/**
 * Import Existing Key screen.
 * Two methods:
 *   1. Paste JSON directly into a text field
 *   2. Pick key.json file via document picker
 */

import React, { useState } from 'react';
import {
  View, Text, ScrollView, TextInput,
  TouchableOpacity, Alert, Pressable,
} from 'react-native';
import { router } from 'expo-router';
import * as DocumentPicker from 'expo-document-picker';
import * as Clipboard from 'expo-clipboard';
import { saveKeyFile } from '@/lib/storage';
import { useStore } from '@/lib/store';
import { Button } from '@/components/ui/Button';
import type { KeyFile } from '@/lib/types';

type Tab = 'paste' | 'file';

const REQUIRED_FIELDS: (keyof KeyFile)[] = ['pub_key', 'priv_key', 'x25519_pub', 'x25519_priv'];

function validateKeyFile(raw: string): KeyFile {
  let parsed: any;
  try {
    parsed = JSON.parse(raw.trim());
  } catch {
    throw new Error('Invalid JSON — check that you copied the full key file contents.');
  }
  for (const field of REQUIRED_FIELDS) {
    if (!parsed[field] || typeof parsed[field] !== 'string') {
      throw new Error(`Missing or invalid field: "${field}"`);
    }
    if (!/^[0-9a-f]+$/i.test(parsed[field])) {
      throw new Error(`Field "${field}" must be a hex string.`);
    }
  }
  return parsed as KeyFile;
}

export default function ImportKeyScreen() {
  const setKeyFile = useStore(s => s.setKeyFile);

  const [tab,      setTab]      = useState<Tab>('paste');
  const [jsonText, setJsonText] = useState('');
  const [fileName, setFileName] = useState<string | null>(null);
  const [loading,  setLoading]  = useState(false);
  const [error,    setError]    = useState<string | null>(null);

  // ── Shared: save validated key and navigate ──────────────────────────────
  async function applyKey(kf: KeyFile) {
    setLoading(true);
    setError(null);
    try {
      await saveKeyFile(kf);
      setKeyFile(kf);
      router.replace('/(app)/chats');
    } catch (e: any) {
      setError(e.message);
    } finally {
      setLoading(false);
    }
  }

  // ── Method 1: paste JSON ─────────────────────────────────────────────────
  async function handlePasteImport() {
    setError(null);
    const text = jsonText.trim();
    if (!text) {
      // Try reading clipboard if field is empty
      const clip = await Clipboard.getStringAsync();
      if (clip) setJsonText(clip);
      return;
    }
    try {
      const kf = validateKeyFile(text);
      await applyKey(kf);
    } catch (e: any) {
      setError(e.message);
    }
  }

  // ── Method 2: pick file ──────────────────────────────────────────────────
  async function pickFile() {
    setError(null);
    try {
      const result = await DocumentPicker.getDocumentAsync({
        type: ['application/json', 'text/plain', '*/*'],
        copyToCacheDirectory: true,
      });
      if (result.canceled) return;

      const asset = result.assets[0];
      setFileName(asset.name);

      // Use fetch() — readAsStringAsync is deprecated in newer expo-file-system
      const response = await fetch(asset.uri);
      const raw = await response.text();

      const kf = validateKeyFile(raw);
      await applyKey(kf);
    } catch (e: any) {
      setError(e.message);
    }
  }

  const tabStyle = (t: Tab) => ({
    flex: 1 as const,
    paddingVertical: 10,
    alignItems: 'center' as const,
    borderBottomWidth: 2,
    borderBottomColor: tab === t ? '#2563eb' : 'transparent',
  });

  const tabTextStyle = (t: Tab) => ({
    fontSize: 14,
    fontWeight: '600' as const,
    color: tab === t ? '#fff' : '#8b949e',
  });

  return (
    <ScrollView
      style={{ flex: 1, backgroundColor: '#0d1117' }}
      contentContainerStyle={{ paddingHorizontal: 20, paddingTop: 60, paddingBottom: 40 }}
      keyboardShouldPersistTaps="handled"
      keyboardDismissMode="on-drag"
    >
      {/* Back */}
      <Pressable onPress={() => router.back()} style={{ marginBottom: 24, alignSelf: 'flex-start' }}>
        <Text style={{ color: '#2563eb', fontSize: 15 }}>← Back</Text>
      </Pressable>

      <Text style={{ color: '#fff', fontSize: 28, fontWeight: '700', marginBottom: 6 }}>
        Import Key
      </Text>
      <Text style={{ color: '#8b949e', fontSize: 15, lineHeight: 22, marginBottom: 24 }}>
        Restore your account from an existing{' '}
        <Text style={{ color: '#fff', fontFamily: 'monospace' }}>key.json</Text>.
      </Text>

      {/* Tabs */}
      <View style={{
        flexDirection: 'row',
        borderBottomWidth: 1, borderBottomColor: '#30363d',
        marginBottom: 24,
      }}>
        <TouchableOpacity style={tabStyle('paste')} onPress={() => setTab('paste')}>
          <Text style={tabTextStyle('paste')}>📋  Paste JSON</Text>
        </TouchableOpacity>
        <TouchableOpacity style={tabStyle('file')} onPress={() => setTab('file')}>
          <Text style={tabTextStyle('file')}>📁  Open File</Text>
        </TouchableOpacity>
      </View>

      {/* ── Paste tab ── */}
      {tab === 'paste' && (
        <View style={{ gap: 12 }}>
          <Text style={{ color: '#8b949e', fontSize: 12, fontWeight: '600',
            textTransform: 'uppercase', letterSpacing: 1 }}>
            Key JSON
          </Text>

          <View style={{
            backgroundColor: '#161b22',
            borderWidth: 1,
            borderColor: error ? '#f85149' : jsonText ? '#2563eb' : '#30363d',
            borderRadius: 12,
            padding: 12,
          }}>
            <TextInput
              value={jsonText}
              onChangeText={t => { setJsonText(t); setError(null); }}
              placeholder={'{\n  "pub_key": "...",\n  "priv_key": "...",\n  "x25519_pub": "...",\n  "x25519_priv": "..."\n}'}
              placeholderTextColor="#8b949e"
              multiline
              numberOfLines={8}
              autoCapitalize="none"
              autoCorrect={false}
              style={{
                color: '#fff',
                fontFamily: 'monospace',
                fontSize: 12,
                lineHeight: 18,
                minHeight: 160,
                textAlignVertical: 'top',
              }}
            />
          </View>

          {/* Paste from clipboard shortcut */}
          {!jsonText && (
            <TouchableOpacity
              onPress={async () => {
                const clip = await Clipboard.getStringAsync();
                if (clip) { setJsonText(clip); setError(null); }
                else Alert.alert('Clipboard empty', 'Copy your key JSON first.');
              }}
              style={{
                flexDirection: 'row', alignItems: 'center', gap: 8,
                padding: 12, backgroundColor: '#161b22',
                borderWidth: 1, borderColor: '#30363d', borderRadius: 12,
              }}
            >
              <Text style={{ fontSize: 18 }}>📋</Text>
              <Text style={{ color: '#8b949e', fontSize: 14 }}>Paste from clipboard</Text>
            </TouchableOpacity>
          )}

          {error && (
            <View style={{
              backgroundColor: 'rgba(248,81,73,0.1)',
              borderWidth: 1, borderColor: 'rgba(248,81,73,0.3)',
              borderRadius: 10, padding: 12,
            }}>
              <Text style={{ color: '#f85149', fontSize: 13, lineHeight: 18 }}>⚠ {error}</Text>
            </View>
          )}

          <Button
            size="lg"
            loading={loading}
            disabled={!jsonText.trim()}
            onPress={handlePasteImport}
          >
            Import Key
          </Button>
        </View>
      )}

      {/* ── File tab ── */}
      {tab === 'file' && (
        <View style={{ gap: 12 }}>
          <TouchableOpacity
            onPress={pickFile}
            style={{
              backgroundColor: '#161b22',
              borderWidth: 2, borderColor: '#30363d',
              borderRadius: 16, borderStyle: 'dashed',
              padding: 32, alignItems: 'center', gap: 12,
            }}
          >
            <Text style={{ fontSize: 40 }}>📂</Text>
            <Text style={{ color: '#fff', fontSize: 16, fontWeight: '600' }}>
              {fileName ?? 'Choose key.json'}
            </Text>
            <Text style={{ color: '#8b949e', fontSize: 13, textAlign: 'center' }}>
              Tap to browse files
            </Text>
          </TouchableOpacity>

          {fileName && (
            <View style={{
              flexDirection: 'row', alignItems: 'center', gap: 10,
              backgroundColor: 'rgba(63,185,80,0.1)',
              borderWidth: 1, borderColor: 'rgba(63,185,80,0.3)',
              borderRadius: 10, padding: 12,
            }}>
              <Text style={{ fontSize: 18 }}>📄</Text>
              <Text style={{ color: '#3fb950', fontSize: 13, flex: 1 }} numberOfLines={1}>
                {fileName}
              </Text>
            </View>
          )}

          {error && (
            <View style={{
              backgroundColor: 'rgba(248,81,73,0.1)',
              borderWidth: 1, borderColor: 'rgba(248,81,73,0.3)',
              borderRadius: 10, padding: 12,
            }}>
              <Text style={{ color: '#f85149', fontSize: 13, lineHeight: 18 }}>⚠ {error}</Text>
            </View>
          )}

          {loading && (
            <Text style={{ color: '#8b949e', textAlign: 'center', fontSize: 14 }}>
              Validating key…
            </Text>
          )}
        </View>
      )}

      {/* Format hint */}
      <View style={{
        marginTop: 28, padding: 14,
        backgroundColor: '#161b22',
        borderWidth: 1, borderColor: '#30363d', borderRadius: 12,
      }}>
        <Text style={{ color: '#8b949e', fontSize: 12, fontWeight: '600',
          marginBottom: 8, textTransform: 'uppercase', letterSpacing: 1 }}>
          Expected format
        </Text>
        <Text style={{ color: '#8b949e', fontFamily: 'monospace', fontSize: 11, lineHeight: 17 }}>
          {`{\n  "pub_key":     "<64 hex chars>",\n  "priv_key":    "<128 hex chars>",\n  "x25519_pub":  "<64 hex chars>",\n  "x25519_priv": "<64 hex chars>"\n}`}
        </Text>
      </View>
    </ScrollView>
  );
}