type SessionEntry = {
  type: string;
  message?: { role: string; content?: unknown };
};

const MAX_PROMPT_CHARS = 4_000;
const MAX_TITLE_CHARS = 60;

type TextPart = {
  type?: string;
  text?: string;
};

export function shouldArmAutoNaming(
  entries: SessionEntry[],
  currentName: string | undefined,
): boolean {
  return !currentName?.trim() && countUserMessages(entries) === 0;
}

export function countUserMessages(entries: SessionEntry[]): number {
  return entries.filter(isUserMessageEntry).length;
}

export function extractUserText(content: unknown): string {
  if (typeof content === "string") return normalizePrompt(content);
  if (!Array.isArray(content)) return "";

  return normalizePrompt(
    content
      .filter(isTextPart)
      .map((part) => part.text)
      .join("\n"),
  );
}

export function getRecentUserPrompt(entries: SessionEntry[], maxChars = MAX_PROMPT_CHARS): string {
  const messages: string[] = [];
  let length = 0;

  for (let index = entries.length - 1; index >= 0; index -= 1) {
    const entry = entries[index];
    if (!isUserMessageEntry(entry)) continue;

    const text = extractUserText(entry.message.content);
    if (!text) continue;

    const separatorLength = messages.length > 0 ? 2 : 0;
    const remaining = maxChars - length - separatorLength;
    if (remaining <= 0) break;

    messages.unshift(text.slice(0, remaining));
    length += Math.min(text.length, remaining) + separatorLength;
    if (text.length > remaining) break;
  }

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

export function sanitizeSessionName(value: string): string | undefined {
  const firstLine = value
    .replace(/^```[a-z0-9_-]*\s*/i, "")
    .replace(/```$/g, "")
    .split(/\r?\n/)
    .map((line) => line.trim())
    .find(Boolean);

  if (!firstLine) return undefined;

  let title = firstLine
    .replace(/^(title|session name)\s*:\s*/i, "")
    .replace(/^[-*]\s*/, "")
    .replace(/[.?!:;,]+$/g, "")
    .replace(/^['"`]+|['"`]+$/g, "")
    .replace(/\s+/g, " ")
    .trim();

  if (!title) return undefined;
  if (title.length <= MAX_TITLE_CHARS) return title;

  title = title.slice(0, MAX_TITLE_CHARS).trimEnd();
  const lastSpace = title.lastIndexOf(" ");
  if (lastSpace > 20) title = title.slice(0, lastSpace);
  return title.trim() || undefined;
}

function isUserMessageEntry(entry: SessionEntry): entry is SessionEntry & {
  type: "message";
  message: { role: "user"; content: unknown };
} {
  return entry.type === "message" && entry.message?.role === "user";
}

function isTextPart(value: unknown): value is TextPart & { type: "text"; text: string } {
  return Boolean(
    value &&
      typeof value === "object" &&
      (value as TextPart).type === "text" &&
      typeof (value as TextPart).text === "string",
  );
}

function normalizePrompt(value: string): string {
  return value.replace(/\r\n/g, "\n").trim().slice(0, MAX_PROMPT_CHARS);
}