import React, { useRef, useState, useEffect, useCallback } from 'react';
import {
  View, Text, StyleSheet, TouchableOpacity, TextInput, Alert,
  ActivityIndicator, KeyboardAvoidingView, Platform,
  ScrollView, useWindowDimensions, BackHandler, Keyboard,
} from 'react-native';
import { WebView } from 'react-native-webview';
import * as FileSystem from 'expo-file-system/legacy';
import * as Sharing from 'expo-sharing';
import { useSafeAreaInsets } from 'react-native-safe-area-context';
import { theme, getLanguage } from '../theme';

const MONACO_HTML = require('../../assets/monaco.html');

// ── Snippet bar data ─────────────────────────────────────────────────────────
// Covers: JS/TS, Python, HTML, CSS, Java, Kotlin, C/C++, Rust, Go, Swift, PHP, Ruby, SQL, Shell …
const SNIPPETS = [
  // cursor navigation
  { t: '←',  tip: 'cursor ←' },
  { t: '→',  tip: 'cursor →' },
  { t: '⇥',  tip: 'Indent' },
  { t: '⇤',  tip: 'Dedent' },
  { sep: true },
  // brackets
  { t: '(' }, { t: ')' },
  { t: '{' }, { t: '}' },
  { t: '[' }, { t: ']' },
  { t: '<' }, { t: '>' },
  { sep: true },
  // punctuation
  { t: ';' }, { t: ':' }, { t: ',' }, { t: '.' },
  { t: '!' }, { t: '?' }, { t: '@' }, { t: '#' },
  { sep: true },
  // assignment / compare
  { t: '=' }, { t: '=>' }, { t: '==' }, { t: '===' },
  { t: '!=' }, { t: '!==' }, { t: '>=' }, { t: '<=' },
  { sep: true },
  // string / template
  { t: '"' }, { t: "'" }, { t: '`' }, { t: '\\' },
  { sep: true },
  // arithmetic / bitwise
  { t: '+' }, { t: '-' }, { t: '*' }, { t: '/' },
  { t: '%' }, { t: '**' }, { t: '&' }, { t: '|' },
  { t: '^' }, { t: '~' }, { t: '<<' }, { t: '>>' },
  { sep: true },
  // logical / nullish
  { t: '&&' }, { t: '||' }, { t: '??' }, { t: '?.' },
  { sep: true },
  // compound assign
  { t: '+=' }, { t: '-=' }, { t: '*=' }, { t: '/=' },
  { t: '%=' }, { t: '**=' }, { t: '&&=' }, { t: '||=' },
  { sep: true },
  // comment
  { t: '//' }, { t: '/*' }, { t: '*/' },
  { t: '<!--' }, { t: '-->' }, { t: '#!' },
  { sep: true },
  // misc
  { t: '_' }, { t: '$' }, { t: '...' }, { t: '::' },
  { t: '->' }, { t: '<-' }, { t: '|>' }, { t: '::=' },
];


export default function EditorScreen({ route, navigation }) {
  const { width, height } = useWindowDimensions();
  const isLandscape = width > height;
  const insets = useSafeAreaInsets();
  const { fileUri, fileName } = route.params;

  const webviewRef = useRef(null);
  const nativeInputRef = useRef(null);
  const saveGoBackRef = useRef(false);
  const syncToNativeRef = useRef(false);

  const [editorReady, setEditorReady] = useState(false);
  const [isDirty, setIsDirty]         = useState(false);
  const [saving, setSaving]           = useState(false);
  const [fontSize, setFontSize]       = useState(15);
  const [wordWrap, setWordWrap]       = useState(false);
  const [snippetOpen, setSnippetOpen] = useState(true);
  const [cursor, setCursor]           = useState({ line: 1, col: 1, sel: 0 });
  const [kbdVisible, setKbdVisible]   = useState(false);
  const [nativeMode, setNativeMode]   = useState(Platform.OS === 'android');
  const [nativeContent, setNativeContent] = useState('');
  const [nativeSel, setNativeSel] = useState({ start: 0, end: 0 });

  useEffect(() => {
    const show = Keyboard.addListener('keyboardDidShow', () => setKbdVisible(true));
    const hide = Keyboard.addListener('keyboardDidHide', () => setKbdVisible(false));
    return () => { show.remove(); hide.remove(); };
  }, []);

  const loadFile = useCallback(async () => {
    try {
      const content = await FileSystem.readAsStringAsync(fileUri, { encoding: FileSystem.EncodingType.UTF8 });
      setNativeContent(content);
      sendCommand('setContent', { content, language: getLanguage(fileName) });
    } catch (e) {
      Alert.alert('Error reading file', e.message);
    }
  }, [fileUri, fileName]);

  useEffect(() => { if (editorReady) loadFile(); }, [editorReady, loadFile]);

  useEffect(() => {
    const h = BackHandler.addEventListener('hardwareBackPress', () => { handleBack(); return true; });
    return () => h.remove();
  }, [isDirty]);

  function sendCommand(type, extra = {}) {
    if (!webviewRef.current) return;
    const msg = JSON.stringify({ type, ...extra });
    webviewRef.current.injectJavaScript(
      `(function(){document.dispatchEvent(new MessageEvent('message',{data:${JSON.stringify(msg)}}));})();true;`
    );
  }

  function handleBack() {
    if (isDirty) {
      Alert.alert('Unsaved changes', 'Save before leaving?', [
        { text: 'Discard', style: 'destructive', onPress: () => navigation.goBack() },
        { text: 'Save & Exit', onPress: () => doSave(true) },
        { text: 'Cancel', style: 'cancel' },
      ]);
    } else { navigation.goBack(); }
  }

  function doSave(thenGoBack = false) {
    saveGoBackRef.current = thenGoBack;
    setSaving(true);
    if (nativeMode) writeContent(nativeContent);
    else sendCommand('getContent');
  }

  async function writeContent(content) {
    try {
      await FileSystem.writeAsStringAsync(fileUri, content, { encoding: FileSystem.EncodingType.UTF8 });
      setIsDirty(false);
      sendCommand('markClean');
    } catch (e) {
      Alert.alert('Save failed', e.message);
    } finally {
      setSaving(false);
      if (saveGoBackRef.current) { saveGoBackRef.current = false; navigation.goBack(); }
    }
  }

  function onMessage(event) {
    try {
      const msg = JSON.parse(event.nativeEvent.data);
      if (msg.type === 'ready')               setEditorReady(true);
      else if (msg.type === 'contentChanged') setIsDirty(true);
      else if (msg.type === 'content') {
        if (syncToNativeRef.current) {
          syncToNativeRef.current = false;
          setNativeContent(msg.content || '');
        } else {
          writeContent(msg.content);
        }
      }
      else if (msg.type === 'fontSizeChanged') setFontSize(msg.size);
      else if (msg.type === 'wordWrapChanged') setWordWrap(msg.enabled);
      else if (msg.type === 'cursor')         setCursor({ line: msg.line, col: msg.col, sel: msg.sel });
    } catch {}
  }

  useEffect(() => {
    if (!editorReady) return;
    if (!nativeMode) {
      sendCommand('setContent', { content: nativeContent, language: getLanguage(fileName) });
    }
  }, [nativeMode, editorReady]);

  function updateNativeCursor(text, start, end) {
    const upTo = text.slice(0, start);
    const line = upTo.split('\n').length;
    const col = start - upTo.lastIndexOf('\n');
    setCursor({ line, col, sel: Math.max(0, end - start) });
  }

  function toggleEditorMode() {
    if (nativeMode) {
      setNativeMode(false);
      return;
    }
    syncToNativeRef.current = true;
    sendCommand('getContent');
    setNativeMode(true);
  }

  function nativeInsertText(t) {
    const s = nativeSel.start;
    const e = nativeSel.end;
    const next = nativeContent.slice(0, s) + t + nativeContent.slice(e);
    const p = s + t.length;
    setNativeContent(next);
    setNativeSel({ start: p, end: p });
    setIsDirty(true);
    updateNativeCursor(next, p, p);
    requestAnimationFrame(() => nativeInputRef.current?.focus());
  }

  function runEditorAction(type, extra = {}) {
    if (!nativeMode) {
      sendCommand(type, extra);
      return;
    }
    if (type === 'focusKeyboard') {
      nativeInputRef.current?.focus();
      return;
    }
    if (type === 'insertText') {
      nativeInsertText(extra.text || '');
      return;
    }
    if (type === 'fontSize') {
      const next = Math.max(10, Math.min(32, fontSize + (extra.delta || 0)));
      setFontSize(next);
      return;
    }
    if (type === 'toggleWordWrap') return;
  }

  const langLabel = getLanguage(fileName).toUpperCase();
  const compact   = isLandscape;
  const snipH     = compact ? 30 : 36;
  const snipFs    = compact ? 11 : 13;

  return (
    <KeyboardAvoidingView
      style={[styles.container, { paddingTop: insets.top }]}
      behavior={Platform.OS === 'ios' ? 'padding' : undefined}
    >
      {/* ── Top bar ── */}
      <View style={[styles.topBar, compact && styles.topBarCompact]}>
        <TouchableOpacity style={styles.backBtn} onPress={handleBack}>
          <Text style={[styles.backBtnText, compact && { fontSize: 22 }]}>‹</Text>
        </TouchableOpacity>
        <View style={styles.fileInfo}>
          <Text style={[styles.fileName, compact && { fontSize: 12 }]} numberOfLines={1}>{fileName}</Text>
          <Text style={styles.langBadge}>{langLabel}</Text>
          {isDirty && <View style={styles.dirtyDot} />}
        </View>
        {/* Status inline */}
        <Text style={styles.statusInline}>
          {cursor.line}:{cursor.col}{cursor.sel > 0 ? ` [${cursor.sel}]` : ''}
        </Text>
        <TouchableOpacity
          style={[styles.saveBtn, isDirty && styles.saveBtnActive]}
          onPress={() => doSave(false)}
          disabled={!isDirty || saving}
        >
          {saving
            ? <ActivityIndicator size="small" color={theme.colors.bg} />
            : <Text style={[styles.saveBtnText, isDirty && styles.saveBtnTextActive]}>Save</Text>}
        </TouchableOpacity>
      </View>

      {/* ── Main area: left sidebar + editor ── */}
      <View style={styles.mainArea}>

        {/* LEFT SIDEBAR ── vertical toolbar */}
        <View style={styles.leftSidebar}>
          <ScrollView
            showsVerticalScrollIndicator={false}
            keyboardShouldPersistTaps="always"
            contentContainerStyle={styles.sidebarContent}
          >
            <SBtn label="↩"   onPress={() => sendCommand('undo')} />
            <SBtn label="↪"   onPress={() => sendCommand('redo')} />
              <SSep />
              <SBtn label={nativeMode ? 'RN' : 'WEB'} active={!nativeMode} onPress={toggleEditorMode} />
            <SSep />
              <SBtn label="⌕"   onPress={() => runEditorAction('find')} />
              <SBtn label="fmt" onPress={() => runEditorAction('format')} />
            <SBtn label="⌨"   active={kbdVisible}
                onPress={() => kbdVisible ? Keyboard.dismiss() : runEditorAction('focusKeyboard')} />
            <SSep />
              <SBtn label="dup" onPress={() => runEditorAction('duplicateLine')} />
              <SBtn label="//"  onPress={() => runEditorAction('toggleComment')} />
              <SBtn label="↑"   onPress={() => runEditorAction('lineUp')} />
              <SBtn label="↓"   onPress={() => runEditorAction('lineDown')} />
            <SSep />
              <SBtn label="A-"  onPress={() => runEditorAction('fontSize', { delta: -1 })} />
            <SBtn label={`${fontSize}`} disabled />
              <SBtn label="A+"  onPress={() => runEditorAction('fontSize', { delta: 1 })} />
            <SSep />
              <SBtn label="⇌"   active={wordWrap} onPress={() => runEditorAction('toggleWordWrap')} />
            <SSep />
            <SBtn label="↑↑"  onPress={() => Sharing.shareAsync(fileUri)} />
          </ScrollView>
        </View>

        {/* EDITOR */}
        <View style={styles.editorWrap}>
          {!editorReady && (
            <View style={styles.editorLoading}>
              <ActivityIndicator size="large" color={theme.colors.accent} />
              <Text style={styles.editorLoadingText}>Loading Monaco…</Text>
            </View>
          )}
          {nativeMode ? (
            <TextInput
              ref={nativeInputRef}
              style={[styles.nativeInput, { fontSize }]}
              multiline
              value={nativeContent}
              onChangeText={(t) => {
                setNativeContent(t);
                setIsDirty(true);
              }}
              onSelectionChange={(e) => {
                const s = e.nativeEvent.selection.start;
                const en = e.nativeEvent.selection.end;
                setNativeSel({ start: s, end: en });
                updateNativeCursor(nativeContent, s, en);
              }}
              autoCorrect={false}
              autoCapitalize="none"
              spellCheck={false}
              keyboardAppearance="dark"
              textAlignVertical="top"
              selectionColor={theme.colors.accent}
              placeholder="Native editor mode (stable keyboard)"
              placeholderTextColor={theme.colors.textMuted}
            />
          ) : (
            <WebView
              ref={webviewRef}
              source={MONACO_HTML}
              style={styles.webview}
              onMessage={onMessage}
              javaScriptEnabled
              domStorageEnabled
              originWhitelist={['*']}
              mixedContentMode="always"
              allowFileAccess
              allowUniversalAccessFromFileURLs
              scalesPageToFit={false}
              textZoom={100}
              overScrollMode="never"
              nestedScrollEnabled={true}
              keyboardDisplayRequiresUserAction={false}
              hideKeyboardAccessoryView={true}
              showsVerticalScrollIndicator={false}
              showsHorizontalScrollIndicator={false}
              onError={(e) => Alert.alert('WebView Error', e.nativeEvent.description)}
            />
          )}
        </View>
      </View>

      {/* ── Symbols bar — sits flush above keyboard ── */}
      <View style={[styles.snippetBar, { paddingBottom: insets.bottom }]}>
        <TouchableOpacity style={styles.snippetToggleRow} onPress={() => setSnippetOpen(o => !o)}>
          <Text style={styles.snippetToggleLabel}>
            {snippetOpen ? '▾ Symbols' : '▸ Symbols'}
          </Text>
          <Text style={styles.snippetToggleHint}>
            {snippetOpen ? 'hide' : 'show'}
          </Text>
        </TouchableOpacity>

        {snippetOpen && (
          <ScrollView
            horizontal
            showsHorizontalScrollIndicator={false}
            keyboardShouldPersistTaps="always"
            contentContainerStyle={styles.snippetScroll}
          >
            {SNIPPETS.map((s, i) =>
              s.sep
                ? <View key={`sp${i}`} style={styles.snippetSep} />
                : (
                  <TouchableOpacity
                    key={`${s.t}${i}`}
                    style={[styles.snippetBtn, { height: snipH }]}
                    onPress={() => runEditorAction('insertText', { text: s.t })}
                  >
                    <Text style={[styles.snippetBtnText, { fontSize: snipFs }]}>{s.t}</Text>
                  </TouchableOpacity>
                )
            )}
          </ScrollView>
        )}
      </View>
    </KeyboardAvoidingView>
  );
}

// ── Sub-components ────────────────────────────────────────────────────────────
function SBtn({ label, onPress, active, disabled }) {
  return (
    <TouchableOpacity
      style={[styles.sideBtn, active && styles.sideBtnActive]}
      onPress={onPress}
      disabled={disabled}
      activeOpacity={0.65}
    >
      <Text style={[styles.sideBtnText, active && styles.sideBtnTextActive, disabled && styles.sideBtnDim]}>
        {label}
      </Text>
    </TouchableOpacity>
  );
}

function SSep() { return <View style={styles.sidebarSep} />; }

const styles = StyleSheet.create({
  container: { flex: 1, backgroundColor: theme.colors.bg },

  // top bar
  topBar: {
    flexDirection: 'row', alignItems: 'center', gap: 8,
    paddingHorizontal: 10, paddingVertical: 8,
    backgroundColor: theme.colors.surface,
    borderBottomWidth: 1, borderBottomColor: theme.colors.border,
  },
  topBarCompact: { paddingVertical: 5 },
  backBtn: { padding: 4 },
  backBtnText: { color: theme.colors.accent, fontSize: 26, lineHeight: 28, fontWeight: '300' },
  fileInfo: { flex: 1, flexDirection: 'row', alignItems: 'center', gap: 6, overflow: 'hidden' },
  fileName: { color: theme.colors.text, fontSize: 13, fontWeight: '700', flexShrink: 1 },
  langBadge: {
    color: theme.colors.textMuted, fontSize: 10, fontWeight: '700',
    backgroundColor: theme.colors.surface2,
    paddingHorizontal: 5, paddingVertical: 2, borderRadius: 4,
  },
  dirtyDot: { width: 7, height: 7, borderRadius: 4, backgroundColor: theme.colors.accentOrange },
  statusInline: {
    color: '#6b7280', fontSize: 10,
    fontFamily: Platform.OS === 'android' ? 'monospace' : 'Courier New',
  },
  saveBtn: { paddingHorizontal: 12, paddingVertical: 6, borderRadius: 8, borderWidth: 1, borderColor: theme.colors.border },
  saveBtnActive: { backgroundColor: theme.colors.accent, borderColor: theme.colors.accent },
  saveBtnText: { color: theme.colors.textMuted, fontSize: 13, fontWeight: '700' },
  saveBtnTextActive: { color: theme.colors.bg },

  // main layout
  mainArea: { flex: 1, flexDirection: 'row' },

  // left sidebar
  leftSidebar: {
    width: 44,
    backgroundColor: theme.colors.surface,
    borderRightWidth: 1, borderRightColor: theme.colors.border,
  },
  sidebarContent: {
    alignItems: 'center', paddingVertical: 6, gap: 3,
  },
  sideBtn: {
    width: 36, height: 36, borderRadius: 8,
    backgroundColor: theme.colors.surface2,
    alignItems: 'center', justifyContent: 'center',
  },
  sideBtnActive: { backgroundColor: theme.colors.accent },
  sideBtnText: { color: theme.colors.text, fontSize: 11, fontWeight: '700' },
  sideBtnTextActive: { color: theme.colors.bg },
  sideBtnDim: { color: theme.colors.textMuted },
  sidebarSep: {
    width: 24, height: 1,
    backgroundColor: theme.colors.border,
    marginVertical: 3,
  },

  // editor
  editorWrap: { flex: 1, position: 'relative' },
  webview: { flex: 1, backgroundColor: theme.colors.bg },
  nativeInput: {
    flex: 1,
    color: theme.colors.text,
    backgroundColor: theme.colors.bg,
    paddingHorizontal: 10,
    paddingTop: 12,
    fontFamily: Platform.OS === 'android' ? 'monospace' : 'Courier New',
  },
  editorLoading: {
    ...StyleSheet.absoluteFillObject, backgroundColor: theme.colors.bg,
    alignItems: 'center', justifyContent: 'center', zIndex: 10, gap: 12,
  },
  editorLoadingText: { color: theme.colors.textMuted, fontSize: 14 },

  // snippet bar — no extra padding, KAV pushes it up flush against keyboard
  snippetBar: {
    backgroundColor: theme.colors.surface,
    borderTopWidth: 1, borderTopColor: theme.colors.border,
  },
  snippetToggleRow: {
    flexDirection: 'row', alignItems: 'center', justifyContent: 'space-between',
    paddingHorizontal: 12, paddingVertical: 4,
    borderBottomWidth: 1, borderBottomColor: theme.colors.border + '60',
  },
  snippetToggleLabel: { color: theme.colors.accent, fontSize: 12, fontWeight: '700' },
  snippetToggleHint:  { color: theme.colors.textMuted, fontSize: 11 },
  snippetScroll: { flexDirection: 'row', alignItems: 'center', paddingHorizontal: 8, gap: 3, paddingVertical: 3 },
  snippetBtn: {
    minWidth: 34, paddingHorizontal: 7, borderRadius: 7,
    backgroundColor: theme.colors.surface2,
    alignItems: 'center', justifyContent: 'center',
  },
  snippetBtnText: { color: theme.colors.accentGreen, fontWeight: '700', fontFamily: Platform.OS === 'android' ? 'monospace' : 'Courier New' },
  snippetSep: { width: 1, height: 20, backgroundColor: theme.colors.border + '80', marginHorizontal: 3 },
});