/**
 * Browser-side Markdown export utilities.
 *
 * Generates downloadable `.md` files from conversations and saved responses.
 * All file generation and download triggering happens entirely in the browser
 * without a server round-trip (Requirement 11.4).
 *
 * Output format:
 *   ---
 *   date: YYYY-MM-DD
 *   model: claude-3-5-sonnet
 *   type: conversation | response
 *   ---
 *
 *   # Question text
 *
 *   Answer body
 *
 *   ## Sources
 *
 *   1. [Title](url) — domain
 *   2. Title — domain
 */

import type { Conversation, QueryResult, SavedResponse } from "../types";

// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------

/**
 * Generates a Markdown export of a full conversation and triggers a browser
 * file download.
 *
 * The filename follows the pattern: `health-marketing-{YYYYMMDD}-{slug}.md`
 * where `slug` is derived from the first user question.
 *
 * Requirements: 11.1, 11.3
 */
export function exportConversation(conversation: Conversation): void {
  const today = formatDate(new Date());
  const frontMatter = buildFrontMatter(today, "conversation");

  const sections: string[] = [frontMatter];

  // Iterate over message pairs: user message followed by assistant message.
  const { messages, results } = conversation;
  for (let i = 0; i < messages.length; i++) {
    const msg = messages[i];
    if (msg.role !== "user") continue;

    const question = msg.content;
    const assistantMsg = messages[i + 1];
    const answer =
      assistantMsg && assistantMsg.role === "assistant"
        ? assistantMsg.content
        : "";

    // results are keyed by the assistant message index (as a string).
    const resultKey = String(i + 1);
    const result = results[resultKey] ?? null;

    sections.push(buildQASection(question, answer, result));
  }

  const markdown = sections.join("\n\n");
  const firstQuestion = messages.find((m) => m.role === "user")?.content ?? "";
  const slug = slugify(firstQuestion);
  const filename = `health-marketing-${today.replace(/-/g, "")}-${slug}.md`;

  triggerDownload(markdown, filename);
}

/**
 * Generates a Markdown export of a single Q&A pair and triggers a browser
 * file download.
 *
 * Requirements: 11.2, 11.3
 */
export function exportSingleResponse(
  question: string,
  answer: string,
  result: QueryResult
): void {
  const today = formatDate(new Date());
  const frontMatter = buildFrontMatter(today, "response");
  const qaSection = buildQASection(question, answer, result);
  const markdown = `${frontMatter}\n\n${qaSection}`;

  const slug = slugify(question);
  const filename = `health-marketing-${today.replace(/-/g, "")}-${slug}.md`;

  triggerDownload(markdown, filename);
}

/**
 * Generates a Markdown export of all saved responses concatenated into a
 * single file, separated by `---` dividers, and triggers a browser file
 * download.
 *
 * Requirements: 11.1, 11.3
 */
export function exportAllSavedResponses(saved: SavedResponse[]): void {
  const today = formatDate(new Date());
  const frontMatter = buildFrontMatter(today, "saved-responses");

  const responseSections = saved.map((sr) =>
    buildQASection(sr.question, sr.answer, sr.result)
  );

  const markdown =
    frontMatter + "\n\n" + responseSections.join("\n\n---\n\n");

  const filename = `health-marketing-${today.replace(/-/g, "")}-saved-responses.md`;

  triggerDownload(markdown, filename);
}

// ---------------------------------------------------------------------------
// Internal helpers
// ---------------------------------------------------------------------------

/**
 * Formats a Date as `YYYY-MM-DD` (local date, not UTC).
 */
function formatDate(date: Date): string {
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, "0");
  const day = String(date.getDate()).padStart(2, "0");
  return `${year}-${month}-${day}`;
}

/**
 * Builds the YAML front-matter block.
 *
 * Example:
 *   ---
 *   date: 2024-01-15
 *   model: claude-3-5-sonnet
 *   type: conversation
 *   ---
 */
function buildFrontMatter(date: string, type: string): string {
  return `---\ndate: ${date}\nmodel: claude-3-5-sonnet\ntype: ${type}\n---`;
}

/**
 * Builds a single Q&A section: H1 question, answer body, and Sources section.
 *
 * Example:
 *   # What are the advertising rules for chiropractors?
 *
 *   [answer body here]
 *
 *   ## Sources
 *
 *   1. [Section Title](https://example.com) — domain
 *   2. Section Title — domain
 */
function buildQASection(
  question: string,
  answer: string,
  result: QueryResult | null
): string {
  const parts: string[] = [];

  parts.push(`# ${question}`);
  parts.push(answer);

  if (result && result.citations.length > 0) {
    const sourceLines = result.citations.map((citation) => {
      const prefix = `${citation.index}.`;
      const titlePart = citation.source_url
        ? `[${citation.title}](${citation.source_url})`
        : citation.title;
      return `${prefix} ${titlePart} — ${citation.domain}`;
    });
    parts.push(`## Sources\n\n${sourceLines.join("\n")}`);
  }

  return parts.join("\n\n");
}

/**
 * Converts a question string into a URL-safe slug for use in filenames.
 *
 * - Lowercases the string
 * - Replaces spaces with hyphens
 * - Removes non-alphanumeric characters (except hyphens)
 * - Truncates to 40 characters
 * - Trims trailing hyphens
 */
function slugify(text: string): string {
  return text
    .toLowerCase()
    .replace(/\s+/g, "-")
    .replace(/[^a-z0-9-]/g, "")
    .slice(0, 40)
    .replace(/-+$/, "");
}

/**
 * Triggers a browser file download using the Blob + URL.createObjectURL
 * + anchor click pattern.
 */
function triggerDownload(content: string, filename: string): void {
  const blob = new Blob([content], { type: "text/markdown;charset=utf-8" });
  const url = URL.createObjectURL(blob);

  const anchor = document.createElement("a");
  anchor.href = url;
  anchor.download = filename;
  anchor.style.display = "none";

  document.body.appendChild(anchor);
  anchor.click();
  document.body.removeChild(anchor);

  // Release the object URL to free memory.
  URL.revokeObjectURL(url);
}