// Package control wires the control plane together: inventory, catalog,
// placement and reconciliation, and publishes the result to the router.
package control

import (
	"context"
	"fmt"
	"log/slog"
	"strings"
	"sync"
	"time"

	"gitea.mynodes.xyz/ilker/llmgw/internal/control/catalog"
	"gitea.mynodes.xyz/ilker/llmgw/internal/control/inventory"
	"gitea.mynodes.xyz/ilker/llmgw/internal/control/reconciler"
	"gitea.mynodes.xyz/ilker/llmgw/internal/router/endpoint"
)

// EndpointSink receives the endpoint list. The router implements it.
//
// It is an interface so the control plane does not depend on the router: when
// the two split into separate processes, this becomes a watch stream and
// nothing above it changes (plan §3.1).
type EndpointSink interface {
	SetEndpoints(ctx context.Context, infos []endpoint.Info)
}

// Config tunes the control plane.
type Config struct {
	Reconciler reconciler.Config
	// PublishInterval is how often the endpoint list is republished even when
	// nothing appears to have changed. Events drive the common case; this is
	// the backstop.
	PublishInterval time.Duration
}

// DefaultConfig returns sensible defaults.
func DefaultConfig() Config {
	return Config{
		Reconciler:      reconciler.DefaultConfig(),
		PublishInterval: time.Second,
	}
}

// Controller owns the control plane's state.
type Controller struct {
	cfg  Config
	log  *slog.Logger
	inv  *inventory.Store
	cat  *catalog.Catalog
	rec  *reconciler.Reconciler
	sink EndpointSink

	mu   sync.Mutex
	last string // fingerprint of the last published list

	stop chan struct{}
	done chan struct{}
	once sync.Once
}

// New builds a controller.
func New(cfg Config, cat *catalog.Catalog, disp reconciler.Dispatcher, sink EndpointSink, log *slog.Logger) *Controller {
	if log == nil {
		log = slog.Default()
	}
	if cfg.PublishInterval <= 0 {
		cfg.PublishInterval = time.Second
	}
	inv := inventory.NewStore()
	return &Controller{
		cfg:  cfg,
		log:  log,
		inv:  inv,
		cat:  cat,
		rec:  reconciler.New(cfg.Reconciler, cat, inv, disp, log),
		sink: sink,
		stop: make(chan struct{}),
		done: make(chan struct{}),
	}
}

// Inventory exposes the node inventory, which the agent service feeds.
func (c *Controller) Inventory() *inventory.Store { return c.inv }

// Reconciler exposes the reconciliation loop, for status reports and ctl.
func (c *Controller) Reconciler() *reconciler.Reconciler { return c.rec }

// Catalog exposes the model catalog.
func (c *Controller) Catalog() *catalog.Catalog { return c.cat }

// Start runs the reconciler and begins publishing endpoints.
func (c *Controller) Start(ctx context.Context) {
	c.rec.Start(ctx)

	go func() {
		defer close(c.done)
		t := time.NewTicker(c.cfg.PublishInterval)
		defer t.Stop()

		c.Publish(ctx)
		for {
			select {
			case <-c.stop:
				return
			case <-ctx.Done():
				return
			case <-t.C:
				c.Publish(ctx)
			}
		}
	}()
}

// Close stops the control plane.
func (c *Controller) Close() {
	c.once.Do(func() {
		close(c.stop)
		<-c.done
		c.rec.Close()
	})
}

// Publish pushes the current Ready replicas to the sink.
//
// It is exported so tests can drive it deterministically instead of racing a
// ticker, and it skips the push when nothing changed: replacing the list is
// cheap but resynchronizes the metric pollers, and doing that every second for
// no reason adds churn to every engine's /metrics.
func (c *Controller) Publish(ctx context.Context) {
	infos := c.endpoints()

	fp := fingerprint(infos)
	c.mu.Lock()
	unchanged := fp == c.last
	c.last = fp
	c.mu.Unlock()
	if unchanged {
		return
	}

	c.log.Info("publishing endpoints", "count", len(infos))
	c.sink.SetEndpoints(ctx, infos)
}

// endpoints converts Ready replicas into the router's view.
func (c *Controller) endpoints() []endpoint.Info {
	ready := c.rec.ReadyReplicas()
	out := make([]endpoint.Info, 0, len(ready))

	for _, rep := range ready {
		m, ok := c.cat.Resolve(rep.Model)
		if !ok {
			// The model left the catalog while a replica was still running.
			// The reconciler will tear it down; until then, do not route to it.
			continue
		}
		// Clients may address a model by any of its names, and the router
		// matches endpoints by the resolved name plus aliases.
		names := append([]string{m.Name}, m.Aliases...)

		prof, _ := m.ProfileByName(rep.Profile)
		out = append(out, endpoint.Info{
			ID:       rep.ID,
			URL:      strings.TrimRight(rep.Endpoint, "/"),
			Models:   names,
			Engine:   prof.Engine,
			Pool:     rep.Pool,
			Weight:   rep.Weight,
			Priority: prof.Priority,
		})
	}
	return out
}

// fingerprint summarizes a list so an unchanged one can be skipped.
func fingerprint(infos []endpoint.Info) string {
	var b strings.Builder
	for _, i := range infos {
		fmt.Fprintf(&b, "%s|%s|%s|%s|%v|%g|%d;", i.ID, i.URL, i.Engine, i.Pool, i.Models, i.Weight, i.Priority)
	}
	return b.String()
}