/*
   Copyright 2022 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 kv

import (
	"context"
	"fmt"
	"os"
	"sync"
	"sync/atomic"
	"time"

	"github.com/erigontech/mdbx-go/mdbx"
	"github.com/ledgerwatch/erigon-lib/common"
)

func DefaultPageSize() uint64 {
	osPageSize := os.Getpagesize()
	if osPageSize < 4096 { // reduce further may lead to errors (because some data is just big)
		osPageSize = 4096
	} else if osPageSize > mdbx.MaxPageSize {
		osPageSize = mdbx.MaxPageSize
	}
	osPageSize = osPageSize / 4096 * 4096 // ensure it's rounded
	return uint64(osPageSize)
}

// BigChunks - read `table` by big chunks - restart read transaction after each 1 minutes
func BigChunks(db RoDB, table string, from []byte, walker func(tx Tx, k, v []byte) (bool, error)) error {
	rollbackEvery := time.NewTicker(1 * time.Minute)

	var stop bool
	for !stop {
		if err := db.View(context.Background(), func(tx Tx) error {
			c, err := tx.Cursor(table)
			if err != nil {
				return err
			}
			defer c.Close()

			k, v, err := c.Seek(from)
		Loop:
			for ; k != nil; k, v, err = c.Next() {
				if err != nil {
					return err
				}

				// break loop before walker() call, to make sure all keys are received by walker() exactly once
				select {
				case <-rollbackEvery.C:

					break Loop
				default:
				}

				ok, err := walker(tx, k, v)
				if err != nil {
					return err
				}
				if !ok {
					stop = true
					break
				}
			}

			if k == nil {
				stop = true
			}

			from = common.Copy(k) // next transaction will start from this key

			return nil
		}); err != nil {
			return err
		}
	}
	return nil
}

var (
	bytesTrue  = []byte{1}
	bytesFalse = []byte{0}
)

func bytes2bool(in []byte) bool {
	if len(in) < 1 {
		return false
	}
	return in[0] == 1
}

var ErrChanged = fmt.Errorf("key must not change")

// EnsureNotChangedBool - used to store immutable config flags in db. protects from human mistakes
func EnsureNotChangedBool(tx GetPut, bucket string, k []byte, value bool) (ok, enabled bool, err error) {
	vBytes, err := tx.GetOne(bucket, k)
	if err != nil {
		return false, enabled, err
	}
	if vBytes == nil {
		if value {
			vBytes = bytesTrue
		} else {
			vBytes = bytesFalse
		}
		if err := tx.Put(bucket, k, vBytes); err != nil {
			return false, enabled, err
		}
	}

	enabled = bytes2bool(vBytes)
	return value == enabled, enabled, nil
}

func GetBool(tx Getter, bucket string, k []byte) (enabled bool, err error) {
	vBytes, err := tx.GetOne(bucket, k)
	if err != nil {
		return false, err
	}
	return bytes2bool(vBytes), nil
}

func ReadAhead(ctx context.Context, db RoDB, progress *atomic.Bool, table string, from []byte, amount uint32) (clean func()) {
	if db == nil {
		return func() {}
	}
	if ok := progress.CompareAndSwap(false, true); !ok {
		return func() {}
	}
	ctx, cancel := context.WithCancel(ctx)
	wg := sync.WaitGroup{}
	clean = func() {
		cancel()
		wg.Wait()
	}
	wg.Add(1)
	go func() {
		defer wg.Done()
		defer progress.Store(false)
		_ = db.View(ctx, func(tx Tx) error {
			c, err := tx.Cursor(table)
			if err != nil {
				return err
			}
			defer c.Close()

			for k, v, err := c.Seek(from); k != nil && amount > 0; k, v, err = c.Next() {
				if err != nil {
					return err
				}
				if len(v) > 0 {
					_, _ = v[0], v[len(v)-1]
				}
				amount--
				select {
				case <-ctx.Done():
					return ctx.Err()
				default:
				}
			}
			return nil
		})
	}()
	return clean
}

// FirstKey - candidate on move to kv.Tx interface
func FirstKey(tx Tx, table string) ([]byte, error) {
	c, err := tx.Cursor(table)
	if err != nil {
		return nil, err
	}
	defer c.Close()
	k, _, err := c.First()
	if err != nil {
		return nil, err
	}
	return k, nil
}

// LastKey - candidate on move to kv.Tx interface
func LastKey(tx Tx, table string) ([]byte, error) {
	c, err := tx.Cursor(table)
	if err != nil {
		return nil, err
	}
	defer c.Close()
	k, _, err := c.Last()
	if err != nil {
		return nil, err
	}
	return k, nil
}

// NextSubtree does []byte++. Returns false if overflow.
func NextSubtree(in []byte) ([]byte, bool) {
	r := make([]byte, len(in))
	copy(r, in)
	for i := len(r) - 1; i >= 0; i-- {
		if r[i] != 255 {
			r[i]++
			return r, true
		}

		r = r[:i] // make it shorter, because in tries after 11ff goes 12, but not 1200
	}
	return nil, false
}