export type ReplyParseConfidence = 'high' | 'medium' | 'low';
export type ReplyParsingStrategy =
  | 'custom-boundary'
  | 'provider-header'
  | 'quoted-block'
  | 'signature-trim'
  | 'fallback';

export interface ReplyTokenMetadata {
  conversationToken?: string;
  ticketId?: string;
  commentId?: string;
  threadId?: string;
  projectId?: string;
}

export interface ReplyParserInput {
  text: string;
  html?: string;
}

export interface ReplyParserConfig {
  /** Text markers that should be treated as the explicit reply delimiter. */
  replyDelimiters: string[];
  /** Attribute name injected into outbound HTML to mark the reply boundary. */
  htmlBoundaryAttribute: string;
  /** Prefix used for outbound hidden token attributes. */
  htmlTokenAttributePrefix: string;
  /** Pattern used to extract hidden reply tokens from plain text emails. */
  textTokenPattern: RegExp;
  /** Additional plain text markers for reply boundaries (localized variants). */
  localizedReplyPhrases: RegExp[];
  /** Providers emit headers like `On … wrote:` signalling quoted content. */
  providerReplyHeaders: RegExp[];
  /** Forwarded message markers that indicate legacy content. */
  forwardedReplyHeaders: RegExp[];
  /** Signature markers that typically separate the reply from signatures. */
  signatureMarkers: RegExp[];
  /** Maximum number of lines (from the bottom) to scan for signatures. */
  maxSignatureScanLines: number;
}

export interface ReplyParseResult {
  sanitizedText: string;
  sanitizedHtml?: string;
  confidence: ReplyParseConfidence;
  strategy: ReplyParsingStrategy;
  appliedHeuristics: string[];
  tokens: ReplyTokenMetadata | null;
  warnings: string[];
}

const DEFAULT_CONFIG: ReplyParserConfig = {
  replyDelimiters: [
    '--- Please reply above this line ---',
    'Please reply above this line',
    'Reply above this line',
    'Répondez au-dessus de cette ligne',
  ],
  htmlBoundaryAttribute: 'data-alga-reply-boundary',
  htmlTokenAttributePrefix: 'data-alga-',
  textTokenPattern: /\[ALGA-REPLY-TOKEN (?<token>[A-Z0-9:+\-_/]+)(?: ticketId=(?<ticket>[A-Za-z0-9\-]+))?(?: projectId=(?<project>[A-Za-z0-9\-]+))?(?: commentId=(?<comment>[A-Za-z0-9\-]+))?(?: threadId=(?<thread>[A-Za-z0-9\-]+))?\]/i,
  localizedReplyPhrases: [
    /répondez au-dessus de cette ligne/i,
    /responda acima desta linha/i,
    /antworten sie oberhalb dieser zeile/i,
  ],
  providerReplyHeaders: [
    /^on .+wrote:$/i,
    /^on .+ schrieb:.*/i,
    /^el .+ escribió:.*/i,
    /^le .+ a écrit :/i,
    /^am .+ schrieb .+/i,
    /^from:\s?.+/i,
    /^de:\s?.+/i,
    /^sent:\s?.+/i,
    /^envoyé :\s?.+/i,
    /^to:\s?.+/i,
    /^cc:\s?.+/i,
    /^subject:\s?.+/i,
    /^répondre à :\s?.+/i,
  ],
  forwardedReplyHeaders: [
    /^begin forwarded message/i,
    /^forwarded message/i,
    /^-----original message-----$/i,
  ],
  signatureMarkers: [
    /^--\s*$/, // Standard signature delimiter
    /^__+$/, // Outlook variant
    /^thanks[,]?$/i,
    /^thank you[,]?$/i,
    /^best[,]?$/i,
    /^best regards[,]?$/i,
    /^regards[,]?$/i,
    /^sent from my iphone/i,
    /^sent from my ipad/i,
    /^sent from my android/i,
    /^sent from outlook/i,
    /^sent from windows mail/i,
  ],
  maxSignatureScanLines: 12,
};

interface TrimResult {
  text: string;
  matched?: string;
  heuristic?: string;
}

const blockquoteRegex = /<blockquote[\s\S]*?$/i;
const htmlCommentTokenRegex = /<!--\s*alga:reply-token:(?<payload>[^-]+)-->?/i;
const htmlTokenAttributeRegex = /data-alga-reply-token="(?<token>[^"]+)"/i;
const htmlTicketAttributeRegex = /data-alga-ticket-id="(?<ticket>[^"]+)"/i;
const htmlCommentAttributeRegex = /data-alga-comment-id="(?<comment>[^"]+)"/i;
const htmlProjectAttributeRegex = /data-alga-project-id="(?<project>[^"]+)"/i;
const htmlThreadAttributeRegex = /data-alga-thread-id="(?<thread>[^"]+)"/i;
const textTokenInlineRegex = /ALGA-REPLY-TOKEN:(?<token>[A-Z0-9:+\-_/]+)/i;
const textTicketInlineRegex = /ALGA-TICKET-ID:(?<ticket>[A-Za-z0-9\-]+)/i;
const textCommentInlineRegex = /ALGA-COMMENT-ID:(?<comment>[A-Za-z0-9\-]+)/i;
const textThreadInlineRegex = /ALGA-THREAD-ID:(?<thread>[A-Za-z0-9\-]+)/i;
const textProjectInlineRegex = /ALGA-PROJECT-ID:(?<project>[A-Za-z0-9\-]+)/i;

function stripTokenArtifacts(text: string, config: ReplyParserConfig): TrimResult {
  const lines = normalizeText(text).split('\n');
  const filtered = lines.filter((line) => {
    const trimmed = line.trim();
    if (!trimmed) {
      return true;
    }
    if (config.textTokenPattern.test(trimmed)) {
      return false;
    }
    if (/ALGA-REPLY-TOKEN[:\s]/i.test(trimmed)) {
      return false;
    }
    if (/ALGA-(TICKET|COMMENT|THREAD|PROJECT)-ID[:=]/i.test(trimmed)) {
      return false;
    }
    return true;
  });

  if (filtered.length !== lines.length) {
    return {
      text: filtered.join('\n').trim(),
      matched: 'token-artifact',
      heuristic: 'token-strip',
    };
  }

  return { text: text.trim() };
}

const NAMED_HTML_ENTITIES: Record<string, string> = {
  amp: '&',
  lt: '<',
  gt: '>',
  quot: '"',
  apos: "'",
  nbsp: ' ',
};

/** Normalize line endings and collapse stray carriage returns. */
function normalizeText(value: string): string {
  return value.replace(/\r\n?/g, '\n');
}

function decodeHtml(value: string): string {
  return value
    .replace(/&(#?)([xX]?)([0-9a-fA-F]+);/g, (match, isNumeric: string, hexMarker: string, body: string) => {
      if (!isNumeric) {
        const replacement = NAMED_HTML_ENTITIES[body.toLowerCase()];
        return replacement !== undefined ? replacement : match;
      }

      const parsed = hexMarker ? parseInt(body, 16) : parseInt(body, 10);
      if (Number.isFinite(parsed)) {
        return String.fromCodePoint(parsed);
      }
      return match;
    });
}

function trimAtExplicitDelimiter(text: string, config: ReplyParserConfig): TrimResult {
  const normalized = normalizeText(text);
  let bestIndex = -1;
  let matched: string | undefined;

  for (const delimiter of config.replyDelimiters) {
    const idx = normalized.toLowerCase().indexOf(delimiter.toLowerCase());
    if (idx >= 0 && (bestIndex === -1 || idx < bestIndex)) {
      bestIndex = idx;
      matched = delimiter;
    }
  }

  if (bestIndex >= 0) {
    return {
      text: normalized.slice(0, bestIndex).trim(),
      matched,
      heuristic: 'explicit-boundary',
    };
  }

  for (const localized of config.localizedReplyPhrases) {
    const match = localized.exec(normalized);
    if (match && (bestIndex === -1 || match.index < bestIndex)) {
      bestIndex = match.index;
      matched = match[0];
    }
  }

  if (bestIndex >= 0) {
    return {
      text: normalized.slice(0, bestIndex).trim(),
      matched,
      heuristic: 'localized-boundary',
    };
  }

  return { text: normalized };
}

function trimHtmlAtBoundary(html: string, config: ReplyParserConfig): TrimResult {
  const attributeIndex = html.toLowerCase().indexOf(config.htmlBoundaryAttribute.toLowerCase());

  if (attributeIndex >= 0) {
    return {
      text: html.slice(0, attributeIndex).trim(),
      matched: config.htmlBoundaryAttribute,
      heuristic: 'html-boundary',
    };
  }

  // Fallback: cut at first blockquote which usually encapsulates quoted history.
  const blockquoteMatch = blockquoteRegex.exec(html);
  if (blockquoteMatch) {
    return {
      text: html.slice(0, blockquoteMatch.index).trim(),
      matched: '<blockquote',
      heuristic: 'html-blockquote-trim',
    };
  }

  return { text: html.trim() };
}

function stripProviderHeaders(text: string, config: ReplyParserConfig): TrimResult {
  const lines = normalizeText(text).split('\n');
  const kept: string[] = [];
  let matched: string | undefined;
  let heuristic: string | undefined;
  let removedQuoted = false;

  for (let i = 0; i < lines.length; i += 1) {
    const rawLine = lines[i];
    const line = rawLine.trim();

    if (!line && kept.length === 0) {
      continue;
    }

    if (config.forwardedReplyHeaders.some((regex) => regex.test(line))) {
      matched = line;
      heuristic = 'forwarded-header';
      break;
    }

    if (config.providerReplyHeaders.some((regex) => regex.test(line))) {
      matched = line;
      heuristic = 'provider-header';
      break;
    }

    if (line.startsWith('>')) {
      removedQuoted = true;
      continue;
    }

    kept.push(rawLine);
  }

  const cleaned = kept.join('\n').trim();
  if (heuristic) {
    return { text: cleaned, matched, heuristic };
  }
  if (removedQuoted) {
    return { text: cleaned, matched: 'quoted-line', heuristic: 'quote-prefix' };
  }
  return { text: cleaned };
}

function stripSignature(text: string, config: ReplyParserConfig): TrimResult {
  const lines = normalizeText(text).split('\n');
  let cutoff: number | undefined;

  for (let i = lines.length - 1, scanned = 0; i >= 0 && scanned < config.maxSignatureScanLines; i -= 1, scanned += 1) {
    const line = lines[i].trim();
    if (!line) {
      continue;
    }
    if (config.signatureMarkers.some((regex) => regex.test(line))) {
      cutoff = i;
    }
  }

  if (cutoff !== undefined) {
    return {
      text: lines.slice(0, cutoff).join('\n').trim(),
      matched: 'signature',
      heuristic: 'signature-trim',
    };
  }

  return { text: text.trim() };
}

function compactWhitespace(text: string): string {
  return text
    .split('\n')
    .map((line) => line.trimEnd())
    .join('\n')
    .replace(/\n{3,}/g, '\n\n')
    .trim();
}

function extractTokensFromHtml(html: string): ReplyTokenMetadata | null {
  const payload: ReplyTokenMetadata = {};
  const tokenMatch = htmlTokenAttributeRegex.exec(html) || htmlCommentTokenRegex.exec(html);
  if (tokenMatch?.groups?.token) {
    payload.conversationToken = tokenMatch.groups.token;
  } else if (tokenMatch?.groups?.payload) {
    payload.conversationToken = tokenMatch.groups.payload.trim();
  }

  const ticketMatch = htmlTicketAttributeRegex.exec(html);
  if (ticketMatch?.groups?.ticket) {
    payload.ticketId = ticketMatch.groups.ticket;
  }

  const commentMatch = htmlCommentAttributeRegex.exec(html);
  if (commentMatch?.groups?.comment) {
    payload.commentId = commentMatch.groups.comment;
  }

  const threadMatch = htmlThreadAttributeRegex.exec(html);
  if (threadMatch?.groups?.thread) {
    payload.threadId = threadMatch.groups.thread;
  }

  const projectMatch = htmlProjectAttributeRegex.exec(html);
  if (projectMatch?.groups?.project) {
    payload.projectId = projectMatch.groups.project;
  }

  return Object.keys(payload).length > 0 ? payload : null;
}

function extractTokensFromText(text: string, config: ReplyParserConfig): ReplyTokenMetadata | null {
  const payload: ReplyTokenMetadata = {};
  const normalized = normalizeText(text);

  let structuredMatch = config.textTokenPattern.exec(normalized);

  // Fallback: Attempt to recover multi-line tokens broken by email clients (e.g. Gmail wrapping + quoting)
  if (!structuredMatch) {
    const tokenStart = normalized.indexOf('[ALGA-REPLY-TOKEN');
    if (tokenStart >= 0) {
      // Grab a generous chunk to cover the full wrapped token
      const chunk = normalized.slice(tokenStart, tokenStart + 1000);
      // Remove newlines, '>' markers, and collapse extra spaces to reconstruct a single line
      const cleanChunk = chunk.replace(/[\r\n]+[\s>]*|>/g, ' ').replace(/\s+/g, ' ');
      structuredMatch = config.textTokenPattern.exec(cleanChunk);
    }
  }

  if (structuredMatch?.groups?.token) {
    payload.conversationToken = structuredMatch.groups.token;
    if (structuredMatch.groups.ticket) {
      payload.ticketId = structuredMatch.groups.ticket;
    }
    if (structuredMatch.groups.comment) {
      payload.commentId = structuredMatch.groups.comment;
    }
    if (structuredMatch.groups.thread) {
      payload.threadId = structuredMatch.groups.thread;
    }
    if (structuredMatch.groups.project) {
      payload.projectId = structuredMatch.groups.project;
    }
  }

  const inlineToken = textTokenInlineRegex.exec(normalized);
  if (inlineToken?.groups?.token) {
    payload.conversationToken = inlineToken.groups.token;
  }

  const inlineTicket = textTicketInlineRegex.exec(normalized);
  if (inlineTicket?.groups?.ticket) {
    payload.ticketId = inlineTicket.groups.ticket;
  }

  const inlineComment = textCommentInlineRegex.exec(normalized);
  if (inlineComment?.groups?.comment) {
    payload.commentId = inlineComment.groups.comment;
  }

  const inlineThread = textThreadInlineRegex.exec(normalized);
  if (inlineThread?.groups?.thread) {
    payload.threadId = inlineThread.groups.thread;
  }

  const inlineProject = textProjectInlineRegex.exec(normalized);
  if (inlineProject?.groups?.project) {
    payload.projectId = inlineProject.groups.project;
  }

  return Object.keys(payload).length > 0 ? payload : null;
}

function mergeTokenMetadata(primary: ReplyTokenMetadata | null, secondary: ReplyTokenMetadata | null): ReplyTokenMetadata | null {
  if (!primary && !secondary) {
    return null;
  }

  return {
    conversationToken: primary?.conversationToken || secondary?.conversationToken,
    ticketId: primary?.ticketId || secondary?.ticketId,
    commentId: primary?.commentId || secondary?.commentId,
    threadId: primary?.threadId || secondary?.threadId,
    projectId: primary?.projectId || secondary?.projectId,
  };
}

/**
 * Attempt to parse the inbound reply body using layered heuristics.
 */
export function parseEmailReply(input: ReplyParserInput, config: Partial<ReplyParserConfig> = {}): ReplyParseResult {
  const mergedConfig: ReplyParserConfig = { ...DEFAULT_CONFIG, ...config };
  const warnings: string[] = [];
  const appliedHeuristics: string[] = [];

  const originalText = input.text || '';
  const originalHtml = input.html;

  const htmlTokens = originalHtml ? extractTokensFromHtml(originalHtml) : null;
  const textTokens = extractTokensFromText(originalText, mergedConfig);
  const tokens = mergeTokenMetadata(htmlTokens, textTokens);

  // Step 1: explicit boundary trimming (text + html)
  let { text: trimmedText, matched: textBoundary, heuristic: textBoundaryHeuristic } = trimAtExplicitDelimiter(
    originalText,
    mergedConfig,
  );

  const tokenStrip = stripTokenArtifacts(trimmedText, mergedConfig);
  trimmedText = tokenStrip.text;
  if (tokenStrip.heuristic) {
    appliedHeuristics.push(tokenStrip.heuristic);
  }

  let trimmedHtmlResult: TrimResult | undefined;
  if (originalHtml) {
    trimmedHtmlResult = trimHtmlAtBoundary(originalHtml, mergedConfig);
  }

  if (textBoundaryHeuristic) {
    appliedHeuristics.push(textBoundaryHeuristic);
  }
  if (trimmedHtmlResult?.heuristic) {
    appliedHeuristics.push(trimmedHtmlResult.heuristic);
  }

  let strategy: ReplyParsingStrategy = textBoundary || trimmedHtmlResult?.matched ? 'custom-boundary' : 'fallback';
  let confidence: ReplyParseConfidence = strategy === 'custom-boundary' ? 'high' : 'low';

  if (!textBoundary) {
    const providerTrim = stripProviderHeaders(trimmedText, mergedConfig);
    if (providerTrim.heuristic) {
      trimmedText = providerTrim.text;
      appliedHeuristics.push(providerTrim.heuristic);
      strategy = providerTrim.heuristic === 'provider-header' ? 'provider-header' : 'quoted-block';
      confidence = confidence === 'high' ? 'high' : 'medium';
    }
  }

  const signatureTrim = stripSignature(trimmedText, mergedConfig);
  if (signatureTrim.heuristic) {
    trimmedText = signatureTrim.text;
    appliedHeuristics.push(signatureTrim.heuristic);
    strategy = strategy === 'fallback' ? 'signature-trim' : strategy;
    confidence = confidence === 'low' ? 'medium' : confidence;
  }

  trimmedText = compactWhitespace(trimmedText);
  if (!trimmedText) {
    // Fallback to original content if heuristics ate everything
    trimmedText = originalText.trim();
    if (!trimmedText) {
      warnings.push('Inbound email body was empty after parsing.');
    } else {
      warnings.push('Reply heuristics yielded empty body; using original text.');
    }
    strategy = 'fallback';
    confidence = tokens ? 'medium' : 'low';
  }

  let sanitizedHtml: string | undefined;
  if (originalHtml) {
    const baselineHtml = trimmedHtmlResult ? trimmedHtmlResult.text : originalHtml;
    // Attempt to keep html aligned with text heuristics by removing blockquotes if none already removed
    if (!trimmedHtmlResult?.heuristic?.includes('blockquote')) {
      const blockquoteMatch = blockquoteRegex.exec(baselineHtml);
      if (blockquoteMatch) {
        sanitizedHtml = baselineHtml.slice(0, blockquoteMatch.index).trim();
        appliedHeuristics.push('html-blockquote-trim');
        if (strategy === 'fallback') {
          strategy = 'quoted-block';
          confidence = confidence === 'low' ? 'medium' : confidence;
        }
      } else {
        sanitizedHtml = baselineHtml.trim();
      }
    } else {
      sanitizedHtml = baselineHtml.trim();
    }

    // Remove common signature wrappers from HTML by trimming final paragraphs that match markers
    if (sanitizedHtml) {
      const signatureRegexes = mergedConfig.signatureMarkers
        .map((regex) => regex.source.replace(/^\^/, '').replace(/\$$/, ''))
        .join('|');
      const htmlSignatureRegex = new RegExp(
        `(<p[^>]*>\s*(?:${signatureRegexes})\s*<\/p>|<div[^>]*>\s*(?:${signatureRegexes})\s*<\/div>)`,
        'i',
      );
      sanitizedHtml = sanitizedHtml.replace(htmlSignatureRegex, '').trim();
    }

    if (!sanitizedHtml) {
      sanitizedHtml = undefined;
    }
  }

  if (tokens && confidence === 'low') {
    confidence = 'medium';
  }

  return {
    sanitizedText: decodeHtml(trimmedText),
    sanitizedHtml: sanitizedHtml ? decodeHtml(sanitizedHtml) : undefined,
    confidence,
    strategy,
    appliedHeuristics,
    tokens,
    warnings,
  };
}

export function getDefaultReplyParserConfig(): ReplyParserConfig {
  return { ...DEFAULT_CONFIG };
}