using Microsoft.EntityFrameworkCore;
using Prefab.Catalog.Data;
using Prefab.Catalog.Domain.Entities;
using Prefab.Shared.Catalog.Products;

namespace Prefab.Catalog.Domain.Services;

/// <summary>
/// Calculates price quotes for configured catalog products by combining base price, numeric adjustments, and percent deltas.
/// </summary>
public interface IPricingService
{
    /// <summary>
    /// Produces a unit price and line-item breakdown for a shopper’s selections.
    /// </summary>
    Task<QuotePrice.Response> QuoteAsync(QuotePrice.Request request, CancellationToken cancellationToken = default);
}

/// <summary>
/// Default Catalog pricing implementation that reads product/option data on demand and applies the PercentScope rules.
/// </summary>
public sealed class PricingService(IModuleDbReadOnly db) : IPricingService
{
    public async Task<QuotePrice.Response> QuoteAsync(QuotePrice.Request request, CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(request);

        if (request.ProductId is null && string.IsNullOrWhiteSpace(request.Sku))
        {
            throw new ArgumentException("Either ProductId or Sku must be supplied.", nameof(request));
        }

        var product = await FindProductAsync(request, cancellationToken)
            ?? throw new InvalidOperationException("Product could not be located for pricing.");

        var optionsSource = product.Kind == ProductKind.Model
            ? product
            : product.ParentProduct ?? throw new InvalidOperationException("Variant product is missing its model definition.");

        var optionLookup = optionsSource.Options
            .Where(o => o.DeletedOn is null)
            .ToDictionary(o => o.Id);

        var basePrice = product.Price ?? 0m;
        var numericTotal = 0m;
        var choiceAbsTotal = 0m;
        var breakdownEntries = new List<SelectionBreakdown>();

        foreach (var selection in request.Selections)
        {
            if (!optionLookup.TryGetValue(selection.OptionDefinitionId, out var option))
            {
                throw new InvalidOperationException($"Option definition '{selection.OptionDefinitionId}' was not found for product '{optionsSource.Id}'.");
            }

            switch (option.DataType)
            {
                case OptionDataType.Number:
                {
                    var (delta, chosenDescription) = HandleNumber(option, selection);
                    numericTotal += delta;
                    breakdownEntries.Add(SelectionBreakdown.Fixed(option.Name, chosenDescription, delta));
                    break;
                }
                case OptionDataType.Choice:
                {
                    if (selection.OptionValueId is null)
                    {
                        throw new InvalidOperationException($"Selection for option '{option.Name}' must include an option value identifier.");
                    }

                    var value = option.Values.FirstOrDefault(v => v.DeletedOn == null && v.Id == selection.OptionValueId)
                        ?? throw new InvalidOperationException($"Option value '{selection.OptionValueId}' was not found for option '{option.Name}'.");

                    var chosenDescription = value.Label;
                    var delta = value.PriceDelta ?? 0m;

                    switch (value.PriceDeltaKind)
                    {
                        case PriceDeltaKind.Absolute:
                            choiceAbsTotal += delta;
                            breakdownEntries.Add(SelectionBreakdown.Fixed(option.Name, chosenDescription, delta));
                            break;
                        case PriceDeltaKind.Percent:
                            breakdownEntries.Add(SelectionBreakdown.Percent(option, value, chosenDescription, delta));
                            break;
                        default:
                            throw new NotSupportedException($"Price delta kind '{value.PriceDeltaKind}' is not supported.");
                    }

                    break;
                }
                default:
                    throw new NotSupportedException($"Option data type '{option.DataType}' is not supported.");
            }
        }

        var percentSelections = breakdownEntries.Where(e => e.Kind == BreakdownKind.Percent).ToList();
        var percentTotal = 0m;
        PercentScope? selectedScope = null;

        foreach (var entry in percentSelections)
        {
            var scope = entry.OptionDefinition.PercentScope ?? PercentScope.BaseOnly;
            if (selectedScope is null)
            {
                selectedScope = scope;
            }
            else if (selectedScope.Value != scope)
            {
                throw new InvalidOperationException("Percent options for a product must share the same percent scope.");
            }

            var scopeBase = scope switch
            {
                PercentScope.BaseOnly => basePrice,
                PercentScope.NumericOnly => numericTotal,
                PercentScope.BasePlusNumeric => basePrice + numericTotal,
                _ => basePrice
            };

            var delta = scopeBase * (entry.PercentValue / 100m);
            entry.Value = delta;
            percentTotal += delta;
        }

        var final = Math.Max(
            0m,
            Math.Round(basePrice + numericTotal + choiceAbsTotal + percentTotal, 2, MidpointRounding.AwayFromZero));

        var breakdown = breakdownEntries
            .Select(e => new QuotePrice.QuoteBreakdown(
                e.Option,
                e.Chosen,
                Math.Round(e.Value, 2, MidpointRounding.AwayFromZero)))
            .ToList();

        return new QuotePrice.Response(final, breakdown);
    }

    /// <summary>
    /// Resolves a model or variant to price, including the parent model so option metadata is always available.
    /// </summary>
    private async Task<Product?> FindProductAsync(QuotePrice.Request request, CancellationToken cancellationToken)
    {
        var products = db.Products
            .Where(p => p.DeletedOn == null)
            .AsNoTracking()
            .Include(p => p.Options).ThenInclude(o => o.Values)
            .Include(p => p.Options).ThenInclude(o => o.Tiers)
            .Include(p => p.ParentProduct).ThenInclude(pp => pp!.Options).ThenInclude(o => o.Values)
            .Include(p => p.ParentProduct).ThenInclude(pp => pp!.Options).ThenInclude(o => o.Tiers);

        if (!string.IsNullOrWhiteSpace(request.Sku))
        {
            var sku = request.Sku!.Trim().ToUpperInvariant();
            return await products.FirstOrDefaultAsync(p => p.Sku != null && p.Sku.ToUpper() == sku, cancellationToken);
        }

        return await products.FirstOrDefaultAsync(p => p.Id == request.ProductId, cancellationToken);
    }

    /// <summary>
    /// Computes the price delta for numeric options with clamping, stepping, and tier evaluation.
    /// </summary>
    private static (decimal Delta, string ChosenDescription) HandleNumber(OptionDefinition option, QuotePrice.Selection selection)
    {
        if (selection.NumericValue is null)
        {
            throw new InvalidOperationException($"Selection for option '{option.Name}' must include a numeric value.");
        }

        var requested = selection.NumericValue.Value;

        var clamped = option.Min.HasValue ? Math.Max(requested, option.Min.Value) : requested;
        clamped = option.Max.HasValue ? Math.Min(clamped, option.Max.Value) : clamped;

        if (option.Step is > 0)
        {
            var step = option.Step.Value;
            clamped = Math.Round(clamped / step, MidpointRounding.AwayFromZero) * step;
            if (option.Min.HasValue)
            {
                clamped = Math.Max(clamped, option.Min.Value);
            }
            if (option.Max.HasValue)
            {
                clamped = Math.Min(clamped, option.Max.Value);
            }
        }

        var applicableTier = option.Tiers
            .Where(t => t.DeletedOn == null && clamped >= t.FromInclusive && (t.ToInclusive == null || clamped <= t.ToInclusive.Value))
            .OrderByDescending(t => t.FromInclusive)
            .FirstOrDefault();

        var rate = applicableTier?.UnitRate ?? option.PricePerUnit ?? 0m;
        var flat = applicableTier?.FlatDelta ?? 0m;

        var chosenDescription = option.Unit is { Length: > 0 }
            ? $"{clamped:0.##} {option.Unit}"
            : clamped.ToString("0.##");

        return ((rate * clamped) + flat, chosenDescription);
    }

    private enum BreakdownKind
    {
        Fixed,
        Percent
    }

    private sealed class SelectionBreakdown
    {
        private SelectionBreakdown(
            string option,
            string chosen,
            BreakdownKind kind,
            OptionDefinition optionDefinition,
            OptionValue? optionValue,
            decimal value,
            decimal percentValue)
        {
            Option = option;
            Chosen = chosen;
            Kind = kind;
            OptionDefinition = optionDefinition;
            OptionValue = optionValue;
            Value = value;
            PercentValue = percentValue;
        }

        public string Option { get; }

        public string Chosen { get; }

        public BreakdownKind Kind { get; }

        public OptionDefinition OptionDefinition { get; }

        public OptionValue? OptionValue { get; }

        public decimal Value { get; set; }

        public decimal PercentValue { get; }

        public static SelectionBreakdown Fixed(string option, string chosen, decimal value) =>
            new(option, chosen, BreakdownKind.Fixed, null!, null, value, 0m);

        public static SelectionBreakdown Percent(OptionDefinition option, OptionValue value, string chosen, decimal percent) =>
            new(option.Name, chosen, BreakdownKind.Percent, option, value, 0m, percent);
    }
}