108 lines
2.7 KiB
Go
108 lines
2.7 KiB
Go
package flags
|
|
|
|
import (
|
|
"fmt"
|
|
"log"
|
|
"os"
|
|
"reflect"
|
|
"strings"
|
|
"text/tabwriter"
|
|
)
|
|
|
|
type Arg struct {
|
|
Val string
|
|
Help string
|
|
}
|
|
|
|
// type constraint
|
|
type Val interface {
|
|
string | bool
|
|
}
|
|
|
|
// with generic Val field, instantiate like Flag[string]
|
|
// NOTE: struct inheritance would be easier, but Flag[bool] is much cooler than FlagBool.
|
|
// and actually more readable for the initOpts function, which serves as documentation.
|
|
// so the complexity seems to be all paid up front here in this pkg.
|
|
type Flag[T Val] struct {
|
|
Long string
|
|
Short string
|
|
Val T
|
|
Help string
|
|
}
|
|
|
|
// generic Flag validity check
|
|
// NOTE: you cannot define a method on an instantiated type, only the generic
|
|
// https://www.reddit.com/r/golang/comments/1n6xasx/comment/nc3dbhd/
|
|
func (f Flag[Val]) IsSet() bool {
|
|
// must do this weird dance: convert to empty interface, then cast:
|
|
switch any(f.Val).(type) {
|
|
case string:
|
|
return any(f.Val).(string) != ""
|
|
case bool:
|
|
return any(f.Val).(bool)
|
|
default:
|
|
return false
|
|
}
|
|
}
|
|
|
|
func (f Arg) IsSet() bool {
|
|
return f.Val != ""
|
|
}
|
|
|
|
func HasDashPrefix(s string) bool {
|
|
return strings.HasPrefix(s, "-")
|
|
}
|
|
|
|
// check for non-dashed value ahead in the args slice
|
|
func missingValue(args []string, i int) bool {
|
|
return i+1 == len(args) || HasDashPrefix(args[i+1])
|
|
}
|
|
|
|
// if no value ahead in the args, print error and exit
|
|
func validValueOrExit(args []string, i int) {
|
|
if missingValue(args, i) {
|
|
log.Printf("um: %s needs a value assignment\n", args[i])
|
|
log.Fatal("try: um [cmd] --help")
|
|
}
|
|
}
|
|
|
|
// 1. validate a Flag[string] by looking ahead in args, if missing, os.Exit(1)
|
|
// 2. increment the i to skip that value and return
|
|
// 3. fetch that value and return
|
|
func ValidateIncrementFetchOrExit(args []string, i int) (int, string) {
|
|
validValueOrExit(args, i)
|
|
return i + 1, args[i+1]
|
|
}
|
|
|
|
// print out help string by reflecting over fields of provided opts struct
|
|
// and os.Exit(0)
|
|
func Help(subcmd string, opts any) {
|
|
v := reflect.ValueOf(opts)
|
|
t := v.Type()
|
|
|
|
w := tabwriter.NewWriter(os.Stdout, 0, 0, 3, ' ', 0)
|
|
positional := ""
|
|
|
|
for i := 0; i < v.NumField(); i++ {
|
|
field := t.Field(i)
|
|
value := v.Field(i)
|
|
switch value.Interface().(type) {
|
|
case Arg:
|
|
positional += fmt.Sprintf(" [%s]", strings.ToLower(field.Name))
|
|
fmt.Fprintf(w, "[%v]\tstring\t%v\n", strings.ToLower(field.Name), value.FieldByName("Help"))
|
|
case Flag[string], Flag[bool]:
|
|
if field.Name != "Help" {
|
|
positional += fmt.Sprintf(" [%s]", value.FieldByName("Long"))
|
|
}
|
|
fmt.Fprintf(w, "%v | %v\t%v\t%v\n",
|
|
value.FieldByName("Long"),
|
|
value.FieldByName("Short"),
|
|
value.FieldByName("Val").Type(),
|
|
value.FieldByName("Help"),
|
|
)
|
|
}
|
|
}
|
|
log.Printf("um %s%s\n", subcmd, positional)
|
|
w.Flush()
|
|
os.Exit(0)
|
|
}
|