/*

 flyd.js - The extraction of flyd's central function which was sufficient for the example to work.

           It lacks many important functions of flyd, so use the original version on your project:
           https://github.com/paldepind/flyd

           However it is changed slightly to ensure that subsequent updates run in the same order
           as the original order, which simplified the initial implementation. It may also be
           simpler to study operations on this 100-line version.

           Original license of flyd is included below.

 The MIT License (MIT)

 Copyright (c) 2015 Simon Friis Vindum

 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in all
 copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.

*/

var flyd = (function () {

    var inStream
    var order = []
    var orderNextIdx = -1

    // pure functions start here

    function allDependentsHaveValues(stream) {
        return stream.deps.every(function(s) {
            return s.val !== void(0)
        })
    }

    // pure functions end here

    function updateStream(s) {
        if (allDependentsHaveValues(s)) {
            inStream = s
            var returnVal = s.fn(s)
            if (returnVal !== undefined) {
                s(returnVal)
            }
            inStream = undefined
            s.shouldUpdate = false
        }
    }

    function findDeps(s) {
        var i, listeners = s.listeners
        if (s.queued === false) {
            s.queued = true
            for (i = 0; i < listeners.length; ++i) {
                findDeps(listeners[i])
            }
            order[++orderNextIdx] = s
        }
    }

    function updateDeps(s) {
        var i, o, list, listeners = s.listeners
        for (i = 0; i < listeners.length; ++i) {
            list = listeners[i]
            list.shouldUpdate = true
            findDeps(list)

        }
        for (; orderNextIdx >= 0; --orderNextIdx) {
            o = order[orderNextIdx]
            if (o.shouldUpdate === true) updateStream(o)
            o.queued = false
        }
    }

    function createStream() {
        function stream(n) {
            var i, list
            if (arguments.length === 0) {
                return stream.val
            } else {
                stream.val = n
                if (inStream === undefined) {
                    updateDeps(stream)
                } else if (inStream === stream) {
                    for (i = 0; i < stream.listeners.length; ++i) {
                        list = stream.listeners[i]
                        list.shouldUpdate = true
                    }
                } else {
                    debugger;
                    throw new Error('Restore toUpdate') // was: toUpdate.push(s)
                }
                return stream
            }
        }
        stream.val = void(0)
        stream.listeners = []
        stream.queued = false

        return stream
    }

    function createDependentStream(deps, fn) {
        var i, s = createStream()
        s.fn = fn
        s.deps = deps
        s.shouldUpdate = false
        for (i = 0; i < deps.length; ++i) {
            deps[i].listeners.unshift(s)
        }
        return s
    }

    function stream(arg, fn) {
        var s = createDependentStream(arg, fn)
        updateStream(s)
        return s
    }

    return stream
})()