// v1.14.x-html-artifact-panes: artifact writer + slug derivation.
//
// Writes Markdown and HTML artifacts to `<projectRoot>/.boocode/artifacts/`
// as plain files. Returns `{path, url}` where:
//   - path is the absolute on-disk path
//   - url is a project-scoped REST URL pointing at the GET download route
//     registered in routes/artifacts.ts. The route streams the file with
//     Content-Disposition: attachment.
//
// Path safety: we do NOT use path_guard.ts (it realpaths and throws ENOENT
// for files that don't exist yet, which artifact creation requires).
// Instead we mirror the v1.13.18 codecontext_client.ts pattern: resolve
// the candidate path against the realpath'd projectRoot, then verify the
// result starts with projectRoot + sep (or equals projectRoot).

import { mkdir, realpath, writeFile } from 'node:fs/promises';
import { resolve, sep } from 'node:path';
import { PathScopeError } from './path_guard.js';
import type { Message } from '../types/api.js';

export interface HtmlArtifactPayload {
  html_content: string;
  char_count: number;
  title: string | null;
}

export interface ArtifactWriteResult {
  path: string;
  url: string;
}

const ARTIFACT_SUBDIR = '.boocode/artifacts';

// ---- slug helpers ----

// Lowercase, replace non-alnum runs with '-', trim leading/trailing '-',
// collapse repeated '-', cap at 60 chars. Empty → 'artifact'.
function slugify(input: string): string {
  const cleaned = input
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, '-')
    .replace(/^-+|-+$/g, '')
    .replace(/-{2,}/g, '-')
    .slice(0, 60)
    .replace(/^-+|-+$/g, '');
  return cleaned || 'artifact';
}

function firstHeading(md: string): string | null {
  // Match the first `# ` ATX heading at the start of a line.
  const m = md.match(/^[ \t]*#[ \t]+(.+?)\s*$/m);
  if (!m) return null;
  const text = m[1]?.trim() ?? '';
  return text.length > 0 ? text : null;
}

function firstNWords(s: string, n: number): string {
  const words = s.trim().split(/\s+/).filter(Boolean).slice(0, n);
  return words.join(' ');
}

export function deriveMarkdownSlug(messageContent: string): string {
  const heading = firstHeading(messageContent);
  if (heading) return slugify(heading);
  const sixWords = firstNWords(messageContent, 6);
  return slugify(sixWords);
}

// Strip HTML tags for inner-text extraction. Crude but sufficient for slug
// derivation — we're not rendering, just finding readable words.
function stripTags(html: string): string {
  return html
    .replace(/<script\b[^<]*(?:(?!<\/script>)<[^<]*)*<\/script>/gi, ' ')
    .replace(/<style\b[^<]*(?:(?!<\/style>)<[^<]*)*<\/style>/gi, ' ')
    .replace(/<[^>]+>/g, ' ')
    .replace(/\s+/g, ' ')
    .trim();
}

function extractTitleTag(html: string): string | null {
  const m = html.match(/<title[^>]*>([\s\S]*?)<\/title>/i);
  if (!m) return null;
  const text = stripTags(m[1] ?? '').trim();
  return text.length > 0 ? text : null;
}

function extractH1(html: string): string | null {
  const m = html.match(/<h1[^>]*>([\s\S]*?)<\/h1>/i);
  if (!m) return null;
  const text = stripTags(m[1] ?? '').trim();
  return text.length > 0 ? text : null;
}

export function deriveHtmlSlug(payload: {
  html_content: string;
  title: string | null;
}): string {
  if (payload.title && payload.title.trim().length > 0) {
    return slugify(payload.title);
  }
  const title = extractTitleTag(payload.html_content);
  if (title) return slugify(title);
  const h1 = extractH1(payload.html_content);
  if (h1) return slugify(h1);
  const inner = stripTags(payload.html_content);
  return slugify(firstNWords(inner, 6));
}

// Derive title for the html_artifact part payload: <title> → first <h1> →
// first 80 chars of inner text. Returns null if nothing useful is found.
export function deriveHtmlTitle(html: string): string | null {
  const t = extractTitleTag(html);
  if (t) return t;
  const h1 = extractH1(html);
  if (h1) return h1;
  const inner = stripTags(html);
  if (inner.length === 0) return null;
  return inner.slice(0, 80);
}

// ---- HTML detection (B4) ----

// Returns the inner HTML content if `text` is a recognised HTML artifact:
//   - starts with <!DOCTYPE html> (case-insensitive, whitespace-trimmed), OR
//   - wrapped entirely in a fenced ```html ... ``` block.
// Returns null if neither matches.
export function detectHtmlArtifact(text: string): string | null {
  const trimmed = text.trim();
  if (trimmed.length === 0) return null;
  if (/^<!doctype\s+html/i.test(trimmed)) {
    return trimmed;
  }
  // Fenced ```html block consuming the entire (trimmed) message. Allow an
  // optional trailing newline before the closing fence.
  const fence = trimmed.match(/^```html\s*\n([\s\S]*?)\n?```\s*$/i);
  if (fence) {
    const inner = fence[1] ?? '';
    if (/^\s*<!doctype\s+html/i.test(inner) || /<html[\s>]/i.test(inner)) {
      return inner.trim();
    }
  }
  return null;
}

// ---- path resolution ----

// Resolve `<projectRoot>/.boocode/artifacts/<filename>` and verify the
// result stays under projectRoot. Mirrors the v1.13.18 codecontext_client.ts
// approach: realpath projectRoot first, then prefix-check the candidate.
// Throws on escape.
async function resolveArtifactPath(
  projectRoot: string,
  filename: string,
): Promise<{ resolvedRoot: string; artifactsDir: string; absPath: string }> {
  const resolvedRoot = await realpath(projectRoot);
  const artifactsDir = resolve(resolvedRoot, ARTIFACT_SUBDIR);
  const absPath = resolve(artifactsDir, filename);
  // Lexical prefix check on the resolved candidates. (The `!== resolvedRoot`
  // branch was dead — ARTIFACT_SUBDIR is non-empty so artifactsDir always
  // differs from resolvedRoot.)
  if (!artifactsDir.startsWith(resolvedRoot + sep)) {
    throw new PathScopeError(
      `artifacts dir escapes project root: ${artifactsDir}`,
    );
  }
  if (!absPath.startsWith(artifactsDir + sep)) {
    throw new PathScopeError(
      `artifact filename escapes artifacts dir: ${filename}`,
    );
  }
  return { resolvedRoot, artifactsDir, absPath };
}

// After mkdir, realpath the artifacts dir and re-verify it stays under
// resolvedRoot. Closes the symlink-escape gap: if `.boocode/artifacts` (or
// any ancestor below resolvedRoot) is a symlink pointing outside the
// project, the lexical check in resolveArtifactPath passes but the actual
// write lands outside the sandbox. Throws PathScopeError on escape.
async function assertArtifactsDirSafe(
  artifactsDir: string,
  resolvedRoot: string,
): Promise<void> {
  const realDir = await realpath(artifactsDir);
  if (realDir !== resolvedRoot && !realDir.startsWith(resolvedRoot + sep)) {
    throw new PathScopeError(
      `artifacts dir resolves outside project root: ${realDir}`,
    );
  }
}

// Pure decision helper for whether finalizeCompletion should write the
// `html_artifact` part. Exported for unit testing the cap-skip branch.
// Returns `{write: true, byteLen}` when the payload is under the cap, or
// `{write: false, byteLen, reason: 'cap_exceeded'}` when oversize.
export type HtmlArtifactDecision =
  | { write: true; byteLen: number }
  | { write: false; byteLen: number; reason: 'cap_exceeded' };

export function decideHtmlArtifactWrite(
  htmlContent: string,
): HtmlArtifactDecision {
  const byteLen = Buffer.byteLength(htmlContent, 'utf8');
  if (byteLen > HTML_ARTIFACT_MAX_BYTES) {
    return { write: false, byteLen, reason: 'cap_exceeded' };
  }
  return { write: true, byteLen };
}

function buildUrl(projectId: string, filename: string): string {
  return `/api/projects/${projectId}/artifacts/${encodeURIComponent(filename)}`;
}

export interface WriteContext {
  projectId: string;
  projectRoot: string;
}

export async function writeMarkdownArtifact(
  message: Pick<Message, 'content'>,
  ctx: WriteContext,
): Promise<ArtifactWriteResult> {
  const slug = deriveMarkdownSlug(message.content);
  const filename = `${slug}-${Date.now()}.md`;
  const { resolvedRoot, artifactsDir, absPath } = await resolveArtifactPath(
    ctx.projectRoot,
    filename,
  );
  await mkdir(artifactsDir, { recursive: true });
  await assertArtifactsDirSafe(artifactsDir, resolvedRoot);
  await writeFile(absPath, message.content, 'utf8');
  return { path: absPath, url: buildUrl(ctx.projectId, filename) };
}

export async function writeHtmlArtifact(
  payload: HtmlArtifactPayload,
  ctx: WriteContext,
): Promise<ArtifactWriteResult> {
  const slug = deriveHtmlSlug(payload);
  const filename = `${slug}-${Date.now()}.html`;
  const { resolvedRoot, artifactsDir, absPath } = await resolveArtifactPath(
    ctx.projectRoot,
    filename,
  );
  await mkdir(artifactsDir, { recursive: true });
  await assertArtifactsDirSafe(artifactsDir, resolvedRoot);
  await writeFile(absPath, payload.html_content, 'utf8');
  return { path: absPath, url: buildUrl(ctx.projectId, filename) };
}

// 1MB cap on HTML artifacts (proposal S6). Larger payloads are not written
// to the `html_artifact` part — the assistant text lands as plain content
// and a warning is logged. Streaming abort was considered but the graceful
// "no artifact, plain text falls back" path is simpler and lossless from
// the user's perspective.
export const HTML_ARTIFACT_MAX_BYTES = 1_048_576;