# Item.Margin

    'use strict'

    utils = require 'src/utils'
    signal = require 'src/signal'
    assert = require 'src/assert'

# **Class** Margin

    module.exports = (Renderer, Impl, itemUtils, Item) -> (ctor, opts) -> class Margin extends itemUtils.DeepObject
        @__name__ = 'Margin'

        propertyName = opts?.propertyName or 'margin'

        itemUtils.defineProperty
            constructor: ctor
            name: propertyName
            defaultValue: 0
            valueConstructor: Margin
            setter: (_super) -> (val=0) ->
                margin = @[propertyName]
                if typeof val is 'string'
                    arr = val.split ' '
                    for elem, i in arr
                        arr[i] = parseFloat elem
                    switch arr.length
                        when 3
                            margin.top = arr[0]
                            margin.right = arr[1]
                            margin.bottom = arr[2]
                            margin.left = arr[1]
                        when 2
                            margin.top = arr[0]
                            margin.right = arr[1]
                            margin.bottom = arr[0]
                            margin.left = arr[1]
                        when 1
                            margin.left = margin.top = margin.right = margin.bottom = arr[0]
                        else
                            margin.top = arr[0]
                            margin.right = arr[1]
                            margin.bottom = arr[2]
                            margin.left = arr[3]
                else if Array.isArray(val)
                    margin.top = val[0] if val.length > 0
                    margin.right = val[1] if val.length > 1
                    margin.bottom = val[2] if val.length > 2
                    margin.left = val[3] if val.length > 3
                else if utils.isObject(val)
                    margin.left = val.left if val.left?
                    margin.top = val.top if val.top?
                    margin.right = val.right if val.right?
                    margin.bottom = val.bottom if val.bottom?
                else
                    margin.left = margin.top = margin.right = margin.bottom = val
                _super.call @, val
                return

        constructor: (ref) ->
            super ref
            @_left = 0
            @_top = 0
            @_right = 0
            @_bottom = 0

            Object.preventExtensions @

Margins are used in anchors and within layout items.

```javascript
Rectangle {
    width: 100
    height: 100
    color: 'red'
    Rectangle {
        width: 100
        height: 50
        color: 'yellow'
        anchors.left: parent.right
        margin.left: 20
    }
}
```

```javascript
Column {
    Rectangle { color: 'red'; width: 50; height: 50; }
    Rectangle { color: 'yellow'; width: 50; height: 50; margin.top: 20; }
    Rectangle { color: 'green'; width: 50; height: 50; }
}
```

        createMarginProp = (type, extraProp) ->
            developmentSetter = (val) ->
                assert typeof val is 'number' and isFinite(val)
                , "margin.#{type} expects a finite number; `#{val}` given"

            extraPropSignal = "on#{utils.capitalize(extraProp)}Change"
            itemUtils.defineProperty
                constructor: Margin
                name: type
                defaultValue: 0
                setter: (_super) -> (val) ->
                    extraOldVal = @[extraProp]
                    _super.call @, val
                    @[extraPropSignal].emit extraOldVal
                namespace: propertyName
                parentConstructor: ctor
                developmentSetter: developmentSetter

## *Float* Margin::left = `0`

## *Signal* Margin::onLeftChange(*Float* oldValue)

        createMarginProp 'left', 'horizontal'

## *Float* Margin::top = `0`

## *Signal* Margin::onTopChange(*Float* oldValue)

        createMarginProp 'top', 'vertical'

## *Float* Margin::right = `0`

## *Signal* Margin::onRightChange(*Float* oldValue)

        createMarginProp 'right', 'horizontal'

## *Float* Margin::bottom = `0`

## *Signal* Margin::onBottomChange(*Float* oldValue)

        createMarginProp 'bottom', 'vertical'

## *Float* Margin::horizontal = `0`

Sum of the left and right margin.

## *Signal* Margin::onHorizontalChange(*Float* oldValue)

        signal.Emitter.createSignal @, 'onHorizontalChange'

        utils.defineProperty @::, 'horizontal', null, ->
            @_left + @_right
        , (val) ->
            @left = @right = val / 2

## *Float* Margin::vertical = `0`

Sum of the top and bottom margin.

## *Signal* Margin::onVerticalChange(*Float* oldValue)

        signal.Emitter.createSignal @, 'onVerticalChange'

        utils.defineProperty @::, 'vertical', null, ->
            @_top + @_bottom
        , (val) ->
            @top = @bottom = val / 2

## *Float* Margin::valueOf()

        valueOf: ->
            if @left is @top and @top is @right and @right is @bottom
                @left
            else
                throw new Error "margin values are different"

        toJSON: ->
            left: @left
            top: @top
            right: @right
            bottom: @bottom

# Glossary

- [Item.Margin](#class-margin)