git ssb

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var MutantMap = require('./map')
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var computed = require('./computed')
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var resolve = require('./resolve')
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var KeyValue = require('./lib/key-value')
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var isObservable = require('./is-observable')
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module.exports = Lookup
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function Lookup (obs, lambdaOrKey, opts) {
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  var mapped = MutantMap(obs, function (item, invalidateOn) {
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    if (typeof lambdaOrKey === 'function') {
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      var value = lambdaOrKey(item, invalidateOn)
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      if (isObservable(value) && value._type === 'MutantKeyValue') {
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        return value // passthru
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      } else if (Array.isArray(value)) {
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        return KeyValue(value[0], value[1])
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      } else {
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        return KeyValue(value, item)
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      }
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    } else if (typeof lambdaOrKey === 'string') {
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      return KeyValue(item[lambdaOrKey], item)
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    }
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  })
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  var raw = {}
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  var value = {}
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  var keys = new Set()
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  var instance = computed.extended(mapped, function update () {
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    var currentKeys = []
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    for (var i = 0; i < mapped.getLength(); i++) {
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      var item = mapped.get(i)
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      if (item) {
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        var key = resolve(item.key)
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        if (key != null) {
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          var rawValue = item.value
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          currentKeys.push(key)
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          keys.add(key)
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          raw[key] = rawValue
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          value[key] = resolve(rawValue)
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        }
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      }
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    }
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    // remove deleted keys
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    Array.from(keys.values()).filter(function (k) {
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      return !currentKeys.includes(k)
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    }).forEach(function (key) {
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      keys.delete(key)
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      delete raw[key]
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      delete value[key]
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    })
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    return value
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  })
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  var result = function MutantLookup (listener) {
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    return instance(listener)
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  }
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  result.keys = function () {
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    instance.checkUpdated()
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    return Array.from(keys.values())
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  }
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  result.get = function (key) {
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    instance.checkUpdated()
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    return raw[key]
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  }
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  return result
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}
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