/*
   Copyright 2020 Docker Compose CLI authors

   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 remote

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/compose-spec/compose-go/v2/loader"
	"github.com/distribution/reference"
	"github.com/docker/buildx/store/storeutil"
	"github.com/docker/buildx/util/imagetools"
	"github.com/docker/cli/cli/command"
	v1 "github.com/opencontainers/image-spec/specs-go/v1"
)

const OCI_REMOTE_ENABLED = "COMPOSE_EXPERIMENTAL_OCI_REMOTE"

func ociRemoteLoaderEnabled() (bool, error) {
	if v := os.Getenv(OCI_REMOTE_ENABLED); v != "" {
		enabled, err := strconv.ParseBool(v)
		if err != nil {
			return false, fmt.Errorf("COMPOSE_EXPERIMENTAL_OCI_REMOTE environment variable expects boolean value: %w", err)
		}
		return enabled, err
	}
	return false, nil
}

func NewOCIRemoteLoader(dockerCli command.Cli, offline bool) loader.ResourceLoader {
	return ociRemoteLoader{
		dockerCli: dockerCli,
		offline:   offline,
		known:     map[string]string{},
	}
}

type ociRemoteLoader struct {
	dockerCli command.Cli
	offline   bool
	known     map[string]string
}

const prefix = "oci://"

func (g ociRemoteLoader) Accept(path string) bool {
	return strings.HasPrefix(path, prefix)
}

func (g ociRemoteLoader) Load(ctx context.Context, path string) (string, error) {
	enabled, err := ociRemoteLoaderEnabled()
	if err != nil {
		return "", err
	}
	if !enabled {
		return "", fmt.Errorf("experimental OCI remote resource is disabled. %q must be set", OCI_REMOTE_ENABLED)
	}

	if g.offline {
		return "", nil
	}

	local, ok := g.known[path]
	if !ok {
		ref, err := reference.ParseDockerRef(path[len(prefix):])
		if err != nil {
			return "", err
		}

		opt, err := storeutil.GetImageConfig(g.dockerCli, nil)
		if err != nil {
			return "", err
		}
		resolver := imagetools.New(opt)

		content, descriptor, err := resolver.Get(ctx, ref.String())
		if err != nil {
			return "", err
		}

		cache, err := cacheDir()
		if err != nil {
			return "", fmt.Errorf("initializing remote resource cache: %w", err)
		}

		local = filepath.Join(cache, descriptor.Digest.Hex())
		composeFile := filepath.Join(local, "compose.yaml")
		if _, err = os.Stat(local); os.IsNotExist(err) {
			var manifest v1.Manifest
			err = json.Unmarshal(content, &manifest)
			if err != nil {
				return "", err
			}

			err2 := g.pullComposeFiles(ctx, local, composeFile, manifest, ref, resolver)
			if err2 != nil {
				return "", err2
			}
		}
		g.known[path] = local
	}

	return filepath.Join(local, "compose.yaml"), nil
}

func (g ociRemoteLoader) Dir(path string) string {
	return g.known[path]
}

func (g ociRemoteLoader) pullComposeFiles(ctx context.Context, local string, composeFile string, manifest v1.Manifest, ref reference.Named, resolver *imagetools.Resolver) error {
	err := os.MkdirAll(local, 0o700)
	if err != nil {
		return err
	}

	f, err := os.Create(composeFile)
	if err != nil {
		return err
	}
	defer f.Close() //nolint:errcheck

	if manifest.ArtifactType != "application/vnd.docker.compose.project" {
		return fmt.Errorf("%s is not a compose project OCI artifact, but %s", ref.String(), manifest.ArtifactType)
	}

	for i, layer := range manifest.Layers {
		digested, err := reference.WithDigest(ref, layer.Digest)
		if err != nil {
			return err
		}
		content, _, err := resolver.Get(ctx, digested.String())
		if err != nil {
			return err
		}
		if i > 0 {
			_, err = f.Write([]byte("\n---\n"))
			if err != nil {
				return err
			}
		}
		_, err = f.Write(content)
		if err != nil {
			return err
		}
	}
	return nil
}

var _ loader.ResourceLoader = ociRemoteLoader{}
