package channel

import (
	"context"
	"fmt"
	"sync"

	"github.com/gochat/gochat/internal/model"
)

// ChannelRegistry is the plugin registration center for channel providers.
// Reference: P2D §4 — replaces Chatwoot's channel_type enum with runtime registration
// New channels just implement ChannelProvider + call Register(), no core code changes needed.
type ChannelRegistry struct {
	mu        sync.RWMutex
	providers map[ChannelType]ChannelProvider
}

// Global registry instance — all providers register here via init() or explicit call
var globalRegistry = &ChannelRegistry{
	providers: make(map[ChannelType]ChannelProvider),
}

// Register adds a channel provider to the global registry.
// Returns error if a provider of the same type is already registered.
// Pattern: each channel package calls channel.Register() in its init() function.
func Register(provider ChannelProvider) error {
	globalRegistry.mu.Lock()
	defer globalRegistry.mu.Unlock()

	ct := provider.Type()
	if _, exists := globalRegistry.providers[ct]; exists {
		return fmt.Errorf("channel type %s already registered", ct)
	}
	globalRegistry.providers[ct] = provider
	return nil
}

// MustRegister is like Register but panics on duplicate registration.
// Used in init() functions where failure is a programming error.
func MustRegister(provider ChannelProvider) {
	if err := Register(provider); err != nil {
		panic(err)
	}
}

// Get retrieves a channel provider by type from the global registry.
func Get(ct ChannelType) (ChannelProvider, error) {
	globalRegistry.mu.RLock()
	defer globalRegistry.mu.RUnlock()

	provider, ok := globalRegistry.providers[ct]
	if !ok {
		return nil, fmt.Errorf("channel type %s not registered", ct)
	}
	return provider, nil
}

// MustGet is like Get but panics if provider not found.
func MustGet(ct ChannelType) ChannelProvider {
	provider, err := Get(ct)
	if err != nil {
		panic(err)
	}
	return provider
}

// GetRegistry returns the global channel registry instance.
// Used by MessageBroker and other components that need access to the registry struct.
func GetRegistry() *ChannelRegistry {
	return globalRegistry
}

// RegisterOnInstance adds a channel provider to this registry instance.
// Returns error if a provider of the same type is already registered.
// This is the instance-level counterpart of the global Register() function.
func (r *ChannelRegistry) RegisterOnInstance(provider ChannelProvider) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	ct := provider.Type()
	if _, exists := r.providers[ct]; exists {
		return fmt.Errorf("channel type %s already registered", ct)
	}
	r.providers[ct] = provider
	return nil
}

// GetOnRegistry retrieves a channel provider by type from a specific registry instance.
func (r *ChannelRegistry) Get(ct ChannelType) (ChannelProvider, error) {
	r.mu.RLock()
	defer r.mu.RUnlock()

	provider, ok := r.providers[ct]
	if !ok {
		return nil, fmt.Errorf("channel type %s not registered", ct)
	}
	return provider, nil
}

// List returns all registered channel types.
func List() []ChannelType {
	globalRegistry.mu.RLock()
	defer globalRegistry.mu.RUnlock()

	types := make([]ChannelType, 0, len(globalRegistry.providers))
	for ct := range globalRegistry.providers {
		types = append(types, ct)
	}
	return types
}

// ListProviders returns all registered provider instances.
func ListProviders() []ChannelProvider {
	globalRegistry.mu.RLock()
	defer globalRegistry.mu.RUnlock()

	providers := make([]ChannelProvider, 0, len(globalRegistry.providers))
	for _, p := range globalRegistry.providers {
		providers = append(providers, p)
	}
	return providers
}

// IsRegistered checks if a channel type is registered.
func IsRegistered(ct ChannelType) bool {
	globalRegistry.mu.RLock()
	defer globalRegistry.mu.RUnlock()
	_, exists := globalRegistry.providers[ct]
	return exists
}

// ProcessIncomingMessage is the unified inbound message processing pipeline.
// Reference: P2D §8 — all inbound messages flow through this pipeline
// This is the primary entry point for webhook handlers and polling workers.
func ProcessIncomingMessage(ctx context.Context, ct ChannelType, inbox *model.Inbox, rawPayload []byte) (*IncomingMessage, error) {
	provider, err := Get(ct)
	if err != nil {
		return nil, fmt.Errorf("no provider for channel type %s: %w", ct, err)
	}
	return provider.ProcessIncoming(ctx, inbox, rawPayload)
}

// SendMessageToChannel is the unified outbound message sending pipeline.
// Reference: P2D §8 — all outbound messages flow through this pipeline
func SendMessageToChannel(ctx context.Context, ct ChannelType, inbox *model.Inbox, message *model.Message, contact *model.Contact) (*SendResult, error) {
	provider, err := Get(ct)
	if err != nil {
		return nil, fmt.Errorf("no provider for channel type %s: %w", ct, err)
	}
	return provider.SendMessage(ctx, inbox, message, contact)
}

// ValidateWebhookRequest delegates webhook validation to the appropriate provider.
func ValidateWebhookRequest(ctx context.Context, ct ChannelType, inbox *model.Inbox, request *WebhookRequest) error {
	provider, err := Get(ct)
	if err != nil {
		return fmt.Errorf("no provider for channel type %s: %w", ct, err)
	}
	return provider.ValidateWebhookRequest(ctx, inbox, request)
}