using System.Text.Json.Serialization;
using Microsoft.EntityFrameworkCore;
using YesChef.Api.Auth;
using YesChef.Api.Data;
using YesChef.Api.Entities;

namespace YesChef.Api.Features.Units;

public static class UnitEndpoints
{
    /// <summary>Discriminator so the client can route subsequent PUT/DELETE
    /// calls to the right code path. Global units cannot be edited.</summary>
    [JsonConverter(typeof(JsonStringEnumConverter<UnitKind>))]
    public enum UnitKind { Global, Family }

    public record UnitDto(
        int Id,
        UnitKind Kind,
        string? Code,
        string SingularName,
        string PluralName,
        string Abbreviation,
        UnitCategory Category,
        bool IsBase,
        int SortOrder);

    public record CreateUnitRequest(
        string SingularName,
        string PluralName,
        string Abbreviation,
        UnitCategory Category,
        int SortOrder = 100);

    public record UpdateUnitRequest(
        string SingularName,
        string PluralName,
        string Abbreviation,
        UnitCategory Category,
        int SortOrder);

    public static RouteGroupBuilder MapUnitEndpoints(this RouteGroupBuilder group)
    {
        // Effective catalog: global ∪ this family's customs. Client caches.
        group.MapGet("/", async (YesChefDb db, HttpContext http) =>
        {
            var familyId = http.User.GetFamilyId();

            var globalRows = await db.UnitsOfMeasure.AsNoTracking()
                .OrderBy(u => u.SortOrder).ThenBy(u => u.SingularName)
                .ToListAsync();
            var familyRows = await db.FamilyUnitsOfMeasure.AsNoTracking()
                .Where(u => u.FamilyId == familyId)
                .OrderBy(u => u.SortOrder).ThenBy(u => u.SingularName)
                .ToListAsync();

            var dtos = globalRows.Select(u => new UnitDto(
                    u.Id, UnitKind.Global, u.Code, u.SingularName, u.PluralName,
                    u.Abbreviation, u.Category, u.IsBase, u.SortOrder))
                .Concat(familyRows.Select(u => new UnitDto(
                    u.Id, UnitKind.Family, null, u.SingularName, u.PluralName,
                    u.Abbreviation, u.Category, IsBase: false, u.SortOrder)));

            return Results.Ok(dtos);
        });

        group.MapPost("/", async (CreateUnitRequest request, YesChefDb db, HttpContext http) =>
        {
            var familyId = http.User.GetFamilyId();
            if (ValidateNames(request.SingularName, request.PluralName, request.Abbreviation) is { } badRequest)
                return badRequest;

            var singular = request.SingularName.Trim();
            var plural = request.PluralName.Trim();
            var abbrev = request.Abbreviation.Trim();

            if (await AbbreviationCollidesAsync(db, familyId, abbrev, excludeFamilyUnitId: null))
                return Results.Conflict(new { error = $"A unit with abbreviation \"{abbrev}\" already exists." });

            var unit = new FamilyUnitOfMeasure
            {
                FamilyId = familyId,
                SingularName = singular,
                PluralName = plural,
                Abbreviation = abbrev,
                Category = request.Category,
                SortOrder = request.SortOrder,
            };
            db.FamilyUnitsOfMeasure.Add(unit);
            await db.SaveChangesAsync();

            return Results.Created($"/api/units/family/{unit.Id}", ToDto(unit));
        });

        group.MapPut("/family/{id:int}", async (int id, UpdateUnitRequest request, YesChefDb db, HttpContext http) =>
        {
            var familyId = http.User.GetFamilyId();
            var unit = await db.FamilyUnitsOfMeasure.FirstOrDefaultAsync(u => u.Id == id && u.FamilyId == familyId);
            if (unit is null) return Results.NotFound();

            if (ValidateNames(request.SingularName, request.PluralName, request.Abbreviation) is { } badRequest)
                return badRequest;

            var abbrev = request.Abbreviation.Trim();
            if (!string.Equals(abbrev, unit.Abbreviation, StringComparison.Ordinal) &&
                await AbbreviationCollidesAsync(db, familyId, abbrev, excludeFamilyUnitId: id))
                return Results.Conflict(new { error = $"A unit with abbreviation \"{abbrev}\" already exists." });

            unit.SingularName = request.SingularName.Trim();
            unit.PluralName = request.PluralName.Trim();
            unit.Abbreviation = abbrev;
            unit.Category = request.Category;
            unit.SortOrder = request.SortOrder;
            await db.SaveChangesAsync();

            return Results.Ok(ToDto(unit));
        });

        group.MapDelete("/family/{id:int}", async (int id, YesChefDb db, HttpContext http) =>
        {
            var familyId = http.User.GetFamilyId();
            var unit = await db.FamilyUnitsOfMeasure.FirstOrDefaultAsync(u => u.Id == id && u.FamilyId == familyId);
            if (unit is null) return Results.NotFound();

            // Block deletion when any recipe ingredient or shopping list item
            // still references the unit.
            var inUseByRecipe = await db.RecipeIngredients.AnyAsync(i => i.FamilyUnitOfMeasureId == id);
            if (inUseByRecipe) return Results.Conflict(new { error = "Unit is in use by one or more recipes." });
            var inUseByList = await db.ShoppingListItems.AnyAsync(i => i.FamilyUnitOfMeasureId == id);
            if (inUseByList) return Results.Conflict(new { error = "Unit is in use by one or more shopping lists." });

            db.FamilyUnitsOfMeasure.Remove(unit);
            await db.SaveChangesAsync();
            return Results.NoContent();
        });

        return group;
    }

    private static IResult? ValidateNames(string singular, string plural, string abbreviation)
    {
        if (string.IsNullOrWhiteSpace(singular)) return Results.BadRequest(new { error = "Singular name is required." });
        if (string.IsNullOrWhiteSpace(plural)) return Results.BadRequest(new { error = "Plural name is required." });
        if (string.IsNullOrWhiteSpace(abbreviation)) return Results.BadRequest(new { error = "Abbreviation is required." });
        return null;
    }

    private static async Task<bool> AbbreviationCollidesAsync(
        YesChefDb db, int familyId, string abbreviation, int? excludeFamilyUnitId)
    {
        // Effective uniqueness spans the global catalog AND this family's
        // customs. DB indexes guard each table individually; this check
        // catches cross-table collisions before they get to the user.
        if (await db.UnitsOfMeasure.AnyAsync(u => u.Abbreviation == abbreviation))
            return true;
        return await db.FamilyUnitsOfMeasure.AnyAsync(u =>
            u.FamilyId == familyId &&
            u.Abbreviation == abbreviation &&
            (excludeFamilyUnitId == null || u.Id != excludeFamilyUnitId));
    }

    private static UnitDto ToDto(FamilyUnitOfMeasure u) => new(
        u.Id, UnitKind.Family, Code: null, u.SingularName, u.PluralName,
        u.Abbreviation, u.Category, IsBase: false, u.SortOrder);
}