import { writeFileSync, mkdtempSync } from 'node:fs';
import { tmpdir } from 'node:os';
import { join } from 'node:path';
import { run, log, maskSecrets } from './util.js';

/**
 * 透過 opencode CLI 分析 git diff，產生 PR 標題與描述。
 */
export class OpenCode {
  /**
   * @param {object} opts
   * @param {string} opts.baseUrl
   * @param {string} opts.model
   * @param {string} opts.provider
   * @param {string} [opts.language]
   */
  constructor({ baseUrl, model, provider, language = 'Traditional Chinese (繁體中文)' }) {
    this.baseUrl = baseUrl;
    this.model = model;
    this.provider = provider;
    this.language = language;
  }

  /** 是否有足夠設定可以呼叫 opencode。 */
  isConfigured() {
    return Boolean(this.baseUrl && this.model && this.provider);
  }

  /**
   * 在暫存目錄寫出 opencode.json，將自訂 provider 設為 OpenAI 相容端點。
   *
   * @returns {string} config 檔路徑
   */
  _writeConfig() {
    const dir = mkdtempSync(join(tmpdir(), 'opencode-'));
    const options = { baseURL: this.baseUrl };

    const config = {
      $schema: 'https://opencode.ai/config.json',
      provider: {
        [this.provider]: {
          npm: '@ai-sdk/openai-compatible',
          name: this.provider,
          options,
          models: {
            [this.model]: { name: this.model },
          },
        },
      },
    };

    const path = join(dir, 'opencode.json');
    writeFileSync(path, JSON.stringify(config, null, 2));
    return path;
  }

  /**
   * 呼叫 opencode 產生標題與描述。
   *
   * @param {object} ctx
   * @param {string} ctx.sourceBranch
   * @param {string} ctx.targetBranch
   * @param {string} ctx.commitMessages
   * @param {string} ctx.diffStat
   * @param {string} ctx.diff 已截斷的 diff
   * @returns {Promise<{ title: string, description: string } | null>}
   */
  async summarize(ctx) {
    if (!this.isConfigured()) {
      log.warn('opencode 參數不完整（需要 base_url / model / provider），略過 AI 摘要');
      return null;
    }

    const configPath = this._writeConfig();
    const prompt = buildPrompt({ ...ctx, language: this.language });

    log.info(`呼叫 opencode（${this.provider}/${this.model}）分析 diff...`);
    const result = run(
      'opencode',
      ['run', '--model', `${this.provider}/${this.model}`, prompt],
      {
        cwd: tmpdir(),
        env: {
          ...process.env,
          OPENCODE_CONFIG: configPath,
          // 確保 opencode 有可寫的 HOME / 設定目錄
          HOME: process.env.HOME || '/root',
        },
        timeout: 5 * 60 * 1000,
      },
    );

    if (result.status !== 0) {
      log.warn(`opencode 執行失敗 (${result.status})：${maskSecrets(result.stderr).slice(0, 500)}`);
      return null;
    }

    const parsed = extractResult(result.stdout);
    if (!parsed) {
      log.warn('無法從 opencode 輸出解析出標題/描述');
      return null;
    }
    return parsed;
  }
}

function buildPrompt({ sourceBranch, targetBranch, commitMessages, diffStat, diff, language }) {
  return [
    `You are an assistant that writes high-quality Pull Request titles and descriptions.`,
    `Analyze the following git changes for a PR merging branch "${sourceBranch}" into "${targetBranch}".`,
    ``,
    `Write the title and description in ${language}.`,
    `The title should be a concise one-line summary (ideally following Conventional Commits style, e.g. "feat: ...").`,
    `The description should be Markdown and include: a short summary, a bullet list of key changes, and any notable impact or risk.`,
    ``,
    `Respond with ONLY a single JSON object, no code fences, no extra text:`,
    `{"title": "...", "description": "..."}`,
    ``,
    `=== Commits ===`,
    commitMessages || '(no commit messages)',
    ``,
    `=== Changed files (stat) ===`,
    diffStat || '(no stat)',
    ``,
    `=== Diff ===`,
    diff || '(no diff)',
  ].join('\n');
}

/** 去除 ANSI 控制碼。 */
function stripAnsi(text) {
  // eslint-disable-next-line no-control-regex
  return text.replace(/\x1b\[[0-9;]*[a-zA-Z]/g, '');
}

/**
 * 從 opencode 輸出中擷取含 title 的 JSON 物件並解析。
 *
 * @param {string} stdout
 * @returns {{ title: string, description: string } | null}
 */
export function extractResult(stdout) {
  const text = stripAnsi(stdout || '');

  // 掃描所有平衡的 {...} 區塊，挑出第一個能成功解析且含 title 的物件
  for (const candidate of findJsonObjects(text)) {
    // LLM 常在字串值內輸出未跳脫的換行，先嘗試原始解析，失敗再嘗試修正
    for (const variant of [candidate, escapeControlCharsInStrings(candidate)]) {
      try {
        const obj = JSON.parse(variant);
        if (obj && typeof obj === 'object' && obj.title) {
          return {
            title: String(obj.title).trim(),
            description: String(obj.description || '').trim(),
          };
        }
      } catch {
        // 試下一個變體 / 候選
      }
    }
  }
  return null;
}

/** 將字串值內未跳脫的控制字元（換行、tab 等）跳脫，修正 LLM 常見的無效 JSON。 */
function escapeControlCharsInStrings(text) {
  let out = '';
  let inString = false;
  let escape = false;
  for (let i = 0; i < text.length; i++) {
    const ch = text[i];
    if (inString) {
      if (escape) {
        out += ch;
        escape = false;
        continue;
      }
      if (ch === '\\') {
        out += ch;
        escape = true;
        continue;
      }
      if (ch === '"') {
        out += ch;
        inString = false;
        continue;
      }
      if (ch === '\n') { out += '\\n'; continue; }
      if (ch === '\r') { out += '\\r'; continue; }
      if (ch === '\t') { out += '\\t'; continue; }
      out += ch;
    } else {
      out += ch;
      if (ch === '"') inString = true;
    }
  }
  return out;
}

/** 以括號平衡方式找出文字中所有最外層的 {...} 區塊。 */
function findJsonObjects(text) {
  const objects = [];
  let depth = 0;
  let start = -1;
  let inString = false;
  let escape = false;

  for (let i = 0; i < text.length; i++) {
    const ch = text[i];
    if (inString) {
      if (escape) escape = false;
      else if (ch === '\\') escape = true;
      else if (ch === '"') inString = false;
      continue;
    }
    if (ch === '"') {
      inString = true;
    } else if (ch === '{') {
      if (depth === 0) start = i;
      depth++;
    } else if (ch === '}') {
      depth--;
      if (depth === 0 && start !== -1) {
        objects.push(text.slice(start, i + 1));
        start = -1;
      }
    }
  }
  return objects;
}