Add tests for CSV export

expenses_manager/expenses/csv_export.py

@@ -0,0 +1,201 @@
+"""Dialectos CSV, formateo de celdas y volcado de filas en streaming.
+
+Va en módulo propio y no en views.py (ya anotado como deuda por tamaño): así el
+dialecto y el formateo se prueban sin levantar un cliente HTTP.
+"""
+
+import csv
+from dataclasses import dataclass
+from datetime import date as date_cls
+
+from django.db.models import Q
+
+from .models import Expense, Income, Transfer
+
+
+class _Echo:
+    """Objeto tipo fichero que devuelve lo que le escriben, para csv.writer."""
+
+    def write(self, value):
+        return value
+
+
+@dataclass(frozen=True)
+class CsvDialect:
+    delimiter: str
+    decimal_sep: str
+    date_format: str
+    bool_true: str
+    bool_false: str
+    bom: bool
+
+
+# Abre con doble clic en el Excel español.
+EXCEL_ES = CsvDialect(";", ",", "%d/%m/%Y", "Sí", "No", bom=True)
+# Salida RFC-4180 para pandas o para reimportar.
+STANDARD = CsvDialect(",", ".", "%Y-%m-%d", "true", "false", bom=False)
+
+DIALECTS = {"excel": EXCEL_ES, "std": STANDARD}
+DEFAULT_DIALECT = "excel"
+
+
+def fmt_amount(value, dialect):
+    """Decimal -> texto plano, sin separador de miles a propósito.
+
+    El formateo por locale de Django metería "1.234,56" y partiría la fila en
+    dos en el dialecto de Excel. Aquí no se usa floatformat ni
+    django.utils.formats. None sale como celda vacía: "no hay comisión" no es
+    lo mismo que una comisión de cero.
+    """
+    if value is None:
+        return ""
+
+    return f"{value:.2f}".replace(".", dialect.decimal_sep)
+
+
+def fmt_date(value, dialect):
+    return value.strftime(dialect.date_format) if value else ""
+
+
+def fmt_bool(value, dialect):
+    return dialect.bool_true if value else dialect.bool_false
+
+
+def stream_csv(header, rows, dialect):
+    """Va soltando el CSV fila a fila, para StreamingHttpResponse."""
+    writer = csv.writer(_Echo(), delimiter=dialect.delimiter, quoting=csv.QUOTE_MINIMAL)
+
+    # El BOM se emite como texto y lo codifica la respuesta con su charset.
+    if dialect.bom:
+        yield ""
+
+    yield writer.writerow(header)
+    for row in rows:
+        yield writer.writerow(row)
+
+
+def csv_filename(stem, date_from, date_to):
+    """gastos_2026-01-01_2026-10-01.csv, o con la fecha de hoy si no hay rango."""
+    span = [d.isoformat() for d in (date_from, date_to) if d]
+
+    return "_".join([stem, *(span or [date_cls.today().isoformat()])]) + ".csv"
+
+
+def _by_date(queryset, date_from, date_to):
+    """Recorta el rango y ordena.
+
+    El desempate por id no es adorno: un order_by solo por fecha puede salir en
+    distinto orden en SQLite local y en el PostgreSQL del NAS.
+    """
+    if date_from:
+        queryset = queryset.filter(date__gte=date_from)
+    if date_to:
+        queryset = queryset.filter(date__lte=date_to)
+
+    return queryset.order_by("date", "id")
+
+
+# chunk_size es obligatorio al combinar iterator() con prefetch_related: sin él
+# el prefetch se ignora y las etiquetas saldrían vacías o con un N+1.
+CHUNK = 2000
+
+
+def expenses_export(user, date_from, date_to, account, dialect):
+    queryset = (
+        Expense.objects.filter(owner=user)
+        .select_related("account", "category", "category__parent")
+        .prefetch_related("tags")
+    )
+    if account:
+        queryset = queryset.filter(account=account)
+
+    header = [
+        "Fecha",
+        "Importe",
+        "Categoría",
+        "Categoría padre",
+        "Cuenta",
+        "Concepto",
+        "Etiquetas",
+        "Traspaso",
+    ]
+
+    def rows():
+        for expense in _by_date(queryset, date_from, date_to).iterator(
+            chunk_size=CHUNK
+        ):
+            category = expense.category
+            yield [
+                fmt_date(expense.date, dialect),
+                fmt_amount(expense.amount, dialect),
+                category.name,
+                # La categoría padre sale del JOIN, no recorriendo la jerarquía
+                # por fila. Si algún día se quiere la ruta completa a cualquier
+                # profundidad, eso es un dict en memoria, nunca más SQL.
+                category.parent.name if category.parent else "",
+                expense.account.name,
+                expense.description,
+                # Unidas con | porque la coma y el punto y coma son
+                # delimitadores en uno u otro dialecto.
+                "|".join(tag.name for tag in expense.tags.all()),
+                fmt_bool(expense.is_transfer, dialect),
+            ]
+
+    return header, rows()
+
+
+def incomes_export(user, date_from, date_to, account, dialect):
+    queryset = Income.objects.filter(owner=user).select_related("account")
+    if account:
+        queryset = queryset.filter(account=account)
+
+    header = ["Fecha", "Importe", "Cuenta", "Concepto", "Traspaso"]
+
+    def rows():
+        for income in _by_date(queryset, date_from, date_to).iterator(
+            chunk_size=CHUNK
+        ):
+            yield [
+                fmt_date(income.date, dialect),
+                fmt_amount(income.amount, dialect),
+                income.account.name,
+                income.name,
+                fmt_bool(income.is_transfer, dialect),
+            ]
+
+    return header, rows()
+
+
+def transfers_export(user, date_from, date_to, account, dialect):
+    queryset = Transfer.objects.filter(owner=user).select_related(
+        "from_account", "to_account"
+    )
+    # Filtrar por cuenta es "traspasos en los que participa": da igual si entra
+    # o sale, el movimiento está en el extracto de esa cuenta.
+    if account:
+        queryset = queryset.filter(Q(from_account=account) | Q(to_account=account))
+
+    header = ["Fecha", "Importe", "Cuenta origen", "Cuenta destino", "Comisión"]
+
+    def rows():
+        for transfer in _by_date(queryset, date_from, date_to).iterator(
+            chunk_size=CHUNK
+        ):
+            yield [
+                fmt_date(transfer.date, dialect),
+                fmt_amount(transfer.amount, dialect),
+                transfer.from_account.name,
+                transfer.to_account.name,
+                fmt_amount(transfer.fee_amount, dialect),
+            ]
+
+    return header, rows()
+
+
+# kind -> (nombre de fichero, constructor). Los nombres salen en Descargas, así
+# que van en español.
+EXPORTS = {
+    "expenses": ("gastos", expenses_export),
+    "incomes": ("ingresos", incomes_export),
+    "transfers": ("traspasos", transfers_export),
+}

expenses_manager/expenses/forms.py

@@ -1,4 +1,5 @@
 from django import forms
+from .csv_export import DEFAULT_DIALECT
 from .models import (
     Expense,
     Category,
@@ -233,5 +234,66 @@ class GoalForm(forms.ModelForm):
                 )
         else:
             cleaned["period"] = Goal.PERIOD_NONE
-        
+
+        return cleaned
+
+
+class ExportForm(forms.Form):
+    """Filtros de la exportación a CSV. Valida la pantalla y la descarga.
+
+    Los filtros son a propósito solo rango de fechas y cuenta: la gracia de un
+    CSV es filtrar fuera, y duplicar aquí la fila de filtros avanzados de
+    expense_list serían dos UIs que divergen.
+    """
+
+    KIND_CHOICES = [
+        ("expenses", "Gastos"),
+        ("incomes", "Ingresos"),
+        ("transfers", "Traspasos"),
+    ]
+    FMT_CHOICES = [
+        ("excel", "Excel español — separador ; y decimales con coma"),
+        ("std", "CSV estándar — separador , y decimales con punto"),
+    ]
+
+    kind = forms.ChoiceField(choices=KIND_CHOICES, label="Qué exportar")
+    date_from = forms.DateField(
+        required=False,
+        label="Desde",
+        widget=forms.DateInput(format="%Y-%m-%d", attrs={"type": "date"}),
+    )
+    date_to = forms.DateField(
+        required=False,
+        label="Hasta",
+        widget=forms.DateInput(format="%Y-%m-%d", attrs={"type": "date"}),
+    )
+    account = forms.ModelChoiceField(
+        queryset=Account.objects.none(),
+        required=False,
+        label="Cuenta",
+        empty_label="Todas las cuentas",
+    )
+    fmt = forms.ChoiceField(
+        choices=FMT_CHOICES, label="Formato", initial=DEFAULT_DIALECT
+    )
+
+    def __init__(self, *args, **kwargs):
+        user = kwargs.pop("user")
+        super().__init__(*args, **kwargs)
+
+        # Activas e inactivas: se exporta histórico, y una cuenta cerrada tiene
+        # movimientos que interesan.
+        self.fields["account"].queryset = Account.objects.filter(owner=user)
+        self.fields["date_from"].input_formats = ["%Y-%m-%d"]
+        self.fields["date_to"].input_formats = ["%Y-%m-%d"]
+
+    def clean(self):
+        cleaned = super().clean()
+        date_from, date_to = cleaned.get("date_from"), cleaned.get("date_to")
+
+        # En un listado un rango invertido se ignora; aquí no, porque el
+        # resultado sería un fichero vacío descargado sin explicación.
+        if date_from and date_to and date_from > date_to:
+            self.add_error("date_to", "La fecha final es anterior a la inicial.")
+
         return cleaned

expenses_manager/expenses/templates/expenses/base.html

@@ -43,6 +43,7 @@
                             <a href="{% url 'category_list' %}">Categorías</a>
                             <a href="{% url 'tag_list' %}">Etiquetas</a>
                             <a href="{% url 'goal_list' %}">Objetivos</a>
+                            <a href="{% url 'export_index' %}">Exportar datos</a>
                         </div>
                     </div>
 

expenses_manager/expenses/templates/expenses/export_form.html

@@ -0,0 +1,30 @@
+{% extends "expenses/base.html" %}
+
+{% block title %}Exportar datos{% endblock %}
+
+{% block content %}
+    <h1>Exportar datos</h1>
+
+    <p>Descarga tus movimientos en CSV para abrirlos en Excel o tratarlos aparte.</p>
+
+    <div class="messages">
+        <div class="message warning">
+            Los dos movimientos de cada traspaso también salen en el CSV de gastos y
+            en el de ingresos, marcados con «Traspaso = Sí». Sumar los tres ficheros
+            cuenta el mismo dinero dos veces.
+        </div>
+        <div class="message warning">
+            La comisión de un traspaso sale en el CSV de gastos como gasto normal
+            («Traspaso = No»), porque es dinero que sale de verdad del patrimonio.
+        </div>
+    </div>
+
+    <form method="get" action="{% url 'export_download' %}" class="app-form">
+        {% include "expenses/_form_fields.html" %}
+
+        <div class="form-actions">
+            <button type="submit" class="btn btn-primary">Descargar CSV</button>
+            <a class="btn btn-secondary" href="{% url 'settings_index' %}">Volver</a>
+        </div>
+    </form>
+{% endblock %}

expenses_manager/expenses/templates/settings/index.html

@@ -24,6 +24,11 @@
         <h2>Objetivos</h2>
         <p>Define y controla tus metas de gasto.</p>
     </a>
+
+    <a class="settings-card" href="{% url 'export_index' %}">
+        <h2>Exportar datos</h2>
+        <p>Descarga tus gastos, ingresos o traspasos en CSV.</p>
+    </a>
 </div>
 
 {% endblock %}

expenses_manager/expenses/tests/test_export.py

@@ -0,0 +1,547 @@
+"""Exportación a CSV: dialectos, filtros y aislamiento por usuario.
+
+Lo que más se mira aquí es el dialecto de Excel: el BOM y la coma decimal son
+justo lo que hace que el fichero se abra con doble clic en vez de salir todo en
+una columna. Las filas se leen siempre con csv.reader y nunca con split(), que
+partiría por la mitad cualquier concepto con el delimitador dentro.
+"""
+
+import csv
+import io
+from datetime import date
+from decimal import Decimal
+
+import pytest
+from django.urls import reverse
+
+from expenses.csv_export import (
+    EXCEL_ES,
+    STANDARD,
+    csv_filename,
+    fmt_amount,
+    fmt_bool,
+    fmt_date,
+)
+from expenses.models import Account, Category, Expense, Income, Tag, Transfer
+
+pytestmark = pytest.mark.django_db
+
+
+# --------------------------------------------------------------------------
+# Utilidades
+# --------------------------------------------------------------------------
+
+
+def body(response):
+    """El cuerpo completo de una StreamingHttpResponse, como texto."""
+    return b"".join(response.streaming_content).decode("utf-8")
+
+
+def read_rows(response, delimiter=";"):
+    text = body(response).lstrip("")
+
+    return list(csv.reader(io.StringIO(text), delimiter=delimiter))
+
+
+def download(client, **params):
+    params.setdefault("fmt", "excel")
+
+    return client.get(reverse("export_download"), params)
+
+
+@pytest.fixture
+def savings(user):
+    return Account.objects.create(
+        owner=user, name="Ahorro", initial_balance=Decimal("0"), active=True
+    )
+
+
+def make_transfer(user, from_account, to_account, amount="400", on=None, fee=None):
+    transfer = Transfer(
+        owner=user,
+        date=on or date(2024, 5, 11),
+        amount=Decimal(amount),
+        from_account=from_account,
+        to_account=to_account,
+        fee_amount=Decimal(fee) if fee is not None else None,
+    )
+    transfer.sync()
+    return transfer
+
+
+# --------------------------------------------------------------------------
+# Formateo (sin base de datos ni HTTP)
+# --------------------------------------------------------------------------
+
+
+def test_excel_dialect_formats_amounts_with_a_comma():
+    assert fmt_amount(Decimal("1234.56"), EXCEL_ES) == "1234,56"
+
+
+def test_standard_dialect_formats_amounts_with_a_dot():
+    assert fmt_amount(Decimal("1234.56"), STANDARD) == "1234.56"
+
+
+def test_amounts_never_carry_a_thousands_separator():
+    # Un "1.234,56" partiría la fila en dos en el dialecto de Excel.
+    assert fmt_amount(Decimal("1234567.80"), EXCEL_ES) == "1234567,80"
+
+
+def test_amounts_always_keep_two_decimals():
+    assert fmt_amount(Decimal("5"), EXCEL_ES) == "5,00"
+
+
+def test_a_missing_amount_is_an_empty_cell_not_a_zero():
+    assert fmt_amount(None, EXCEL_ES) == ""
+
+
+def test_dates_follow_the_dialect():
+    assert fmt_date(date(2026, 1, 31), EXCEL_ES) == "31/01/2026"
+    assert fmt_date(date(2026, 1, 31), STANDARD) == "2026-01-31"
+
+
+def test_booleans_follow_the_dialect():
+    assert fmt_bool(True, EXCEL_ES) == "Sí"
+    assert fmt_bool(False, EXCEL_ES) == "No"
+    assert fmt_bool(True, STANDARD) == "true"
+    assert fmt_bool(False, STANDARD) == "false"
+
+
+def test_filename_carries_the_range():
+    name = csv_filename("gastos", date(2026, 1, 1), date(2026, 10, 1))
+
+    assert name == "gastos_2026-01-01_2026-10-01.csv"
+
+
+def test_filename_without_a_range_carries_todays_date():
+    assert csv_filename("gastos", None, None) == f"gastos_{date.today().isoformat()}.csv"
+
+
+# --------------------------------------------------------------------------
+# Las tres descargas responden
+# --------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize("kind", ["expenses", "incomes", "transfers"])
+def test_every_kind_downloads_a_csv(auth_client, kind):
+    response = download(auth_client, kind=kind)
+
+    assert response.status_code == 200
+    assert response["Content-Type"] == "text/csv; charset=utf-8"
+    assert ".csv" in response["Content-Disposition"]
+
+
+def test_the_download_is_an_attachment_with_a_spanish_filename(auth_client):
+    response = download(auth_client, kind="transfers")
+
+    assert "attachment" in response["Content-Disposition"]
+    assert "traspasos_" in response["Content-Disposition"]
+
+
+def test_the_export_screen_renders(auth_client):
+    response = auth_client.get(reverse("export_index"))
+
+    assert response.status_code == 200
+    assert "form" in response.context
+
+
+def test_the_settings_page_links_to_the_export_screen(auth_client):
+    # Un {% url %} mal escrito ahí no lo ve manage.py check: revienta en runtime.
+    response = auth_client.get(reverse("settings_index"))
+
+    assert response.status_code == 200
+    assert reverse("export_index") in response.content.decode()
+
+
+def test_the_export_screen_needs_a_login(client):
+    response = client.get(reverse("export_index"))
+
+    assert response.status_code == 302
+
+
+def test_the_download_needs_a_login(client):
+    response = client.get(reverse("export_download"), {"kind": "expenses"})
+
+    assert response.status_code == 302
+
+
+# --------------------------------------------------------------------------
+# Dialectos en la salida real
+# --------------------------------------------------------------------------
+
+
+def test_excel_csv_starts_with_a_bom(auth_client, account, category):
+    Expense.objects.create(
+        owner=account.owner,
+        account=account,
+        category=category,
+        amount=Decimal("1234.56"),
+        date=date(2024, 5, 11),
+    )
+
+    response = download(auth_client, kind="expenses", fmt="excel")
+
+    assert body(response).startswith("")
+
+
+def test_standard_csv_has_no_bom(auth_client):
+    response = download(auth_client, kind="expenses", fmt="std")
+
+    assert not body(response).startswith("")
+
+
+def test_excel_csv_uses_semicolons_and_decimal_commas(auth_client, account, category):
+    Expense.objects.create(
+        owner=account.owner,
+        account=account,
+        category=category,
+        amount=Decimal("1234.56"),
+        date=date(2024, 5, 11),
+    )
+
+    rows = read_rows(download(auth_client, kind="expenses", fmt="excel"))
+
+    assert rows[0][0] == "Fecha"
+    assert rows[1][0] == "11/05/2024"
+    assert rows[1][1] == "1234,56"
+
+
+def test_standard_csv_uses_commas_and_decimal_dots(auth_client, account, category):
+    Expense.objects.create(
+        owner=account.owner,
+        account=account,
+        category=category,
+        amount=Decimal("1234.56"),
+        date=date(2024, 5, 11),
+    )
+
+    rows = read_rows(download(auth_client, kind="expenses", fmt="std"), delimiter=",")
+
+    assert rows[1][0] == "2024-05-11"
+    assert rows[1][1] == "1234.56"
+
+
+def test_a_concept_with_the_delimiter_inside_stays_in_one_cell(
+    auth_client, account, category
+):
+    Expense.objects.create(
+        owner=account.owner,
+        account=account,
+        category=category,
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+        description="Cena; con punto y coma, y coma",
+    )
+
+    rows = read_rows(download(auth_client, kind="expenses"))
+
+    assert rows[1][5] == "Cena; con punto y coma, y coma"
+
+
+# --------------------------------------------------------------------------
+# Columnas
+# --------------------------------------------------------------------------
+
+
+def test_expense_rows_carry_parent_category_and_tags(auth_client, user, account):
+    parent = Category.objects.create(owner=user, name="Casa")
+    child = Category.objects.create(owner=user, name="Luz", parent=parent)
+    expense = Expense.objects.create(
+        owner=user,
+        account=account,
+        category=child,
+        amount=Decimal("60"),
+        date=date(2024, 5, 11),
+        description="Factura",
+    )
+    expense.tags.add(
+        Tag.objects.create(owner=user, name="fijo"),
+        Tag.objects.create(owner=user, name="hogar"),
+    )
+
+    rows = read_rows(download(auth_client, kind="expenses"))
+
+    assert rows[1][2] == "Luz"
+    assert rows[1][3] == "Casa"
+    assert rows[1][4] == account.name
+    # Unidas con | porque la coma y el ; son delimitadores en uno u otro dialecto.
+    assert sorted(rows[1][6].split("|")) == ["fijo", "hogar"]
+
+
+def test_a_top_level_category_leaves_the_parent_cell_empty(
+    auth_client, user, account, category
+):
+    Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+    )
+
+    rows = read_rows(download(auth_client, kind="expenses"))
+
+    assert rows[1][3] == ""
+
+
+def test_income_rows_carry_account_and_concept(auth_client, user, account):
+    Income.objects.create(
+        owner=user,
+        account=account,
+        name="Nómina",
+        amount=Decimal("1500"),
+        date=date(2024, 5, 11),
+    )
+
+    rows = read_rows(download(auth_client, kind="incomes"))
+
+    assert rows[0] == ["Fecha", "Importe", "Cuenta", "Concepto", "Traspaso"]
+    assert rows[1][2] == account.name
+    assert rows[1][3] == "Nómina"
+
+
+def test_transfer_rows_carry_both_accounts(auth_client, user, account, savings):
+    make_transfer(user, account, savings, amount="400")
+
+    rows = read_rows(download(auth_client, kind="transfers"))
+
+    assert rows[0] == [
+        "Fecha",
+        "Importe",
+        "Cuenta origen",
+        "Cuenta destino",
+        "Comisión",
+    ]
+    assert rows[1][1] == "400,00"
+    assert rows[1][2] == account.name
+    assert rows[1][3] == savings.name
+
+
+def test_a_transfer_without_a_fee_leaves_the_fee_cell_empty(
+    auth_client, user, account, savings
+):
+    make_transfer(user, account, savings)
+
+    rows = read_rows(download(auth_client, kind="transfers"))
+
+    # Vacío y no "0,00": un cero es un dato, y aquí el dato es "no hubo".
+    assert rows[1][4] == ""
+
+
+def test_a_transfer_with_a_fee_carries_it(auth_client, user, account, savings):
+    make_transfer(user, account, savings, fee="1.50")
+
+    rows = read_rows(download(auth_client, kind="transfers"))
+
+    assert rows[1][4] == "1,50"
+
+
+# --------------------------------------------------------------------------
+# Las patas del traspaso y la comisión: los dos avisos de la pantalla
+# --------------------------------------------------------------------------
+
+
+def test_transfer_legs_also_show_up_flagged_in_the_movement_csvs(
+    auth_client, user, account, savings
+):
+    make_transfer(user, account, savings, amount="400")
+
+    expense_rows = read_rows(download(auth_client, kind="expenses"))
+    income_rows = read_rows(download(auth_client, kind="incomes"))
+
+    # Sumar los tres ficheros duplica: esto es lo que avisa la pantalla.
+    assert [r[7] for r in expense_rows[1:]] == ["Sí"]
+    assert [r[4] for r in income_rows[1:]] == ["Sí"]
+
+
+def test_the_fee_is_exported_as_a_normal_expense(auth_client, user, account, savings):
+    make_transfer(user, account, savings, amount="400", fee="1.50")
+
+    rows = read_rows(download(auth_client, kind="expenses"))
+    by_amount = {row[1]: row for row in rows[1:]}
+
+    # La pata va marcada como traspaso; la comisión no, porque es dinero que
+    # sale de verdad del patrimonio.
+    assert by_amount["400,00"][7] == "Sí"
+    assert by_amount["1,50"][7] == "No"
+
+
+# --------------------------------------------------------------------------
+# Filtros
+# --------------------------------------------------------------------------
+
+
+def test_the_date_range_filters_both_ends(auth_client, user, account, category):
+    for day in (1, 15, 28):
+        Expense.objects.create(
+            owner=user,
+            account=account,
+            category=category,
+            amount=Decimal(day),
+            date=date(2024, 5, day),
+        )
+
+    rows = read_rows(
+        download(
+            auth_client,
+            kind="expenses",
+            date_from="2024-05-10",
+            date_to="2024-05-20",
+        )
+    )
+
+    assert [row[0] for row in rows[1:]] == ["15/05/2024"]
+
+
+def test_the_account_filter_narrows_expenses(auth_client, user, account, savings, category):
+    for target in (account, savings):
+        Expense.objects.create(
+            owner=user,
+            account=target,
+            category=category,
+            amount=Decimal("10"),
+            date=date(2024, 5, 11),
+        )
+
+    rows = read_rows(download(auth_client, kind="expenses", account=account.pk))
+
+    assert [row[4] for row in rows[1:]] == [account.name]
+
+
+def test_the_account_filter_catches_transfers_on_either_side(
+    auth_client, user, account, savings
+):
+    third = Account.objects.create(
+        owner=user, name="Bolsillo", initial_balance=Decimal("0"), active=True
+    )
+    make_transfer(user, account, savings, amount="100")
+    make_transfer(user, savings, account, amount="200")
+    make_transfer(user, savings, third, amount="300")
+
+    rows = read_rows(download(auth_client, kind="transfers", account=account.pk))
+
+    assert sorted(row[1] for row in rows[1:]) == ["100,00", "200,00"]
+
+
+def test_rows_come_out_ordered_by_date(auth_client, user, account, category):
+    for day in (28, 1, 15):
+        Expense.objects.create(
+            owner=user,
+            account=account,
+            category=category,
+            amount=Decimal("10"),
+            date=date(2024, 5, day),
+        )
+
+    rows = read_rows(download(auth_client, kind="expenses"))
+
+    assert [row[0] for row in rows[1:]] == [
+        "01/05/2024",
+        "15/05/2024",
+        "28/05/2024",
+    ]
+
+
+def test_an_inactive_account_can_still_be_chosen(auth_client, user, account, category):
+    # Se exporta histórico: una cuenta cerrada tiene movimientos que interesan.
+    account.active = False
+    account.save()
+    Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+    )
+
+    rows = read_rows(download(auth_client, kind="expenses", account=account.pk))
+
+    assert len(rows) == 2
+
+
+# --------------------------------------------------------------------------
+# Aislamiento por usuario
+# --------------------------------------------------------------------------
+
+
+def test_another_users_data_never_reaches_the_csv(
+    auth_client, user, account, category, django_user_model
+):
+    intruder = django_user_model.objects.create_user(username="otro", password="x")
+    their_account = Account.objects.create(
+        owner=intruder, name="Cuenta ajena", initial_balance=Decimal("0"), active=True
+    )
+    their_category = Category.objects.create(owner=intruder, name="Ajena")
+    Expense.objects.create(
+        owner=intruder,
+        account=their_account,
+        category=their_category,
+        amount=Decimal("999"),
+        date=date(2024, 5, 11),
+        description="No es mío",
+    )
+    Income.objects.create(
+        owner=intruder,
+        account=their_account,
+        name="Nómina ajena",
+        amount=Decimal("888"),
+        date=date(2024, 5, 11),
+    )
+    Expense.objects.create(
+        owner=user,
+        account=account,
+        category=category,
+        amount=Decimal("10"),
+        date=date(2024, 5, 11),
+        description="Mío",
+    )
+
+    expenses_csv = body(download(auth_client, kind="expenses"))
+    incomes_csv = body(download(auth_client, kind="incomes"))
+
+    assert "Mío" in expenses_csv
+    assert "No es mío" not in expenses_csv
+    assert "999" not in expenses_csv
+    assert "Nómina ajena" not in incomes_csv
+
+
+def test_another_users_account_cannot_be_used_as_a_filter(
+    auth_client, django_user_model
+):
+    intruder = django_user_model.objects.create_user(username="otro", password="x")
+    their_account = Account.objects.create(
+        owner=intruder, name="Cuenta ajena", initial_balance=Decimal("0"), active=True
+    )
+
+    response = download(auth_client, kind="expenses", account=their_account.pk)
+
+    assert response.status_code == 400
+
+
+# --------------------------------------------------------------------------
+# Parámetros inválidos
+# --------------------------------------------------------------------------
+
+
+def test_an_unknown_kind_is_rejected(auth_client):
+    assert download(auth_client, kind="everything").status_code == 400
+
+
+def test_an_unknown_format_is_rejected(auth_client):
+    assert download(auth_client, kind="expenses", fmt="pdf").status_code == 400
+
+
+def test_a_broken_date_is_rejected(auth_client):
+    response = download(auth_client, kind="expenses", date_from="ayer")
+
+    assert response.status_code == 400
+
+
+def test_an_inverted_range_is_rejected(auth_client):
+    response = download(
+        auth_client, kind="expenses", date_from="2024-05-20", date_to="2024-05-10"
+    )
+
+    # En un listado un rango invertido se ignora; aquí descargaría un fichero
+    # vacío sin explicación, así que se corta.
+    assert response.status_code == 400

expenses_manager/expenses/urls.py

@@ -33,6 +33,8 @@ urlpatterns = [
     path('categories/<int:pk>/edit/', views.category_edit, name='category_edit'),
     path('categories/<int:pk>/delete/', views.category_delete, name='category_delete'),
     path('settings/', views.settings_index, name='settings_index'),
+    path('export/', views.export_index, name='export_index'),
+    path('export/download/', views.export_download, name='export_download'),
     path('goals/', views.goal_list, name='goal_list'),
     path('goals/new/', views.goal_create, name='goal_create'),
     path('goals/<int:pk>/edit/', views.goal_edit, name='goal_edit'),

expenses_manager/expenses/views.py

@@ -23,7 +23,9 @@ from .forms import (
     CategoryForm,
     GoalForm,
     TransferForm,
+    ExportForm,
 )
+from .csv_export import DIALECTS, EXPORTS, csv_filename, stream_csv
 
 from django.core.paginator import Paginator
 from django.db.models import Sum, Count, Min, ProtectedError
@@ -36,6 +38,7 @@ from django.db.models.functions import (
 )
 
 from django.contrib.auth.decorators import login_required
+from django.http import HttpResponseBadRequest, StreamingHttpResponse
 from django.utils.http import url_has_allowed_host_and_scheme
 from django.shortcuts import get_object_or_404, render, redirect
 from django.urls import reverse
@@ -1667,3 +1670,41 @@ def transfer_delete(request, pk):
         "transfers/confirm_delete.html",
         {"active_menu": "transfers", "transfer": transfer},
     )
+
+
+@login_required
+def export_index(request):
+    # Se enlaza el form si la URL trae algo para que, al volver de una descarga
+    # con parámetros mal puestos, se vean los errores en la pantalla.
+    form = ExportForm(request.GET or None, user=request.user)
+
+    return render(
+        request,
+        "expenses/export_form.html",
+        {"active_menu": "settings", "form": form},
+    )
+
+
+@login_required
+def export_download(request):
+    form = ExportForm(request.GET, user=request.user)
+    if not form.is_valid():
+        return HttpResponseBadRequest("Parámetros de exportación no válidos.")
+
+    data = form.cleaned_data
+    dialect = DIALECTS[data["fmt"]]
+    stem, build_export = EXPORTS[data["kind"]]
+    header, rows = build_export(
+        request.user, data["date_from"], data["date_to"], data["account"], dialect
+    )
+
+    # Streaming y no HttpResponse: con los volúmenes de hoy da igual en memoria,
+    # pero el coste de código es el mismo.
+    response = StreamingHttpResponse(
+        stream_csv(header, rows, dialect),
+        content_type="text/csv; charset=utf-8",
+    )
+    filename = csv_filename(stem, data["date_from"], data["date_to"])
+    response["Content-Disposition"] = f'attachment; filename="{filename}"'
+
+    return response