import 'dart:io';

import 'package:flutter/services.dart';

/// Minimum RAM (bytes) required for on-device Gemma 4 E2B inference.
///
/// 4 GiB matches Planner AC-6 of #218. The Gemma 4 E2B weights alone are
/// ~2.4GB; adding KV-cache + Flutter runtime + OS headroom puts us at 4GB
/// total as the practical floor below which AC-7 cold-start budgets fail.
const int kAiMinRamBytes = 4 * 1024 * 1024 * 1024;

/// Abstraction over the platform-channel RAM query, so tests can inject a
/// fake without touching MethodChannel.
abstract class DeviceCapabilities {
  /// Returns total physical RAM in bytes, or `null` if unknown / unsupported
  /// (non-Android host, channel error). Callers must treat `null` as "do
  /// not enable the AI gate" (fail-closed).
  Future<int?> totalRamBytes();

  /// Convenience: `true` iff [totalRamBytes] returns ≥ [kAiMinRamBytes].
  /// `null` from [totalRamBytes] → `false` (fail-closed).
  Future<bool> meetsAiMinRam() async {
    final bytes = await totalRamBytes();
    if (bytes == null) return false;
    return bytes >= kAiMinRamBytes;
  }
}

/// Real implementation. Calls `MainActivity.kt` over a MethodChannel.
class PlatformDeviceCapabilities implements DeviceCapabilities {
  PlatformDeviceCapabilities({MethodChannel? channel})
      : _channel = channel ??
            const MethodChannel('life_helper/device_caps');

  final MethodChannel _channel;

  @override
  Future<int?> totalRamBytes() async {
    // Channel is Android-only — return null on iOS/host tests rather than
    // throwing MissingPluginException.
    if (!Platform.isAndroid) return null;
    try {
      final v = await _channel.invokeMethod<int>('totalMemoryBytes');
      return v;
    } on PlatformException {
      return null;
    } on MissingPluginException {
      return null;
    }
  }

  @override
  Future<bool> meetsAiMinRam() async {
    final bytes = await totalRamBytes();
    if (bytes == null) return false;
    return bytes >= kAiMinRamBytes;
  }
}