/**
 * UsageTracker — 工具使用统计核心
 *
 * agent_end 时从 session jsonl 增量扫描，只处理当前 turn 新增的行。
 * 用 cursor（byte offset）记录每个 session 处理到哪了，避免重复累加。
 */

import { readFileSync, writeFileSync, mkdirSync } from "node:fs";
import { dirname } from "node:path";
import { withFileLock } from "@pi-atelier/shared-utils/file-lock";
import { parseNewEntries } from "./session-parser";
import type {
	UsageStatsData,
} from "./types";

/** 空统计数据 */
function emptyData(): UsageStatsData {
	return { version: 2, cursors: {}, daily: {}, tools: {} };
}

/** 从 version=1 数据迁移 */
function migrateV1(raw: any): UsageStatsData {
	return {
		version: 2,
		cursors: {},
		daily: raw.daily ?? {},
		tools: raw.tools ?? {},
	};
}

/** 获取今天的 YYYY-MM-DD */
function today(): string {
	return new Date().toISOString().slice(0, 10);
}

/** 获取 N 天前的 YYYY-MM-DD */
function daysAgo(n: number): string {
	return new Date(Date.now() - n * 86400000).toISOString().slice(0, 10);
}

export class UsageTracker {
	private filePath: string;
	private data: UsageStatsData;

	constructor(filePath: string) {
		this.filePath = filePath;
		this.data = this.load();
	}

	/**
	 * 从 session jsonl 文件增量扫描 toolCall / toolResult，
	 * 只处理 cursor 之后的新行，更新 daily 统计。
	 */
	processSessionFile(sessionId: string, jsonlPath: string): void {
		const cursor = this.data.cursors[sessionId] ?? 0;
		const result = parseNewEntries(jsonlPath, cursor);
		if (!result) return;

		const day = today();
		for (const [toolName, delta] of Object.entries(result.stats)) {
			this.ensureDay(day);
			this.ensureToolDaily(day, toolName);
			this.data.daily[day][toolName].ai += delta.ai;
			this.data.daily[day][toolName].errors += delta.errors;
			if (delta.ai > 0) this.updateMeta(toolName);
		}

		this.data.cursors[sessionId] = result.newOffset;
	}

	/** 记录一次用户命令调用 */
	recordUserCall(toolName: string): void {
		const day = today();
		this.ensureDay(day);
		this.ensureToolDaily(day, toolName);
		this.data.daily[day][toolName].user += 1;
		this.updateMeta(toolName);
	}

	/** 查询已迁移到 query.ts 的 buildReport(tracker.getStats(), options) */

	/** 持久化到磁盘 */
	flush(): void {
		try {
			const dir = dirname(this.filePath);
			mkdirSync(dir, { recursive: true });
			withFileLock(this.filePath, () => {
				writeFileSync(this.filePath, JSON.stringify(this.data, null, 2), "utf-8");
			});
		} catch {
			// 持久化失败不应阻塞主流程
		}
	}

	/** 清理超过 maxDays 的 daily 数据和过期 cursor */
	cleanup(maxDays: number): void {
		const cutoff = daysAgo(maxDays);
		for (const day of Object.keys(this.data.daily)) {
			if (day < cutoff) {
				delete this.data.daily[day];
			}
		}
		// 清理超过 30 天的 cursor（session 已无参考价值）
		const cursorCutoff = Object.keys(this.data.cursors).length;
		if (cursorCutoff > 100) {
			// 只保留最近 50 个 session 的 cursor
			const keys = Object.keys(this.data.cursors);
			for (const key of keys.slice(0, keys.length - 50)) {
				delete this.data.cursors[key];
			}
		}
	}

	/** 获取内部数据引用（测试用） */
	getStats(): UsageStatsData {
		return this.data;
	}

	/** 设置内部数据（测试用） */
	_setData(data: UsageStatsData): void {
		this.data = data;
	}

	// ---- private ----

	private ensureDay(day: string): void {
		if (!this.data.daily[day]) {
			this.data.daily[day] = {};
		}
	}

	private ensureToolDaily(day: string, toolName: string): void {
		if (!this.data.daily[day][toolName]) {
			this.data.daily[day][toolName] = { ai: 0, user: 0, errors: 0 };
		}
	}

	private updateMeta(toolName: string): void {
		const now = new Date().toISOString();
		if (!this.data.tools[toolName]) {
			this.data.tools[toolName] = {
				firstUsed: now,
				lastUsed: now,
				totalAi: 0,
				totalUser: 0,
			};
		} else {
			this.data.tools[toolName].lastUsed = now;
		}
		// 从 daily 重新计算 total
		let totalAi = 0;
		let totalUser = 0;
		for (const dayData of Object.values(this.data.daily)) {
			const stats = dayData[toolName];
			if (stats) {
				totalAi += stats.ai;
				totalUser += stats.user;
			}
		}
		this.data.tools[toolName].totalAi = totalAi;
		this.data.tools[toolName].totalUser = totalUser;
	}

	private load(): UsageStatsData {
		try {
			const raw = readFileSync(this.filePath, "utf-8");
			const data = JSON.parse(raw);
			if (data) {
				if (data.version === 2 && data.cursors && data.daily && data.tools) {
					return data as UsageStatsData;
				}
				if (data.version === 1) {
					return migrateV1(data);
				}
			}
		} catch {
			// 文件不存在或损坏 → 空
		}
		return emptyData();
	}
}