/**
 * 用量记录存储与查询。
 * 零 pi 依赖的纯业务模块。
 *
 * 把每次响应带出的 usage 追加到本地日志（NDJSON），可按时间/会话聚合汇总。
 */

import { existsSync, readFileSync, writeFileSync, mkdirSync, appendFileSync } from "node:fs";
import { dirname, join } from "node:path";
import { homedir } from "node:os";
import type { UsageRecord, UsageStats } from "./pricing.ts";
import { summarizeStats } from "./pricing.ts";

export interface StoreIO {
  exists(path: string): boolean;
  append(path: string, line: string): void;
  readLines(path: string): string[];
  mkdir(dir: string): void;
  dirname(path: string): string;
}

const nodeStore: StoreIO = {
  exists: existsSync,
  append: (p, l) => appendFileSync(p, l + "\n"),
  readLines: (p) => (existsSync(p) ? readFileSync(p, "utf-8").split("\n").filter(Boolean) : []),
  mkdir: (d) => mkdirSync(d, { recursive: true }),
  dirname,
};

const ENV_STORE_PATH = "PI_OPENCODE_USAGE_STORE";

export function defaultStorePath(): string {
  return join(homedir(), ".pi", "agent", "opencode-usage.jsonl");
}

export function getStorePath(env = process.env): string {
  return env[ENV_STORE_PATH] ?? defaultStorePath();
}

export class UsageStore {
  private io: StoreIO;
  private path: string;

  constructor(path = getStorePath(), io: StoreIO = nodeStore) {
    this.path = path;
    this.io = io;
  }

  get pathString(): string {
    return this.path;
  }

  append(record: UsageRecord): void {
    this.io.mkdir(this.io.dirname(this.path));
    this.io.append(this.path, JSON.stringify(record));
  }

  readAll(): UsageRecord[] {
    const out: UsageRecord[] = [];
    for (const line of this.io.readLines(this.path)) {
      try {
        out.push(JSON.parse(line) as UsageRecord);
      } catch {
        /* skip malformed */
      }
    }
    return out;
  }

  /** 按时间范围（epoch ms）过滤汇总。since 未给则从头；until 未给则到现在。 */
  summarize(opts: { since?: number; until?: number; sessionId?: string } = {}): UsageStats {
    const now = Date.now();
    const until = opts.until ?? now;
    const since = opts.since ?? 0;
    const recs = this.readAll().filter((r) => r.ts >= since && r.ts <= until && (opts.sessionId === undefined || r.sessionId === opts.sessionId));
    return summarizeStats(recs);
  }
}

export function formatStats(stats: UsageStats, label = ""): string {
  const head = label ? `${label}: ` : "";
  const cost = stats.cost;
  const lines = [
    `${head}${stats.records} requests`,
    `  tokens: in=${stats.prompt} out=${stats.completion} cached=${stats.cached} cacheWrite=${stats.cacheWrite}`,
    `  est. cost: $${cost.total.toFixed(6)} (in $${cost.input} / out $${cost.output} / cacheRead $${cost.cacheRead} / cacheWrite $${cost.cacheWrite})`,
    `  cache hit rate: ${(stats.cacheHitRate * 100).toFixed(1)}%`,
  ];
  return lines.join("\n");
}