geo3x3.effekt

module geo3x3
import text/string
import mutable/array

def intdiv(n: Double, m: Double): Int = {
  if (n > m) {
    1 + intdiv(n - m, m)
  } else {
    0
  }
}
def int2str(n: Int) = {
  if (n == 0) {
    "0"
  } else if (n == 1) {
    "1"
  } else if (n == 2) {
    "2"
  } else if (n == 3) {
    "3"
  } else if (n == 4) {
    "4"
  } else if (n == 5) {
    "5"
  } else if (n == 6) {
    "6"
  } else if (n == 7) {
    "7"
  } else if (n == 8) {
    "8"
  } else {
    "9"
  }
}
def encode_fn(code: String, level: Int, i: Int, lat: Double, lng: Double, unit: Double): String = {
  if (i >= level) {
    code
  } else {
    var x: Int = intdiv(lng, unit)
    var y: Int = intdiv(lat, unit)
    var c: String = int2str(1 + x + y * 3)
    encode_fn(
      infixConcat(code, c),
      level,
      i + 1,
      lat - y.toDouble * unit,
      lng - x.toDouble * unit,
      unit / 3.0
    )
  }
}

def encode(lat: Double, lng: Double, level: Int): String = {
  if (level < 1) {
    ""
  } else {
    encode_fn(
      if (lng >= 0.0) "E" else "W",
      level,
      1,
      lat + 90.0,
      if (lng >= 0.0) lng else lng + 180.0,
      180.0 / 3.0
    )
  }
}

record Result(lat: Double, lng: Double, level: Int, unit: Double)

def decode_fn(code: String, lat: Double, lng: Double, level: Int, unit: Double): Result = {
  if (length(code) == 0) {
    Result(lat + unit * 3.0 / 2.0 - 90.0, lng + unit * 3.0 / 2.0, level, unit * 3.0)
  } else {
    var n = unsafeToInt(unsafeGet(split(code, ""), 0)) - 1
    decode_fn(
      substring(code, 1),
      lat + (n / 3).toDouble * unit,
      lng + mod(n, 3).toDouble * unit,
      level + 1,
      unit / 3.0
    )
  }
}
def decode_fne(code: String): Result = {
  decode_fn(code, 0.0, 0.0, 1, 180.0 / 3.0)
}
def decode_fnw(code: String): Result = {
  var res = decode_fne(code)
  Result(res.lat, res.lng - 180.0, res.level, res.unit)
}
def decode(code: String): Result = {
  var c = unsafeGet(split(code, ""), 0)
  if (c == "W") {
    decode_fnw(substring(code, 1))
  } else if (c == "E") {
    decode_fne(substring(code, 1))
  } else {
    Result(0.0, 0.0, 1, 0.0)
  }
}