package store

import (
	"fmt"
	"io"
	"os"
	"path"

	"git.phc.dm.unipi.it/phc/storage/utils"
)

type Store interface {
	// Create a new object by reading from the given io.Reader and returns its new id
	Create(r io.Reader) (string, error)

	// Read the object identified by "id" into the given io.Writer
	Read(id string, w io.Writer) error

	// Update the object identified by "id" by reading from the given io.Reader
	Update(id string, r io.Reader) error

	// Delete the object with the given id
	Delete(id string) error
}

//
// In Memory Byte Store
//

type memStore struct {
	objects map[string][]byte
}

func NewMemStore() Store {
	return &memStore{
		objects: map[string][]byte{},
	}
}

// Create a new object by reading from the given io.Reader and returns its new id
func (m *memStore) Create(r io.Reader) (string, error) {
	id := utils.GenerateRandomString(16)

	data, err := io.ReadAll(r)
	if err != nil {
		return "", err
	}

	m.objects[id] = data
	return id, nil
}

// Read the object identified by "id" into the given io.Writer
func (m *memStore) Read(id string, w io.Writer) error {
	data, found := m.objects[id]
	if !found {
		return fmt.Errorf("object with id %q not found", id)
	}

	if _, err := w.Write(data); err != nil {
		return err
	}

	return nil
}

// Update the object identified by "id" by reading from the given io.Reader
func (m *memStore) Update(id string, r io.Reader) error {
	data, err := io.ReadAll(r)
	if err != nil {
		return err
	}

	m.objects[id] = data
	return nil
}

// Delete the object with the given id
func (m *memStore) Delete(id string) error {
	if _, found := m.objects[id]; !found {
		return fmt.Errorf("object with id %q not found", id)
	}

	delete(m.objects, id)

	return nil
}

//
// Dir Store
//

type DirStore struct {
	// BaseDir is the root folder of this Store
	BaseDir string

	// Prefix is the number of letters to use for the first layer of folders
	Prefix int
}

func (d *DirStore) split(id string) (prefix, rest string) {
	return id[:d.Prefix], id[d.Prefix:]
}

func (d *DirStore) Create(r io.Reader) (string, error) {
	id := utils.GenerateRandomString(16)
	prefix, rest := d.split(id)

	os.MkdirAll(path.Join(d.BaseDir, prefix), os.ModePerm)

	f, err := os.Create(path.Join(d.BaseDir, prefix, rest))
	if err != nil {
		return "", err
	}

	if _, err := io.Copy(f, r); err != nil {
		return "", err
	}

	return id, nil
}

func (d *DirStore) Read(id string, w io.Writer) error {
	prefix, rest := d.split(id)

	f, err := os.Open(path.Join(d.BaseDir, prefix, rest))
	if err != nil {
		return err
	}

	if _, err := io.Copy(w, f); err != nil {
		return err
	}

	return nil
}

func (d *DirStore) Update(id string, r io.Reader) error {
	panic("TODO: Not implemented")
}

func (d *DirStore) Delete(id string) error {
	panic("TODO: Not implemented")
}