```
 */
module.exports.taste = function(negotiationRule, err) {
  if (negotiationRule === undefined) { throw new Error('Unexpected usage of `.taste()`.  1st argument (the negotiation rule, or "taste", to be check for) is mandatory.'); }
  if (!_.isString(negotiationRule) && (!_.isObject(negotiationRule) || _.isArray(negotiationRule))) { throw new Error('Unexpected usage of `.taste()`.  1st argument (the negotiation rule, or "taste", to check for) must be a string or dictionary (aka plain JS object), like the kind you\'d use for a similar purpose in Lodash or bluebird.  But instead, got: '+util.inspect(negotiationRule, {depth: 5})); }
  if (err === undefined) { throw new Error('Unexpected usage of `.taste()`.  2nd argument (the Error to taste) is mandatory.'); }

  // Non-errors always fail the taste test.
  if (!_.isError(err)) {
    return false;
  }

  if (_.isString(negotiationRule)) {
    return (err.code === negotiationRule);
  }
  else {
    return _.matches(negotiationRule)(err);
  }
};






// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// FUTURE: Additionally, this additional layer of wrapping could take care of improving
// stack traces, even in the case where an Error comes up from inside the implementation.
// If done carefully, this can be done in a way that protects characteristics of the
// internal Error (e.g. its "code", etc.), while also providing a better stack trace.
//
// For example, something like this:
// ```
// /**
//  * flaverr.traceFrom()
//  *
//  * Return a modified version of the specified error.
//  *
//  */
// module.exports.traceFrom = function (omen, err) {
//   var relevantPropNames = _.difference(
//     _.union(
//       ['name', 'message'],
//       Object.getOwnPropertyNames(err)
//     ),
//     ['stack']
//   );
//   var errTemplate = _.pick(err, relevantPropNames);
//   errTemplate.raw = err;//<< could override stuff-- that's ok (see below).
//   var _mainFlaverrFn = module.exports;
//   var newError = _mainFlaverrFn(errTemplate, omen);
//   return newError;
// };
// ```
// > Note that, above, we also kept the original error (and thus _its_ trace) and
// > attached that as a separate property.  If the original error already has "raw",
// > that's ok.  This is one thing that it makes sense for us to mutate-- and any
// > attempt to do otherwise would probably be more confusing (you can imagine a `while`
// > loop where we add underscores in front of the string "raw" ad infinitum, and then
// > eventually, when there are no conflicts, use that as a keyname.  But again, that
// > ends up being more confusing from a userland perspective.)
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Why not `flaverr.try()`?
//
// Turns out it'd be a bit of a mess.
//
// More history / background:
// https://gist.github.com/mikermcneil/c1bc2d57f5bedae810295e5ed8c5f935
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

