package server

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"

	"github.com/nspcc-dev/neo-go/pkg/core/storage"
)

type dump []blockDump

type blockDump struct {
	Block   uint32              `json:"block"`
	Size    int                 `json:"size"`
	Storage []storage.Operation `json:"storage"`
}

func newDump() *dump {
	return new(dump)
}

func (d *dump) add(index uint32, batch *storage.MemBatch) {
	ops := storage.BatchToOperations(batch)
	*d = append(*d, blockDump{
		Block:   index,
		Size:    len(ops),
		Storage: ops,
	})
}

func (d *dump) tryPersist(prefix string, index uint32) error {
	if len(*d) == 0 {
		return nil
	}
	path, err := getPath(prefix, index)
	if err != nil {
		return err
	}
	old, err := readFile(path)
	if err == nil {
		*old = append(*old, *d...)
	} else {
		old = d
	}
	f, err := os.Create(path)
	if err != nil {
		return err
	}
	defer f.Close()

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

	*d = (*d)[:0]

	return nil
}

func readFile(path string) (*dump, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	d := newDump()
	if err := json.Unmarshal(data, d); err != nil {
		return nil, err
	}
	return d, err
}

// getPath returns filename for storing blocks up to index.
// Directory structure is the following:
// https://github.com/NeoResearch/neo-storage-audit#folder-organization-where-to-find-the-desired-block
// Dir `BlockStorage_$DIRNO` contains blocks up to $DIRNO (from $DIRNO-100k)
// Inside it there are files grouped by 1k blocks.
// File dump-block-$FILENO.json contains blocks from $FILENO-999, $FILENO
// Example: file `BlockStorage_100000/dump-block-6000.json` contains blocks from 5001 to 6000.
func getPath(prefix string, index uint32) (string, error) {
	dirN := ((index + 99999) / 100000) * 100000
	dir := fmt.Sprintf("BlockStorage_%d", dirN)

	path := filepath.Join(prefix, dir)
	info, err := os.Stat(path)
	if os.IsNotExist(err) {
		err := os.MkdirAll(path, os.ModePerm)
		if err != nil {
			return "", err
		}
	} else if !info.IsDir() {
		return "", fmt.Errorf("file `%s` is not a directory", path)
	}

	fileN := ((index + 999) / 1000) * 1000
	file := fmt.Sprintf("dump-block-%d.json", fileN)
	return filepath.Join(path, file), nil
}