import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';

function envFlag(value, fallback = false) {
  const raw = String(value ?? '').trim().toLowerCase();
  if (!raw) return fallback;
  return ['1', 'true', 'yes', 'on'].includes(raw);
}

export function dshExecutorEnabled(env = process.env) {
  return envFlag(env.MEMIND_TOOL_GATEWAY_DSH_ENABLED, false);
}

export function expandHome(value) {
  const text = String(value ?? '').trim();
  if (!text) return text;
  if (text.startsWith('~/')) return path.join(os.homedir(), text.slice(2));
  if (text === '~') return os.homedir();
  return text;
}

export function resolveDshCommand(env = process.env) {
  if (envFlag(env.MEMIND_DSH_FORCE_NPX, false)) {
    return {
      command: String(env.MEMIND_DSH_NPX_BIN ?? 'npx').trim() || 'npx',
      viaNpx: true,
    };
  }

  const fileCandidates = [
    env.MEMIND_DSH_BIN,
    env.DSH_BIN,
    '~/.local/bin/dsh',
  ].map((item) => expandHome(String(item ?? '').trim())).filter(Boolean);

  for (const candidate of fileCandidates) {
    if (fs.existsSync(candidate)) {
      return { command: candidate, viaNpx: false };
    }
  }

  const bare = String(env.DSH_BIN ?? 'dsh').trim();
  if (bare && !bare.includes('/')) {
    return { command: bare, viaNpx: false };
  }

  return {
    command: String(env.MEMIND_DSH_NPX_BIN ?? 'npx').trim() || 'npx',
    viaNpx: true,
  };
}

export function buildDshExecutorInstruction(instruction) {
  const base = String(instruction ?? '').trim();
  if (!base) return base;
  return [
    base,
    '',
    'Execution constraints:',
    '- Work only inside the provided workspace cwd',
    '- Do not run git commit/push or production deploy commands',
    '- Prefer minimal, reviewable diffs',
    '- Summarize changed files in the final answer',
  ].join('\n');
}

export function buildDshExecutorLaunchPlan({
  cwd,
  instruction,
  env = process.env,
  runtimeEnv = {},
} = {}) {
  if (!dshExecutorEnabled(env)) {
    return {
      ok: false,
      executor: 'dsh',
      message: 'DeepSeek Harness 执行器未启用（MEMIND_TOOL_GATEWAY_DSH_ENABLED）',
    };
  }

  const workspace = path.resolve(String(cwd ?? env.MEMIND_DSH_EXECUTOR_WORKSPACE ?? process.cwd()));
  const prompt = buildDshExecutorInstruction(instruction);
  if (!prompt) {
    return {
      ok: false,
      executor: 'dsh',
      message: 'DeepSeek Harness 执行器需要 instruction',
    };
  }

  const resolved = resolveDshCommand(env);
  const args = resolved.viaNpx
    ? ['-y', '@deepseek-ai/dsh', '--profile', 'headless', prompt]
    : ['--profile', 'headless', prompt];

  const launchEnv = {
    ...runtimeEnv,
  };
  if (!launchEnv.DEEPSEEK_API_KEY && env.DEEPSEEK_API_KEY) {
    launchEnv.DEEPSEEK_API_KEY = env.DEEPSEEK_API_KEY;
  }

  return {
    ok: true,
    executor: 'dsh',
    executorLabel: 'DeepSeek Harness',
    cwd: workspace,
    command: resolved.command,
    args,
    env: launchEnv,
    notes: [
      'DeepSeek Harness headless one-shot task via dsh --profile headless.',
      'Developer preview: keep disabled by default and route only whitelisted task types.',
    ],
  };
}