package ledger

import (
	"context"
	"fmt"
	"net"
	"net/url"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/tech/sendico/pkg/discovery"
	"github.com/tech/sendico/pkg/merrors"
	"github.com/tech/sendico/pkg/mlogger"
	"github.com/tech/sendico/pkg/mservice"
	"go.uber.org/zap"
)

type DiscoveryConfig struct {
	Logger   mlogger.Logger
	Registry *discovery.Registry
	Timeout  time.Duration
}

type discoveryEndpoint struct {
	address  string
	insecure bool
	raw      string
}

func (e discoveryEndpoint) key() string {
	return fmt.Sprintf("%s|%t", e.address, e.insecure)
}

type discoveryClient struct {
	logger   mlogger.Logger
	registry *discovery.Registry
	timeout  time.Duration

	mu          sync.Mutex
	client      Client
	endpointKey string
}

func NewDiscoveryClient(cfg DiscoveryConfig) (Client, error) {
	if cfg.Registry == nil {
		return nil, merrors.InvalidArgument("treasury ledger discovery registry is required", "registry")
	}
	if cfg.Timeout <= 0 {
		cfg.Timeout = 5 * time.Second
	}
	logger := cfg.Logger
	if logger != nil {
		logger = logger.Named("treasury_ledger_discovery")
	}
	return &discoveryClient{
		logger:   logger,
		registry: cfg.Registry,
		timeout:  cfg.Timeout,
	}, nil
}

func (c *discoveryClient) Close() error {
	if c == nil {
		return nil
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.client != nil {
		err := c.client.Close()
		c.client = nil
		c.endpointKey = ""
		return err
	}
	return nil
}

func (c *discoveryClient) GetAccount(ctx context.Context, accountID string) (*Account, error) {
	client, err := c.resolveClient(ctx)
	if err != nil {
		return nil, err
	}
	return client.GetAccount(ctx, accountID)
}

func (c *discoveryClient) GetBalance(ctx context.Context, accountID string) (*Balance, error) {
	client, err := c.resolveClient(ctx)
	if err != nil {
		return nil, err
	}
	return client.GetBalance(ctx, accountID)
}

func (c *discoveryClient) ExternalCredit(ctx context.Context, req PostRequest) (*OperationResult, error) {
	client, err := c.resolveClient(ctx)
	if err != nil {
		return nil, err
	}
	return client.ExternalCredit(ctx, req)
}

func (c *discoveryClient) ExternalDebit(ctx context.Context, req PostRequest) (*OperationResult, error) {
	client, err := c.resolveClient(ctx)
	if err != nil {
		return nil, err
	}
	return client.ExternalDebit(ctx, req)
}

func (c *discoveryClient) resolveClient(_ context.Context) (Client, error) {
	if c == nil || c.registry == nil {
		return nil, merrors.Internal("treasury ledger discovery is unavailable")
	}
	endpoint, err := c.resolveEndpoint()
	if err != nil {
		return nil, err
	}
	key := endpoint.key()

	c.mu.Lock()
	defer c.mu.Unlock()

	if c.client != nil && c.endpointKey == key {
		return c.client, nil
	}
	if c.client != nil {
		_ = c.client.Close()
		c.client = nil
		c.endpointKey = ""
	}
	next, err := New(Config{
		Endpoint: endpoint.address,
		Timeout:  c.timeout,
		Insecure: endpoint.insecure,
	})
	if err != nil {
		return nil, err
	}
	c.client = next
	c.endpointKey = key
	if c.logger != nil {
		c.logger.Info("Discovered ledger endpoint selected",
			zap.String("service", string(mservice.Ledger)),
			zap.String("invoke_uri", endpoint.raw),
			zap.String("address", endpoint.address),
			zap.Bool("insecure", endpoint.insecure))
	}
	return c.client, nil
}

func (c *discoveryClient) resolveEndpoint() (discoveryEndpoint, error) {
	entries := c.registry.List(time.Now(), true)
	type match struct {
		entry   discovery.RegistryEntry
		opMatch bool
	}
	matches := make([]match, 0, len(entries))
	requiredOps := discovery.LedgerServiceOperations()
	for _, entry := range entries {
		if !matchesService(entry.Service, mservice.Ledger) {
			continue
		}
		matches = append(matches, match{
			entry:   entry,
			opMatch: discovery.HasAnyOperation(entry.Operations, requiredOps),
		})
	}
	if len(matches) == 0 {
		return discoveryEndpoint{}, merrors.NoData("discovery: ledger service unavailable")
	}
	sort.Slice(matches, func(i, j int) bool {
		if matches[i].opMatch != matches[j].opMatch {
			return matches[i].opMatch
		}
		if matches[i].entry.RoutingPriority != matches[j].entry.RoutingPriority {
			return matches[i].entry.RoutingPriority > matches[j].entry.RoutingPriority
		}
		if matches[i].entry.ID != matches[j].entry.ID {
			return matches[i].entry.ID < matches[j].entry.ID
		}
		return matches[i].entry.InstanceID < matches[j].entry.InstanceID
	})
	return parseDiscoveryEndpoint(matches[0].entry.InvokeURI)
}

func matchesService(service string, candidate mservice.Type) bool {
	service = strings.TrimSpace(service)
	if service == "" || strings.TrimSpace(string(candidate)) == "" {
		return false
	}
	return strings.EqualFold(service, strings.TrimSpace(string(candidate)))
}

func parseDiscoveryEndpoint(raw string) (discoveryEndpoint, error) {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return discoveryEndpoint{}, merrors.InvalidArgument("discovery: invoke uri is required")
	}

	if !strings.Contains(raw, "://") {
		if _, _, splitErr := net.SplitHostPort(raw); splitErr != nil {
			return discoveryEndpoint{}, merrors.InvalidArgument("discovery: invoke uri must include host:port")
		}
		return discoveryEndpoint{address: raw, insecure: true, raw: raw}, nil
	}

	parsed, err := url.Parse(raw)
	if err != nil || parsed.Scheme == "" {
		if err != nil {
			return discoveryEndpoint{}, err
		}
		return discoveryEndpoint{}, merrors.InvalidArgument("discovery: invoke uri must include host:port")
	}

	scheme := strings.ToLower(strings.TrimSpace(parsed.Scheme))
	switch scheme {
	case "grpc":
		address := strings.TrimSpace(parsed.Host)
		if _, _, splitErr := net.SplitHostPort(address); splitErr != nil {
			return discoveryEndpoint{}, merrors.InvalidArgument("discovery: invoke uri must include host:port")
		}
		return discoveryEndpoint{address: address, insecure: true, raw: raw}, nil
	case "grpcs":
		address := strings.TrimSpace(parsed.Host)
		if _, _, splitErr := net.SplitHostPort(address); splitErr != nil {
			return discoveryEndpoint{}, merrors.InvalidArgument("discovery: invoke uri must include host:port")
		}
		return discoveryEndpoint{address: address, insecure: false, raw: raw}, nil
	case "dns", "passthrough":
		return discoveryEndpoint{address: raw, insecure: true, raw: raw}, nil
	default:
		return discoveryEndpoint{}, merrors.InvalidArgument("discovery: unsupported invoke uri scheme")
	}
}