/**
 * Turn envelope classifier — T029, <2ms budget.
 *
 * Derives turn_type from the messages envelope using deterministic
 * heuristics (no neural inference). Falls back to 'unknown' when
 * the envelope is empty or unclassifiable.
 *
 * Classification priority (first match wins):
 *   1. tool_result  — last message is role=tool
 *   2. planning     — planning/architecture signals in recent content
 *   3. subagent     — subagent/exploration context markers
 *   4. main_loop    — default agent loop turn (messages present)
 *   5. unknown      — no messages or empty envelope
 */

import type { Message, TurnType } from '../types/index.js';

// ─── Constants ────────────────────────────────────────────────────────────────

const TOOL_RESULT_SIZE_THRESHOLD = 50_000;

const PLANNING_PATTERNS: readonly RegExp[] = [
  /\b(?:plan|planning|architect(?:ure)?|design|refactor|migration)\b/i,
  /\b(?:step\s*\d|phase\s*\d|breakdown|strategy|trade-?off)\b/i,
  /^#+\s*(?:plan|design|architecture)/im,
  // Repo-hygiene / destructive-intent (SP-176, #97) — escalate off main_loop
  /\b(?:clean\s*up(?:\s+the)?\s+repo|repo\s+cleanup|cleanup\s+the\s+repo)\b/i,
  /\b(?:clean\s*up|cleanup|mistakenly\s+added|accidentally\s+added|accidental\s+add)\b/i,
  /\b(?:unstage|git\s+rm|rm\s+-rf|force\s+push|git\s+reset\s+--hard|destructive)\b/i,
];

const SUBAGENT_PATTERNS: readonly RegExp[] = [
  /\b(?:subagent|sub-agent|exploration|explore|search|investigate)\b/i,
  /\b(?:spawned|delegat(?:e|ed|ing)|parallel\s+agent)\b/i,
  /\b(?:Task|Agent)\.(?:create|spawn|launch)\b/,
];

// ─── Classifier ───────────────────────────────────────────────────────────────

export function classifyTurnEnvelope(
  messages: readonly Message[] | undefined,
): TurnType {
  if (!messages || messages.length === 0) {
    return 'unknown';
  }

  const lastMessage = messages[messages.length - 1]!;

  if (isToolResult(lastMessage)) {
    return 'tool_result';
  }

  if (hasPlanningSignals(messages)) {
    return 'planning';
  }

  if (hasSubagentSignals(messages)) {
    return 'subagent';
  }

  return 'main_loop';
}

// ─── Signal detectors ─────────────────────────────────────────────────────────

function isToolResult(message: Message): boolean {
  if (message.role !== 'tool') return false;
  return message.content.length <= TOOL_RESULT_SIZE_THRESHOLD;
}

function hasPlanningSignals(messages: readonly Message[]): boolean {
  const window = recentWindow(messages, 3);
  for (const msg of window) {
    if (matchesAny(msg.content, PLANNING_PATTERNS)) {
      return true;
    }
  }
  return false;
}

function hasSubagentSignals(messages: readonly Message[]): boolean {
  const window = recentWindow(messages, 3);
  for (const msg of window) {
    if (matchesAny(msg.content, SUBAGENT_PATTERNS)) {
      return true;
    }
  }
  return false;
}

// ─── Helpers ──────────────────────────────────────────────────────────────────

function recentWindow(
  messages: readonly Message[],
  count: number,
): readonly Message[] {
  const start = Math.max(0, messages.length - count);
  return messages.slice(start);
}

function matchesAny(text: string, patterns: readonly RegExp[]): boolean {
  for (const pattern of patterns) {
    if (pattern.test(text)) {
      return true;
    }
  }
  return false;
}