src/streamlit_app.py

import streamlit as st
import plotly.graph_objects as go
import numpy as np
import pandas as pd

# =============================================================================
# 1. CONFIGURATION & DATA
# =============================================================================

st.set_page_config(
    page_title="Biomaterials Stress-Strain Explorer",
    page_icon="🦷",
    layout="wide",
    initial_sidebar_state="expanded"
)

# Material Database: Dental & Biomaterials
MATERIALS = {
    "🦷 Dental Amalgam": {
        "E": 80000, "yield": 200, "uts": 260, "strain": 0.006, "type": "brittle",
        "desc": "Traditional restorative alloy. High stiffness, low ductility.",
        "color": "#4A90D9"
    },
    "🦷 Composite Resin": {
        "E": 12000, "yield": 90, "uts": 120, "strain": 0.035, "type": "semi-ductile",
        "desc": "Tooth-colored restorative. Moderate stiffness and ductility.",
        "color": "#E8A838"
    },
    "🦷 Zirconia (Y-TZP)": {
        "E": 200000, "yield": 900, "uts": 1100, "strain": 0.003, "type": "brittle",
        "desc": "High-strength ceramic. Extremely stiff, very brittle failure.",
        "color": "#9B59B6"
    },
    "🦷 Gold Alloy (Type IV)": {
        "E": 85000, "yield": 350, "uts": 500, "strain": 0.12, "type": "ductile",
        "desc": "Cast noble metal. Excellent ductility and fatigue resistance.",
        "color": "#F39C12"
    },
    "🦷 Titanium (Grade 5)": {
        "E": 110000, "yield": 850, "uts": 950, "strain": 0.10, "type": "ductile",
        "desc": "Ti-6Al-4V alloy. Standard for implants. High strength-to-weight.",
        "color": "#3498DB"
    },
    "🦷 Glass Ionomer": {
        "E": 8000, "yield": 40, "uts": 55, "strain": 0.008, "type": "brittle",
        "desc": "Adhesive cement. Low strength, fluoride release.",
        "color": "#1ABC9C"
    },
    "🦴 Cortical Bone": {
        "E": 17000, "yield": 120, "uts": 150, "strain": 0.018, "type": "semi-ductile",
        "desc": "Dense outer bone. Anisotropic, moderate stiffness.",
        "color": "#ECF0F1"
    },
    "🧬 PEEK": {
        "E": 3600, "yield": 95, "uts": 100, "strain": 0.06, "type": "ductile",
        "desc": "Polyetheretherketone. Used in spinal implants. Low modulus matches bone.",
        "color": "#E74C3C"
    },
    "🧬 UHMWPE": {
        "E": 800, "yield": 20, "uts": 30, "strain": 0.35, "type": "ductile",
        "desc": "Ultra-high molecular weight polyethylene. Joint bearing surface.",
        "color": "#F1C40F"
    },
    "⚙️ Stainless Steel 316L": {
        "E": 193000, "yield": 205, "uts": 505, "strain": 0.40, "type": "ductile",
        "desc": "Austenitic steel. Surgical instruments and temporary implants.",
        "color": "#7F8C8D"
    }
}

# =============================================================================
# 2. PHYSICS ENGINE (Curve Generation)
# =============================================================================

def generate_stress_strain(E, sigma_y, sigma_uts, epsilon_break, material_type):
    """
    Generates a realistic stress-strain curve using a piecewise model.
    1. Elastic: Linear (Hooke's Law)
    2. Plastic: Cosine transition to UTS
    3. Necking: Power-law decay to fracture
    """
    # Calculate yield strain
    epsilon_y = sigma_y / E
    
    # Determine strain at UTS based on material type
    if material_type == "brittle":
        epsilon_uts = epsilon_y * 1.1
    elif material_type == "semi-ductile":
        epsilon_uts = epsilon_y + (epsilon_break - epsilon_y) * 0.5
    else: # ductile
        epsilon_uts = epsilon_y + (epsilon_break - epsilon_y) * 0.4

    # Generate strain points
    n_points = 1000
    epsilon = np.linspace(0, epsilon_break, n_points)
    sigma = np.zeros_like(epsilon)

    for i, eps in enumerate(epsilon):
        if eps <= epsilon_y:
            # Elastic Region
            sigma[i] = E * eps
        elif eps <= epsilon_uts:
            # Strain Hardening Region (Smooth transition)
            # Normalize position between yield and UTS
            t = (eps - epsilon_y) / (epsilon_uts - epsilon_y)
            # Use cosine for smooth hardening
            sigma[i] = sigma_y + (sigma_uts - sigma_y) * (0.5 * (1 - np.cos(np.pi * t)))
        else:
            # Necking / Softening Region
            t = (eps - epsilon_uts) / (epsilon_break - epsilon_uts)
            # Stress drops from UTS to near 0
            sigma[i] = sigma_uts * (1 - 0.95 * (t ** 0.7))
            
    return epsilon, np.maximum(sigma, 0)

# =============================================================================
# 3. ACCESSIBILITY HELPERS
# =============================================================================

def inject_accessibility_css():
    """Injects CSS for high contrast and large text modes."""
    st.markdown("""
    <style>
    /* High Contrast Mode */
    .high-contrast .st-emotion-cache-1lcbcih {
        background-color: #000000 !important;
        color: #FFFFFF !important;
    }
    .high-contrast .st-emotion-cache-18ni7ap {
        background-color: #000000 !important;
        color: #00FF00 !important;
        border: 2px solid #00FF00;
    }
    .high-contrast .st-emotion-cache-1v0mb8g {
        color: #FFFF00 !important;
    }
    /* Large Text Mode */
    .large-text .st-emotion-cache-1lcbcih {
        font-size: 1.5em !important;
    }
    .large-text .st-emotion-cache-18ni7ap {
        font-size: 1.5em !important;
    }
    .large-text .st-emotion-cache-1v0mb8g {
        font-size: 1.5em !important;
    }
    /* Screen Reader Only Text */
    .sr-only {
        position: absolute;
        width: 1px;
        height: 1px;
        padding: 0;
        margin: -1px;
        overflow: hidden;
        clip: rect(0, 0, 0, 0);
        white-space: nowrap;
        border: 0;
    }
    </style>
    """, unsafe_allow_html=True)

# =============================================================================
# 4. MAIN APP LOGIC
# =============================================================================

def main():
    inject_accessibility_css()
    
    # --- Sidebar: Controls & Accessibility ---
    with st.sidebar:
        st.header("⚙️ Controls")
        
        # Material Selection
        selected_material = st.selectbox(
            "Select Material Preset", 
            options=list(MATERIALS.keys()),
            index=0
        )
        
        st.markdown("---")
        st.header("📊 Parameters")
        
        # Get current preset values
        preset = MATERIALS[selected_material]
        
        # Widgets
        col1, col2 = st.columns(2)
        with col1:
            E = st.slider("Young's Modulus (MPa)", 100, 300000, int(preset["E"]), 100)
            sigma_y = st.slider("Yield Strength (MPa)", 10, 1500, int(preset["yield"]), 10)
        with col2:
            sigma_uts = st.slider("UTS (MPa)", 10, 1500, int(preset["uts"]), 10)
            epsilon_break = st.slider("Strain at Break", 0.001, 0.50, float(preset["strain"]), 0.001)
            
        st.markdown("---")
        st.header("♿ Accessibility")
        
        # Accessibility Toggles
        high_contrast = st.toggle("High Contrast Mode", value=False)
        large_text = st.toggle("Large Text Mode", value=False)
        screen_reader_mode = st.toggle("Verbose Descriptions", value=False)
        
        # Apply CSS classes based on toggles
        css_classes = []
        if high_contrast: css_classes.append("high-contrast")
        if large_text: css_classes.append("large-text")
        
        if css_classes:
            st.markdown(f'<div class="{" ".join(css_classes)}">', unsafe_allow_html=True)

    # --- Main Content ---
    
    # Title
    st.title("Biomaterials Stress-Strain Explorer")
    
    # Description Area
    st.subheader(f"Material: {selected_material}")
    st.info(preset["desc"])
    
    # Screen Reader Description (Hidden visually but readable)
    if screen_reader_mode:
        st.markdown(f"""
        <p class="sr-only">
        Chart displays stress-strain curve for {selected_material}. 
        Young's Modulus is {E} MPa. 
        Yield Strength is {sigma_y} MPa. 
        Ultimate Tensile Strength is {sigma_uts} MPa. 
        Fracture occurs at strain {epsilon_break}.
        </p>
        """, unsafe_allow_html=True)

    # --- Calculation ---
    strain, stress = generate_stress_strain(E, sigma_y, sigma_uts, epsilon_break, preset["type"])
    
    # --- Plotly Chart ---
    fig = go.Figure()
    
    # 1. The Stress-Strain Curve
    fig.add_trace(go.Scatter(
        x=strain, 
        y=stress, 
        mode='lines', 
        name='Stress-Strain',
        line=dict(color=preset["color"], width=4),
        hovertemplate="Strain: %{x:.3f}<br>Stress: %{y:.1f} MPa<extra></extra>"
    ))
    
    # 2. Elastic Modulus Line (Dashed, up to yield)
    epsilon_y = sigma_y / E
    fig.add_trace(go.Scatter(
        x=[0, epsilon_y], 
        y=[0, sigma_y], 
        mode='lines', 
        name='Elastic Modulus',
        line=dict(color='red', width=2, dash='dash'),
        hoverinfo="skip"
    ))
    
    # 3. Annotations for Key Points
    annotations = []
    
    # Yield Point
    annotations.append(dict(
        x=epsilon_y, y=sigma_y, 
        xref="x", yref="y",
        text=f"Yield Point<br>σ={sigma_y} MPa",
        showarrow=True, arrowhead=2, arrowsize=1, arrowwidth=2, arrowcolor="orange",
        bordercolor="orange", borderwidth=1, borderpad=4, bgcolor="white",
        font=dict(family="Arial", size=12, color="orange")
    ))
    
    # UTS Point
    # Find index closest to UTS for accurate annotation placement
    uts_idx = np.argmax(stress)
    uts_strain = strain[uts_idx]
    annotations.append(dict(
        x=uts_strain, y=sigma_uts, 
        xref="x", yref="y",
        text=f"UTS<br>σ={sigma_uts} MPa",
        showarrow=True, arrowhead=2, arrowsize=1, arrowwidth=2, arrowcolor="purple",
        bordercolor="purple", borderwidth=1, borderpad=4, bgcolor="white",
        font=dict(family="Arial", size=12, color="purple")
    ))
    
    # Fracture Point
    annotations.append(dict(
        x=epsilon_break, y=0, 
        xref="x", yref="y",
        text=f"Fracture<br>ε={epsilon_break}",
        showarrow=True, arrowhead=2, arrowsize=1, arrowwidth=2, arrowcolor="black",
        bordercolor="black", borderwidth=1, borderpad=4, bgcolor="white",
        font=dict(family="Arial", size=12, color="black")
    ))
    
    fig.update_layout(
        annotations=annotations,
        xaxis_title="Strain (ε) - Dimensionless",
        yaxis_title="Stress (σ) - MPa",
        title="Stress-Strain Curve",
        template="plotly_white" if not high_contrast else "plotly_dark",
        hovermode="x unified",
        legend=dict(x=0.01, y=0.99, bgcolor="rgba(255,255,255,0.8)"),
        margin=dict(l=50, r=50, t=50, b=50)
    )
    
    # Accessibility: If high contrast, force dark background on plot
    if high_contrast:
        fig.update_layout(paper_bgcolor="black", plot_bgcolor="black")
        fig.update_xaxes(gridcolor="gray", zerolinecolor="white", tickfont=dict(color="white"))
        fig.update_yaxes(gridcolor="gray", zerolinecolor="white", tickfont=dict(color="white"))

    st.plotly_chart(fig, use_container_width=True)
    
    # --- Data Table (For Accessibility/Reference) ---
    st.subheader("📋 Key Mechanical Properties")
    
    df_props = pd.DataFrame({
        "Property": ["Young's Modulus", "Yield Strength", "Ultimate Tensile Strength", "Strain at Break", "Yield Strain", "Toughness (Approx)"],
        "Value": [
            f"{E} MPa",
            f"{sigma_y} MPa",
            f"{sigma_uts} MPa",
            f"{epsilon_break}",
            f"{epsilon_y:.4f}",
            f"{np.trapezoid(stress, strain):.1f} MJ/m³"
        ],
        "Description": [
            "Stiffness in elastic region",
            "Onset of plastic deformation",
            "Maximum stress before necking",
            "Strain at fracture",
            "Calculated as σ_y / E",
            "Area under curve (Energy absorbed)"
        ]
    })
    
    st.dataframe(df_props, use_container_width=True, hide_index=True)
    
    # Close the div if we opened it for CSS classes
    if css_classes:
        st.markdown("</div>", unsafe_allow_html=True)

if __name__ == "__main__":
    main()