const assert = require('assert')
const _ = require('lodash')

const d = [ // test data
  {x: 1, y: 1, z: 'a'},
  {x: 1, y: 1, z: 'b'},
  {x: 2, y: 1, z: 'c'},
  {x: 2, y: 2, z: 'd'},
  {x: 2, y: 3, z: 'e'},
  {x: 3, y: 1, z: 'f'}
]

const e = [ // expected result
  {k1: 1, k2: 1, data: [{x: 1, y: 1, z: 'a'}, {x: 1, y: 1, z: 'b'}]},
  {k1: 2, k2: 1, data: [{x: 2, y: 1, z: 'c'}]},
  {k1: 2, k2: 2, data: [{x: 2, y: 2, z: 'd'}]},
  {k1: 2, k2: 3, data: [{x: 2, y: 3, z: 'e'}]},
  {k1: 3, k2: 1, data: [{x: 3, y: 1, z: 'f'}]}
]

function genrows(groups, groupKey) {
  return _.toPairs(groups)
    .map(([key, data]) => ({[groupKey]: key, data}))
}

function gengroups(arr, iteratee, key) {
  const grouped = _.groupBy(arr, iteratee)
  return genrows(grouped, key)
}

function grouparray(data, props) {
  let result = [{data}]

  props.map((prop, i) => {
    const key = prop.key || `k${i + 1}`
    const iteratee = prop.iteratee || prop

    result = _.flatten(result.map(row => {
      return gengroups(row.data, iteratee, key)
        .map(group => Object.assign({}, row, {
          [key]: group[key],
          data: group.data
        }))
    }))

  })

  return _.flatten(result)
}

console.log('final', grouparray(d, ['x', 'y']))

// e[0].data[0].x = 274

assert.deepEqual(grouparray(d, ['x', {
  iteratee: (data) => data.y
}]), e)

console.log('deepEqual', true)

// console.log('expected full', JSON.stringify(e, null, '  '))
// console.log('final full', JSON.stringify(grouparray(d, ['x', 'y']), null, '  '))


const exptected = [
  {
    "k1": 1,
    "k2": 1,
    "data": [
      {
        "x": 1,
        "y": 1,
        "z": "a"
      },
      {
        "x": 1,
        "y": 1,
        "z": "b"
      }
    ]
  },
  {
    "k1": 2,
    "k2": 1,
    "data": [
      {
        "x": 2,
        "y": 1,
        "z": "c"
      }
    ]
  },
  {
    "k1": 2,
    "k2": 2,
    "data": [
      {
        "x": 2,
        "y": 2,
        "z": "d"
      }
    ]
  },
  {
    "k1": 2,
    "k2": 3,
    "data": [
      {
        "x": 2,
        "y": 3,
        "z": "e"
      }
    ]
  },
  {
    "k1": 3,
    "k2": 1,
    "data": [
      {
        "x": 3,
        "y": 1,
        "z": "f"
      }
    ]
  }
]
const final = [
  {
    "data": [
      {
        "x": 1,
        "y": 1,
        "z": "a"
      },
      {
        "x": 1,
        "y": 1,
        "z": "b"
      }
    ],
    "k1": "1",
    "k2": "1"
  },
  {
    "data": [
      {
        "x": 2,
        "y": 1,
        "z": "c"
      }
    ],
    "k1": "2",
    "k2": "1"
  },
  {
    "data": [
      {
        "x": 2,
        "y": 2,
        "z": "d"
      }
    ],
    "k1": "2",
    "k2": "2"
  },
  {
    "data": [
      {
        "x": 2,
        "y": 3,
        "z": "e"
      }
    ],
    "k1": "2",
    "k2": "3"
  },
  {
    "data": [
      {
        "x": 3,
        "y": 1,
        "z": "f"
      }
    ],
    "k1": "3",
    "k2": "1"
  }
]