using Microsoft.EntityFrameworkCore;
using BudgetApp.Data;

namespace BudgetApp.Services;

public class CategoryService(ApplicationDbContext db)
{
    private readonly ApplicationDbContext _db = db;

    private static readonly (string Name, string Icon)[] DefaultCategories =
    [
        ("Groceries", "🛒"),
        ("Rent / Mortgage", "🏠"),
        ("Utilities", "💡"),
        ("Transport", "🚗"),
        ("Eating Out", "🍽️"),
        ("Entertainment", "🎬"),
        ("Health", "🏥"),
        ("Insurance", "🛡️"),
        ("Salary", "💰"),
        ("Savings", "🏦"),
        ("Subscriptions", "📱"),
        ("Shopping", "🛍️"),
        ("Education", "📚"),
        ("Travel", "✈️"),
        ("Gifts", "🎁"),
        ("Loan", "🏧"),
        ("Credit Card", "💳"),
        ("Childcare", "👶")
    ];

    public async Task<List<Category>> GetCategoriesAsync(string userId)
    {
        return await _db.Categories
            .Where(c => c.UserId == userId)
            .OrderBy(c => c.Name)
            .ToListAsync();
    }

    public async Task EnsureDefaultCategoriesAsync(string userId)
    {
        var existing = await _db.Categories
            .Where(c => c.UserId == userId)
            .ToListAsync();

        if (existing.Count == 0)
        {
            var defaults = DefaultCategories.Select(d => new Category
            {
                Name = d.Name,
                Icon = d.Icon,
                IsDefault = true,
                UserId = userId
            });

            _db.Categories.AddRange(defaults);
            await _db.SaveChangesAsync();
            return;
        }

        // Backfill icons and IsDefault on existing default categories
        var defaultLookup = DefaultCategories.ToDictionary(d => d.Name, d => d.Icon);
        bool updated = false;

        foreach (var category in existing)
        {
            if (string.IsNullOrEmpty(category.Icon) && defaultLookup.TryGetValue(category.Name, out var icon))
            {
                category.Icon = icon;
                updated = true;
            }
            if (!category.IsDefault && defaultLookup.ContainsKey(category.Name))
            {
                category.IsDefault = true;
                updated = true;
            }
        }

        if (updated)
        {
            await _db.SaveChangesAsync();
        }
    }

    public async Task CreateCategoryAsync(Category category)
    {
        _db.Categories.Add(category);
        await _db.SaveChangesAsync();
    }

    public async Task UpdateCategoryAsync(int id, string userId, string name, string icon)
    {
        var category = await _db.Categories
            .FirstOrDefaultAsync(c => c.Id == id && c.UserId == userId);
        if (category is not null)
        {
            if (category.IsDefault) return;
            category.Name = name;
            category.Icon = icon;
            await _db.SaveChangesAsync();
        }
    }

    public async Task DeleteCategoryAsync(int id, string userId)
    {
        var category = await _db.Categories
            .FirstOrDefaultAsync(c => c.Id == id && c.UserId == userId);
        if (category is not null)
        {
            if (category.IsDefault) return;
            _db.Categories.Remove(category);
            await _db.SaveChangesAsync();
        }
    }
}