package monitor

import (
	"context"
	"database/sql"
	"fmt"
	"log/slog"
	"time"

	"git.wntrmute.dev/mc/mcp/internal/config"
	"git.wntrmute.dev/mc/mcp/internal/registry"
	"git.wntrmute.dev/mc/mcp/internal/runtime"
)

// Monitor watches container states and compares them to the registry,
// recording events and firing alerts on drift or flapping.
type Monitor struct {
	db      *sql.DB
	runtime runtime.Runtime
	cfg     config.MonitorConfig
	logger  *slog.Logger
	alerter *Alerter
	stopCh  chan struct{}
	done    chan struct{}

	prevState map[string]string // key: "service/component", value: observed state
}

// New creates a Monitor with the given dependencies.
func New(db *sql.DB, rt runtime.Runtime, cfg config.MonitorConfig, nodeName string, logger *slog.Logger) *Monitor {
	return &Monitor{
		db:        db,
		runtime:   rt,
		cfg:       cfg,
		logger:    logger,
		alerter:   NewAlerter(cfg, nodeName, db, logger),
		stopCh:    make(chan struct{}),
		done:      make(chan struct{}),
		prevState: make(map[string]string),
	}
}

// Start launches the monitoring goroutine.
func (m *Monitor) Start() {
	go m.run()
}

// Stop signals the monitoring goroutine to stop and waits for it to exit.
func (m *Monitor) Stop() {
	close(m.stopCh)
	<-m.done
}

func (m *Monitor) run() {
	defer close(m.done)
	defer func() {
		if r := recover(); r != nil {
			m.logger.Error("monitor panic recovered", "panic", fmt.Sprintf("%v", r))
		}
	}()

	ticker := time.NewTicker(m.cfg.Interval.Duration)
	defer ticker.Stop()

	for {
		select {
		case <-m.stopCh:
			return
		case <-ticker.C:
			m.tick()
		}
	}
}

func (m *Monitor) tick() {
	defer func() {
		if r := recover(); r != nil {
			m.logger.Error("monitor tick panic recovered", "panic", fmt.Sprintf("%v", r))
		}
	}()

	ctx := context.Background()

	// Get the current runtime state of all containers.
	containers, err := m.runtime.List(ctx)
	if err != nil {
		m.logger.Error("monitor: list containers", "error", err)
		return
	}

	// Index runtime containers by name for fast lookup.
	runtimeState := make(map[string]string, len(containers))
	for _, c := range containers {
		runtimeState[c.Name] = c.State
	}

	// Walk all registered services and their components.
	services, err := registry.ListServices(m.db)
	if err != nil {
		m.logger.Error("monitor: list services", "error", err)
		return
	}

	seen := make(map[string]struct{})

	for _, svc := range services {
		components, err := registry.ListComponents(m.db, svc.Name)
		if err != nil {
			m.logger.Error("monitor: list components", "error", err, "service", svc.Name)
			continue
		}

		for _, comp := range components {
			key := comp.Service + "/" + comp.Name
			seen[key] = struct{}{}
			containerName := comp.Service + "-" + comp.Name

			observed := "unknown"
			if state, ok := runtimeState[containerName]; ok {
				observed = state
			}

			prev, hasPrev := m.prevState[key]
			if !hasPrev {
				prev = comp.ObservedState
			}

			if observed != prev {
				if err := registry.InsertEvent(m.db, comp.Service, comp.Name, prev, observed); err != nil {
					m.logger.Error("monitor: insert event", "error", err, "key", key)
				}

				if err := registry.UpdateComponentState(m.db, comp.Service, comp.Name, "", observed); err != nil {
					m.logger.Error("monitor: update observed state", "error", err, "key", key)
				}

				m.logger.Info("state change", "service", comp.Service, "component", comp.Name, "prev", prev, "observed", observed)
			}

			m.alerter.Evaluate(comp.Service, comp.Name, comp.DesiredState, observed, prev)

			m.prevState[key] = observed
		}
	}

	// Evict entries for components that no longer exist in the registry.
	for key := range m.prevState {
		if _, ok := seen[key]; !ok {
			delete(m.prevState, key)
		}
	}

	// Prune old events.
	if _, err := registry.PruneEvents(m.db, time.Now().Add(-m.cfg.Retention.Duration)); err != nil {
		m.logger.Error("monitor: prune events", "error", err)
	}
}