from pathlib import Path
from typing import List, Tuple

import matplotlib.pyplot as plt


def read_points(filename: str) -> List[Tuple[float, float, float]]:
    pts = []
    for line in Path(filename).read_text(encoding="utf-8").splitlines():
        line = line.strip()
        if not line or line.startswith("#"):
            continue
        parts = line.split()
        if len(parts) < 3:
            continue
        x = float(parts[0])
        y = float(parts[1])
        phi = float(parts[2])
        pts.append((x, y, phi))
    return pts


def phi_vs_x_at_y(
    points: List[Tuple[float, float, float]], y_target: float, tol: float = 1e-6
):
    xs = []
    phis = []
    for x, y, phi in points:
        if abs(y - y_target) <= tol:
            xs.append(x)
            phis.append(phi)
    paired = sorted(zip(xs, phis), key=lambda p: p[0])
    if not paired:
        return [], []
    xs_sorted, phis_sorted = zip(*paired)
    return list(xs_sorted), list(phis_sorted)


p1 = read_points("points1.txt")
p2 = read_points("points2.txt")

x1, yphi1 = phi_vs_x_at_y(p1, 10.0)
x2, yphi2 = phi_vs_x_at_y(p2, 10.0)

plt.figure(figsize=(10, 5))
if x1:
    plt.plot(x1, yphi1, marker="o", linestyle="-", label="points1.txt (Y=10)")
if x2:
    plt.plot(x2, yphi2, marker="s", linestyle="--", label="points2.txt (Y=10)")
plt.xlabel("X (см)")
plt.ylabel("φ (В)")
plt.title("Зависимость φ = φ(X) при Y = 10 см")
plt.grid(alpha=0.4)
plt.legend()
plt.savefig("phi_vs_x_Y10.png", dpi=300)