package txlog

import (
	"fmt"
	"io"
	"os"

	bin "gordenko.dev/dima/bin/little"
	"gordenko.dev/dima/qb"
	"gordenko.dev/dima/qb/atree"
	"gordenko.dev/dima/qb/util"
)

func LoadSnapshot(fileName string) (snapshot Snapshot, err error) {
	var (
		hasher = util.NewHasher()
		header = make([]byte, metricHeaderSize)
		body   = make([]byte, atree.PageSize)
	)

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

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

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

		metric.MetricID, _ = bin.GetUint32(header[0:])
		metric.MetricType = qb.MetricType(header[4])
		metric.FracDigits = header[5]
		metric.LastPageNo, _ = bin.GetUint32(header[6:])
		metric.Since, _ = bin.GetUint32(header[10:])
		metric.SinceValue, _ = bin.GetFloat64(header[14:])
		metric.Until, _ = bin.GetUint32(header[22:])
		metric.UntilValue, _ = bin.GetFloat64(header[26:])
		tSize, _ := bin.GetUint16(header[34:])
		vSize, _ := bin.GetUint16(header[36:])

		buf := body[:tSize]
		err = bin.ReadNInto(src, buf)
		if err != nil {
			return
		}
		// FIX
		// metric.Timestamps = chunkenc.NewReverseTimeDeltaCompressor(
		// 	conbuf.NewFromBuffer(buf),
		// 	int(tSize),
		// )

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

		// FIX
		// if metric.MetricType == qb.Cumulative {
		// 	metric.Values = chunkenc.NewReverseCumulativeDeltaCompressor(
		// 		conbuf.NewFromBuffer(buf),
		// 		int(vSize),
		// 		metric.FracDigits,
		// 	)
		// } else {
		// 	metric.Values = chunkenc.NewReverseInstantDeltaCompressor(
		// 		conbuf.NewFromBuffer(buf),
		// 		int(vSize),
		// 		metric.FracDigits,
		// 	)
		// }
		// s.metrics[metricID] = &metric
	}
	// FIX
	// err = restoreFreeList(s.dataFreeList, src)
	// if err != nil {
	// 	return fmt.Errorf("restore dataFreeList: %s", err)
	// }
	// FIX
	// 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 {
		err = fmt.Errorf("calculated checksum %d not equal written checksum %d",
			calculatedChecksum, writtenChecksum)
		return
	}
	return
}

// serialized + frozen pages count

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