Mix calculator

backend/app/api/mix_calculator.py

@@ -0,0 +1,95 @@
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.orm import Session
+
+from app.api.deps import AuthSession, require_client_module_access
+from app.db.session import get_db
+from app.schemas.mix_calculator import (
+    MixCalculatorOptionsRead,
+    MixCalculatorPreviewRead,
+    MixCalculatorSessionCreate,
+    MixCalculatorSessionRead,
+    MixCalculatorSessionSummaryRead,
+    MixCalculatorSessionUpdate,
+)
+from app.services.mix_calculator_service import (
+    build_mix_calculator_options,
+    calculate_mix_calculator_preview,
+    serialize_mix_calculator_session,
+    create_mix_calculator_session,
+    get_mix_calculator_session,
+    update_mix_calculator_session,
+    list_mix_calculator_sessions,
+    can_view_all_mix_calculator_sessions,
+)
+
+router = APIRouter(prefix="/api/mix-calculator", tags=["mix-calculator"])
+
+
+@router.get("/options", response_model=MixCalculatorOptionsRead)
+def mix_calculator_options(
+    session: AuthSession = Depends(require_client_module_access("mix_calculator")),
+    db: Session = Depends(get_db),
+):
+    return build_mix_calculator_options(db, tenant_id=session.tenant_id or "")
+
+
+@router.get("", response_model=list[MixCalculatorSessionSummaryRead])
+def mix_calculator_sessions(
+    session: AuthSession = Depends(require_client_module_access("mix_calculator")),
+    db: Session = Depends(get_db),
+):
+    return list_mix_calculator_sessions(db, auth_session=session)
+
+
+@router.post("/preview", response_model=MixCalculatorPreviewRead)
+def preview_mix_calculator_session(
+    payload: MixCalculatorSessionCreate,
+    session: AuthSession = Depends(require_client_module_access("mix_calculator", "edit")),
+    db: Session = Depends(get_db),
+):
+    try:
+        return calculate_mix_calculator_preview(db, tenant_id=session.tenant_id or "", payload=payload)
+    except ValueError as exc:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(exc)) from exc
+
+
+@router.post("", response_model=MixCalculatorSessionRead, status_code=status.HTTP_201_CREATED)
+def create_saved_mix_calculator_session(
+    payload: MixCalculatorSessionCreate,
+    session: AuthSession = Depends(require_client_module_access("mix_calculator", "edit")),
+    db: Session = Depends(get_db),
+):
+    try:
+        return create_mix_calculator_session(db, auth_session=session, payload=payload)
+    except ValueError as exc:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(exc)) from exc
+
+
+@router.get("/{session_id}", response_model=MixCalculatorSessionRead)
+def read_mix_calculator_session(
+    session_id: int,
+    session: AuthSession = Depends(require_client_module_access("mix_calculator")),
+    db: Session = Depends(get_db),
+):
+    session_record = get_mix_calculator_session(db, auth_session=session, session_id=session_id)
+    if session_record is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Mix calculator session not found")
+    return serialize_mix_calculator_session(session_record, session)
+
+
+@router.patch("/{session_id}", response_model=MixCalculatorSessionRead)
+def patch_mix_calculator_session(
+    session_id: int,
+    payload: MixCalculatorSessionUpdate,
+    session: AuthSession = Depends(require_client_module_access("mix_calculator", "edit")),
+    db: Session = Depends(get_db),
+):
+    session_record = get_mix_calculator_session(db, auth_session=session, session_id=session_id)
+    if session_record is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Mix calculator session not found")
+    if not can_view_all_mix_calculator_sessions(session) and session_record.prepared_by_user_id != session.user_id:
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="You can only edit your own mix calculator sessions")
+    try:
+        return update_mix_calculator_session(db, auth_session=session, session_record=session_record, payload=payload)
+    except ValueError as exc:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(exc)) from exc

backend/app/db/migrations.py

@@ -15,6 +15,8 @@ TENANT_TABLES = {
     "raw_material_price_versions": None,
     "mixes": None,
     "mix_ingredients": None,
+    "mix_calculator_sessions": None,
+    "mix_calculator_session_lines": None,
     "products": None,
     "scenarios": None,
     "costing_results": None,
@@ -230,6 +232,37 @@ def sync_tenant_ids(engine: Engine) -> dict[str, int]:
                 """
                 ),
             ),
+            (
+                "mix_calculator_sessions",
+                text(
+                """
+                UPDATE mix_calculator_sessions
+                SET tenant_id = COALESCE(
+                    (
+                        SELECT products.tenant_id
+                        FROM products
+                        WHERE products.id = mix_calculator_sessions.product_id
+                    ),
+                    :default_tenant
+                )
+                WHERE tenant_id IS NULL OR tenant_id = '' OR tenant_id = 'default'
+                """
+                ),
+            ),
+            (
+                "mix_calculator_session_lines",
+                text(
+                """
+                UPDATE mix_calculator_session_lines
+                SET tenant_id = (
+                    SELECT mix_calculator_sessions.tenant_id
+                    FROM mix_calculator_sessions
+                    WHERE mix_calculator_sessions.id = mix_calculator_session_lines.session_id
+                )
+                WHERE tenant_id IS NULL OR tenant_id = '' OR tenant_id = 'default'
+                """
+                ),
+            ),
             (
                 "scenarios",
                 text(

backend/app/main.py

@@ -14,6 +14,7 @@ import uvicorn
 
 from app.api.auth import router as auth_router
 from app.api.client_access import router as client_access_router
+from app.api.mix_calculator import router as mix_calculator_router
 from app.api.mixes import router as mixes_router
 from app.api.powerbi import router as powerbi_router
 from app.api.products import router as products_router
@@ -74,6 +75,7 @@ app.include_router(auth_router)
 app.include_router(client_access_router)
 app.include_router(raw_materials_router)
 app.include_router(mixes_router)
+app.include_router(mix_calculator_router)
 app.include_router(products_router)
 app.include_router(scenarios_router)
 app.include_router(powerbi_router)
@@ -95,6 +97,7 @@ def root():
             "admin_login": "/api/auth/admin/login",
             "raw_materials": "/api/raw-materials",
             "mixes": "/api/mixes",
+            "mix_calculator": "/api/mix-calculator",
             "products": "/api/products",
             "scenarios": "/api/scenarios",
             "client_access": "/api/client-access",

backend/app/models/__init__.py

@@ -1,5 +1,6 @@
 from app.models.assumption import FreightCostRule, PackagingCostRule, ProcessCostRule
 from app.models.client_access import ClientAccessAuditEvent, ClientAccount, ClientFeatureAccess, ClientUser, ClientUserModulePermission
+from app.models.mix_calculator import MixCalculatorSession, MixCalculatorSessionLine
 from app.models.mix import Mix, MixIngredient
 from app.models.product import Product
 from app.models.raw_material import RawMaterial, RawMaterialPriceVersion
@@ -14,6 +15,8 @@ __all__ = [
     "CostingResult",
     "FreightCostRule",
     "Mix",
+    "MixCalculatorSession",
+    "MixCalculatorSessionLine",
     "MixIngredient",
     "PackagingCostRule",
     "ProcessCostRule",

backend/app/models/mix_calculator.py

@@ -0,0 +1,57 @@
+from __future__ import annotations
+
+from datetime import date, datetime
+
+from sqlalchemy import Date, DateTime, Float, ForeignKey, Integer, String, Text, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.db.session import Base
+
+
+class MixCalculatorSession(Base):
+    __tablename__ = "mix_calculator_sessions"
+    __table_args__ = (UniqueConstraint("tenant_id", "session_number", name="uq_mix_calculator_session_number"),)
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    tenant_id: Mapped[str] = mapped_column(String(64), default="default", index=True)
+    session_number: Mapped[str] = mapped_column(String(32), index=True)
+    client_name: Mapped[str] = mapped_column(String(255), index=True)
+    product_id: Mapped[int] = mapped_column(ForeignKey("products.id"), index=True)
+    product_name: Mapped[str] = mapped_column(String(255))
+    mix_id: Mapped[int] = mapped_column(ForeignKey("mixes.id"), index=True)
+    mix_name: Mapped[str] = mapped_column(String(255))
+    mix_date: Mapped[date] = mapped_column(Date, index=True)
+    batch_size_kg: Mapped[float] = mapped_column(Float)
+    total_bags: Mapped[float] = mapped_column(Float)
+    total_kg: Mapped[float] = mapped_column(Float)
+    product_unit_of_measure: Mapped[str] = mapped_column(String(64))
+    product_unit_size_kg: Mapped[float] = mapped_column(Float)
+    prepared_by_user_id: Mapped[int | None] = mapped_column(ForeignKey("client_users.id"), nullable=True, index=True)
+    prepared_by_name: Mapped[str] = mapped_column(String(255))
+    created_by: Mapped[str] = mapped_column(String(255))
+    status: Mapped[str] = mapped_column(String(32), default="saved")
+    notes: Mapped[str | None] = mapped_column(Text, nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow)
+    updated_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+
+    lines: Mapped[list["MixCalculatorSessionLine"]] = relationship(
+        back_populates="session",
+        cascade="all, delete-orphan",
+        order_by="MixCalculatorSessionLine.sort_order",
+    )
+
+
+class MixCalculatorSessionLine(Base):
+    __tablename__ = "mix_calculator_session_lines"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    tenant_id: Mapped[str] = mapped_column(String(64), default="default", index=True)
+    session_id: Mapped[int] = mapped_column(ForeignKey("mix_calculator_sessions.id"), index=True)
+    raw_material_id: Mapped[int | None] = mapped_column(nullable=True)
+    raw_material_name: Mapped[str] = mapped_column(String(255))
+    required_kg: Mapped[float] = mapped_column(Float)
+    mix_percentage: Mapped[float] = mapped_column(Float)
+    unit: Mapped[str] = mapped_column(String(64))
+    sort_order: Mapped[int] = mapped_column(Integer, default=0)
+
+    session: Mapped[MixCalculatorSession] = relationship(back_populates="lines")

backend/app/schemas/mix_calculator.py

@@ -0,0 +1,103 @@
+from datetime import date, datetime
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class MixCalculatorProductOptionRead(BaseModel):
+    product_id: int
+    client_name: str
+    product_name: str
+    mix_id: int
+    mix_name: str
+    unit_of_measure: str
+    unit_size_kg: float
+    mix_total_kg: float
+
+
+class MixCalculatorOptionsRead(BaseModel):
+    clients: list[str]
+    products: list[MixCalculatorProductOptionRead]
+
+
+class MixCalculatorSessionLineRead(BaseModel):
+    id: int | None = None
+    raw_material_id: int | None
+    raw_material_name: str
+    required_kg: float
+    mix_percentage: float
+    unit: str
+    sort_order: int
+
+
+class MixCalculatorSessionBase(BaseModel):
+    mix_date: date
+    client_name: str
+    product_id: int
+    batch_size_kg: float = Field(gt=0)
+    prepared_by_name: str = Field(min_length=1, max_length=255)
+    status: str = "saved"
+    notes: str | None = None
+
+
+class MixCalculatorSessionCreate(MixCalculatorSessionBase):
+    pass
+
+
+class MixCalculatorSessionUpdate(BaseModel):
+    mix_date: date | None = None
+    client_name: str | None = None
+    product_id: int | None = None
+    batch_size_kg: float | None = Field(default=None, gt=0)
+    prepared_by_name: str | None = Field(default=None, min_length=1, max_length=255)
+    status: str | None = None
+    notes: str | None = None
+
+
+class MixCalculatorPreviewRead(BaseModel):
+    client_name: str
+    product_id: int
+    product_name: str
+    mix_id: int
+    mix_name: str
+    mix_date: date
+    batch_size_kg: float
+    total_bags: float
+    total_kg: float
+    product_unit_of_measure: str
+    product_unit_size_kg: float
+    prepared_by_name: str
+    status: str
+    notes: str | None
+    warnings: list[str]
+    lines: list[MixCalculatorSessionLineRead]
+
+
+class MixCalculatorSessionSummaryRead(BaseModel):
+    id: int
+    tenant_id: str
+    session_number: str
+    client_name: str
+    product_id: int
+    product_name: str
+    mix_id: int
+    mix_name: str
+    mix_date: date
+    batch_size_kg: float
+    total_bags: float
+    total_kg: float
+    product_unit_of_measure: str
+    product_unit_size_kg: float
+    prepared_by_user_id: int | None
+    prepared_by_name: str
+    created_by: str
+    status: str
+    notes: str | None
+    created_at: datetime
+    updated_at: datetime
+    warnings: list[str]
+    is_owner: bool
+    model_config = ConfigDict(from_attributes=True)
+
+
+class MixCalculatorSessionRead(MixCalculatorSessionSummaryRead):
+    lines: list[MixCalculatorSessionLineRead]

backend/app/seed.py

@@ -72,8 +72,8 @@ def seed_client_access(db):
     )
 
     enabled_feature_map = {
-        "hunter-premium-produce": {"dashboard", "raw_materials", "mix_master", "products", "scenarios", "powerbi_export", "client_access"},
-        "loft-grains": {"dashboard", "products", "powerbi_export"},
+        "hunter-premium-produce": {"dashboard", "raw_materials", "mix_master", "mix_calculator", "products", "scenarios", "powerbi_export", "client_access"},
+        "loft-grains": {"dashboard", "mix_calculator", "products", "powerbi_export"},
     }
 
     for client in (specialty, loft):

backend/app/services/client_access_service.py

@@ -17,6 +17,7 @@ MODULE_CATALOG = (
     ("dashboard", "Dashboard", "workspace", "Top-level operational dashboard"),
     ("raw_materials", "Raw Materials", "costing", "Maintain live material costs and versions"),
     ("mix_master", "Mix Master", "costing", "Create and maintain mix worksheets"),
+    ("mix_calculator", "Mix Calculator", "production", "Create and review client-specific mix calculation sessions"),
     ("products", "Products", "pricing", "Review finished product pricing"),
     ("scenarios", "Scenarios", "planning", "Run scenario overrides and comparisons"),
     ("powerbi_export", "Power BI Export", "reporting", "Expose client access data to BI consumers"),
@@ -43,6 +44,7 @@ def client_access_query() -> Select[tuple[ClientAccount]]:
 
 def list_client_accounts(db: Session) -> list[ClientAccount]:
     ensure_client_user_module_permissions(db)
+    ensure_client_feature_access(db)
     return db.scalars(client_access_query()).all()
 
 
@@ -50,9 +52,19 @@ def get_client_user_by_email(db: Session, *, email: str, tenant_id: str | None =
     statement = select(ClientUser).where(ClientUser.email == email)
     if tenant_id:
         statement = statement.where(ClientUser.tenant_id == tenant_id)
-    return db.scalar(
+    user = db.scalar(
         statement.options(selectinload(ClientUser.module_permissions)).order_by(ClientUser.id.desc())
     )
+    if user is None:
+        return None
+
+    if ensure_user_module_permissions(db, user):
+        db.commit()
+        return db.scalar(
+            statement.options(selectinload(ClientUser.module_permissions)).order_by(ClientUser.id.desc())
+        )
+
+    return user
 
 
 def module_access_map(user: ClientUser) -> dict[str, str]:
@@ -66,13 +78,15 @@ def has_access_level(access_level: str | None, minimum_level: str) -> bool:
 def default_access_level_for_role(role: str, module_key: str) -> str:
     normalized = role.strip().lower()
     if normalized == "superadmin":
-        return "manage" if module_key == "client_access" else "edit"
+        return "manage" if module_key in {"client_access", "mix_calculator"} else "edit"
     if normalized == "admin":
+        if module_key == "mix_calculator":
+            return "manage"
         return "edit" if module_key != "client_access" else "none"
     if normalized == "operator":
-        return "edit" if module_key in {"dashboard", "raw_materials", "mix_master", "products", "scenarios"} else "none"
+        return "edit" if module_key in {"dashboard", "raw_materials", "mix_master", "mix_calculator", "products", "scenarios"} else "none"
     if normalized == "viewer":
-        return "view" if module_key in {"dashboard", "products", "powerbi_export"} else "none"
+        return "view" if module_key in {"dashboard", "mix_calculator", "products", "powerbi_export"} else "none"
     return "none"
 
 
@@ -106,6 +120,45 @@ def ensure_client_user_module_permissions(db: Session) -> None:
         db.commit()
 
 
+def ensure_client_feature_access(db: Session) -> None:
+    clients = db.scalars(
+        select(ClientAccount).options(
+            selectinload(ClientAccount.users).selectinload(ClientUser.module_permissions),
+            selectinload(ClientAccount.features),
+        )
+    ).all()
+    changed = False
+
+    for client in clients:
+        existing_feature_keys = {feature.feature_key for feature in client.features}
+        permission_levels: dict[str, str] = {}
+
+        for user in client.users:
+            for permission in user.module_permissions:
+                current_level = permission_levels.get(permission.module_key, "none")
+                if ACCESS_LEVEL_ORDER.get(permission.access_level, 0) > ACCESS_LEVEL_ORDER.get(current_level, 0):
+                    permission_levels[permission.module_key] = permission.access_level
+
+        for feature_key, feature_name, feature_group, description in MODULE_CATALOG:
+            if feature_key in existing_feature_keys:
+                continue
+            db.add(
+                ClientFeatureAccess(
+                    tenant_id=client.tenant_id,
+                    client_account_id=client.id,
+                    feature_key=feature_key,
+                    feature_name=feature_name,
+                    feature_group=feature_group,
+                    description=description,
+                    enabled=has_access_level(permission_levels.get(feature_key), "view"),
+                )
+            )
+            changed = True
+
+    if changed:
+        db.commit()
+
+
 def serialize_client_user(user: ClientUser) -> dict:
     return {
         "id": user.id,

backend/app/services/costing_engine.py

@@ -177,7 +177,7 @@ def _apply_margin(cost: float, margin: float | None) -> float | None:
     return round(cost / (1 - margin), 4)
 
 
-def _extract_unit_quantity_kg(unit_of_measure: str) -> float:
+def extract_unit_quantity_kg(unit_of_measure: str) -> float:
     normalized = unit_of_measure.strip().lower()
     if normalized == "tonne":
         return 1000.0
@@ -199,7 +199,7 @@ def calculate_product_cost(db: Session, product_id: int, overrides: dict | None
 
     mix_result = calculate_mix_cost(db, product.mix_id, overrides=overrides)
     warnings = list(mix_result["warnings"])
-    sale_unit_kg = _extract_unit_quantity_kg(product.unit_of_measure)
+    sale_unit_kg = extract_unit_quantity_kg(product.unit_of_measure)
 
     mix_cost_per_kg = mix_result["mix_cost_per_kg"] or 0.0
     cleaned_product_cost = round(mix_cost_per_kg * sale_unit_kg, 4)

backend/app/services/mix_calculator_service.py

@@ -0,0 +1,311 @@
+from __future__ import annotations
+
+from datetime import date
+
+from sqlalchemy import select
+from sqlalchemy.orm import Session, selectinload
+
+from app.api.deps import AuthSession
+from app.models.mix import Mix, MixIngredient
+from app.models.mix_calculator import MixCalculatorSession, MixCalculatorSessionLine
+from app.models.product import Product
+from app.schemas.mix_calculator import MixCalculatorSessionCreate, MixCalculatorSessionUpdate
+from app.services.costing_engine import extract_unit_quantity_kg
+
+
+def can_view_all_mix_calculator_sessions(session: AuthSession) -> bool:
+    return session.client_role in {"superadmin", "admin"}
+
+
+def _build_session_access_query(session: AuthSession):
+    query = select(MixCalculatorSession).where(MixCalculatorSession.tenant_id == session.tenant_id)
+    if can_view_all_mix_calculator_sessions(session):
+        return query
+    return query.where(MixCalculatorSession.prepared_by_user_id == session.user_id)
+
+
+def _load_product_for_calculation(db: Session, tenant_id: str, product_id: int) -> Product | None:
+    return db.scalar(
+        select(Product)
+        .where(Product.id == product_id, Product.tenant_id == tenant_id)
+        .options(selectinload(Product.mix).selectinload(Mix.ingredients).selectinload(MixIngredient.raw_material))
+    )
+
+
+def _fractional_bag_warning(batch_size_kg: float, total_bags: float, unit_of_measure: str) -> str | None:
+    rounded_bags = round(total_bags)
+    if abs(total_bags - rounded_bags) < 1e-9:
+        return None
+    return (
+        f"Batch size {batch_size_kg:g}kg produces {total_bags:.2f} bags for {unit_of_measure}. "
+        "This is not a whole-bag quantity."
+    )
+
+
+def calculate_mix_calculator_preview(
+    db: Session,
+    *,
+    tenant_id: str,
+    payload: MixCalculatorSessionCreate | MixCalculatorSessionUpdate | dict,
+):
+    values = payload if isinstance(payload, dict) else payload.model_dump(exclude_unset=False)
+    product = _load_product_for_calculation(db, tenant_id, int(values["product_id"]))
+    if product is None:
+        raise ValueError("Product not found")
+    if product.client_name != values["client_name"]:
+        raise ValueError("Selected product does not belong to the chosen client")
+    if product.mix is None:
+        raise ValueError("Product mix is not configured")
+
+    source_total_kg = round(sum(ingredient.quantity_kg for ingredient in product.mix.ingredients), 4)
+    if source_total_kg <= 0:
+        raise ValueError("Product mix has no source kilograms to scale")
+
+    batch_size_kg = float(values["batch_size_kg"])
+    scale_factor = batch_size_kg / source_total_kg
+    unit_size_kg = extract_unit_quantity_kg(product.unit_of_measure)
+    total_bags = round(batch_size_kg / unit_size_kg, 4) if unit_size_kg > 0 else 0.0
+
+    warnings: list[str] = []
+    bag_warning = _fractional_bag_warning(batch_size_kg, total_bags, product.unit_of_measure)
+    if bag_warning:
+        warnings.append(bag_warning)
+
+    lines = []
+    for index, ingredient in enumerate(product.mix.ingredients, start=1):
+        mix_percentage = round((ingredient.quantity_kg / source_total_kg) * 100, 4)
+        required_kg = round(ingredient.quantity_kg * scale_factor, 4)
+        raw_material = ingredient.raw_material
+        lines.append(
+            {
+                "raw_material_id": raw_material.id if raw_material is not None else ingredient.raw_material_id,
+                "raw_material_name": raw_material.name if raw_material is not None else f"Raw material {ingredient.raw_material_id}",
+                "required_kg": required_kg,
+                "mix_percentage": mix_percentage,
+                "unit": raw_material.unit_of_measure if raw_material is not None else "kg",
+                "sort_order": index,
+            }
+        )
+
+    return {
+        "client_name": product.client_name,
+        "product_id": product.id,
+        "product_name": product.name,
+        "mix_id": product.mix_id,
+        "mix_name": product.mix.name,
+        "mix_date": values["mix_date"],
+        "batch_size_kg": round(batch_size_kg, 4),
+        "total_bags": total_bags,
+        "total_kg": round(batch_size_kg, 4),
+        "product_unit_of_measure": product.unit_of_measure,
+        "product_unit_size_kg": round(unit_size_kg, 4),
+        "prepared_by_name": values["prepared_by_name"],
+        "status": values.get("status") or "saved",
+        "notes": values.get("notes"),
+        "warnings": warnings,
+        "lines": lines,
+    }
+
+
+def build_mix_calculator_options(db: Session, *, tenant_id: str) -> dict:
+    products = db.scalars(
+        select(Product)
+        .where(Product.tenant_id == tenant_id)
+        .options(selectinload(Product.mix).selectinload(Mix.ingredients))
+        .order_by(Product.client_name, Product.name)
+    ).all()
+
+    product_rows = []
+    clients = sorted({product.client_name for product in products})
+    for product in products:
+        mix_total_kg = round(sum(ingredient.quantity_kg for ingredient in (product.mix.ingredients if product.mix else [])), 4)
+        product_rows.append(
+            {
+                "product_id": product.id,
+                "client_name": product.client_name,
+                "product_name": product.name,
+                "mix_id": product.mix_id,
+                "mix_name": product.mix.name if product.mix else "",
+                "unit_of_measure": product.unit_of_measure,
+                "unit_size_kg": round(extract_unit_quantity_kg(product.unit_of_measure), 4),
+                "mix_total_kg": mix_total_kg,
+            }
+        )
+
+    return {"clients": clients, "products": product_rows}
+
+
+def serialize_mix_calculator_session(session_record: MixCalculatorSession, auth_session: AuthSession) -> dict:
+    total_bags = round(session_record.total_bags, 4)
+    warnings: list[str] = []
+    bag_warning = _fractional_bag_warning(session_record.batch_size_kg, total_bags, session_record.product_unit_of_measure)
+    if bag_warning:
+        warnings.append(bag_warning)
+
+    return {
+        "id": session_record.id,
+        "tenant_id": session_record.tenant_id,
+        "session_number": session_record.session_number,
+        "client_name": session_record.client_name,
+        "product_id": session_record.product_id,
+        "product_name": session_record.product_name,
+        "mix_id": session_record.mix_id,
+        "mix_name": session_record.mix_name,
+        "mix_date": session_record.mix_date,
+        "batch_size_kg": round(session_record.batch_size_kg, 4),
+        "total_bags": total_bags,
+        "total_kg": round(session_record.total_kg, 4),
+        "product_unit_of_measure": session_record.product_unit_of_measure,
+        "product_unit_size_kg": round(session_record.product_unit_size_kg, 4),
+        "prepared_by_user_id": session_record.prepared_by_user_id,
+        "prepared_by_name": session_record.prepared_by_name,
+        "created_by": session_record.created_by,
+        "status": session_record.status,
+        "notes": session_record.notes,
+        "created_at": session_record.created_at,
+        "updated_at": session_record.updated_at,
+        "warnings": warnings,
+        "is_owner": session_record.prepared_by_user_id == auth_session.user_id,
+        "lines": [
+            {
+                "id": line.id,
+                "raw_material_id": line.raw_material_id,
+                "raw_material_name": line.raw_material_name,
+                "required_kg": round(line.required_kg, 4),
+                "mix_percentage": round(line.mix_percentage, 4),
+                "unit": line.unit,
+                "sort_order": line.sort_order,
+            }
+            for line in session_record.lines
+        ],
+    }
+
+
+def list_mix_calculator_sessions(db: Session, *, auth_session: AuthSession) -> list[dict]:
+    sessions = db.scalars(
+        _build_session_access_query(auth_session)
+        .options(selectinload(MixCalculatorSession.lines))
+        .order_by(MixCalculatorSession.created_at.desc(), MixCalculatorSession.id.desc())
+    ).all()
+    return [serialize_mix_calculator_session(session_record, auth_session) for session_record in sessions]
+
+
+def get_mix_calculator_session(db: Session, *, auth_session: AuthSession, session_id: int) -> MixCalculatorSession | None:
+    return db.scalar(
+        _build_session_access_query(auth_session)
+        .where(MixCalculatorSession.id == session_id)
+        .options(selectinload(MixCalculatorSession.lines))
+    )
+
+
+def _next_session_number(db: Session, *, tenant_id: str, mix_date: date) -> str:
+    prefix = f"HPP-{mix_date.strftime('%Y%m%d')}-"
+    existing = db.scalars(
+        select(MixCalculatorSession.session_number)
+        .where(
+            MixCalculatorSession.tenant_id == tenant_id,
+            MixCalculatorSession.mix_date == mix_date,
+            MixCalculatorSession.session_number.like(f"{prefix}%"),
+        )
+    ).all()
+    sequence = 1
+    if existing:
+        sequence = max(int(value.rsplit("-", 1)[-1]) for value in existing) + 1
+    return f"{prefix}{sequence:04d}"
+
+
+def create_mix_calculator_session(db: Session, *, auth_session: AuthSession, payload: MixCalculatorSessionCreate) -> dict:
+    preview = calculate_mix_calculator_preview(db, tenant_id=auth_session.tenant_id or "", payload=payload)
+    session_record = MixCalculatorSession(
+        tenant_id=auth_session.tenant_id or "default",
+        session_number=_next_session_number(db, tenant_id=auth_session.tenant_id or "default", mix_date=payload.mix_date),
+        client_name=preview["client_name"],
+        product_id=preview["product_id"],
+        product_name=preview["product_name"],
+        mix_id=preview["mix_id"],
+        mix_name=preview["mix_name"],
+        mix_date=preview["mix_date"],
+        batch_size_kg=preview["batch_size_kg"],
+        total_bags=preview["total_bags"],
+        total_kg=preview["total_kg"],
+        product_unit_of_measure=preview["product_unit_of_measure"],
+        product_unit_size_kg=preview["product_unit_size_kg"],
+        prepared_by_user_id=auth_session.user_id,
+        prepared_by_name=preview["prepared_by_name"],
+        created_by=auth_session.email,
+        status=preview["status"],
+        notes=preview["notes"],
+    )
+    session_record.lines = [
+        MixCalculatorSessionLine(
+            tenant_id=auth_session.tenant_id or "default",
+            raw_material_id=line["raw_material_id"],
+            raw_material_name=line["raw_material_name"],
+            required_kg=line["required_kg"],
+            mix_percentage=line["mix_percentage"],
+            unit=line["unit"],
+            sort_order=line["sort_order"],
+        )
+        for line in preview["lines"]
+    ]
+    db.add(session_record)
+    db.commit()
+    db.refresh(session_record)
+    db.refresh(session_record, attribute_names=["lines"])
+    return serialize_mix_calculator_session(session_record, auth_session)
+
+
+def update_mix_calculator_session(
+    db: Session,
+    *,
+    auth_session: AuthSession,
+    session_record: MixCalculatorSession,
+    payload: MixCalculatorSessionUpdate,
+) -> dict:
+    merged_values = {
+        "mix_date": session_record.mix_date,
+        "client_name": session_record.client_name,
+        "product_id": session_record.product_id,
+        "batch_size_kg": session_record.batch_size_kg,
+        "prepared_by_name": session_record.prepared_by_name,
+        "status": session_record.status,
+        "notes": session_record.notes,
+    }
+    merged_values.update(payload.model_dump(exclude_unset=True))
+    preview = calculate_mix_calculator_preview(db, tenant_id=auth_session.tenant_id or "", payload=merged_values)
+
+    session_record.client_name = preview["client_name"]
+    session_record.product_id = preview["product_id"]
+    session_record.product_name = preview["product_name"]
+    session_record.mix_id = preview["mix_id"]
+    session_record.mix_name = preview["mix_name"]
+    session_record.mix_date = preview["mix_date"]
+    session_record.batch_size_kg = preview["batch_size_kg"]
+    session_record.total_bags = preview["total_bags"]
+    session_record.total_kg = preview["total_kg"]
+    session_record.product_unit_of_measure = preview["product_unit_of_measure"]
+    session_record.product_unit_size_kg = preview["product_unit_size_kg"]
+    session_record.prepared_by_name = preview["prepared_by_name"]
+    session_record.status = preview["status"]
+    session_record.notes = preview["notes"]
+
+    session_record.lines.clear()
+    session_record.lines.extend(
+        [
+            MixCalculatorSessionLine(
+                tenant_id=auth_session.tenant_id or "default",
+                raw_material_id=line["raw_material_id"],
+                raw_material_name=line["raw_material_name"],
+                required_kg=line["required_kg"],
+                mix_percentage=line["mix_percentage"],
+                unit=line["unit"],
+                sort_order=line["sort_order"],
+            )
+            for line in preview["lines"]
+        ]
+    )
+
+    db.commit()
+    db.refresh(session_record)
+    db.refresh(session_record, attribute_names=["lines"])
+    return serialize_mix_calculator_session(session_record, auth_session)

backend/tests/test_costing_engine.py

@@ -11,11 +11,13 @@ from app.db.session import Base
 from app.main import app
 from app.models.assumption import FreightCostRule, PackagingCostRule, ProcessCostRule
 from app.models.client_access import ClientAccessAuditEvent, ClientAccount, ClientFeatureAccess, ClientUser
+from app.schemas.mix_calculator import MixCalculatorSessionCreate
 from app.models.mix import Mix, MixIngredient
 from app.models.product import Product
 from app.models.raw_material import RawMaterial, RawMaterialPriceVersion
 from app.services.client_access_service import build_client_access_export, ensure_user_module_permissions, serialize_client_account
 from app.services.costing_engine import calculate_mix_cost, calculate_product_cost, calculate_raw_material_cost
+from app.services.mix_calculator_service import calculate_mix_calculator_preview
 
 
 def build_session() -> Session:
@@ -86,30 +88,83 @@ def test_mix_and_product_cost_breakdown():
     assert product_result["wholesale_price"] == 17.3268
 
 
+def test_mix_calculator_preview_scales_saved_mix_and_warns_on_fractional_bags():
+    db = build_session()
+
+    maize = RawMaterial(name="Maize", unit_of_measure="tonne", kg_per_unit=1000, status="active")
+    barley = RawMaterial(name="Barley", unit_of_measure="tonne", kg_per_unit=1000, status="active")
+    db.add_all([maize, barley])
+    db.flush()
+
+    mix = Mix(tenant_id="specialty-feeds", client_name="Specialty Feeds", name="Pigeon Mix", status="active", version=1)
+    db.add(mix)
+    db.flush()
+    db.add_all(
+        [
+            MixIngredient(tenant_id="specialty-feeds", mix_id=mix.id, raw_material_id=maize.id, quantity_kg=180),
+            MixIngredient(tenant_id="specialty-feeds", mix_id=mix.id, raw_material_id=barley.id, quantity_kg=100),
+        ]
+    )
+    db.flush()
+
+    product = Product(
+        tenant_id="specialty-feeds",
+        client_name="Specialty Feeds",
+        name="Specialty Pigeon Breeder 20kg",
+        mix_id=mix.id,
+        sale_type="standard",
+        own_bag=False,
+        unit_of_measure="20kg bag",
+        items_per_pallet=50,
+        bagging_process="standard_bagging",
+    )
+    db.add(product)
+    db.commit()
+
+    preview = calculate_mix_calculator_preview(
+        db,
+        tenant_id="specialty-feeds",
+        payload=MixCalculatorSessionCreate(
+            mix_date=date(2026, 4, 29),
+            client_name="Specialty Feeds",
+            product_id=product.id,
+            batch_size_kg=550,
+            prepared_by_name="Shift A",
+            notes="Mid-morning run",
+        ),
+    )
+
+    assert preview["batch_size_kg"] == 550
+    assert preview["total_bags"] == 27.5
+    assert preview["lines"][0]["required_kg"] == 353.5714
+    assert preview["lines"][1]["required_kg"] == 196.4286
+    assert len(preview["warnings"]) == 1
+    assert "not a whole-bag quantity" in preview["warnings"][0]
+
+
 def test_root_and_login_endpoints():
-    client = TestClient(app)
+    with TestClient(app) as client:
+        root_response = client.get("/")
+        assert root_response.status_code == 200
+        assert root_response.json()["endpoints"]["client_login"] == "/api/auth/client/login"
+        assert root_response.json()["endpoints"]["admin_login"] == "/api/auth/admin/login"
 
-    root_response = client.get("/")
-    assert root_response.status_code == 200
-    assert root_response.json()["endpoints"]["client_login"] == "/api/auth/client/login"
-    assert root_response.json()["endpoints"]["admin_login"] == "/api/auth/admin/login"
+        client_login_response = client.post(
+            "/api/auth/client/login",
+            json={"email": settings.client_email, "password": settings.client_password},
+        )
+        assert client_login_response.status_code == 200
+        assert client_login_response.json()["email"] == settings.client_email
+        assert client_login_response.json()["tenant_id"] == settings.client_tenant_id
+        assert client_login_response.json()["client_role"] == "superadmin"
+        assert client_login_response.json()["module_permissions"]["client_access"] == "manage"
 
-    client_login_response = client.post(
-        "/api/auth/client/login",
-        json={"email": settings.client_email, "password": settings.client_password},
-    )
-    assert client_login_response.status_code == 200
-    assert client_login_response.json()["email"] == settings.client_email
-    assert client_login_response.json()["tenant_id"] == settings.client_tenant_id
-    assert client_login_response.json()["client_role"] == "superadmin"
-    assert client_login_response.json()["module_permissions"]["client_access"] == "manage"
-
-    admin_login_response = client.post(
-        "/api/auth/admin/login",
-        json={"email": settings.admin_email, "password": settings.admin_password},
-    )
-    assert admin_login_response.status_code == 200
-    assert admin_login_response.json()["email"] == settings.admin_email
+        admin_login_response = client.post(
+            "/api/auth/admin/login",
+            json={"email": settings.admin_email, "password": settings.admin_password},
+        )
+        assert admin_login_response.status_code == 200
+        assert admin_login_response.json()["email"] == settings.admin_email
 
 
 def test_client_access_export_helpers():
@@ -220,6 +275,61 @@ def test_client_access_endpoints():
         assert len(superadmin_access_response.json()) == 1
 
 
+def test_mix_calculator_endpoints_respect_owner_visibility():
+    with TestClient(app) as client:
+        superadmin_login = client.post(
+            "/api/auth/client/login",
+            json={"email": settings.client_email, "password": settings.client_password},
+        )
+        assert superadmin_login.status_code == 200
+        superadmin_headers = {"Authorization": f"Bearer {superadmin_login.json()['token']}"}
+
+        options_response = client.get("/api/mix-calculator/options", headers=superadmin_headers)
+        assert options_response.status_code == 200
+        assert options_response.json()["products"][0]["product_name"] == "Hunter Orchard Blend 20kg"
+
+        create_response = client.post(
+            "/api/mix-calculator",
+            json={
+                "mix_date": "2026-04-29",
+                "client_name": "Hunter Premium Produce",
+                "product_id": 1,
+                "batch_size_kg": 560,
+                "prepared_by_name": "Amelia Hart",
+                "notes": "Morning production run",
+            },
+            headers=superadmin_headers,
+        )
+        assert create_response.status_code == 201
+        created = create_response.json()
+        assert created["session_number"].startswith("HPP-20260429-")
+        assert created["total_bags"] == 28
+        assert created["lines"][0]["required_kg"] == 360
+
+        patch_response = client.patch(
+            f"/api/mix-calculator/{created['id']}",
+            json={"batch_size_kg": 550},
+            headers=superadmin_headers,
+        )
+        assert patch_response.status_code == 200
+        assert patch_response.json()["total_bags"] == 27.5
+        assert len(patch_response.json()["warnings"]) == 1
+
+        operator_login = client.post(
+            "/api/auth/client/login",
+            json={"email": "ethan.cole@hunterpremiumproduce.example", "password": settings.client_password},
+        )
+        assert operator_login.status_code == 200
+        operator_headers = {"Authorization": f"Bearer {operator_login.json()['token']}"}
+
+        operator_list_response = client.get("/api/mix-calculator", headers=operator_headers)
+        assert operator_list_response.status_code == 200
+        assert operator_list_response.json() == []
+
+        operator_detail_response = client.get(f"/api/mix-calculator/{created['id']}", headers=operator_headers)
+        assert operator_detail_response.status_code == 404
+
+
 def test_module_permission_blocks_client_module_access():
     with TestClient(app) as client:
         admin_login_response = client.post(
@@ -229,7 +339,7 @@ def test_module_permission_blocks_client_module_access():
         admin_headers = {"Authorization": f"Bearer {admin_login_response.json()['token']}"}
         access_response = client.get("/api/client-access", headers=admin_headers)
         first_client = access_response.json()[0]
-        first_user = first_client["users"][0]
+        first_user = next(user for user in first_client["users"] if user["email"] == settings.client_email)
 
         permission = next(
             permission for permission in first_user["module_permissions"] if permission["module_key"] == "raw_materials"