# Code coverage report for dynamic-dijkstra/index.js

# all files / dynamic-dijkstra/ index.js

75.57% Statements 99/131
57.53% Branches 42/73
73.91% Functions 17/23
81.51% Lines 97/119

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     'use strict'
    var _Heap = require('heap')
    var Heap = function (cmp) { return new _Heap(cmp) }
    var LOG = false

    module.exports = function (opts) {
      var exports = {}

      function getValueFromEdge(hops, j, v) {
        return opts.add(hops[j], v)
      }

      function getNewValue(hops, j, k, v) {
        return opts.min(hops[k], getValueFromEdge(hops, j, v))
      }

      function isUnchangedByEdge (hops, j, k, v) {
        return hops[k] === opts.add(hops[j], v)
      }

      function isUnchanged (hops, j, k, v) {
        return hops[k] === getNewValue(hops, j, k, v)
      }

      //"increment" is an edge that shortens graph distances
      //adding a new edge always decreases hops, or decreasing
      //the weight of an edge. (see the literature on dynamic graphs)
      function isIncrement (value, old_value) {
        return (
          opts.isAdd(value) && (
            opts.isRemove(old_value) || (opts.min(value, old_value) == value)
          )
        )
      }

      //take a graph, and return it's inverse
      exports.reverse = function (g) {
        var _g = {}
        for(var k in g) {
          for(var j in g[k]) {
            _g[j] = _g[j] || {}
            _g[j][k] = g[k][j]
          }
        }
        return _g
      }

      function _loop (g, max, hops, next, _hops) {
        Iif(!_hops) throw new Error('_hops must be provided')
        while(!next.empty()) {
          var j = next.pop()
          if(opts.expand(hops[j], max))
            for(var k in g[j]) {
              var _h = getNewValue(hops, j, k, g[j][k])
              Iif(isNaN(_h)) throw new Error('NaN')
              if(_h != hops[k]) {
                _hops[k] = hops[k] = _h
                next.push(k)
              }
            }
        }
        return _hops
      }

      exports.traverse = exports.brute = function (g, _g, max, from) {
        var hops = {}
        hops[from] = opts.initial()
        var next = Heap(function (a, b) {
           return hops[a] - hops[b]
        }, function (k) { return hops[k] })
        next.push(from)
        return _loop(g, max, hops, next, hops)
      }

      //find all nodes reachable via `from` with hops at > was
      exports.uncertain = function (g, hops, max, start) {
        var was = hops[start]
        var maybe = {}
        maybe[start] = true
        var next = Heap(function (a, b) {
          return hops[a] - hops[b]
        })
        next.push(start)
        while(!next.empty()) {
          var j = next.pop()
          for(var k in g[j])
            if(
              isUnchangedByEdge(hops, j,k,g[j][k])
            //hops[k] === opts.add(hops[j], g[j][k])
            ) {
              Eif(!maybe[k]) {
                maybe[k] = true
                next.push(k)
              }
            }
        }
        return maybe
      }

      exports.sources = function (_g, hops, maybe) {
        Iif(!_g) throw new Error('backlink graph must be provided')
        var update = {}
        for(var k in maybe)
          Eif(hops[k])
            for(var j in _g[k])
              if(!maybe[j] && hops[j] != null)
                update[j] = true
        return update
      }

      function update_graphs(g, _g, from, to, value) {
        g[from] = g[from] || {}
        _g[to] = _g[to] || {}
        g[from][to] = _g[to][from] = value
      }

      exports.update = function (g, _g, hops, max, start, from,to,value) {
        var _hops = {}
        Iif(hops[start] == null) hops[start] = opts.initial()
        var old_value = g[from] && g[from][to]
        //handle follow (aka increments)
        //TODO: if number is greater, treat that is decrement
        Iif(isIncrement(value, old_value)) {
          update_graphs(g, _g, from, to, value)

          //if from isn't within hops, then to won't be in hops either.
          if(hops[from] == null || from == to) return {}

          var h = getNewValue(hops, from, to, value)
          //if destination is max or more, do not add edge
          if(!opts.expand(hops[from], max)) return {}

          if(h != hops[to]) {
            _hops[to] = hops[to] = h
            //if this edge is at the limit, we are done.
            if(!opts.expand(hops[to], max)) return _hops

            //setup heap and run dijkstra's algorithm
            var next = Heap(function (a, b) { return hops[a] - hops[b] })
            next.push(to)
            return _loop(g, max, hops, next, _hops)
          }
        }
        //handle unfollow and block (aka decrements)
        else {
          Iif(!value && !_g) throw new Error('expected increment:'+value)
          var j = from, k = to, v = value, _v = g[from] && g[from][to]

          //shortcut 1: detect cases that won't change the hops
          Iif(
            to === start || //can't block yourself, so don't update hops.
            ( //already closer
              //if previous value was null, or previous didn't set the hops value anyway.
              //and the hops value will be the same, then don't update hops.
              (_v == null  || !isUnchangedByEdge(hops, j, k, _v)) &&
              isUnchanged(hops, j, k, v)
            ) || (
              //if this edge _did_ set the hops value, check if there is another edge which also sets it.
              //this catches the case when someone unfollows, but there is another follow path the same length.
              //only applies when there was a previous edge.
                (_v == null || isUnchangedByEdge(hops, j, k, _v)) &&
                isUnchanged(hops, j, k, v) &&
                //quickly check if any other edges set hops
                (function () {
                  for(var _j in _g[k])
                    Iif(_j !== j && isUnchangedByEdge(hops, _j, k, g[_j][k]))
                      return true
                }())
            )
          ) {
            //won't change hops, so update graph and return
            update_graphs(g, _g, from, to, value)
            return null

          }
          //shortcut 2. detect cases that will add exactly 1 element to hops
          else Iif (v === null && hops[j] >= 0) {
            //only adds the new item, but won't expand since this is a block.
            update_graphs(g, _g, j,k,v)
            if(opts.expand(hops[j], 3)) //XXX is this really where the default is set?
              _hops[k] = hops[k] = opts.add(hops[j], v)
            return _hops
          }
          //the long way. calculate all hops that may be changed by this edge and recalculate them.
          else {
            var next = Heap(function (a, b) {
              return hops[a] - hops[b]
            }, function (k) { return hops[k] })

            var maybe = exports.uncertain(g, hops, max, to)
            var sources = exports.sources(_g, hops, maybe)

            update_graphs(g, _g, from, to, value)

            sources[from] = true
            var pre = {}
            for(var _k in maybe) {
              pre[_k] = hops[_k]
              delete hops[_k]
            }

            var diff = exports.updateAll(g, hops, max, sources, _hops)

            for(var k in pre)
              Iif(diff[k] == pre[k])
                delete diff[k]

            return diff
          }
        }
      }

      exports.updateAll = function (g, hops, max, sources, _hops) {
        var next = Heap(function (a, b) { return hops[a] - hops[b] })

        for(var k in sources) next.push(k)

        return _loop(g, max, hops, next, _hops)
      }

      return exports
    }