cadence.go

package main

import (
  "fmt"
  "math"
  "os"
  "strconv"
  "strings"
)

func printHelp() {
  fmt.Print(`Running cadence calculator - Written by Felix Gertz
Calculates optimal cadence (steps per minute)
for specfic pace and body height relations to gain optimal hip extension.

Just put in your body height and optionally a specific pace
and you will get the optimal cadence for a natural movement of your legs
assumed they land underneath your body.

Usage:
  cadence bodyHeightInCm [paceMinKm]

Example:
  cadence 177
  cadence 177 4:00
`)
}

// Calculates the optimal running cadence for given speed and body height
func calcCadence(speedKmh float64, bodyHeightCm int) (int) {
  cadenceSpm := 
    math.Ceil(160 + (speedKmh - 6) * 2.5 - (float64(bodyHeightCm) - 170) / 2)
  return int(cadenceSpm)
}

func speedToPace(speedKmh float64) (string) {
  paceMinkm := 60 / speedKmh
  minutes := math.Floor(paceMinkm)
  seconds := math.Floor((paceMinkm - minutes) * 60)

  return fmt.Sprintf("%02d:%02d", int(minutes), int(seconds))
}

// Converts min/km to km/h
func paceToSpeed(pace *string) (float64, error) {
  var segments []string = strings.Split(*pace, ":")
  if len(segments) != 2 {
    return 0, fmt.Errorf("Cannot parse pace string: %s", *pace)
  }

  minutes, parseErr := strconv.Atoi(segments[0]);
  if parseErr != nil {
    return 0, 
      fmt.Errorf("Cannot parse minutes portion of pace string: %s", *pace)
  }

  seconds, parseErr := strconv.Atoi(segments[1]);
  if parseErr != nil {
    return 0,
      fmt.Errorf("Cannot parse seconds portion of pace string: %s", *pace)
  }

  return 60 / (float64(minutes) + float64(seconds) / 60), nil
}

func parseArguments() (int, string, error) {
  var bodyHeight int
  var pace string
  var parseErr error

  switch len(os.Args[1:]) {
    case 2:
      pace = os.Args[2]
      fallthrough
    case 1:
      bodyHeight, parseErr = strconv.Atoi(os.Args[1])
      if parseErr != nil {
        return 0, "", 
          fmt.Errorf("Could not parse body height argument: %s", os.Args[1])
      }
    default:
      return 0, "", fmt.Errorf("Wrong number of arguments")
  }

  return bodyHeight, pace, nil
}

func main() {
  onError := func(err error) {
    if err != nil {
      printHelp()
      fmt.Fprintf(os.Stderr, "\nError: %s\n", err)
      os.Exit(1)
    }
  }

  printResultline := func(speed float64, bodyHeight int) {
    fmt.Printf("%s %d\n", speedToPace(speed), calcCadence(speed, bodyHeight))
  }

  bodyHeight, pace, err := parseArguments()
  onError(err)	

  fmt.Printf("Pace (min/km) and cadence (spm) for %dcm body height\n", bodyHeight)

  if len(pace) > 0 {
    speed, err := paceToSpeed(&pace)
    onError(err)
    printResultline(speed, bodyHeight)
  } else {
    for speed := 7.0; speed <= 26.0; speed += 0.4 {
      printResultline(speed, bodyHeight)
    }
  }
}