// 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.

package ofdgo

import (
	"context"
)

// pdfObjectChunkLimit 限制导入暂存片段的容量，不限制页面对象数量
const pdfObjectChunkLimit = 256

// pdfObjectBuffer 分块收集导入对象，提交前只整理一次连续数据
type pdfObjectBuffer struct {
	parts [][]GraphicObject
	size  int
}

// objectValidation 在单次导入中共享不可变资源的校验结果，隔离局部编辑器
// 返回: *editorValidation 当前编辑器的构建校验会话
func (p *pdfImporter) objectValidation() *editorValidation {
	if p.validation == nil || p.validation.Editor != p.editor {
		p.validation = &editorValidation{Editor: p.editor}
	}
	return p.validation
}

// appendObject 追加本次导入对象，按需建立独立暂存缓冲
// 入参: object 独立导入对象
func (p *pdfImporter) appendObject(object GraphicObject) {
	if p.objects == nil {
		p.objects = &pdfObjectBuffer{}
	}
	p.objects.append(object)
}

// append 追加对象，小批量连续存储，超过阈值后不复制前序片段
// 入参: object 独立对象
func (b *pdfObjectBuffer) append(object GraphicObject) {
	index := len(b.parts) - 1
	if index == 0 && len(b.parts[0]) == cap(b.parts[0]) && cap(b.parts[0]) < pdfObjectChunkLimit {
		part := b.parts[0]
		next := make([]GraphicObject, len(part), min(pdfObjectChunkLimit, max(1, cap(part)*2)))
		copy(next, part)
		b.parts[0] = next
	}
	if index < 0 || len(b.parts[index]) == cap(b.parts[index]) {
		capacity := pdfObjectChunkLimit
		if index < 0 {
			capacity = 1
		}
		b.parts = append(b.parts, make([]GraphicObject, 0, capacity))
		index++
	}
	b.parts[index] = append(b.parts[index], object)
	b.size++
}

// len 获取暂存对象数量，空缓冲返回零
// 返回: int 对象数量
func (b *pdfObjectBuffer) len() int {
	if b == nil {
		return 0
	}
	return b.size
}

// truncate 回滚到已有对象位置，清理丢弃对象及片段引用
// 入参: size 保留对象数量
func (b *pdfObjectBuffer) truncate(size int) {
	if size < 0 || size > b.len() {
		panic("invalid PDF object buffer size")
	}
	if size == b.len() {
		return
	}
	remaining := size
	for index, part := range b.parts {
		if remaining <= len(part) {
			clear(part[remaining:])
			b.parts[index] = part[:remaining]
			clear(b.parts[index+1:])
			b.parts = b.parts[:index+1]
			b.size = size
			return
		}
		remaining -= len(part)
	}
}

// data 按绘制顺序整理独立对象数组，取消时保留原片段供重试
// 入参: ctx 取消上下文
// 返回: []GraphicObject 暂存数据, error 取消错误
func (b *pdfObjectBuffer) data(ctx context.Context) ([]GraphicObject, error) {
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	if b.len() == 0 {
		return nil, nil
	}
	if len(b.parts) == 1 {
		return b.parts[0][:b.size:b.size], nil
	}
	objects := make([]GraphicObject, b.size)
	offset := 0
	for _, part := range b.parts {
		if err := ctx.Err(); err != nil {
			return nil, err
		}
		offset += copy(objects[offset:], part)
	}
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	b.parts[0] = objects
	clear(b.parts[1:])
	b.parts = b.parts[:1]
	return objects, nil
}

// commitObjects 将当前页面待转换对象写入编辑文档
// 返回: error 对象写入错误
func (p *pdfImporter) commitObjects() error {
	if p.objects.len() == 0 {
		return nil
	}
	objects, err := p.objects.data(p.ctx)
	if err != nil {
		return err
	}
	objects, err = p.sharedClipObjects(objects)
	if err != nil {
		return err
	}
	if err := p.objectValidation().appendOwnedObjects(p.ctx, p.page, objects); err != nil {
		return err
	}
	p.objects = nil
	return nil
}