package blobovnicza

import (
	"context"
	"fmt"

	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.etcd.io/bbolt"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
)

func (b *Blobovnicza) iterateBuckets(tx *bbolt.Tx, f func(uint64, uint64, *bbolt.Bucket) (bool, error)) error {
	return b.iterateBucketKeys(func(lower uint64, upper uint64, key []byte) (bool, error) {
		buck := tx.Bucket(key)
		if buck == nil {
			// expected to happen:
			//  - before initialization step (incorrect usage by design)
			//  - if DB is corrupted (in future this case should be handled)
			return false, fmt.Errorf("(%T) could not get bucket %s", b, stringifyBounds(lower, upper))
		}

		return f(lower, upper, buck)
	})
}

func (b *Blobovnicza) iterateBucketKeys(f func(uint64, uint64, []byte) (bool, error)) error {
	return b.iterateBounds(func(lower, upper uint64) (bool, error) {
		return f(lower, upper, bucketKeyFromBounds(upper))
	})
}

func (b *Blobovnicza) iterateBounds(f func(uint64, uint64) (bool, error)) error {
	objLimitBound := upperPowerOfTwo(b.objSizeLimit)

	for upper := firstBucketBound; upper <= max(objLimitBound, firstBucketBound); upper *= 2 {
		var lower uint64

		if upper != firstBucketBound {
			lower = upper/2 + 1
		}

		if stop, err := f(lower, upper); err != nil {
			return err
		} else if stop {
			break
		}
	}

	return nil
}

func max(a, b uint64) uint64 {
	if a > b {
		return a
	}

	return b
}

// IterationElement represents a unit of elements through which Iterate operation passes.
type IterationElement struct {
	addr oid.Address

	data []byte
}

// ObjectData returns stored object in a binary representation.
func (x IterationElement) ObjectData() []byte {
	return x.data
}

// Address returns address of the stored object.
func (x IterationElement) Address() oid.Address {
	return x.addr
}

// IterationHandler is a generic processor of IterationElement.
type IterationHandler func(IterationElement) error

// IteratePrm groups the parameters of Iterate operation.
type IteratePrm struct {
	decodeAddresses bool

	withoutData bool

	handler IterationHandler

	ignoreErrors bool
}

// DecodeAddresses sets flag to unmarshal object addresses.
func (x *IteratePrm) DecodeAddresses() {
	x.decodeAddresses = true
}

// WithoutData sets flag to not read data of the objects.
func (x *IteratePrm) WithoutData() {
	x.withoutData = true
}

// SetHandler sets handler to be called iteratively.
func (x *IteratePrm) SetHandler(h IterationHandler) {
	x.handler = h
}

// IgnoreErrors makes all errors to be ignored.
func (x *IteratePrm) IgnoreErrors() {
	x.ignoreErrors = true
}

// IterateRes groups the resulting values of Iterate operation.
type IterateRes struct {
}

// Iterate goes through all stored objects, and passes IterationElement to parameterized handler until error return.
//
// Decodes object addresses if DecodeAddresses was called. Don't read object data if WithoutData was called.
//
// Returns handler's errors directly. Returns nil after iterating finish.
//
// Handler should not retain object data. Handler must not be nil.
func (b *Blobovnicza) Iterate(ctx context.Context, prm IteratePrm) (IterateRes, error) {
	ctx, span := tracing.StartSpanFromContext(ctx, "Blobovnicza.Iterate",
		trace.WithAttributes(
			attribute.String("path", b.path),
			attribute.Bool("decode_addresses", prm.decodeAddresses),
			attribute.Bool("without_data", prm.withoutData),
			attribute.Bool("ignore_errors", prm.ignoreErrors),
		))
	defer span.End()

	var elem IterationElement

	if err := b.boltDB.View(func(tx *bbolt.Tx) error {
		return tx.ForEach(func(name []byte, buck *bbolt.Bucket) error {
			return buck.ForEach(func(k, v []byte) error {
				select {
				case <-ctx.Done():
					return ctx.Err()
				default:
				}
				if prm.decodeAddresses {
					if err := addressFromKey(&elem.addr, k); err != nil {
						if prm.ignoreErrors {
							return nil
						}
						return fmt.Errorf("could not decode address key: %w", err)
					}
				}

				if !prm.withoutData {
					elem.data = v
				}

				return prm.handler(elem)
			})
		})
	}); err != nil {
		return IterateRes{}, err
	}

	return IterateRes{}, nil
}

// IterateAddresses is a helper function which iterates over Blobovnicza and passes addresses of the objects to f.
func IterateAddresses(ctx context.Context, blz *Blobovnicza, f func(oid.Address) error) error {
	var prm IteratePrm

	prm.DecodeAddresses()
	prm.WithoutData()

	prm.SetHandler(func(elem IterationElement) error {
		return f(elem.Address())
	})

	_, err := blz.Iterate(ctx, prm)

	return err
}