using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Security.Cryptography;
using System.Text;
using Domain.Entities.Members;
using Domain.Entities.Store.ValueObject;

namespace Domain.Entities.Store;

/// <summary>
/// 쿠폰 코드 풀의 개별 코드. Code(평문) + CodeHash(SHA-256 hex) 동시 저장.
/// 조회/UNIQUE는 CodeHash, 사용자 표시는 Code.
/// 상태 머신: Available -> Reserved (결제 진행) -> Issued (결제 완료, 회원 보관함) -> Used (실제 사용).
/// </summary>
public class CouponCode
{
    [ForeignKey(nameof(CouponID))]
    public virtual Coupon? Coupon { get; private set; }

    [ForeignKey(nameof(IssuedToMemberID))]
    public virtual Member? IssuedToMember { get; private set; }

    [Key]
    public int ID { get; private set; }

    public int CouponID { get; private set; }

    /// <summary>실제 사용자에게 노출되는 코드 평문 (예: "ABCD-1234-EFGH-5678").</summary>
    public string Code { get; private set; } = default!;

    /// <summary>SHA-256 hex 해시 (대문자, 64자). UNIQUE 인덱스 대상.</summary>
    public string CodeHash { get; private set; } = default!;

    public CouponCodeStatus Status { get; private set; } = CouponCodeStatus.Available;

    public int? IssuedToMemberID { get; private set; }

    public DateTime? IssuedAt { get; private set; }

    public DateTime? UsedAt { get; private set; }

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

    [Timestamp]
    public byte[] RowVersion { get; private set; } = default!;

    private CouponCode() { }

    public static CouponCode Create(int couponID, string code)
    {
        if (couponID <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(couponID));
        }

        if (string.IsNullOrWhiteSpace(code))
        {
            throw new ArgumentException("Code is required.", nameof(code));
        }

        if (code.Length > 100)
        {
            throw new ArgumentOutOfRangeException(nameof(code), "Code must be <= 100 chars.");
        }

        return new CouponCode
        {
            CouponID = couponID,
            Code = code,
            CodeHash = ComputeHash(code),
            Status = CouponCodeStatus.Available
        };
    }

    /// <summary>
    /// CSV import 전용. 외부 시스템에서 마이그레이션할 때 사용. Used 상태로 즉시 생성.
    /// IssuedAt/UsedAt 은 UTC 로 전달.
    /// </summary>
    public static CouponCode CreateUsedForImport(
        int couponID,
        string code,
        int memberID,
        DateTime issuedAtUtc,
        DateTime usedAtUtc
    ) {
        if (couponID <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(couponID));
        }

        if (memberID <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(memberID));
        }

        if (string.IsNullOrWhiteSpace(code))
        {
            throw new ArgumentException("Code is required.", nameof(code));
        }

        if (code.Length > 100)
        {
            throw new ArgumentOutOfRangeException(nameof(code), "Code must be <= 100 chars.");
        }

        if (issuedAtUtc > usedAtUtc)
        {
            throw new ArgumentException("IssuedAt must be <= UsedAt.", nameof(issuedAtUtc));
        }

        return new CouponCode
        {
            CouponID = couponID,
            Code = code,
            CodeHash = ComputeHash(code),
            Status = CouponCodeStatus.Used,
            IssuedToMemberID = memberID,
            IssuedAt = issuedAtUtc,
            UsedAt = usedAtUtc
        };
    }

    /// <summary>
    /// 결제 진행 중 사전 점유. Available -> Reserved.
    /// 호출 측에서 SQL UPDATE 조건 절(`WHERE Status=Available`)로 동시성 충돌 방지 권장.
    /// </summary>
    public void Reserve()
    {
        if (Status != CouponCodeStatus.Available)
        {
            throw new InvalidOperationException($"Cannot reserve from status {Status}.");
        }

        Status = CouponCodeStatus.Reserved;
    }

    /// <summary>결제 실패/취소 시 Reserved -> Available 복귀.</summary>
    public void ReleaseReservation()
    {
        if (Status != CouponCodeStatus.Reserved)
        {
            throw new InvalidOperationException($"Cannot release reservation from status {Status}.");
        }

        Status = CouponCodeStatus.Available;
    }

    /// <summary>결제 완료 시 Reserved -> Issued. 회원 보관함에 발급됨.</summary>
    public void Issue(int memberID)
    {
        if (memberID <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(memberID));
        }

        if (Status != CouponCodeStatus.Reserved)
        {
            throw new InvalidOperationException($"Cannot issue from status {Status}.");
        }

        Status = CouponCodeStatus.Issued;
        IssuedToMemberID = memberID;
        IssuedAt = DateTime.UtcNow;
    }

    /// <summary>사용자가 보관함에서 "사용" 클릭 시 Issued -> Used.</summary>
    public void MarkUsed()
    {
        if (Status != CouponCodeStatus.Issued)
        {
            throw new InvalidOperationException($"Cannot mark used from status {Status}.");
        }

        Status = CouponCodeStatus.Used;
        UsedAt = DateTime.UtcNow;
    }

    /// <summary>환불 시 Issued -> Available 재사용 가능. Used 상태에서는 환불 거부 정책.</summary>
    public void RestoreToAvailable()
    {
        if (Status == CouponCodeStatus.Used)
        {
            throw new InvalidOperationException("이미 사용된 쿠폰 코드는 환불 후 재사용 불가합니다.");
        }

        Status = CouponCodeStatus.Available;
        IssuedToMemberID = null;
        IssuedAt = null;
        UsedAt = null;
    }

    /// <summary>
    /// 관리자 일괄 만료. Available 또는 Issued 코드만 만료 가능.
    /// Issued 출발 시 IssuedToMemberID / IssuedAt 보존 (복귀 시 회원 정보 복원에 사용).
    /// Reserved (결제 진행 중) / Used (사용 완료) 코드는 정합성 보호를 위해 만료 거부.
    /// </summary>
    public void Expire()
    {
        if (Status != CouponCodeStatus.Available && Status != CouponCodeStatus.Issued)
        {
            throw new InvalidOperationException($"Cannot expire from status {Status}. (Available 또는 Issued 만 만료 가능)");
        }

        Status = CouponCodeStatus.Expired;
    }

    /// <summary>
    /// 만료 코드 복귀. Expired 에서만 호출 가능.
    /// UsedAt 이 있으면 거부 (이중 안전 — 실제로는 Used 가 만료된 적이 없어 항상 null 이어야 함).
    /// IssuedToMemberID 가 있으면 Issued 로, 없으면 Available 로 복귀.
    /// </summary>
    public void RestoreFromExpired()
    {
        if (Status != CouponCodeStatus.Expired)
        {
            throw new InvalidOperationException($"Cannot restore from status {Status}. (Expired 만 복귀 가능)");
        }

        if (UsedAt.HasValue)
        {
            throw new InvalidOperationException("이미 사용된 쿠폰 코드는 복귀할 수 없습니다.");
        }

        Status = IssuedToMemberID.HasValue ? CouponCodeStatus.Issued : CouponCodeStatus.Available;
    }

    private static string ComputeHash(string code)
    {
        var bytes = Encoding.UTF8.GetBytes(code);
        var hash = SHA256.HashData(bytes);
        return Convert.ToHexString(hash);
    }
}