/**
 * Context compaction: heuristic fallback + optional one-shot LLM summary.
 *
 * Tool schemas are reserved out of historyBudget. Compact against conversation
 * tokens only — never treat a large tool list as "history is full".
 */

const truncate = require('./truncate.js');

const CHAR_PER_TOKEN = 3;
const THRESHOLD = 0.68;
const MIN_SUMMARY = 80;
const MIN_COMPACT_MESSAGES = 4;
const COMPACT_PROMPT =
  'Summarize this coding-agent conversation. Use exactly these sections:\n' +
  '1. Goal\n' +
  '2. Done\n' +
  '3. Files / decisions\n' +
  '4. Open work\n' +
  '5. Next action\n' +
  'Be specific (paths, names, errors). Do not say the conversation was compacted.';
const VOICE_COMPACT_PROMPT =
  'Summarize this spoken assistant conversation for the next turn. Use exactly these sections:\n' +
  '1. Latest user request\n' +
  '2. Facts from tools\n' +
  '3. What was already answered\n' +
  '4. Open follow-ups, original goal, user preferences and corrections\n' +
  'Be specific. Do not greet. Do not say the conversation was compacted.';

function contentChars(content) {
  if (content == null) return 0;
  if (typeof content === 'string') return content.length;
  if (Array.isArray(content)) {
    let n = 0;
    for (let i = 0; i < content.length; i++) {
      const p = content[i];
      if (p == null) continue;
      if (typeof p === 'string') n += p.length;
      else if (p.text) n += String(p.text).length;
      else if (p.type === 'image_url' || p.image_url) n += 1600;
      else n += JSON.stringify(p).length;
    }
    return n;
  }
  return JSON.stringify(content).length;
}

function messageChars(m) {
  if (!m) return 0;
  let n = contentChars(m.content);
  if (m.tool_calls) n += JSON.stringify(m.tool_calls).length;
  if (m.name) n += String(m.name).length;
  return n + 8;
}

function nonSystemCount(messages) {
  let n = 0;
  for (const m of messages || []) {
    if (m && m.role !== 'system') n += 1;
  }
  return n;
}

function conversationTokens(messages) {
  let n = 0;
  for (const m of messages || []) n += messageChars(m);
  return Math.ceil(n / CHAR_PER_TOKEN);
}

function toolTokens(tools) {
  return Math.ceil(JSON.stringify(tools || []).length / CHAR_PER_TOKEN);
}

function estimateTokens(messages, tools) {
  return conversationTokens(messages) + toolTokens(tools);
}

function historyBudget(ctxSize, tools, attempt, extraTokens = 0) {
  const cap = ctxSize > 0 ? Number(ctxSize) : 8192;
  const toolTok = toolTokens(tools);
  const reserve = Math.max(384, Math.floor(cap * (0.18 + (Number(attempt) || 0) * 0.08)));
  return Math.max(240, Math.floor(cap * 0.72) - toolTok - reserve - extraTokens);
}

function shouldCompact(messages, tools, ctxSize, extraTokens = 0) {
  const budget = historyBudget(ctxSize, tools, 0, extraTokens);
  const tokens = conversationTokens(messages);
  // Large first requests or tool results can overflow before four messages.
  // A small greeting must not be discarded merely because schemas are large.
  return tokens > budget && (nonSystemCount(messages) >= MIN_COMPACT_MESSAGES || conversationTokens((messages || []).filter((m) => m.role !== 'system')) > 1024);
}

function isOverflowError(err) {
  const s = String((err && err.message) || err || '');
  return /context window|context.?length|too many tokens|maximum context|prompt too (?:long|large)|prompt exceeds|ContextOverflow|reduce the prompt size/i.test(
    s
  );
}

function usage(messages, tools, ctxSize) {
  return snapshot(estimateTokens(messages, tools), ctxSize);
}

function snapshot(used, ctxSize) {
  const limit = ctxSize > 0 ? Number(ctxSize) : 8192;
  const n = Math.max(0, Math.round(Number(used) || 0));
  const pct = limit ? Math.min(100, Math.round((n / limit) * 1000) / 10) : 0;
  return {
    used: n,
    limit,
    pct,
    threshold: Math.round(THRESHOLD * 100),
    over: n > Math.floor(limit * THRESHOLD),
  };
}

function isDegenerate(summary) {
  const s = String(summary || '').trim();
  if (s.length < MIN_SUMMARY) return true;
  if (/conversation compacted/i.test(s)) return true;
  if (/^\s*\[earlier conversation compacted\]\s*$/i.test(s)) return true;
  return false;
}

function isRealUser(m) {
  if (!m || m.role !== 'user') return false;
  const c = String(m.content || '');
  if (c.indexOf('<system-reminder>') >= 0) return false;
  if (c.indexOf('[conversation summary]') >= 0) return false;
  if (c.indexOf('[memory]') === 0) return false;
  if (c.indexOf('[git status]') === 0) return false;
  return true;
}

// Keep native tool exchanges atomic: results must never outlive their calls.
function messageGroups(messages) {
  const groups = [];
  for (const message of messages) {
    const previous = groups[groups.length - 1];
    if (message.role === 'tool') {
      const calls = previous && previous[0].tool_calls;
      if (calls && calls.some((call) => call.id === message.tool_call_id)) previous.push(message);
      continue;
    }
    groups.push([message]);
  }
  return groups;
}

function rebuildHistory(messages, summary) {
  const list = Array.isArray(messages) ? messages : [];
  const systems = list.filter((m) => m.role === 'system');
  const lastUser = lastRealUserIndex(list);
  // Older turns belong in the summary, never after the latest request.
  const tail = lastUser >= 0 ? list.slice(lastUser) : list.filter((m) => m.role !== 'system');
  return systems.concat(
    { role: 'user', content: '[conversation summary]\n' + String(summary || '').trim() },
    messageGroups(tail.filter((m) => m.role !== 'system')).flat()
  );
}

function truncateMsg(m, maxChars) {
  if (!m) return m;
  const copy = Object.assign({}, m);
  const c = copy.content;
  if (typeof c === 'string' && c.length > maxChars) {
    copy.content = truncate.truncateWithMarker(c, maxChars);
  } else if (Array.isArray(c)) {
    copy.content = c.map((part) => {
      if (!part || typeof part !== 'object') return part;
      if (typeof part.text === 'string' && part.text.length > maxChars) {
        return Object.assign({}, part, { text: truncate.truncateWithMarker(part.text, maxChars) });
      }
      return part;
    });
  }
  return copy;
}

function lastRealUserIndex(list) {
  for (let i = list.length - 1; i >= 0; i--) {
    if (isRealUser(list[i])) return i;
  }
  return -1;
}

function overHistoryBudget(keep, budget) {
  return conversationTokens(keep) > budget;
}

function heuristicCompact(messages, opts) {
  opts = opts || {};
  const budget = opts.budgetTokens || 6000;
  const list = messages || [];
  const tokens = conversationTokens(list);
  if (tokens <= budget || (!opts.aggressive && nonSystemCount(list) < MIN_COMPACT_MESSAGES && conversationTokens(list.filter((m) => m.role !== 'system')) <= 1024))
    return list.slice();

  const systems = list.filter((m) => m.role === 'system');
  const lastUser = lastRealUserIndex(list);
  const request = lastUser >= 0 ? list[lastUser] : null;
  const older = list.slice(0, lastUser >= 0 ? lastUser : 0).filter((m) => m.role !== 'system');
  const tail = list.slice(lastUser >= 0 ? lastUser + 1 : 0).filter((m) => m.role !== 'system');
  let groups = messageGroups(tail);
  // Preserve an existing summary across repeated compactions. The fallback
  // carries real excerpts rather than replacing memory with a generic notice.
  const memory = transcript(older.concat(tail));
  const fixed = systems.concat(request ? [request] : []);
  const spareChars = Math.max(0, (budget - conversationTokens(fixed) - 12) * CHAR_PER_TOKEN);
  const summaryCap = Math.min(2400, Math.floor(spareChars * (groups.length ? 0.4 : 1)));
  let summary = memory && summaryCap >= 64
    ? { role: 'user', content: '[conversation summary]\n' + boundedExcerpt(memory, summaryCap) }
    : null;
  const assemble = () => systems.concat(summary ? [summary] : [], request ? [request] : [], groups.flat());
  let keep = assemble();
  // Shrink bulky results first; preserve call ids, arguments and ordering.
  for (const cap of [1600, 600, 180]) {
    if (!overHistoryBudget(keep, budget)) break;
    groups = groups.map((group) => group.map((m) => truncateMsg(m, cap)));
    keep = assemble();
  }
  while (overHistoryBudget(keep, budget) && groups.length) {
    groups.shift();
    keep = assemble();
  }
  if (overHistoryBudget(keep, budget) && summary) {
    summary = null;
    keep = assemble();
  }
  // The system instructions and latest request are never silently truncated.
  // If these alone exceed the window, the caller reports the overflow.
  return keep;
}

function boundedExcerpt(text, maxChars) {
  if (text.length <= maxChars) return text;
  const marker = '\n[earlier details omitted]\n';
  const remaining = Math.max(0, maxChars - marker.length);
  const head = Math.floor(remaining * 0.6);
  return text.slice(0, head) + marker + text.slice(-(remaining - head));
}

function compact(messages, opts) {
  return heuristicCompact(messages, opts);
}

function transcript(messages) {
  return (messages || [])
    .map((m) => {
      const role = m && m.role ? m.role : 'unknown';
      const name = m && m.name ? ' ' + m.name : '';
      const content = m && m.content != null ? m.content : '';
      const body = typeof content === 'string' ? content : JSON.stringify(content);
      if (body.startsWith('[conversation summary]')) return body.slice('[conversation summary]'.length).trim();
      return role + name + ':\n' + body + (m && m.tool_calls ? '\nTool calls: ' + JSON.stringify(m.tool_calls) : '');
    })
    .join('\n\n');
}

function isVoice(opts) {
  return !!(opts && opts.voice);
}

function autoContinue(messages, opts) {
  if (isVoice(opts)) return null;
  const list = messages || [];
  const last = list[list.length - 1];
  if (!last) return null;
  if (last.role === 'tool' || last.role === 'assistant') {
    return {
      role: 'user',
      content:
        '<system-reminder>\nContinue the work from the summary. Do not wait for a new user request.\n</system-reminder>',
    };
  }
  return null;
}

function compactReminder(opts) {
  if (isVoice(opts)) {
    return (
      '<system-reminder>\n' +
      'Context was compacted. Trust the summary and the last user request. Answer that request. Do not greet again.\n' +
      '</system-reminder>'
    );
  }
  return (
    '<system-reminder>\n' +
    'Context was compacted. Trust the summary and the last user request. Re-read files before further edits. Follow AGENTS.md if present.\n' +
    '</system-reminder>'
  );
}

async function compactWithLlm(messages, opts) {
  opts = opts || {};
  const fallback = () => heuristicCompact(messages, opts);
  if (!opts.aggressive && nonSystemCount(messages) < MIN_COMPACT_MESSAGES && conversationTokens((messages || []).filter((m) => m.role !== 'system')) <= 1024) {
    return (messages || []).slice();
  }
  const complete = opts.complete;
  if (typeof complete !== 'function') return fallback();
  const voice = isVoice(opts);
  const cap =
    opts.maxTranscriptChars ||
    Math.max(1500, Math.min(24000, Math.floor((opts.budgetTokens || 4000) * CHAR_PER_TOKEN * 0.45)));
  const body = truncate.truncateWithMarker(transcript((messages || []).filter((m) => m.role !== 'system')), cap);
  const prompt = voice ? VOICE_COMPACT_PROMPT : COMPACT_PROMPT;
  const sys = voice
    ? 'Reply with the four summary sections only. No tools. Do not greet.'
    : 'Reply with the five summary sections only. No tools.';
  try {
    const result = await complete({
      history: [
        { role: 'system', content: sys },
        { role: 'user', content: prompt + '\n\n---\n\n' + body },
      ],
      tools: [],
    });
    const summary = result && result.text;
    if (isDegenerate(summary)) return fallback();
    return heuristicCompact(rebuildHistory(messages, summary), Object.assign({}, opts, { aggressive: true }));
  } catch (_) {
    return fallback();
  }
}

module.exports = {
  CHAR_PER_TOKEN,
  THRESHOLD,
  MIN_SUMMARY,
  MIN_COMPACT_MESSAGES,
  COMPACT_PROMPT,
  VOICE_COMPACT_PROMPT,
  conversationTokens,
  toolTokens,
  estimateTokens,
  historyBudget,
  shouldCompact,
  nonSystemCount,
  isOverflowError,
  usage,
  snapshot,
  isDegenerate,
  rebuildHistory,
  heuristicCompact,
  compact,
  autoContinue,
  compactReminder,
  compactWithLlm,
};