package copy

import (
	"context"
	"errors"
	"fmt"
	"strings"

	"github.com/containers/image/v5/manifest"
	"github.com/containers/image/v5/types"
	"github.com/sirupsen/logrus"
)

// preferredManifestMIMETypes lists manifest MIME types in order of our preference, if we can't use the original manifest and need to convert.
// Prefer v2s2 to v2s1 because v2s2 does not need to be changed when uploading to a different location.
// Include v2s1 signed but not v2s1 unsigned, because docker/distribution requires a signature even if the unsigned MIME type is used.
var preferredManifestMIMETypes = []string{manifest.DockerV2Schema2MediaType, manifest.DockerV2Schema1SignedMediaType}

// orderedSet is a list of strings (MIME types or platform descriptors in our case), with each string appearing at most once.
type orderedSet struct {
	list     []string
	included map[string]struct{}
}

// newOrderedSet creates a correctly initialized orderedSet.
// [Sometimes it would be really nice if Golang had constructors…]
func newOrderedSet() *orderedSet {
	return &orderedSet{
		list:     []string{},
		included: map[string]struct{}{},
	}
}

// append adds s to the end of os, only if it is not included already.
func (os *orderedSet) append(s string) {
	if _, ok := os.included[s]; !ok {
		os.list = append(os.list, s)
		os.included[s] = struct{}{}
	}
}

// determineManifestConversionInputs contains the inputs for determineManifestConversion.
type determineManifestConversionInputs struct {
	srcMIMEType string // MIME type of the input manifest

	destSupportedManifestMIMETypes []string // MIME types supported by the destination, per types.ImageDestination.SupportedManifestMIMETypes()

	forceManifestMIMEType      string // User’s choice of forced manifest MIME type
	requiresOCIEncryption      bool   // Restrict to manifest formats that can support OCI encryption
	cannotModifyManifestReason string // The reason the manifest cannot be modified, or an empty string if it can
}

// manifestConversionPlan contains the decisions made by determineManifestConversion.
type manifestConversionPlan struct {
	// The preferred manifest MIME type (whether we are converting to it or using it unmodified).
	// We compute this only to show it in error messages; without having to add this context
	// in an error message, we would be happy enough to know only that no conversion is needed.
	preferredMIMEType                string
	preferredMIMETypeNeedsConversion bool     // True if using preferredMIMEType requires a conversion step.
	otherMIMETypeCandidates          []string // Other possible alternatives, in order
}

// determineManifestConversion returns a plan for what formats, and possibly conversions, to use based on in.
func determineManifestConversion(in determineManifestConversionInputs) (manifestConversionPlan, error) {
	srcType := in.srcMIMEType
	normalizedSrcType := manifest.NormalizedMIMEType(srcType)
	if srcType != normalizedSrcType {
		logrus.Debugf("Source manifest MIME type %s, treating it as %s", srcType, normalizedSrcType)
		srcType = normalizedSrcType
	}

	destSupportedManifestMIMETypes := in.destSupportedManifestMIMETypes
	if in.forceManifestMIMEType != "" {
		destSupportedManifestMIMETypes = []string{in.forceManifestMIMEType}
	}

	if len(destSupportedManifestMIMETypes) == 0 && (!in.requiresOCIEncryption || manifest.MIMETypeSupportsEncryption(srcType)) {
		return manifestConversionPlan{ // Anything goes; just use the original as is, do not try any conversions.
			preferredMIMEType:       srcType,
			otherMIMETypeCandidates: []string{},
		}, nil
	}
	supportedByDest := map[string]struct{}{}
	for _, t := range destSupportedManifestMIMETypes {
		if !in.requiresOCIEncryption || manifest.MIMETypeSupportsEncryption(t) {
			supportedByDest[t] = struct{}{}
		}
	}

	// destSupportedManifestMIMETypes is a static guess; a particular registry may still only support a subset of the types.
	// So, build a list of types to try in order of decreasing preference.
	// FIXME? This treats manifest.DockerV2Schema1SignedMediaType and manifest.DockerV2Schema1MediaType as distinct,
	// although we are not really making any conversion, and it is very unlikely that a destination would support one but not the other.
	// In practice, schema1 is probably the lowest common denominator, so we would expect to try the first one of the MIME types
	// and never attempt the other one.
	prioritizedTypes := newOrderedSet()

	// First of all, prefer to keep the original manifest unmodified.
	if _, ok := supportedByDest[srcType]; ok {
		prioritizedTypes.append(srcType)
	}
	if in.cannotModifyManifestReason != "" {
		// We could also drop this check and have the caller
		// make the choice; it is already doing that to an extent, to improve error
		// messages.  But it is nice to hide the “if we can't modify, do no conversion”
		// special case in here; the caller can then worry (or not) only about a good UI.
		logrus.Debugf("We can't modify the manifest, hoping for the best...")
		return manifestConversionPlan{ // Take our chances - FIXME? Or should we fail without trying?
			preferredMIMEType:       srcType,
			otherMIMETypeCandidates: []string{},
		}, nil
	}

	// Then use our list of preferred types.
	for _, t := range preferredManifestMIMETypes {
		if _, ok := supportedByDest[t]; ok {
			prioritizedTypes.append(t)
		}
	}

	// Finally, try anything else the destination supports.
	for _, t := range destSupportedManifestMIMETypes {
		prioritizedTypes.append(t)
	}

	logrus.Debugf("Manifest has MIME type %s, ordered candidate list [%s]", srcType, strings.Join(prioritizedTypes.list, ", "))
	if len(prioritizedTypes.list) == 0 { // Coverage: destSupportedManifestMIMETypes is not empty (or we would have exited in the “Anything goes” case above), so this should never happen.
		return manifestConversionPlan{}, errors.New("Internal error: no candidate MIME types")
	}
	res := manifestConversionPlan{
		preferredMIMEType:       prioritizedTypes.list[0],
		otherMIMETypeCandidates: prioritizedTypes.list[1:],
	}
	res.preferredMIMETypeNeedsConversion = res.preferredMIMEType != srcType
	if !res.preferredMIMETypeNeedsConversion {
		logrus.Debugf("... will first try using the original manifest unmodified")
	}
	return res, nil
}

// isMultiImage returns true if img is a list of images
func isMultiImage(ctx context.Context, img types.UnparsedImage) (bool, error) {
	_, mt, err := img.Manifest(ctx)
	if err != nil {
		return false, err
	}
	return manifest.MIMETypeIsMultiImage(mt), nil
}

// determineListConversion takes the current MIME type of a list of manifests,
// the list of MIME types supported for a given destination, and a possible
// forced value, and returns the MIME type to which we should convert the list
// of manifests (regardless of whether we are converting to it or using it
// unmodified) and a slice of other list types which might be supported by the
// destination.
func (c *copier) determineListConversion(currentListMIMEType string, destSupportedMIMETypes []string, forcedListMIMEType string) (string, []string, error) {
	// If there's no list of supported types, then anything we support is expected to be supported.
	if len(destSupportedMIMETypes) == 0 {
		destSupportedMIMETypes = manifest.SupportedListMIMETypes
	}
	// If we're forcing it, replace the list of supported types with the forced value.
	if forcedListMIMEType != "" {
		destSupportedMIMETypes = []string{forcedListMIMEType}
	}

	prioritizedTypes := newOrderedSet()
	// The first priority is the current type, if it's in the list, since that lets us avoid a
	// conversion that isn't strictly necessary.
	for _, t := range destSupportedMIMETypes {
		if t == currentListMIMEType {
			prioritizedTypes.append(currentListMIMEType)
			break
		}
	}
	// Pick out the other list types that we support.
	for _, t := range destSupportedMIMETypes {
		if manifest.MIMETypeIsMultiImage(t) {
			prioritizedTypes.append(t)
		}
	}

	logrus.Debugf("Manifest list has MIME type %s, ordered candidate list [%s]", currentListMIMEType, strings.Join(destSupportedMIMETypes, ", "))
	if len(prioritizedTypes.list) == 0 {
		return "", nil, fmt.Errorf("destination does not support any supported manifest list types (%v)", manifest.SupportedListMIMETypes)
	}
	selectedType := prioritizedTypes.list[0]
	otherSupportedTypes := prioritizedTypes.list[1:]
	if selectedType != currentListMIMEType {
		logrus.Debugf("... will convert to %s first, and then try %v", selectedType, otherSupportedTypes)
	} else {
		logrus.Debugf("... will use the original manifest list type, and then try %v", otherSupportedTypes)
	}
	// Done.
	return selectedType, otherSupportedTypes, nil
}
