import { createHash } from 'node:crypto';
import { mkdir, readFile, rename, writeFile } from 'node:fs/promises';
import { join } from 'node:path';

import { TaskStatus, isTerminalStatus } from './task-state.js';
import type { TaskState } from './task-state.js';

// ---------------------------------------------------------------------------
// Persisted profile state — cooldown / failure tracking for provider profiles
// Spec reference: §8.1
// ---------------------------------------------------------------------------

export interface PersistedProfileState {
  id: string;
  configDir: string;
  cooldownUntil?: number;
  failureCount: number;
  lastFailureReason?: string;
}

// ---------------------------------------------------------------------------
// Top-level persisted state envelope
// ---------------------------------------------------------------------------

export interface PersistedState {
  version: 1;
  tasks: TaskState[];
  profiles: PersistedProfileState[];
  lastSavedAt: string;
}

// ---------------------------------------------------------------------------
// persistenceDir — deterministic per-workspace directory
// ---------------------------------------------------------------------------

export function persistenceDir(root: string, cwd: string): string {
  const hash = createHash('md5').update(cwd).digest('hex');
  return join(root, hash);
}

// ---------------------------------------------------------------------------
// saveState — atomic write: write tmp → rename
// ---------------------------------------------------------------------------

export async function saveState(dir: string, state: PersistedState): Promise<void> {
  await mkdir(dir, { recursive: true });
  const target = join(dir, 'state.json');
  const tmp = join(dir, `state.json.tmp.${process.pid}`);
  await writeFile(tmp, JSON.stringify(state, null, 2), 'utf-8');
  await rename(tmp, target);
}

// ---------------------------------------------------------------------------
// loadState — read + parse, null on missing or corrupt
// ---------------------------------------------------------------------------

export async function loadState(dir: string): Promise<PersistedState | null> {
  try {
    const raw = await readFile(join(dir, 'state.json'), 'utf-8');
    return JSON.parse(raw) as PersistedState;
  } catch {
    return null;
  }
}

// ---------------------------------------------------------------------------
// applyRecovery — per-task recovery on server restart
// Spec reference: §9.2 steps 1–2
// ---------------------------------------------------------------------------

export function applyRecovery(task: TaskState, hasCrashRecovery: boolean): TaskState {
  // 1. Terminal states restore as-is
  if (isTerminalStatus(task.status)) {
    return task;
  }

  // 2. Adapters without crash recovery → UNKNOWN
  if (!hasCrashRecovery) {
    const now = new Date().toISOString();
    return {
      ...task,
      status: TaskStatus.UNKNOWN,
      error: `Server restarted; ${task.provider} sessions don't survive restarts`,
      completedAt: now,
      // Auto-expire recovered tasks after 60 seconds (vs 300s default)
      keepAlive: 60_000,
      output: [
        ...task.output,
        `[recovery] Task was ${task.status} when server restarted; marked UNKNOWN`,
      ],
      recovered: true,
    };
  }

  // 3. Has crash recovery (e.g. Codex) — return as-is; adapter handles externally
  return task;
}