import * as DocumentPicker from 'expo-document-picker';
import * as FileSystem from 'expo-file-system/legacy';
import { useSQLiteContext } from 'expo-sqlite';
import { useState } from 'react';
import { Alert, Pressable, ScrollView, StyleSheet, Text, View } from 'react-native';
import { insertActivity } from '@/db/queries';

type ImportState =
  | { status: 'idle' }
  | { status: 'loading' }
  | { status: 'done'; title: string; id: string }
  | { status: 'error'; message: string };

export default function ImportScreen() {
  const db = useSQLiteContext();
  const [state, setState] = useState<ImportState>({ status: 'idle' });

  async function pickFile() {
    setState({ status: 'loading' });
    try {
      const result = await DocumentPicker.getDocumentAsync({
        type: ['*/*'],
        copyToCacheDirectory: true,
      });
      if (result.canceled || !result.assets?.[0]) {
        setState({ status: 'idle' });
        return;
      }

      const asset = result.assets[0];
      const name = asset.name ?? '';
      const uri = asset.uri;
      const lower = name.toLowerCase();

      if (lower.endsWith('.json')) {
        await importBasJson(uri, db);
        const detail = JSON.parse(await FileSystem.readAsStringAsync(uri));
        setState({ status: 'done', title: detail.title ?? detail.id, id: detail.id });
      } else if (['.fit', '.gpx', '.tcx', '.fit.gz', '.gpx.gz', '.tcx.gz'].some(ext => lower.endsWith(ext))) {
        // Phase 1: Pyodide extraction. Placeholder for now.
        Alert.alert(
          'Extraction coming in Phase 1',
          `File "${name}" received. FIT/GPX/TCX extraction via Pyodide will be added in Phase 1. For now, you can import a pre-extracted BAS .json file.`,
        );
        setState({ status: 'idle' });
      } else {
        setState({ status: 'error', message: `Unsupported file type: ${name}` });
      }
    } catch (e: unknown) {
      setState({ status: 'error', message: e instanceof Error ? e.message : String(e) });
    }
  }

  async function importBasJson(uri: string, dbCtx: typeof db) {
    const text = await FileSystem.readAsStringAsync(uri);
    const detail = JSON.parse(text);

    if (!detail.id || !detail.started_at) {
      throw new Error('Not a valid BAS activity JSON (missing id or started_at)');
    }

    // Simple hash: SHA-256 not available without a library, use content length + id as stand-in.
    // Phase 1 will use a proper hash.
    const hash = `${detail.id}-${text.length}`;

    // Copy to permanent storage
    const origDir = `${FileSystem.documentDirectory}originals/`;
    await FileSystem.makeDirectoryAsync(origDir, { intermediates: true });
    const dest = `${origDir}${detail.id}.json`;
    await FileSystem.copyAsync({ from: uri, to: dest });

    await insertActivity(dbCtx, {
      id: detail.id,
      source_hash: hash,
      detail_json: text,
      timeseries_json: null,
      geojson: null,
      original_path: dest,
      origin: 'local',
    });
  }

  return (
    <ScrollView style={styles.container} contentContainerStyle={styles.content}>
      <Text style={styles.header}>Import</Text>

      <Text style={styles.body}>
        Import a FIT, GPX, or TCX file to extract and store it locally.
        You can also import a pre-extracted BAS <Text style={styles.code}>.json</Text> file directly.
      </Text>

      <Pressable
        style={[styles.button, state.status === 'loading' && styles.buttonDisabled]}
        onPress={state.status !== 'loading' ? pickFile : undefined}
      >
        <Text style={styles.buttonText}>
          {state.status === 'loading' ? 'Importing…' : '＋ Pick file'}
        </Text>
      </Pressable>

      {state.status === 'done' && (
        <View style={styles.success}>
          <Text style={styles.successText}>✓ Imported: {state.title}</Text>
        </View>
      )}

      {state.status === 'error' && (
        <View style={styles.error}>
          <Text style={styles.errorText}>{state.message}</Text>
        </View>
      )}

      <View style={styles.divider} />

      <Text style={styles.sectionTitle}>Supported formats</Text>
      {[
        ['FIT', 'Garmin, Wahoo, Karoo native format'],
        ['GPX', 'Most GPS devices and apps'],
        ['TCX', 'Garmin Training Center'],
        ['BAS JSON', 'Pre-extracted Bincio format'],
      ].map(([fmt, desc]) => (
        <View key={fmt} style={styles.formatRow}>
          <Text style={styles.formatName}>{fmt}</Text>
          <Text style={styles.formatDesc}>{desc}</Text>
        </View>
      ))}

      <View style={styles.notice}>
        <Text style={styles.noticeText}>
          FIT/GPX/TCX extraction runs entirely on your device via the Bincio
          extraction engine. No data is uploaded.
        </Text>
      </View>
    </ScrollView>
  );
}

const styles = StyleSheet.create({
  container: { flex: 1, backgroundColor: '#09090b' },
  content: { padding: 16, paddingTop: 60, paddingBottom: 40 },
  header: { color: '#fff', fontSize: 22, fontWeight: '700', marginBottom: 12 },
  body: { color: '#a1a1aa', fontSize: 14, lineHeight: 20, marginBottom: 24 },
  code: { color: '#60a5fa', fontFamily: 'monospace' },
  button: {
    backgroundColor: '#2563eb', borderRadius: 10,
    paddingVertical: 14, alignItems: 'center', marginBottom: 16,
  },
  buttonDisabled: { opacity: 0.5 },
  buttonText: { color: '#fff', fontWeight: '600', fontSize: 16 },
  success: {
    backgroundColor: '#14532d', borderRadius: 8,
    padding: 12, marginBottom: 16,
  },
  successText: { color: '#86efac', fontSize: 14 },
  error: {
    backgroundColor: '#450a0a', borderRadius: 8,
    padding: 12, marginBottom: 16,
  },
  errorText: { color: '#fca5a5', fontSize: 14 },
  divider: { height: 1, backgroundColor: '#27272a', marginVertical: 24 },
  sectionTitle: { color: '#a1a1aa', fontSize: 12, fontWeight: '600', marginBottom: 12, letterSpacing: 0.5 },
  formatRow: { flexDirection: 'row', gap: 12, marginBottom: 10 },
  formatName: { color: '#f4f4f5', fontSize: 13, fontWeight: '600', width: 72 },
  formatDesc: { color: '#71717a', fontSize: 13, flex: 1 },
  notice: {
    marginTop: 8, backgroundColor: '#18181b',
    borderRadius: 8, padding: 12, borderWidth: 1, borderColor: '#27272a',
  },
  noticeText: { color: '#71717a', fontSize: 12, lineHeight: 18 },
});