/**
 * Fixups for code the model wrote as markdown.
 *
 * Vicinae renders fences through `MdCodeBlock.qml`, which gives a dark panel, a
 * header showing the language, a Copy button, and syntax colouring resolved by
 * KSyntaxHighlighting. That last part is why the label matters beyond
 * cosmetics: `syntax::highlight` looks the language up with
 * `definitionForName(language)` and then `definitionForFileName("file." + language)`,
 * so `ts` resolves through `file.ts` and `bash` through its definition name,
 * while an unrecognised string such as `terminal` still renders as a label but
 * produces no highlighting at all. A wrong label is therefore worse than none,
 * and inference stays deliberately conservative.
 */

/** First words that mark a block as shell rather than a programming language. */
const SHELL_COMMANDS = new Set([
  "apt",
  "brew",
  "bun",
  "cat",
  "cd",
  "chmod",
  "chown",
  "code",
  "cp",
  "curl",
  "df",
  "docker",
  "du",
  "echo",
  "export",
  "find",
  "gh",
  "git",
  "grep",
  "htop",
  "jq",
  "kill",
  "kubectl",
  "ln",
  "ls",
  "make",
  "man",
  "mkdir",
  "mv",
  "nano",
  "node",
  "npm",
  "npx",
  "open",
  "pacman",
  "pip",
  "pnpm",
  "ps",
  "psql",
  "pwd",
  "python",
  "rm",
  "rsync",
  "scp",
  "sed",
  "source",
  "ssh",
  "sudo",
  "systemctl",
  "tar",
  "top",
  "touch",
  "unzip",
  "vim",
  "wget",
  "which",
  "yarn",
  "zip",
]);

const FENCE = "```";
/**
 * An opening fence, with an optional language.
 *
 * The language has to be part of this pattern. A closing ``` and an opening
 * bare ``` are the same two lines apart from context, so a pattern that only
 * matched bare fences treated every closing fence as a new opening one and
 * swallowed the rest of the answer.
 */
const OPENING_FENCE = /^(\s*)(`{3,}|~{3,})\s*([^\s`~]*)\s*$/;
/** A closing fence is the marker and nothing else. */
const CLOSING_FENCE = /^\s*(`{3,}|~{3,})\s*$/;
const STANDALONE_CODE_SPAN = /^\s*`([^`\n]+)`\s*[.!]?\s*$/;

/**
 * A line that is nothing but a bare http(s) URL, give or take a bullet.
 *
 * Vicinae only makes a URL clickable when markdown presents it as a link. Its
 * parser attaches the `table` and `strikethrough` GFM extensions and nothing
 * else, so the `autolink` extension is off: a bare URL renders as plain dead
 * text. `MarkdownModel` turns `CMARK_NODE_LINK` into `<a href=...>`, and the
 * selection controller opens that anchor on release, so `[label](url)` is the
 * one form the user can actually click.
 */
const BARE_URL = /^https?:\/\/\S+$/;
/** Sentence punctuation a model appends to a URL that is not part of it. */
const TRAILING_SENTENCE_PUNCTUATION = /[.,;:!?]+$/;
/** One inline code span that holds nothing but a URL. */
const STANDALONE_URL_SPAN = /^`([^`\n]+)`[.!]?$/;
/** A bullet or numbered-list marker, kept so a list of links stays a list. */
const LIST_MARKER = /^([ \t]*(?:[-*+]|\d+[.)])[ \t]+)(.*)$/;

/** A GFM table row: it opens and closes with a pipe. */
const TABLE_ROW = /^\s*\|.*\|\s*$/;
/**
 * The delimiter row under a header.
 *
 * The test is not how many dashes there are, because GFM wants only one per
 * column. It is that the line could be nothing else: pipes, dashes, colons and
 * spaces, with at least one dash to tell it apart from a row of empty cells.
 */
const TABLE_DELIMITER_ROW = /^\s*\|?[\s:|-]*-[\s:|-]*\|?\s*$/;

function significantLines(code: string): string[] {
  return code
    .split("\n")
    .map((line) => line.trim())
    .filter((line) => line.length > 0 && !line.startsWith("#") && !line.startsWith("//"));
}

function looksLikeShell(code: string): boolean {
  const lines = significantLines(code);
  if (lines.length === 0) return false;

  // An explicit prompt marker, or a leading `~` path, is about as clear as it gets.
  if (lines.some((line) => /^[$>] /.test(line) || line.startsWith("~/"))) return true;

  // A shell command as the first word of the first meaningful line.
  const [firstWord] = lines[0].split(/\s+/);
  if (SHELL_COMMANDS.has(firstWord)) return true;

  // Failing that, a pipeline or chained command between two known commands.
  if (/[|&]{1,2}/.test(code)) {
    return lines.some((line) => {
      const [word] = line.split(/\s+/);
      return SHELL_COMMANDS.has(word.replace(/[|&].*$/, ""));
    });
  }

  return false;
}

function looksLikeJson(code: string): boolean {
  const trimmed = code.trim();
  if (!trimmed.startsWith("{") && !trimmed.startsWith("[")) return false;

  try {
    const parsed: unknown = JSON.parse(trimmed);
    return typeof parsed === "object" && parsed !== null;
  } catch {
    return false;
  }
}

/** TypeScript-specific syntax. Plain JS is left unlabelled rather than guessed at. */
function looksLikeTypeScript(code: string): boolean {
  return (
    /\binterface\s+\w+\s*\{/.test(code) ||
    /\btype\s+\w+\s*=/.test(code) ||
    /\bas\s+const\b/.test(code) ||
    /:\s*(string|number|boolean|void|unknown|never)\b/.test(code) ||
    /<\w+>(\s*\(|\s*=|\s*=>)/.test(code) ||
    /\b(implements|readonly)\s+/.test(code)
  );
}

function looksLikePython(code: string): boolean {
  return (
    /^\s*def\s+\w+\s*\(/m.test(code) ||
    /^\s*from\s+[\w.]+\s+import\s+/m.test(code) ||
    /^\s*import\s+\w+$/m.test(code) ||
    /\bself\./.test(code) ||
    /^\s*(async\s+)?def\s+/m.test(code)
  );
}

/**
 * Best-effort language tag, or `undefined` when nothing is clear enough.
 * Order matters: a shell pipeline can contain what look like code fragments.
 */
export function inferLanguage(code: string): string | undefined {
  if (code.trim().length === 0) return undefined;

  if (looksLikeShell(code)) return "bash";
  if (looksLikeJson(code)) return "json";
  if (looksLikeTypeScript(code)) return "ts";
  if (looksLikePython(code)) return "python";

  return undefined;
}

/** Copies a fenced block through verbatim, returning the index just past it. */
function copyFence(lines: string[], out: string[], start: number): number {
  let index = start;

  out.push(lines[index]);
  index += 1;

  while (index < lines.length && !CLOSING_FENCE.test(lines[index])) {
    out.push(lines[index]);
    index += 1;
  }

  if (index < lines.length) {
    out.push(lines[index]);
    index += 1;
  }

  return index;
}

/**
 * Turns a paragraph that is nothing but one inline code span into a fence.
 *
 * Models reliably fence multi-line code and just as reliably answer "what is the
 * command for X" with a lone `` `pwd` ``. A single inline chip is the worst
 * presentation for that answer: no Copy button, no language, no colouring. The
 * rule is narrow on purpose, a whole line that is exactly one span, so
 * ``run `pwd` to check`` is left alone while a standalone command is promoted.
 *
 * Existing fences are copied through untouched, so a span-like line inside a
 * code block is never rewritten.
 */
export function promoteStandaloneCodeSpans(markdown: string): string {
  const lines = markdown.split("\n");
  const out: string[] = [];
  let index = 0;

  while (index < lines.length) {
    const fence = OPENING_FENCE.exec(lines[index]);

    if (fence) {
      index = copyFence(lines, out, index);
      continue;
    }

    const span = STANDALONE_CODE_SPAN.exec(lines[index]);
    if (span) {
      const code = span[1].trim();
      out.push(FENCE + (inferLanguage(code) ?? ""), code, FENCE);
      index += 1;
      continue;
    }

    out.push(lines[index]);
    index += 1;
  }

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

/**
 * Adds a language to fences that have none, leaving labelled fences untouched.
 *
 * Only bare opening fences are rewritten, so the model's own choice always wins.
 */
export function labelCodeFences(markdown: string): string {
  const lines = markdown.split("\n");
  const out: string[] = [];
  let index = 0;

  while (index < lines.length) {
    const openingLine = lines[index];
    const opener = OPENING_FENCE.exec(openingLine);

    if (!opener) {
      out.push(openingLine);
      index += 1;
      continue;
    }

    const [, indent, marker, existing] = opener;
    const body: string[] = [];
    index += 1;

    while (index < lines.length && !CLOSING_FENCE.test(lines[index])) {
      body.push(lines[index]);
      index += 1;
    }

    const closing = index < lines.length ? lines[index] : "";
    if (closing) index += 1;

    // A fence the model already labelled is left exactly as written.
    if (existing) out.push(openingLine);
    else {
      const language = inferLanguage(body.join("\n"));
      out.push(language ? `${indent}${marker}${language}` : openingLine);
    }

    out.push(...body);
    if (closing) out.push(closing);
  }

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

/** A URL with the sentence punctuation after it removed. */
function asBareUrl(candidate: string): string | undefined {
  const trimmed = candidate.trim();
  if (!BARE_URL.test(trimmed)) return undefined;
  return trimmed.replace(TRAILING_SENTENCE_PUNCTUATION, "");
}

/**
 * Wraps a URL as a markdown link, using the address itself as the label so the
 * destination stays readable rather than turning into a generic word.
 *
 * A destination containing parentheses (plenty of Wikipedia articles) has to
 * be wrapped in pointy brackets or the parser reads the first `)` as the end of
 * the destination and leaves the rest as trailing prose.
 */
function asLink(url: string): string {
  // Square brackets in the *label* would end the link text early, which is why
  // an IPv6 literal such as `http://[::1]/` needs them escaped. The destination
  // tolerates brackets, but not parentheses, which is what the pointy form is
  // for.
  const label = url.replace(/[[\]]/g, "\\$&");
  const destination = /[()]/.test(url) ? `<${url}>` : url;
  return `[${label}](${destination})`;
}

/**
 * The URLs of a fence whose every non-empty line is one, or `undefined` when
 * the block is real code.
 *
 * Deliberately narrow: one line that is not a URL disqualifies the whole block,
 * so a `curl` invocation that happens to contain an address is never touched.
 */
function urlOnlyBlock(lines: string[]): string[] | undefined {
  const urls: string[] = [];

  for (const line of lines) {
    const trimmed = line.trim();
    if (trimmed.length === 0) continue;

    const url = asBareUrl(trimmed);
    if (!url) return undefined;
    urls.push(url);
  }

  return urls.length > 0 ? urls : undefined;
}

/** Rewrites a line that is only a URL, or only a span holding one, into a link. */
function linkifyLine(line: string): string {
  const marker = LIST_MARKER.exec(line);
  const prefix = marker ? marker[1] : (line.match(/^[ \t]*/)?.[0] ?? "");
  const rest = marker ? marker[2] : line.slice(prefix.length);

  const span = STANDALONE_URL_SPAN.exec(rest.trim());
  const url = asBareUrl(span ? span[1] : rest);

  return url ? `${prefix}${asLink(url)}` : line;
}

/**
 * Turns URLs the model wrote as code back into links.
 *
 * This is the reported bug: asked for a few GitHub projects, the model answers
 * with a fenced block of bare addresses. A fence renders through
 * `MdCodeBlock.qml` as a dark panel with a Copy button and no link handling at
 * all, so the one thing the user wants to do with a URL is the one thing they
 * cannot. The same applies to a lone `` `https://...` `` span.
 *
 * Three shapes are recovered, and only these:
 *
 * 1. A fence whose entire body is URLs.
 * 2. A line that is exactly one inline span holding a URL.
 * 3. A line that is exactly a URL, bulleted or not.
 *
 * Existing fences holding anything else are copied through untouched, so real
 * code is never rewritten.
 */
export function restoreUrlLinks(markdown: string): string {
  const lines = markdown.split("\n");
  const out: string[] = [];
  let index = 0;

  while (index < lines.length) {
    if (!OPENING_FENCE.test(lines[index])) {
      out.push(linkifyLine(lines[index]));
      index += 1;
      continue;
    }

    const body: string[] = [];
    let cursor = index + 1;
    while (cursor < lines.length && !CLOSING_FENCE.test(lines[cursor])) {
      body.push(lines[cursor]);
      cursor += 1;
    }

    const closing = cursor < lines.length;
    const urls = urlOnlyBlock(body);

    if (urls) out.push(...urls.map(asLink));
    else {
      out.push(lines[index], ...body);
      if (closing) out.push(lines[cursor]);
    }

    index = cursor + (closing ? 1 : 0);
  }

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

/**
 * Inserts the blank line a table needs to start at all.
 *
 * A GFM table cannot interrupt a paragraph, so a table written straight after a
 * line of prose is not a table: it renders as a paragraph of pipes and dashes,
 * which is how a perfectly good answer turns into noise. The blank line looks
 * unnecessary, so models leave it out.
 *
 * Only a real table start is touched, which is a row followed by a delimiter
 * row, so prose that happens to contain a pipe is left alone. Fences are copied
 * through untouched for the same reason, since a table shown as example code
 * must stay exactly as written.
 */
export function separateTables(markdown: string): string {
  const lines = markdown.split("\n");
  const out: string[] = [];
  let index = 0;

  while (index < lines.length) {
    if (OPENING_FENCE.test(lines[index])) {
      index = copyFence(lines, out, index);
      continue;
    }

    const startsTable =
      TABLE_ROW.test(lines[index]) && index + 1 < lines.length && TABLE_DELIMITER_ROW.test(lines[index + 1]);

    // Only when something would otherwise swallow it. A table already at a block
    // boundary, after a blank line or after a fenced block, needs nothing: the
    // fence has already ended the preceding block.
    const previous = out[out.length - 1];
    const atBlockBoundary =
      previous === undefined || previous.trim().length === 0 || CLOSING_FENCE.test(previous);

    if (startsTable && !atBlockBoundary) out.push("");

    out.push(lines[index]);
    index += 1;
  }

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

/**
 * The full pre-render pass, in order.
 *
 * Tables are separated first because they change block boundaries: a blank line
 * has to exist before anything else looks at the line. Links are restored next
 * so a recovered URL leaves no span for the promoter to fence again. Promotion
 * then runs before labelling, so a promoted block is seen as an ordinary fence
 * by the labeller, which is also harmless when promotion already inferred a
 * language.
 */
export function repairCodeBlocks(markdown: string): string {
  return labelCodeFences(promoteStandaloneCodeSpans(restoreUrlLinks(separateTables(markdown))));
}