package cache

import (
	"bytes"
	"encoding/gob"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	bolt "go.etcd.io/bbolt"

	"git.cw.tr/mukan-network/mukan-ignite/ignite/pkg/errors"
)

var ErrorNotFound = errors.New("no value was found with the provided key")

// Storage is meant to be passed around and used by the New function (which provides namespacing and type-safety).
type Storage struct {
	path, version string
}

// Cache is a namespaced and type-safe key-value store.
type Cache[T any] struct {
	storage   Storage
	namespace string
}

// NewStorage sets up the storage needed for later cache usage
// path is the full path (including filename) to the database file to use.
// It does not need to be closed as this happens automatically in each call to the cache.
func NewStorage(path string, options ...StorageOption) (Storage, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return Storage{}, err
	}

	s := Storage{path: path}
	for _, apply := range options {
		apply(&s)
	}
	return s, nil
}

// New creates a namespaced and typesafe key-value Cache.
func New[T any](storage Storage, namespace string) Cache[T] {
	if storage.version != "" {
		namespace = fmt.Sprint(storage.version, namespace)
	}

	return Cache[T]{
		storage:   storage,
		namespace: namespace,
	}
}

// Key creates a single composite key from a list of keyParts.
func Key(keyParts ...string) string {
	return strings.Join(keyParts, "")
}

// Clear deletes all namespaces and cached values.
func (s Storage) Clear() error {
	db, err := openDB(s.path)
	if err != nil {
		return err
	}
	defer db.Close()

	return db.Update(func(tx *bolt.Tx) error {
		return tx.ForEach(func(name []byte, _ *bolt.Bucket) error {
			return tx.DeleteBucket(name)
		})
	})
}

// Put sets key to value within the namespace
// If the key already exists, it will be overwritten.
func (c Cache[T]) Put(key string, value T) error {
	db, err := openDB(c.storage.path)
	if err != nil {
		return err
	}
	defer db.Close()

	var buf bytes.Buffer
	encoder := gob.NewEncoder(&buf)
	if err := encoder.Encode(value); err != nil {
		return err
	}
	result := buf.Bytes()

	return db.Update(func(tx *bolt.Tx) error {
		b, err := tx.CreateBucketIfNotExists([]byte(c.namespace))
		if err != nil {
			return err
		}
		return b.Put([]byte(key), result)
	})
}

// Get fetches the value of key within the namespace.
// If no value exists, it will return found == false.
func (c Cache[T]) Get(key string) (val T, err error) {
	db, err := openDB(c.storage.path)
	if err != nil {
		return val, err
	}
	defer db.Close()

	err = db.View(func(tx *bolt.Tx) error {
		b := tx.Bucket([]byte(c.namespace))
		if b == nil {
			return ErrorNotFound
		}
		c := b.Cursor()
		if k, v := c.Seek([]byte(key)); bytes.Equal(k, []byte(key)) {
			if v == nil {
				return ErrorNotFound
			}

			var decodedVal T
			d := gob.NewDecoder(bytes.NewReader(v))
			if err := d.Decode(&decodedVal); err != nil {
				return err
			}

			val = decodedVal
		} else {
			return ErrorNotFound
		}

		return nil
	})

	return val, err
}

// Delete removes a value for key within the namespace.
func (c Cache[T]) Delete(key string) error {
	db, err := openDB(c.storage.path)
	if err != nil {
		return err
	}
	defer db.Close()

	return db.Update(func(tx *bolt.Tx) error {
		b := tx.Bucket([]byte(c.namespace))
		if b == nil {
			return nil
		}

		return b.Delete([]byte(key))
	})
}

func openDB(path string) (*bolt.DB, error) {
	return bolt.Open(path, 0o640, &bolt.Options{Timeout: 1 * time.Minute})
}