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"use strict";
var method = require("../method/core")
// Method is designed to work with data structures representing application
// state. Calling it with a state should return object representing `delta`
// that has being applied to a previous state to get to a current state.
//
// Example
//
// diff(state) // => { "item-id-1": { title: "some title" } "item-id-2": null }
var diff = method("diff@diffpatcher")
// diff between `null` / `undefined` to any hash is a hash itself.
diff.define(null, function(from, to) { return to })
diff.define(undefined, function(from, to) { return to })
diff.define(Object, function(from, to) {
return calculate(from, to || {}) || {}
})
function calculate(from, to) {
var diff = {}
var changes = 0
Object.keys(from).forEach(function(key) {
changes = changes + 1
if (!(key in to) && from[key] != null) diff[key] = null
else changes = changes - 1
})
Object.keys(to).forEach(function(key) {
changes = changes + 1
var previous = from[key]
var current = to[key]
if (previous === current) return (changes = changes - 1)
if (typeof(current) !== "object") return diff[key] = current
if (typeof(previous) !== "object") return diff[key] = current
var delta = calculate(previous, current)
if (delta) diff[key] = delta
else changes = changes - 1
})
return changes ? diff : null
}
diff.calculate = calculate
module.exports = diff
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