package pool

import (
	"context"
	"crypto/ecdsa"
	"errors"
	"fmt"
	"math/rand"
	"sync"
	"time"

	"github.com/nspcc-dev/neofs-api-go/pkg/client"
	"github.com/nspcc-dev/neofs-api-go/pkg/object"
	"github.com/nspcc-dev/neofs-api-go/pkg/owner"
	"github.com/nspcc-dev/neofs-api-go/pkg/session"
)

// BuilderOptions contains options used to build connection pool.
type BuilderOptions struct {
	Key                     *ecdsa.PrivateKey
	NodeConnectionTimeout   time.Duration
	NodeRequestTimeout      time.Duration
	ClientRebalanceInterval time.Duration
	SessionExpirationEpoch  uint64
	weights                 []float64
	addresses               []string
}

// Builder is an interim structure used to collect node addresses/weights and
// build connection pool subsequently.
type Builder struct {
	addresses []string
	weights   []float64
}

// AddNode adds address/weight pair to node PoolBuilder list.
func (pb *Builder) AddNode(address string, weight float64) *Builder {
	pb.addresses = append(pb.addresses, address)
	pb.weights = append(pb.weights, weight)
	return pb
}

// Build creates new pool based on current PoolBuilder state and options.
func (pb *Builder) Build(ctx context.Context, options *BuilderOptions) (Pool, error) {
	if len(pb.addresses) == 0 {
		return nil, errors.New("no NeoFS peers configured")
	}

	options.weights = adjustWeights(pb.weights)
	options.addresses = pb.addresses
	return newPool(ctx, options)
}

// Pool is an interface providing connection artifacts on request.
type Pool interface {
	client.Object
	Connection() (client.Client, *session.Token, error)
	OwnerID() *owner.ID
}

type clientPack struct {
	client       client.Client
	sessionToken *session.Token
	healthy      bool
}

var _ Pool = (*pool)(nil)

type pool struct {
	lock        sync.RWMutex
	sampler     *Sampler
	owner       *owner.ID
	clientPacks []*clientPack
}

func newPool(ctx context.Context, options *BuilderOptions) (Pool, error) {
	clientPacks := make([]*clientPack, len(options.weights))
	for i, address := range options.addresses {
		c, err := client.New(client.WithDefaultPrivateKey(options.Key),
			client.WithURIAddress(address, nil),
			client.WithDialTimeout(options.NodeConnectionTimeout))
		if err != nil {
			return nil, err
		}
		st, err := c.CreateSession(ctx, options.SessionExpirationEpoch)
		if err != nil {
			address := "unknown"
			if epi, err := c.EndpointInfo(ctx); err == nil {
				address = epi.NodeInfo().Address()
			}
			return nil, fmt.Errorf("failed to create neofs session token for client %s: %w", address, err)
		}
		clientPacks[i] = &clientPack{client: c, sessionToken: st, healthy: true}
	}
	source := rand.NewSource(time.Now().UnixNano())
	sampler := NewSampler(options.weights, source)
	wallet, err := owner.NEO3WalletFromPublicKey(&options.Key.PublicKey)
	if err != nil {
		return nil, err
	}
	ownerID := owner.NewIDFromNeo3Wallet(wallet)

	pool := &pool{sampler: sampler, owner: ownerID, clientPacks: clientPacks}
	go startRebalance(ctx, pool, options)
	return pool, nil
}

func startRebalance(ctx context.Context, p *pool, options *BuilderOptions) {
	ticker := time.NewTimer(options.ClientRebalanceInterval)
	buffer := make([]float64, len(options.weights))

	for range ticker.C {
		updateNodesHealth(ctx, p, options, buffer)
		ticker.Reset(options.ClientRebalanceInterval)
	}
}

func updateNodesHealth(ctx context.Context, p *pool, options *BuilderOptions, bufferWeights []float64) {
	if len(bufferWeights) != len(p.clientPacks) {
		bufferWeights = make([]float64, len(p.clientPacks))
	}
	healthyChanged := false
	wg := sync.WaitGroup{}
	for i, cPack := range p.clientPacks {
		wg.Add(1)
		go func(i int, netmap client.Netmap) {
			defer wg.Done()
			ok := true
			tctx, c := context.WithTimeout(ctx, options.NodeRequestTimeout)
			defer c()
			if _, err := netmap.EndpointInfo(tctx); err != nil {
				ok = false
				bufferWeights[i] = 0
			}
			if ok {
				bufferWeights[i] = options.weights[i]
			}

			p.lock.Lock()
			if p.clientPacks[i].healthy != ok {
				p.clientPacks[i].healthy = ok
				healthyChanged = true
			}
			p.lock.Unlock()
		}(i, cPack.client)
	}
	wg.Wait()

	if healthyChanged {
		probabilities := adjustWeights(bufferWeights)
		source := rand.NewSource(time.Now().UnixNano())
		p.lock.Lock()
		p.sampler = NewSampler(probabilities, source)
		p.lock.Unlock()
	}
}

func adjustWeights(weights []float64) []float64 {
	adjusted := make([]float64, len(weights))
	sum := 0.0
	for _, weight := range weights {
		sum += weight
	}
	if sum > 0 {
		for i, weight := range weights {
			adjusted[i] = weight / sum
		}
	}

	return adjusted
}

func (p *pool) Connection() (client.Client, *session.Token, error) {
	p.lock.RLock()
	defer p.lock.RUnlock()
	if len(p.clientPacks) == 1 {
		cp := p.clientPacks[0]
		if cp.healthy {
			return cp.client, cp.sessionToken, nil
		}
		return nil, nil, errors.New("no healthy client")
	}
	attempts := 3 * len(p.clientPacks)
	for k := 0; k < attempts; k++ {
		i := p.sampler.Next()
		if cp := p.clientPacks[i]; cp.healthy {
			return cp.client, cp.sessionToken, nil
		}
	}
	return nil, nil, errors.New("no healthy client")
}

func (p *pool) OwnerID() *owner.ID {
	return p.owner
}

func (p *pool) conn(option []client.CallOption) (client.Client, []client.CallOption, error) {
	conn, token, err := p.Connection()
	if err != nil {
		return nil, nil, err
	}
	return conn, append(option, client.WithSession(token)), nil
}

func (p *pool) PutObject(ctx context.Context, params *client.PutObjectParams, option ...client.CallOption) (*object.ID, error) {
	conn, options, err := p.conn(option)
	if err != nil {
		return nil, err
	}
	return conn.PutObject(ctx, params, options...)
}

func (p *pool) DeleteObject(ctx context.Context, params *client.DeleteObjectParams, option ...client.CallOption) error {
	conn, options, err := p.conn(option)
	if err != nil {
		return err
	}
	return conn.DeleteObject(ctx, params, options...)
}

func (p *pool) GetObject(ctx context.Context, params *client.GetObjectParams, option ...client.CallOption) (*object.Object, error) {
	conn, options, err := p.conn(option)
	if err != nil {
		return nil, err
	}
	return conn.GetObject(ctx, params, options...)
}

func (p *pool) GetObjectHeader(ctx context.Context, params *client.ObjectHeaderParams, option ...client.CallOption) (*object.Object, error) {
	conn, options, err := p.conn(option)
	if err != nil {
		return nil, err
	}
	return conn.GetObjectHeader(ctx, params, options...)
}

func (p *pool) ObjectPayloadRangeData(ctx context.Context, params *client.RangeDataParams, option ...client.CallOption) ([]byte, error) {
	conn, options, err := p.conn(option)
	if err != nil {
		return nil, err
	}
	return conn.ObjectPayloadRangeData(ctx, params, options...)
}

func (p *pool) ObjectPayloadRangeSHA256(ctx context.Context, params *client.RangeChecksumParams, option ...client.CallOption) ([][32]byte, error) {
	conn, options, err := p.conn(option)
	if err != nil {
		return nil, err
	}
	return conn.ObjectPayloadRangeSHA256(ctx, params, options...)
}

func (p *pool) ObjectPayloadRangeTZ(ctx context.Context, params *client.RangeChecksumParams, option ...client.CallOption) ([][64]byte, error) {
	conn, options, err := p.conn(option)
	if err != nil {
		return nil, err
	}
	return conn.ObjectPayloadRangeTZ(ctx, params, options...)
}

func (p *pool) SearchObject(ctx context.Context, params *client.SearchObjectParams, option ...client.CallOption) ([]*object.ID, error) {
	conn, options, err := p.conn(option)
	if err != nil {
		return nil, err
	}
	return conn.SearchObject(ctx, params, options...)
}