/**
 * Bringing Markdown back in.
 *
 * Notes leave this app as `.md` files, and as a `.zip` when there are pictures
 * or drawings beside them. Both come back here. A `.zip` written by the exporter
 * makes the round trip nearly whole: the text, the tables, the task boxes, the
 * embedded images — re-uploaded as attachments so they are encrypted at rest
 * again like anything else — and the drawing, which returns as the PNG it was
 * exported as.
 *
 * The one thing that cannot come back as it left is a drawing's *strokes*. A
 * PNG is pixels; the vectors that produced it are not recoverable from it. The
 * drawing therefore returns as a picture in the note — visible, exportable,
 * printable, but no longer editable with the pen. That is stated in the result
 * rather than glossed over, because silently downgrading someone's data is the
 * kind of surprise that is only discovered months later.
 */

import * as sync from "../syncEngine";
import * as db from "../offlineStore";
import { serializeNoteContent, type DocNode } from "../editor/content";
import { markdownToNote } from "./markdownImport";
import { readZip, type ZipFile } from "./zipRead";
import type { NoteMeta } from "../types";

export interface ImportProgress {
  done: number;
  total: number;
  label: string;
}

/* How far to look for further pages of one note's drawing. A bound rather than
 * a limit anyone should reach: without one, a malformed archive would have this
 * loop asking for filenames forever. */
const MAX_DRAWING_PAGES = 200;

export interface ImportResult {
  notes: NoteMeta[];
  /** Notes whose drawing came back as a picture instead of editable strokes. */
  flattenedDrawings: number;
  /** Images referenced by a note but not present in the archive. */
  missingImages: number;
  /** Files that could not be read at all, by name. */
  failed: string[];
}

const MARKDOWN = /\.(md|markdown|txt)$/i;
const IMAGE_EXT: Record<string, string> = {
  png: "image/png",
  jpg: "image/jpeg",
  jpeg: "image/jpeg",
  webp: "image/webp",
  gif: "image/gif",
  avif: "image/avif",
};

const mimeOf = (name: string) => IMAGE_EXT[name.split(".").pop()?.toLowerCase() ?? ""] ?? null;

const baseName = (path: string) =>
  path
    .split("/")
    .pop()!
    .replace(/\.[^.]+$/, "");

/** Resolves `../bilder/x.png` against the folder the note file sits in. */
function resolvePath(from: string, target: string): string {
  if (/^[a-z]+:/i.test(target)) return target; // absolute URL — not an archive path
  const parts = from.split("/").slice(0, -1);
  for (const segment of decodeURIComponent(target).split("/")) {
    if (segment === "." || segment === "") continue;
    if (segment === "..") parts.pop();
    else parts.push(segment);
  }
  return parts.join("/");
}

/* ── documents ── */

/** Depth-first walk that may replace a node with another (or with nothing). */
function mapNodes(node: DocNode, fn: (n: DocNode) => DocNode | null): DocNode | null {
  const mapped = fn(node);
  if (!mapped) return null;
  if (Array.isArray(mapped.content)) {
    mapped.content = mapped.content.map((c) => mapNodes(c, fn)).filter((c): c is DocNode => c !== null);
  }
  return mapped;
}

/** The exporter's stand-in for a drawing, so it can be swapped for the real PNG. */
const isDrawingMarker = (n: DocNode) =>
  n.type === "blockquote" && JSON.stringify(n.content ?? "").includes("Zeichnung");

/* ── one note ── */

interface Sources {
  /** Archive path → bytes, for resolving relative image references. */
  files: Map<string, Uint8Array>;
}

async function uploadPicture(bytes: Uint8Array, name: string): Promise<string | null> {
  const mime = mimeOf(name) ?? "image/png";
  try {
    // A copy, because a view onto the archive buffer would carry the whole
    // archive into the Blob.
    const copy = new Uint8Array(bytes.byteLength);
    copy.set(bytes);
    const blob = new Blob([copy.buffer], { type: mime });
    const dataUrl = await new Promise<string>((resolve, reject) => {
      const r = new FileReader();
      r.onload = () => resolve(String(r.result));
      r.onerror = () => reject(r.error);
      r.readAsDataURL(blob);
    });
    const { id } = await sync.uploadAttachment(dataUrl, name);
    // Seed the offline cache from bytes already in hand, so the picture shows
    // immediately instead of being fetched back from the server.
    await db.putAttachmentBlob(id, blob).catch(() => {});
    return id;
  } catch {
    return null;
  }
}

async function importOne(
  markdownPath: string,
  source: string,
  folderId: string,
  sources: Sources,
  result: ImportResult
): Promise<NoteMeta | null> {
  const parsed = markdownToNote(source);
  const title = parsed.title || baseName(markdownPath) || "Importiert";

  /* Pictures first: the document has to name attachment ids, not archive paths. */
  const uploaded = new Map<string, string>();
  for (const reference of new Set(parsed.imagePaths)) {
    const path = resolvePath(markdownPath, reference);
    const bytes = sources.files.get(path);
    if (!bytes) {
      result.missingImages++;
      continue;
    }
    const id = await uploadPicture(bytes, path);
    if (id) uploaded.set(reference, id);
    else result.missingImages++;
  }

  /* The drawing, if the archive carried one.
   *
   * Four layouts exist. A notebook export files it under `drawings/`, a
   * single-note export writes it beside the file as `<name>-drawing.png`, and
   * both had German names — `zeichnungen/`, `-zeichnung` — before the interface
   * was put into English. All four are read: an archive written last year is
   * exactly the archive someone reaches for.
   *
   * Only the first two were being looked for until now, which meant a drawing
   * exported by this very app came back as nothing at all.
   *
   * A drawing may run over several pages. Page one keeps the plain name and the
   * rest are numbered after it, so they come back in order.
   */
  const base = baseName(markdownPath);
  const drawingIds: string[] = [];
  for (const suffix of ["", ...Array.from({ length: MAX_DRAWING_PAGES - 1 }, (_, i) => `-${i + 2}`)]) {
    const path = [
      `drawings/${base}${suffix}.png`,
      `${base}-drawing${suffix}.png`,
      `zeichnungen/${base}${suffix}.png`,
      `${base}-zeichnung${suffix}.png`,
    ].find((p) => sources.files.has(p));
    const bytes = path ? sources.files.get(path) : null;
    if (!path || !bytes) break; // pages are consecutive; the first gap is the end
    const id = await uploadPicture(bytes, path);
    if (id) drawingIds.push(id);
  }
  if (drawingIds.length) result.flattenedDrawings++;

  const asPicture = (id: string) => ({
    type: "image",
    attrs: { attachmentId: id, alt: "Drawing", src: null },
  });

  let replaced = false;
  let doc = mapNodes(parsed.doc, (n) => {
    if (n.type === "image") {
      const id = n.attrs?.src ? uploaded.get(n.attrs.src) : null;
      // An image whose file is not in the archive keeps its address: if it was a
      // web URL it still works, and if it was a missing file the note at least
      // records what used to be there.
      return id ? { ...n, attrs: { ...n.attrs, attachmentId: id, src: null } } : n;
    }
    // The exporter leaves a note saying the drawing lies beside the file. Now it
    // is back inside the note, so the note about it would be wrong.
    const first = drawingIds[0];
    if (first && isDrawingMarker(n)) {
      replaced = true;
      return asPicture(first);
    }
    return n;
  })!;

  // The marker stands for the drawing as a whole, so it can only become the
  // first page; the others follow it at the end. With no marker at all (a
  // hand-written archive, or an older export) every page goes there.
  const trailing = replaced ? drawingIds.slice(1) : drawingIds;
  if (trailing.length) {
    doc = { ...doc, content: [...(doc.content ?? []), ...trailing.map(asPicture)] };
  }

  const note = await sync.createNote(folderId);
  await sync.updateNoteTitle(note.id, title);
  await sync.updateNoteContent(
    note.id,
    serializeNoteContent(doc),
    [],
    [...uploaded.values(), ...drawingIds]
  );
  return { ...note, title };
}

/* ── entry point ── */

const textOf = (bytes: Uint8Array) => new TextDecoder().decode(bytes);

/**
 * Imports the chosen files into a notebook.
 *
 * Each `.md` becomes one note; each `.zip` is unpacked and every Markdown file
 * inside becomes one. A file that cannot be read is named in the result rather
 * than aborting the rest — importing forty notes should not fail because the
 * thirty-first is damaged.
 */
export async function importFiles(
  files: File[],
  folderId: string,
  onProgress?: (p: ImportProgress) => void
): Promise<ImportResult> {
  const result: ImportResult = { notes: [], flattenedDrawings: 0, missingImages: 0, failed: [] };

  /* Everything is unpacked first, so the total is honest: a single ZIP can hold
     forty notes, and a progress bar that only counts files chosen would sit at
     "1 of 1" for a minute. */
  const jobs: Array<{ path: string; source: string; sources: Sources }> = [];

  for (const file of files) {
    try {
      if (/\.zip$/i.test(file.name)) {
        const members: ZipFile[] = await readZip(await file.arrayBuffer());
        const map = new Map(members.map((m) => [m.name, m.bytes]));
        const sources: Sources = { files: map };
        const markdown = members.filter((m) => MARKDOWN.test(m.name));
        for (const m of markdown) {
          // Our own archives carry an index file. It is a table of contents, not
          // a note, and importing it would add a phantom note linking to files
          // that no longer exist. A lone README is taken at face value, since
          // then it is the only thing in there to import.
          if (markdown.length > 1 && /^readme\.md$/i.test(m.name)) continue;
          jobs.push({ path: m.name, source: textOf(m.bytes), sources });
        }
      } else if (MARKDOWN.test(file.name)) {
        jobs.push({ path: file.name, source: await file.text(), sources: { files: new Map() } });
      } else {
        result.failed.push(file.name);
      }
    } catch (err) {
      console.error(`[import] ${file.name}:`, err);
      result.failed.push(file.name);
    }
  }

  for (const [i, job] of jobs.entries()) {
    onProgress?.({ done: i, total: jobs.length, label: baseName(job.path) });
    try {
      const note = await importOne(job.path, job.source, folderId, job.sources, result);
      if (note) result.notes.push(note);
    } catch (err) {
      console.error(`[import] ${job.path}:`, err);
      result.failed.push(job.path);
    }
  }
  onProgress?.({ done: jobs.length, total: jobs.length, label: "" });

  return result;
}