import { appendFile, mkdir, readFile, readdir, rename, rm, writeFile } from "node:fs/promises";
import type { Dirent } from "node:fs";
import { join } from "node:path";
import type { BaseEvent } from "../types.js";

function dayPath(eventsDir: string, date: Date): string { return join(eventsDir, String(date.getUTCFullYear()), String(date.getUTCMonth() + 1).padStart(2, "0"), String(date.getUTCDate()).padStart(2, "0")); }

export class EventStore {
  constructor(private readonly eventsDir: string) {}
  async append(value: BaseEvent): Promise<void> {
    const date = new Date(value.timestamp);
    const directory = dayPath(this.eventsDir, date);
    await mkdir(directory, { recursive: true, mode: 0o700 });
    await appendFile(join(directory, `${value.runId}.jsonl`), `${JSON.stringify(value)}\n`, { encoding: "utf8", mode: 0o600 });
  }
  async all(): Promise<BaseEvent[]> {
    const files: string[] = [];
    const walk = async (directory: string): Promise<void> => {
      let entries: Dirent<string>[];
      try { entries = await readdir(directory, { withFileTypes: true }); } catch (error) { if ((error as NodeJS.ErrnoException).code === "ENOENT") return; throw error; }
      await Promise.all(entries.map(async (entry) => entry.isDirectory() ? walk(join(directory, entry.name)) : entry.name.endsWith(".jsonl") ? files.push(join(directory, entry.name)) : undefined));
    };
    await walk(this.eventsDir);
    const events = (await Promise.all(files.sort().map(async (file) => (await readFile(file, "utf8")).split("\n").filter(Boolean).map((line) => JSON.parse(line) as BaseEvent)))).flat();
    return events.sort((a, b) => a.timestamp.localeCompare(b.timestamp));
  }

  async prune(retentionDays: number, now = Date.now()): Promise<number> {
    const cutoff = now - retentionDays * 86_400_000;
    const files: string[] = [];
    const walk = async (directory: string): Promise<void> => {
      let entries: Dirent<string>[];
      try { entries = await readdir(directory, { withFileTypes: true }); } catch (error) { if ((error as NodeJS.ErrnoException).code === "ENOENT") return; throw error; }
      await Promise.all(entries.map(async (entry) => entry.isDirectory() ? walk(join(directory, entry.name)) : entry.name.endsWith(".jsonl") ? files.push(join(directory, entry.name)) : undefined));
    };
    await walk(this.eventsDir);
    let deleted = 0;
    for (const file of files) {
      const lines = (await readFile(file, "utf8")).split("\n").filter(Boolean);
      const kept = lines.filter((line) => {
        try { return Date.parse((JSON.parse(line) as BaseEvent).timestamp) >= cutoff; }
        catch { return true; }
      });
      if (kept.length === lines.length) continue;
      if (!kept.length) await rm(file);
      else {
        const temporary = `${file}.${Date.now()}.tmp`;
        await writeFile(temporary, `${kept.join("\n")}\n`, { encoding: "utf8", mode: 0o600 });
        await rename(temporary, file);
      }
      deleted += lines.length - kept.length;
    }
    return deleted;
  }
}