go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/common/flag/choice.go (about)

     1  // Copyright 2019 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package flag
    16  
    17  import (
    18  	"strings"
    19  
    20  	"go.chromium.org/luci/common/errors"
    21  )
    22  
    23  // Choice is an implementation of flag.Value for parsing a
    24  // multiple-choice string.
    25  type Choice struct {
    26  	choices []string
    27  	output  *string
    28  }
    29  
    30  // NewChoice creates a Choice value
    31  func NewChoice(output *string, choices ...string) Choice {
    32  	return Choice{choices: choices, output: output}
    33  }
    34  
    35  // String implements the flag.Value interface.
    36  func (f Choice) String() string {
    37  	if f.output == nil {
    38  		return ""
    39  	}
    40  	return *f.output
    41  }
    42  
    43  // Set implements the flag.Value interface.
    44  func (f Choice) Set(s string) error {
    45  	if f.output == nil {
    46  		return errors.Reason("Choice pointer is nil").Err()
    47  	}
    48  	for _, choice := range f.choices {
    49  		if s == choice {
    50  			*f.output = s
    51  			return nil
    52  		}
    53  	}
    54  	valid := strings.Join(f.choices, ", ")
    55  	return errors.Reason("%s is not a valid choice; please select one of: %s", s, valid).Err()
    56  }