// SPDX-License-Identifier: Apache-2.0

// Package sando is the small production runtime for code generated by Hime-san.
// It contains rendering contracts and context-specific output helpers, but no
// router, HTTP server, middleware, or development tooling.
package sando

import (
	"context"
	"errors"
	"io"
	"reflect"
)

// ABI identifies the generated-code contract implemented by this version of
// the runtime. Generated files should reference this constant so that their
// expected ABI is visible to readers and tooling.
const ABI = "sando.v1"

// RuntimeABI is a descriptive alias for ABI.
const RuntimeABI = ABI

var (
	// ErrNilComponent is returned when Render is asked to render a nil
	// component, including a typed nil held in a Component interface.
	ErrNilComponent = errors.New("sando: nil component")
	// ErrNilContext is returned when a component is rendered with a nil
	// context.Context.
	ErrNilContext = errors.New("sando: nil context")
	// ErrNilWriter is returned when a component is rendered with a nil writer.
	ErrNilWriter = errors.New("sando: nil writer")
)

// Component is the complete production rendering contract. Components are
// values rather than HTTP handlers so applications retain ownership of
// buffering, routing, headers, status codes, and error policy.
type Component interface {
	Render(context.Context, io.Writer) error
}

// ComponentFunc adapts a function to Component.
type ComponentFunc func(context.Context, io.Writer) error

// Render calls f with ctx and w.
func (f ComponentFunc) Render(ctx context.Context, w io.Writer) error {
	if f == nil {
		return ErrNilComponent
	}
	if ctx == nil {
		return ErrNilContext
	}
	if isNil(w) {
		return ErrNilWriter
	}
	return f(ctx, w)
}

// Render renders component into w. It reports nil inputs as errors rather than
// panicking, including typed nil component and writer values.
func Render(ctx context.Context, w io.Writer, component Component) error {
	if ctx == nil {
		return ErrNilContext
	}
	if isNil(w) {
		return ErrNilWriter
	}
	if isNil(component) {
		return ErrNilComponent
	}
	return component.Render(ctx, w)
}

// isNil recognizes typed nil values stored in interfaces. It is intentionally
// confined to API boundary validation and is not a component registry.
func isNil(value any) bool {
	if value == nil {
		return true
	}

	rv := reflect.ValueOf(value)
	switch rv.Kind() {
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
		return rv.IsNil()
	default:
		return false
	}
}