using Microsoft.EntityFrameworkCore;
using MealPlanner.Data;
using MealPlanner.Models;

namespace MealPlanner.Services;

public class MealPlanService(AppDbContext db, TheMealDbClient mealDbClient, RecipeService recipeService)
{
    public async Task<MealPlan> GenerateWeekPlanAsync(string userId, DateOnly weekStart)
    {
        // Remove existing plan for this week if present
        var existing = await db.MealPlans
            .Include(p => p.Entries)
            .FirstOrDefaultAsync(p => p.UserId == userId && p.WeekStart == weekStart);
        if (existing is not null)
        {
            db.MealPlans.Remove(existing);
            await db.SaveChangesAsync();
        }

        var plan = new MealPlan
        {
            Id = Guid.NewGuid(),
            UserId = userId,
            WeekStart = weekStart,
            CreatedAt = DateTime.UtcNow,
        };

        // Get own recipes to optionally mix in (up to 3)
        var ownRecipes = await db.Recipes
            .Include(r => r.Ingredients)
            .Where(r => r.UserId == userId)
            .ToListAsync();

        var usedRecipeIds = new HashSet<Guid>();
        var entries = new List<MealPlanEntry>();

        // Shuffle own recipes and pick up to 3
        var ownToUse = ownRecipes
            .OrderBy(_ => Random.Shared.Next())
            .Take(Math.Min(3, ownRecipes.Count))
            .ToList();

        int ownIndex = 0;

        for (int dayOffset = 0; dayOffset < 7; dayOffset++)
        {
            var date = weekStart.AddDays(dayOffset);
            Recipe? recipe = null;

            // Use an own recipe for this slot if available
            if (ownIndex < ownToUse.Count)
            {
                recipe = ownToUse[ownIndex++];
            }
            else
            {
                // Fetch random from TheMealDB, retry if duplicate
                for (int attempt = 0; attempt < 5; attempt++)
                {
                    var candidate = await mealDbClient.GetRandomAsync();
                    if (candidate is null) continue;
                    if (candidate.ExternalId is not null && usedRecipeIds.Any(id =>
                        db.Recipes.Any(r => r.Id == id && r.ExternalId == candidate.ExternalId)))
                        continue;

                    recipe = await recipeService.EnsurePersistedAsync(candidate);
                    break;
                }
            }

            if (recipe is null) continue;

            usedRecipeIds.Add(recipe.Id);
            entries.Add(new MealPlanEntry
            {
                Id = Guid.NewGuid(),
                MealPlanId = plan.Id,
                Date = date,
                RecipeId = recipe.Id,
            });
        }

        plan.Entries = entries;
        db.MealPlans.Add(plan);
        await db.SaveChangesAsync();

        return await LoadPlanWithDetailsAsync(plan.Id) ?? plan;
    }

    public async Task<MealPlan?> GetCurrentPlanAsync(string userId)
    {
        var today = DateOnly.FromDateTime(DateTime.UtcNow);
        var weekStart = GetWeekStart(today);
        return await GetPlanAsync(userId, weekStart);
    }

    public async Task<MealPlan?> GetPlanAsync(string userId, DateOnly weekStart)
    {
        var plan = await db.MealPlans
            .Where(p => p.UserId == userId && p.WeekStart == weekStart)
            .Select(p => p.Id)
            .FirstOrDefaultAsync();

        if (plan == default) return null;
        return await LoadPlanWithDetailsAsync(plan);
    }

    public async Task<MealPlanEntry?> SwapEntryAsync(Guid entryId, Guid newRecipeId, string userId)
    {
        var entry = await db.MealPlanEntries
            .Include(e => e.MealPlan)
            .FirstOrDefaultAsync(e => e.Id == entryId);

        if (entry is null) return null;
        if (entry.MealPlan.UserId != userId) throw new UnauthorizedAccessException();

        var recipe = await db.Recipes.FindAsync(newRecipeId);
        if (recipe is null) return null;

        entry.RecipeId = newRecipeId;
        await db.SaveChangesAsync();

        return await db.MealPlanEntries
            .Include(e => e.Recipe).ThenInclude(r => r.Ingredients)
            .FirstOrDefaultAsync(e => e.Id == entryId);
    }

    public async Task<MealPlanEntry?> RerollEntryAsync(Guid entryId, string userId)
    {
        var entry = await db.MealPlanEntries
            .Include(e => e.MealPlan).ThenInclude(p => p.Entries)
            .FirstOrDefaultAsync(e => e.Id == entryId);

        if (entry is null) return null;
        if (entry.MealPlan.UserId != userId) throw new UnauthorizedAccessException();

        var usedExternalIds = await db.MealPlanEntries
            .Where(e => e.MealPlanId == entry.MealPlanId)
            .Include(e => e.Recipe)
            .Select(e => e.Recipe.ExternalId)
            .ToListAsync();

        Recipe? newRecipe = null;
        for (int attempt = 0; attempt < 10; attempt++)
        {
            var candidate = await mealDbClient.GetRandomAsync();
            if (candidate is null) continue;
            if (usedExternalIds.Contains(candidate.ExternalId)) continue;

            newRecipe = await recipeService.EnsurePersistedAsync(candidate);
            break;
        }

        if (newRecipe is null) return null;

        entry.RecipeId = newRecipe.Id;
        await db.SaveChangesAsync();

        return await db.MealPlanEntries
            .Include(e => e.Recipe).ThenInclude(r => r.Ingredients)
            .FirstOrDefaultAsync(e => e.Id == entryId);
    }

    private async Task<MealPlan?> LoadPlanWithDetailsAsync(Guid planId)
    {
        return await db.MealPlans
            .Include(p => p.Entries)
                .ThenInclude(e => e.Recipe)
                    .ThenInclude(r => r.Ingredients)
            .FirstOrDefaultAsync(p => p.Id == planId);
    }

    public static DateOnly GetWeekStart(DateOnly date)
    {
        // Monday as week start
        int diff = ((int)date.DayOfWeek - (int)DayOfWeek.Monday + 7) % 7;
        return date.AddDays(-diff);
    }
}