range.js

var ltgt = require('ltgt')

//compare two array items
function isArrayLike (a) {
  return Array.isArray(a) || Buffer.isBuffer(a)
}

function isPrimitive (a) {
  return 'string' === typeof a || 'number' === typeof a
}

function has(o, k) {
  return Object.hasOwnProperty.call(o, k)
}

function compare (a, b) {
  if(isArrayLike(a) && isArrayLike(b)) {
    var l = Math.min(a.length, b.length)
    for(var i = 0; i < l; i++) {
      var c = compare(a[i], b[i])
      if(c) return c
    }
    return a.length - b.length
  }
  if(isPrimitive(a) && isPrimitive(b))
    return a < b ? -1 : a > b ? 1 : 0

  throw new Error('items not comparable:'
    + JSON.stringify(a) + ' ' + JSON.stringify(b))
}

//this assumes that the prefix is of the form:
// [Array, string]

function prefix (a, b) {
  if(a.length > b.length) return false
  var l = a.length - 1
  var lastA = a[l]
  var lastB = b[l]

  if(typeof lastA !== typeof lastB)
    return false

  if('string' == typeof lastA
    && 0 != lastB.indexOf(lastA))
      return false
  
  //handle cas where there is no key prefix
  //(a hook on an entire sublevel)
  if(a.length == 1 && isArrayLike(lastA)) l ++
  
  while(l--) {
    if(compare(a[l], b[l])) return false
  }
  return true
}

exports = module.exports = function (range, key, _compare) {
  _compare = _compare || compare
  //handle prefix specially,
  //check that everything up to the last item is equal
  //then check the last item starts with
  if(isArrayLike(range)) return prefix(range, key)

  return ltgt.contains(range, key, _compare)
}

function addPrefix(prefix, range) {
  var o = ltgt.toLtgt(range, null, function (key) {
    return [prefix, key]
  })

  //if there where no ranges, then then just use a prefix.
  if(!has(o, 'gte') && !has(o, 'lte')) return [prefix]

  return o
}

exports.compare = compare
exports.prefix = prefix
exports.addPrefix = addPrefix