/**
 * FilesScreen – list of documents processed by DocuElevate.
 */

import React, { useCallback, useEffect, useState } from "react";
import {
  ActivityIndicator,
  FlatList,
  Pressable,
  RefreshControl,
  StyleSheet,
  Text,
  View,
} from "react-native";
import type { FileRecord } from "../services/api";
import api from "../services/api";

function formatBytes(bytes: number | null): string {
  if (bytes === null || bytes === undefined) return "–";
  if (bytes < 1024) return `${bytes} B`;
  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
  return `${(bytes / 1024 / 1024).toFixed(1)} MB`;
}

function formatDate(iso: string): string {
  try {
    return new Date(iso).toLocaleDateString(undefined, {
      year: "numeric",
      month: "short",
      day: "numeric",
    });
  } catch {
    return iso;
  }
}

function statusEmoji(status: string): string {
  const map: Record<string, string> = {
    processed: "✅",
    processing: "⚙️",
    queued: "⏳",
    failed: "❌",
    uploaded: "⬆️",
  };
  return map[status?.toLowerCase()] ?? "📄";
}

export default function FilesScreen() {
  const [files, setFiles] = useState<FileRecord[]>([]);
  const [loading, setLoading] = useState(true);
  const [refreshing, setRefreshing] = useState(false);
  const [page, setPage] = useState(1);
  const [hasMore, setHasMore] = useState(true);
  const [error, setError] = useState<string | null>(null);

  const fetchFiles = useCallback(
    async (pageNum: number, replace: boolean) => {
      try {
        const data = await api.listFiles(pageNum, 20);
        if (replace) {
          setFiles(data);
        } else {
          setFiles((prev) => [...prev, ...data]);
        }
        setHasMore(data.length === 20);
        setError(null);
      } catch (err: unknown) {
        setError(err instanceof Error ? err.message : "Failed to load files");
      }
    },
    []
  );

  useEffect(() => {
    (async () => {
      setLoading(true);
      await fetchFiles(1, true);
      setLoading(false);
    })();
  }, [fetchFiles]);

  const handleRefresh = useCallback(async () => {
    setRefreshing(true);
    setPage(1);
    await fetchFiles(1, true);
    setRefreshing(false);
  }, [fetchFiles]);

  const handleLoadMore = useCallback(async () => {
    if (!hasMore || loading || refreshing) return;
    const next = page + 1;
    setPage(next);
    await fetchFiles(next, false);
  }, [fetchFiles, hasMore, loading, page, refreshing]);

  if (loading) {
    return (
      <View style={styles.center}>
        <ActivityIndicator size="large" color="#1e40af" />
      </View>
    );
  }

  if (error) {
    return (
      <View style={styles.center}>
        <Text style={styles.errorText}>{error}</Text>
        <Pressable style={styles.retryButton} onPress={handleRefresh}>
          <Text style={styles.retryText}>Retry</Text>
        </Pressable>
      </View>
    );
  }

  return (
    <FlatList
      style={styles.list}
      data={files}
      keyExtractor={(item) => String(item.id)}
      contentContainerStyle={styles.listContent}
      renderItem={({ item }) => <FileRow file={item} />}
      refreshControl={
        <RefreshControl refreshing={refreshing} onRefresh={handleRefresh} />
      }
      onEndReached={handleLoadMore}
      onEndReachedThreshold={0.4}
      ListEmptyComponent={
        <View style={styles.emptyState}>
          <Text style={styles.emptyEmoji}>📂</Text>
          <Text style={styles.emptyText}>No documents yet.</Text>
          <Text style={styles.emptyHint}>
            Upload a document from the Upload tab to get started.
          </Text>
        </View>
      }
      ListFooterComponent={
        hasMore && files.length > 0 ? (
          <ActivityIndicator color="#1e40af" style={{ marginVertical: 16 }} />
        ) : null
      }
    />
  );
}

function FileRow({ file }: { file: FileRecord }) {
  return (
    <View style={rowStyles.row}>
      <Text style={rowStyles.icon}>{statusEmoji(file.status)}</Text>
      <View style={rowStyles.info}>
        <Text style={rowStyles.filename} numberOfLines={1}>
          {file.filename}
        </Text>
        <Text style={rowStyles.meta}>
          {formatDate(file.created_at)} · {formatBytes(file.file_size)}
        </Text>
      </View>
      <Text style={rowStyles.status}>{file.status}</Text>
    </View>
  );
}

const styles = StyleSheet.create({
  list: { flex: 1, backgroundColor: "#f9fafb" },
  listContent: { padding: 16 },
  center: {
    flex: 1,
    alignItems: "center",
    justifyContent: "center",
    backgroundColor: "#f9fafb",
    padding: 24,
  },
  errorText: { color: "#dc2626", fontSize: 15, textAlign: "center", marginBottom: 16 },
  retryButton: {
    backgroundColor: "#1e40af",
    borderRadius: 8,
    paddingHorizontal: 24,
    paddingVertical: 10,
  },
  retryText: { color: "#fff", fontWeight: "600" },
  emptyState: { alignItems: "center", paddingTop: 60 },
  emptyEmoji: { fontSize: 48, marginBottom: 12 },
  emptyText: { fontSize: 16, color: "#374151", marginBottom: 8 },
  emptyHint: {
    fontSize: 13,
    color: "#6b7280",
    textAlign: "center",
    paddingHorizontal: 32,
  },
});

const rowStyles = StyleSheet.create({
  row: {
    flexDirection: "row",
    alignItems: "center",
    backgroundColor: "#fff",
    borderRadius: 10,
    padding: 14,
    marginBottom: 10,
    shadowColor: "#000",
    shadowOpacity: 0.04,
    shadowOffset: { width: 0, height: 2 },
    shadowRadius: 4,
    elevation: 2,
  },
  icon: { fontSize: 22, marginRight: 12 },
  info: { flex: 1 },
  filename: {
    fontSize: 14,
    fontWeight: "600",
    color: "#111827",
    marginBottom: 4,
  },
  meta: { fontSize: 12, color: "#6b7280" },
  status: {
    fontSize: 11,
    color: "#6b7280",
    fontWeight: "500",
    textTransform: "capitalize",
  },
});