import {promoteBinary, promoteUnary} from './helpers.js'
import {Vector} from './Vector.js'

import {ReturnType} from '#core/Type.js'
import {match} from '#core/TypePatterns.js'
import {ReturnsAs} from '#generic/helpers.js'

export const normsq = match(Vector, (math, V) => {
   const compNormsq = math.normsq.resolve(V.Component)
   const sum = math.sum.resolve(Vector(ReturnType(compNormsq)))
   return ReturnsAs(sum, v => sum(v.map(compNormsq)))
})
// abs and norm differ only on Vector (and perhaps other collections) --
// norm computes overall by the generic formula, whereas abs distributes
// elementwise:
export const abs = promoteUnary('abs')
export const add = promoteBinary('add')

export const sum = match(Vector, (math, V) => {
   const add = math.add.resolve([V.Component, V.Component])
   const haszero = math.haszero(V.Component)
   const zero = haszero ? math.zero(V.Component) : undefined
   return ReturnsAs(add, v => {
      if (v.length === 0) {
         if (haszero) return zero
         throw new TypeError(`Can't sum empty ${V}: no zero element`)
      }
      let ix = 0
      let retval = v[ix]
      while (++ix < v.length) retval = add(retval, v[ix])
      return retval
   })
})