import React, { useState, useEffect, useCallback } from "react";
import { debugLog } from "../utils/config";
import TroubleshootingGuide from "./TroubleshootingGuide";
import "./DataViewer.css";

const DataViewer = ({ s3Url, onDownload, showPreviewOnly = false }) => {
  const [data, setData] = useState([]);
  const [columns, setColumns] = useState([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  const [currentPage, setCurrentPage] = useState(1);
  const [rowsPerPage] = useState(10);

  const fetchData = useCallback(async () => {
    try {
      setLoading(true);
      setError(null);

      debugLog("Fetching data from S3 URL:", s3Url);

      // Try multiple approaches to fetch the data
      let response;

      // Method 1: Direct fetch with CORS
      try {
        response = await fetch(s3Url, {
          method: "GET",
          headers: {
            Accept: "text/csv,text/plain,application/octet-stream,*/*",
          },
          mode: "cors",
        });
      } catch (corsError) {
        debugLog("CORS fetch failed, trying no-cors:", corsError);

        // Method 2: Try with no-cors mode (limited but might work)
        try {
          response = await fetch(s3Url, {
            method: "GET",
            mode: "no-cors",
          });
        } catch (noCorsError) {
          debugLog("No-cors fetch also failed:", noCorsError);
          throw new Error(
            "Unable to preview data due to CORS restrictions. You can still download the file directly."
          );
        }
      }

      if (!response.ok && response.status !== 0) {
        // If direct fetch fails, provide helpful error messages
        if (response.status === 403 || response.status === 401) {
          throw new Error(
            "Access denied. The file may require authentication or have expired."
          );
        } else if (response.status === 404) {
          throw new Error(
            "File not found. The download link may have expired."
          );
        } else {
          throw new Error(
            `Unable to fetch data (${response.status}). You can still download the file directly.`
          );
        }
      }

      // For no-cors responses, we can't read the content
      if (response.type === "opaque") {
        throw new Error(
          "Preview not available due to CORS restrictions. Please download the file to view the data."
        );
      }

      const csvText = await response.text();

      if (!csvText || csvText.trim().length === 0) {
        throw new Error("The downloaded file appears to be empty");
      }

      const parsedData = parseCSV(csvText);

      if (parsedData.length > 0) {
        setColumns(Object.keys(parsedData[0]));
        setData(parsedData);
        debugLog("Data parsed successfully:", {
          rows: parsedData.length,
          columns: Object.keys(parsedData[0]).length,
          sampleData: parsedData.slice(0, 2),
        });
      } else {
        throw new Error("No valid data rows found in the file");
      }
    } catch (err) {
      setError(err.message);
      debugLog("Error fetching data:", err);
    } finally {
      setLoading(false);
    }
  }, [s3Url]);

  useEffect(() => {
    if (s3Url) {
      fetchData();
    }
  }, [s3Url, fetchData]);

  const parseCSV = (csvText) => {
    try {
      const lines = csvText.trim().split("\n");
      if (lines.length < 2) return [];

      // Handle different CSV formats and potential quotes
      const parseCSVLine = (line) => {
        const result = [];
        let current = "";
        let inQuotes = false;

        for (let i = 0; i < line.length; i++) {
          const char = line[i];

          if (char === '"') {
            inQuotes = !inQuotes;
          } else if (char === "," && !inQuotes) {
            result.push(current.trim());
            current = "";
          } else {
            current += char;
          }
        }

        result.push(current.trim());
        return result.map((value) => value.replace(/^"(.*)"$/, "$1")); // Remove outer quotes
      };

      const headers = parseCSVLine(lines[0]);
      const rows = [];

      for (let i = 1; i < lines.length; i++) {
        if (lines[i].trim() === "") continue; // Skip empty lines

        const values = parseCSVLine(lines[i]);
        if (values.length > 0 && values.some((val) => val.trim() !== "")) {
          const row = {};
          headers.forEach((header, index) => {
            row[header] = values[index] || "";
          });
          rows.push(row);
        }
      }

      return rows;
    } catch (err) {
      debugLog("Error parsing CSV:", err);
      throw new Error(
        "Failed to parse CSV data. The file format may be invalid."
      );
    }
  };

  const getPaginatedData = () => {
    const startIndex = (currentPage - 1) * rowsPerPage;
    const endIndex = startIndex + rowsPerPage;
    return data.slice(startIndex, endIndex);
  };

  const totalPages = Math.ceil(data.length / rowsPerPage);

  const handleDownload = () => {
    if (onDownload) {
      onDownload();
    } else {
      window.open(s3Url, "_blank");
    }
  };

  if (loading) {
    return (
      <div className="data-viewer loading">
        <div className="spinner"></div>
        <p>Loading data preview...</p>
      </div>
    );
  }

  if (error) {
    return (
      <div className="data-viewer error">
        <div className="status-message error">
          <div className="status-message-icon">❌</div>
          <div className="status-message-content">
            <h4>Unable to Preview Data</h4>
            <p>{error}</p>
            <div
              className="error-help"
              style={{ marginTop: "0.75rem", fontSize: "0.875rem" }}
            >
              <strong>
                Don't worry! Your data has been generated successfully.
              </strong>
              <br />
              <strong>Possible solutions:</strong>
              <ul
                style={{
                  marginTop: "0.5rem",
                  paddingLeft: "1.5rem",
                  textAlign: "left",
                }}
              >
                {!showPreviewOnly && (
                  <li>
                    <strong>Download the file directly</strong> using the button
                    below
                  </li>
                )}
                <li>
                  The preview may fail due to browser security restrictions
                </li>
                <li>
                  Your generated data is still available and ready
                  {showPreviewOnly ? "" : " to download"}
                </li>
              </ul>
            </div>
          </div>
        </div>
        <div
          className="error-actions"
          style={{ marginTop: "1.5rem", textAlign: "center" }}
        >
          {!showPreviewOnly && (
            <button
              className="btn btn-primary btn-large"
              onClick={handleDownload}
              style={{
                marginRight: "0.75rem",
                padding: "12px 24px",
                fontSize: "1rem",
              }}
            >
              📥 Download Generated Data
            </button>
          )}
          <button
            className="btn btn-secondary"
            onClick={() => fetchData()}
            style={{ marginLeft: showPreviewOnly ? "0" : "0.75rem" }}
          >
            🔄 Try Preview Again
          </button>
        </div>

        <div
          className="success-note"
          style={{
            marginTop: "1.5rem",
            padding: "1rem",
            background: "var(--success-light, #e8f5e8)",
            borderRadius: "8px",
            border: "1px solid var(--success, #28a745)",
            textAlign: "center",
          }}
        >
          <div
            style={{
              color: "var(--success, #28a745)",
              fontWeight: "bold",
              marginBottom: "0.5rem",
            }}
          >
            ✅ Data Generation Completed Successfully!
          </div>
          <div style={{ fontSize: "0.875rem", color: "var(--text-secondary)" }}>
            The preview failed, but your synthetic data has been generated and
            is ready for download.
          </div>
        </div>

        <TroubleshootingGuide
          generatedDataLink={s3Url}
          onDownload={handleDownload}
        />
      </div>
    );
  }

  if (data.length === 0) {
    return (
      <div className="data-viewer empty">
        <div className="status-message warning">
          <div className="status-message-icon">⚠️</div>
          <div className="status-message-content">
            <h4>No Data Available</h4>
            <p>The generated file appears to be empty.</p>
          </div>
        </div>
        {!showPreviewOnly && (
          <div className="download-section" style={{ marginTop: "1rem" }}>
            <button className="btn btn-primary" onClick={handleDownload}>
              📥 Download File
            </button>
          </div>
        )}
      </div>
    );
  }

  return (
    <div className="data-viewer">
      <div className="data-viewer-header">
        <div className="data-info">
          <h4>📊 Generated Data {showPreviewOnly ? "Preview" : ""}</h4>
          <p>
            Showing {getPaginatedData().length} of {data.length} rows •{" "}
            {columns.length} columns
          </p>
        </div>
        {!showPreviewOnly && (
          <button
            className="btn btn-success download-btn"
            onClick={handleDownload}
          >
            📥 Download Complete File
          </button>
        )}
      </div>

      <div className="data-table-container">
        <table className="data-table">
          <thead>
            <tr>
              {columns.map((column, index) => (
                <th key={index} title={column}>
                  {column}
                </th>
              ))}
            </tr>
          </thead>
          <tbody>
            {getPaginatedData().map((row, index) => (
              <tr key={index}>
                {columns.map((column, colIndex) => (
                  <td key={colIndex} title={row[column]}>
                    {row[column]}
                  </td>
                ))}
              </tr>
            ))}
          </tbody>
        </table>
      </div>

      {totalPages > 1 && (
        <div className="pagination">
          <button
            className="btn btn-secondary"
            onClick={() => setCurrentPage((prev) => Math.max(prev - 1, 1))}
            disabled={currentPage === 1}
          >
            ← Previous
          </button>

          <span className="pagination-info">
            Page {currentPage} of {totalPages}
          </span>

          <button
            className="btn btn-secondary"
            onClick={() =>
              setCurrentPage((prev) => Math.min(prev + 1, totalPages))
            }
            disabled={currentPage === totalPages}
          >
            Next →
          </button>
        </div>
      )}

      {showPreviewOnly && data.length > 0 && (
        <div
          className="preview-note"
          style={{
            marginTop: "1rem",
            padding: "0.75rem",
            background: "var(--bg-tertiary)",
            borderRadius: "8px",
            fontSize: "0.875rem",
            color: "var(--text-secondary)",
            textAlign: "center",
          }}
        >
          💡 Showing first {Math.min(data.length, rowsPerPage * totalPages)}{" "}
          rows. Download the complete file to view all {data.length} rows.
        </div>
      )}
    </div>
  );
};

export default DataViewer;