import { existsSync, mkdirSync, readFileSync, renameSync, writeFileSync } from "node:fs";
import { dirname, join } from "node:path";
import type { HelpState, LegacyHelpState, PersistResult } from "../types.ts";
import { emptyState, migrateState } from "./migrate.ts";

export interface StatePaths {
  stateDir: string;
  stateFile: string;
  legacyStateFile: string;
}

export function createStatePaths(agentDir: string): StatePaths {
  const stateDir = join(agentDir, "state", "pi-dynamic-help");
  return {
    stateDir,
    stateFile: join(stateDir, "state.json"),
    legacyStateFile: join(agentDir, "state", "dynamic-help.json"),
  };
}

function parseJsonFile<T>(path: string): { ok: true; value: T } | { ok: false; error: unknown } | { ok: undefined } {
  if (!existsSync(path)) return { ok: undefined };
  try {
    return { ok: true, value: JSON.parse(readFileSync(path, "utf-8")) as T };
  } catch (error) {
    return { ok: false, error };
  }
}

function timestamp(): string {
  return new Date().toISOString().replace(/[-:]/g, "").replace(/\..*$/, "").replace("T", "-");
}

export function backupCorruptState(path: string): string | undefined {
  if (!existsSync(path)) return undefined;
  const backup = join(dirname(path), `state.corrupt-${timestamp()}.json`);
  renameSync(path, backup);
  return backup;
}

export function loadState(paths: StatePaths): { state: HelpState; warnings: string[] } {
  const warnings: string[] = [];
  const current = parseJsonFile<LegacyHelpState | HelpState>(paths.stateFile);
  if (current.ok === true) return { state: migrateState(current.value), warnings };
  if (current.ok === false) {
    try {
      const backup = backupCorruptState(paths.stateFile);
      warnings.push(`状态文件损坏，已备份为 ${backup}`);
    } catch (error) {
      warnings.push(`状态文件损坏，且备份失败：${String(error)}`);
    }
  }

  const legacy = parseJsonFile<LegacyHelpState>(paths.legacyStateFile);
  if (legacy.ok === true) return { state: migrateState(legacy.value), warnings };
  if (legacy.ok === false) warnings.push("旧状态文件无法解析，已忽略");
  return { state: emptyState(), warnings };
}

export function saveState(paths: StatePaths, state: HelpState): PersistResult {
  try {
    mkdirSync(paths.stateDir, { recursive: true });
    const tmp = `${paths.stateFile}.tmp-${process.pid}-${Date.now()}`;
    writeFileSync(tmp, `${JSON.stringify(state, null, 2)}\n`);
    renameSync(tmp, paths.stateFile);
    return { ok: true };
  } catch (error) {
    return { ok: false, warning: `帮助状态保存失败：${String(error)}` };
  }
}