// Package vector provides vector storage capabilities.
package vector

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"os"
	"path/filepath"
	"sync"
)

// Config holds vector store configuration.
type Config struct {
	Type             string `yaml:"type"`
	PersistDir       string `yaml:"persist_dir"`
	SimilarityMetric string `yaml:"similarity_metric"`
}

// Document represents an indexed document.
type Document struct {
	ID       string
	Content  string
	Vector   []float32
	Metadata map[string]any
}

// SearchResult represents a search result.
type SearchResult struct {
	ID       string
	Content  string
	Score    float64
	Metadata map[string]any
}

type scoredDoc struct {
	id    string
	score float64
}

// Store defines the interface for vector storage.
type Store interface {
	// Add adds documents to the store.
	Add(ctx context.Context, docs []*Document) error

	// Search finds similar documents.
	Search(ctx context.Context, vector []float32, limit int) ([]*SearchResult, error)

	// Delete removes a document by ID.
	Delete(ctx context.Context, id string) error

	// Get retrieves a document by ID.
	Get(ctx context.Context, id string) (*Document, error)

	// Count returns the number of documents.
	Count(ctx context.Context) (int, error)

	// Clear removes all documents.
	Clear(ctx context.Context) error
}

// NewStore creates a new vector store.
func NewStore(config *Config) Store {
	switch config.Type {
	case "memory":
		return NewMemoryStore(config)
	case "chromem":
		return NewChromemStore(config)
	default:
		return NewMemoryStore(config)
	}
}

// MemoryStore implements Store with in-memory storage.
type MemoryStore struct {
	config  *Config
	mu      sync.RWMutex
	docs    map[string]*Document
	vectors [][]float32
}

// NewMemoryStore creates an in-memory vector store.
func NewMemoryStore(config *Config) *MemoryStore {
	return &MemoryStore{
		config: config,
		docs:   make(map[string]*Document),
	}
}

// Add adds documents to the store.
func (s *MemoryStore) Add(ctx context.Context, docs []*Document) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	for _, doc := range docs {
		if doc.ID == "" {
			doc.ID = generateID(doc.Content)
		}
		s.docs[doc.ID] = doc
		s.vectors = append(s.vectors, doc.Vector)
	}

	// Persist if directory is set
	if s.config.PersistDir != "" {
		return s.persist()
	}

	return nil
}

// Search finds similar documents using cosine similarity.
func (s *MemoryStore) Search(ctx context.Context, vector []float32, limit int) ([]*SearchResult, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	var scored []*scoredDoc

	for id, doc := range s.docs {
		if doc.Vector != nil {
			score := cosineSimilarity(vector, doc.Vector)
			scored = append(scored, &scoredDoc{id: id, score: score})
		}
	}

	sortByScore(scored)

	results := make([]*SearchResult, 0, limit)
	for i := 0; i < len(scored) && i < limit; i++ {
		doc := s.docs[scored[i].id]
		results = append(results, &SearchResult{
			ID:       doc.ID,
			Content:  doc.Content,
			Score:    scored[i].score,
			Metadata: doc.Metadata,
		})
	}

	return results, nil
}

// Delete removes a document by ID.
func (s *MemoryStore) Delete(ctx context.Context, id string) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	delete(s.docs, id)

	// Rebuild vectors slice
	s.vectors = nil
	for _, doc := range s.docs {
		s.vectors = append(s.vectors, doc.Vector)
	}

	return nil
}

// Get retrieves a document by ID.
func (s *MemoryStore) Get(ctx context.Context, id string) (*Document, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	doc, ok := s.docs[id]
	if !ok {
		return nil, fmt.Errorf("document not found: %s", id)
	}

	return doc, nil
}

// Count returns the number of documents.
func (s *MemoryStore) Count(ctx context.Context) (int, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	return len(s.docs), nil
}

// Clear removes all documents.
func (s *MemoryStore) Clear(ctx context.Context) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.docs = make(map[string]*Document)
	s.vectors = nil

	return nil
}

// persist saves documents to disk.
func (s *MemoryStore) persist() error {
	if s.config.PersistDir == "" {
		return nil
	}

	// Create directory if needed
	if err := os.MkdirAll(s.config.PersistDir, 0755); err != nil {
		return err
	}

	// Save documents
	dataFile := filepath.Join(s.config.PersistDir, "documents.json")
	// TODO: Implement actual JSON serialization

	_ = dataFile // Placeholder

	return nil
}

// ChromemStore wraps chromem-go for production use.
type ChromemStore struct {
	config *Config
	// TODO: Add chromem-go client
}

// NewChromemStore creates a chromem-backed store.
func NewChromemStore(config *Config) *ChromemStore {
	return &ChromemStore{config: config}
}

func (s *ChromemStore) Add(ctx context.Context, docs []*Document) error {
	// TODO: Implement with chromem-go
	return fmt.Errorf("chromem store not implemented")
}

func (s *ChromemStore) Search(ctx context.Context, vector []float32, limit int) ([]*SearchResult, error) {
	return nil, fmt.Errorf("chromem store not implemented")
}

func (s *ChromemStore) Delete(ctx context.Context, id string) error {
	return fmt.Errorf("chromem store not implemented")
}

func (s *ChromemStore) Get(ctx context.Context, id string) (*Document, error) {
	return nil, fmt.Errorf("chromem store not implemented")
}

func (s *ChromemStore) Count(ctx context.Context) (int, error) {
	return 0, fmt.Errorf("chromem store not implemented")
}

func (s *ChromemStore) Clear(ctx context.Context) error {
	return fmt.Errorf("chromem store not implemented")
}

// Helper functions

func generateID(content string) string {
	hash := sha256.Sum256([]byte(content))
	return hex.EncodeToString(hash[:12])
}

func cosineSimilarity(a, b []float32) float64 {
	if len(a) != len(b) {
		return 0
	}

	var dotProduct, normA, normB float64
	for i := range a {
		dotProduct += float64(a[i]) * float64(b[i])
		normA += float64(a[i]) * float64(a[i])
		normB += float64(b[i]) * float64(b[i])
	}

	if normA == 0 || normB == 0 {
		return 0
	}

	return dotProduct / (sqrt(normA) * sqrt(normB))
}

func sqrt(x float64) float64 {
	// Simple Newton's method for square root
	if x == 0 {
		return 0
	}
	z := x
	for i := 0; i < 10; i++ {
		z = z - (z*z-x)/(2*z)
	}
	return z
}

func sortByScore(docs []*scoredDoc) {
	for i := 1; i < len(docs); i++ {
		for j := i; j > 0 && docs[j].score > docs[j-1].score; j-- {
			docs[j], docs[j-1] = docs[j-1], docs[j]
		}
	}
}