implemnet customer master used for both B2B and B2C.

Backend/ERPCore/Controllers/CustomersController.cs

@@ -0,0 +1,69 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Customers;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+/// <summary>Customer master endpoints for Phase 1 sales.</summary>
+[Route("api/v1/customers")]
+public sealed class CustomersController : ApiControllerBase
+{
+    private readonly ICustomerService _customers;
+
+    public CustomersController(ICustomerService customers) => _customers = customers;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<CustomerDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<CustomerDto>>> List(
+        [FromQuery] PageQuery query,
+        [FromQuery] EntityStatus? status,
+        [FromQuery] CustomerType? customerType,
+        CancellationToken ct)
+        => Ok(await _customers.ListAsync(query, status, customerType, ct));
+
+    [HttpGet("{customerId:int}")]
+    [ProducesResponseType(typeof(CustomerDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<CustomerDto>> GetById(int customerId, CancellationToken ct)
+    {
+        var result = await _customers.GetAsync(customerId, ct);
+        if (result is null) return NotFound();
+
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(CustomerDto), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<ActionResult<CustomerDto>> Create([FromBody] CreateCustomerRequest request, CancellationToken ct)
+    {
+        var result = await _customers.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/customers/{result.Value.CustomerId}", result.Value);
+    }
+
+    [HttpPut("{customerId:int}")]
+    [ProducesResponseType(typeof(CustomerDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<CustomerDto>> Update(int customerId, [FromBody] UpdateCustomerRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _customers.UpdateAsync(customerId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPatch("{customerId:int}/status")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> SetStatus(int customerId, [FromBody] UpdateCustomerStatusRequest request, CancellationToken ct)
+    {
+        await _customers.SetStatusAsync(customerId, request.Status, ct);
+        return NoContent();
+    }
+}

Backend/ERPCore/Domain/Entities/Customer.cs

@@ -0,0 +1,38 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+/// <summary>
+/// Customer master for both B2B and B2C sales.
+/// Phase 1 keeps this lean: identity, contact, tax, credit, and default warehouse.
+/// </summary>
+public class Customer
+{
+    public int CustomerId { get; set; }
+    public string CustomerCode { get; set; } = string.Empty;
+    public CustomerType CustomerType { get; set; } = CustomerType.B2C;
+
+    public string Name { get; set; } = string.Empty;
+    public string? DisplayName { get; set; }
+    public string? Phone { get; set; }
+    public string? Email { get; set; }
+
+    public string? AddressLine1 { get; set; }
+    public string? AddressLine2 { get; set; }
+    public string? City { get; set; }
+    public string? Country { get; set; }
+
+    public string? TaxRegistrationNo { get; set; }
+    public decimal CreditLimit { get; set; }
+    public int CreditDays { get; set; }
+
+    public int? DefaultWarehouseId { get; set; }
+    public Warehouse? DefaultWarehouse { get; set; }
+
+    public EntityStatus Status { get; set; } = EntityStatus.Active;
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>PostgreSQL xmin-backed optimistic concurrency token (ETag source).</summary>
+    public uint RowVersion { get; set; }
+}

Backend/ERPCore/Domain/Enums/CustomerType.cs

@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+public enum CustomerType
+{
+    B2B = 1,
+    B2C = 2,
+    WalkIn = 3
+}

Backend/ERPCore/Dtos/Customers/CustomerDtos.cs

@@ -0,0 +1,66 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Customers;
+
+/// <summary>Customer resource used by sales documents.</summary>
+public sealed record CustomerDto(
+    int CustomerId,
+    string CustomerCode,
+    CustomerType CustomerType,
+    string Name,
+    string? DisplayName,
+    string? Phone,
+    string? Email,
+    string? AddressLine1,
+    string? AddressLine2,
+    string? City,
+    string? Country,
+    string? TaxRegistrationNo,
+    decimal CreditLimit,
+    int CreditDays,
+    int? DefaultWarehouseId,
+    EntityStatus Status,
+    DateTime CreatedAt,
+    DateTime? UpdatedAt);
+
+public sealed class CreateCustomerRequest
+{
+    [Required, StringLength(50)] public string CustomerCode { get; set; } = string.Empty;
+    [Required, EnumDataType(typeof(CustomerType))] public CustomerType CustomerType { get; set; } = CustomerType.B2C;
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+    [StringLength(200)] public string? DisplayName { get; set; }
+    [StringLength(30)] public string? Phone { get; set; }
+    [StringLength(100)] public string? Email { get; set; }
+    [StringLength(250)] public string? AddressLine1 { get; set; }
+    [StringLength(250)] public string? AddressLine2 { get; set; }
+    [StringLength(100)] public string? City { get; set; }
+    [StringLength(100)] public string? Country { get; set; }
+    [StringLength(50)] public string? TaxRegistrationNo { get; set; }
+    [Range(0, double.MaxValue)] public decimal CreditLimit { get; set; }
+    [Range(0, int.MaxValue)] public int CreditDays { get; set; }
+    public int? DefaultWarehouseId { get; set; }
+}
+
+public sealed class UpdateCustomerRequest
+{
+    [Required, StringLength(50)] public string CustomerCode { get; set; } = string.Empty;
+    [Required, EnumDataType(typeof(CustomerType))] public CustomerType CustomerType { get; set; } = CustomerType.B2C;
+    [Required, StringLength(200)] public string Name { get; set; } = string.Empty;
+    [StringLength(200)] public string? DisplayName { get; set; }
+    [StringLength(30)] public string? Phone { get; set; }
+    [StringLength(100)] public string? Email { get; set; }
+    [StringLength(250)] public string? AddressLine1 { get; set; }
+    [StringLength(250)] public string? AddressLine2 { get; set; }
+    [StringLength(100)] public string? City { get; set; }
+    [StringLength(100)] public string? Country { get; set; }
+    [StringLength(50)] public string? TaxRegistrationNo { get; set; }
+    [Range(0, double.MaxValue)] public decimal CreditLimit { get; set; }
+    [Range(0, int.MaxValue)] public int CreditDays { get; set; }
+    public int? DefaultWarehouseId { get; set; }
+}
+
+public sealed class UpdateCustomerStatusRequest
+{
+    [Required, EnumDataType(typeof(EntityStatus))] public EntityStatus Status { get; set; }
+}

Backend/ERPCore/Infra/Persistence/Configurations/CustomerConfiguration.cs

@@ -0,0 +1,50 @@
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+public sealed class CustomerConfiguration : IEntityTypeConfiguration<Customer>
+{
+    public void Configure(EntityTypeBuilder<Customer> builder)
+    {
+        builder.ToTable("customers");
+        builder.HasKey(c => c.CustomerId);
+
+        builder.Property(c => c.CustomerCode).IsRequired().HasMaxLength(50);
+        builder.HasIndex(c => c.CustomerCode).IsUnique();
+
+        builder.Property(c => c.CustomerType)
+            .HasConversion<string>().HasMaxLength(20).IsRequired()
+            .HasDefaultValue(CustomerType.B2C);
+
+        builder.Property(c => c.Name).IsRequired().HasMaxLength(200);
+        builder.Property(c => c.DisplayName).HasMaxLength(200);
+        builder.Property(c => c.Phone).HasMaxLength(30);
+        builder.Property(c => c.Email).HasMaxLength(100);
+        builder.Property(c => c.AddressLine1).HasMaxLength(250);
+        builder.Property(c => c.AddressLine2).HasMaxLength(250);
+        builder.Property(c => c.City).HasMaxLength(100);
+        builder.Property(c => c.Country).HasMaxLength(100);
+        builder.Property(c => c.TaxRegistrationNo).HasMaxLength(50);
+
+        builder.Property(c => c.CreditLimit).HasPrecision(18, 4);
+        builder.Property(c => c.CreditDays).IsRequired();
+
+        builder.HasOne(c => c.DefaultWarehouse)
+            .WithMany()
+            .HasForeignKey(c => c.DefaultWarehouseId)
+            .OnDelete(DeleteBehavior.SetNull);
+
+        builder.Property(c => c.Status)
+            .HasConversion<string>().HasMaxLength(20).IsRequired()
+            .HasDefaultValue(EntityStatus.Active);
+
+        builder.Property(c => c.CreatedAt).IsRequired();
+        builder.Property(c => c.RowVersion).IsRowVersion();
+
+        builder.HasIndex(c => c.Status);
+        builder.HasIndex(c => c.CustomerType);
+    }
+}

Backend/ERPCore/Infra/Persistence/ErpDbContext.cs

@@ -22,6 +22,7 @@ public class ErpDbContext : DbContext
     }
 
     // --- Master Data (docs/10 Part C.1) ---
+    public DbSet<Customer> Customers => Set<Customer>();
     public DbSet<Category> Categories => Set<Category>();
     public DbSet<SubCategory> SubCategories => Set<SubCategory>();
     public DbSet<Brand> Brands => Set<Brand>();

Backend/ERPCore/Program.cs

@@ -7,6 +7,7 @@ using ERPCore.Infra.UoW;
 using ERPCore.Repositories;
 using ERPCore.Repositories.Interfaces;
 using ERPCore.Services;
+using ERPCore.Services.Interfaces;
 using ERPCore.Services.Auth;
 using ERPCore.Services.Hrm;
 using ERPCore.Services.Interfaces;
@@ -62,6 +63,7 @@ builder.Services.AddScoped<IUnitOfWork, UnitOfWork>();
 builder.Services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
 
 // Master-data services (docs/11 §2)
+builder.Services.AddScoped<ICustomerService, CustomerService>();
 builder.Services.AddScoped<IItemService, ItemService>();
 builder.Services.AddScoped<IUomService, UomService>();
 builder.Services.AddScoped<ICategoryService, CategoryService>();

Backend/ERPCore/Services/CustomerService.cs

@@ -0,0 +1,168 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Customers;
+using ERPCore.Infra.UoW;
+using ERPCore.Repositories.Interfaces;
+using ERPCore.Services.Interfaces;
+using ERPCore.System.Errors;
+using Microsoft.EntityFrameworkCore;
+
+namespace ERPCore.Services;
+
+public sealed class CustomerService : ICustomerService
+{
+    private readonly IRepository<Customer> _customers;
+    private readonly IRepository<Warehouse> _warehouses;
+    private readonly IUnitOfWork _uow;
+
+    public CustomerService(IRepository<Customer> customers, IRepository<Warehouse> warehouses, IUnitOfWork uow)
+    {
+        _customers = customers;
+        _warehouses = warehouses;
+        _uow = uow;
+    }
+
+    public async Task<PagedResponse<CustomerDto>> ListAsync(PageQuery query, EntityStatus? status, CustomerType? customerType, CancellationToken ct = default)
+    {
+        var q = _customers.Query().AsNoTracking();
+        if (!string.IsNullOrWhiteSpace(query.Q))
+        {
+            var term = query.Q.Trim();
+            q = q.Where(c => EF.Functions.ILike(c.Name, $"%{term}%")
+                             || EF.Functions.ILike(c.CustomerCode, $"%{term}%")
+                             || (c.DisplayName != null && EF.Functions.ILike(c.DisplayName, $"%{term}%")));
+        }
+        if (status is not null) q = q.Where(c => c.Status == status);
+        if (customerType is not null) q = q.Where(c => c.CustomerType == customerType);
+
+        var total = await q.CountAsync(ct);
+        var rows = await q.OrderBy(c => c.Name)
+            .Skip(query.Skip).Take(query.PageSize)
+            .Select(c => new CustomerDto(
+                c.CustomerId, c.CustomerCode, c.CustomerType, c.Name, c.DisplayName, c.Phone, c.Email,
+                c.AddressLine1, c.AddressLine2, c.City, c.Country, c.TaxRegistrationNo,
+                c.CreditLimit, c.CreditDays, c.DefaultWarehouseId, c.Status, c.CreatedAt, c.UpdatedAt))
+            .ToListAsync(ct);
+
+        return PagedResponse<CustomerDto>.Create(rows, query.Page, query.PageSize, total);
+    }
+
+    public async Task<ETagged<CustomerDto>?> GetAsync(int customerId, CancellationToken ct = default)
+    {
+        var customer = await _customers.Query().AsNoTracking()
+            .FirstOrDefaultAsync(c => c.CustomerId == customerId, ct);
+        return customer is null ? null : new ETagged<CustomerDto>(Map(customer), customer.RowVersion);
+    }
+
+    public async Task<ETagged<CustomerDto>> CreateAsync(CreateCustomerRequest request, CancellationToken ct = default)
+    {
+        var code = request.CustomerCode.Trim();
+        var name = request.Name.Trim();
+
+        if (await _customers.Query().AnyAsync(c => c.CustomerCode.ToLower() == code.ToLower(), ct))
+            throw new ConflictException($"A customer code '{code}' already exists.");
+
+        if (!string.IsNullOrWhiteSpace(request.Email))
+        {
+            var email = request.Email.Trim();
+            if (await _customers.Query().AnyAsync(c => c.Email != null && c.Email.ToLower() == email.ToLower(), ct))
+                throw new ConflictException($"A customer with email '{email}' already exists.");
+        }
+
+        if (request.DefaultWarehouseId is not null)
+        {
+            var exists = await _warehouses.Query().AnyAsync(w => w.WarehouseId == request.DefaultWarehouseId, ct);
+            if (!exists) throw new NotFoundException($"Warehouse {request.DefaultWarehouseId} was not found.");
+        }
+
+        var customer = new Customer
+        {
+            CustomerCode = code,
+            CustomerType = request.CustomerType,
+            Name = name,
+            DisplayName = Normalize(request.DisplayName),
+            Phone = Normalize(request.Phone),
+            Email = Normalize(request.Email),
+            AddressLine1 = Normalize(request.AddressLine1),
+            AddressLine2 = Normalize(request.AddressLine2),
+            City = Normalize(request.City),
+            Country = Normalize(request.Country),
+            TaxRegistrationNo = Normalize(request.TaxRegistrationNo),
+            CreditLimit = request.CreditLimit,
+            CreditDays = request.CreditDays,
+            DefaultWarehouseId = request.DefaultWarehouseId,
+            Status = EntityStatus.Active,
+            CreatedAt = DateTime.UtcNow
+        };
+
+        await _customers.AddAsync(customer, ct);
+        await _uow.SaveChangesAsync(ct);
+
+        return new ETagged<CustomerDto>(Map(customer), customer.RowVersion);
+    }
+
+    public async Task<ETagged<CustomerDto>> UpdateAsync(int customerId, UpdateCustomerRequest request, uint expectedRowVersion, CancellationToken ct = default)
+    {
+        var customer = await _customers.GetByIdAsync(customerId, ct)
+            ?? throw new NotFoundException($"Customer {customerId} was not found.");
+
+        if (customer.RowVersion != expectedRowVersion)
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The customer was modified by another request.", 412);
+
+        var code = request.CustomerCode.Trim();
+        var name = request.Name.Trim();
+
+        if (!string.Equals(customer.CustomerCode, code, StringComparison.Ordinal)
+            && await _customers.Query().AnyAsync(c => c.CustomerCode.ToLower() == code.ToLower() && c.CustomerId != customerId, ct))
+            throw new ConflictException($"A customer code '{code}' already exists.");
+
+        if (!string.Equals(customer.Email, request.Email?.Trim(), StringComparison.OrdinalIgnoreCase)
+            && !string.IsNullOrWhiteSpace(request.Email)
+            && await _customers.Query().AnyAsync(c => c.Email != null && c.Email.ToLower() == request.Email!.Trim().ToLower() && c.CustomerId != customerId, ct))
+            throw new ConflictException($"A customer with email '{request.Email.Trim()}' already exists.");
+
+        if (request.DefaultWarehouseId is not null)
+        {
+            var exists = await _warehouses.Query().AnyAsync(w => w.WarehouseId == request.DefaultWarehouseId, ct);
+            if (!exists) throw new NotFoundException($"Warehouse {request.DefaultWarehouseId} was not found.");
+        }
+
+        customer.CustomerCode = code;
+        customer.CustomerType = request.CustomerType;
+        customer.Name = name;
+        customer.DisplayName = Normalize(request.DisplayName);
+        customer.Phone = Normalize(request.Phone);
+        customer.Email = Normalize(request.Email);
+        customer.AddressLine1 = Normalize(request.AddressLine1);
+        customer.AddressLine2 = Normalize(request.AddressLine2);
+        customer.City = Normalize(request.City);
+        customer.Country = Normalize(request.Country);
+        customer.TaxRegistrationNo = Normalize(request.TaxRegistrationNo);
+        customer.CreditLimit = request.CreditLimit;
+        customer.CreditDays = request.CreditDays;
+        customer.DefaultWarehouseId = request.DefaultWarehouseId;
+        customer.UpdatedAt = DateTime.UtcNow;
+
+        await _uow.SaveChangesAsync(ct);
+        return new ETagged<CustomerDto>(Map(customer), customer.RowVersion);
+    }
+
+    public async Task SetStatusAsync(int customerId, EntityStatus status, CancellationToken ct = default)
+    {
+        var customer = await _customers.GetByIdAsync(customerId, ct)
+            ?? throw new NotFoundException($"Customer {customerId} was not found.");
+
+        customer.Status = status;
+        customer.UpdatedAt = DateTime.UtcNow;
+        await _uow.SaveChangesAsync(ct);
+    }
+
+    private static CustomerDto Map(Customer c) => new(
+        c.CustomerId, c.CustomerCode, c.CustomerType, c.Name, c.DisplayName, c.Phone, c.Email,
+        c.AddressLine1, c.AddressLine2, c.City, c.Country, c.TaxRegistrationNo,
+        c.CreditLimit, c.CreditDays, c.DefaultWarehouseId, c.Status, c.CreatedAt, c.UpdatedAt);
+
+    private static string? Normalize(string? value) => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+}

Backend/ERPCore/Services/Interfaces/ICustomerService.cs

@@ -0,0 +1,15 @@
+using ERPCore.Common.Http;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Customers;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Services.Interfaces;
+
+public interface ICustomerService
+{
+    Task<PagedResponse<CustomerDto>> ListAsync(PageQuery query, EntityStatus? status, CustomerType? customerType, CancellationToken ct = default);
+    Task<ETagged<CustomerDto>?> GetAsync(int customerId, CancellationToken ct = default);
+    Task<ETagged<CustomerDto>> CreateAsync(CreateCustomerRequest request, CancellationToken ct = default);
+    Task<ETagged<CustomerDto>> UpdateAsync(int customerId, UpdateCustomerRequest request, uint expectedRowVersion, CancellationToken ct = default);
+    Task SetStatusAsync(int customerId, EntityStatus status, CancellationToken ct = default);
+}