import {
  closeSync,
  fsyncSync,
  mkdirSync,
  openSync,
  readFileSync,
  renameSync,
  unlinkSync,
  writeFileSync,
} from "node:fs";
import { dirname } from "node:path";
import type { AppConfig } from "../config.js";

export interface Settings {
  workspace?: string;
  /** Legacy input fields are ignored when loading/evaluating installation settings. */
  provider?: string;
  model?: string;
  thinking?: string;
}

export interface SettingsDurability {
  syncDirectory(directory: string): void;
}

export interface SettingsSnapshot {
  exists: boolean;
  rawBase64: string;
}

/**
 * Settings files are installation defaults only. Personal workspace/model/thinking choices
 * belong to the browser and must never be written back here by request handlers.
 */

/** Read settings from cfg.settingsFile. Returns {} if missing or invalid. */
export function loadSettings(cfg: AppConfig): Settings {
  try {
    const raw = readFileSync(cfg.settingsFile, "utf8");
    const parsed = JSON.parse(raw);
    if (parsed && typeof parsed === "object") {
      const value = parsed as Record<string, unknown>;
      return {
        ...(typeof value.workspace === "string" ? { workspace: value.workspace } : {}),
        ...(typeof value.thinking === "string" ? { thinking: value.thinking } : {}),
      };
    }
    return {};
  } catch {
    return {};
  }
}

/** Capture exact file existence and bytes so host-side configuration can compensate losslessly. */
export function captureSettingsSnapshot(cfg: AppConfig): SettingsSnapshot {
  try {
    return { exists: true, rawBase64: readFileSync(cfg.settingsFile).toString("base64") };
  } catch (error) {
    if ((error as NodeJS.ErrnoException).code === "ENOENT") {
      return { exists: false, rawBase64: "" };
    }
    throw error;
  }
}

/** Restore a previously captured settings file exactly, including the clean absent state. */
export function restoreSettingsSnapshot(
  cfg: AppConfig,
  snapshot: SettingsSnapshot,
  durability: SettingsDurability = defaultDurability,
): void {
  if (typeof snapshot.exists !== "boolean" || typeof snapshot.rawBase64 !== "string") {
    throw new Error("invalid settings snapshot");
  }
  const raw = Buffer.from(snapshot.rawBase64, "base64");
  if (raw.toString("base64") !== snapshot.rawBase64 || (!snapshot.exists && raw.length !== 0)) {
    throw new Error("invalid settings snapshot");
  }
  const directory = dirname(cfg.settingsFile);
  mkdirSync(directory, { recursive: true });
  if (snapshot.exists) {
    replaceSettingsFile(cfg.settingsFile, raw);
  } else {
    try {
      unlinkSync(cfg.settingsFile);
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code !== "ENOENT") throw error;
    }
  }
  durability.syncDirectory(directory);
}

/** Persist settings (pretty JSON). Creates the parent directory if needed. */
export function saveSettings(
  cfg: AppConfig,
  s: Settings,
  durability: SettingsDurability = defaultDurability,
): Settings {
  mkdirSync(dirname(cfg.settingsFile), { recursive: true });
  const directory = dirname(cfg.settingsFile);
  let previous: Buffer | undefined;
  try {
    previous = readFileSync(cfg.settingsFile);
  } catch (error) {
    if ((error as NodeJS.ErrnoException).code !== "ENOENT") throw error;
  }

  replaceSettingsFile(cfg.settingsFile, Buffer.from(JSON.stringify(s, null, 2) + "\n", "utf8"));
  try {
    durability.syncDirectory(directory);
  } catch (durabilityError) {
    try {
      if (previous === undefined) unlinkSync(cfg.settingsFile);
      else replaceSettingsFile(cfg.settingsFile, previous);
      durability.syncDirectory(directory);
    } catch {
      throw new Error("settings durability failed and previous settings could not be restored", {
        cause: durabilityError,
      });
    }
    throw durabilityError;
  }
  return s;
}

let temporarySequence = 0;

function replaceSettingsFile(path: string, contents: Buffer): void {
  const temporary = `${path}.tmp-${process.pid}-${Date.now()}-${temporarySequence++}`;
  const fd = openSync(temporary, "wx", 0o600);
  try {
    writeFileSync(fd, contents);
    fsyncSync(fd);
  } catch (error) {
    try { closeSync(fd); } catch { /* preserve the write error */ }
    try { unlinkSync(temporary); } catch { /* best effort */ }
    throw error;
  }
  closeSync(fd);
  try {
    renameSync(temporary, path);
  } catch (error) {
    try { unlinkSync(temporary); } catch { /* best effort */ }
    throw error;
  }
}

const defaultDurability: SettingsDurability = {
  syncDirectory(directory: string): void {
    // The core image runs Linux. Windows durability is owned by the host-side Go executable.
    if (process.platform === "win32") return;
    const dirFd = openSync(directory, "r");
    try { fsyncSync(dirFd); } finally { closeSync(dirFd); }
  },
};