package updater

import (
	"context"
	"errors"
	"fmt"

	"github.com/docker/docker/api/types/registry"

	"github.com/shcizo/package-updater/internal/imageref"
)

// DistributionClient is the subset of the Docker SDK the Resolver needs.
// *client.Client satisfies it.
type DistributionClient interface {
	DistributionInspect(ctx context.Context, imageRef, encodedRegistryAuth string) (registry.DistributionInspect, error)
}

// Resolver turns "repo:tag" into "repo:tag@digest" by asking the local
// daemon, which contacts the registry.
type Resolver struct {
	cli  DistributionClient
	auth *RegistryAuth
}

// NewResolver returns a Resolver. auth may be nil (anonymous access).
func NewResolver(cli DistributionClient, auth *RegistryAuth) *Resolver {
	return &Resolver{cli: cli, auth: auth}
}

// Resolve returns ref pinned to the digest its tag currently points at. It
// fails for a ref without a tag or with a digest already.
func (r *Resolver) Resolve(ctx context.Context, ref string) (string, error) {
	p := imageref.Parse(ref)
	switch {
	case p.Digest != "":
		return "", fmt.Errorf("image %q already has a digest", ref)
	case p.Tag == "":
		return "", fmt.Errorf("image %q has no tag to resolve", ref)
	}
	info, err := r.cli.DistributionInspect(ctx, ref, r.auth.For(p.Repo))
	if err != nil {
		return "", fmt.Errorf("resolve %s: %w", ref, err)
	}
	if info.Descriptor.Digest == "" {
		return "", errors.New("resolve " + ref + ": registry returned no digest")
	}
	return ref + "@" + info.Descriptor.Digest.String(), nil
}