// Copyright 2022 Google LLC
//
// 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.

package fn

import (
	"fmt"
	"io"
	"os"

	"sigs.k8s.io/kustomize/kyaml/errors"
	"sigs.k8s.io/kustomize/kyaml/kio"
)

// AsMain evaluates the ResourceList from STDIN to STDOUT.
// `input` can be
// - a `ResourceListProcessor` which implements `Process` method
// - a function `Runner` which implements `Run` method
func AsMain(input interface{}) error {
	err := func() error {
		var p ResourceListProcessor
		switch input := input.(type) {
		case runnerProcessor:
			p = input
		case ResourceListProcessorFunc:
			p = input
		default:
			return fmt.Errorf("unknown input type %T", input)
		}
		in, err := io.ReadAll(os.Stdin)
		if err != nil {
			return fmt.Errorf("unable to read from stdin: %v", err)
		}
		out, err := Run(p, in)
		// If there is an error, we don't return the error immediately.
		// We write out to stdout before returning any error.
		_, outErr := os.Stdout.Write(out)
		if outErr != nil {
			return outErr
		}
		return err
	}()
	if err != nil {
		Logf("failed to evaluate function: %v", err)
	}
	return err
}

// Run evaluates the function. input must be a resourceList in yaml format. An
// updated resourceList will be returned.
func Run(p ResourceListProcessor, input []byte) ([]byte, error) {
	switch input := p.(type) {
	case runnerProcessor:
		p = input
	case ResourceListProcessorFunc:
		p = input
	default:
		return nil, fmt.Errorf("unknown input type %T", input)
	}
	rl, err := ParseResourceList(input)
	if err != nil {
		return nil, err
	}
	success, fnErr := p.Process(rl)
	out, yamlErr := rl.ToYAML()
	if yamlErr != nil {
		return out, yamlErr
	}
	if fnErr != nil {
		return out, fnErr
	}
	if !success {
		return out, fmt.Errorf("error: function failure")
	}
	return out, nil
}

func Execute(p ResourceListProcessor, r io.Reader, w io.Writer) error {
	rw := &byteReadWriter{
		kio.ByteReadWriter{
			Reader: r,
			Writer: w,
			// We should not set the id annotation in the function, since we should not
			// overwrite what the orchestrator set.
			OmitReaderAnnotations: true,
			// We should not remove the id annotations in the function, since the
			// orchestrator (e.g. kpt) may need them.
			KeepReaderAnnotations: true,
		},
	}
	return execute(p, rw)
}

func execute(p ResourceListProcessor, rw *byteReadWriter) error {
	// Read the input
	rl, err := rw.Read()
	if err != nil {
		return errors.WrapPrefixf(err, "failed to read ResourceList input")
	}
	success, fnErr := p.Process(rl)
	// Write the output
	if err := rw.Write(rl); err != nil {
		return errors.WrapPrefixf(err, "failed to write ResourceList output")
	}
	if fnErr != nil {
		return fnErr
	}
	if !success {
		return fmt.Errorf("error: function failure")
	}
	return nil
}