package ocean

import (
	"encoding/json"
	"os"
	"path/filepath"
	"reflect"
	"sync"
)

type Collection[T any] interface {
	All() <-chan *T
	Clear()
	Delete(key string)
	Exists(key string) bool
	Filter(func(*T) bool) <-chan *T
	Get(key string) (value *T, err error)
	Set(key string, value *T)
}

// collection is a hash map of homogeneous data.
type collection[T any] struct {
	data      sync.Map
	name      string
	directory string
}

// New creates a new collection with the given name.
func New[T any](directories ...string) (*collection[T], error) {
	name := reflect.TypeOf((*T)(nil)).Elem().Name()
	home, err := os.UserHomeDir()

	if err != nil {
		return nil, err
	}

	directories = append([]string{home, ".ocean"}, directories...)
	directories = append(directories, name)
	directory := filepath.Join(directories...)
	err = os.MkdirAll(directory, 0700)

	if err != nil {
		return nil, err
	}

	c := &collection[T]{
		name:      directories[len(directories)-1],
		directory: directory,
	}

	return c, c.loadFromDisk()
}

// All returns a channel of all objects in the collection.
func (c *collection[T]) All() <-chan *T {
	channel := make(chan *T)

	go func() {
		c.data.Range(func(key, value any) bool {
			channel <- value.(*T)
			return true
		})

		close(channel)
	}()

	return channel
}

// Filter returns a channel of all objects that pass the given filter function.
func (c *collection[T]) Filter(filter func(*T) bool) <-chan *T {
	channel := make(chan *T)

	go func() {
		c.data.Range(func(key, value any) bool {
			if filter(value.(*T)) {
				channel <- value.(*T)
			}

			return true
		})

		close(channel)
	}()

	return channel
}

// Get returns the value for the given key.
func (c *collection[T]) Get(key string) (*T, error) {
	value, exists := c.data.Load(key)

	if !exists {
		return nil, &KeyNotFoundError{Key: key}
	}

	return value.(*T), nil
}

// Set sets the value for the given key.
func (c *collection[T]) Set(key string, value *T) {
	c.data.Store(key, value)
	err := c.writeFileToDisk(key, value)

	if err != nil {
		panic(err)
	}
}

// Delete deletes a key from the collection.
func (c *collection[T]) Delete(key string) {
	if !c.Exists(key) {
		return
	}

	c.data.Delete(key)
	os.Remove(c.keyFile(key))
}

// Exists returns whether or not the key exists.
func (c *collection[T]) Exists(key string) bool {
	_, exists := c.data.Load(key)
	return exists
}

// Clear deletes all objects from the collection.
func (c *collection[T]) Clear() {
	c.data.Range(func(key, value any) bool {
		c.Delete(key.(string))
		return true
	})
}

// keyFile returns the file path for the given key.
func (c *collection[T]) keyFile(key string) string {
	return filepath.Join(c.directory, key)
}

// loadFromDisk loads the collection data from the disk.
func (c *collection[T]) loadFromDisk() error {
	file, err := os.Open(c.directory)

	if err != nil {
		return err
	}

	files, err := file.Readdirnames(0)

	for _, key := range files {
		fileError := c.loadFileFromDisk(key)

		if fileError != nil {
			return fileError
		}
	}

	if err != nil {
		return err
	}

	return file.Close()
}

// loadFileFromDisk loads a single file from the disk.
func (c *collection[T]) loadFileFromDisk(key string) error {
	file, err := os.Open(filepath.Join(c.directory, key))

	if err != nil {
		return err
	}

	value := new(T)
	decoder := json.NewDecoder(file)
	err = decoder.Decode(value)

	if err != nil {
		file.Close()
		return err
	}

	c.data.Store(key, value)
	return file.Close()
}

// writeFileToDisk writes the value for the key to disk as a JSON file.
func (c *collection[T]) writeFileToDisk(key string, value *T) error {
	fileName := c.keyFile(key)
	file, err := os.Create(fileName)

	if err != nil {
		return err
	}

	encoder := json.NewEncoder(file)
	err = encoder.Encode(value)

	if err != nil {
		file.Close()
		return err
	}

	return file.Close()
}