package recon

import (
	"context"
	"sort"
	"sync"

	"github.com/panjf2000/ants/v2"
)

// Engine orchestrates parallel fanout across registered ReconSource implementations.
//
// Sources are registered once at startup (typically by phase-specific init()
// functions). SweepAll runs every enabled source in its own goroutine via an
// ants worker pool, aggregates their findings, and returns the combined slice.
// Deduplication is intentionally NOT performed here — callers use
// pkg/recon.Dedup (plan 09-03) on the returned slice.
type Engine struct {
	mu      sync.RWMutex
	sources map[string]ReconSource
}

// NewEngine returns an Engine with an empty source registry.
func NewEngine() *Engine {
	return &Engine{sources: make(map[string]ReconSource)}
}

// Register adds a source, keyed by s.Name(). Registering the same name twice
// replaces the previous instance (idempotent for identical sources).
func (e *Engine) Register(s ReconSource) {
	e.mu.Lock()
	defer e.mu.Unlock()
	e.sources[s.Name()] = s
}

// Get returns a registered source by name and true, or nil and false.
func (e *Engine) Get(name string) (ReconSource, bool) {
	e.mu.RLock()
	defer e.mu.RUnlock()
	s, ok := e.sources[name]
	return s, ok
}

// List returns registered source names in sorted order.
func (e *Engine) List() []string {
	e.mu.RLock()
	defer e.mu.RUnlock()
	names := make([]string, 0, len(e.sources))
	for n := range e.sources {
		names = append(names, n)
	}
	sort.Strings(names)
	return names
}

// SweepAll fans out to every enabled source in parallel via an ants pool and
// returns the aggregated findings. It respects ctx cancellation at the
// collection loop. Deduplication is performed by callers.
func (e *Engine) SweepAll(ctx context.Context, cfg Config) ([]Finding, error) {
	e.mu.RLock()
	active := make([]ReconSource, 0, len(e.sources))
	for _, s := range e.sources {
		if s.Enabled(cfg) {
			active = append(active, s)
		}
	}
	e.mu.RUnlock()

	if len(active) == 0 {
		return nil, nil
	}

	pool, err := ants.NewPool(len(active))
	if err != nil {
		return nil, err
	}
	defer pool.Release()

	out := make(chan Finding, 256)
	var wg sync.WaitGroup
	for _, s := range active {
		s := s
		wg.Add(1)
		if err := pool.Submit(func() {
			defer wg.Done()
			_ = s.Sweep(ctx, cfg.Query, out)
		}); err != nil {
			wg.Done()
		}
	}
	go func() {
		wg.Wait()
		close(out)
	}()

	var all []Finding
	for {
		select {
		case f, ok := <-out:
			if !ok {
				return all, nil
			}
			all = append(all, f)
		case <-ctx.Done():
			// Drain remaining so goroutines don't block on send.
			go func() {
				for range out {
				}
			}()
			return all, ctx.Err()
		}
	}
}