import { readdirSync, readFileSync } from "node:fs";
import { join } from "node:path";
import { getAgentDir } from "@earendil-works/pi-coding-agent";

/** 一条用量记录 = 一次带 usage 的模型响应 */
export interface UsageRecord {
	/** 条目时间戳（ms），决定日期归属：跨天会话会被拆到不同天 */
	ts: number;
	/** 项目 = 会话的 cwd 绝对路径 */
	project: string;
	provider: string;
	model: string;
	sessionId: string;
	sessionFile: string;
	/** 会话首条用户消息摘要，用于在会话层辨认「这是哪次对话」 */
	sessionTitle: string;
	input: number;
	output: number;
	cacheRead: number;
	cacheWrite: number;
}

/** 会话目录名反解出的路径不可靠：原路径中的 `-` 与被转义的 `/` 无法区分，仅在缺 session header 时兜底 */
function projectFromDirName(dirName: string): string {
	return `/${dirName.replace(/^--/, "").replace(/--$/, "")}`;
}

function num(v: unknown): number {
	return typeof v === "number" && Number.isFinite(v) ? v : 0;
}

/**
 * 解析单个会话文件的内容。纯函数，不碰文件系统，便于测试。
 * @param dirName 会话所在目录名，仅当文件缺少 session header 时用于兜底推断项目
 */
export function parseSessionText(text: string, dirName: string, sessionFile: string): UsageRecord[] {
	const records: UsageRecord[] = [];
	let project = "";
	let sessionId = "";
	let title = "";

	for (const line of text.split("\n")) {
		if (!line.trim()) continue;

		// 会话文件混有各扩展写入的自定义条目，坏行是已知边界而非异常，跳过
		let entry: any;
		try {
			entry = JSON.parse(line);
		} catch {
			continue;
		}

		if (entry?.type === "session") {
			if (typeof entry.cwd === "string") project = entry.cwd;
			if (typeof entry.id === "string") sessionId = entry.id;
			continue;
		}

		if (!title && entry?.message?.role === "user") {
			const blocks = entry.message.content;
			const text = Array.isArray(blocks)
				? blocks.find((b: any) => b?.type === "text")?.text
				: typeof blocks === "string"
					? blocks
					: "";
			title = String(text ?? "")
				.replace(/\s+/g, " ")
				.trim()
				.slice(0, 60);
		}

		const usage = entry?.message?.usage;
		if (!usage) continue;

		const ts = Date.parse(entry.timestamp ?? "");
		records.push({
			ts: Number.isNaN(ts) ? 0 : ts,
			project: project || projectFromDirName(dirName),
			provider: entry.message.provider ?? "unknown",
			// 路由型 provider 的实际模型与请求模型不同，以实际响应的为准
			model: entry.message.responseModel ?? entry.message.model ?? "unknown",
			sessionId,
			sessionFile,
			sessionTitle: "",
			input: num(usage.input),
			output: num(usage.output),
			cacheRead: num(usage.cacheRead),
			cacheWrite: num(usage.cacheWrite),
		});
	}

	// 回填：sessionId 与 title 可能在部分 usage 条目之后才被读到
	for (const r of records) {
		r.sessionId = sessionId;
		r.sessionTitle = title;
	}

	return records;
}

/** 扫描本机全部会话文件。目录读不到直接抛，由命令入口边界处理 */
export function scanUsage(sessionsDir = join(getAgentDir(), "sessions")): UsageRecord[] {
	const records: UsageRecord[] = [];

	for (const dir of readdirSync(sessionsDir, { withFileTypes: true })) {
		if (!dir.isDirectory()) continue;
		const dirPath = join(sessionsDir, dir.name);

		for (const file of readdirSync(dirPath)) {
			if (!file.endsWith(".jsonl")) continue;
			const filePath = join(dirPath, file);
			records.push(...parseSessionText(readFileSync(filePath, "utf8"), dir.name, filePath));
		}
	}

	return records;
}