using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Text.RegularExpressions;

namespace Lagerbestand.Models;

/// <summary>
/// Represents a physical storage location in the warehouse.
/// Storage locations are identified by a 4-digit code in ABCD format:
/// - A: Gebäude (1=Werkstatt mit 3 Reihen, 2=Lager mit 5 Reihen)
/// - B: Regalreihe (Werkstatt: 1-3, Lager: 1-5)
/// - C: Seite/Ebene (1=links oben, 2=links unten, 3=rechts oben, 4=rechts unten)
/// - D: Platz längs (1-9)
/// Example: 2235 = Lager, Reihe 2, rechts oben, Platz 5
/// </summary>
public class StorageLocation
{
    /// <summary>
    /// Regex pattern for valid location codes: ABCD format
    /// A = 1-2 (Gebäude), B = 1-5 (Reihe), C = 1-4 (Seite/Ebene), D = 1-9 (Platz)
    /// </summary>
    public const string LocationCodePattern = @"^[12][1-5][1-4][1-9]$";

    /// <summary>
    /// Minimum row number
    /// </summary>
    public const int MinRow = 1;

    /// <summary>
    /// Maximum row number (Lager, Gebäude 2)
    /// </summary>
    public const int MaxRow = 5;

    /// <summary>
    /// Maximum row number for Werkstatt (Gebäude 1)
    /// </summary>
    public const int MaxRowWerkstatt = 3;

    /// <summary>
    /// Maximum row number for Lager (Gebäude 2)
    /// </summary>
    public const int MaxRowLager = 5;

    /// <summary>
    /// Minimum slot number (längs)
    /// </summary>
    public const int MinSlot = 1;

    /// <summary>
    /// Maximum slot number (längs)
    /// </summary>
    public const int MaxSlot = 9;

    /// <summary>
    /// Number of positions per lengthwise slot (links/rechts × oben/unten)
    /// </summary>
    public const int PositionsPerSlot = 4;

    [Key]
    public Guid Id { get; set; } = Guid.NewGuid();

    /// <summary>
    /// Unique 4-digit location code in ABCD format (e.g., "2235").
    /// This is the primary human-readable identifier.
    /// </summary>
    [Required]
    [MaxLength(4)]
    [RegularExpression(LocationCodePattern, ErrorMessage = "Ungültiges Code-Format. Erwartet: ABCD (z.B. 2235)")]
    public string Code { get; set; } = string.Empty;

    /// <summary>
    /// Storage building (Werkstatt=1, Lager=2).
    /// Corresponds to position A in the location code.
    /// </summary>
    [Required]
    public AreaType Area { get; set; } = AreaType.Lager;

    /// <summary>
    /// Shelf row number within the building (Werkstatt: 1-3, Lager: 1-5).
    /// Corresponds to position B in the location code.
    /// </summary>
    [Required]
    [Range(MinRow, MaxRow, ErrorMessage = "Reihe muss zwischen 1 und 5 liegen.")]
    public int Row { get; set; } = 1;

    /// <summary>
    /// Position within the shelf slot: side (links/rechts) and level (oben/unten).
    /// Corresponds to position C in the location code.
    /// </summary>
    [Required]
    public ShelfPosition Position { get; set; } = ShelfPosition.LinksOben;

    /// <summary>
    /// Lengthwise slot number within the row (1-9).
    /// Corresponds to position D in the location code.
    /// </summary>
    [Required]
    [Range(MinSlot, MaxSlot, ErrorMessage = "Platz muss zwischen 1 und 9 liegen.")]
    public int SlotNumber { get; set; } = 1;

    /// <summary>
    /// Whether this location is currently occupied by a tire stack.
    /// </summary>
    public bool IsOccupied { get; set; }

    /// <summary>
    /// The ID of the tire stack currently stored at this location (if occupied).
    /// </summary>
    public Guid? TireStackId { get; set; }

    /// <summary>
    /// Navigation property to the tire stack at this location.
    /// </summary>
    [ForeignKey(nameof(TireStackId))]
    public TireStack? OccupiedTireStack { get; set; }

    /// <summary>
    /// When the current tire stack was placed at this location.
    /// </summary>
    public DateTime? OccupiedSince { get; set; }

    /// <summary>
    /// Optional notes about this location.
    /// </summary>
    [MaxLength(500)]
    public string? Notes { get; set; }

    /// <summary>
    /// Whether this location is available for new storage (not blocked).
    /// </summary>
    public bool IsAvailable { get; set; } = true;

    /// <summary>
    /// Whether this location is active in the system.
    /// </summary>
    public bool IsActive { get; set; } = true;

    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;

    public DateTime? UpdatedAt { get; set; }

    /// <summary>
    /// Navigation property for tire stacks stored at this location (legacy support).
    /// </summary>
    public ICollection<TireStack> TireStacks { get; set; } = new List<TireStack>();

    /// <summary>
    /// Display name showing the human-readable location.
    /// </summary>
    [NotMapped]
    public string DisplayName => $"{Area.GetDisplayName()}, Reihe {Row}, {Position.GetDisplayName()}, Platz {SlotNumber}";

    /// <summary>
    /// Short display for compact views.
    /// </summary>
    [NotMapped]
    public string ShortDisplay => $"{Area.GetDisplayName()} R{Row} {Position.GetShortName()} P{SlotNumber}";

    /// <summary>
    /// Full path description of the location.
    /// </summary>
    [NotMapped]
    public string FullPath => $"{Area.GetBuildingLabel()} / Reihe {Row} / {Position.GetDisplayName()} / Platz {SlotNumber}";

    /// <summary>
    /// Current occupancy count (number of stacks stored).
    /// </summary>
    [NotMapped]
    public int CurrentOccupancy => IsOccupied ? 1 : 0;

    /// <summary>
    /// Capacity is always 1 for the new system (one stack per location).
    /// </summary>
    [NotMapped]
    public int Capacity => 1;

    /// <summary>
    /// Generates the location code from the component parts.
    /// </summary>
    public void GenerateCode()
    {
        Code = $"{(int)Area}{Row}{(int)Position}{SlotNumber}";
    }

    /// <summary>
    /// Parses the location code and populates the Area, Row, Position, and SlotNumber properties.
    /// </summary>
    /// <returns>True if parsing was successful</returns>
    public bool ParseCode()
    {
        if (string.IsNullOrWhiteSpace(Code) || Code.Length != 4)
            return false;

        if (!Regex.IsMatch(Code, LocationCodePattern))
            return false;

        if (!AreaTypeExtensions.TryFromCode(Code[0], out var area))
            return false;

        if (!int.TryParse(Code[1].ToString(), out var row) || row < MinRow || row > area.GetMaxRow())
            return false;

        if (!ShelfPositionExtensions.TryFromCode(Code[2], out var position))
            return false;

        if (!int.TryParse(Code[3].ToString(), out var slot) || slot < MinSlot || slot > MaxSlot)
            return false;

        Area = area;
        Row = row;
        Position = position;
        SlotNumber = slot;
        return true;
    }

    /// <summary>
    /// Validates that the current Code matches the Area, Row, Position, and SlotNumber values.
    /// </summary>
    public bool ValidateCodeConsistency()
    {
        var expectedCode = $"{(int)Area}{Row}{(int)Position}{SlotNumber}";
        return Code == expectedCode;
    }

    /// <summary>
    /// Assigns a tire stack to this location.
    /// </summary>
    /// <param name="tireStackId">The ID of the tire stack to assign</param>
    /// <exception cref="InvalidOperationException">If location is already occupied</exception>
    public void AssignTireStack(Guid tireStackId)
    {
        if (IsOccupied)
            throw new InvalidOperationException($"Lagerplatz {Code} ist bereits belegt.");

        TireStackId = tireStackId;
        IsOccupied = true;
        OccupiedSince = DateTime.UtcNow;
        UpdatedAt = DateTime.UtcNow;
    }

    /// <summary>
    /// Clears the tire stack from this location.
    /// </summary>
    public void ClearLocation()
    {
        TireStackId = null;
        OccupiedTireStack = null;
        IsOccupied = false;
        OccupiedSince = null;
        UpdatedAt = DateTime.UtcNow;
    }
}