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coinflip.go
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coinflip.go
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// Copyright 2022 Markus Holmström (MawKKe) [email protected]
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// coinflip: CLI program that simulates a coin flip
package main
import (
"crypto/rand"
"fmt"
"math/big"
"os"
)
// genRandomBit generates random integer with value 0 or 1.
func genRandomUpto(lim int) (int, error) {
// Our fate shall be decided by true randomness,
// not some silly pseudo-random number generator.
i, err := rand.Int(rand.Reader, big.NewInt(int64(lim)))
if err != nil {
return 0, err
}
return int(i.Int64()), nil
}
func choose(choices []string, gen func(int) (int, error)) (string, error) {
if len(choices) < 2 {
return "", fmt.Errorf("expected at least 2 arguments to choose(), got %d", len(choices))
}
i, err := gen(len(choices))
if err != nil {
return "", fmt.Errorf("problem generating random number: %w", err)
}
return choices[i], nil
}
func pickRandomly(choices []string) (string, error) {
return choose(choices, genRandomUpto)
}
func printUsage(ec int) {
fmt.Printf("Usage: %v coinflip|yesno|choose\n", os.Args[0])
os.Exit(ec)
}
func main() {
if len(os.Args) < 2 {
fmt.Printf("error: not enough arguments\n\n")
printUsage(1)
}
cmd, args := os.Args[1], os.Args[2:]
if cmd == "help" {
printUsage(0)
}
res, err := func(cmd string, extraArgs []string) (string, error) {
switch cmd {
case "coinflip":
return pickRandomly([]string{"tails", "heads"})
case "yesno":
return pickRandomly([]string{"no", "yes"})
case "choose":
return pickRandomly(extraArgs)
default:
return "", fmt.Errorf("unknown subcommand '%v'", cmd)
}
}(cmd, args)
if err != nil {
fmt.Printf("error: %v\n", err)
os.Exit(1)
}
fmt.Println(res)
}