import { router, useLocalSearchParams } from "expo-router";
import { useEffect, useMemo, useState } from "react";
import {
  Alert,
  KeyboardAvoidingView,
  Platform,
  Pressable,
  ScrollView,
  StyleSheet,
  Text,
  View,
} from "react-native";
import { useSafeAreaInsets } from "react-native-safe-area-context";

import { AppBackground } from "@/components/AppBackground";
import { LineItemEditor, type EditableLineItem } from "@/components/invoices/LineItemEditor";
import { LoadingScreen } from "@/components/LoadingScreen";
import { Button } from "@/components/ui/Button";
import { Card } from "@/components/ui/Card";
import { DateTimeField } from "@/components/ui/DateTimeField";
import { Input } from "@/components/ui/Input";
import { fonts, spacing } from "@/constants/theme";
import { useAppTheme } from "@/contexts/ThemeContext";
import { useNativeTabBarHeight, useTabBarScrollPadding } from "@/lib/tab-bar-insets";
import { formatCurrency } from "@/lib/format";
import type { ThemeColors } from "@/lib/theme-palette";
import { useThemedStyles } from "@/lib/use-themed-styles";
import { api } from "@/lib/trpc";

export default function InvoiceEditScreen() {
  const { colors } = useAppTheme();
  const styles = useThemedStyles(createInvoiceEditStyles);
  const { id } = useLocalSearchParams<{ id: string }>();
  const utils = api.useUtils();
  const insets = useSafeAreaInsets();
  const tabBarHeight = useNativeTabBarHeight();
  const scrollPadding = useTabBarScrollPadding();

  const invoiceQuery = api.invoices.getById.useQuery(
    { id: id ?? "" },
    { enabled: Boolean(id) },
  );

  const [notes, setNotes] = useState("");
  const [dueDate, setDueDate] = useState(() => new Date());
  const [items, setItems] = useState<EditableLineItem[]>([]);
  const [expandedIndex, setExpandedIndex] = useState<number | null>(null);
  const [error, setError] = useState<string | null>(null);
  const [footerHeight, setFooterHeight] = useState(0);

  useEffect(() => {
    const invoice = invoiceQuery.data;
    if (!invoice) return;
    setNotes(invoice.notes ?? "");
    setDueDate(new Date(invoice.dueDate));
    setItems(
      invoice.items.map((item) => ({
        id: item.id,
        date: new Date(item.date),
        description: item.description,
        hours: String(item.hours),
        rate: String(item.rate),
      })),
    );
    setExpandedIndex(null);
  }, [invoiceQuery.data]);

  const updateInvoice = api.invoices.update.useMutation({
    onSuccess: () => {
      void utils.invoices.getById.invalidate({ id: id ?? "" });
      void utils.invoices.getAll.invalidate();
      void utils.dashboard.getStats.invalidate();
      Alert.alert("Saved", "Invoice updated", [
        { text: "OK", onPress: () => router.back() },
      ]);
    },
    onError: (err) => setError(err.message),
  });

  const invoice = invoiceQuery.data;

  const subtotal = useMemo(
    () =>
      items.reduce((sum, item) => {
        const hours = Number(item.hours) || 0;
        const rate = Number(item.rate) || 0;
        return sum + hours * rate;
      }, 0),
    [items],
  );

  const taxRate = invoice?.taxRate ?? 0;
  const taxAmount = subtotal * (taxRate / 100);
  const total = subtotal + taxAmount;
  const currency = invoice?.currency ?? "USD";

  if (!id) {
    return <LoadingScreen message="Invalid invoice" />;
  }

  if (invoiceQuery.isLoading) {
    return <LoadingScreen message="Loading invoice…" />;
  }

  if (!invoice) {
    return <LoadingScreen message="Invoice not found" />;
  }

  function updateItem(index: number, patch: Partial<EditableLineItem>) {
    setItems((prev) => prev.map((item, i) => (i === index ? { ...item, ...patch } : item)));
  }

  function addItem() {
    const nextIndex = items.length;
    setItems((prev) => [
      ...prev,
      {
        date: new Date(),
        description: "",
        hours: "1",
        rate: prev[prev.length - 1]?.rate ?? "0",
      },
    ]);
    setExpandedIndex(nextIndex);
  }

  function removeItem(index: number) {
    if (items.length <= 1) {
      Alert.alert("Cannot remove", "An invoice needs at least one line item.");
      return;
    }
    setItems((prev) => prev.filter((_, i) => i !== index));
    setExpandedIndex((current) => {
      if (current === null) return null;
      if (current === index) return null;
      return current > index ? current - 1 : current;
    });
  }

  function handleSave() {
    setError(null);

    const parsedItems: Array<{
      date: Date;
      description: string;
      hours: number;
      rate: number;
    }> = [];

    for (const item of items) {
      const hours = Number(item.hours);
      const rate = Number(item.rate);
      if (!item.description.trim()) {
        setError("Each line needs a description");
        return;
      }
      if (Number.isNaN(hours) || hours < 0) {
        setError("Hours must be a valid number");
        return;
      }
      if (Number.isNaN(rate) || rate < 0) {
        setError("Rate must be a valid number");
        return;
      }
      parsedItems.push({
        date: item.date,
        description: item.description.trim(),
        hours,
        rate,
      });
    }

    updateInvoice.mutate({
      id,
      notes,
      dueDate,
      items: parsedItems,
    });
  }

  return (
    <AppBackground>
      <KeyboardAvoidingView
        behavior={Platform.OS === "ios" ? "padding" : undefined}
        style={styles.flex}
      >
        <ScrollView
          contentContainerStyle={[
            styles.container,
            { paddingBottom: scrollPadding + footerHeight },
          ]}
          contentInsetAdjustmentBehavior={Platform.OS === "ios" ? "never" : undefined}
          scrollIndicatorInsets={{ bottom: scrollPadding + footerHeight }}
          keyboardShouldPersistTaps="handled"
        >
          <View style={styles.hero}>
            <Text style={styles.invoiceNumber}>
              {invoice.invoicePrefix}
              {invoice.invoiceNumber}
            </Text>
            <Text style={styles.clientName}>{invoice.client?.name ?? "Client"}</Text>
          </View>

          <Card>
            <DateTimeField label="Due date" mode="date" value={dueDate} onChange={setDueDate} />
            <Input
              label="Notes"
              value={notes}
              onChangeText={setNotes}
              placeholder="Optional notes for the client"
              multiline
              style={styles.notesInput}
            />
          </Card>

          <Card title="Line items">
            {items.map((item, index) => (
              <LineItemEditor
                key={item.id ?? `new-${index}`}
                item={item}
                currency={currency}
                expanded={expandedIndex === index}
                onToggle={() =>
                  setExpandedIndex((current) => (current === index ? null : index))
                }
                onChange={(patch) => updateItem(index, patch)}
                onRemove={() => removeItem(index)}
              />
            ))}

            <Pressable accessibilityRole="button" onPress={addItem} style={styles.addLine}>
              <Text style={styles.addLineText}>+ Add line</Text>
            </Pressable>

            <View style={styles.totals}>
              <TotalRow label="Subtotal" value={formatCurrency(subtotal, currency)} />
              {taxRate > 0 ? (
                <TotalRow
                  label={`Tax (${taxRate}%)`}
                  value={formatCurrency(taxAmount, currency)}
                />
              ) : null}
              <TotalRow label="Total" value={formatCurrency(total, currency)} bold />
            </View>
          </Card>

          {error ? <Text style={styles.error}>{error}</Text> : null}
        </ScrollView>

        <View
          onLayout={(event) => setFooterHeight(event.nativeEvent.layout.height)}
          style={[
            styles.footer,
            {
              bottom: tabBarHeight,
              paddingBottom: Math.max(insets.bottom, spacing.sm),
            },
          ]}
        >
          <Button title="Save changes" loading={updateInvoice.isPending} onPress={handleSave} />
        </View>
      </KeyboardAvoidingView>
    </AppBackground>
  );
}

function TotalRow({
  label,
  value,
  bold,
}: {
  label: string;
  value: string;
  bold?: boolean;
}) {
  const { colors } = useAppTheme();
  return (
    <View style={totalStyles.row}>
      <Text
        style={[
          totalStyles.label,
          { color: colors.mutedForeground },
          bold && totalStyles.bold,
          bold && { color: colors.foreground },
        ]}
      >
        {label}
      </Text>
      <Text
        style={[
          totalStyles.value,
          { color: colors.foreground },
          bold && totalStyles.bold,
        ]}
      >
        {value}
      </Text>
    </View>
  );
}

const totalStyles = StyleSheet.create({
  row: {
    flexDirection: "row",
    justifyContent: "space-between",
    alignItems: "center",
  },
  label: {
    fontFamily: fonts.body,
    fontSize: 14,
  },
  value: {
    fontFamily: fonts.bodyMedium,
    fontSize: 14,
  },
  bold: {
    fontFamily: fonts.bodySemiBold,
    fontSize: 15,
  },
});

const createInvoiceEditStyles = (colors: ThemeColors, _isDark: boolean) =>
  StyleSheet.create({
  flex: { flex: 1 },
  container: {
    padding: spacing.md,
    gap: spacing.md,
  },
  hero: {
    gap: 4,
  },
  invoiceNumber: {
    fontSize: 24,
    lineHeight: 28,
    fontFamily: fonts.heading,
    color: colors.foreground,
  },
  clientName: {
    fontSize: 14,
    fontFamily: fonts.body,
    color: colors.mutedForeground,
  },
  notesInput: {
    minHeight: 72,
    textAlignVertical: "top",
  },
  addLine: {
    paddingTop: spacing.sm,
    paddingBottom: spacing.xs,
  },
  addLineText: {
    fontFamily: fonts.bodySemiBold,
    fontSize: 14,
    color: colors.primary,
  },
  totals: {
    marginTop: spacing.sm,
    paddingTop: spacing.sm,
    borderTopWidth: 1,
    borderTopColor: colors.border,
    gap: 6,
  },
  error: {
    color: colors.destructive,
    fontFamily: fonts.body,
    fontSize: 14,
  },
  footer: {
    position: "absolute",
    left: 0,
    right: 0,
    paddingHorizontal: spacing.md,
    paddingTop: spacing.sm,
    borderTopWidth: 1,
    borderTopColor: colors.border,
    backgroundColor: colors.cardGlass,
  },
});