package storage

import (
	"fmt"
	"math"
	"sync"
	"sync/atomic"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/decimal"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
)

const (
	// The maximum number of rows per block.
	maxRowsPerBlock = 8 * 1024

	// The maximum size of values in the block.
	maxBlockSize = 8 * maxRowsPerBlock
)

// Block represents a block of time series values for a single TSID.
type Block struct {
	bh blockHeader

	// nextIdx is the next index for reading timestamps and values.
	nextIdx int

	timestamps []int64
	values     []int64

	// Marshaled representation of block header.
	headerData []byte

	// Marshaled representation of timestamps.
	timestampsData []byte

	// Marshaled representation of values.
	valuesData []byte
}

// Reset resets b.
func (b *Block) Reset() {
	b.bh = blockHeader{}
	b.nextIdx = 0
	b.timestamps = b.timestamps[:0]
	b.values = b.values[:0]

	b.headerData = b.headerData[:0]
	b.timestampsData = b.timestampsData[:0]
	b.valuesData = b.valuesData[:0]
}

// CopyFrom copies src to b.
func (b *Block) CopyFrom(src *Block) {
	b.bh = src.bh
	b.nextIdx = 0
	b.timestamps = append(b.timestamps[:0], src.timestamps[src.nextIdx:]...)
	b.values = append(b.values[:0], src.values[src.nextIdx:]...)

	b.headerData = append(b.headerData[:0], src.headerData...)
	b.timestampsData = append(b.timestampsData[:0], src.timestampsData...)
	b.valuesData = append(b.valuesData[:0], src.valuesData...)
}

func getBlock() *Block {
	v := blockPool.Get()
	if v == nil {
		return &Block{}
	}
	return v.(*Block)
}

func putBlock(b *Block) {
	b.Reset()
	blockPool.Put(b)
}

var blockPool sync.Pool

func (b *Block) fixupTimestamps() {
	b.bh.MinTimestamp = b.timestamps[b.nextIdx]
	b.bh.MaxTimestamp = b.timestamps[len(b.timestamps)-1]
}

// RowsCount returns the number of rows in the block.
func (b *Block) RowsCount() int {
	return int(b.bh.RowsCount)
}

// Init initializes b with the given tsid, timestamps, values and scale.
func (b *Block) Init(tsid *TSID, timestamps, values []int64, scale int16, precisionBits uint8) {
	b.Reset()
	b.bh.TSID = *tsid
	b.bh.Scale = scale
	b.bh.PrecisionBits = precisionBits
	b.timestamps = append(b.timestamps[:0], timestamps...)
	b.values = append(b.values[:0], values...)
}

// nextRow advances to the next row.
//
// Returns false if there are no more rows in the block.
func (b *Block) nextRow() bool {
	if b.nextIdx == len(b.values) {
		return false
	}
	b.nextIdx++
	return true
}

// assertUnmarshaled makes sure the block is unmarshaled.
func (b *Block) assertUnmarshaled() {
	if len(b.valuesData) > 0 {
		logger.Panicf("BUG: valuesData must be empty; got %d bytes", len(b.valuesData))
	}
	if len(b.timestampsData) > 0 {
		logger.Panicf("BUG: timestampsData must be empty; got %d bytes", len(b.timestampsData))
	}
	if len(b.values) != len(b.timestamps) {
		logger.Panicf("BUG: the number of values must match the number of timestamps; got %d vs %d", len(b.values), len(b.timestamps))
	}
	if b.nextIdx > len(b.values) {
		logger.Panicf("BUG: nextIdx cannot exceed the number of values; got %d vs %d", b.nextIdx, len(b.values))
	}
}

// assertMergeable makes sure b and ib are mergeable, i.e. they have the same
// tsid and scale.
func (b *Block) assertMergeable(ib *Block) {
	if b.bh.TSID.MetricID != ib.bh.TSID.MetricID {
		logger.Panicf("BUG: unequal TSID: %q vs %q", &b.bh.TSID, &ib.bh.TSID)
	}
	if b.bh.Scale != ib.bh.Scale {
		logger.Panicf("BUG: unequal Scale: %d vs %d", b.bh.Scale, ib.bh.Scale)
	}
}

// tooBig returns true if the block is too big to be extended.
func (b *Block) tooBig() bool {
	if b.bh.RowsCount >= maxRowsPerBlock || len(b.values[b.nextIdx:]) >= maxRowsPerBlock {
		return true
	}
	if len(b.valuesData) >= maxBlockSize {
		return true
	}
	return false
}

func (b *Block) deduplicateSamplesDuringMerge() {
	if len(b.values) == 0 {
		// Nothing to dedup or the data is already marshaled.
		return
	}
	srcTimestamps := b.timestamps[b.nextIdx:]
	srcValues := b.values[b.nextIdx:]
	timestamps, values := deduplicateSamplesDuringMerge(srcTimestamps, srcValues)
	dedups := len(srcTimestamps) - len(timestamps)
	atomic.AddUint64(&dedupsDuringMerge, uint64(dedups))
	b.timestamps = b.timestamps[:b.nextIdx+len(timestamps)]
	b.values = b.values[:b.nextIdx+len(values)]
}

var dedupsDuringMerge uint64

func (b *Block) rowsCount() int {
	if len(b.values) == 0 {
		return int(b.bh.RowsCount)
	}
	return len(b.values[b.nextIdx:])
}

// MarshalData marshals the block into binary representation.
func (b *Block) MarshalData(timestampsBlockOffset, valuesBlockOffset uint64) ([]byte, []byte, []byte) {
	if len(b.values) == 0 {
		// The data has been already marshaled.

		// b.valuesData and b.timestampsData may be empty for certain
		// b.bh.*MarshalType values, so don't check them.

		if b.nextIdx != 0 {
			logger.Panicf("BUG: nextIdx must be zero; got %d", b.nextIdx)
		}
		if int(b.bh.TimestampsBlockSize) != len(b.timestampsData) {
			logger.Panicf("BUG: invalid TimestampsBlockSize; got %d; expecting %d", b.bh.TimestampsBlockSize, len(b.timestampsData))
		}
		if int(b.bh.ValuesBlockSize) != len(b.valuesData) {
			logger.Panicf("BUG: invalid ValuesBlockSize; got %d; expecting %d", b.bh.ValuesBlockSize, len(b.valuesData))
		}
		if b.bh.RowsCount <= 0 {
			logger.Panicf("BUG: RowsCount must be greater than 0; got %d", b.bh.RowsCount)
		}

		// headerData must be always recreated, since it contains timestampsBlockOffset and valuesBlockOffset.
		b.bh.TimestampsBlockOffset = timestampsBlockOffset
		b.bh.ValuesBlockOffset = valuesBlockOffset
		b.headerData = b.bh.Marshal(b.headerData[:0])

		return b.headerData, b.timestampsData, b.valuesData
	}

	if b.nextIdx > len(b.values) {
		logger.Panicf("BUG: nextIdx cannot exceed values size; got %d vs %d", b.nextIdx, len(b.values))
	}

	timestamps := b.timestamps[b.nextIdx:]
	values := b.values[b.nextIdx:]
	if len(values) == 0 {
		logger.Panicf("BUG: values cannot be empty; nextIdx=%d, timestampsBlockOffset=%d, valuesBlockOffset=%d", b.nextIdx, timestampsBlockOffset, valuesBlockOffset)
	}
	if len(values) != len(timestamps) {
		logger.Panicf("BUG: the number of values must match the number of timestamps; got %d vs %d", len(values), len(timestamps))
	}

	b.valuesData, b.bh.ValuesMarshalType, b.bh.FirstValue = encoding.MarshalValues(b.valuesData[:0], values, b.bh.PrecisionBits)
	b.bh.ValuesBlockOffset = valuesBlockOffset
	b.bh.ValuesBlockSize = uint32(len(b.valuesData))
	b.values = b.values[:0]

	b.timestampsData, b.bh.TimestampsMarshalType, b.bh.MinTimestamp = encoding.MarshalTimestamps(b.timestampsData[:0], timestamps, b.bh.PrecisionBits)
	b.bh.TimestampsBlockOffset = timestampsBlockOffset
	b.bh.TimestampsBlockSize = uint32(len(b.timestampsData))
	b.bh.MaxTimestamp = timestamps[len(timestamps)-1]
	b.timestamps = b.timestamps[:0]

	b.bh.RowsCount = uint32(len(values))
	b.headerData = b.bh.Marshal(b.headerData[:0])

	b.nextIdx = 0

	return b.headerData, b.timestampsData, b.valuesData
}

// UnmarshalData unmarshals block data.
func (b *Block) UnmarshalData() error {
	// blockHeader (b.bh) must be already unmarshaled.

	if len(b.values) > 0 {
		// The data has been already unmarshaled.
		if len(b.valuesData) > 0 {
			logger.Panicf("BUG: valuesData must be empty; contains %d bytes", len(b.valuesData))
		}
		if len(b.timestampsData) > 0 {
			logger.Panicf("BUG: timestampsData must be empty; contains %d bytes", len(b.timestampsData))
		}
		return nil
	}

	if b.bh.RowsCount <= 0 {
		return fmt.Errorf("RowsCount must be greater than 0; got %d", b.bh.RowsCount)
	}

	var err error

	b.timestamps, err = encoding.UnmarshalTimestamps(b.timestamps[:0], b.timestampsData, b.bh.TimestampsMarshalType, b.bh.MinTimestamp, int(b.bh.RowsCount))
	if err != nil {
		return err
	}
	if b.bh.PrecisionBits < 64 {
		// Recover timestamps order after lossy compression.
		encoding.EnsureNonDecreasingSequence(b.timestamps, b.bh.MinTimestamp, b.bh.MaxTimestamp)
	}
	b.timestampsData = b.timestampsData[:0]

	b.values, err = encoding.UnmarshalValues(b.values[:0], b.valuesData, b.bh.ValuesMarshalType, b.bh.FirstValue, int(b.bh.RowsCount))
	if err != nil {
		return err
	}
	b.valuesData = b.valuesData[:0]

	if len(b.timestamps) != len(b.values) {
		return fmt.Errorf("timestamps and values count mismatch; got %d vs %d", len(b.timestamps), len(b.values))
	}

	b.nextIdx = 0

	return nil
}

// AppendRowsWithTimeRangeFilter filters samples from b according to tr and appends them to dst*.
//
// It is expected that UnmarshalData has been already called on b.
func (b *Block) AppendRowsWithTimeRangeFilter(dstTimestamps []int64, dstValues []float64, tr TimeRange) ([]int64, []float64) {
	timestamps, values := b.filterTimestamps(tr)
	dstTimestamps = append(dstTimestamps, timestamps...)
	dstValues = decimal.AppendDecimalToFloat(dstValues, values, b.bh.Scale)
	return dstTimestamps, dstValues
}

func (b *Block) filterTimestamps(tr TimeRange) ([]int64, []int64) {
	timestamps := b.timestamps

	// Skip timestamps smaller than tr.MinTimestamp.
	i := 0
	for i < len(timestamps) && timestamps[i] < tr.MinTimestamp {
		i++
	}

	// Skip timestamps bigger than tr.MaxTimestamp.
	j := len(timestamps)
	for j > i && timestamps[j-1] > tr.MaxTimestamp {
		j--
	}

	if i == j {
		return nil, nil
	}
	return timestamps[i:j], b.values[i:j]
}

// MarshalPortable marshals b to dst, so it could be portably migrated to other VictoriaMetrics instance.
//
// The marshaled value must be unmarshaled with UnmarshalPortable function.
func (b *Block) MarshalPortable(dst []byte) []byte {
	b.MarshalData(0, 0)

	dst = encoding.MarshalVarInt64(dst, b.bh.MinTimestamp)
	dst = encoding.MarshalVarInt64(dst, b.bh.FirstValue)
	dst = encoding.MarshalVarUint64(dst, uint64(b.bh.RowsCount))
	dst = encoding.MarshalVarInt64(dst, int64(b.bh.Scale))
	dst = append(dst, byte(b.bh.TimestampsMarshalType))
	dst = append(dst, byte(b.bh.ValuesMarshalType))
	dst = encoding.MarshalBytes(dst, b.timestampsData)
	dst = encoding.MarshalBytes(dst, b.valuesData)

	return dst
}

// UnmarshalPortable unmarshals block from src to b and returns the remaining tail.
//
// It is assumed that the block has been marshaled with MarshalPortable.
func (b *Block) UnmarshalPortable(src []byte) ([]byte, error) {
	b.Reset()

	// Read header
	src, firstTimestamp, err := encoding.UnmarshalVarInt64(src)
	if err != nil {
		return src, fmt.Errorf("cannot unmarshal firstTimestamp: %w", err)
	}
	b.bh.MinTimestamp = firstTimestamp
	src, firstValue, err := encoding.UnmarshalVarInt64(src)
	if err != nil {
		return src, fmt.Errorf("cannot unmarshal firstValue: %w", err)
	}
	b.bh.FirstValue = firstValue
	src, rowsCount, err := encoding.UnmarshalVarUint64(src)
	if err != nil {
		return src, fmt.Errorf("cannot unmarshal rowsCount: %w", err)
	}
	if rowsCount > math.MaxUint32 {
		return src, fmt.Errorf("got too big rowsCount=%d; it mustn't exceed %d", rowsCount, uint32(math.MaxUint32))
	}
	b.bh.RowsCount = uint32(rowsCount)
	src, scale, err := encoding.UnmarshalVarInt64(src)
	if err != nil {
		return src, fmt.Errorf("cannot unmarshal scale: %w", err)
	}
	if scale < math.MinInt16 {
		return src, fmt.Errorf("got too small scale=%d; it mustn't be smaller than %d", scale, math.MinInt16)
	}
	if scale > math.MaxInt16 {
		return src, fmt.Errorf("got too big scale=%d; it mustn't exceeed %d", scale, math.MaxInt16)
	}
	b.bh.Scale = int16(scale)
	if len(src) < 1 {
		return src, fmt.Errorf("cannot unmarshal marshalType for timestamps from %d bytes; need at least %d bytes", len(src), 1)
	}
	b.bh.TimestampsMarshalType = encoding.MarshalType(src[0])
	src = src[1:]
	if len(src) < 1 {
		return src, fmt.Errorf("cannot unmarshal marshalType for values from %d bytes; need at least %d bytes", len(src), 1)
	}
	b.bh.ValuesMarshalType = encoding.MarshalType(src[0])
	src = src[1:]
	b.bh.PrecisionBits = 64

	// Read data
	src, timestampsData, err := encoding.UnmarshalBytes(src)
	if err != nil {
		return src, fmt.Errorf("cannot read timestampsData: %w", err)
	}
	b.timestampsData = append(b.timestampsData[:0], timestampsData...)
	src, valuesData, err := encoding.UnmarshalBytes(src)
	if err != nil {
		return src, fmt.Errorf("cannot read valuesData: %w", err)
	}
	b.valuesData = append(b.valuesData[:0], valuesData...)

	// Validate
	if err := b.bh.validate(); err != nil {
		return src, fmt.Errorf("invalid blockHeader: %w", err)
	}
	if err := b.UnmarshalData(); err != nil {
		return src, fmt.Errorf("invalid data: %w", err)
	}

	return src, nil
}