ofdgo/internal/webui/webui_native.go

// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//go:build !js || !wasm

package webui

import (
	"bytes"
	"context"
	"encoding"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"maps"
	"math"
	"reflect"
	"runtime"
	"strings"
	"sync"

	"github.com/xiaoqidun/ofdgo"
)

const (
	platformTypeUndefined = iota
	platformTypeNumber
	platformTypeString
	platformTypeBoolean
	platformTypeObject
	platformTypeFunction
)

// nativeFields 缓存可直接展开的JSON字段，空值使用标准编码
var nativeFields sync.Map

// NativeResolver 将授权标识解析为随机读取源，生命周期由宿主管理
// 入参: token 资源授权标识
// 返回: io.ReaderAt 随机读取器, int64 资源大小, error 解析错误
type NativeResolver func(token string) (io.ReaderAt, int64, error)

// NativeOutputRequest 请求为整次批量转换预留唯一输出入口
type NativeOutputRequest struct {
	Destination           any
	Base, Extension, MIME string
	Paged                 bool
}

// NativeOutputTarget 保存预留目标，Name为根目录下可整体删除的入口名
// Destination交给OpenWriter，分页写入名为Base/页文件名，单文件写入名为Base.Extension
type NativeOutputTarget struct {
	Destination any
	Base, Name  string
}

// NativeEngine 保存独立会话，页面渲染可并行，修改等待已开始的只读任务完成
// 同一实例的回调不可重入Call或Close
// hooks应在首次Call前配置，Resolve返回的资源需保持有效直到相应会话关闭
type NativeEngine struct {
	businessEngine
	// Resources 协调会话的计算与缓存，需在首次Call前配置
	Resources *ofdgo.Resources
	// ConversionPool 协调不同会话的批量转换资源
	ConversionPool *ofdgo.ConversionPool
	// RenderParallelism 限制同时渲染的页面数，零值使用可用处理器数
	RenderParallelism int
	// Resolve 按授权标识提供资源读取源
	Resolve NativeResolver
	// LoadFont 按名称读取系统字体数据
	LoadFont func(context.Context, string) ([]byte, error)
	// OpenWriter 必须防止覆盖已有文件，成功时Close提交，失败时仅调用可选Abort
	// 不支持Abort的输出由宿主负责回收，宿主也负责回滚已完成的批量输出
	OpenWriter func(context.Context, any, string) (io.WriteCloser, error)
	// ReserveOutput 为单次批量预留整体入口，返回错误时由宿主释放未交付的预留
	ReserveOutput func(context.Context, NativeOutputRequest) (NativeOutputTarget, error)
	// CleanupOutput 必须幂等，以兼容前端收到output事件后重复removeEntry
	CleanupOutput func(context.Context, NativeOutputTarget) error
	gate          chan struct{}
	once          sync.Once
	saves         sync.WaitGroup
	closed        bool
	renderMu      sync.Mutex
	renderCount   int
	renderDone    chan struct{}
	renderSlots   chan struct{}
	renderIdle    []*Session
}

// nativeReader 在会话当前操作上下文中分块读取，不捕获已结束请求的上下文
type nativeReader struct {
	engine *NativeEngine
	input  io.ReaderAt
}

// nativeCall 保存单次worker适配状态
type nativeCall struct {
	engine      *NativeEngine
	ctx         context.Context
	emit        func(any)
	output      io.WriteCloser
	buffer      bytes.Buffer
	destination any
	files       []any
	currentName string
	mime        string
	size        int64
	exporting   bool
	batch       bool
	base        string
	extension   string
	paged       bool
	reserved    *NativeOutputTarget
	committed   bool
}

// platformValue 仅承载JSON参数、字节与宿主回调，不执行脚本
type platformValue struct{ value any }

// nativeCallback 同步宿主回调
type nativeCallback func(...any) (any, error)

// nativeField 保存字段名称、位置及空值省略规则
type nativeField struct {
	name      string
	index     int
	omitEmpty bool
}

// NewNativeEngine 创建独立业务会话，resolver不接收未经授权的文件路径
func NewNativeEngine(resolve NativeResolver) *NativeEngine { return &NativeEngine{Resolve: resolve} }

// Call 执行worker输入协议，返回ok/data/error，字节保持[]byte，emit不含请求id
// 入参: ctx 取消上下文, name 原操作名, args worker参数, emit 同步进度通知
// 返回: map[string]any 操作结果，宿主负责将二进制转换为资源句柄
// nativeFile只接受授权标识，size以Resolve结果为准，不接受路径字符串或nativeData输出标识
// 输出目标为nil时导出返回data.blob，批量返回data.files中的name、mime及file字节
// 批量输出到非nil目标时必须同时提供ReserveOutput和CleanupOutput，避免误清理既有文件
// 取消为协作式检查，不能抢占宿主阻塞的ReadAt、字体读取或加密库内部计算
func (e *NativeEngine) Call(ctx context.Context, name string, args []any, emit func(any)) (result map[string]any) {
	e.once.Do(func() {
		e.gate = make(chan struct{}, 1)
		e.renderSlots = make(chan struct{}, e.renderParallelism())
		e.resolveInput = e.input
		e.conversionPool = e.ConversionPool
		e.resources = e.Resources
	})
	if ctx == nil {
		ctx = context.Background()
	}
	if name == "ofdgoRenderPage" {
		select {
		case e.renderSlots <- struct{}{}:
			defer func() { <-e.renderSlots }()
		case <-ctx.Done():
			return nativeFailure(ctx.Err())
		}
		if e.resources != nil {
			release, err := e.resources.Acquire(ctx, 64<<20)
			if err != nil {
				return nativeFailure(err)
			}
			defer release()
		}
	}
	select {
	case e.gate <- struct{}{}:
	case <-ctx.Done():
		return nativeFailure(ctx.Err())
	}
	locked := true
	defer func() {
		if locked {
			<-e.gate
		}
	}()
	if err := ctx.Err(); err != nil {
		return nativeFailure(err)
	}
	if e.closed {
		return nativeFailure(fmt.Errorf("native engine is closed"))
	}
	if name == "ofdgoRenderPage" && e.currentSession != nil && e.pdf == nil {
		defer func() {
			if failure := recover(); failure != nil {
				result = nativeFailure(fmt.Errorf("%v", failure))
			}
		}()
		worker, err := e.renderSession(ctx)
		if err != nil {
			return nativeFailure(err)
		}
		operation := &businessEngine{currentSession: worker, currentEditor: e.currentEditor, ctx: ctx}
		values := make([]platformValue, len(args))
		for i, arg := range args {
			values[i] = platformValueOf(arg)
		}
		if len(values) > 0 && operation.currentEditor != nil {
			pageErr := e.prepareRender(operation, values[0].Int())
			if pageErr != nil {
				return nativeFailure(pageErr)
			}
		}
		operation.currentEditor = nil
		e.renderMu.Lock()
		if e.renderCount == 0 {
			e.renderDone = make(chan struct{})
		}
		e.renderCount++
		e.renderMu.Unlock()
		<-e.gate
		locked = false
		defer func() {
			worker.Renderer.OutputContext = context.Background()
			e.renderMu.Lock()
			if result != nil && result["ok"] == true && ctx.Err() == nil {
				e.currentSession.svgFonts = maps.Clone(worker.svgFonts)
				clear(worker.pageCache)
				worker.textCache.Clear()
				clear(worker.svgFonts)
				e.renderIdle = append(e.renderIdle, worker)
			}
			e.renderCount--
			if e.renderCount == 0 {
				close(e.renderDone)
			}
			e.renderMu.Unlock()
		}()
		data, err := operation.safeCall(operation.renderPage, values)
		if err != nil {
			return nativeFailure(err)
		}
		result = nativePlain(data).(map[string]any)
		if result["ok"] != true {
			return result
		}
		page := result["data"].(map[string]any)
		known := make(map[string]bool)
		if len(args) > 4 {
			for i := 0; i < values[4].Length(); i++ {
				known[values[4].Index(i).String()] = true
			}
		}
		for _, value := range page["fonts"].([]any) {
			font := value.(map[string]any)
			if name := font["name"].(string); !known[name] {
				font["data"] = worker.svgFonts[name]
			}
		}
		if e.currentEditor != nil && !(len(values) > 6 && values[6].Bool()) {
			objects, textErr := e.renderObjects(operation, values[0].Int())
			if textErr != nil {
				return nativeFailure(textErr)
			}
			page["objects"] = nativePlain(objects)
		}
		if err := ctx.Err(); err != nil {
			return nativeFailure(err)
		}
		return result
	}
	if err := e.waitRenders(ctx); err != nil {
		return nativeFailure(err)
	}
	e.renderIdle = nil
	if name == "ofdgoSaveSnapshot" {
		snapshot := e.saveSnapshot
		e.saveSnapshot = nil
		if snapshot == nil {
			return nativeFailure(fmt.Errorf("save snapshot is not prepared"))
		}
		output := &NativeEngine{OpenWriter: e.OpenWriter}
		output.currentEditor = snapshot
		e.saves.Add(1)
		defer e.saves.Done()
		<-e.gate
		locked = false
		defer output.Close()
		return output.Call(ctx, "ofdgoSaveDocument", args, emit)
	}
	e.ctx = ctx
	if e.currentSession != nil {
		e.currentSession.Renderer.OutputContext = ctx
	}
	defer func() {
		if e.currentSession != nil {
			e.currentSession.Renderer.OutputContext = context.Background()
		}
		e.ctx = nil
		if failure := recover(); failure != nil {
			if err, ok := failure.(error); ok {
				result = nativeFailure(err)
			} else {
				result = nativeFailure(fmt.Errorf("%v", failure))
			}
		}
	}()
	fn := e.businessCommands()[name]
	if fn == nil {
		return nativeFailure(fmt.Errorf("unknown operation: %s", name))
	}
	if err := e.checkDocument(name); err != nil {
		return nativeFailure(err)
	}
	call := &nativeCall{engine: e, ctx: ctx, emit: emit}
	if e.pdf != nil {
		e.pdf.progress = platformValueOf(call.progress("conversion", "", true))
		e.pdf.font = platformValueOf(nativeCallback(call.font))
	}
	defer func() {
		if err := call.abort(); err != nil {
			if result == nil || result["ok"] == true {
				result = nativeFailure(err)
			} else {
				result["error"] = fmt.Sprintf("%v; cleanup: %v", result["error"], err)
			}
		}
	}()
	prepared, err := call.prepare(name, append([]any(nil), args...))
	if err != nil {
		return nativeFailure(err)
	}
	values := make([]platformValue, len(prepared))
	for i, arg := range prepared {
		values[i] = platformValueOf(arg)
	}
	if err := e.preparePDF(name, values); err != nil {
		return nativeFailure(err)
	}
	data, err := e.safeCall(fn, values)
	if err != nil {
		return nativeFailure(err)
	}
	if err := ctx.Err(); err != nil {
		return nativeFailure(err)
	}
	if wrapped, ok := data.(platformValue); ok {
		result = nativePlain(wrapped).(map[string]any)
	} else {
		result = map[string]any{"ok": true, "data": nativePlain(data)}
	}
	if err := call.finish(name, result); err != nil {
		return nativeFailure(err)
	}
	return result
}

// Close 释放会话，不关闭宿主持有的ReaderAt资源
func (e *NativeEngine) Close() error {
	e.once.Do(func() {
		e.gate = make(chan struct{}, 1)
		e.renderSlots = make(chan struct{}, e.renderParallelism())
		e.resolveInput = e.input
	})
	e.gate <- struct{}{}
	defer func() { <-e.gate }()
	e.closed = true
	e.clearPDF()
	_, _ = e.discardPrint(nil)
	_ = e.waitRenders(context.Background())
	e.renderIdle = nil
	e.saveSnapshot = nil
	e.saves.Wait()
	var err error
	if e.currentSession != nil {
		err = e.currentSession.Close()
	}
	if e.pendingImport != nil {
		err = errors.Join(err, e.pendingImport.Close())
	}
	e.currentSession, e.currentEditor, e.pendingImport, e.copiedObjects, e.portableObjects, e.copiedStyle = nil, nil, nil, nil, nil, nil
	return err
}

// waitRenders 等待已开始的页面任务，取消等待不修改当前会话
// 入参: ctx 等待上下文
// 返回: error 取消错误
func (e *NativeEngine) waitRenders(ctx context.Context) error {
	e.renderMu.Lock()
	done, count := e.renderDone, e.renderCount
	e.renderMu.Unlock()
	if count == 0 {
		return ctx.Err()
	}
	select {
	case <-done:
		return ctx.Err()
	case <-ctx.Done():
		return ctx.Err()
	}
}

// renderParallelism 返回首次调用时采用的页面并行数
// 返回: int 同时运行的页面任务数
func (e *NativeEngine) renderParallelism() int {
	if e.RenderParallelism > 0 {
		return e.RenderParallelism
	}
	return runtime.GOMAXPROCS(0)
}

// renderSession 复用独立只读会话，调用时已持有引擎门控
// 入参: ctx 渲染上下文
// 返回: *Session 渲染会话, error 准备错误
func (e *NativeEngine) renderSession(ctx context.Context) (*Session, error) {
	e.renderMu.Lock()
	defer e.renderMu.Unlock()
	if count := len(e.renderIdle); count > 0 {
		worker := e.renderIdle[count-1]
		e.renderIdle[count-1] = nil
		e.renderIdle = e.renderIdle[:count-1]
		worker.Renderer.OutputContext = ctx
		return worker, nil
	}
	source := e.currentSession
	renderer, err := source.Renderer.Fork(ctx)
	if err != nil {
		return nil, err
	}
	return &Session{Reader: renderer.Reader, Renderer: renderer, doc: source.doc, fontFS: source.fontFS,
		pageCache: make(map[int]*ofdgo.PageContent), boxCache: append([]pageBoxInfo(nil), source.boxCache...),
		textCache: ofdgo.NewPageTextCache(sessionTextCacheBytes), svgFonts: make(map[string][]byte), editing: source.editing}, nil
}

// prepareRender 同步当前编辑页面的图元标识，避免并行访问编辑器缓存
// 入参: operation 只读任务, index 页面索引
// 返回: error 页面或取消错误
func (e *NativeEngine) prepareRender(operation *businessEngine, index int) error {
	e.renderMu.Lock()
	defer e.renderMu.Unlock()
	page, err := operation.currentEditor.Page(index)
	if err != nil {
		return err
	}
	return operation.syncEditorPageIDs(index, page)
}

// renderObjects 读取编辑图元信息，渲染状态由当前任务独立持有
// 入参: operation 只读任务, index 页面索引
// 返回: []any 图元信息, error 提取错误
func (e *NativeEngine) renderObjects(operation *businessEngine, index int) ([]any, error) {
	e.renderMu.Lock()
	defer e.renderMu.Unlock()
	operation.currentEditor = e.currentEditor
	if !reflect.DeepEqual(e.currentEditor.Backends(), operation.currentSession.Renderer.Backends()) {
		e.currentEditor.SetRenderBackends(operation.currentSession.Renderer.Backends())
	}
	text, err := operation.currentSession.PageText(index)
	if err != nil {
		return nil, err
	}
	return operation.editorObjects(index, text)
}

// input 读取授权源并以宿主报告的大小为准
func (e *NativeEngine) input(ctx context.Context, value any) (io.ReaderAt, int64, error) {
	if err := ctx.Err(); err != nil {
		return nil, 0, err
	}
	if p, ok := value.(platformValue); ok {
		value = p.value
	}
	if data, ok := value.([]byte); ok {
		return nativeReader{engine: e, input: bytes.NewReader(data)}, int64(len(data)), nil
	}
	descriptor, ok := value.(map[string]any)
	if !ok {
		return nil, 0, fmt.Errorf("expected bytes or nativeFile descriptor")
	}
	token, ok := descriptor["nativeFile"].(string)
	if !ok || token == "" || e.Resolve == nil {
		return nil, 0, fmt.Errorf("unauthorized native file")
	}
	input, size, err := e.Resolve(token)
	if err != nil {
		return nil, 0, err
	}
	if input == nil || size < 0 {
		return nil, 0, fmt.Errorf("invalid native file input")
	}
	return nativeReader{engine: e, input: input}, size, nil
}

// ReadAt 分块传递取消检查，宿主ReadAt自身阻塞时由宿主控制超时
func (r nativeReader) ReadAt(data []byte, offset int64) (int, error) {
	total := 0
	for len(data) > 0 {
		if err := r.engine.operationContext().Err(); err != nil {
			return total, err
		}
		n := min(len(data), 256<<10)
		got, err := r.input.ReadAt(data[:n], offset)
		total += got
		if err != nil {
			return total, err
		}
		if got != n {
			return total, io.ErrUnexpectedEOF
		}
		data, offset = data[n:], offset+int64(n)
	}
	return total, nil
}

// readBytes 分块读取完整资源并检查取消状态
// 入参: ctx 调用上下文, value 资源参数
// 返回: []byte 资源数据, error 读取错误
func (e *NativeEngine) readBytes(ctx context.Context, value any) ([]byte, error) {
	input, size, err := e.input(ctx, value)
	if err != nil {
		return nil, err
	}
	if size > int64(int(^uint(0)>>1)) {
		return nil, fmt.Errorf("resource exceeds address space")
	}
	output := make([]byte, int(size))
	for offset := int64(0); offset < size; {
		if err := ctx.Err(); err != nil {
			return nil, err
		}
		n := int(min(int64(256<<10), size-offset))
		got, err := input.ReadAt(output[int(offset):int(offset)+n], offset)
		if got != n {
			return nil, io.ErrUnexpectedEOF
		}
		if err != nil && err != io.EOF {
			return nil, err
		}
		offset += int64(got)
	}
	return output, nil
}

// nativePlain 保留字节并转换JSON结构
func nativePlain(value any) any {
	switch v := value.(type) {
	case platformValue:
		return nativePlain(v.value)
	case []byte:
		return v
	case map[string]any:
		result := make(map[string]any, len(v))
		for k, item := range v {
			result[k] = nativePlain(item)
		}
		return result
	case nil:
		return nil
	}
	v := reflect.ValueOf(value)
	if v.Kind() == reflect.Slice || v.Kind() == reflect.Array {
		result := make([]any, v.Len())
		for i := range result {
			result[i] = nativePlain(v.Index(i).Interface())
		}
		return result
	}
	if v.Kind() == reflect.Pointer {
		if v.IsNil() {
			return nil
		}
		return nativePlain(v.Elem().Interface())
	}
	if v.Kind() == reflect.Struct {
		if fields := nativeStructFields(v.Type()); fields != nil {
			result := make(map[string]any, len(fields))
			for _, field := range fields {
				item := v.Field(field.index)
				if field.omitEmpty {
					switch item.Kind() {
					case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
						if item.Len() == 0 {
							continue
						}
					default:
						if item.Kind() != reflect.Struct && item.IsZero() {
							continue
						}
					}
				}
				result[field.name] = nativePlain(item.Interface())
			}
			return result
		}
		data, err := json.Marshal(value)
		if err != nil {
			panic(err)
		}
		var result any
		if err := json.Unmarshal(data, &result); err != nil {
			panic(err)
		}
		if fields, ok := result.(map[string]any); ok {
			for i := 0; i < v.NumField(); i++ {
				field := v.Type().Field(i)
				if !field.IsExported() {
					continue
				}
				name := strings.Split(field.Tag.Get("json"), ",")[0]
				if name == "-" {
					continue
				}
				if field.Anonymous && name == "" {
					if embedded, ok := nativePlain(v.Field(i).Interface()).(map[string]any); ok {
						for key, value := range embedded {
							if _, exists := fields[key]; exists {
								fields[key] = value
							}
						}
					}
					continue
				}
				if name == "" {
					name = field.Name
				}
				if _, exists := fields[name]; exists {
					fields[name] = nativePlain(v.Field(i).Interface())
				}
			}
		}
		return result
	}
	if v.Kind() == reflect.Float32 || v.Kind() == reflect.Float64 {
		if number := v.Float(); math.IsNaN(number) || math.IsInf(number, 0) {
			_, err := json.Marshal(value)
			panic(err)
		}
	}
	return value
}

// nativeStructFields 按类型复用普通结构体字段，自定义编码和嵌入字段交给JSON处理
// 入参: value 结构体类型
// 返回: []nativeField 字段列表，nil表示使用标准编码
func nativeStructFields(value reflect.Type) []nativeField {
	if fields, ok := nativeFields.Load(value); ok {
		return fields.([]nativeField)
	}
	var fields []nativeField
	if nativePlainType(value, make(map[reflect.Type]bool)) {
		fields = make([]nativeField, 0, value.NumField())
		for i := 0; i < value.NumField(); i++ {
			field := value.Field(i)
			if !field.IsExported() || field.Tag.Get("json") == "-" {
				continue
			}
			name, options, _ := strings.Cut(field.Tag.Get("json"), ",")
			if name == "" {
				name = field.Name
			}
			fields = append(fields, nativeField{name: name, index: i, omitEmpty: options == "omitempty"})
		}
	}
	stored, _ := nativeFields.LoadOrStore(value, fields)
	return stored.([]nativeField)
}

// nativePlainType 检查类型是否可直接展开，递归引用及复杂字段沿用标准编码
// 入参: value 字段类型, visiting 当前类型路径
// 返回: bool 是否可直接展开
func nativePlainType(value reflect.Type, visiting map[reflect.Type]bool) bool {
	if visiting[value] || value.Implements(reflect.TypeFor[json.Marshaler]()) || value.Implements(reflect.TypeFor[encoding.TextMarshaler]()) || reflect.PointerTo(value).Implements(reflect.TypeFor[json.Marshaler]()) || reflect.PointerTo(value).Implements(reflect.TypeFor[encoding.TextMarshaler]()) || value == reflect.TypeFor[json.Number]() {
		return false
	}
	visiting[value] = true
	defer delete(visiting, value)
	switch value.Kind() {
	case reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.Float32, reflect.Float64, reflect.String:
		return true
	case reflect.Pointer, reflect.Slice, reflect.Array:
		return nativePlainType(value.Elem(), visiting)
	case reflect.Struct:
		names := make(map[string]bool)
		for i := 0; i < value.NumField(); i++ {
			field := value.Field(i)
			if field.Anonymous {
				return false
			}
			if !field.IsExported() || field.Tag.Get("json") == "-" {
				continue
			}
			name, options, _ := strings.Cut(field.Tag.Get("json"), ",")
			if name == "" {
				name = field.Name
			}
			if name == "-" || names[name] || options != "" && options != "omitempty" || !nativePlainType(field.Type, visiting) {
				return false
			}
			for _, char := range name {
				if char != '_' && char != '-' && (char < 'a' || char > 'z') && (char < 'A' || char > 'Z') && (char < '0' || char > '9') {
					return false
				}
			}
			names[name] = true
		}
		return true
	}
	return false
}

// nativeFailure 转换结构化业务错误
func nativeFailure(err error) map[string]any {
	result := nativePlain(failureResult(err)).(map[string]any)
	if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
		result["canceled"] = true
	}
	return result
}

// event 发送标准worker进度
func (c *nativeCall) event(value map[string]any) {
	if c.emit != nil {
		c.emit(value)
	}
}

// checkpoint 检查操作取消
func (c *nativeCall) checkpoint(...any) (any, error) { return nil, c.ctx.Err() }

// progress 创建标准进度回调
func (c *nativeCall) progress(kind, stage string, phased bool) nativeCallback {
	return func(args ...any) (any, error) {
		if err := c.ctx.Err(); err != nil {
			return nil, err
		}
		event := map[string]any{"type": kind}
		if stage != "" {
			event["stage"] = stage
		}
		if phased {
			event["phase"], event["completed"], event["total"] = args[0], args[1], args[2]
		} else {
			event["completed"], event["total"] = args[0], args[1]
		}
		c.event(event)
		return nil, c.ctx.Err()
	}
}

// readCallback 创建有界随机读取回调
func (c *nativeCall) readCallback(value any) (nativeCallback, int64, error) {
	input, size, err := c.engine.input(c.ctx, value)
	if err != nil {
		return nil, 0, err
	}
	return func(args ...any) (any, error) {
		if err := c.ctx.Err(); err != nil {
			return nil, err
		}
		offset, n := int64(platformValueOf(args[0]).Float()), platformValueOf(args[1]).Int()
		if offset < 0 || n < 0 || n > 256<<10 || offset > size || int64(n) > size-offset {
			return nil, fmt.Errorf("invalid native read range")
		}
		data := make([]byte, n)
		got, err := input.ReadAt(data, offset)
		if got != n {
			return nil, io.ErrUnexpectedEOF
		}
		if err != nil && err != io.EOF {
			return nil, err
		}
		return data, nil
	}, size, nil
}

// write 写出数据块
func (c *nativeCall) write(args ...any) (any, error) {
	if err := c.ctx.Err(); err != nil {
		return nil, err
	}
	value := platformValueOf(args[0])
	data, ok := value.value.([]byte)
	if !ok {
		return nil, fmt.Errorf("expected output bytes")
	}
	var writer io.Writer = &c.buffer
	if c.output != nil {
		writer = c.output
	}
	n, err := writer.Write(data)
	c.size += int64(n)
	if err == nil && n != len(data) {
		err = io.ErrShortWrite
	}
	return nil, err
}

// open 创建宿主输出，目标只交给授权hook解释
func (c *nativeCall) open(name string) error {
	c.currentName = name
	c.buffer.Reset()
	if c.destination == nil {
		return nil
	}
	if c.engine.OpenWriter == nil {
		return fmt.Errorf("native output resolver is not configured")
	}
	var err error
	c.output, err = c.engine.OpenWriter(c.ctx, c.destination, name)
	if err == nil && c.output == nil {
		return fmt.Errorf("native output resolver returned nil")
	}
	return err
}

// boundary 处理批量输出文件边界
func (c *nativeCall) boundary(args ...any) (any, error) {
	if err := c.ctx.Err(); err != nil {
		return nil, err
	}
	action, name := args[0].(string), args[1].(string)
	if action == "open" {
		if c.paged {
			name = c.base + "/" + name
		} else {
			name = c.base + "." + c.extension
		}
		return nil, c.open(name)
	}
	file := map[string]any{"name": c.currentName, "mime": c.mime}
	if c.output != nil {
		if err := c.output.Close(); err != nil {
			return nil, err
		}
		c.output = nil
	} else {
		file["file"] = append([]byte(nil), c.buffer.Bytes()...)
	}
	c.files = append(c.files, file)
	c.buffer.Reset()
	return nil, nil
}

// font 按需请求授权字体
func (c *nativeCall) font(args ...any) (any, error) {
	if err := c.ctx.Err(); err != nil {
		return nil, err
	}
	if c.engine.LoadFont == nil {
		return nil, fmt.Errorf("native font resolver is not configured")
	}
	return c.engine.LoadFont(c.ctx, args[0].(string))
}

// fileCallback 逐个读取图片或附件
func (c *nativeCall) fileCallback(files platformValue) nativeCallback {
	return func(args ...any) (any, error) {
		data, err := c.engine.readBytes(c.ctx, files.Index(platformValueOf(args[0]).Int()).value)
		if err != nil {
			return nil, err
		}
		return map[string]any{"bytes": data}, nil
	}
}

// prepare 将worker输入转换为共用业务参数
func (c *nativeCall) prepare(name string, args []any) ([]any, error) {
	checkpoint := nativeCallback(c.checkpoint)
	write := nativeCallback(c.write)
	switch name {
	case "ofdgoDetectFormat":
		if len(args) != 1 {
			return nil, fmt.Errorf("missing detection input")
		}
		read, size, err := c.readCallback(args[0])
		return []any{read, size, checkpoint}, err
	case "ofdgoConvertFile":
		if len(args) != 4 {
			return nil, fmt.Errorf("missing conversion input")
		}
		read, size, err := c.readCallback(args[0])
		if err != nil {
			return nil, err
		}
		c.destination, c.batch = args[3], true
		options := platformValueOf(args[1])
		c.base = nativeOutputBase(options.Get("base"))
		for _, f := range ofdgo.OutputFormats() {
			if f.Value == options.Get("format").String() {
				c.mime = f.MIME
				c.extension, c.paged = f.Extension, f.Paged
			}
		}
		if c.extension == "" {
			return nil, fmt.Errorf("unsupported conversion format")
		}
		if c.destination != nil {
			if c.engine.ReserveOutput == nil || c.engine.CleanupOutput == nil {
				return nil, fmt.Errorf("batch destination requires reservation and cleanup hooks")
			}
			target, err := c.engine.ReserveOutput(c.ctx, NativeOutputRequest{Destination: c.destination, Base: c.base, Extension: c.extension, MIME: c.mime, Paged: c.paged})
			if err != nil {
				return nil, err
			}
			c.reserved = &target
			if target.Destination == nil || target.Base == "" || target.Name == "" || nativeOutputBase(platformValueOf(target.Base)) != target.Base {
				return nil, fmt.Errorf("invalid reserved output target")
			}
			c.destination, c.base = target.Destination, target.Base
			c.event(map[string]any{"type": "output", "name": target.Name})
		}
		return []any{read, size, args[1], write, c.progress("conversion", "", true), nativeCallback(c.boundary), checkpoint, args[2], nativeCallback(c.font)}, nil
	case "ofdgoPackFiles":
		if len(args) != 3 {
			return nil, fmt.Errorf("missing archive input")
		}
		entries := platformValueOf(args[0])
		metadata := make([]any, entries.Length())
		readers := make([]nativeCallback, entries.Length())
		for i := range readers {
			entry := entries.Index(i)
			read, size, err := c.readCallback(entry.Get("file").value)
			if err != nil {
				return nil, err
			}
			readers[i] = read
			metadata[i] = map[string]any{"name": entry.Get("name").String(), "size": size}
		}
		c.destination, c.exporting = args[1], true
		if err := c.open(""); err != nil {
			return nil, err
		}
		progress := nativeCallback(func(values ...any) (any, error) {
			c.event(map[string]any{"type": "conversion", "phase": "pack", "completed": values[0], "total": values[1]})
			return nil, c.ctx.Err()
		})
		return []any{metadata, nativeCallback(func(values ...any) (any, error) { return readers[platformValueOf(values[0]).Int()], nil }), write, progress, checkpoint, args[2]}, nil
	case "ofdgoChangeAttachment":
		if len(args) > 3 && (args[0] == "add" || args[0] == "replace") {
			args[3] = c.fileCallback(platformValueOf(args[3]))
		}
	case "ofdgoChangeResource":
		if len(args) > 4 && (args[0] == "add" || args[0] == "replace") {
			data, err := c.engine.readBytes(c.ctx, args[4])
			if err != nil {
				return nil, err
			}
			args[4] = data
		}
	case "ofdgoImportImages":
		if len(args) != 5 {
			return nil, fmt.Errorf("missing image import input")
		}
		files := platformValueOf(args[0])
		names := make([]any, files.Length())
		for i := range names {
			names[i] = files.Index(i).Get("name").String()
		}
		args[0] = names
		args = append(args, c.fileCallback(files))
	}
	switch name {
	case "ofdgoResources", "ofdgoPrepareSave":
		return append(args, checkpoint), nil
	case "ofdgoImportPages", "ofdgoImportDocuments", "ofdgoImportImages":
		return append(args, c.progress("import", "", true)), nil
	case "ofdgoOpenPDF":
		return append(args, c.progress("conversion", "", true), nativeCallback(c.font)), nil
	case "ofdgoExportImages", "ofdgoExportPage", "ofdgoExportDocument", "ofdgoExportAttachment", "ofdgoExportResource", "ofdgoExportMedia", "ofdgoExportVersion", "ofdgoSaveDocument", "ofdgoSaveSigned":
		if len(args) == 0 {
			return nil, fmt.Errorf("missing output arguments")
		}
		c.destination, c.exporting = args[len(args)-1], true
		args = args[:len(args)-1]
		if err := c.open(""); err != nil {
			return nil, err
		}
		saving := name == "ofdgoSaveDocument" || name == "ofdgoSaveSigned"
		var indices, compression any
		if saving {
			if name != "ofdgoSaveSigned" && len(args) > 0 {
				if m, ok := args[len(args)-1].(map[string]any); ok && m["mode"] != nil {
					compression = m
					args = args[:len(args)-1]
				}
			}
			if len(args) == 0 {
				return nil, fmt.Errorf("missing save page selection")
			}
			indices, args = args[0], args[1:]
		}
		args = append(args, write)
		if name == "ofdgoExportDocument" {
			args = append(args, c.progress("export", "pages", false))
		}
		if name == "ofdgoExportVersion" {
			args = append(args, c.progress("export", "prepare", true), checkpoint)
		}
		if saving {
			args = append(args, c.progress("export", "prepare", true))
			if compression != nil {
				args = append(args, indices, compression, checkpoint)
			} else if indices != nil {
				args = append(args, indices)
			}
		} else {
			for _, arg := range args {
				if m, ok := arg.(map[string]any); ok && m["mode"] != nil {
					args = append(args, checkpoint)
					break
				}
			}
		}
	}
	return args, nil
}

// finish 完成输出并保留原生字节
func (c *nativeCall) finish(name string, result map[string]any) error {
	if !c.exporting && !c.batch {
		return nil
	}
	data, ok := result["data"].(map[string]any)
	if !ok {
		return fmt.Errorf("invalid output result")
	}
	if c.batch {
		if data["unchanged"] == true && c.size == 0 {
			c.files = []any{}
			if err := c.abort(); err != nil {
				return err
			}
		}
		data["files"] = c.files
	} else if c.output != nil {
		if err := c.output.Close(); err != nil {
			return err
		}
		c.output = nil
	} else {
		data["blob"] = c.buffer.Bytes()
		c.buffer = bytes.Buffer{}
	}
	data["size"] = c.size
	c.committed = true
	if c.exporting && name != "ofdgoExportMedia" && name != "ofdgoPackFiles" {
		c.event(map[string]any{"type": "export", "stage": "save"})
	}
	return nil
}

// abort 失败时释放尚未提交的宿主输出，支持可选Abort回滚
func (c *nativeCall) abort() error {
	var err error
	if c.output != nil {
		if output, ok := c.output.(interface{ Abort() error }); ok {
			err = output.Abort()
		}
		c.output = nil
	}
	if c.reserved != nil && !c.committed {
		target := *c.reserved
		c.reserved = nil
		err = errors.Join(err, c.engine.CleanupOutput(context.WithoutCancel(c.ctx), target))
	}
	return err
}

// nativeOutputBase 清理worker输出文件名，冲突后缀由宿主排他创建决定
func nativeOutputBase(value platformValue) string {
	base := "document"
	if value.Type() == platformTypeString {
		base = value.String()
	}
	base = strings.Map(func(r rune) rune {
		if r < 32 || strings.ContainsRune("<>:\"/\\|?*", r) {
			return '_'
		}
		return r
	}, base)
	base = strings.TrimRight(base, ". ")
	if base == "" {
		return "document"
	}
	return base
}

// inputFromValue 读取宿主授权的随机读取源
func (e *businessEngine) inputFromValue(value platformValue) (*ofdgo.Input, error) {
	reader, size, err := e.resolveInput(e.operationContext(), value.value)
	if err != nil {
		return nil, err
	}
	return ofdgo.NewInput(reader, size)
}

// platformValueOf 包装参数
func platformValueOf(v any) platformValue {
	if p, ok := v.(platformValue); ok {
		return p
	}
	return platformValue{v}
}

// platformNull 返回空参数
func platformNull() platformValue { return platformValue{} }

// Type 返回协议参数类型
func (v platformValue) Type() int {
	switch v.value.(type) {
	case nil:
		return platformTypeUndefined
	case string:
		return platformTypeString
	case bool:
		return platformTypeBoolean
	case nativeCallback:
		return platformTypeFunction
	case float64, float32, int, int64, uint64, json.Number:
		return platformTypeNumber
	default:
		return platformTypeObject
	}
}

// IsNull 检查空参数
func (v platformValue) IsNull() bool { return v.value == nil }

// IsUndefined 检查缺省参数
func (v platformValue) IsUndefined() bool { return v.value == nil }

// String 读取字符串
func (v platformValue) String() string {
	if v.value == nil {
		return "<undefined>"
	}
	return fmt.Sprint(v.value)
}

// Bool 读取布尔参数
func (v platformValue) Bool() bool {
	b, ok := v.value.(bool)
	if !ok {
		panic("expected boolean")
	}
	return b
}

// Float 读取数值参数
func (v platformValue) Float() float64 {
	switch n := v.value.(type) {
	case float64:
		return n
	case float32:
		return float64(n)
	case int:
		return float64(n)
	case int64:
		return float64(n)
	case uint64:
		return float64(n)
	case json.Number:
		f, err := n.Float64()
		if err != nil {
			panic(err)
		}
		return f
	default:
		panic("expected number")
	}
}

// Int 读取整数参数
func (v platformValue) Int() int { return int(v.Float()) }

// Get 读取对象字段
func (v platformValue) Get(key string) platformValue {
	if m, ok := v.value.(map[string]any); ok {
		return platformValueOf(m[key])
	}
	if key == "length" || key == "byteLength" {
		return platformValueOf(v.Length())
	}
	return platformNull()
}

// Length 读取数组长度
func (v platformValue) Length() int {
	if v.value == nil {
		return 0
	}
	return reflect.ValueOf(v.value).Len()
}

// Index 读取数组元素
func (v platformValue) Index(i int) platformValue {
	return platformValueOf(reflect.ValueOf(v.value).Index(i).Interface())
}

// Invoke 调用宿主函数
func (v platformValue) Invoke(args ...any) platformValue {
	result, err := v.value.(nativeCallback)(args...)
	if err != nil {
		panic(err)
	}
	return platformValueOf(result)
}

// platformCopyBytes 复制读取块
func platformCopyBytes(dst []byte, src platformValue) int {
	return copy(dst, src.value.([]byte))
}

// platformJSON 编码小参数
func platformJSON(v platformValue) string {
	data, err := json.Marshal(v.value)
	if err != nil {
		panic(err)
	}
	return string(data)
}

// platformParseJSON 解析小参数
func platformParseJSON(data []byte) map[string]any {
	var v map[string]any
	if err := json.Unmarshal(data, &v); err != nil {
		panic(err)
	}
	return v
}

// bytesToJS 保留原生二进制数据
func bytesToJS(data []byte) platformValue { return platformValueOf(data) }

// bytesFromJS 读取字节或授权资源
func (e *businessEngine) bytesFromJS(v platformValue) ([]byte, error) {
	if data, ok := v.value.([]byte); ok {
		return append([]byte(nil), data...), nil
	}
	input, err := e.inputFromValue(v)
	if err != nil {
		return nil, err
	}
	defer input.Close()
	return io.ReadAll(io.NewSectionReader(input, 0, input.Size()))
}

// successResult 保留二进制返回结构
func successResult(data any) platformValue {
	return platformValueOf(map[string]any{"ok": true, "data": data})
}

// awaitExport 执行可取消宿主回调
func awaitExport(fn platformValue, args ...any) error {
	_, err := fn.value.(nativeCallback)(args...)
	return err
}

// loadConversionFont 读取宿主授权字体
func (e *businessEngine) loadConversionFont(fn platformValue, name string) ([]byte, error) {
	result, err := fn.value.(nativeCallback)(name)
	if err != nil {
		return nil, err
	}
	return e.bytesFromJS(platformValueOf(result))
}