# app.py
# Simple Unit Converter for Hugging Face Spaces (Gradio)
# No models or APIs required — pure Python

import gradio as gr

# Base units: Length -> meter, Mass -> kilogram, Volume -> liter
UNITS = {
    "Length": {
        "m": 1.0,
        "cm": 0.01,
        "km": 1000.0,
        "in": 0.0254,
        "ft": 0.3048,
        "yd": 0.9144,
        "mi": 1609.344,
    },
    "Mass": {
        "kg": 1.0,
        "g": 0.001,
        "lb": 0.45359237,
        "oz": 0.028349523125,
    },
    "Volume": {
        "L": 1.0,
        "mL": 0.001,
        "gal": 3.785411784,      # US liquid gallon
        "qt": 0.946352946,       # US liquid quart
        "cup": 0.2365882365,     # US cup
    }
}

TEMP_UNITS = ["C", "F", "K"]
CATEGORIES = ["Length", "Mass", "Temperature", "Volume"]


def convert_temperature(value: float, from_u: str, to_u: str) -> float:
    if from_u == "K" and value < 0:
        raise ValueError("Kelvin cannot be negative.")
    # to Celsius
    if from_u == "C":
        c = value
    elif from_u == "F":
        c = (value - 32.0) * 5.0 / 9.0
    elif from_u == "K":
        c = value - 273.15
    else:
        raise ValueError("Unknown temperature unit.")
    # from Celsius to target
    if to_u == "C":
        return c
    elif to_u == "F":
        return c * 9.0 / 5.0 + 32.0
    elif to_u == "K":
        return c + 273.15
    else:
        raise ValueError("Unknown temperature unit.")


def convert_via_base(value: float, category: str, from_u: str, to_u: str) -> float:
    factors = UNITS[category]
    if from_u not in factors or to_u not in factors:
        raise ValueError("Unsupported unit for this category.")
    base_val = value * factors[from_u]   # to base (meter/kg/liter)
    return base_val / factors[to_u]


def convert(category: str, value, from_unit: str, to_unit: str, decimals: int):
    if value is None or str(value).strip() == "":
        return "Please enter a number."
    try:
        value = float(value)
    except:
        return "Please enter a valid number (e.g., 12.5)."
    try:
        if category == "Temperature":
            result = convert_temperature(value, from_unit, to_unit)
        else:
            result = convert_via_base(value, category, from_unit, to_unit)
        fmt = f"{{:.{int(decimals)}f}}"
        return f"{value} {from_unit} = {fmt.format(result)} {to_unit}"
    except Exception as e:
        return f"Error: {e}"


def units_for_category(category: str):
    if category == "Temperature":
        choices = TEMP_UNITS
    else:
        choices = list(UNITS[category].keys())
    default_from = choices[0]
    default_to = choices[1] if len(choices) > 1 else choices[0]
    return (
        gr.update(choices=choices, value=default_from),
        gr.update(choices=choices, value=default_to),
    )


with gr.Blocks(title="Simple Unit Converter") as demo:
    gr.Markdown(
        """
        # Simple Unit Converter
        A tiny web app to convert units (Length, Mass, Volume, Temperature).
        No models or APIs — pure Python.
        """
    )

    with gr.Row():
        category = gr.Dropdown(CATEGORIES, value="Length", label="Category")
        decimals = gr.Slider(minimum=0, maximum=10, step=1, value=3, label="Decimal places")

    value_in = gr.Number(label="Input value", value=1.0)

    with gr.Row():
        from_unit = gr.Dropdown(list(UNITS["Length"].keys()), value="m", label="From unit")
        to_unit = gr.Dropdown(list(UNITS["Length"].keys()), value="ft", label="To unit")

    convert_btn = gr.Button("Convert")
    output = gr.Textbox(label="Result", lines=1)

    category.change(fn=units_for_category, inputs=category, outputs=[from_unit, to_unit])

    convert_btn.click(fn=convert, inputs=[category, value_in, from_unit, to_unit, decimals], outputs=output)

    gr.Examples(
        examples=[
            ["Length", 1, "m", "ft", 3],
            ["Length", 12, "in", "cm", 2],
            ["Mass", 2.5, "kg", "lb", 3],
            ["Volume", 3, "L", "gal", 4],
            ["Temperature", 100, "C", "F", 1],
            ["Temperature", 300, "K", "C", 2],
        ],
        inputs=[category, value_in, from_unit, to_unit, decimals],
        label="Examples (click to fill the form)"
    )

if __name__ == "__main__":
    # Spaces runs your script and will serve the Gradio app automatically.
    demo.launch()