crossplane

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/*
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Copyright 2023 The Crossplane Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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    http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package upbound
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import (
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	"encoding/json"
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	"io"
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	"strings"
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	"github.com/alecthomas/kong"
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)
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// JSON returns a Resolver that retrieves values from a JSON source.
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// Based slightly off of https://github.com/alecthomas/kong/blob/f48da244f54370c0cb63e22b0e500e5459a491bf/resolver.go#L33-L60
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// Hyphens in flag names are replaced with underscores.
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func JSON(base, overlay io.Reader) (kong.Resolver, error) {
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	baseValues := map[string]interface{}{}
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	overlayValues := map[string]interface{}{}
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	err := json.NewDecoder(base).Decode(&baseValues)
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	if err != nil {
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		return nil, err
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	}
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	err = json.NewDecoder(overlay).Decode(&overlayValues)
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	if err != nil {
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		return nil, err
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	}
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	var f kong.ResolverFunc = func(_ *kong.Context, _ *kong.Path, flag *kong.Flag) (interface{}, error) {
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		name := strings.ReplaceAll(flag.Name, "-", "_")
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		bRaw, bOk := resolveValue(name, flag.Envs, baseValues)
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		oRaw, oOk := resolveValue(name, flag.Envs, overlayValues)
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		// if found in base and in overlay AND is not the defaultValue for overlay
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		if bOk && oOk && flag.Default != oRaw {
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			return oRaw, nil
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		}
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		if bOk {
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			return bRaw, nil
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		}
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		if oOk {
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			return oRaw, nil
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		}
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		return nil, nil
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	}
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	return f, nil
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}
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func resolveValue(fieldName string, envVarsName []string, vals map[string]interface{}) (interface{}, bool) {
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	// attempt to lookup by field name first
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	raw, ok := vals[fieldName]
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	if !ok {
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		// fall back to env var name
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		for _, envVarName := range envVarsName {
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			raw, ok = vals[envVarName]
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			if ok {
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				break
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			}
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		}
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		if !ok {
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			return nil, false
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		}
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	}
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	return raw, true
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}
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