package windsurf

import (
	"context"
	"fmt"
	"log/slog"
	"net"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/docker/docker/api/types/container"
	"github.com/docker/docker/api/types/filters"
	"github.com/docker/docker/client"
)

type DockerDiscoveryConfig struct {
	// ContainerNamePrefix filters containers whose name starts with this prefix.
	// Default: "sub2api-windsurf-ls"
	ContainerNamePrefix string

	// FallbackHost is used when Docker hostnames can't be resolved (local dev).
	// Default: "127.0.0.1"
	FallbackHost string

	// DefaultCSRFToken is the CSRF token for LS gRPC calls.
	DefaultCSRFToken string

	// ProbeInterval controls how often health probes run.
	// Default: 30s
	ProbeInterval time.Duration

	// ProbeTimeout is the TCP dial timeout for health checks.
	// Default: 3s
	ProbeTimeout time.Duration

	// DiscoverInterval controls how often Docker API is polled for new containers.
	// Default: 60s
	DiscoverInterval time.Duration
}

func (c *DockerDiscoveryConfig) defaults() {
	if c.ContainerNamePrefix == "" {
		c.ContainerNamePrefix = "sub2api-windsurf-ls"
	}
	if c.FallbackHost == "" {
		c.FallbackHost = "127.0.0.1"
	}
	if c.DefaultCSRFToken == "" {
		c.DefaultCSRFToken = DefaultCSRF
	}
	if c.ProbeInterval <= 0 {
		c.ProbeInterval = 30 * time.Second
	}
	if c.ProbeTimeout <= 0 {
		c.ProbeTimeout = 3 * time.Second
	}
	if c.DiscoverInterval <= 0 {
		c.DiscoverInterval = 60 * time.Second
	}
}

type lsInstance struct {
	ContainerID   string
	ContainerName string
	Host          string
	Port          int
	CSRFToken     string
	Client        *LocalLSClient
	Healthy       atomic.Bool
	DiscoveredAt  time.Time
	LastProbeAt   time.Time
	LastProbeErr  string
}

type DockerDiscoveryConnector struct {
	cfg       DockerDiscoveryConfig
	mu        sync.RWMutex
	instances []*lsInstance
	robin     atomic.Uint64
	cancel    context.CancelFunc
	done      chan struct{}
}

func NewDockerDiscoveryConnector(cfg DockerDiscoveryConfig) *DockerDiscoveryConnector {
	cfg.defaults()
	ctx, cancel := context.WithCancel(context.Background())
	c := &DockerDiscoveryConnector{
		cfg:    cfg,
		cancel: cancel,
		done:   make(chan struct{}),
	}
	go c.loop(ctx)
	return c
}

func (c *DockerDiscoveryConnector) Mode() string { return "docker" }

func (c *DockerDiscoveryConnector) Acquire(_ context.Context, _ string) (*LSLease, error) {
	c.mu.RLock()
	defer c.mu.RUnlock()

	healthy := c.healthyInstances()
	if len(healthy) == 0 {
		return nil, fmt.Errorf("no healthy LS instances available")
	}

	idx := c.robin.Add(1) - 1
	inst := healthy[idx%uint64(len(healthy))]

	return &LSLease{
		Mode:     "docker",
		Endpoint: fmt.Sprintf("%s:%d", inst.Host, inst.Port),
		Client:   inst.Client,
		Release:  func() {},
	}, nil
}

// AcquireByID returns the LS instance matching containerID. Falls back to round-robin if not found.
func (c *DockerDiscoveryConnector) AcquireByID(containerID string) (*LSLease, error) {
	if containerID == "" {
		return c.Acquire(context.Background(), "")
	}

	c.mu.RLock()
	defer c.mu.RUnlock()

	for _, inst := range c.instances {
		if inst.ContainerID == containerID || inst.ContainerName == containerID {
			if !inst.Healthy.Load() {
				slog.Warn("windsurf_ls_bound_unhealthy", "container", containerID)
			}
			return &LSLease{
				Mode:     "docker",
				Endpoint: fmt.Sprintf("%s:%d", inst.Host, inst.Port),
				Client:   inst.Client,
				Release:  func() {},
			}, nil
		}
	}

	slog.Warn("windsurf_ls_bound_not_found", "container", containerID, "fallback", "round-robin")
	return c.acquireRoundRobin()
}

func (c *DockerDiscoveryConnector) acquireRoundRobin() (*LSLease, error) {
	healthy := c.healthyInstances()
	if len(healthy) == 0 {
		return nil, fmt.Errorf("no healthy LS instances available")
	}
	idx := c.robin.Add(1) - 1
	inst := healthy[idx%uint64(len(healthy))]
	return &LSLease{
		Mode:     "docker",
		Endpoint: fmt.Sprintf("%s:%d", inst.Host, inst.Port),
		Client:   inst.Client,
		Release:  func() {},
	}, nil
}

func (c *DockerDiscoveryConnector) Health(_ context.Context) error {
	c.mu.RLock()
	defer c.mu.RUnlock()
	if len(c.healthyInstances()) == 0 {
		return fmt.Errorf("no healthy LS instances")
	}
	return nil
}

func (c *DockerDiscoveryConnector) Status() *LSConnectorStatus {
	c.mu.RLock()
	defer c.mu.RUnlock()
	healthy := c.healthyInstances()
	return &LSConnectorStatus{
		Mode:      "docker",
		Healthy:   len(healthy) > 0,
		Instances: len(c.instances),
		Endpoint:  c.endpointSummary(healthy),
	}
}

func (c *DockerDiscoveryConnector) Shutdown() {
	c.cancel()
	<-c.done
}

// healthyInstances returns instances where Healthy is true. Caller must hold at least RLock.
func (c *DockerDiscoveryConnector) healthyInstances() []*lsInstance {
	var result []*lsInstance
	for _, inst := range c.instances {
		if inst.Healthy.Load() {
			result = append(result, inst)
		}
	}
	return result
}

func (c *DockerDiscoveryConnector) endpointSummary(healthy []*lsInstance) string {
	if len(healthy) == 0 {
		return "none"
	}
	parts := make([]string, len(healthy))
	for i, inst := range healthy {
		parts[i] = fmt.Sprintf("%s:%d", inst.Host, inst.Port)
	}
	return strings.Join(parts, ",")
}

func (c *DockerDiscoveryConnector) loop(ctx context.Context) {
	defer close(c.done)

	c.discover(ctx)
	c.probeAll(ctx)

	discoverTick := time.NewTicker(c.cfg.DiscoverInterval)
	probeTick := time.NewTicker(c.cfg.ProbeInterval)
	defer discoverTick.Stop()
	defer probeTick.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-discoverTick.C:
			c.discover(ctx)
		case <-probeTick.C:
			c.probeAll(ctx)
		}
	}
}

func (c *DockerDiscoveryConnector) discover(ctx context.Context) {
	cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
	if err != nil {
		slog.Warn("windsurf_ls_docker_client_error", "error", err)
		return
	}
	defer cli.Close()

	containers, err := cli.ContainerList(ctx, container.ListOptions{
		Filters: filters.NewArgs(
			filters.Arg("status", "running"),
		),
	})
	if err != nil {
		slog.Warn("windsurf_ls_docker_list_error", "error", err)
		return
	}

	var found []*lsInstance
	for _, ctr := range containers {
		name := containerName(ctr.Names)
		if !strings.Contains(name, "windsurf-ls") {
			continue
		}

		host, port, csrfToken := c.extractEndpoint(ctr)
		if port == 0 {
			continue
		}

		found = append(found, &lsInstance{
			ContainerID:   ctr.ID[:12],
			ContainerName: name,
			Host:          host,
			Port:          port,
			CSRFToken:     csrfToken,
			DiscoveredAt:  time.Now(),
		})
	}

	c.mu.Lock()
	c.reconcile(found)
	c.mu.Unlock()

	slog.Info("windsurf_ls_discovery", "found", len(found), "total", len(c.instances))
}

func containerName(names []string) string {
	for _, n := range names {
		return strings.TrimPrefix(n, "/")
	}
	return ""
}

func (c *DockerDiscoveryConnector) extractEndpoint(ctr container.Summary) (string, int, string) {
	host := containerName(ctr.Names)
	csrfToken := c.cfg.DefaultCSRFToken

	for _, env := range ctr.Labels {
		// labels can carry csrf overrides if needed
		_ = env
	}

	if _, err := net.LookupHost(host); err != nil {
		host = c.cfg.FallbackHost
	}

	for _, p := range ctr.Ports {
		if p.PrivatePort == 42099 || p.PrivatePort == 42100 || (p.PublicPort >= 42099 && p.PublicPort <= 42200) {
			port := int(p.PublicPort)
			if port == 0 {
				port = int(p.PrivatePort)
			}

			// When port has a host-bound IP (e.g. 127.0.0.1:42100->42100),
			// use that IP instead of the container name. This ensures the
			// backend can reach the LS when running on the host (go run)
			// rather than inside the Docker network.
			if p.IP != "" && p.PublicPort > 0 {
				host = p.IP
				port = int(p.PublicPort)
			} else if host == c.cfg.FallbackHost && p.PublicPort > 0 {
				port = int(p.PublicPort)
			}

			for _, e := range envFromLabels(ctr.Labels) {
				if strings.HasPrefix(e, "LS_CSRF_TOKEN=") {
					csrfToken = strings.TrimPrefix(e, "LS_CSRF_TOKEN=")
				}
			}

			return host, port, csrfToken
		}
	}

	return host, 0, csrfToken
}

func envFromLabels(labels map[string]string) []string {
	var result []string
	for k, v := range labels {
		if strings.HasPrefix(k, "windsurf.") {
			result = append(result, strings.TrimPrefix(k, "windsurf.")+"="+v)
		}
	}
	return result
}

// reconcile merges discovered containers into the existing pool. Caller must hold Lock.
func (c *DockerDiscoveryConnector) reconcile(found []*lsInstance) {
	existing := make(map[string]*lsInstance)
	for _, inst := range c.instances {
		existing[inst.ContainerID] = inst
	}

	var merged []*lsInstance
	for _, f := range found {
		if old, ok := existing[f.ContainerID]; ok {
			old.Host = f.Host
			old.Port = f.Port
			merged = append(merged, old)
		} else {
			f.Client = NewLocalLSClient(f.Port, f.CSRFToken)
			if f.Host != "localhost" && f.Host != "127.0.0.1" {
				f.Client.BaseURL = fmt.Sprintf("http://%s:%d", f.Host, f.Port)
			}
			merged = append(merged, f)
		}
	}

	if len(merged) == 0 && len(c.instances) > 0 {
		slog.Warn("windsurf_ls_discovery_empty", "keeping_old", len(c.instances))
		return
	}

	c.instances = merged
}

func (c *DockerDiscoveryConnector) probeAll(ctx context.Context) {
	c.mu.RLock()
	snapshot := make([]*lsInstance, len(c.instances))
	copy(snapshot, c.instances)
	c.mu.RUnlock()

	for _, inst := range snapshot {
		healthy := c.probeOne(ctx, inst)
		inst.Healthy.Store(healthy)
		inst.LastProbeAt = time.Now()
		if healthy {
			inst.LastProbeErr = ""
		}
	}
}

func (c *DockerDiscoveryConnector) probeOne(_ context.Context, inst *lsInstance) bool {
	addr := fmt.Sprintf("%s:%d", inst.Host, inst.Port)
	conn, err := net.DialTimeout("tcp", addr, c.cfg.ProbeTimeout)
	if err != nil {
		inst.LastProbeErr = err.Error()
		if inst.Healthy.Load() {
			slog.Warn("windsurf_ls_unhealthy", "container", inst.ContainerName, "addr", addr, "error", err)
		}
		return false
	}
	conn.Close()
	if !inst.Healthy.Load() {
		slog.Info("windsurf_ls_healthy", "container", inst.ContainerName, "addr", addr)
	}
	return true
}

// InstanceStatuses returns detailed status for each discovered instance (for admin API).
func (c *DockerDiscoveryConnector) InstanceStatuses() []DockerLSInstanceStatus {
	c.mu.RLock()
	defer c.mu.RUnlock()

	result := make([]DockerLSInstanceStatus, len(c.instances))
	for i, inst := range c.instances {
		result[i] = DockerLSInstanceStatus{
			ContainerID:   inst.ContainerID,
			ContainerName: inst.ContainerName,
			Host:          inst.Host,
			Port:          inst.Port,
			Healthy:       inst.Healthy.Load(),
			DiscoveredAt:  inst.DiscoveredAt,
			LastProbeAt:   inst.LastProbeAt,
			LastProbeErr:  inst.LastProbeErr,
		}
	}
	return result
}

type DockerLSInstanceStatus struct {
	ContainerID   string    `json:"container_id"`
	ContainerName string    `json:"container_name"`
	Host          string    `json:"host"`
	Port          int       `json:"port"`
	Healthy       bool      `json:"healthy"`
	DiscoveredAt  time.Time `json:"discovered_at"`
	LastProbeAt   time.Time `json:"last_probe_at"`
	LastProbeErr  string    `json:"last_probe_err,omitempty"`
}

// NewCompatDockerConnector creates a discovery connector with a static fallback entry.
// It uses the legacy host/port/csrf config as an initial static instance, then overlays
// Docker API auto-discovery. If the configured host can't resolve, it falls back to 127.0.0.1.
func NewCompatDockerConnector(host string, port int, discoveryCfg DockerDiscoveryConfig) *DockerDiscoveryConnector {
	resolvedHost := host
	if _, err := net.LookupHost(host); err != nil {
		resolvedHost = "127.0.0.1"
		slog.Info("windsurf_ls_host_fallback", "original", host, "resolved", resolvedHost)
	}

	if discoveryCfg.DefaultCSRFToken == "" {
		discoveryCfg.DefaultCSRFToken = DefaultCSRF
	}
	discoveryCfg.FallbackHost = "127.0.0.1"
	discoveryCfg.defaults()

	ctx, cancel := context.WithCancel(context.Background())
	c := &DockerDiscoveryConnector{
		cfg:    discoveryCfg,
		cancel: cancel,
		done:   make(chan struct{}),
	}

	csrfToken := discoveryCfg.DefaultCSRFToken
	staticInst := &lsInstance{
		ContainerID:   "static",
		ContainerName: fmt.Sprintf("static-%s-%d", host, port),
		Host:          resolvedHost,
		Port:          port,
		CSRFToken:     csrfToken,
		Client:        NewLocalLSClient(port, csrfToken),
		DiscoveredAt:  time.Now(),
	}
	if resolvedHost != "localhost" && resolvedHost != "127.0.0.1" {
		staticInst.Client.BaseURL = fmt.Sprintf("http://%s:%d", resolvedHost, port)
	}

	c.mu.Lock()
	c.instances = []*lsInstance{staticInst}
	c.mu.Unlock()

	go c.loop(ctx)
	return c
}

// parsePortFromEnv extracts port from LS_PORT environment variable value.
func parsePortFromEnv(envVars []string) int {
	for _, e := range envVars {
		if strings.HasPrefix(e, "LS_PORT=") {
			p, err := strconv.Atoi(strings.TrimPrefix(e, "LS_PORT="))
			if err == nil {
				return p
			}
		}
	}
	return 0
}