/*
   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 (
	"bytes"
	"fmt"
	"sort"
	"strconv"

	"github.com/c2h5oh/datasize"
	"github.com/ledgerwatch/erigon-lib/kv"
)

const (
	//SliceBuffer - just simple slice w
	SortableSliceBuffer = iota
	//SortableAppendBuffer - map[k] [v1 v2 v3]
	SortableAppendBuffer
	// SortableOldestAppearedBuffer - buffer that keeps only the oldest entries.
	// if first v1 was added under key K, then v2; only v1 will stay
	SortableOldestAppearedBuffer

	BufIOSize = 64 * 4096 // 64 pages | default is 1 page | increasing further doesn't show speedup on SSD
)

var BufferOptimalSize = 256 * datasize.MB /*  var because we want to sometimes change it from tests or command-line flags */

type Buffer interface {
	Put(k, v []byte)
	Get(i int) sortableBufferEntry
	Len() int
	Reset()
	GetEntries() []sortableBufferEntry
	Sort()
	CheckFlushSize() bool
	SetComparator(cmp kv.CmpFunc)
}

type sortableBufferEntry struct {
	key   []byte
	value []byte
}

var (
	_ Buffer = &sortableBuffer{}
	_ Buffer = &appendSortableBuffer{}
	_ Buffer = &oldestEntrySortableBuffer{}
)

func NewSortableBuffer(bufferOptimalSize datasize.ByteSize) *sortableBuffer {
	return &sortableBuffer{
		entries:     make([]sortableBufferEntry, 0),
		size:        0,
		optimalSize: int(bufferOptimalSize.Bytes()),
	}
}

type sortableBuffer struct {
	entries     []sortableBufferEntry
	size        int
	optimalSize int
	comparator  kv.CmpFunc
}

func (b *sortableBuffer) Put(k, v []byte) {
	b.size += len(k)
	b.size += len(v)
	b.entries = append(b.entries, sortableBufferEntry{k, v})
}

func (b *sortableBuffer) Size() int {
	return b.size
}

func (b *sortableBuffer) Len() int {
	return len(b.entries)
}

func (b *sortableBuffer) SetComparator(cmp kv.CmpFunc) {
	b.comparator = cmp
}

func (b *sortableBuffer) Less(i, j int) bool {
	if b.comparator != nil {
		return b.comparator(b.entries[i].key, b.entries[j].key, b.entries[i].value, b.entries[j].value) < 0
	}
	return bytes.Compare(b.entries[i].key, b.entries[j].key) < 0
}

func (b *sortableBuffer) Swap(i, j int) {
	b.entries[i], b.entries[j] = b.entries[j], b.entries[i]
}

func (b *sortableBuffer) Get(i int) sortableBufferEntry {
	return b.entries[i]
}

func (b *sortableBuffer) Reset() {
	b.entries = nil
	b.size = 0
}
func (b *sortableBuffer) Sort() {
	sort.Stable(b)
}

func (b *sortableBuffer) GetEntries() []sortableBufferEntry {
	return b.entries
}

func (b *sortableBuffer) CheckFlushSize() bool {
	return b.size >= b.optimalSize
}

func NewAppendBuffer(bufferOptimalSize datasize.ByteSize) *appendSortableBuffer {
	return &appendSortableBuffer{
		entries:     make(map[string][]byte),
		size:        0,
		optimalSize: int(bufferOptimalSize.Bytes()),
	}
}

type appendSortableBuffer struct {
	entries     map[string][]byte
	size        int
	optimalSize int
	sortedBuf   []sortableBufferEntry
	comparator  kv.CmpFunc
}

func (b *appendSortableBuffer) Put(k, v []byte) {
	ks := string(k)
	stored, ok := b.entries[ks]
	if !ok {
		b.size += len(k)
	}
	b.size += len(v)
	stored = append(stored, v...)
	b.entries[ks] = stored
}

func (b *appendSortableBuffer) SetComparator(cmp kv.CmpFunc) {
	b.comparator = cmp
}

func (b *appendSortableBuffer) Size() int {
	return b.size
}

func (b *appendSortableBuffer) Len() int {
	return len(b.entries)
}
func (b *appendSortableBuffer) Sort() {
	for i := range b.entries {
		b.sortedBuf = append(b.sortedBuf, sortableBufferEntry{key: []byte(i), value: b.entries[i]})
	}
	sort.Stable(b)
}

func (b *appendSortableBuffer) Less(i, j int) bool {
	if b.comparator != nil {
		return b.comparator(b.sortedBuf[i].key, b.sortedBuf[j].key, b.sortedBuf[i].value, b.sortedBuf[j].value) < 0
	}
	return bytes.Compare(b.sortedBuf[i].key, b.sortedBuf[j].key) < 0
}

func (b *appendSortableBuffer) Swap(i, j int) {
	b.sortedBuf[i], b.sortedBuf[j] = b.sortedBuf[j], b.sortedBuf[i]
}

func (b *appendSortableBuffer) Get(i int) sortableBufferEntry {
	return b.sortedBuf[i]
}
func (b *appendSortableBuffer) Reset() {
	b.sortedBuf = nil
	b.entries = make(map[string][]byte)
	b.size = 0
}

func (b *appendSortableBuffer) GetEntries() []sortableBufferEntry {
	return b.sortedBuf
}

func (b *appendSortableBuffer) CheckFlushSize() bool {
	return b.size >= b.optimalSize
}

func NewOldestEntryBuffer(bufferOptimalSize datasize.ByteSize) *oldestEntrySortableBuffer {
	return &oldestEntrySortableBuffer{
		entries:     make(map[string][]byte),
		size:        0,
		optimalSize: int(bufferOptimalSize.Bytes()),
	}
}

type oldestEntrySortableBuffer struct {
	entries     map[string][]byte
	size        int
	optimalSize int
	sortedBuf   []sortableBufferEntry
	comparator  kv.CmpFunc
}

func (b *oldestEntrySortableBuffer) SetComparator(cmp kv.CmpFunc) {
	b.comparator = cmp
}

func (b *oldestEntrySortableBuffer) Put(k, v []byte) {
	ks := string(k)
	_, ok := b.entries[ks]
	if ok {
		// if we already had this entry, we are going to keep it and ignore new value
		return
	}

	b.size += len(k)*2 + len(v)
	b.entries[ks] = v
}

func (b *oldestEntrySortableBuffer) Size() int {
	return b.size
}

func (b *oldestEntrySortableBuffer) Len() int {
	return len(b.entries)
}

func (b *oldestEntrySortableBuffer) Sort() {
	for k, v := range b.entries {
		b.sortedBuf = append(b.sortedBuf, sortableBufferEntry{key: []byte(k), value: v})
	}
	sort.Stable(b)
}

func (b *oldestEntrySortableBuffer) Less(i, j int) bool {
	if b.comparator != nil {
		return b.comparator(b.sortedBuf[i].key, b.sortedBuf[j].key, b.sortedBuf[i].value, b.sortedBuf[j].value) < 0
	}
	return bytes.Compare(b.sortedBuf[i].key, b.sortedBuf[j].key) < 0
}

func (b *oldestEntrySortableBuffer) Swap(i, j int) {
	b.sortedBuf[i], b.sortedBuf[j] = b.sortedBuf[j], b.sortedBuf[i]
}

func (b *oldestEntrySortableBuffer) Get(i int) sortableBufferEntry {
	return b.sortedBuf[i]
}
func (b *oldestEntrySortableBuffer) Reset() {
	b.sortedBuf = nil
	b.entries = make(map[string][]byte)
	b.size = 0
}

func (b *oldestEntrySortableBuffer) GetEntries() []sortableBufferEntry {
	return b.sortedBuf
}

func (b *oldestEntrySortableBuffer) CheckFlushSize() bool {
	return b.size >= b.optimalSize
}

func getBufferByType(tp int, size datasize.ByteSize) Buffer {
	switch tp {
	case SortableSliceBuffer:
		return NewSortableBuffer(size)
	case SortableAppendBuffer:
		return NewAppendBuffer(size)
	case SortableOldestAppearedBuffer:
		return NewOldestEntryBuffer(size)
	default:
		panic("unknown buffer type " + strconv.Itoa(tp))
	}
}

func getTypeByBuffer(b Buffer) int {
	switch b.(type) {
	case *sortableBuffer:
		return SortableSliceBuffer
	case *appendSortableBuffer:
		return SortableAppendBuffer
	case *oldestEntrySortableBuffer:
		return SortableOldestAppearedBuffer
	default:
		panic(fmt.Sprintf("unknown buffer type: %T ", b))
	}
}