"use client";

// MarkdownBlock — tiny zero-dep Markdown renderer. Handles the subset
// the refiner emits: h1/h2/h3 headings, - / * bullets, 1. numbered
// lists, `**bold**`, `` `code` ``, blank-line-separated paragraphs.
// Not a general-purpose renderer — deliberately small to avoid a
// react-markdown dep for one canvas surface.

import React from "react";

const mono =
  "ui-monospace, SFMono-Regular, SF Mono, Menlo, Monaco, Consolas, monospace";

type Block =
  | { kind: "h1" | "h2" | "h3"; text: string; id?: string }
  | { kind: "p"; text: string }
  | { kind: "ul"; items: string[] }
  | { kind: "ol"; items: string[] }
  | { kind: "code"; lang: string; text: string };

/** Stable slug for a heading, so the reader's outline can scroll to it. */
export function headingId(text: string, ordinal: number): string {
  const slug = text
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, "-")
    .replace(/^-+|-+$/g, "")
    .slice(0, 60);
  return `h-${ordinal}-${slug || "section"}`;
}

/** The headings of a document, for an outline rail. */
export function outlineOf(
  md: string,
): Array<{ id: string; text: string; level: 1 | 2 | 3 }> {
  return parse(md).flatMap((b, idx) =>
    b.kind === "h1" || b.kind === "h2" || b.kind === "h3"
      ? [
          {
            id: b.id ?? headingId(b.text, idx),
            text: b.text,
            level: Number(b.kind.slice(1)) as 1 | 2 | 3,
          },
        ]
      : [],
  );
}

function parse(md: string): Block[] {
  const lines = md.replace(/\r\n/g, "\n").split("\n");
  const blocks: Block[] = [];
  let i = 0;
  while (i < lines.length) {
    const line = lines[i];
    const trimmed = line.trim();
    if (!trimmed) {
      i++;
      continue;
    }
    // Fenced code block. Agent output is full of ```rust / ```toml
    // blocks; without this they render as mangled paragraphs.
    const fence = /^```([A-Za-z0-9_+-]*)\s*$/.exec(trimmed);
    if (fence) {
      const lang = fence[1] ?? "";
      const body: string[] = [];
      i++;
      while (i < lines.length && !/^```\s*$/.test(lines[i].trim())) {
        body.push(lines[i]);
        i++;
      }
      i++; // consume the closing fence (or run off the end on an unclosed block)
      blocks.push({ kind: "code", lang, text: body.join("\n") });
      continue;
    }
    // Headings
    const h = /^(#{1,6})\s+(.*)$/.exec(trimmed);
    if (h) {
      // h4-h6 are rare in agent output; render them as h3 rather than
      // dropping the text into a paragraph.
      const level = Math.min(h[1].length, 3) as 1 | 2 | 3;
      const text = h[2];
      blocks.push({
        kind: (`h${level}` as "h1" | "h2" | "h3"),
        text,
        id: headingId(text, blocks.length),
      });
      i++;
      continue;
    }
    // Bullet list
    if (/^[-*]\s+/.test(trimmed)) {
      const items: string[] = [];
      while (i < lines.length && /^[-*]\s+/.test(lines[i].trim())) {
        items.push(lines[i].trim().replace(/^[-*]\s+/, ""));
        i++;
      }
      blocks.push({ kind: "ul", items });
      continue;
    }
    // Numbered list
    if (/^\d+\.\s+/.test(trimmed)) {
      const items: string[] = [];
      while (i < lines.length && /^\d+\.\s+/.test(lines[i].trim())) {
        items.push(lines[i].trim().replace(/^\d+\.\s+/, ""));
        i++;
      }
      blocks.push({ kind: "ol", items });
      continue;
    }
    // Paragraph — greedily accumulate until blank line or block boundary
    const paraLines: string[] = [];
    while (
      i < lines.length &&
      lines[i].trim() &&
      !/^(#{1,6})\s+/.test(lines[i].trim()) &&
      !/^```/.test(lines[i].trim()) &&
      !/^[-*]\s+/.test(lines[i].trim()) &&
      !/^\d+\.\s+/.test(lines[i].trim())
    ) {
      paraLines.push(lines[i].trim());
      i++;
    }
    if (paraLines.length) blocks.push({ kind: "p", text: paraLines.join(" ") });
  }
  return blocks;
}

// Inline: **bold**, `code`. Simple sequential scan.
function renderInline(text: string): React.ReactNode[] {
  const out: React.ReactNode[] = [];
  const re = /(\*\*[^*]+\*\*|`[^`]+`)/g;
  let last = 0;
  let m: RegExpExecArray | null;
  let key = 0;
  while ((m = re.exec(text)) !== null) {
    if (m.index > last) out.push(text.slice(last, m.index));
    const tok = m[0];
    if (tok.startsWith("**")) {
      out.push(
        <strong key={key++} style={{ color: "#f3f3f5" }}>
          {tok.slice(2, -2)}
        </strong>,
      );
    } else {
      out.push(
        <code
          key={key++}
          style={{
            fontFamily: mono,
            fontSize: 11.5,
            padding: "1px 5px",
            borderRadius: 4,
            background: "rgba(255,255,255,.06)",
            color: "#ffb44a",
          }}
        >
          {tok.slice(1, -1)}
        </code>,
      );
    }
    last = m.index + tok.length;
  }
  if (last < text.length) out.push(text.slice(last));
  return out;
}

export function MarkdownBlock({ source }: { source: string }) {
  const blocks = React.useMemo(() => parse(source), [source]);
  return (
    <div
      style={{
        display: "flex",
        flexDirection: "column",
        gap: 10,
        color: "#cfcfd5",
        fontSize: 13,
        lineHeight: 1.55,
      }}
    >
      {blocks.map((b, idx) => {
        if (b.kind === "h1")
          return (
            <h1
              key={idx}
              id={b.id}
              style={{
                margin: "8px 0 2px",
                fontSize: 17,
                color: "#f3f3f5",
                fontWeight: 600,
                letterSpacing: ".01em",
              }}
            >
              {renderInline(b.text)}
            </h1>
          );
        if (b.kind === "h2")
          return (
            <h2
              key={idx}
              id={b.id}
              style={{
                margin: "10px 0 -2px",
                fontSize: 12,
                color: "#7cd6e0",
                fontFamily: mono,
                letterSpacing: ".14em",
                textTransform: "uppercase",
                fontWeight: 600,
              }}
            >
              {renderInline(b.text)}
            </h2>
          );
        if (b.kind === "h3")
          return (
            <h3
              key={idx}
              id={b.id}
              style={{
                margin: "6px 0 -4px",
                fontSize: 11.5,
                color: "#a0a0a8",
                fontFamily: mono,
                letterSpacing: ".10em",
                textTransform: "uppercase",
                fontWeight: 500,
              }}
            >
              {renderInline(b.text)}
            </h3>
          );
        if (b.kind === "code")
          return (
            <pre
              key={idx}
              style={{
                margin: 0,
                padding: "10px 12px",
                borderRadius: 8,
                border: "1px solid rgba(255,255,255,.07)",
                background: "rgba(0,0,0,.45)",
                color: "#e0e0e5",
                fontFamily: mono,
                fontSize: 11.5,
                lineHeight: 1.5,
                // Code is the one thing that may scroll sideways; the
                // page itself must never scroll horizontally.
                overflowX: "auto",
                whiteSpace: "pre",
              }}
            >
              {b.lang && (
                <span
                  style={{
                    display: "block",
                    marginBottom: 6,
                    fontSize: 9.5,
                    letterSpacing: ".12em",
                    textTransform: "uppercase",
                    color: "#6a6a72",
                  }}
                >
                  {b.lang}
                </span>
              )}
              <code>{b.text}</code>
            </pre>
          );
        if (b.kind === "p")
          return (
            <p key={idx} style={{ margin: 0 }}>
              {renderInline(b.text)}
            </p>
          );
        if (b.kind === "ul")
          return (
            <ul
              key={idx}
              style={{
                margin: 0,
                paddingLeft: 18,
                display: "flex",
                flexDirection: "column",
                gap: 4,
              }}
            >
              {b.items.map((it, i) => (
                <li key={i}>{renderInline(it)}</li>
              ))}
            </ul>
          );
        if (b.kind === "ol")
          return (
            <ol
              key={idx}
              style={{
                margin: 0,
                paddingLeft: 20,
                display: "flex",
                flexDirection: "column",
                gap: 4,
              }}
            >
              {b.items.map((it, i) => (
                <li key={i}>{renderInline(it)}</li>
              ))}
            </ol>
          );
        return null;
      })}
    </div>
  );
}