src/streamlit_app.py

import streamlit as st
import pandas as pd
import numpy as np
from sklearn.model_selection import train_test_split
from sklearn.ensemble import RandomForestClassifier, RandomForestRegressor
from sklearn.linear_model import LogisticRegression, LinearRegression
from sklearn.metrics import (
    accuracy_score, precision_score, recall_score, f1_score,
    mean_absolute_error, mean_squared_error, r2_score,
    classification_report, confusion_matrix
)
from sklearn.preprocessing import LabelEncoder
import plotly.express as px
import plotly.graph_objects as go
import seaborn as sns
import matplotlib.pyplot as plt
import io

# Metadata
AUTHOR = "Eduardo Nacimiento García"
EMAIL = "enacimie@ull.edu.es"
LICENSE = "Apache 2.0"

# Page config
st.set_page_config(
    page_title="SimpleML",
    page_icon="🤖",
    layout="wide",
    initial_sidebar_state="expanded",
)

# Title
st.title("🤖 SimpleML")
st.markdown(f"**Author:** {AUTHOR} | **Email:** {EMAIL} | **License:** {LICENSE}")
st.write("""
Upload a CSV or use the demo dataset to train a machine learning model (classification or regression) in seconds.
""")

# === GENERATE DEMO DATASET ===
@st.cache_data
def create_demo_data(task="classification"):
    np.random.seed(42)
    n = 500
    data = {
        "Age": np.random.normal(35, 12, n).astype(int),
        "Income": np.random.normal(45000, 15000, n),
        "Experience": np.random.randint(0, 20, n),
        "Education_Level": np.random.choice(["High School", "Bachelor", "Master", "PhD"], n),
        "City": np.random.choice(["Madrid", "Barcelona", "Valencia", "Seville"], n),
    }
    df = pd.DataFrame(data)

    if task == "classification":
        # Create binary target: Purchase (0/1)
        purchase_prob = (
            0.3 +
            (df["Income"] > df["Income"].median()) * 0.4 +
            (df["Experience"] > 10) * 0.2 +
            (df["Education_Level"] == "Master") * 0.1 +
            (df["Education_Level"] == "PhD") * 0.15
        )
        df["Purchase"] = np.random.binomial(1, np.clip(purchase_prob, 0, 1), n)
        return df

    elif task == "regression":
        # Create continuous target: Salary
        df["Salary"] = (
            25000 +
            df["Experience"] * 1500 +
            (df["Income"] / 100) +
            (df["Age"] * 100) +
            (df["Education_Level"] == "Master") * 8000 +
            (df["Education_Level"] == "PhD") * 15000 +
            np.random.normal(0, 5000, n)
        )
        return df

# === LOAD DATA ===
if "demo_loaded" not in st.session_state:
    st.session_state.demo_loaded = False
    st.session_state.task_type = "classification"

if st.button("🧪 Load Classification Demo Dataset"):
    st.session_state.demo_loaded = True
    st.session_state.task_type = "classification"
    st.session_state.df = create_demo_data("classification")
    st.success("✅ Classification demo loaded!")

if st.button("🧪 Load Regression Demo Dataset"):
    st.session_state.demo_loaded = True
    st.session_state.task_type = "regression"
    st.session_state.df = create_demo_data("regression")
    st.success("✅ Regression demo loaded!")

uploaded_file = st.file_uploader("📂 Upload your CSV file", type=["csv"])

# Use demo or uploaded file
if uploaded_file:
    df = pd.read_csv(uploaded_file)
    st.session_state.df = df
    st.session_state.demo_loaded = False
    st.success("✅ File uploaded successfully.")
elif "df" in st.session_state:
    df = st.session_state.df
    task_type = st.session_state.task_type
    if st.session_state.demo_loaded:
        st.info(f"Using **{task_type}** demo dataset.")
else:
    df = None
    st.info("👆 Upload a CSV or load a demo dataset to begin.")
    st.stop()

# Show data preview
with st.expander("🔍 Data Preview (first 10 rows)"):
    st.dataframe(df.head(10))

# === TARGET & FEATURE SELECTION ===
st.subheader("🎯 Select Target Variable")
target_col = st.selectbox("Target column (y):", df.columns)

# Auto-detect task type if not demo
if "task_type" not in st.session_state or not st.session_state.demo_loaded:
    if df[target_col].nunique() <= 10 and df[target_col].dtype == 'object' or df[target_col].dtype.name == 'category':
        task_type = "classification"
    elif df[target_col].dtype in [np.int64, np.float64] and df[target_col].nunique() <= 10:
        task_type = "classification"
    else:
        task_type = "regression"
else:
    task_type = st.session_state.task_type

st.write(f"**Detected task:** `{task_type}`")

# Select features
feature_cols = [col for col in df.columns if col != target_col]
selected_features = st.multiselect(
    "Select features (X):",
    feature_cols,
    default=feature_cols
)

if not selected_features:
    st.warning("⚠️ Please select at least one feature.")
    st.stop()

# Prepare data
X = df[selected_features].copy()
y = df[target_col].copy()

# Handle categorical variables
le_dict = {}
for col in X.select_dtypes(include=['object', 'category']).columns:
    le = LabelEncoder()
    X[col] = le.fit_transform(X[col].astype(str))
    le_dict[col] = le

if task_type == "classification" and y.dtype == 'object':
    le_target = LabelEncoder()
    y = le_target.fit_transform(y.astype(str))
    class_names = le_target.classes_
else:
    class_names = None

# Train/test split
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)

# === MODEL SELECTION ===
st.subheader("⚙️ Choose Model")

if task_type == "classification":
    model_choice = st.selectbox("Model:", ["Random Forest Classifier", "Logistic Regression"])
    if model_choice == "Random Forest Classifier":
        model = RandomForestClassifier(n_estimators=100, random_state=42)
    else:
        model = LogisticRegression(max_iter=1000, random_state=42)
else:
    model_choice = st.selectbox("Model:", ["Random Forest Regressor", "Linear Regression"])
    if model_choice == "Random Forest Regressor":
        model = RandomForestRegressor(n_estimators=100, random_state=42)
    else:
        model = LinearRegression()

# Train model
model.fit(X_train, y_train)
y_pred = model.predict(X_test)

# === RESULTS ===
st.header("📈 Results")

if task_type == "classification":
    # Metrics
    acc = accuracy_score(y_test, y_pred)
    prec = precision_score(y_test, y_pred, average='weighted')
    rec = recall_score(y_test, y_pred, average='weighted')
    f1 = f1_score(y_test, y_pred, average='weighted')

    st.subheader("📊 Classification Metrics")
    col1, col2, col3, col4 = st.columns(4)
    col1.metric("Accuracy", f"{acc:.3f}")
    col2.metric("Precision", f"{prec:.3f}")
    col3.metric("Recall", f"{rec:.3f}")
    col4.metric("F1-Score", f"{f1:.3f}")

    # Classification report
    with st.expander("📋 Detailed Classification Report"):
        if class_names is not None:
            report = classification_report(y_test, y_pred, target_names=class_names, output_dict=True)
        else:
            report = classification_report(y_test, y_pred, output_dict=True)
        st.dataframe(pd.DataFrame(report).transpose())

    # Confusion Matrix
    st.subheader("🧩 Confusion Matrix")
    cm = confusion_matrix(y_test, y_pred)
    fig = px.imshow(
        cm,
        text_auto=True,
        labels=dict(x="Predicted", y="Actual"),
        x=class_names if class_names is not None else [f"Class {i}" for i in range(cm.shape[1])],
        y=class_names if class_names is not None else [f"Class {i}" for i in range(cm.shape[0])],
        title="Confusion Matrix"
    )
    st.plotly_chart(fig, use_container_width=True)

else:  # regression
    mae = mean_absolute_error(y_test, y_pred)
    mse = mean_squared_error(y_test, y_pred)
    rmse = np.sqrt(mse)
    r2 = r2_score(y_test, y_pred)

    st.subheader("📊 Regression Metrics")
    col1, col2, col3, col4 = st.columns(4)
    col1.metric("MAE", f"{mae:.2f}")
    col2.metric("MSE", f"{mse:.2f}")
    col3.metric("RMSE", f"{rmse:.2f}")
    col4.metric("R²", f"{r2:.3f}")

    # Prediction vs Actual plot
    st.subheader("📉 Predicted vs Actual")
    fig = px.scatter(x=y_test, y=y_pred, labels={'x': 'Actual', 'y': 'Predicted'}, title="Predicted vs Actual Values")
    fig.add_trace(go.Scatter(x=[y_test.min(), y_test.max()], y=[y_test.min(), y_test.max()],
                             mode='lines', name='Ideal Fit', line=dict(dash='dash', color='red')))
    st.plotly_chart(fig, use_container_width=True)

# Feature Importance (for tree-based models)
if "Forest" in model_choice:
    st.subheader("🔑 Feature Importance")
    importance = model.feature_importances_
    feat_imp_df = pd.DataFrame({
        'Feature': selected_features,
        'Importance': importance
    }).sort_values('Importance', ascending=False)

    fig = px.bar(feat_imp_df, x='Importance', y='Feature', orientation='h', title="Feature Importance")
    st.plotly_chart(fig, use_container_width=True)

    with st.expander("📋 Feature Importance Table"):
        st.dataframe(feat_imp_df)

# === PREDICTION DEMO ===
st.header("🔮 Make a Prediction")

st.write("Enter values below to predict:")

input_data = {}
for feature in selected_features:
    if feature in le_dict:
        # Categorical
        original_values = df[feature].dropna().unique()
        choice = st.selectbox(f"{feature}:", original_values, key=f"pred_{feature}")
        input_data[feature] = le_dict[feature].transform([str(choice)])[0]
    else:
        # Numeric
        if df[feature].dtype in [np.int64, np.int32]:
            val = st.number_input(f"{feature}:", value=int(df[feature].median()), step=1, key=f"pred_{feature}")
        else:
            val = st.number_input(f"{feature}:", value=float(df[feature].median()), step=0.1, key=f"pred_{feature}")
        input_data[feature] = val

if st.button("🚀 Predict"):
    input_df = pd.DataFrame([input_data])
    prediction = model.predict(input_df)[0]
    if task_type == "classification" and class_names is not None:
        prediction = class_names[prediction]
    st.success(f"**Prediction:** `{prediction}`")

# Footer
st.markdown("---")
st.caption(f"© {AUTHOR} | License {LICENSE} | Contact: {EMAIL}")