git ssb

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const nest = require('depnest')
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const { h, computed } = require('mutant')
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const hexrgb = require('hex-rgb')
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exports.gives = nest('tag.html.tag')
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exports.needs = nest({
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  'about.obs.color': 'first'
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})
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exports.create = function(api) {
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  return nest({ 'tag.html.tag': function({ tagName, tagId }, handleRemove) {
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    var removeTag
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    if (handleRemove) {
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      removeTag = h('a', {
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        'ev-click': handleRemove
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      }, 'x')
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    } else {
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      removeTag = '';
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    }
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    const backgroundColor = api.about.obs.color(tagId)
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    const fontColor = computed(backgroundColor, contrast)
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    return h(
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      'Tag',
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      {
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        style: {
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          'background-color': backgroundColor,
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          'color': fontColor
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        }
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      },
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      [
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        h('span', tagName),
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        removeTag
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      ]
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    )
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  }})
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}
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function contrast(backgroundColor) {
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  const { red, green, blue } = hexrgb(backgroundColor)
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  const C = [ red/255, green/255, blue/255 ]
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  for ( var i = 0; i < C.length; ++i ) {
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    if ( C[i] <= 0.03928 ) {
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      C[i] = C[i] / 12.92
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    } else {
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      C[i] = Math.pow( ( C[i] + 0.055 ) / 1.055, 2.4);
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    }
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  }
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  const L = 0.2126 * C[0] + 0.7152 * C[1] + 0.0722 * C[2]
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  if (L > 0.179) {
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    return '#000'
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  } else {
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    return '#fff'
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  }
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}
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