package vaultik

import (
	"encoding/json"
	"errors"
	"fmt"
	"strings"

	"sneak.berlin/go/vaultik/internal/log"
)

// PruneOptions contains options for the prune command
type PruneOptions struct {
	Force bool
	JSON  bool
}

// errNukeRequiresForce guards the destructive remote nuke operation.
var errNukeRequiresForce = errors.New(
	"nuke requires --force (this deletes ALL remote snapshots and blobs)")

// metadataDirName is the top-level remote directory holding snapshot
// metadata.
const metadataDirName = "metadata"

// blobKeyParts is the "/"-separated segment count of a blob object key
// (blobs/<aa>/<bb>/<hash>).
const blobKeyParts = 4

// NukeRemote deletes every snapshot's metadata and every blob from remote
// storage, along with any object an upload cut off part-way left under a
// temporary `.partial` name. After this returns successfully the bucket
// prefix is empty and the next backup starts from scratch.
//
// Refuses to run unless force is true. The caller is responsible for
// confirming with the user.
func (v *Vaultik) NukeRemote(force bool) error {
	if !force {
		return errNukeRequiresForce
	}

	v.UI.Beginf("Removing all snapshot metadata from backup destination store.")

	_, err := v.RemoveAllSnapshots(&RemoveOptions{Force: true})
	if err != nil {
		return fmt.Errorf("removing all snapshots: %w", err)
	}

	v.UI.Beginf("Removing any blobs still present in backup destination store.")

	err = v.PruneBlobs(&PruneOptions{Force: true})
	if err != nil {
		return fmt.Errorf("pruning blobs: %w", err)
	}

	// The file and rclone listings skip `.partial` objects, so the two
	// steps above never delete them.
	for _, prefix := range []string{"metadata/", "blobs/"} {
		err = v.Storage.DeletePartialUploads(v.ctx, prefix)
		if err != nil {
			return fmt.Errorf("deleting partial uploads: %w", err)
		}
	}

	v.UI.Completef("Backup destination store is now empty.")

	return nil
}

// PruneBlobsResult contains the result of a blob prune operation
//
//nolint:tagliatelle // snake_case is the established JSON output format
type PruneBlobsResult struct {
	BlobsFound   int   `json:"blobs_found"`
	BlobsDeleted int   `json:"blobs_deleted"`
	BlobsFailed  int   `json:"blobs_failed,omitempty"`
	BytesFreed   int64 `json:"bytes_freed"`
}

// Prune removes orphaned data from the local index database AND
// unreferenced blobs from the backup destination store. This is the
// single user-facing prune entry point — the split between local and
// remote cleanup is an implementation detail. Calling code should
// prefer this method over PruneDatabase or PruneBlobs individually
// unless it specifically wants one half.
func (v *Vaultik) Prune(opts *PruneOptions) error {
	err := v.EnsureStorageBinding()
	if err != nil {
		return err
	}
	// First reconcile local snapshot records against remote metadata:
	// any local snapshot whose manifest is missing from the destination
	// store is treated as gone. This used to be the separate 'snapshot
	// cleanup' command and is now folded in so a single 'vaultik prune'
	// gets the local index fully back in sync with the destination.
	err = v.CleanupLocalSnapshots(opts)
	if err != nil {
		return fmt.Errorf("reconciling local snapshots with remote: %w", err)
	}

	_, err = v.PruneDatabase()
	if err != nil {
		return fmt.Errorf("pruning local database: %w", err)
	}

	return v.PruneBlobs(opts)
}

// PruneBlobs removes unreferenced blobs from storage
func (v *Vaultik) PruneBlobs(opts *PruneOptions) error {
	log.Info("Starting prune operation")

	allBlobsReferenced, err := v.collectReferencedBlobs()
	if err != nil {
		return err
	}

	allBlobs, err := v.listAllRemoteBlobs()
	if err != nil {
		return err
	}

	unreferencedBlobs, totalSize := v.findUnreferencedBlobs(allBlobs, allBlobsReferenced)

	result := &PruneBlobsResult{BlobsFound: len(unreferencedBlobs)}

	if len(unreferencedBlobs) == 0 {
		log.Info("No unreferenced blobs found")

		if opts.JSON {
			return v.outputPruneBlobsJSON(result)
		}

		v.printlnStdout("No unreferenced blobs to remove.")

		return nil
	}

	log.Info("Found unreferenced blobs",
		"count", len(unreferencedBlobs), "total_size", ubytes(totalSize))

	if !opts.JSON {
		v.stdoutf("Found %d unreferenced blob(s) totaling %s\n",
			len(unreferencedBlobs), ubytes(totalSize))
	}

	if !opts.Force && !opts.JSON {
		v.stdoutf("\nDelete %d unreferenced blob(s)? [y/N] ", len(unreferencedBlobs))

		var confirm string

		_, err = v.scanStdin(&confirm)
		if err != nil {
			v.printlnStdout("Cancelled")

			return nil //nolint:nilerr // read failure means no confirmation
		}

		if strings.ToLower(confirm) != "y" {
			v.printlnStdout("Cancelled")

			return nil
		}
	}

	v.deleteUnreferencedBlobs(unreferencedBlobs, allBlobs, result)

	if opts.JSON {
		return v.outputPruneBlobsJSON(result)
	}

	v.stdoutf("\nDeleted %d blob(s) totaling %s\n",
		result.BlobsDeleted, ubytes(result.BytesFreed))

	if result.BlobsFailed > 0 {
		v.stdoutf("Failed to delete %d blob(s)\n", result.BlobsFailed)
	}

	return nil
}

// collectReferencedBlobs downloads all manifests and returns the set of
// referenced blob hashes.
//
// Every manifest must be read successfully. A manifest that cannot be
// downloaded or decoded means its snapshot's blobs are unknown, so
// treating them as unreferenced would let prune delete data a snapshot
// still needs. Rather than risk that silent loss, any failure returns an
// error naming the remote key and prune deletes nothing.
func (v *Vaultik) collectReferencedBlobs() (map[string]bool, error) {
	log.Info("Listing remote snapshots")
	// IDs returned by listUniqueSnapshotIDs are remote keys (hashed
	// subdirectories under metadata/), not human snapshot IDs.
	remoteKeys, err := v.listUniqueSnapshotIDs()
	if err != nil {
		return nil, fmt.Errorf("listing snapshot keys: %w", err)
	}

	log.Info("Found manifests in remote storage", "count", len(remoteKeys))

	allBlobsReferenced := make(map[string]bool)

	for _, remoteKey := range remoteKeys {
		log.Debug("Processing manifest", "remote_key", remoteKey)

		manifest, err := v.downloadManifestByKey(remoteKey)
		if err != nil {
			return nil, fmt.Errorf("reading manifest %s: %w", remoteKey, err)
		}

		for _, blob := range manifest.Blobs {
			allBlobsReferenced[blob.Hash] = true
		}
	}

	log.Info("Processed manifests",
		"count", len(remoteKeys), "unique_blobs_referenced", len(allBlobsReferenced))

	return allBlobsReferenced, nil
}

// listUniqueSnapshotIDs returns deduplicated snapshot IDs from remote metadata
func (v *Vaultik) listUniqueSnapshotIDs() ([]string, error) {
	objectCh := v.Storage.ListStream(v.ctx, "metadata/")
	seen := make(map[string]bool)

	var snapshotIDs []string

	for object := range objectCh {
		if object.Err != nil {
			return nil, fmt.Errorf("listing metadata objects: %w", object.Err)
		}

		parts := strings.Split(object.Key, "/")
		if len(parts) >= minSnapshotIDParts &&
			parts[0] == metadataDirName && parts[1] != "" {
			if strings.HasSuffix(object.Key, "/") ||
				strings.Contains(object.Key, "/manifest.json.zst") {
				snapshotID := parts[1]
				if !seen[snapshotID] {
					seen[snapshotID] = true
					snapshotIDs = append(snapshotIDs, snapshotID)
				}
			}
		}
	}

	return snapshotIDs, nil
}

// listAllRemoteBlobs returns a map of all blob hashes to their sizes in remote storage
func (v *Vaultik) listAllRemoteBlobs() (map[string]int64, error) {
	log.Info("Listing all blobs in storage")

	allBlobs := make(map[string]int64)
	blobObjectCh := v.Storage.ListStream(v.ctx, "blobs/")

	for object := range blobObjectCh {
		if object.Err != nil {
			return nil, fmt.Errorf("listing blobs: %w", object.Err)
		}

		parts := strings.Split(object.Key, "/")
		if len(parts) != blobKeyParts || parts[0] != "blobs" {
			continue
		}

		// The object name is read from the destination store and is not
		// trusted. A name that is not a blob hash (e.g. a short or
		// non-hex string) would panic the later hash[:2]/hash[2:4] path
		// build, so skip it with a warning rather than delete it.
		if !isBlobHash(parts[3]) {
			log.Warn("Skipping non-conforming object under blobs/",
				"key", object.Key)

			continue
		}

		allBlobs[parts[3]] = object.Size
	}

	log.Info("Found blobs in storage", "count", len(allBlobs))

	return allBlobs, nil
}

// findUnreferencedBlobs returns blob hashes not referenced by any
// manifest and their total size.
func (v *Vaultik) findUnreferencedBlobs(
	allBlobs map[string]int64, referenced map[string]bool,
) ([]string, int64) {
	var (
		unreferenced []string
		totalSize    int64
	)

	for hash, size := range allBlobs {
		if !referenced[hash] {
			unreferenced = append(unreferenced, hash)
			totalSize += size
		}
	}

	return unreferenced, totalSize
}

// deleteUnreferencedBlobs deletes the given blobs from storage and
// populates the result.
func (v *Vaultik) deleteUnreferencedBlobs(
	unreferencedBlobs []string, allBlobs map[string]int64, result *PruneBlobsResult,
) {
	log.Info("Deleting unreferenced blobs")

	for i, hash := range unreferencedBlobs {
		blobPath := fmt.Sprintf("blobs/%s/%s/%s", hash[:2], hash[2:4], hash)

		err := v.Storage.Delete(v.ctx, blobPath)
		if err != nil {
			log.Error("Failed to delete blob", "hash", hash, "error", err)

			continue
		}

		result.BlobsDeleted++
		result.BytesFreed += allBlobs[hash]

		if (i+1)%progressLogEvery == 0 || i == len(unreferencedBlobs)-1 {
			log.Info("Deletion progress",
				"deleted", i+1,
				"total", len(unreferencedBlobs),
				"percent", fmt.Sprintf("%.1f%%",
					float64(i+1)/float64(len(unreferencedBlobs))*percentScale),
			)
		}
	}

	result.BlobsFailed = len(unreferencedBlobs) - result.BlobsDeleted

	log.Info("Prune complete",
		"deleted_count", result.BlobsDeleted,
		"deleted_size", ubytes(result.BytesFreed),
		"failed", result.BlobsFailed,
	)
}

// outputPruneBlobsJSON outputs the prune result as JSON
func (v *Vaultik) outputPruneBlobsJSON(result *PruneBlobsResult) error {
	encoder := json.NewEncoder(v.Stdout)
	encoder.SetIndent("", "  ")

	return encoder.Encode(result)
}