/*
 *  Copyright (c) 2023-2026, Easy-Agents (fuhai999@gmail.com).
 *  <p>
 *  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
 *  <p>
 *  http://www.apache.org/licenses/LICENSE-2.0
 *  <p>
 *  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 com.easyagents.core.file2text.extractor.impl;

import com.easyagents.core.file2text.DocumentReadErrorCode;
import com.easyagents.core.file2text.DocumentReadException;
import com.easyagents.core.file2text.DocumentReadSupport;
import com.easyagents.core.file2text.DocumentTextSegment;
import com.easyagents.core.file2text.LightweightDocumentReadRequest;
import com.easyagents.core.file2text.LightweightDocumentReadResult;
import com.easyagents.core.file2text.extractor.FileExtractor;
import com.easyagents.core.file2text.source.DocumentSource;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.encryption.InvalidPasswordException;
import org.apache.pdfbox.text.PDFTextStripper;

import java.io.IOException;
import java.io.InputStream;
import java.util.Collections;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * PDF 文本提取器
 * 支持标准 PDF（非扫描件）
 */
public class PdfTextExtractor implements FileExtractor {

    private static final Set<String> SUPPORTED_MIME_TYPES;
    private static final Set<String> SUPPORTED_EXTENSIONS;

    static {
        Set<String> mimeTypes = new HashSet<>();
        mimeTypes.add("application/pdf");
        SUPPORTED_MIME_TYPES = Collections.unmodifiableSet(mimeTypes);

        Set<String> extensions = new HashSet<>();
        extensions.add("pdf");
        SUPPORTED_EXTENSIONS = Collections.unmodifiableSet(extensions);
    }

    @Override
    public boolean supports(DocumentSource source) {
        String mimeType = source.getMimeType();
        String fileName = source.getFileName();

        if (mimeType != null && SUPPORTED_MIME_TYPES.contains(mimeType)) {
            return true;
        }

        if (fileName != null) {
            String ext = getExtension(fileName);
            return "pdf".equalsIgnoreCase(ext);
        }

        return false;
    }

    @Override
    public String extractText(DocumentSource source) throws IOException {
        return read(new LightweightDocumentReadRequest(source)).getText();
    }

    /**
     * 按页读取 PDF 文本层。
     *
     * @param request 读取请求
     * @return 按页结构化结果
     * @throws IOException PDF I/O 失败
     */
    @Override
    public LightweightDocumentReadResult read(LightweightDocumentReadRequest request) throws IOException {
        DocumentSource source = request.getSource();
        try (InputStream is = source.openStream();
             PDDocument doc = PDDocument.load(is)) {
            if (doc.isEncrypted()) {
                throw new DocumentReadException(DocumentReadErrorCode.DOCUMENT_ENCRYPTED,
                        "Encrypted PDF is not supported");
            }
            int pages = doc.getNumberOfPages();
            if (pages > request.getMaxPdfPages()) {
                throw new DocumentReadException(DocumentReadErrorCode.DOCUMENT_STRUCTURE_LIMIT_EXCEEDED,
                        "PDF page count exceeds " + request.getMaxPdfPages());
            }
            PDFTextStripper stripper = new PDFTextStripper();
            List<DocumentTextSegment> segments = new ArrayList<>();
            int offset = 0;
            for (int page = 1; page <= pages; page++) {
                request.checkCancelled();
                stripper.setStartPage(page);
                stripper.setEndPage(page);
                String text = stripper.getText(doc).trim();
                if (!text.isEmpty()) {
                    DocumentTextSegment segment = DocumentReadSupport.segment(
                            "page-" + page, text, "PAGE", "第 " + page + " 页", offset, List.of());
                    segments.add(segment);
                    offset = segment.getEndIndex() + 1;
                }
            }
            return DocumentReadSupport.result(source, segments, request);
        } catch (InvalidPasswordException e) {
            throw new DocumentReadException(DocumentReadErrorCode.DOCUMENT_ENCRYPTED,
                    "Encrypted PDF is not supported", e);
        } catch (DocumentReadException e) {
            throw e;
        } catch (Exception e) {
            throw new DocumentReadException(DocumentReadErrorCode.DOCUMENT_CORRUPTED,
                    "Failed to extract PDF text", e);
        }
    }

    @Override
    public int getOrder() {
        return 10;
    }

    private String getExtension(String fileName) {
        if (fileName == null || !fileName.contains(".")) return null;
        int lastDot = fileName.lastIndexOf('.');
        return fileName.substring(lastDot + 1);
    }
}
