// Package blob handles the creation of blobs - the final storage units for Vaultik.
// A blob is a large file (up to 10GB) containing many compressed and encrypted chunks
// from multiple source files. Blobs are content-addressed, meaning their filename
// is derived from the SHA256 hash of their compressed and encrypted content.
//
// The blob creation process:
// 1. Chunks are accumulated from multiple files
// 2. The collection is compressed using zstd
// 3. The compressed data is encrypted using age
// 4. The encrypted blob is hashed to create its content-addressed name
// 5. The blob is uploaded to S3 using the hash as the filename
//
// This design optimizes storage efficiency by batching many small chunks into
// larger blobs, reducing the number of S3 operations and associated costs.
package blob

import (
	"context"
	"database/sql"
	"encoding/hex"
	"fmt"
	"io"
	"sync"
	"time"

	"git.eeqj.de/sneak/vaultik/internal/blobgen"
	"git.eeqj.de/sneak/vaultik/internal/database"
	"git.eeqj.de/sneak/vaultik/internal/log"
	"github.com/google/uuid"
	"github.com/spf13/afero"
)

// BlobHandler is a callback function invoked when a blob is finalized and ready for upload.
// The handler receives a BlobWithReader containing the blob metadata and a reader for
// the compressed and encrypted blob content. The handler is responsible for uploading
// the blob to storage and cleaning up any temporary files.
type BlobHandler func(blob *BlobWithReader) error

// PackerConfig holds configuration for creating a Packer.
// All fields except BlobHandler are required.
type PackerConfig struct {
	MaxBlobSize      int64                  // Maximum size of a blob before forcing finalization
	CompressionLevel int                    // Zstd compression level (1-19, higher = better compression)
	Recipients       []string               // Age recipients for encryption
	Repositories     *database.Repositories // Database repositories for tracking blob metadata
	BlobHandler      BlobHandler            // Optional callback when blob is ready for upload
	Fs               afero.Fs               // Filesystem for temporary files
}

// Packer accumulates chunks and packs them into blobs.
// It handles compression, encryption, and coordination with the database
// to track blob metadata. Packer is thread-safe.
type Packer struct {
	maxBlobSize      int64
	compressionLevel int
	recipients       []string               // Age recipients for encryption
	blobHandler      BlobHandler            // Called when blob is ready
	repos            *database.Repositories // For creating blob records
	fs               afero.Fs               // Filesystem for temporary files

	// Mutex for thread-safe blob creation
	mu sync.Mutex

	// Current blob being packed
	currentBlob   *blobInProgress
	finishedBlobs []*FinishedBlob // Only used if no handler provided
}

// blobInProgress represents a blob being assembled
type blobInProgress struct {
	id        string          // UUID of the blob
	chunks    []*chunkInfo    // Track chunk metadata
	chunkSet  map[string]bool // Track unique chunks in this blob
	tempFile  afero.File      // Temporary file for encrypted compressed data
	writer    *blobgen.Writer // Unified compression/encryption/hashing writer
	startTime time.Time
	size      int64 // Current uncompressed size
}

// ChunkRef represents a chunk to be added to a blob.
// The Hash is the content-addressed identifier (SHA256) of the chunk,
// and Data contains the raw chunk bytes. After adding to a blob,
// the Data can be safely discarded as it's written to the blob immediately.
type ChunkRef struct {
	Hash string // SHA256 hash of the chunk data
	Data []byte // Raw chunk content
}

// chunkInfo tracks chunk metadata in a blob
type chunkInfo struct {
	Hash   string
	Offset int64
	Size   int64
}

// FinishedBlob represents a completed blob ready for storage
type FinishedBlob struct {
	ID           string
	Hash         string
	Data         []byte // Compressed data
	Chunks       []*BlobChunkRef
	CreatedTS    time.Time
	Uncompressed int64
	Compressed   int64
}

// BlobChunkRef represents a chunk's position within a blob
type BlobChunkRef struct {
	ChunkHash string
	Offset    int64
	Length    int64
}

// BlobWithReader wraps a FinishedBlob with its data reader
type BlobWithReader struct {
	*FinishedBlob
	Reader   io.ReadSeeker
	TempFile afero.File // Optional, only set for disk-based blobs
}

// NewPacker creates a new blob packer that accumulates chunks into blobs.
// The packer will automatically finalize blobs when they reach MaxBlobSize.
// Returns an error if required configuration fields are missing or invalid.
func NewPacker(cfg PackerConfig) (*Packer, error) {
	if len(cfg.Recipients) == 0 {
		return nil, fmt.Errorf("recipients are required - blobs must be encrypted")
	}
	if cfg.MaxBlobSize <= 0 {
		return nil, fmt.Errorf("max blob size must be positive")
	}
	if cfg.Fs == nil {
		return nil, fmt.Errorf("filesystem is required")
	}
	return &Packer{
		maxBlobSize:      cfg.MaxBlobSize,
		compressionLevel: cfg.CompressionLevel,
		recipients:       cfg.Recipients,
		blobHandler:      cfg.BlobHandler,
		repos:            cfg.Repositories,
		fs:               cfg.Fs,
		finishedBlobs:    make([]*FinishedBlob, 0),
	}, nil
}

// SetBlobHandler sets the handler to be called when a blob is finalized.
// The handler is responsible for uploading the blob to storage.
// If no handler is set, finalized blobs are stored in memory and can be
// retrieved with GetFinishedBlobs().
func (p *Packer) SetBlobHandler(handler BlobHandler) {
	p.mu.Lock()
	defer p.mu.Unlock()
	p.blobHandler = handler
}

// AddChunk adds a chunk to the current blob being packed.
// If adding the chunk would exceed MaxBlobSize, returns ErrBlobSizeLimitExceeded.
// In this case, the caller should finalize the current blob and retry.
// The chunk data is written immediately and can be garbage collected after this call.
// Thread-safe.
func (p *Packer) AddChunk(chunk *ChunkRef) error {
	p.mu.Lock()
	defer p.mu.Unlock()

	// Initialize new blob if needed
	if p.currentBlob == nil {
		if err := p.startNewBlob(); err != nil {
			return fmt.Errorf("starting new blob: %w", err)
		}
	}

	// Check if adding this chunk would exceed blob size limit
	// Use conservative estimate: assume no compression
	// Skip size check if chunk already exists in blob
	if !p.currentBlob.chunkSet[chunk.Hash] {
		currentSize := p.currentBlob.size
		newSize := currentSize + int64(len(chunk.Data))

		if newSize > p.maxBlobSize && len(p.currentBlob.chunks) > 0 {
			// Return error indicating size limit would be exceeded
			return ErrBlobSizeLimitExceeded
		}
	}

	// Add chunk to current blob
	if err := p.addChunkToCurrentBlob(chunk); err != nil {
		return err
	}

	return nil
}

// Flush finalizes any in-progress blob, compressing, encrypting, and hashing it.
// This should be called after all chunks have been added to ensure no data is lost.
// If a BlobHandler is set, it will be called with the finalized blob.
// Thread-safe.
func (p *Packer) Flush() error {
	p.mu.Lock()
	defer p.mu.Unlock()

	if p.currentBlob != nil && len(p.currentBlob.chunks) > 0 {
		if err := p.finalizeCurrentBlob(); err != nil {
			return fmt.Errorf("finalizing blob: %w", err)
		}
	}

	return nil
}

// FinalizeBlob finalizes the current blob being assembled.
// This compresses the accumulated chunks, encrypts the result, and computes
// the content-addressed hash. The finalized blob is either passed to the
// BlobHandler (if set) or stored internally.
// Caller must handle retrying any chunk that triggered size limit exceeded.
// Not thread-safe - caller must hold the lock.
func (p *Packer) FinalizeBlob() error {
	p.mu.Lock()
	defer p.mu.Unlock()

	if p.currentBlob == nil {
		return nil
	}

	return p.finalizeCurrentBlob()
}

// GetFinishedBlobs returns all completed blobs and clears the internal list.
// This is only used when no BlobHandler is set. After calling this method,
// the caller is responsible for uploading the blobs to storage.
// Thread-safe.
func (p *Packer) GetFinishedBlobs() []*FinishedBlob {
	p.mu.Lock()
	defer p.mu.Unlock()

	blobs := p.finishedBlobs
	p.finishedBlobs = make([]*FinishedBlob, 0)
	return blobs
}

// startNewBlob initializes a new blob (must be called with lock held)
func (p *Packer) startNewBlob() error {
	// Generate UUID for the blob
	blobID := uuid.New().String()

	// Create blob record in database
	if p.repos != nil {
		blob := &database.Blob{
			ID:               blobID,
			Hash:             "temp-placeholder-" + blobID, // Temporary placeholder until finalized
			CreatedTS:        time.Now().UTC(),
			FinishedTS:       nil,
			UncompressedSize: 0,
			CompressedSize:   0,
			UploadedTS:       nil,
		}
		err := p.repos.WithTx(context.Background(), func(ctx context.Context, tx *sql.Tx) error {
			return p.repos.Blobs.Create(ctx, tx, blob)
		})
		if err != nil {
			return fmt.Errorf("creating blob record: %w", err)
		}
	}

	// Create temporary file
	tempFile, err := afero.TempFile(p.fs, "", "vaultik-blob-*.tmp")
	if err != nil {
		return fmt.Errorf("creating temp file: %w", err)
	}

	// Create blobgen writer for unified compression/encryption/hashing
	writer, err := blobgen.NewWriter(tempFile, p.compressionLevel, p.recipients)
	if err != nil {
		_ = tempFile.Close()
		_ = p.fs.Remove(tempFile.Name())
		return fmt.Errorf("creating blobgen writer: %w", err)
	}

	p.currentBlob = &blobInProgress{
		id:        blobID,
		chunks:    make([]*chunkInfo, 0),
		chunkSet:  make(map[string]bool),
		startTime: time.Now().UTC(),
		tempFile:  tempFile,
		writer:    writer,
		size:      0,
	}

	log.Debug("Created new blob container", "blob_id", blobID, "temp_file", tempFile.Name())
	return nil
}

// addChunkToCurrentBlob adds a chunk to the current blob (must be called with lock held)
func (p *Packer) addChunkToCurrentBlob(chunk *ChunkRef) error {
	// Skip if chunk already in current blob
	if p.currentBlob.chunkSet[chunk.Hash] {
		log.Debug("Skipping duplicate chunk already in current blob", "chunk_hash", chunk.Hash)
		return nil
	}

	// Track offset before writing
	offset := p.currentBlob.size

	// Write to the blobgen writer (compression -> encryption -> disk)
	if _, err := p.currentBlob.writer.Write(chunk.Data); err != nil {
		return fmt.Errorf("writing to blob stream: %w", err)
	}

	// Track chunk info
	chunkSize := int64(len(chunk.Data))
	chunkInfo := &chunkInfo{
		Hash:   chunk.Hash,
		Offset: offset,
		Size:   chunkSize,
	}
	p.currentBlob.chunks = append(p.currentBlob.chunks, chunkInfo)
	p.currentBlob.chunkSet[chunk.Hash] = true

	// Store blob-chunk association in database immediately
	if p.repos != nil {
		blobChunk := &database.BlobChunk{
			BlobID:    p.currentBlob.id,
			ChunkHash: chunk.Hash,
			Offset:    offset,
			Length:    chunkSize,
		}
		err := p.repos.WithTx(context.Background(), func(ctx context.Context, tx *sql.Tx) error {
			return p.repos.BlobChunks.Create(ctx, tx, blobChunk)
		})
		if err != nil {
			log.Error("Failed to store blob-chunk association in database", "error", err,
				"blob_id", p.currentBlob.id, "chunk_hash", chunk.Hash)
			// Continue anyway - we can reconstruct this later if needed
		}
	}

	// Update total size
	p.currentBlob.size += chunkSize

	log.Debug("Added chunk to blob container",
		"blob_id", p.currentBlob.id,
		"chunk_hash", chunk.Hash,
		"chunk_size", len(chunk.Data),
		"offset", offset,
		"blob_chunks", len(p.currentBlob.chunks),
		"uncompressed_size", p.currentBlob.size)

	return nil
}

// finalizeCurrentBlob completes the current blob (must be called with lock held)
func (p *Packer) finalizeCurrentBlob() error {
	if p.currentBlob == nil {
		return nil
	}

	// Close blobgen writer to flush all data
	if err := p.currentBlob.writer.Close(); err != nil {
		p.cleanupTempFile()
		return fmt.Errorf("closing blobgen writer: %w", err)
	}

	// Sync file to ensure all data is written
	if err := p.currentBlob.tempFile.Sync(); err != nil {
		p.cleanupTempFile()
		return fmt.Errorf("syncing temp file: %w", err)
	}

	// Get the final size (encrypted if applicable)
	finalSize, err := p.currentBlob.tempFile.Seek(0, io.SeekCurrent)
	if err != nil {
		p.cleanupTempFile()
		return fmt.Errorf("getting file size: %w", err)
	}

	// Reset to beginning for reading
	if _, err := p.currentBlob.tempFile.Seek(0, io.SeekStart); err != nil {
		p.cleanupTempFile()
		return fmt.Errorf("seeking to start: %w", err)
	}

	// Get hash from blobgen writer (of final encrypted data)
	finalHash := p.currentBlob.writer.Sum256()
	blobHash := hex.EncodeToString(finalHash)

	// Create chunk references with offsets
	chunkRefs := make([]*BlobChunkRef, 0, len(p.currentBlob.chunks))

	for _, chunk := range p.currentBlob.chunks {
		chunkRefs = append(chunkRefs, &BlobChunkRef{
			ChunkHash: chunk.Hash,
			Offset:    chunk.Offset,
			Length:    chunk.Size,
		})
	}

	// Update blob record in database with hash and sizes
	if p.repos != nil {
		err := p.repos.WithTx(context.Background(), func(ctx context.Context, tx *sql.Tx) error {
			return p.repos.Blobs.UpdateFinished(ctx, tx, p.currentBlob.id, blobHash,
				p.currentBlob.size, finalSize)
		})
		if err != nil {
			p.cleanupTempFile()
			return fmt.Errorf("updating blob record: %w", err)
		}
	}

	// Create finished blob
	finished := &FinishedBlob{
		ID:           p.currentBlob.id,
		Hash:         blobHash,
		Data:         nil, // We don't load data into memory anymore
		Chunks:       chunkRefs,
		CreatedTS:    p.currentBlob.startTime,
		Uncompressed: p.currentBlob.size,
		Compressed:   finalSize,
	}

	compressionRatio := float64(finished.Compressed) / float64(finished.Uncompressed)
	log.Info("Finalized blob (compressed and encrypted)",
		"hash", blobHash,
		"chunks", len(chunkRefs),
		"uncompressed", finished.Uncompressed,
		"compressed", finished.Compressed,
		"ratio", fmt.Sprintf("%.2f", compressionRatio),
		"duration", time.Since(p.currentBlob.startTime))

	// Call blob handler if set
	if p.blobHandler != nil {
		// Reset file position for handler
		if _, err := p.currentBlob.tempFile.Seek(0, io.SeekStart); err != nil {
			p.cleanupTempFile()
			return fmt.Errorf("seeking for handler: %w", err)
		}

		// Create a blob reader that includes the data stream
		blobWithReader := &BlobWithReader{
			FinishedBlob: finished,
			Reader:       p.currentBlob.tempFile,
			TempFile:     p.currentBlob.tempFile,
		}

		if err := p.blobHandler(blobWithReader); err != nil {
			p.cleanupTempFile()
			return fmt.Errorf("blob handler failed: %w", err)
		}
		// Note: blob handler is responsible for closing/cleaning up temp file
		p.currentBlob = nil
	} else {
		log.Debug("No blob handler callback configured", "blob_hash", blobHash[:8]+"...")
		// No handler, need to read data for legacy behavior
		if _, err := p.currentBlob.tempFile.Seek(0, io.SeekStart); err != nil {
			p.cleanupTempFile()
			return fmt.Errorf("seeking to read data: %w", err)
		}

		data, err := io.ReadAll(p.currentBlob.tempFile)
		if err != nil {
			p.cleanupTempFile()
			return fmt.Errorf("reading blob data: %w", err)
		}
		finished.Data = data

		p.finishedBlobs = append(p.finishedBlobs, finished)

		// Cleanup
		p.cleanupTempFile()
		p.currentBlob = nil
	}

	return nil
}

// cleanupTempFile removes the temporary file
func (p *Packer) cleanupTempFile() {
	if p.currentBlob != nil && p.currentBlob.tempFile != nil {
		name := p.currentBlob.tempFile.Name()
		_ = p.currentBlob.tempFile.Close()
		_ = p.fs.Remove(name)
	}
}

// PackChunks is a convenience method to pack multiple chunks at once
func (p *Packer) PackChunks(chunks []*ChunkRef) error {
	for _, chunk := range chunks {
		err := p.AddChunk(chunk)
		if err == ErrBlobSizeLimitExceeded {
			// Finalize current blob and retry
			if err := p.FinalizeBlob(); err != nil {
				return fmt.Errorf("finalizing blob before retry: %w", err)
			}
			// Retry the chunk
			if err := p.AddChunk(chunk); err != nil {
				return fmt.Errorf("adding chunk %s after finalize: %w", chunk.Hash, err)
			}
		} else if err != nil {
			return fmt.Errorf("adding chunk %s: %w", chunk.Hash, err)
		}
	}

	return p.Flush()
}