/*
   Copyright 2021 Erigon contributors

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package etl

import (
	"bufio"
	"encoding/binary"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"runtime"

	"github.com/ledgerwatch/erigon-lib/common"
	"github.com/ledgerwatch/log/v3"
)

type dataProvider interface {
	Next(keyBuf, valBuf []byte) ([]byte, []byte, error)
	Dispose() uint64 // Safe for repeated call, doesn't return error - means defer-friendly
}

type fileDataProvider struct {
	file       *os.File
	reader     io.Reader
	byteReader io.ByteReader // Different interface to the same object as reader
}

// FlushToDisk - `doFsync` is true only for 'critical' collectors (which should not loose).
func FlushToDisk(b Buffer, tmpdir string, doFsync bool, lvl log.Lvl) (dataProvider, error) {
	if b.Len() == 0 {
		return nil, nil
	}
	// if we are going to create files in the system temp dir, we don't need any
	// subfolders.
	if tmpdir != "" {
		if err := os.MkdirAll(tmpdir, 0755); err != nil {
			return nil, err
		}
	}

	bufferFile, err := ioutil.TempFile(tmpdir, "erigon-sortable-buf-")
	if err != nil {
		return nil, err
	}
	if doFsync {
		defer bufferFile.Sync() //nolint:errcheck
	}

	w := bufio.NewWriterSize(bufferFile, BufIOSize)
	defer w.Flush() //nolint:errcheck

	defer func() {
		b.Reset() // run it after buf.flush and file.sync
		var m runtime.MemStats
		if lvl >= log.LvlInfo {
			common.ReadMemStats(&m)
		}
		log.Log(lvl,
			"Flushed buffer file",
			"name", bufferFile.Name(),
			"alloc", common.ByteCount(m.Alloc), "sys", common.ByteCount(m.Sys))
	}()

	if err = b.Write(w); err != nil {
		return nil, fmt.Errorf("error writing entries to disk: %w", err)
	}

	return &fileDataProvider{file: bufferFile, reader: nil}, nil
}

func (p *fileDataProvider) Next(keyBuf, valBuf []byte) ([]byte, []byte, error) {
	if p.reader == nil {
		_, err := p.file.Seek(0, 0)
		if err != nil {
			return nil, nil, err
		}
		r := bufio.NewReaderSize(p.file, BufIOSize)
		p.reader = r
		p.byteReader = r

	}
	return readElementFromDisk(p.reader, p.byteReader, keyBuf, valBuf)
}

func (p *fileDataProvider) Dispose() uint64 {
	info, _ := os.Stat(p.file.Name())
	_ = p.file.Close()
	_ = os.Remove(p.file.Name())
	if info == nil {
		return 0
	}
	return uint64(info.Size())
}

func (p *fileDataProvider) String() string {
	return fmt.Sprintf("%T(file: %s)", p, p.file.Name())
}

func readElementFromDisk(r io.Reader, br io.ByteReader, keyBuf, valBuf []byte) ([]byte, []byte, error) {
	n, err := binary.ReadUvarint(br)
	if err != nil {
		return nil, nil, err
	}
	if n > 0 {
		// Reallocate the slice or extend it if there is enough capacity
		if len(keyBuf)+int(n) > cap(keyBuf) {
			newKeyBuf := make([]byte, len(keyBuf)+int(n))
			copy(newKeyBuf, keyBuf)
			keyBuf = newKeyBuf
		} else {
			keyBuf = keyBuf[:len(keyBuf)+int(n)]
		}
		if _, err = io.ReadFull(r, keyBuf[len(keyBuf)-int(n):]); err != nil {
			return nil, nil, err
		}
	}
	if n, err = binary.ReadUvarint(br); err != nil {
		return nil, nil, err
	}
	if n > 0 {
		// Reallocate the slice or extend it if there is enough capacity
		if len(valBuf)+int(n) > cap(valBuf) {
			newValBuf := make([]byte, len(valBuf)+int(n))
			copy(newValBuf, valBuf)
			valBuf = newValBuf
		} else {
			valBuf = valBuf[:len(valBuf)+int(n)]
		}
		if _, err = io.ReadFull(r, valBuf[len(valBuf)-int(n):]); err != nil {
			return nil, nil, err
		}
	}
	return keyBuf, valBuf, err
}

type memoryDataProvider struct {
	buffer       Buffer
	currentIndex int
}

func KeepInRAM(buffer Buffer) dataProvider {
	return &memoryDataProvider{buffer, 0}
}

func (p *memoryDataProvider) Next(keyBuf, valBuf []byte) ([]byte, []byte, error) {
	if p.currentIndex >= p.buffer.Len() {
		return nil, nil, io.EOF
	}
	key, value := p.buffer.Get(p.currentIndex, keyBuf, valBuf)
	p.currentIndex++
	return key, value, nil
}

func (p *memoryDataProvider) Dispose() uint64 {
	return 0 /* doesn't take space on disk */
}

func (p *memoryDataProvider) String() string {
	return fmt.Sprintf("%T(buffer.Len: %d)", p, p.buffer.Len())
}