// Copyright 2026 Arctel.net
// SPDX-License-Identifier: Apache-2.0

// Package core provides the micro-kernel service bus, generic IoC container, and runtime extensions.
package core

import (
	"errors"
	"fmt"
	"reflect"
	"sync"
)

// Container manages service registration and resolution using Go reflection and generics.
type Container struct {
	mu        sync.RWMutex
	parent    *Container
	services  map[reflect.Type]any
	listeners map[reflect.Type][]func(any)
}

// NewContainer creates a new IoC container instance with an optional parent container.
func NewContainer(parent *Container) *Container {
	return &Container{
		parent:    parent,
		services:  make(map[reflect.Type]any),
		listeners: make(map[reflect.Type][]func(any)),
	}
}

func isNil(i any) bool {
	if i == nil {
		return true
	}
	v := reflect.ValueOf(i)
	switch v.Kind() {
	case reflect.Chan, reflect.Func, reflect.Map, reflect.Pointer, reflect.UnsafePointer, reflect.Interface, reflect.Slice:
		return v.IsNil()
	default:
		return false
	}
}

func (c *Container) remove(targetType reflect.Type) {
	c.mu.Lock()
	defer c.mu.Unlock()
	delete(c.services, targetType)
}

// Provide registers a typed service implementation into the Context hierarchy's root IoC container.
func Provide[T any](ctx *Context, service T) {
	if ctx == nil {
		panic("core: nil context provided to Provide")
	}
	if isNil(service) {
		panic("core: cannot provide nil service")
	}

	targetType := reflect.TypeFor[T]()
	targetContainer := ctx.Root().Container()
	targetContainer.provide(targetType, service)

	ctx.OnDispose(func() error {
		targetContainer.remove(targetType)
		return nil
	})
}

// ProvideScoped registers a typed service implementation strictly in the local Context container.
func ProvideScoped[T any](ctx *Context, service T) {
	if ctx == nil {
		panic("core: nil context provided to ProvideScoped")
	}
	if isNil(service) {
		panic("core: cannot provide nil service")
	}

	targetType := reflect.TypeFor[T]()
	targetContainer := ctx.Container()
	targetContainer.provide(targetType, service)

	ctx.OnDispose(func() error {
		targetContainer.remove(targetType)
		return nil
	})
}

func (c *Container) provide(targetType reflect.Type, service any) {
	c.mu.Lock()
	c.services[targetType] = service

	// Collect any matching listeners to invoke outside the lock
	var callbacks []func(any)
	svcType := reflect.TypeOf(service)
	for lType, cbs := range c.listeners {
		if lType == targetType || (lType.Kind() == reflect.Interface && svcType.Implements(lType)) {
			callbacks = append(callbacks, cbs...)
		}
	}
	c.mu.Unlock()

	for _, cb := range callbacks {
		cb(service)
	}
}

// Inject resolves a registered service of type T from the Context.
func Inject[T any](ctx *Context) (T, error) {
	var zero T
	if ctx == nil {
		return zero, ErrNilContext
	}

	targetType := reflect.TypeFor[T]()
	val, err := ctx.Container().resolve(targetType)
	if err != nil {
		return zero, err
	}

	typedVal, ok := val.(T)
	if !ok {
		return zero, fmt.Errorf("%w: cannot cast %T to %v", ErrServiceNotFound, val, targetType)
	}
	return typedVal, nil
}

func (c *Container) resolve(targetType reflect.Type) (any, error) {
	c.mu.RLock()
	// 1. Direct type match
	if val, ok := c.services[targetType]; ok {
		c.mu.RUnlock()
		return val, nil
	}

	// 2. Interface assignment scan
	if targetType.Kind() == reflect.Interface {
		for _, val := range c.services {
			if reflect.TypeOf(val).Implements(targetType) {
				c.mu.RUnlock()
				return val, nil
			}
		}
	}
	c.mu.RUnlock()

	// 3. Fallback to parent container
	if c.parent != nil {
		return c.parent.resolve(targetType)
	}

	return nil, fmt.Errorf("%w: %v", ErrServiceNotFound, targetType)
}

// MustInject resolves a service of type T or panics if the service is not found.
func MustInject[T any](ctx *Context) T {
	s, err := Inject[T](ctx)
	if err != nil {
		panic(fmt.Sprintf("core: failed to inject service %v: %v", reflect.TypeFor[T](), err))
	}
	return s
}

// Has returns true if a service of type T is registered and resolvable in the Context.
func Has[T any](ctx *Context) bool {
	_, err := Inject[T](ctx)
	return err == nil
}

// Using executes the given function synchronously if the required dependency is ready.
func Using[T1 any](ctx *Context, fn func(s1 T1)) error {
	s1, err := Inject[T1](ctx)
	if err != nil {
		return fmt.Errorf("%w: %w", ErrServiceNotReady, err)
	}
	fn(s1)
	return nil
}

// Using2 executes the given function synchronously if both required dependencies are ready.
func Using2[T1, T2 any](ctx *Context, fn func(s1 T1, s2 T2)) error {
	s1, err1 := Inject[T1](ctx)
	s2, err2 := Inject[T2](ctx)
	if err := errors.Join(err1, err2); err != nil {
		return fmt.Errorf("%w: %w", ErrServiceNotReady, err)
	}
	fn(s1, s2)
	return nil
}

// Using3 executes the given function synchronously if all 3 required dependencies are ready.
func Using3[T1, T2, T3 any](ctx *Context, fn func(s1 T1, s2 T2, s3 T3)) error {
	s1, err1 := Inject[T1](ctx)
	s2, err2 := Inject[T2](ctx)
	s3, err3 := Inject[T3](ctx)
	if err := errors.Join(err1, err2, err3); err != nil {
		return fmt.Errorf("%w: %w", ErrServiceNotReady, err)
	}
	fn(s1, s2, s3)
	return nil
}

// When registers a reactive hook that is called immediately if T is already provided,
// or called as soon as T is provided in the future.
func When[T any](ctx *Context, fn func(s T)) {
	if ctx == nil {
		panic("core: nil context provided to When")
	}

	targetType := reflect.TypeFor[T]()
	c := ctx.Container()

	// If already ready, execute immediately
	if s, err := Inject[T](ctx); err == nil {
		fn(s)
	}

	// Also register listener for future calls / updates
	c.mu.Lock()
	defer c.mu.Unlock()
	c.listeners[targetType] = append(c.listeners[targetType], func(val any) {
		if typed, ok := val.(T); ok {
			fn(typed)
		}
	})
}