import { loadInputs, logInputs } from './lib/inputs.js';
import { Git } from './lib/git.js';
import { GiteaClient } from './lib/gitea.js';
import { OpenCode } from './lib/opencode.js';
import { log, maskSecrets } from './lib/util.js';

async function main() {
  const inputs = loadInputs();
  logInputs(inputs);

  const remoteUrl = `${inputs.serverUrl}/${inputs.owner}/${inputs.repo}.git`;

  const git = new Git({ cwd: inputs.workspace, remoteUrl, token: inputs.token });
  const gitea = new GiteaClient({
    serverUrl: inputs.serverUrl,
    owner: inputs.owner,
    repo: inputs.repo,
    token: inputs.token,
  });
  const opencode = new OpenCode({ ...inputs.opencode, language: inputs.language });

  // 1. 準備 git 環境並抓取兩個分支
  log.step('準備 git 環境');
  git.configure();
  git.fetchBranches([inputs.sourceBranch, inputs.targetBranch]);

  // 2. 確認來源分支相對目標分支有變更
  const ahead = git.countAheadCommits(inputs.targetBranch, inputs.sourceBranch);
  if (ahead === 0) {
    log.warn(`來源分支 ${inputs.sourceBranch} 相對 ${inputs.targetBranch} 沒有新的 commit，無需建立 PR`);
    return;
  }
  log.info(`來源分支領先 ${ahead} 個 commit`);

  // 3. 蒐集 diff 內容
  log.step('蒐集 git diff');
  const commitMessages = git.getCommitMessages(inputs.targetBranch, inputs.sourceBranch);
  const diffStat = git.getDiffStat(inputs.targetBranch, inputs.sourceBranch);
  const fullDiff = git.getDiff(inputs.targetBranch, inputs.sourceBranch);
  const { diff, truncated } = truncateDiff(fullDiff, inputs.maxDiffChars);
  if (truncated) log.warn(`diff 過大，已截斷至 ${inputs.maxDiffChars} 字元`);

  // 4. 使用 opencode 產生標題與描述（失敗則 fallback）
  log.step('使用 opencode 產生 PR 標題與描述');
  let summary = await opencode.summarize({
    sourceBranch: inputs.sourceBranch,
    targetBranch: inputs.targetBranch,
    commitMessages,
    diffStat,
    diff,
  });
  if (!summary) {
    log.warn('改用 commit/stat 自動產生標題與描述');
    summary = fallbackSummary({
      source: inputs.sourceBranch,
      target: inputs.targetBranch,
      commitMessages,
      diffStat,
    });
  }
  log.success(`標題: ${summary.title}`);

  // 5. 偵測合併衝突
  log.step('偵測合併衝突');
  const { hasConflict, files } = git.detectConflict(inputs.targetBranch, inputs.sourceBranch);

  if (!hasConflict) {
    // 5a. 無衝突：直接建立 來源 → 目標 的 PR
    log.success('無衝突，建立來源分支 → 目標分支的 PR');
    const { pull, created } = await gitea.createPull({
      head: inputs.sourceBranch,
      base: inputs.targetBranch,
      title: summary.title,
      body: summary.description,
    });
    reportPull(pull, created);
    return;
  }

  // 5b. 有衝突：從目標分支建立解衝突分支，合併來源分支後 PR 回來源分支
  log.warn(`偵測到衝突檔案 (${files.length}): ${files.join(', ')}`);
  const resolveBranch = buildResolveBranchName(inputs.targetBranch, inputs.sourceBranch);

  log.step('建立解衝突分支並合併來源分支');
  const { files: conflictFiles } = git.createResolveBranch({
    target: inputs.targetBranch,
    source: inputs.sourceBranch,
    resolveBranch,
  });

  const body = buildResolveBody({
    source: inputs.sourceBranch,
    target: inputs.targetBranch,
    resolveBranch,
    files: conflictFiles.length ? conflictFiles : files,
    summary,
  });

  log.step('建立解衝突分支 → 來源分支的 PR');
  const { pull, created } = await gitea.createPull({
    head: resolveBranch,
    base: inputs.sourceBranch,
    title: `解衝突: 將 ${inputs.targetBranch} 合併回 ${inputs.sourceBranch}`,
    body,
  });
  reportPull(pull, created);
}

/** 把 diff 截斷至上限字元數。 */
function truncateDiff(diff, maxChars) {
  if (!diff || diff.length <= maxChars) return { diff: diff || '', truncated: false };
  return {
    diff: `${diff.slice(0, maxChars)}\n\n... (diff 已截斷，僅顯示前 ${maxChars} 字元) ...`,
    truncated: true,
  };
}

/** opencode 不可用時，用 commit 訊息與 stat 產生簡單摘要。 */
function fallbackSummary({ source, target, commitMessages, diffStat }) {
  const firstCommit = (commitMessages || '')
    .split('\n')
    .map((l) => l.replace(/^- /, '').trim())
    .find(Boolean);
  const title = firstCommit || `Merge ${source} into ${target}`;
  const description = [
    `## 變更摘要`,
    ``,
    `將 \`${source}\` 合併到 \`${target}\`。`,
    ``,
    `### Commits`,
    commitMessages || '(無)',
    ``,
    `### 變更檔案`,
    '```',
    diffStat || '(無)',
    '```',
  ].join('\n');
  return { title, description };
}

/** 解衝突分支名稱。 */
function buildResolveBranchName(target, source) {
  const runId = process.env.GITHUB_RUN_NUMBER || process.env.GITHUB_RUN_ID || '';
  const safe = (s) => s.replace(/[^a-zA-Z0-9._/-]/g, '-');
  const suffix = runId ? `-${runId}` : '';
  // 截斷主體長度，避免 target/source 過長使分支名稱超出 Git 限制
  const stem = `${safe(target)}-into-${safe(source)}`.slice(0, 180);
  return `resolve-conflict/${stem}${suffix}`;
}

/** 解衝突 PR 的描述。 */
function buildResolveBody({ source, target, resolveBranch, files, summary }) {
  return [
    `## ⚠️ 自動解衝突 PR`,
    ``,
    `來源分支 \`${source}\` 合併到目標分支 \`${target}\` 時偵測到衝突，`,
    `已自動從 \`${target}\` 建立解衝突分支 \`${resolveBranch}\` 並合併 \`${source}\`。`,
    ``,
    `**此 PR 會將 \`${resolveBranch}\` 合併回 \`${source}\`，請在合併前手動解決下列檔案的衝突標記（\`<<<<<<<\`、\`=======\`、\`>>>>>>>\`）：**`,
    ``,
    ...files.map((f) => `- \`${f}\``),
    ``,
    `### ✅ 合併前人工檢查清單`,
    ``,
    `- [ ] 已移除所有檔案中的衝突標記（\`<<<<<<<\`、\`=======\`、\`>>>>>>>\`）`,
    `- [ ] 已確認合併結果可正常建置／執行`,
    `- [ ] 已保留雙方必要變更，無誤刪`,
    ``,
    `解決並合併此 PR 後，\`${source}\` 即可順利合併進 \`${target}\`。`,
    ``,
    `---`,
    ``,
    `### AI 變更摘要`,
    ``,
    summary.description || '(無)',
  ].join('\n');
}

/** 印出 PR 結果。 */
function reportPull(pull, created) {
  const url = pull?.html_url || pull?.url || '';
  const number = pull?.number || '';
  if (created) {
    log.success(`已建立 PR #${number}: ${url}`);
  } else {
    log.info(`PR 已存在 #${number}: ${url}`);
  }
}

main().catch((err) => {
  const detail = err?.stack || err?.message || String(err);
  // 錯誤訊息／stack 可能夾帶 token，輸出到 CI 日誌前先遮蔽
  log.error(maskSecrets(detail, [process.env.GITEA_TOKEN]));
  process.exit(1);
});