import numpy as np

def symmetric_timestamps(total_duration: float, num_points: int, flat_ratio: float = 0.3) -> list:
    """
    Generate symmetric timestamps with increasing → decreasing → flat → increasing spacing pattern.

    Args:
        total_duration (float): The total duration (last timestamp).
        num_points (int): Total number of timestamps (must be >= 3).
        flat_ratio (float): Fraction of timestamps in the constant-spacing center (0.0–0.9).

    Returns:
        List[float]: List of timestamps from 0 to total_duration.
    """
    n = int(num_points*(1-flat_ratio)/2)
    start = np.cos(np.linspace(0, np.pi, n))+2
    end = np.cos(np.linspace(-np.pi, 0, n))+2
    flat = np.ones(num_points-2*n)

    timestamps = np.concatenate((start, flat, end))
    timestamps *= total_duration / timestamps.sum()
    timestamps = np.cumsum(timestamps)

    return timestamps.tolist()



a = symmetric_timestamps(7.5, 30, 0.7)

for i in range(len(a)-1):
    print(f"{a[i]:.2f} - {a[i+1]:.2f} = {a[i+1]-a[i]}")