import { highlight } from "@berry/api/web.ts";
import {
  type Line,
  linesOf,
  type Pair,
  pairs,
  pieces,
  type Range,
  trailing,
  wordChanges,
} from "./model.ts";
import type { FileDiff } from "./types.ts";
import { viewport } from "./viewport.ts";

export type Layout = "unified" | "split";
/** Each side's highlighted lines, once the worker has answered. */
type Lit = { old: Node[][] | null; new: Node[][] | null };
const KIND = { " ": "ctx", "-": "del", "+": "add" } as const;
const CHUNK_ROWS = 64;
type Row = { pair: Pair; line: Line | null };
/** Wrap the text `root` holds within `ranges` in `<mark>`s, through whatever highlighting it carries. */
function wrap(root: Element, ranges: readonly Range[], className: string) {
  if (ranges.length === 0) return;
  const texts: Text[] = [];
  const visit = (node: Node) => {
    if (node.nodeType === 3) texts.push(node as Text);
    else for (const child of [...node.childNodes]) visit(child);
  };
  visit(root);
  let offset = 0;
  for (const text of texts) {
    const start = offset;
    offset += text.data.length;
    // from the last range back, so `text` stays the part before those already wrapped
    for (const [from, to] of [...ranges].reverse()) {
      const a = Math.max(from, start) - start;
      const b = Math.min(to, offset) - start;
      if (a >= b) continue;
      if (b < text.data.length) text.splitText(b);
      const inside = a > 0 ? text.splitText(a) : text;
      const mark = document.createElement("mark");
      mark.className = className;
      inside.replaceWith(mark);
      mark.append(inside);
      if (inside === text) break;
    }
  }
}

/** A line's text, highlighted once that is known, with what changed in it marked. */
function lineText(
  line: Line,
  side: "old" | "new",
  lit: Lit | null,
  words: readonly Range[],
  edit?: (line: number) => void,
) {
  const cell = document.createElement("td");
  if (edit && side === "new" && line.new !== null) {
    cell.addEventListener("dblclick", () => edit(line.new!));
  }
  cell.className = `text ${KIND[line.mark]}`;
  const index = line.at[side];
  const highlighted = index === null ? undefined : lit?.[side]?.[index];
  const text = line.text.replace(/\r$/, "");
  if (highlighted) cell.append(...highlighted.map((node) => node.cloneNode(true)));
  else cell.append(text);
  wrap(cell, words, "word");
  if (line.mark !== " ") {
    const space = trailing(text);
    if (space) wrap(cell, [space], "space");
  }
  if (line.text.endsWith("\r")) {
    cell.append(<span class="badge" title="carriage return">␍</span>);
  }
  if (!line.newline) {
    cell.append(<span class="badge" title="no newline at end of file">⊘</span>);
  }
  return cell;
}

const number = (n: number | null) => <td class="ln">{n === null ? "" : String(n)}</td>;

/** Searchable chunks, with expensive rows and syntax nodes kept only around the viewport. */
export function rendering(root: HTMLElement) {
  const window = viewport(root);
  const waiting = new Set<() => Promise<void>>();
  let lighting = false;
  let disposed = false;

  async function light() {
    if (lighting || disposed) return;
    lighting = true;
    try {
      for (const next of waiting) {
        waiting.delete(next);
        if (disposed) break;
        await next();
      }
    } finally {
      lighting = false;
    }
  }

  return {
    file(
      file: FileDiff,
      layout: Layout,
      unfolded: Set<number>,
      unfold: (at: number) => void,
      edit?: (line: number) => void,
    ) {
      const element = <div class="diff-content" /> as HTMLElement;
      const chunks: ReturnType<typeof window.add>[] = [];
      const words = new Map<Pair, ReturnType<typeof wordChanges>>();
      let lit: Lit | null = null;
      let mounted = 0;
      let visible = 0;
      let attempted = false;
      let pending = false;
      let removed = false;
      let count = 0;
      const illuminate = async () => {
        if (removed || !visible || !mounted || attempted || pending) return;
        attempted = true;
        pending = true;
        const { sides } = linesOf(file);
        const [old, neu] = await Promise.all(
          [sides.old, sides.new].map((lines) =>
            lines.length ? highlight(lines.join("\n"), { path: file.path }).catch(() => null) : null
          ),
        );
        pending = false;
        if (disposed || removed) return;
        if (!mounted) {
          attempted = false;
          return;
        }
        attempted = true;
        if (old === null && neu === null) return;
        lit = { old, new: neu };
        for (const chunk of chunks) chunk.redraw();
      };
      const queue = () => {
        if (!visible || !mounted || attempted || pending || removed) return;
        waiting.add(illuminate);
        void light();
      };

      for (const [at, piece] of pieces(file).entries()) {
        if (piece.kind === "gap" || (piece.kind === "fold" && !unfolded.has(at))) {
          element.append(
            <div class="diff-fold">
              {piece.kind === "gap"
                ? `⋯ ${piece.count} unchanged lines not loaded`
                : (
                  <button type="button" class="link fold" _onclick={() => unfold(at)}>
                    ⋯ {String(piece.lines.length)} unchanged lines
                  </button>
                )}
            </div>,
          );
          count++;
          continue;
        }
        const paired = pairs(piece.lines);
        const partners = new Map<Line, Pair>();
        for (const pair of paired) {
          if (pair.old) partners.set(pair.old, pair);
          if (pair.new) partners.set(pair.new, pair);
        }
        const rows: Row[] = layout === "unified"
          ? piece.lines.map((line) => ({ pair: partners.get(line)!, line }))
          : paired.map((pair) => ({ pair, line: null }));
        count += rows.length;
        for (let start = 0; start < rows.length; start += CHUNK_ROWS) {
          const part = rows.slice(start, start + CHUNK_ROWS);
          const chunk = <div class={`diff-chunk ${layout}`} /> as HTMLElement;
          chunk.style.setProperty("--rows", String(part.length));
          let rich = false;
          let seen = false;
          const draw = (full: boolean) => {
            if (rich !== full) mounted += full ? 1 : -1;
            rich = full;
            if (!full) {
              if (!mounted) {
                lit = null;
                attempted = false;
                words.clear();
              }
              const text = (line: Line | null) => line?.text.replace(/\r$/, "") ?? "";
              chunk.replaceChildren(
                layout === "unified"
                  ? (
                    <pre class="diff-plain">{part.map(({ line }) => text(line)).join("\n") + "\n"}</pre>
                  )
                  : (
                    <div class="diff-plain-split">
                      {(["old", "new"] as const).map((side) => (
                        <pre class="diff-plain">{part.map(({ pair }) => text(pair[side])).join("\n") + "\n"}</pre>
                      ))}
                    </div>
                  ),
              );
              return;
            }
            const table = (
              <table class={`diff ${layout}`}>
                <colgroup>
                  {layout === "unified"
                    ? [<col class="gutter" />, <col class="gutter" />, <col />]
                    : [<col class="gutter" />, <col />, <col class="gutter" />, <col />]}
                </colgroup>
                {part.map(({ pair, line }) => {
                  let changes = words.get(pair);
                  if (changes === undefined) {
                    changes = pair.old && pair.new && pair.old !== pair.new
                      ? wordChanges(pair.old.text, pair.new.text)
                      : null;
                    words.set(pair, changes);
                  }
                  if (line) {
                    const side = line.mark === "-" ? "old" : "new";
                    return (
                      <tr class={KIND[line.mark]}>
                        {number(line.old)}
                        {number(line.new)}
                        {lineText(line, side, lit, changes?.[side] ?? [], edit)}
                      </tr>
                    );
                  }
                  const side = (line: Line | null, which: "old" | "new") =>
                    line
                      ? [
                        number(line[which]),
                        lineText(line, which, lit, changes?.[which] ?? [], edit),
                      ]
                      : [number(null), <td class="text none" />];
                  return <tr>{side(pair.old, "old")}{side(pair.new, "new")}</tr>;
                })}
              </table>
            );
            chunk.replaceChildren(table);
            queue();
          };
          chunks.push(window.add(chunk, draw, (intersects) => {
            if (seen === intersects) return;
            seen = intersects;
            visible += seen ? 1 : -1;
            queue();
          }));
          element.append(chunk);
        }
      }
      return {
        element,
        rows: count,
        dispose() {
          removed = true;
          waiting.delete(illuminate);
          for (const chunk of chunks) chunk.dispose();
          lit = null;
          words.clear();
        },
      };
    },
    dispose() {
      disposed = true;
      waiting.clear();
      window.dispose();
    },
  };
}