index.js

var INVALID_BOUNDS_ERR = "Invalid range bounds: "
module.exports = Range

/**
 * Create a new range object with the given begin and end endpoints.  
 * You can also pass a two character string for bounds. Defaults to` "[]"` for
 * an all inclusive range.
 *
 * You can use any value for endpoints. `Null` is considered infinity for
 * values that don't have a special infinity type like `Number` has `Infinity`.
 *
 * An empty range is one where either of the endpoints is `undefined` (like `new
 * Range`) or a range with two equivalent, but exculsive endpoints
 * (`new Range(5, 5, "[)")`).
 *
 * **Import**:
 * ```javascript
 * var Range = require("strange")
 * ```
 *
 * @example
 * new Range(10, 20) // => {begin: 10, end: 20, bounds: "[]"}
 * new Range(new Date(2000, 5, 18), new Date(2000, 5, 22))
 *
 * @class Range
 * @constructor
 * @param {Object} begin
 * @param {Object} end
 * @param {String} [bounds="[]"]
 */
function Range(begin, end, bounds) {
  if (!(this instanceof Range)) return new Range(begin, end, bounds)

  /**
   * Range's beginning, or left endpoint.
   *
   * @property {Object} begin
   */
  this.begin = begin

  /**
   * Range's end, or right endpoint.
   *
   * @property {Object} end
   */
  this.end = end

  /**
   * Range's bounds.
   *
   * Bounds signify whether the range includes or excludes that particular
   * endpoint.
   *
   * Pair | Meaning
   * -----|--------
   * `()` | open
   * `[]` | closed
   * `[)` | left-closed, right-open
   * `(]` | left-open, right-closed
   *
   * @example
   * new Range(1, 5).bounds // => "[]"
   * new Range(1, 5, "[)").bounds // => "[)"
   *
   * @property {String} bounds
   */
   this.bounds = bounds = bounds === undefined ? "[]" : bounds
   if (!isValidBounds(bounds)) throw new RangeError(INVALID_BOUNDS_ERR + bounds)
}

Range.prototype.begin = undefined
Range.prototype.end = undefined
Range.prototype.bounds = "[]"

/**
 * Compares this range's beginning with the given value.  
 * Returns `-1` if this range begins before the given value, `0` if they're
 * equal and `1` if this range begins after the given value.
 *
 * `null` is considered to signify negative infinity for non-numeric range
 * endpoints.
 *
 * @example
 * new Range(0, 10).compareBegin(5) // => -1
 * new Range(0, 10).compareBegin(0) // => 0
 * new Range(5, 10).compareBegin(0) // => 1
 * new Range(5, 10).compareBegin(null) // => 1
 *
 * @method compareBegin
 * @param {Object} begin
 */
Range.prototype.compareBegin = function(begin) {
  var a = this.begin === null ? -Infinity : this.begin
  var b = begin === null ? -Infinity : begin
  return compare(a, b) || (this.bounds[0] == "[" ? 0 : 1)
}

/**
 * Compares this range's end with the given value.  
 * Returns `-1` if this range ends before the given value, `0` if they're
 * equal and `1` if this range ends after the given value.
 *
 * `null` is considered to signify positive infinity for non-numeric range
 * endpoints.
 *
 * @example
 * new Range(0, 10).compareEnd(5) // => -1
 * new Range(0, 10).compareEnd(10) // => 0
 * new Range(0, 5).compareEnd(10) // => 1
 * new Range(0, 5).compareEnd(null) // => -1
 *
 * @method compareEnd
 * @param {Object} end
 */
Range.prototype.compareEnd = function(end) {
  var a = this.end === null ? Infinity : this.end
  var b = end === null ? Infinity : end
  return compare(a, b) || (this.bounds[1] == "]" ? 0 : -1)
}

/**
 * Check whether the range is empty.  
 * An empty range is one where either of the endpoints is `undefined` (like `new
 * Range`) or a range with two equivalent, but exculsive endpoints
 * (`new Range(5, 5, "[)")`).
 *
 * Equivalence is checked by using the `<` operators, so value objects will be
 * coerced into something comparable by JavaScript. That usually means calling
 * the object's `valueOf` function.
 *
 * @example
 * new Range().isEmpty() // => true
 * new Range(5, 5, "[)").isEmpty() // => true
 * new Range(1, 10).isEmpty() // => false
 *
 * @method isEmpty
 */
Range.prototype.isEmpty = function() {
  var a = this.begin === null ? -Infinity : this.begin
  var b = this.end === null ? Infinity : this.end
  if (a === undefined || b === undefined) return true
  return this.bounds != "[]" && compare(a, b) === 0
}

/**
 * Check whether the range is bounded.  
 * A bounded range is one where neither endpoint is `null` or `Infinity`. An
 * empty range is considered bounded.
 *
 * @example
 * new Range().isBounded() // => true
 * new Range(5, 5).isBounded() // => true
 * new Range(null, new Date(2000, 5, 18).isBounded() // => false
 * new Range(0, Infinity).isBounded() // => false
 * new Range(-Infinity, Infinity).isBounded() // => false
 *
 * @method isBounded
 */
Range.prototype.isBounded = function() {
  if (this.begin === undefined || this.end === undefined) return true
  return !(isInfinity(this.begin) || isInfinity(this.end))
}

/**
 * @method isFinite
 * @alias isBounded
 */
Range.prototype.isFinite = Range.prototype.isBounded

/**
 * Check whether the range is unbounded.  
 * An unbounded range is one where either endpoint is `null` or `Infinity`. An
 * empty range is not considered unbounded.
 *
 * @example
 * new Range().isUnbounded() // => false
 * new Range(5, 5).isUnbounded() // => false
 * new Range(null, new Date(2000, 5, 18).isUnbounded() // => true
 * new Range(0, Infinity).isUnbounded() // => true
 * new Range(-Infinity, Infinity).isUnbounded() // => true
 *
 * @method isUnbounded
 */
Range.prototype.isUnbounded = function() {
  return !this.isBounded()
}

/**
 * @method isInfinite
 * @alias isUnbounded
 */
Range.prototype.isInfinite = Range.prototype.isUnbounded

/**
 * Check if a given value is contained within this range.  
 * Returns `true` or `false`.
 *
 * @example
 * new Range(0, 10).contains(5) // => true
 * new Range(0, 10).contains(10) // => true
 * new Range(0, 10, "[)").contains(10) // => false
 *
 * @method contains
 * @param {Object} value
 */
Range.prototype.contains = function(value) {
  var a = this.begin
  var b = this.end

  return (
    (b === null || (this.bounds[1] === "]" ? value <= b : value < b)) &&
    (a === null || (this.bounds[0] === "[" ? a <= value : a < value))
  )
}

/**
 * Check if this range intersects with another.  
 * Returns `true` or `false`.
 *
 * Ranges that have common points intersect. Ranges that are consecutive and
 * with *inclusive* endpoints are also intersecting. An empty range will never
 * intersect.
 *
 * @example
 * new Range(0, 10).intersects(new Range(5, 7)) // => true
 * new Range(0, 10).intersects(new Range(10, 20)) // => true
 * new Range(0, 10, "[)").intersects(new Range(10, 20)) // => false
 * new Range(0, 10).intersects(new Range(20, 30)) // => false
 *
 * @method intersects
 * @param {Object} other
 */
Range.prototype.intersects = function(other) {
  if (this.isEmpty()) return false
  if (other.isEmpty()) return false

  return (
    Range.compareBeginToEnd(this, other) <= 0 &&
    Range.compareBeginToEnd(other, this) <= 0
  )
}

/**
 * Returns an array of the endpoints and bounds.
 *
 * Useful with [Egal.js](https://github.com/moll/js-egal) or other libraries
 * that compare value objects by their `valueOf` output.
 *
 * @example
 * new Range(1, 10, "[)").valueOf() // => [1, 10, "[)"]
 *
 * @method valueOf
 */
Range.prototype.valueOf = function() {
  return [this.begin, this.end, this.bounds]
}

/**
 * Stringifies a range in `[a,b]` format.
 *
 * This happens to match the string format used by [PostgreSQL's range type
 * format](http://www.postgresql.org/docs/9.4/static/rangetypes.html). You can
 * therefore use stRange.js to parse and stringify ranges for your database.
 *
 * @example
 * new Range(1, 5).toString() // => "[1,5]"
 * new Range(1, 10, "[)").toString() // => "[1,10)"
 *
 * @method toString
 */
Range.prototype.toString = function() {
  // FIXME: How to serialize an empty range with undefined endpoints?
  var a = stringify(this.begin)
  var b = stringify(this.end)
  return this.bounds[0] + a + "," + b + this.bounds[1]
}

/**
 * Stringifies the range when passing it to `JSON.stringify`.  
 * This way you don't need to manually call `toString` when stringifying.
 *
 * @example
 * JSON.stringify(new Range(1, 10)) // "\"[1,10]\""
 *
 * @method toJSON
 * @alias toString
 */
Range.prototype.toJSON = Range.prototype.toString
Range.prototype.inspect = Range.prototype.toString

/**
 * Compares two range's beginnings.  
 * Returns `-1` if `a` begins before `b` begins, `0` if they're equal and `1`
 * if `a` begins after `b`.
 *
 * @example
 * Range.compareBeginToBegin(new Range(0, 10), new Range(5, 15)) // => -1
 * Range.compareBeginToBegin(new Range(0, 10), new Range(0, 15)) // => 0
 * Range.compareBeginToBegin(new Range(0, 10), new Range(0, 15, "()")) // => 1
 *
 * @static
 * @method compareBeginToBegin
 * @param {Object} a
 * @param {Object} b
 */
Range.compareBeginToBegin = function(a, b) {
  var aBegin = a.begin === null ? -Infinity : a.begin
  var bBegin = b.begin === null ? -Infinity : b.begin
  if (a.bounds[0] === b.bounds[0]) return compare(aBegin, bBegin)
  else return compare(aBegin, bBegin) || (b.bounds[0] === "(" ? -1 : 1)
}

/**
 * Compares the first range's beginning to the second's end.  
 * Returns `<0` if `a` begins before `b` ends, `0` if one starts where the other
 * ends and `>1` if `a` begins after `b` ends.
 *
 * @example
 * Range.compareBeginToEnd(new Range(0, 10), new Range(0, 5)) // => -1
 * Range.compareBeginToEnd(new Range(0, 10), new Range(-10, 0)) // => 0
 * Range.compareBeginToEnd(new Range(0, 10), new Range(-10, -5)) // => 1
 *
 * @static
 * @method compareBeginToEnd
 * @param {Object} a
 * @param {Object} b
 */
Range.compareBeginToEnd = function(a, b) {
  var aBegin = a.begin === null ? -Infinity : a.begin
  var bEnd = b.end === null ? Infinity : b.end
  if (a.bounds[0] === "[" && b.bounds[1] === "]") return compare(aBegin, bEnd)
  else return compare(aBegin, bEnd) || 1
}

/**
 * Compares two range's endings.  
 * Returns `-1` if `a` ends before `b` ends, `0` if they're equal and `1`
 * if `a` ends after `b`.
 *
 * @example
 * Range.compareEndToEnd(new Range(0, 10), new Range(5, 15)) // => -1
 * Range.compareEndToEnd(new Range(0, 10), new Range(5, 10)) // => 0
 * Range.compareEndToEnd(new Range(0, 10), new Range(5, 10, "()")) // => 1
 *
 * @static
 * @method compareEndToEnd
 * @param {Object} a
 * @param {Object} b
 */
Range.compareEndToEnd = function(a, b) {
  var aEnd = a.end === null ? Infinity : a.end
  var bEnd = b.end === null ? Infinity : b.end
  if (a.bounds[1] === b.bounds[1]) return compare(aEnd, bEnd)
  else return compare(aEnd, bEnd) || (a.bounds[1] === ")" ? -1 : 1)
}

/**
 * Parses a string stringified by
 * [`Range.prototype.toString`](#Range.prototype.toString).
 *
 * To have it also parse the endpoints to something other than a string, pass
 * a function as the second argument.
 *
 * If you pass `Number` as the _parse_ function and the endpoints are
 * unbounded, they'll be set to `Infinity` for easier computation.
 *
 * @example
 * Range.parse("[a,z)") // => new Range("a", "z", "[)")
 * Range.parse("[42,69]", Number) // => new Range(42, 69)
 * Range.parse("[15,]", Number) // => new Range(15, Infinity)
 * Range.parse("(,3.14]", Number) // => new Range(-Infinity, 3.14, "(]")
 *
 * @static
 * @method parse
 * @param {String} range
 * @param {Function} [parseEndpoint]
 */
Range.parse = function(range, parse) {
  var endpoints = range.slice(1, -1).split(",", 2)
  var begin = endpoints[0] ? parse ? parse(endpoints[0]) : endpoints[0] : null
  var end = endpoints[1] ? parse ? parse(endpoints[1]) : endpoints[1] : null
  if (parse === Number && begin === null) begin = -Infinity
  if (parse === Number && end === null) end = Infinity
  return new Range(begin, end, range[0] + range[range.length - 1])
}

/**
 * Merges two ranges and returns a range that encompasses both of them.  
 * The ranges don't have to be intersecting.
 *
 * @example
 * Range.union(new Range(0, 5), new Range(5, 10)) // => new Range(0, 10)
 * Range.union(new Range(0, 10), new Range(5, 15)) // => new Range(0, 15)
 *
 * var a = new Range(-5, 0, "()")
 * var b = new Range(5, 10)
 * Range.union(a, b) // => new Range(-5, 10, "(]")
 *
 * @static
 * @method union
 * @param {String} union
 * @param {Range} a
 * @param {Range} b
 */
Range.union = function(a, b) {
  var aIsEmpty = a.isEmpty()
  var bIsEmpty = b.isEmpty()
  if (aIsEmpty && bIsEmpty) return new Range
  else if (aIsEmpty) return b
  else if (bIsEmpty) return a

  var begin = Range.compareBeginToBegin(a, b) <= 0 ? a : b
  var end = Range.compareEndToEnd(a, b) <= 0 ? b : a
  return new Range(begin.begin, end.end, begin.bounds[0] + end.bounds[1])
}

function isInfinity(value) {
  return value === null || value === Infinity || value === -Infinity
}

function isValidBounds(bounds) {
   switch (bounds) {
     case "()":
     case "[]":
     case "[)":
     case "(]": return true
     default: return false
   }
}

// The less-than operator ensures coercion with valueOf.
function compare(a, b) { return a < b ? -1 : b < a ? 1 : 0 }
function stringify(value) { return isInfinity(value) ? "" : String(value) }