/**
 * Improved search emails functionality
 */
const config = require('../config');
const { callGraphAPI } = require('../utils/graph-api');
const { ensureAuthenticated } = require('../auth');
const { resolveFolderPath } = require('./folder-utils');
const { formatDateTime } = require('../utils/time-formatter');
const { buildODataFilter, buildDateFilter } = require('../utils/odata-helpers');
const { normalizeMailbox, withMailboxHeaders } = require('../utils/mailbox');

/**
 * Search emails handler
 * @param {object} args - Tool arguments
 * @returns {object} - MCP response
 */
async function handleSearchEmails(args) {
  const folder = args.folder || "inbox";
  // Coerce count — MCP hosts may send numbers as strings
  const count = Math.min(parseInt(args.count, 10) || 10, config.MAX_RESULT_COUNT);
  const query = args.query || '';
  const from = args.from || '';
  const to = args.to || '';
  const subject = args.subject || '';
  // Coerce booleans — MCP hosts may send numbers/booleans as strings
  const hasAttachments = args.hasAttachments === true || args.hasAttachments === 'true' ? true : undefined;
  const unreadOnly = args.unreadOnly === true || args.unreadOnly === 'true' ? true : undefined;
  const strict = args.strict === true || args.strict === 'true';
  const mb = normalizeMailbox(args.mailbox);
  const graphOpts = { headers: withMailboxHeaders(mb) };

  // Date filtering uses the same timezone-aware helpers as list-emails.
  const dateFrom = args.dateFrom || '';
  const dateTo = args.dateTo || '';
  const dateRange = args.dateRange || '';

  try {
    // Get access token
    const accessToken = await ensureAuthenticated();

    // Resolve the folder path
    const endpoint = await resolveFolderPath(accessToken, folder, mb);
    console.error(`Using endpoint: ${endpoint} for folder: ${folder} mailbox=${mb.graphRoot}`);

    // Execute progressive search
    const response = await progressiveSearch(
      endpoint,
      accessToken,
      { query, from, to, subject },
      { hasAttachments, unreadOnly },
      count,
      strict,
      { dateFrom, dateTo, dateRange },
      graphOpts
    );

    return formatSearchResults(response, { dateFrom, dateTo, dateRange, mailbox: mb.kind === 'user' ? mb.smtpOrUpn : null });
  } catch (error) {
    // Handle authentication errors
    if (error.message === 'Authentication required') {
      return {
        content: [{
          type: "text",
          text: "Authentication required. Please use the 'authenticate' tool first."
        }]
      };
    }

    // General error response
    return {
      content: [{
        type: "text",
        text: `Error searching emails: ${error.message}`
      }]
    };
  }
}

/**
 * Execute a search with progressively simpler fallback strategies.
 *
 * Microsoft Graph API constraints on /me/messages:
 *   - $search and $orderby CANNOT be used together (causes 400)
 *   - $search and $filter CANNOT be used together (causes 400)
 *   - $filter and $orderby CAN be used together
 *
 * Strategy:
 *   1. Text terms present → $search with proper KQL (no $orderby, no $filter),
 *      then apply boolean filters client-side
 *   2. Text terms present → retry with each term individually (same approach)
 *   3. Only boolean filters → $filter + $orderby (fully supported)
 *   4. Fallback → recent emails (only when not in strict mode; marked clearly)
 */
async function progressiveSearch(endpoint, accessToken, searchTerms, filterTerms, count, strict = false, dateOpts = {}, graphOpts = {}) {
  const hasTextTerms = !!(searchTerms.query || searchTerms.from || searchTerms.to || searchTerms.subject);
  const hasBooleanFilters = filterTerms.hasAttachments === true || filterTerms.unreadOnly === true;
  const hasDateFilters = !!(dateOpts.dateFrom || dateOpts.dateTo || dateOpts.dateRange);

  // Build timezone-aware date filter once. It will be applied server-side
  // when we can, or client-side after $search results come back.
  const dateConditions = hasDateFilters
    ? buildDateFilter(dateOpts.dateFrom, dateOpts.dateTo, dateOpts.dateRange)
    : [];
  const dateFilterString = buildODataFilter(dateConditions);
  // Parse date bounds for client-side filtering.
  let dateFromMs = null;
  let dateToMs = null;
  if (hasDateFilters && dateConditions.length > 0) {
    for (const cond of dateConditions) {
      const geMatch = cond.match(/receivedDateTime ge ([^)]+)/);
      const leMatch = cond.match(/receivedDateTime le ([^)]+)/);
      if (geMatch) dateFromMs = new Date(geMatch[1]).getTime();
      if (leMatch) dateToMs = new Date(leMatch[1]).getTime();
    }
  }
  const applyDateFilter = (emails) => {
    if (!hasDateFilters || dateConditions.length === 0) return emails;
    return emails.filter(email => {
      const receivedMs = email.receivedDateTime ? new Date(email.receivedDateTime).getTime() : null;
      if (receivedMs == null) return false;
      if (dateFromMs != null && receivedMs < dateFromMs) return false;
      if (dateToMs != null && receivedMs > dateToMs) return false;
      return true;
    });
  };

  // 1. Try combined KQL search (text terms only — boolean filters applied client-side)
  if (hasTextTerms) {
    try {
      const kqlQuery = buildKqlQuery(searchTerms);
      const params = {
        $top: count,
        $select: config.EMAIL_SELECT_FIELDS,
        $search: kqlQuery
        // NOTE: NO $orderby — not allowed with $search
        // NOTE: NO $filter — not allowed with $search
      };

      console.error(`Attempting combined KQL search: ${kqlQuery}`);
      const response = await callGraphAPI(accessToken, 'GET', endpoint, null, params, graphOpts);

      if (response.value && response.value.length > 0) {
        let filtered = applyClientSideFilters(response.value, filterTerms);
        filtered = applyDateFilter(filtered);
        console.error(`Combined search found ${response.value.length} results, ${filtered.length} after filtering`);
        if (filtered.length > 0) {
          return { value: filtered };
        }
      }
    } catch (error) {
      console.error(`Combined KQL search failed: ${error.message}`);
    }

    // 2. Try each search term individually (priority: subject → from → to → query)
    const termPriority = ['subject', 'from', 'to', 'query'];
    for (const term of termPriority) {
      if (!searchTerms[term]) continue;

      try {
        const kqlQuery = buildSingleTermKql(term, searchTerms[term]);
        const params = {
          $top: count,
          $select: config.EMAIL_SELECT_FIELDS,
          $search: kqlQuery
          // NOTE: NO $orderby, NO $filter
        };

        console.error(`Attempting single-term search (${term}): ${kqlQuery}`);
        const response = await callGraphAPI(accessToken, 'GET', endpoint, null, params, graphOpts);

        if (response.value && response.value.length > 0) {
          let filtered = applyClientSideFilters(response.value, filterTerms);
          filtered = applyDateFilter(filtered);
          console.error(`Search on ${term} found ${response.value.length} results, ${filtered.length} after filtering`);
          if (filtered.length > 0) {
            return { value: filtered };
          }
        }
      } catch (error) {
        console.error(`Single-term search (${term}) failed: ${error.message}`);
      }
    }
  }

  // 3. Boolean filters (and/or date filters) — $filter + $orderby is supported
  if (hasBooleanFilters || hasDateFilters) {
    try {
      const filterConditions = [];
      if (filterTerms.hasAttachments === true) filterConditions.push('hasAttachments eq true');
      if (filterTerms.unreadOnly === true) filterConditions.push('isRead eq false');
      if (dateFilterString) filterConditions.push(dateFilterString);

      const params = {
        $top: count,
        $select: config.EMAIL_SELECT_FIELDS,
        $orderby: 'receivedDateTime desc',
        $filter: filterConditions.join(' and ')
      };

      console.error(`Attempting filter-only search: ${params.$filter}`);
      const response = await callGraphAPI(accessToken, 'GET', endpoint, null, params, graphOpts);
      console.error(`Filter-only search found ${response.value?.length || 0} results`);
      return response;
    } catch (error) {
      console.error(`Filter-only search failed: ${error.message}`);
    }
  }

  // 4. Final fallback: recent emails (disabled in strict mode)
  console.error("All search strategies exhausted, falling back to recent emails");
  if (strict) {
    console.error('Strict mode enabled: returning empty results instead of fallback');
    return { value: [], _searchFallback: false, _strict: true, _originalTerms: searchTerms };
  }

  const basicParams = {
    $top: count,
    $select: config.EMAIL_SELECT_FIELDS,
    $orderby: 'receivedDateTime desc'
  };

  if (dateFilterString) {
    basicParams.$filter = dateFilterString;
  }

  const response = await callGraphAPI(accessToken, 'GET', endpoint, null, basicParams, graphOpts);
  console.error(`Fallback to recent emails found ${response.value?.length || 0} results`);

  if (dateFilterString) {
    response.value = applyDateFilter(response.value || []);
  }

  response._searchFallback = true;
  response._originalTerms = searchTerms;
  return response;
}

/**
 * Build a KQL query string for all provided search terms.
 * The entire expression must be wrapped in outer double quotes for Graph API.
 * Example: "subject:invoice from:john@example.com"
 */
function buildKqlQuery(searchTerms) {
  const parts = [];

  if (searchTerms.subject) parts.push(`subject:${searchTerms.subject}`);
  if (searchTerms.from) parts.push(`from:${searchTerms.from}`);
  if (searchTerms.to) parts.push(`to:${searchTerms.to}`);
  if (searchTerms.query) parts.push(searchTerms.query);

  return `"${parts.join(' ')}"`;
}

/**
 * Build a KQL query for a single field term.
 * Example: "from:john@example.com"
 */
function buildSingleTermKql(term, value) {
  if (term === 'query') {
    return `"${value}"`;
  }
  return `"${term}:${value}"`;
}

/**
 * Apply boolean filter conditions to an in-memory array of emails.
 * Used after $search results are returned (since $search + $filter is not supported).
 */
function applyClientSideFilters(emails, filterTerms) {
  return emails.filter(email => {
    if (filterTerms.hasAttachments === true && !email.hasAttachments) return false;
    if (filterTerms.unreadOnly === true && email.isRead !== false) return false;
    return true;
  });
}

/**
 * Format search results into a readable text format
 * @param {object} response - The API response object
 * @param {object} [dateOpts] - Optional date filter metadata for the result message
 * @returns {object} - MCP response object
 */
function formatSearchResults(response, dateOpts = {}) {
  if (!response.value || response.value.length === 0) {
    return {
      content: [{
        type: "text",
        text: `No emails found matching your search criteria.`
      }]
    };
  }

  // Format results
  let emailList = response.value.map((email, index) => {
    const sender = email.from?.emailAddress || { name: 'Unknown', address: 'unknown' };
    const date = formatDateTime(email.receivedDateTime);
    const readStatus = email.isRead ? '' : '[UNREAD] ';
    const threadNote = email.conversationId ? `\nConversationID: ${email.conversationId}` : '';

    return `${index + 1}. ${readStatus}${date} - From: ${sender.name} (${sender.address})\nSubject: ${email.subject}\nID: ${email.id}${threadNote}\n`;
  }).join("\n");

  // Strict mode: no results path
  if (response._strict) {
    return {
      content: [{
        type: "text",
        text: `No emails found matching your search criteria. Strict mode is enabled; no fallback to recent emails was performed.`
      }]
    };
  }

  // Add fallback warning if search had to give up
  let additionalInfo = '';
  if (response._searchFallback) {
    additionalInfo = `\n\n⚠️  FALLBACK: No messages matched the exact search terms. The ${response.value.length} result(s) below are the most recent emails from the folder, not search hits.`;
    // Tag each listing so an automated parser can tell these are fallback results
    emailList = emailList.replace(/^(\d+\.)\s*/gm, '$1 [FALLBACK] ');
  }

  const dateParts = [];
  if (dateOpts.dateRange) dateParts.push(`dateRange: ${dateOpts.dateRange}`);
  if (dateOpts.dateFrom) dateParts.push(`from: ${dateOpts.dateFrom}`);
  if (dateOpts.dateTo) dateParts.push(`to: ${dateOpts.dateTo}`);
  if (dateOpts.mailbox) dateParts.push(`mailbox: ${dateOpts.mailbox}`);
  const dateInfo = dateParts.length > 0 ? ` (${dateParts.join(', ')})` : '';

  return {
    content: [{
      type: "text",
      text: `Found ${response.value.length} emails${dateInfo}:${additionalInfo}\n\n${emailList}`
    }]
  };
}

module.exports = handleSearchEmails;