package vaultik

import (
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"fmt"
	"io"
	"os"
	"time"

	"git.eeqj.de/sneak/vaultik/internal/log"
	"git.eeqj.de/sneak/vaultik/internal/snapshot"
	"github.com/dustin/go-humanize"
	"github.com/klauspost/compress/zstd"
	_ "github.com/mattn/go-sqlite3"
)

// VerifyOptions contains options for the verify command
type VerifyOptions struct {
	Deep bool
	JSON bool
}

// VerifyResult contains the result of a snapshot verification
type VerifyResult struct {
	SnapshotID   string `json:"snapshot_id"`
	Status       string `json:"status"` // "ok" or "failed"
	Mode         string `json:"mode"`   // "shallow" or "deep"
	BlobCount    int    `json:"blob_count"`
	TotalSize    int64  `json:"total_size"`
	Verified     int    `json:"verified"`
	Missing      int    `json:"missing"`
	MissingSize  int64  `json:"missing_size,omitempty"`
	ErrorMessage string `json:"error,omitempty"`
}

// RunDeepVerify executes deep verification operation
func (v *Vaultik) RunDeepVerify(snapshotID string, opts *VerifyOptions) error {
	result := &VerifyResult{
		SnapshotID: snapshotID,
		Mode:       "deep",
	}

	// Check for decryption capability
	if !v.CanDecrypt() {
		result.Status = "failed"
		result.ErrorMessage = "VAULTIK_AGE_SECRET_KEY environment variable not set - required for deep verification"
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return fmt.Errorf("VAULTIK_AGE_SECRET_KEY environment variable not set - required for deep verification")
	}

	log.Info("Starting snapshot verification",
		"snapshot_id", snapshotID,
		"mode", "deep",
	)

	if !opts.JSON {
		v.printfStdout("Deep verification of snapshot: %s\n\n", snapshotID)
	}

	// Step 1: Download manifest
	manifestPath := fmt.Sprintf("metadata/%s/manifest.json.zst", snapshotID)
	log.Info("Downloading manifest", "path", manifestPath)
	if !opts.JSON {
		v.printfStdout("Downloading manifest...\n")
	}

	manifestReader, err := v.Storage.Get(v.ctx, manifestPath)
	if err != nil {
		result.Status = "failed"
		result.ErrorMessage = fmt.Sprintf("failed to download manifest: %v", err)
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return fmt.Errorf("failed to download manifest: %w", err)
	}
	defer func() { _ = manifestReader.Close() }()

	// Decompress manifest
	manifest, err := snapshot.DecodeManifest(manifestReader)
	if err != nil {
		result.Status = "failed"
		result.ErrorMessage = fmt.Sprintf("failed to decode manifest: %v", err)
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return fmt.Errorf("failed to decode manifest: %w", err)
	}

	log.Info("Manifest loaded",
		"manifest_blob_count", manifest.BlobCount,
		"manifest_total_size", humanize.Bytes(uint64(manifest.TotalCompressedSize)),
	)
	if !opts.JSON {
		v.printfStdout("Manifest loaded: %d blobs (%s)\n", manifest.BlobCount, humanize.Bytes(uint64(manifest.TotalCompressedSize)))
	}

	// Step 2: Download and decrypt database (authoritative source)
	dbPath := fmt.Sprintf("metadata/%s/db.zst.age", snapshotID)
	log.Info("Downloading encrypted database", "path", dbPath)
	if !opts.JSON {
		v.printfStdout("Downloading and decrypting database...\n")
	}

	dbReader, err := v.Storage.Get(v.ctx, dbPath)
	if err != nil {
		result.Status = "failed"
		result.ErrorMessage = fmt.Sprintf("failed to download database: %v", err)
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return fmt.Errorf("failed to download database: %w", err)
	}
	defer func() { _ = dbReader.Close() }()

	// Decrypt and decompress database
	tempDB, err := v.decryptAndLoadDatabase(dbReader, v.Config.AgeSecretKey)
	if err != nil {
		result.Status = "failed"
		result.ErrorMessage = fmt.Sprintf("failed to decrypt database: %v", err)
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return fmt.Errorf("failed to decrypt database: %w", err)
	}
	defer func() {
		if tempDB != nil {
			_ = tempDB.Close()
		}
	}()

	// Step 3: Get authoritative blob list from database
	dbBlobs, err := v.getBlobsFromDatabase(snapshotID, tempDB.DB)
	if err != nil {
		result.Status = "failed"
		result.ErrorMessage = fmt.Sprintf("failed to get blobs from database: %v", err)
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return fmt.Errorf("failed to get blobs from database: %w", err)
	}

	result.BlobCount = len(dbBlobs)
	var totalSize int64
	for _, blob := range dbBlobs {
		totalSize += blob.CompressedSize
	}
	result.TotalSize = totalSize

	log.Info("Database loaded",
		"db_blob_count", len(dbBlobs),
		"db_total_size", humanize.Bytes(uint64(totalSize)),
	)
	if !opts.JSON {
		v.printfStdout("Database loaded: %d blobs (%s)\n", len(dbBlobs), humanize.Bytes(uint64(totalSize)))
		v.printfStdout("Verifying manifest against database...\n")
	}

	// Step 4: Verify manifest matches database
	if err := v.verifyManifestAgainstDatabase(manifest, dbBlobs); err != nil {
		result.Status = "failed"
		result.ErrorMessage = err.Error()
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return err
	}

	// Step 5: Verify all blobs exist in S3 (using database as source)
	if !opts.JSON {
		v.printfStdout("Manifest verified.\n")
		v.printfStdout("Checking blob existence in remote storage...\n")
	}
	if err := v.verifyBlobExistenceFromDB(dbBlobs); err != nil {
		result.Status = "failed"
		result.ErrorMessage = err.Error()
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return err
	}

	// Step 6: Deep verification - download and verify blob contents
	if !opts.JSON {
		v.printfStdout("All blobs exist.\n")
		v.printfStdout("Downloading and verifying blob contents (%d blobs, %s)...\n", len(dbBlobs), humanize.Bytes(uint64(totalSize)))
	}
	if err := v.performDeepVerificationFromDB(dbBlobs, tempDB.DB, opts); err != nil {
		result.Status = "failed"
		result.ErrorMessage = err.Error()
		if opts.JSON {
			return v.outputVerifyJSON(result)
		}
		return err
	}

	// Success
	result.Status = "ok"
	result.Verified = len(dbBlobs)

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

	log.Info("✓ Verification completed successfully",
		"snapshot_id", snapshotID,
		"mode", "deep",
		"blobs_verified", len(dbBlobs),
	)

	v.printfStdout("\n✓ Verification completed successfully\n")
	v.printfStdout("  Snapshot:       %s\n", snapshotID)
	v.printfStdout("  Blobs verified: %d\n", len(dbBlobs))
	v.printfStdout("  Total size:     %s\n", humanize.Bytes(uint64(totalSize)))

	return nil
}

// tempDB wraps sql.DB with cleanup
type tempDB struct {
	*sql.DB
	tempPath string
}

func (t *tempDB) Close() error {
	err := t.DB.Close()
	_ = os.Remove(t.tempPath)
	return err
}

// decryptAndLoadDatabase decrypts and loads the binary SQLite database from the encrypted stream
func (v *Vaultik) decryptAndLoadDatabase(reader io.ReadCloser, secretKey string) (*tempDB, error) {
	// Get decryptor
	decryptor, err := v.GetDecryptor()
	if err != nil {
		return nil, fmt.Errorf("failed to get decryptor: %w", err)
	}

	// Decrypt the stream
	decryptedReader, err := decryptor.DecryptStream(reader)
	if err != nil {
		return nil, fmt.Errorf("failed to decrypt database: %w", err)
	}

	// Decompress the binary database
	decompressor, err := zstd.NewReader(decryptedReader)
	if err != nil {
		return nil, fmt.Errorf("failed to create decompressor: %w", err)
	}
	defer decompressor.Close()

	// Create temporary file for the database
	tempFile, err := os.CreateTemp("", "vaultik-verify-*.db")
	if err != nil {
		return nil, fmt.Errorf("failed to create temp file: %w", err)
	}
	tempPath := tempFile.Name()

	// Stream decompress directly to file
	log.Info("Decompressing database...")
	written, err := io.Copy(tempFile, decompressor)
	if err != nil {
		_ = tempFile.Close()
		_ = os.Remove(tempPath)
		return nil, fmt.Errorf("failed to decompress database: %w", err)
	}
	_ = tempFile.Close()

	log.Info("Database decompressed", "size", humanize.Bytes(uint64(written)))

	// Open the database
	db, err := sql.Open("sqlite3", tempPath)
	if err != nil {
		_ = os.Remove(tempPath)
		return nil, fmt.Errorf("failed to open database: %w", err)
	}

	return &tempDB{
		DB:       db,
		tempPath: tempPath,
	}, nil
}

// verifyBlob downloads and verifies a single blob
func (v *Vaultik) verifyBlob(blobInfo snapshot.BlobInfo, db *sql.DB) error {
	// Download blob using shared fetch method
	reader, _, err := v.FetchBlob(v.ctx, blobInfo.Hash, blobInfo.CompressedSize)
	if err != nil {
		return fmt.Errorf("failed to download: %w", err)
	}
	defer func() { _ = reader.Close() }()

	// Get decryptor
	decryptor, err := v.GetDecryptor()
	if err != nil {
		return fmt.Errorf("failed to get decryptor: %w", err)
	}

	// Hash the encrypted blob data as it streams through to decryption
	blobHasher := sha256.New()
	teeReader := io.TeeReader(reader, blobHasher)

	// Decrypt blob (reading through teeReader to hash encrypted data)
	decryptedReader, err := decryptor.DecryptStream(teeReader)
	if err != nil {
		return fmt.Errorf("failed to decrypt: %w", err)
	}

	// Decompress blob
	decompressor, err := zstd.NewReader(decryptedReader)
	if err != nil {
		return fmt.Errorf("failed to decompress: %w", err)
	}
	defer decompressor.Close()

	// Query blob chunks from database to get offsets and lengths
	query := `
		SELECT bc.chunk_hash, bc.offset, bc.length
		FROM blob_chunks bc
		JOIN blobs b ON bc.blob_id = b.id
		WHERE b.blob_hash = ?
		ORDER BY bc.offset
	`
	rows, err := db.QueryContext(v.ctx, query, blobInfo.Hash)
	if err != nil {
		return fmt.Errorf("failed to query blob chunks: %w", err)
	}
	defer func() { _ = rows.Close() }()

	var lastOffset int64 = -1
	chunkCount := 0
	totalRead := int64(0)

	// Verify each chunk in the blob
	for rows.Next() {
		var chunkHash string
		var offset, length int64
		if err := rows.Scan(&chunkHash, &offset, &length); err != nil {
			return fmt.Errorf("failed to scan chunk row: %w", err)
		}

		// Verify chunk ordering
		if offset <= lastOffset {
			return fmt.Errorf("chunks out of order: offset %d after %d", offset, lastOffset)
		}
		lastOffset = offset

		// Read chunk data from decompressed stream
		if offset > totalRead {
			// Skip to the correct offset
			skipBytes := offset - totalRead
			if _, err := io.CopyN(io.Discard, decompressor, skipBytes); err != nil {
				return fmt.Errorf("failed to skip to offset %d: %w", offset, err)
			}
			totalRead = offset
		}

		// Read chunk data
		chunkData := make([]byte, length)
		if _, err := io.ReadFull(decompressor, chunkData); err != nil {
			return fmt.Errorf("failed to read chunk at offset %d: %w", offset, err)
		}
		totalRead += length

		// Verify chunk hash
		hasher := sha256.New()
		hasher.Write(chunkData)
		calculatedHash := hex.EncodeToString(hasher.Sum(nil))

		if calculatedHash != chunkHash {
			return fmt.Errorf("chunk hash mismatch at offset %d: calculated %s, expected %s",
				offset, calculatedHash, chunkHash)
		}

		chunkCount++
	}

	if err := rows.Err(); err != nil {
		return fmt.Errorf("error iterating blob chunks: %w", err)
	}

	// Verify no remaining data in blob - if chunk list is accurate, blob should be fully consumed
	remaining, err := io.Copy(io.Discard, decompressor)
	if err != nil {
		return fmt.Errorf("failed to check for remaining blob data: %w", err)
	}
	if remaining > 0 {
		return fmt.Errorf("blob has %d unexpected trailing bytes not covered by chunk list", remaining)
	}

	// Verify blob hash matches the encrypted data we downloaded
	calculatedBlobHash := hex.EncodeToString(blobHasher.Sum(nil))
	if calculatedBlobHash != blobInfo.Hash {
		return fmt.Errorf("blob hash mismatch: calculated %s, expected %s",
			calculatedBlobHash, blobInfo.Hash)
	}

	log.Info("Blob verified",
		"hash", blobInfo.Hash[:16]+"...",
		"chunks", chunkCount,
		"size", humanize.Bytes(uint64(blobInfo.CompressedSize)),
	)

	return nil
}

// getBlobsFromDatabase gets all blobs for the snapshot from the database
func (v *Vaultik) getBlobsFromDatabase(snapshotID string, db *sql.DB) ([]snapshot.BlobInfo, error) {
	query := `
		SELECT b.blob_hash, b.compressed_size
		FROM snapshot_blobs sb
		JOIN blobs b ON sb.blob_hash = b.blob_hash
		WHERE sb.snapshot_id = ?
		ORDER BY b.blob_hash
	`
	rows, err := db.QueryContext(v.ctx, query, snapshotID)
	if err != nil {
		return nil, fmt.Errorf("failed to query snapshot blobs: %w", err)
	}
	defer func() { _ = rows.Close() }()

	var blobs []snapshot.BlobInfo
	for rows.Next() {
		var hash string
		var size int64
		if err := rows.Scan(&hash, &size); err != nil {
			return nil, fmt.Errorf("failed to scan blob row: %w", err)
		}
		blobs = append(blobs, snapshot.BlobInfo{
			Hash:           hash,
			CompressedSize: size,
		})
	}

	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("error iterating blobs: %w", err)
	}

	return blobs, nil
}

// verifyManifestAgainstDatabase verifies the manifest matches the authoritative database
func (v *Vaultik) verifyManifestAgainstDatabase(manifest *snapshot.Manifest, dbBlobs []snapshot.BlobInfo) error {
	log.Info("Verifying manifest against database")

	// Build map of database blobs
	dbBlobMap := make(map[string]int64)
	for _, blob := range dbBlobs {
		dbBlobMap[blob.Hash] = blob.CompressedSize
	}

	// Build map of manifest blobs
	manifestBlobMap := make(map[string]int64)
	for _, blob := range manifest.Blobs {
		manifestBlobMap[blob.Hash] = blob.CompressedSize
	}

	// Check counts match
	if len(dbBlobMap) != len(manifestBlobMap) {
		log.Warn("Manifest blob count mismatch",
			"database_blobs", len(dbBlobMap),
			"manifest_blobs", len(manifestBlobMap),
		)
		// This is a warning, not an error - database is authoritative
	}

	// Check each manifest blob exists in database with correct size
	for hash, manifestSize := range manifestBlobMap {
		dbSize, exists := dbBlobMap[hash]
		if !exists {
			return fmt.Errorf("manifest contains blob %s not in database", hash)
		}
		if dbSize != manifestSize {
			return fmt.Errorf("blob %s size mismatch: database has %d bytes, manifest has %d bytes",
				hash, dbSize, manifestSize)
		}
	}

	log.Info("✓ Manifest verified against database",
		"manifest_blobs", len(manifestBlobMap),
		"database_blobs", len(dbBlobMap),
	)
	return nil
}

// verifyBlobExistenceFromDB checks that all blobs from database exist in S3
func (v *Vaultik) verifyBlobExistenceFromDB(blobs []snapshot.BlobInfo) error {
	log.Info("Verifying blob existence in S3", "blob_count", len(blobs))

	for i, blob := range blobs {
		// Construct blob path
		blobPath := fmt.Sprintf("blobs/%s/%s/%s", blob.Hash[:2], blob.Hash[2:4], blob.Hash)

		// Check blob exists
		stat, err := v.Storage.Stat(v.ctx, blobPath)
		if err != nil {
			return fmt.Errorf("blob %s missing from storage: %w", blob.Hash, err)
		}

		// Verify size matches
		if stat.Size != blob.CompressedSize {
			return fmt.Errorf("blob %s size mismatch: S3 has %d bytes, database has %d bytes",
				blob.Hash, stat.Size, blob.CompressedSize)
		}

		// Progress update every 100 blobs
		if (i+1)%100 == 0 || i == len(blobs)-1 {
			log.Info("Blob existence check progress",
				"checked", i+1,
				"total", len(blobs),
				"percent", fmt.Sprintf("%.1f%%", float64(i+1)/float64(len(blobs))*100),
			)
		}
	}

	log.Info("✓ All blobs exist in storage")
	return nil
}

// performDeepVerificationFromDB downloads and verifies the content of each blob using database as source
func (v *Vaultik) performDeepVerificationFromDB(blobs []snapshot.BlobInfo, db *sql.DB, opts *VerifyOptions) error {
	// Calculate total bytes for ETA
	var totalBytesExpected int64
	for _, b := range blobs {
		totalBytesExpected += b.CompressedSize
	}

	log.Info("Starting deep verification - downloading and verifying all blobs",
		"blob_count", len(blobs),
		"total_size", humanize.Bytes(uint64(totalBytesExpected)),
	)

	startTime := time.Now()
	bytesProcessed := int64(0)

	for i, blobInfo := range blobs {
		// Verify individual blob
		if err := v.verifyBlob(blobInfo, db); err != nil {
			return fmt.Errorf("blob %s verification failed: %w", blobInfo.Hash, err)
		}

		bytesProcessed += blobInfo.CompressedSize
		elapsed := time.Since(startTime)
		remaining := len(blobs) - (i + 1)

		// Calculate ETA based on bytes processed
		var eta time.Duration
		if bytesProcessed > 0 {
			bytesPerSec := float64(bytesProcessed) / elapsed.Seconds()
			bytesRemaining := totalBytesExpected - bytesProcessed
			if bytesPerSec > 0 {
				eta = time.Duration(float64(bytesRemaining)/bytesPerSec) * time.Second
			}
		}

		log.Info("Verification progress",
			"blobs_done", i+1,
			"blobs_total", len(blobs),
			"blobs_remaining", remaining,
			"bytes_done", bytesProcessed,
			"bytes_done_human", humanize.Bytes(uint64(bytesProcessed)),
			"bytes_total", totalBytesExpected,
			"bytes_total_human", humanize.Bytes(uint64(totalBytesExpected)),
			"elapsed", elapsed.Round(time.Second),
			"eta", eta.Round(time.Second),
		)

		if !opts.JSON {
			v.printfStdout("  Verified %d/%d blobs (%d remaining) - %s/%s - elapsed %s, eta %s\n",
				i+1, len(blobs), remaining,
				humanize.Bytes(uint64(bytesProcessed)),
				humanize.Bytes(uint64(totalBytesExpected)),
				elapsed.Round(time.Second),
				eta.Round(time.Second))
		}
	}

	totalElapsed := time.Since(startTime)
	log.Info("✓ Deep verification completed successfully",
		"blobs_verified", len(blobs),
		"total_bytes", bytesProcessed,
		"total_bytes_human", humanize.Bytes(uint64(bytesProcessed)),
		"duration", totalElapsed.Round(time.Second),
	)

	return nil
}