package database

import (
	"ai-code-assistant/pkg/config"
	"context"
	"embed"
	"errors"
	"fmt"
	"github.com/go-git/go-billy/v5/osfs"
	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/plumbing/cache"
	"github.com/go-git/go-git/v5/storage/filesystem"
	"github.com/golang-migrate/migrate/v4"
	_ "github.com/golang-migrate/migrate/v4/database/postgres"
	"github.com/golang-migrate/migrate/v4/source/iofs"
	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
	_ "github.com/lib/pq"
	"github.com/tmc/langchaingo/embeddings"
	"github.com/tmc/langchaingo/vectorstores"
	"github.com/tmc/langchaingo/vectorstores/pgvector"
	"path/filepath"
	"strconv"
)

//go:embed migrations
var migrations embed.FS

type contextKey string

const (
	contextKeyDB contextKey = "db"
)

func preparedStatements() map[string]string {
	return map[string]string{
		"get_repo":              `SELECT repo_id FROM repos WHERE repo_hash = $1 AND repo_path = $2`,
		"insert_repo":           `INSERT INTO repos (repo_id, repo_hash, repo_path) VALUES ($1, $2, $3) ON CONFLICT DO NOTHING`,
		"get_chunk":             `SELECT document FROM langchain_pg_embedding WHERE JSON_EXTRACT_PATH_TEXT(cmetadata, 'chunk_id')=$1 AND JSON_EXTRACT_PATH_TEXT(cmetadata, 'file_path')=$2 AND JSON_EXTRACT_PATH_TEXT(cmetadata, 'repo_id')=$3`,
		"clear_chunks_for_repo": `DELETE FROM langchain_pg_embedding WHERE JSON_EXTRACT_PATH_TEXT(cmetadata, 'repo_id')=$1`,
	}
}

// Database is a helper that abstracts access to the database as well as handles migrations.
type Database struct {
	pool *pgxpool.Pool
}

// db gets a references to the connection pool.
func (db *Database) db(ctx context.Context) (*pgxpool.Conn, error) {
	conn, err := db.pool.Acquire(ctx)
	if err != nil {
		return nil, err
	}

	for nm, query := range preparedStatements() {
		if _, err := conn.Conn().Prepare(ctx, nm, query); err != nil {
			return nil, fmt.Errorf("problem preparing statement %s: %w", nm, err)
		}
	}

	return conn, nil
}

// UpsertRepo will ensure we have a repository reference for this particular repository path and HEAD reference.
func (db *Database) UpsertRepo(ctx context.Context, repoPath string) (string, bool, error) {
	gitPath := osfs.New(filepath.Join(repoPath, ".git"))

	gitRepo, err := git.Open(filesystem.NewStorage(gitPath, cache.NewObjectLRUDefault()), gitPath)
	if err != nil {
		return "", false, err
	}

	headRef, err := gitRepo.Head()
	if err != nil {
		return "", false, err
	}

	conn, err := db.db(ctx)
	if err != nil {
		return "", false, err
	}
	defer conn.Release()

	var id string

	if err := conn.QueryRow(ctx, "get_repo", headRef.Hash().String(), repoPath).Scan(&id); err == nil {
		return id, true, nil
	} else if !errors.Is(err, pgx.ErrNoRows) {
		return "", false, err
	}

	id = uuid.NewString()

	if _, err := conn.Exec(ctx, "insert_repo", id, headRef.Hash().String(), repoPath); err != nil {
		return "", false, err
	}

	return id, false, nil
}

// GetChunk will get a specified chunk from the database.
func (db *Database) GetChunk(ctx context.Context, chunkID int, path, repoID string) (string, error) {
	conn, err := db.db(ctx)
	if err != nil {
		return "", err
	}
	defer conn.Release()

	var chunk string

	chunkIDStr := strconv.FormatInt(int64(chunkID), 10)

	if err := conn.QueryRow(ctx, "get_chunk", chunkIDStr, path, repoID).Scan(&chunk); err != nil {
		return "", err
	}

	return chunk, nil
}

// ClearChunkIndex will clear all embeddings for a particular repo ID.
func (db *Database) ClearChunkIndex(ctx context.Context, repoID string) error {
	conn, err := db.db(ctx)
	if err != nil {
		return err
	}
	defer conn.Release()

	if _, err := conn.Exec(ctx, "clear_chunks_for_repo", repoID); err != nil {
		return err
	}

	return nil
}

// GetVectorStore gets a vector store capable of storing and searching embeddings.
func (db *Database) GetVectorStore(ctx context.Context, embedder embeddings.Embedder) (vectorstores.VectorStore, func(), error) {
	conn, err := db.db(ctx)
	if err != nil {
		return nil, nil, err
	}

	vectorStore, err := pgvector.New(ctx,
		pgvector.WithConn(conn),
		pgvector.WithEmbedder(embedder),
		pgvector.WithCollectionName("file_chunks"),
	)
	if err != nil {
		return nil, nil, err
	}

	return vectorStore, func() {
		conn.Release()
	}, nil
}

// GetChunkContext will get a specified chunk and surrounding context based on some amount of distance.
func (db *Database) GetChunkContext(ctx context.Context, chunkID, distance int, path, repoID string) (string, error) {
	minChunk := chunkID - distance
	if minChunk < 0 {
		minChunk = 0
	}

	chunkContext := ""

	for chunkID := minChunk; chunkID < chunkID+(distance*2); chunkID++ {
		chunk, err := db.GetChunk(ctx, chunkID, path, repoID)
		if err == nil {
			chunkContext += chunk
		} else if !errors.Is(err, pgx.ErrNoRows) {
			return "", err
		} else {
			break
		}
	}

	return chunkContext, nil
}

// FromConfig generates a new Database from a passed in configuration. Used for bootstrapping.
func FromConfig(ctx context.Context, cfg *config.Configuration) (*Database, error) {
	migFS, err := iofs.New(migrations, "migrations")
	if err != nil {
		return nil, err
	}

	mig, err := migrate.NewWithSourceInstance("iofs", migFS, cfg.Database.ConnString)
	if err != nil {
		return nil, err
	}

	if err := mig.Up(); err != nil && !errors.Is(err, migrate.ErrNoChange) {
		return nil, fmt.Errorf("problem performing database migrations: %w", err)
	}

	pool, err := pgxpool.New(ctx, cfg.Database.ConnString)
	if err != nil {
		return nil, err
	}

	return &Database{pool: pool}, nil
}

// FromContext will retrieve the Database from a Context where WrapContext was used to embed the database in the context.
func FromContext(ctx context.Context) *Database {
	return ctx.Value(contextKeyDB).(*Database)
}

// WrapContext embeds a Database inside a Context so it can be passed to functions.
func WrapContext(ctx context.Context, cfg *Database) context.Context {
	return context.WithValue(ctx, contextKeyDB, cfg)
}