package module

import (
	"fmt"
	"sort"
	"sync"

	"god-eye/internal/eventbus"
)

// Registry stores modules keyed by name. Modules register themselves via
// init() functions by calling Register on the default registry.
type Registry struct {
	mu      sync.RWMutex
	modules map[string]Module
	order   []string // insertion order for deterministic iteration
}

// NewRegistry returns an empty registry. Most callers should use Default()
// which returns the process-wide registry that init() functions populate.
func NewRegistry() *Registry {
	return &Registry{modules: make(map[string]Module)}
}

var (
	defaultRegistry *Registry
	defaultOnce     sync.Once
)

// Default returns the process-wide module registry.
func Default() *Registry {
	defaultOnce.Do(func() {
		defaultRegistry = NewRegistry()
	})
	return defaultRegistry
}

// Register adds m to r. Panics on duplicate name — registration happens at
// init() time, so duplicates indicate a compile-time bug that must surface
// immediately rather than silently overwrite.
func (r *Registry) Register(m Module) {
	if m == nil {
		panic("module.Register: nil module")
	}
	name := m.Name()
	if name == "" {
		panic("module.Register: module has empty Name()")
	}
	r.mu.Lock()
	defer r.mu.Unlock()
	if _, exists := r.modules[name]; exists {
		panic(fmt.Sprintf("module.Register: duplicate module %q", name))
	}
	r.modules[name] = m
	r.order = append(r.order, name)
}

// Register is a shortcut for Default().Register(m). Intended use:
//
//	func init() { module.Register(&myModule{}) }
func Register(m Module) { Default().Register(m) }

// Get returns the module with the given name.
func (r *Registry) Get(name string) (Module, bool) {
	r.mu.RLock()
	defer r.mu.RUnlock()
	m, ok := r.modules[name]
	return m, ok
}

// Names returns all registered module names in insertion order.
func (r *Registry) Names() []string {
	r.mu.RLock()
	defer r.mu.RUnlock()
	out := make([]string, len(r.order))
	copy(out, r.order)
	return out
}

// All returns every registered module in insertion order. The returned slice
// is safe for the caller to iterate but do not mutate it.
func (r *Registry) All() []Module {
	r.mu.RLock()
	defer r.mu.RUnlock()
	out := make([]Module, 0, len(r.order))
	for _, n := range r.order {
		out = append(out, r.modules[n])
	}
	return out
}

// ByPhase returns modules belonging to the given phase, sorted by name for
// stable presentation.
func (r *Registry) ByPhase(p Phase) []Module {
	r.mu.RLock()
	defer r.mu.RUnlock()
	var out []Module
	for _, n := range r.order {
		m := r.modules[n]
		if m.Phase() == p {
			out = append(out, m)
		}
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].Name() < out[j].Name() })
	return out
}

// Select returns the subset of modules that should run for the given config.
// A module is selected when cfg.ModuleEnabled(name) returns true (explicit
// enable wins), OR when cfg leaves it unset and DefaultEnabled() is true.
func (r *Registry) Select(cfg ConfigView) []Module {
	r.mu.RLock()
	defer r.mu.RUnlock()
	var out []Module
	for _, n := range r.order {
		m := r.modules[n]
		if cfg != nil {
			// explicit config: respect it directly
			if cfg.ModuleEnabled(m.Name()) {
				out = append(out, m)
				continue
			}
			// if the config has a non-default opinion (enabled=false), honor it
			// — but ModuleEnabled returning false could also mean "unset".
			// We resolve the ambiguity by checking whether any profile/CLI flag
			// set it via a separate mechanism; for now, fall back to the
			// module's default.
			if m.DefaultEnabled() {
				out = append(out, m)
			}
			continue
		}
		// no config: honor module default
		if m.DefaultEnabled() {
			out = append(out, m)
		}
	}
	return out
}

// ProducersOf returns the modules that declare t in their Produces() set.
// Used by tooling and tests to validate the event-graph integrity.
func (r *Registry) ProducersOf(t eventbus.EventType) []Module {
	r.mu.RLock()
	defer r.mu.RUnlock()
	var out []Module
	for _, n := range r.order {
		m := r.modules[n]
		for _, et := range m.Produces() {
			if et == t {
				out = append(out, m)
				break
			}
		}
	}
	return out
}

// ConsumersOf returns modules that declare t in their Consumes() set.
func (r *Registry) ConsumersOf(t eventbus.EventType) []Module {
	r.mu.RLock()
	defer r.mu.RUnlock()
	var out []Module
	for _, n := range r.order {
		m := r.modules[n]
		for _, et := range m.Consumes() {
			if et == t {
				out = append(out, m)
				break
			}
		}
	}
	return out
}

// Reset clears the registry. Intended for tests only; never call in production
// code.
func (r *Registry) Reset() {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.modules = make(map[string]Module)
	r.order = nil
}