/**
 * @author jackice
 * @date 2026-08-10
 *
 * 纯逻辑模块：不依赖 pi 扩展运行时 API（仅 type-only 导入），便于单元测试。
 * 行为对齐 omp 的 handoff 实现（packages/agent/src/compaction + session-handoff.ts）。
 */

import { mkdirSync, writeFileSync } from "node:fs";
import { join } from "node:path";
import type { AgentMessage } from "@earendil-works/pi-agent-core";
import type { SessionEntry } from "@earendil-works/pi-coding-agent";

const FOCUS_BLOCK_START = "{{#if additionalFocus}}";
const FOCUS_BLOCK_END = "{{/if}}";
const FOCUS_PLACEHOLDER = "{{additionalFocus}}";

/**
 * 渲染 handoff 模板：无 additionalFocus 时移除整个条件块，
 * 有则替换块内占位符。
 */
export function renderHandoffPrompt(template: string, additionalFocus?: string): string {
	const start = template.indexOf(FOCUS_BLOCK_START);
	if (start < 0) return template;
	const end = template.indexOf(FOCUS_BLOCK_END, start);
	if (end < 0) return template;
	const block = template.slice(start, end + FOCUS_BLOCK_END.length);
	if (!additionalFocus) return template.replace(block, "");
	const rendered = block
		.replace(FOCUS_BLOCK_START, "")
		.replace(FOCUS_BLOCK_END, "")
		.replace(FOCUS_PLACEHOLDER, additionalFocus);
	return template.replace(block, rendered);
}

/**
 * 把 handoff 文档包装成注入新会话的上下文消息。
 * 与 omp 的 createHandoffContext 保持一致。
 */
export function wrapHandoffContext(document: string): string {
	return `<handoff-context>\n${document}\n</handoff-context>\n\nThe above is a handoff document from a previous session. Use this context to continue the work seamlessly.`;
}

/**
 * 生成 handoff 文件名（与 omp 一致：ISO 时间戳去掉冒号与点）。
 */
export function createHandoffFileName(date = new Date()): string {
	const fileTimestamp = date.toISOString().replace(/[:.]/g, "-");
	return `handoff-${fileTimestamp}.md`;
}

/**
 * 解析会话的 artifacts 目录（与 omp 一致：会话文件去掉 .jsonl 后缀的同名目录）。
 * 内存会话（无 sessionFile）返回 null。
 */
export function resolveArtifactsDir(sessionFile: string | undefined): string | null {
	if (!sessionFile) return null;
	if (!sessionFile.endsWith(".jsonl")) return null;
	return sessionFile.slice(0, -".jsonl".length);
}

// ── 自动留存决策（压缩前自动存盘） ─────────────────────────────────────

/**
 * 判断自动留存是否启用：CLI flag 优先，其次配置文件，默认关闭。
 */
export function isAutoSaveEnabled(flagValue: boolean | undefined, configValue: boolean | undefined): boolean {
	return flagValue ?? configValue ?? false;
}

/**
 * overflow 恢复会重试被中断的回合，跳过以免干扰主流程。
 */
export function shouldSkipAutoSave(willRetry: boolean | undefined): boolean {
	return willRetry === true;
}

/**
 * 把 handoff 文档保存到会话 artifacts 目录，返回文件路径；无持久化会话时返回 null。
 * 与 omp 存盘位置一致：<session>.jsonl → 同名 <session>/ 目录。
 */
export function saveHandoffDocumentTo(sessionFile: string | undefined, document: string): string | null {
	const artifactsDir = resolveArtifactsDir(sessionFile);
	if (!artifactsDir) return null;
	mkdirSync(artifactsDir, { recursive: true });
	const filePath = join(artifactsDir, createHandoffFileName());
	writeFileSync(filePath, `${document}\n`);
	return filePath;
}

// ── 会话序列化（compaction 感知，来自 pi 官方 handoff 示例） ────────────

function entryToMessage(entry: SessionEntry): AgentMessage | undefined {
	if (entry.type === "message") {
		return entry.message;
	}
	if (entry.type === "compaction") {
		return {
			role: "compactionSummary",
			summary: entry.summary,
			tokensBefore: entry.tokensBefore,
			timestamp: new Date(entry.timestamp).getTime(),
		};
	}
	return undefined;
}

/**
 * 从分支提取交接用消息：无压缩时返回全部消息；
 * 有压缩时保留压缩摘要 + firstKeptEntryId 起保留的消息。
 */
export function getHandoffMessages(branch: SessionEntry[]): AgentMessage[] {
	let compactionIndex = -1;
	for (let i = branch.length - 1; i >= 0; i--) {
		if (branch[i].type === "compaction") {
			compactionIndex = i;
			break;
		}
	}
	if (compactionIndex < 0) {
		return branch.map(entryToMessage).filter((message) => message !== undefined);
	}

	const compaction = branch[compactionIndex];
	const firstKeptIndex =
		compaction.type === "compaction" ? branch.findIndex((entry) => entry.id === compaction.firstKeptEntryId) : -1;
	const compactedBranch = [
		compaction,
		...(firstKeptIndex >= 0 ? branch.slice(firstKeptIndex, compactionIndex) : []),
		...branch.slice(compactionIndex + 1),
	];
	return compactedBranch.map(entryToMessage).filter((message) => message !== undefined);
}