package database

import (
	"fmt"
	"hash/crc32"
	"io"
	"os"
	"path/filepath"

	octopus "gordenko.dev/dima/diploma"
	"gordenko.dev/dima/diploma/atree"
	"gordenko.dev/dima/diploma/bin"
	"gordenko.dev/dima/diploma/chunkenc"
	"gordenko.dev/dima/diploma/conbuf"
	"gordenko.dev/dima/diploma/freelist"
)

/*
Формат:
//lsn - varuint (останній LSN, що змінив дані у RAM)
metricsQty - varuint
[metric]*
где metric - це:
metricID - 4b
metricType - 1b
fracDigits - 1b
rootPageNo - 4b
lastPageNo - 4b
since - 4b
sinceValue - 8b
until - 4b
untilValue - 8b
timestamps size - 2b
values size - 2b
timestams payload - Nb
values payload - Nb
dataFreeList size - varuint
dataFreeList - Nb
indexFreeList size - varuint
indexFreeList - Nb
CRC32 - 4b
*/

const metricHeaderSize = 42

func (s *Database) dumpSnapshot(logNumber int) (err error) {
	var (
		fileName = filepath.Join(s.dir, fmt.Sprintf("%d.snapshot", logNumber))
		hasher   = crc32.NewIEEE()
		prefix   = make([]byte, metricHeaderSize)
	)

	file, err := os.OpenFile(fileName, os.O_CREATE|os.O_WRONLY, 0770)
	if err != nil {
		return
	}

	dst := io.MultiWriter(file, hasher)

	_, err = bin.WriteVarUint64(dst, uint64(len(s.metrics)))
	if err != nil {
		return
	}

	for metricID, metric := range s.metrics {
		tSize := metric.Timestamps.Size()
		vSize := metric.Values.Size()

		bin.PutUint32(prefix[0:], metricID)
		prefix[4] = byte(metric.MetricType)
		prefix[5] = metric.FracDigits
		bin.PutUint32(prefix[6:], metric.RootPageNo)
		bin.PutUint32(prefix[10:], metric.LastPageNo)
		bin.PutUint32(prefix[14:], metric.Since)
		bin.PutFloat64(prefix[18:], metric.SinceValue)
		bin.PutUint32(prefix[26:], metric.Until)
		bin.PutFloat64(prefix[30:], metric.UntilValue)
		bin.PutUint16(prefix[38:], uint16(tSize))
		bin.PutUint16(prefix[40:], uint16(vSize))

		_, err = dst.Write(prefix)
		if err != nil {
			return
		}
		// copy timestamps
		remaining := tSize
		for _, buf := range metric.TimestampsBuf.Chunks() {
			if remaining < len(buf) {
				buf = buf[:remaining]
			}
			_, err = dst.Write(buf)
			if err != nil {
				return
			}
			remaining -= len(buf)
			if remaining == 0 {
				break
			}
		}
		// copy values
		remaining = vSize
		for _, buf := range metric.ValuesBuf.Chunks() {
			if remaining < len(buf) {
				buf = buf[:remaining]
			}
			_, err = dst.Write(buf)
			if err != nil {
				return
			}
			remaining -= len(buf)
			if remaining == 0 {
				break
			}
		}
	}
	// free data pages
	err = freeListWriteTo(s.dataFreeList, dst)
	if err != nil {
		return
	}
	// free index pages
	err = freeListWriteTo(s.indexFreeList, dst)
	if err != nil {
		return
	}

	bin.WriteUint32(file, hasher.Sum32())

	err = file.Sync()
	if err != nil {
		return
	}

	err = file.Close()
	if err != nil {
		return
	}

	prevLogNumber := logNumber - 1
	prevChanges := filepath.Join(s.dir, fmt.Sprintf("%d.changes", prevLogNumber))
	prevSnapshot := filepath.Join(s.dir, fmt.Sprintf("%d.snapshot", prevLogNumber))

	isExist, err := isFileExist(prevChanges)
	if err != nil {
		return
	}

	if isExist {
		err = os.Remove(prevChanges)
		if err != nil {
			octopus.Abort(octopus.DeletePrevChangesFileFailed, err)
		}
	}

	isExist, err = isFileExist(prevSnapshot)
	if err != nil {
		return
	}

	if isExist {
		err = os.Remove(prevSnapshot)
		if err != nil {
			octopus.Abort(octopus.DeletePrevSnapshotFileFailed, err)
		}
	}
	return
}

func (s *Database) loadSnapshot(fileName string) (err error) {
	var (
		hasher     = crc32.NewIEEE()
		metricsQty int
		header     = make([]byte, metricHeaderSize)
		body       = make([]byte, atree.DataPageSize)
	)

	file, err := os.Open(fileName)
	if err != nil {
		return
	}

	src := io.TeeReader(file, hasher)
	u64, _, err := bin.ReadVarUint64(src)
	if err != nil {
		return
	}
	metricsQty = int(u64)

	for range metricsQty {
		var metric _metric
		err = bin.ReadNInto(src, header)
		if err != nil {
			return
		}

		metricID := bin.GetUint32(header[0:])
		metric.MetricType = octopus.MetricType(header[4])
		metric.FracDigits = header[5]
		metric.RootPageNo = bin.GetUint32(header[6:])
		metric.LastPageNo = bin.GetUint32(header[10:])
		metric.Since = bin.GetUint32(header[14:])
		metric.SinceValue = bin.GetFloat64(header[18:])
		metric.Until = bin.GetUint32(header[26:])
		metric.UntilValue = bin.GetFloat64(header[30:])
		tSize := bin.GetUint16(header[38:])
		vSize := bin.GetUint16(header[40:])

		buf := body[:tSize]
		err = bin.ReadNInto(src, buf)
		if err != nil {
			return
		}
		metric.TimestampsBuf = conbuf.NewFromBuffer(buf)

		buf = body[:vSize]
		err = bin.ReadNInto(src, buf)
		if err != nil {
			return
		}
		metric.ValuesBuf = conbuf.NewFromBuffer(buf)

		metric.Timestamps = chunkenc.NewReverseTimeDeltaOfDeltaCompressor(
			metric.TimestampsBuf, int(tSize))

		if metric.MetricType == octopus.Cumulative {
			metric.Values = chunkenc.NewReverseCumulativeDeltaCompressor(
				metric.ValuesBuf, int(vSize), metric.FracDigits)
		} else {
			metric.Values = chunkenc.NewReverseInstantDeltaCompressor(
				metric.ValuesBuf, int(vSize), metric.FracDigits)
		}
		s.metrics[metricID] = &metric
	}

	err = restoreFreeList(s.dataFreeList, src)
	if err != nil {
		return fmt.Errorf("restore dataFreeList: %s", err)
	}

	err = restoreFreeList(s.indexFreeList, src)
	if err != nil {
		return fmt.Errorf("restore indexFreeList: %s", err)
	}

	calculatedChecksum := hasher.Sum32()

	writtenChecksum, err := bin.ReadUint32(file)
	if err != nil {
		return
	}

	if calculatedChecksum != writtenChecksum {
		return fmt.Errorf("calculated checksum %d not equal written checksum %d", calculatedChecksum, writtenChecksum)
	}
	return
}

// HELPERS

func freeListWriteTo(freeList *freelist.FreeList, dst io.Writer) error {
	serialized, err := freeList.Serialize()
	if err != nil {
		octopus.Abort(octopus.FailedFreeListSerialize, err)
	}
	_, err = bin.WriteVarUint64(dst, uint64(len(serialized)))
	if err != nil {
		return err
	}
	_, err = dst.Write(serialized)
	if err != nil {
		return err
	}
	return nil
}

func restoreFreeList(freeList *freelist.FreeList, src io.Reader) error {
	size, _, err := bin.ReadVarUint64(src)
	if err != nil {
		return err
	}
	serialized, err := bin.ReadN(src, int(size))
	if err != nil {
		return err
	}
	freeList.Restore(serialized)
	return nil
}