package rag

import (
	"context"
	"fmt"
	"time"

	"github.com/google/uuid"
)

// Fragment represents a piece of content stored in the RAG system.
type Fragment struct {
	ID        string
	Content   string
	Vector    []float32
	Metadata  map[string]string
	Timestamp time.Time
	ProjectID string
}

// Memory provides persistent memory and semantic search over agent content.
type Memory interface {
	Add(ctx context.Context, fragment Fragment) error
	Search(ctx context.Context, query string, topK int) ([]Fragment, error)
	Forget(ctx context.Context, id string) error
	ForgetAll(ctx context.Context) error
}

// Config holds the settings for creating a Memory.
type Config struct {
	Backend  Backend
	Embedder Embedder
}

// Backend is the interface for storage backends. queryVector is nil when no
// embedder produced one (e.g. it's unavailable or failed); backends that
// can't search without a vector (e.g. a pure vector database like Chroma)
// should return an error in that case, while backends capable of lexical
// search (e.g. SQLite FTS5) can fall back to matching on query instead.
type Backend interface {
	Upsert(ctx context.Context, id string, vector []float32, content string, metadata map[string]string) error
	Search(ctx context.Context, query string, queryVector []float32, topK int) ([]SearchResult, error)
	Forget(ctx context.Context, id string) error
	ForgetAll(ctx context.Context) error
}

// SearchResult represents a matched fragment from a search.
type SearchResult struct {
	ID       string
	Content  string
	Score    float32
	Metadata map[string]string
}

// Embedder generates embeddings for text.
type Embedder interface {
	Embed(ctx context.Context, text string) ([]float32, error)
	Dimensions() int
}

// memory implements Memory using a Backend and Embedder.
type memory struct {
	backend  Backend
	embedder Embedder
}

// New creates a new Memory with the given config.
func New(cfg Config) (Memory, error) {
	if cfg.Backend == nil {
		return nil, fmt.Errorf("backend is required")
	}
	if cfg.Embedder == nil {
		return nil, fmt.Errorf("embedder is required")
	}
	return &memory{
		backend:  cfg.Backend,
		embedder: cfg.Embedder,
	}, nil
}

func (m *memory) Add(ctx context.Context, fragment Fragment) error {
	if fragment.ID == "" {
		fragment.ID = uuid.New().String()
	}
	if fragment.Metadata == nil {
		fragment.Metadata = make(map[string]string)
	}
	fragment.Metadata["project_id"] = fragment.ProjectID
	fragment.Timestamp = time.Now()

	// A failed embedding doesn't block saving: the backend still has the
	// raw content and can index it for lexical search (e.g. FTS5), so the
	// fragment just won't be reachable by vector similarity later.
	vector, err := m.embedder.Embed(ctx, fragment.Content)
	if err != nil {
		vector = nil
	}
	fragment.Vector = vector

	return m.backend.Upsert(ctx, fragment.ID, fragment.Vector, fragment.Content, fragment.Metadata)
}

func (m *memory) Search(ctx context.Context, query string, topK int) ([]Fragment, error) {
	if topK <= 0 {
		topK = 5
	}

	// Same fallback as Add: if embedding the query fails, search proceeds
	// with no vector so the backend can fall back to lexical matching.
	queryVector, err := m.embedder.Embed(ctx, query)
	if err != nil {
		queryVector = nil
	}

	results, err := m.backend.Search(ctx, query, queryVector, topK)
	if err != nil {
		return nil, fmt.Errorf("search: %w", err)
	}

	fragments := make([]Fragment, len(results))
	for i, r := range results {
		fragments[i] = Fragment{
			ID:        r.ID,
			Content:   r.Content,
			Metadata:  r.Metadata,
			ProjectID: r.Metadata["project_id"],
		}
	}
	return fragments, nil
}

func (m *memory) Forget(ctx context.Context, id string) error {
	return m.backend.Forget(ctx, id)
}

func (m *memory) ForgetAll(ctx context.Context) error {
	return m.backend.ForgetAll(ctx)
}