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// SPDX-FileCopyrightText: © 2022 Grégoire Duchêne <gduchene@awhk.org>
// SPDX-License-Identifier: ISC
package core
import (
"flag"
"fmt"
"os"
"strings"
"time"
)
// Flag works like other flag.FlagSet methods, except it is generic. The
// passed ParseFunc will be used to parse raw arguments into a useful T
// value. A valid *T is returned for use by the caller.
func Flag[T any](fs *flag.FlagSet, name string, value T, usage string, parse ParseFunc[T]) *T {
p := new(T)
FlagVar(fs, p, name, value, usage, parse)
return p
}
// FlagVar works like FlagT, except it is up to the caller to supply a
// valid *T.
func FlagVar[T any](fs *flag.FlagSet, p *T, name string, value T, usage string, parse ParseFunc[T]) {
*p = value
fs.Var(&flagValue[T]{Parse: parse, Value: p}, name, usage)
}
// FlagSlice works like FlagT, except slices are created; flags created
// that way can therefore be repeated. A valid *[]T is returned for use
// by the caller.
//
// A separator can also be passed so that multiple values may be passed
// as a single argument. An empty string disables that behavior. Note
// that having a separator still allows for repeated flags, so the
// following, with a ‘,’ separator, are equivalent:
//
// - -flag=val -flag=val-2 -flag=val-3
// - -flag=val,val-2 -flag=val-3
// - -flag=val,val-2,val-3
func FlagSlice[T any](fs *flag.FlagSet, name string, values []T, usage string, parse ParseFunc[T], sep string) *[]T {
p := new([]T)
FlagSliceVar(fs, p, name, values, usage, parse, sep)
return p
}
// FlagSliceVar works like FlagTSlice, except it is up to the caller to
// supply a valid *[]T.
func FlagSliceVar[T any](fs *flag.FlagSet, p *[]T, name string, values []T, usage string, parse ParseFunc[T], sep string) {
if values != nil {
*p = make([]T, len(values))
copy(*p, values)
}
fs.Var(&flagValueSlice[T]{Parse: parse, Separator: sep, Values: p}, name, usage)
}
// InitFlagSet initializes a flag.FlagSet by setting flags in the
// following order: environment variables, then an arbitrary map, then
// command line arguments.
//
// Note that InitFlagSet does not require the use of any of the Flag
// functions defined in this package. Standard flags will work just as
// well.
func InitFlagSet(fs *flag.FlagSet, env []string, cfg map[string]string, args []string) (err error) {
var environ map[string]string
if env != nil {
environ = make(map[string]string, len(env))
for _, kv := range env {
if buf := strings.SplitN(kv, "=", 2); len(buf) == 2 {
environ[buf[0]] = buf[1]
continue
}
if val, ok := os.LookupEnv(kv); ok {
environ[kv] = val
}
}
}
fs.VisitAll(func(f *flag.Flag) {
if err != nil {
return
}
if f.DefValue != f.Value.String() {
if _, ok := f.Value.(interface{ MutableFlag() }); !ok {
return
}
}
var next string
if val, found := environ[strings.ToUpper(strings.ReplaceAll(f.Name, "-", "_"))]; found {
next = val
}
if val, found := cfg[f.Name]; found {
next = val
}
if next != "" {
err = f.Value.Set(next)
}
if f, ok := f.Value.(interface{ resetShouldAppend() }); ok {
f.resetShouldAppend()
}
})
if err == nil && !fs.Parsed() {
return fs.Parse(args)
}
return err
}
// ParseTime parses a string according to the time.RFC3339 format.
func ParseTime(s string) (time.Time, error) {
return time.Parse(time.RFC3339, s)
}
// ParseFunc describes functions that will parse a string and return a
// value or an error.
type ParseFunc[T any] func(string) (T, error)
type flagValue[T any] struct {
Parse ParseFunc[T]
Value *T
}
func (f *flagValue[T]) Set(s string) error {
val, err := f.Parse(s)
if err != nil {
return err
}
*f.Value = val
return nil
}
func (f *flagValue[T]) String() string {
if f.Value == nil {
var zero T
return fmt.Sprintf("%v", zero)
}
return fmt.Sprintf("%v", *f.Value)
}
type flagValueSlice[T any] struct {
Parse ParseFunc[T]
Separator string
Values *[]T
shouldAppend bool
}
func (f *flagValueSlice[T]) Set(s string) error {
vals := []string{s}
if f.Separator != "" {
vals = strings.Split(s, f.Separator)
}
for _, val := range vals {
parsed, err := f.Parse(val)
if err != nil {
return err
}
if f.shouldAppend {
*f.Values = append(*f.Values, parsed)
} else {
*f.Values = []T{parsed}
f.shouldAppend = true
}
}
return nil
}
func (f *flagValueSlice[T]) String() string {
if f.Values == nil {
var zero []T
return fmt.Sprintf("%v", zero)
}
return fmt.Sprintf("%v", *f.Values)
}
func (f *flagValueSlice[T]) resetShouldAppend() { f.shouldAppend = false }
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