import { createHash, randomUUID } from 'node:crypto';
import { readFile, realpath } from 'node:fs/promises';
import path from 'node:path';
import { callSelectedNvim } from './nvim_ui_bridge.mjs';

const POLL_MS = 100;
const state = {
  wantedGeneration: 0,
  active: null,
  activeControl: null,
  last: null,
  queue: Promise.resolve()
};

function delay(milliseconds) {
  return new Promise(resolve => setTimeout(resolve, milliseconds));
}

function errorText(error) {
  return error instanceof Error ? error.message : String(error);
}

async function readJson(file) {
  return JSON.parse(await readFile(file, 'utf8'));
}

function runtimeRoot() {
  return process.env.XDG_RUNTIME_DIR ?? '/run/user/1000';
}

function selectionRoot() {
  return process.env.MCP_CONTAINER_SELECTION_ROOT
    ?? path.join(runtimeRoot(), 'stem/mcp-selected');
}

async function selectedBinding() {
  const selectedDirectory = await realpath(path.join(selectionRoot(), 'current'));
  const [metadata, socketPath] = await Promise.all([
    readJson(path.join(selectedDirectory, 'selection.json')),
    realpath(path.join(selectedDirectory, 'n.sock'))
  ]);
  return {
    metadata,
    socketPath,
    epoch: `${metadata.container_id ?? 'unknown'}:${socketPath}`
  };
}

async function assertBindingCurrent(expected) {
  const current = await selectedBinding();
  if (current.epoch !== expected.epoch) {
    throw new Error('Cel MCP zmienił się podczas replay; wynik starego kontenera został odrzucony.');
  }
}

export function assertExpectedBinding(binding, expected) {
  // Browser activation follows the currently selected teaching session and
  // remains backward compatible. CLI/orchestrator callers pin all fields.
  if (expected == null) return;
  if (typeof expected !== 'object') throw new Error('expected_binding musi być obiektem.');
  for (const field of ['container_id', 'instance', 'profile', 'target']) {
    const wanted = typeof expected[field] === 'string' ? expected[field] : '';
    const actual = typeof binding.metadata[field] === 'string' ? binding.metadata[field] : '';
    if (!wanted || wanted !== actual) {
      throw new Error(`Cel MCP zmienił się przed replay (${field}: ${actual || '?'} != ${wanted || '?'}).`);
    }
  }
}

export function assertExpectedIdentity(actual, expected) {
  // Browser-only calls may omit the pin. Orchestrators send all fields so a
  // card hot reload cannot silently replay a recipe from another revision.
  if (expected == null) return;
  if (typeof expected !== 'object') throw new Error('expected_identity musi być obiektem.');
  for (const field of ['id', 'uuid', 'version', 'source_sha256']) {
    const wanted = typeof expected[field] === 'string' ? expected[field] : '';
    const observed = typeof actual[field] === 'string' ? actual[field] : '';
    if (!wanted || wanted !== observed) {
      throw new Error(`Karta zmieniła się przed replay (${field}: ${observed || '?'} != ${wanted || '?'}).`);
    }
  }
}

async function readCardSnapshot(cardFile) {
  const source = await readFile(cardFile);
  const document = JSON.parse(source.toString('utf8'));
  const card = document.card ?? {};
  return {
    document,
    identity: {
      id: String(card.id ?? ''),
      uuid: String(card.uuid ?? ''),
      version: String(card.version ?? ''),
      source_sha256: createHash('sha256').update(source).digest('hex')
    }
  };
}

async function sha256(file) {
  const hash = createHash('sha256');
  hash.update(await readFile(file));
  return hash.digest('hex');
}

async function gitBlobSha1(file) {
  const content = await readFile(file);
  const hash = createHash('sha1');
  hash.update(`blob ${content.length}\0`);
  hash.update(content);
  return hash.digest('hex');
}

function hostPath(repositoryRoot, containerPath) {
  if (!path.isAbsolute(containerPath)) {
    const resolved = path.resolve(repositoryRoot, containerPath);
    if (resolved === repositoryRoot || resolved.startsWith(`${repositoryRoot}${path.sep}`)) {
      return resolved;
    }
  }
  if (containerPath === '/workspace') return repositoryRoot;
  if (containerPath.startsWith('/workspace/')) {
    return path.join(repositoryRoot, containerPath.slice('/workspace/'.length));
  }
  throw new Error(`Ścieżka spoza /workspace nie jest dozwolona: ${containerPath}`);
}

async function nvimLua(source, args = [], binding = null) {
  return callSelectedNvim(
    'nvim_exec_lua',
    [source, args],
    binding ? { socketPath: binding.socketPath } : {}
  );
}

async function callPinnedNvim(binding, method, parameters = []) {
  return callSelectedNvim(method, parameters, { socketPath: binding.socketPath });
}

async function sendGdb(command, binding) {
  const available = await callPinnedNvim(binding, 'nvim_call_function', [
    'exists',
    ['*TermDebugSendCommand']
  ]);
  if (available !== 1) {
    throw new Error('Termdebug nie udostępnia TermDebugSendCommand');
  }
  return callPinnedNvim(binding, 'nvim_call_function', [
    'TermDebugSendCommand',
    [command]
  ]);
}

async function interruptGdb(binding) {
  return nvimLua(`
    for _, buffer in ipairs(vim.api.nvim_list_bufs()) do
      local name = vim.api.nvim_buf_get_name(buffer)
      if vim.bo[buffer].buftype == 'terminal' and name:find('gdb%-multiarch') then
        local channel = vim.bo[buffer].channel
        if channel and channel > 0 then
          vim.api.nvim_chan_send(channel, string.char(3))
          return true
        end
      end
    end
    return false
  `, [], binding);
}

async function gdbTerminalRunning(binding) {
  return nvimLua(`
    for _, buffer in ipairs(vim.api.nvim_list_bufs()) do
      local name = vim.api.nvim_buf_get_name(buffer)
      if vim.bo[buffer].buftype == 'terminal' and name:find('gdb%-multiarch') then
        local channel = vim.bo[buffer].channel
        if channel and channel > 0 and vim.fn.jobwait({ channel }, 0)[1] == -1 then
          return true
        end
      end
    end
    return false
  `, [], binding);
}

async function cleanupDeadGdbBuffers(binding) {
  return nvimLua(`
    local dead = {}
    for _, buffer in ipairs(vim.api.nvim_list_bufs()) do
      local name = vim.api.nvim_buf_get_name(buffer)
      if vim.bo[buffer].buftype == 'terminal' and name:find('gdb%-multiarch') then
        local channel = vim.bo[buffer].channel
        if not channel or channel <= 0 or vim.fn.jobwait({ channel }, 0)[1] ~= -1 then
          table.insert(dead, buffer)
        end
      end
    end
    for _, buffer in ipairs(dead) do
      for _, window in ipairs(vim.fn.win_findbuf(buffer)) do
        if vim.api.nvim_win_is_valid(window) and #vim.api.nvim_list_wins() > 1 then
          pcall(vim.api.nvim_win_close, window, true)
        end
      end
      if vim.api.nvim_buf_is_valid(buffer) then
        pcall(vim.api.nvim_buf_delete, buffer, { force = true })
      end
    end
    return #dead
  `, [], binding);
}

async function ensureTermdebug(binding) {
  const probe = gdbTerminalRunning(binding);
  let running;
  try {
    running = await Promise.race([
      probe,
      delay(500).then(() => { throw new Error('timeout'); })
    ]);
  } catch {
    // Termdebug cleanup sometimes leaves a hit-enter prompt which blocks an
    // RPC expression while Neovim still accepts input events.
    await callPinnedNvim(binding, 'nvim_input', ['<CR>']).catch(() => undefined);
    running = await probe;
  }
  if (running) {
    await cleanupDeadGdbBuffers(binding);
    await callPinnedNvim(binding, 'nvim_command', ['silent! StudentLayoutFit']).catch(() => undefined);
    return;
  }
  // A failed Termdebug job can leave Neovim at a hit-enter prompt. Feeding
  // Enter only in the dead-GDB branch clears it before the recovery command.
  await callPinnedNvim(binding, 'nvim_input', ['<CR>']).catch(() => undefined);
  await cleanupDeadGdbBuffers(binding);
  await callPinnedNvim(binding, 'nvim_command', ['silent! StudentTermdebug']);
  const deadline = Date.now() + 8000;
  while (Date.now() < deadline) {
    if (await gdbTerminalRunning(binding)) {
      // TermdebugStartPost queues target/directory/dashboard setup.
      await delay(1200);
      await cleanupDeadGdbBuffers(binding);
      await callPinnedNvim(binding, 'nvim_command', ['silent! StudentLayoutFit']).catch(() => undefined);
      return;
    }
    await delay(100);
  }
  throw new Error('Nie udało się automatycznie odtworzyć procesu GDB w Termdebug.');
}

async function assertEditorReady(repositoryRoot, artifact, binding) {
  const modified = await nvimLua(`
    local result = {}
    for _, buffer in ipairs(vim.api.nvim_list_bufs()) do
      if vim.api.nvim_buf_is_loaded(buffer) and vim.bo[buffer].modified then
        table.insert(result, vim.api.nvim_buf_get_name(buffer))
      end
    end
    return result
  `, [], binding);
  if (Array.isArray(modified) && modified.some(name => name.endsWith(artifact.source))) {
    throw new Error('Bufor Task04 ma niezapisane zmiany; zapis lub przebudowa są wymagane przed replay.');
  }
  const elf = await nvimLua('return vim.env.ELF_FILE or ""', [], binding);
  if (typeof elf !== 'string' || !elf) throw new Error('Neovim nie ma ELF_FILE bieżącej sesji.');
  const elfOnHost = hostPath(repositoryRoot, elf);
  if (artifact.source_git_blob) {
    const sourceOnHost = hostPath(repositoryRoot, artifact.source);
    const actualSourceBlob = await gitBlobSha1(sourceOnHost);
    if (actualSourceBlob !== artifact.source_git_blob) {
      throw new Error('Źródło Task04 różni się od wersji użytej do pomiaru karty; przebuduj kartę i snapshoty.');
    }
  }
  if (artifact.hazard3_image_sha256 && binding.metadata.profile === 'hazard3-sim') {
    const imageOnHost = hostPath(repositoryRoot, artifact.hazard3_image);
    const actual = await sha256(imageOnHost);
    if (actual !== artifact.hazard3_image_sha256) {
      throw new Error('Obraz wykonywalny Hazard3 różni się od obrazu użytego do pomiaru karty; zregeneruj snapshoty.');
    }
  }
  return { elf, elfOnHost };
}

async function waitForResult(resultFile, operationId, timeoutMs, binding) {
  const deadline = Date.now() + timeoutMs;
  let latest = null;
  while (Date.now() < deadline) {
    try {
      const current = await readJson(resultFile);
      if (current.operation_id === operationId) {
        latest = current;
        state.active = current;
        if (current.status === 'ready' || current.status === 'failed') return current;
      }
    } catch {
      // GDB writes atomically; absence before the first phase is expected.
    }
    await delay(POLL_MS);
  }
  await interruptGdb(binding).catch(() => undefined);
  await delay(200);
  throw new Error(`Timeout replay; ostatni stan: ${latest?.status ?? 'brak odpowiedzi GDB'}`);
}

async function runActivation({
  repositoryRoot,
  cardFile,
  snapshotRef,
  generation,
  expectedBinding,
  expectedIdentity
}) {
  if (generation !== state.wantedGeneration) {
    return { status: 'cancelled', generation, snapshot_ref: snapshotRef, message: 'Zastąpione nowszym krokiem.' };
  }
  const [cardSnapshot, binding] = await Promise.all([readCardSnapshot(cardFile), selectedBinding()]);
  const card = cardSnapshot.document;
  assertExpectedIdentity(cardSnapshot.identity, expectedIdentity);
  assertExpectedBinding(binding, expectedBinding);
  const selection = binding.metadata;
  const registry = card.debug_checkpoints;
  const recipe = registry?.items?.[snapshotRef];
  if (!recipe) throw new Error(`Brak recepty checkpointu: ${snapshotRef}`);
  if (!registry.targets?.[selection.profile]) {
    throw new Error(`Karta nie ma adaptera replay dla profilu ${selection.profile ?? '?'}.`);
  }
  await assertBindingCurrent(binding);
  await ensureTermdebug(binding);
  await assertEditorReady(repositoryRoot, registry.artifact, binding);
  const operationId = randomUUID();
  const payload = {
    operation_id: operationId,
    generation,
    snapshot_ref: snapshotRef,
    profile: selection.profile,
    semantics: registry.semantics,
    stop: recipe.stop,
    verify: recipe.verify ?? { expressions: [] }
  };
  state.active = {
    status: 'replaying',
    phase: 'dispatch',
    operation_id: operationId,
    generation,
    snapshot_ref: snapshotRef,
    profile: selection.profile
  };
  state.activeControl = { generation, binding };
  await sendGdb('source /workspace/tools/gdb/stem_checkpoint.py', binding);
  const token = Buffer.from(JSON.stringify(payload), 'utf8').toString('base64url');
  await sendGdb(`stem-checkpoint-activate ${token}`, binding);
  const resultFile = path.join(
    repositoryRoot,
    '.stem/instances',
    selection.instance,
    'gdb-sync.json.checkpoint.json'
  );
  const result = await waitForResult(
    resultFile,
    operationId,
    selection.profile === 'rp2350' ? 45000 : 20000,
    binding
  );
  if (result.status !== 'ready') {
    throw new Error(result.message ?? `Replay ${snapshotRef} nie osiągnął stanu ready.`);
  }
  await assertBindingCurrent(binding);
  state.last = result;
  state.active = null;
  state.activeControl = null;
  await callPinnedNvim(binding, 'nvim_command', ['silent! StudentViewReset']).catch(() => undefined);
  await callPinnedNvim(binding, 'nvim_command', ['redraw!']).catch(() => undefined);
  return result;
}

export function checkpointStatus() {
  return { active: state.active, last: state.last, wanted_generation: state.wantedGeneration };
}

export function activateCheckpoint({
  repositoryRoot,
  cardFile,
  snapshotRef,
  generation,
  expectedBinding,
  expectedIdentity
}) {
  if (typeof snapshotRef !== 'string' || !/^task04\.[a-z0-9.-]+$/.test(snapshotRef)) {
    return Promise.reject(new Error('Niepoprawny snapshot_ref.'));
  }
  if (generation != null && (!Number.isSafeInteger(generation) || generation <= 0)) {
    return Promise.reject(new Error('generation musi być dodatnią, bezpieczną liczbą całkowitą.'));
  }
  const nextGeneration = Number.isSafeInteger(generation) && generation > 0
    ? generation
    : state.wantedGeneration + 1;
  state.wantedGeneration = Math.max(state.wantedGeneration + 1, nextGeneration);
  const activeControl = state.activeControl;
  if (
    activeControl
    && activeControl.generation < state.wantedGeneration
    && state.active?.phase === 'run-to-stop'
  ) {
    void interruptGdb(activeControl.binding).catch(() => undefined);
  }
  const request = {
    repositoryRoot,
    cardFile,
    snapshotRef,
    generation: state.wantedGeneration,
    expectedBinding,
    expectedIdentity
  };
  const operation = state.queue.then(() => runActivation(request));
  state.queue = operation.catch(error => {
    state.last = {
      status: 'failed',
      snapshot_ref: snapshotRef,
      generation: request.generation,
      message: errorText(error)
    };
    state.active = null;
    if (state.activeControl?.generation === request.generation) state.activeControl = null;
  });
  return operation;
}