package getsvc

import (
	"context"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/object"
	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
)

type objectGetter interface {
	GetObjectAndWritePayload(ctx context.Context, id oid.ID, rng *objectSDK.Range, writer ChunkWriter) (*objectSDK.Object, error)
	HeadObject(ctx context.Context, id oid.ID) (*objectSDK.Object, error)
}

type assembler struct {
	addr      oid.Address
	splitInfo *objectSDK.SplitInfo
	rng       *objectSDK.Range
	objGetter objectGetter
	head      bool

	currentOffset uint64

	parentObject *objectSDK.Object
}

func newAssembler(
	addr oid.Address,
	splitInfo *objectSDK.SplitInfo,
	rng *objectSDK.Range,
	objGetter objectGetter,
	head bool,
) *assembler {
	return &assembler{
		addr:      addr,
		rng:       rng,
		splitInfo: splitInfo,
		objGetter: objGetter,
		head:      head,
	}
}

// Assemble assembles splitted large object and writes it's content to ObjectWriter.
// It returns parent object.
func (a *assembler) Assemble(ctx context.Context, writer ObjectWriter) (*objectSDK.Object, error) {
	if a.head {
		return a.assembleHeader(ctx, writer)
	}
	sourceObjectID, ok := a.getLastPartOrLinkObjectID()
	if !ok {
		return nil, objectSDK.NewSplitInfoError(a.splitInfo)
	}
	previousID, childrenIDs, err := a.initializeFromSourceObjectID(ctx, sourceObjectID)
	if err != nil {
		return nil, err
	}
	if previousID == nil && len(childrenIDs) == 0 {
		return nil, objectSDK.NewSplitInfoError(a.splitInfo)
	}

	if len(childrenIDs) > 0 {
		if a.rng != nil {
			err = a.assembleObjectByChildrenListRange(ctx, childrenIDs, writer)
		} else {
			err = a.assembleObjectByChildrenList(ctx, childrenIDs, writer)
		}
	} else {
		if a.rng != nil {
			err = a.assemleObjectByPreviousIDInReverseRange(ctx, *previousID, writer)
		} else {
			err = a.assemleObjectByPreviousIDInReverse(ctx, *previousID, writer)
		}
	}
	if err != nil {
		return nil, err
	}
	return a.parentObject, nil
}

func (a *assembler) getLastPartOrLinkObjectID() (oid.ID, bool) {
	sourceObjectID, ok := a.splitInfo.Link()
	if ok {
		return sourceObjectID, true
	}
	sourceObjectID, ok = a.splitInfo.LastPart()
	if ok {
		return sourceObjectID, true
	}
	return oid.ID{}, false
}

func (a *assembler) initializeFromSourceObjectID(ctx context.Context, id oid.ID) (*oid.ID, []oid.ID, error) {
	w := NewSimpleObjectWriter()
	sourceObject, err := a.getChildObject(ctx, id, nil, true, w)
	if err != nil {
		return nil, nil, err
	}
	sourceObject.SetPayload(w.pld)

	parentObject := sourceObject.Parent()
	if parentObject == nil {
		return nil, nil, errChildWithEmptyParent
	}

	a.parentObject = parentObject

	var payload []byte

	if a.rng != nil {
		seekOff := a.rng.GetOffset()
		seekLen := a.rng.GetLength()
		seekTo := seekOff + seekLen
		parentSize := parentObject.PayloadSize()

		if seekTo < seekOff || parentSize < seekOff || parentSize < seekTo {
			return nil, nil, &apistatus.ObjectOutOfRange{}
		}

		sourceSize := sourceObject.PayloadSize()

		a.currentOffset = parentSize - sourceSize

		from := uint64(0)
		if a.currentOffset < seekOff {
			from = seekOff - a.currentOffset
		}

		to := uint64(0)
		if seekOff+seekLen >= a.currentOffset+from {
			to = seekOff + seekLen - a.currentOffset
		}

		payload = sourceObject.Payload()[from:to]
		a.rng.SetLength(a.rng.GetLength() - to + from)
	} else {
		payload = sourceObject.Payload()
	}

	a.parentObject.SetPayload(payload)

	idPrev, ok := sourceObject.PreviousID()
	if ok {
		return &idPrev, sourceObject.Children(), nil
	}

	return nil, sourceObject.Children(), nil
}

func (a *assembler) getChildObject(ctx context.Context, id oid.ID, rng *objectSDK.Range, verifyIsChild bool, writer ChunkWriter) (*objectSDK.Object, error) {
	obj, err := a.objGetter.GetObjectAndWritePayload(ctx, id, rng, writer)
	if err != nil {
		return nil, err
	}

	if verifyIsChild && !a.isChild(obj) {
		return nil, errParentAddressDiffers
	}
	return obj, nil
}

func (a *assembler) assembleObjectByChildrenList(ctx context.Context, childrenIDs []oid.ID, writer ObjectWriter) error {
	if err := writer.WriteHeader(ctx, a.parentObject.CutPayload()); err != nil {
		return err
	}
	return a.assemblePayloadByObjectIDs(ctx, writer, childrenIDs, true)
}

func (a *assembler) assemleObjectByPreviousIDInReverse(ctx context.Context, prevID oid.ID, writer ObjectWriter) error {
	if err := writer.WriteHeader(ctx, a.parentObject.CutPayload()); err != nil {
		return err
	}
	if err := a.assemblePayloadInReverse(ctx, writer, prevID); err != nil {
		return err
	}
	if err := writer.WriteChunk(ctx, a.parentObject.Payload()); err != nil { // last part
		return err
	}
	return nil
}

func (a *assembler) assemblePayloadByObjectIDs(ctx context.Context, writer ObjectWriter, partIDs []oid.ID, verifyIsChild bool) error {
	for i := range partIDs {
		_, err := a.getChildObject(ctx, partIDs[i], nil, verifyIsChild, writer)
		if err != nil {
			return err
		}
	}
	return nil
}

func (a *assembler) assemblePayloadInReverse(ctx context.Context, writer ObjectWriter, prevID oid.ID) error {
	chain, err := a.buildChain(ctx, prevID)
	if err != nil {
		return err
	}

	for left, right := 0, len(chain)-1; left < right; left, right = left+1, right-1 {
		chain[left], chain[right] = chain[right], chain[left]
	}

	return a.assemblePayloadByObjectIDs(ctx, writer, chain, false)
}

func (a *assembler) isChild(obj *objectSDK.Object) bool {
	parent := obj.Parent()
	return parent == nil || equalAddresses(a.addr, object.AddressOf(parent))
}

func (a *assembler) buildChain(ctx context.Context, prevID oid.ID) ([]oid.ID, error) {
	var (
		chain []oid.ID

		hasPrev = true
	)

	// fill the chain end-to-start
	for hasPrev {
		head, err := a.objGetter.HeadObject(ctx, prevID)
		if err != nil {
			return nil, err
		}
		if !a.isChild(head) {
			return nil, errParentAddressDiffers
		}

		id, _ := head.ID()
		chain = append(chain, id)

		prevID, hasPrev = head.PreviousID()
	}

	return chain, nil
}