package database

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"os"
	"sync"

	"git.phc.dm.unipi.it/phc/storage/store"
	"git.phc.dm.unipi.it/phc/storage/utils"
	"golang.org/x/exp/slices"
)

type JsonBucketSettings struct {
	Path string `json:"path"`
}

type jsonBucket struct {
	Name    string   `json:"name"`
	Objects []string `json:"objects"`

	Settings *JsonBucketSettings `json:"settings"`
}

type jsonDB struct {
	mu sync.Mutex

	file string

	PrefixSize int `json:"prefixSize"`

	DashboardState DashboardState         `json:"dashboardState"`
	Buckets        map[string]*jsonBucket `json:"buckets"`

	APIKeys []string `json:"api-keys"`
}

func NewJSON(file string) Database {
	db := &jsonDB{
		file:       file,
		PrefixSize: 2,
		DashboardState: DashboardState{
			Widgets: []MonitorWidget{},
		},
		Buckets: map[string]*jsonBucket{},
		APIKeys: []string{},
	}

	err := db.load()
	if err != nil {
		panic(err)
	}

	return db
}

func (db *jsonDB) setup() error {
	if _, err := os.Stat(db.file); !os.IsNotExist(err) {
		return nil
	}

	log.Printf("missing %q, creating empty database file", db.file)

	f, err := os.Create(db.file)
	defer f.Close()
	if err != nil {
		return err
	}

	enc := json.NewEncoder(f)
	enc.SetIndent("", "    ")
	if err := enc.Encode(&db); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) store() error {
	f, err := os.Create(db.file)
	defer f.Close()
	if err != nil {
		return err
	}

	enc := json.NewEncoder(f)
	enc.SetIndent("", "  ")
	if err := enc.Encode(&db); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) load() error {
	if err := db.setup(); err != nil {
		return err
	}

	f, err := os.Open(db.file)
	defer f.Close()
	if err != nil {
		return err
	}

	if err := json.NewDecoder(f).Decode(&db); err != nil {
		return err
	}

	return nil
}

func withValue[T any](
	transactorFunc func(func() error) error,
	workFunc func() (T, error)) (T, error) {

	var value T

	if err := transactorFunc(func() error {
		var err error
		value, err = workFunc()

		return err
	}); err != nil {
		var zero T
		return zero, err
	}

	return value, nil
}

func (db *jsonDB) writeTransaction(workFunc func() error) error {
	db.mu.Lock()
	defer db.mu.Unlock()

	if err := db.load(); err != nil {
		return err
	}

	if err := workFunc(); err != nil {
		return err
	}

	if err := db.store(); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) readTransaction(transactionFunc func() error) error {
	db.mu.Lock()
	defer db.mu.Unlock()

	if err := db.load(); err != nil {
		return err
	}

	if err := transactionFunc(); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) GetDashboardState() (DashboardState, error) {
	return withValue(db.readTransaction, func() (DashboardState, error) {
		return db.DashboardState, nil
	})
}

func (db *jsonDB) SetDashboardState(state DashboardState) error {
	if err := db.load(); err != nil {
		return err
	}

	db.DashboardState = state

	if err := db.store(); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) CreateAPIKey() (string, error) {
	return withValue(db.writeTransaction, func() (string, error) {
		key := utils.GenerateRandomString(32)
		db.APIKeys = append(db.APIKeys, key)

		return key, nil
	})
}

func (db *jsonDB) AllAPIKeys() ([]string, error) {
	return withValue(db.readTransaction, func() ([]string, error) {
		return db.APIKeys, nil
	})
}

func (db *jsonDB) CheckAPIKey(key string) error {
	return db.readTransaction(func() error {
		if !slices.Contains(db.APIKeys, key) {
			return fmt.Errorf("the given api key %q is invalid", key)
		}

		return nil
	})
}

func (db *jsonDB) RemoveAPIKey(key string) error {
	return db.writeTransaction(func() error {
		i := slices.Index(db.APIKeys, key)
		if i == -1 {
			return fmt.Errorf("the given api key %q is invalid", key)
		}

		db.APIKeys = append(db.APIKeys[:i], db.APIKeys[i+1:]...)

		return nil
	})
}

//
// Bucket Methods
//

func (db *jsonDB) CreateBucket(bucket string, settings any) error {
	return db.writeTransaction(func() error {
		if _, found := db.Buckets[bucket]; found {
			return fmt.Errorf("bucket named %q already present", bucket)
		}

		bi := &jsonBucket{
			Name: bucket,
			Settings: &JsonBucketSettings{
				Path: bucket + "/",
			},
			Objects: []string{},
		}

		if settings != nil {
			bi.Settings = settings.(*JsonBucketSettings)
		}

		if err := store.Create(bi.Settings.Path); err != nil {
			return err
		}

		db.Buckets[bucket] = bi

		return nil
	})
}

func (db *jsonDB) GetBucketSettings(bucket string) (any, error) {
	return withValue(db.readTransaction, func() (any, error) {
		if _, found := db.Buckets[bucket]; !found {
			return nil, fmt.Errorf("bucket named %q not found", bucket)
		}

		return db.Buckets[bucket].Settings, nil
	})
}

func (db *jsonDB) SetBucketSettings(bucket string, settings any) error {
	return db.writeTransaction(func() error {
		b, found := db.Buckets[bucket]
		if !found {
			return fmt.Errorf("bucket named %q not found", bucket)
		}

		b.Settings = settings.(*JsonBucketSettings)

		log.Printf("[Warning] Bucket %q settings changed but bucket migration is not yet implemented (move the folder yourself)", bucket)

		return nil
	})
}

func (db *jsonDB) DeleteBucket(bucket string) error {
	return db.writeTransaction(func() error {
		if _, found := db.Buckets[bucket]; !found {
			return fmt.Errorf("bucket named %q not found", bucket)
		}

		delete(db.Buckets, bucket)

		log.Printf("The bucket named %q was removed but its files are still on disk", bucket)

		return nil
	})
}

func (db *jsonDB) AllBuckets() ([]string, error) {
	return withValue(db.readTransaction, func() ([]string, error) {
		buckets := make([]string, 0, len(db.Buckets))

		for _, b := range db.Buckets {
			buckets = append(buckets, b.Name)
		}

		return buckets, nil
	})
}

func (db *jsonDB) CreateBucketObject(bucket string, r io.Reader) (string, error) {
	return withValue(db.writeTransaction, func() (string, error) {
		b, found := db.Buckets[bucket]
		if !found {
			return "", fmt.Errorf("bucket named %q not found", bucket)
		}

		id, err := store.CreateObject(b.Settings.Path, db.PrefixSize, r)
		if err != nil {
			return "", err
		}

		b.Objects = append(b.Objects, id)

		return id, err
	})
}

func (db *jsonDB) SetBucketObject(bucket, id string, r io.Reader) error {
	return db.writeTransaction(func() error {
		b, found := db.Buckets[bucket]
		if !found {
			return fmt.Errorf("bucket named %q not found", bucket)
		}

		return store.UpdateObject(b.Settings.Path, db.PrefixSize, id, r)
	})
}

func (db *jsonDB) GetBucketObject(bucket, id string, w io.Writer) error {
	return db.readTransaction(func() error {
		b, found := db.Buckets[bucket]
		if !found {
			return fmt.Errorf("bucket named %q not found", bucket)
		}

		return store.ReadObject(b.Settings.Path, db.PrefixSize, id, w)
	})
}

func (db *jsonDB) DeleteBucketObject(bucket, id string) error {
	return db.writeTransaction(func() error {
		b, found := db.Buckets[bucket]
		if !found {
			return fmt.Errorf("bucket named %q not found", bucket)
		}

		if err := store.DeleteObject(b.Settings.Path, db.PrefixSize, id); err != nil {
			return err
		}

		i := slices.Index(b.Objects, id)
		b.Objects = append(b.Objects[:i], b.Objects[i+1:]...)

		return nil
	})
}

func (db *jsonDB) AllBucketObjects(bucket string) ([]string, error) {
	return withValue(db.writeTransaction, func() ([]string, error) {
		b, found := db.Buckets[bucket]
		if !found {
			return nil, fmt.Errorf("bucket named %q not found", bucket)
		}

		objects, err := store.AllObjects(b.Settings.Path)
		if err != nil {
			return nil, err
		}

		b.Objects = objects

		return b.Objects, nil
	})
}