import os

os.environ.setdefault("MPLCONFIGDIR", "/tmp/matplotlib")

import schemdraw
import schemdraw.elements as elm
from schemdraw.segments import SegmentText

FONT_NAME = "LXGW WenKai"
OUTPUT_FILE = "terminal_voltage_diagram.svg"


def add_text(
    drawing,
    position,
    text,
    *,
    rotation=0,
    align=("center", "center"),
    fontsize=18,
):
    element = elm.Element().at(position).anchor("center").hold()
    element.anchors["center"] = (0, 0)
    element.segments.append(
        SegmentText(
            (0, 0),
            text,
            rotation=rotation,
            align=align,
            fontsize=fontsize,
            font=FONT_NAME,
        )
    )
    drawing.add(element)


with schemdraw.Drawing(show=False) as d:
    d.config(
        unit=1.0,
        fontsize=18,
        font=FONT_NAME,
        lw=2.0,
        margin=0.18,
        bgcolor="white",
    )

    # ===== 几何参数 =====
    left_x = 1.5
    top_y = 6.3
    bottom_y = 2.1

    node_x = 6.1
    term_x = 8.45

    # 电池位置
    battery_x = left_x
    battery_bottom_y = 3.55
    battery_len = 1.55

    # 电阻尺寸控制
    top_res_start_x = 3.0
    top_res_len = 2.2

    vertical_res_len = 2.25

    # 关键点
    top_node = (node_x, top_y)
    bottom_node = (node_x, bottom_y)
    a_pos = (term_x, top_y)
    b_pos = (term_x, bottom_y)

    top_battery_end_y = battery_bottom_y + battery_len

    # ===== 左支路 + 电池 =====
    # 下导线到电池
    d.add(
        elm.Line()
        .at((battery_x, bottom_y))
        .up(battery_bottom_y - bottom_y)
        .hold()
    )

    # 电池
    d.add(
        elm.BatteryCell()
        .at((battery_x, battery_bottom_y))
        .up(battery_len)
        .hold()
    )

    # 电池上端到顶端导线
    d.add(
        elm.Line()
        .at((battery_x, top_battery_end_y))
        .up(top_y - top_battery_end_y)
        .hold()
    )

    # ===== 上支路 =====
    d.add(elm.Line().at((battery_x, top_y)).right(top_res_start_x - battery_x).hold())
    d.add(elm.ResistorIEC().at((top_res_start_x, top_y)).right(top_res_len).hold())
    d.add(
        elm.Line()
        .at((top_res_start_x + top_res_len, top_y))
        .right(node_x - (top_res_start_x + top_res_len))
        .hold()
    )

    # 上节点
    d.add(elm.Dot(radius=0.085).at(top_node).hold())

    # a 端
    d.add(elm.Line().at(top_node).right(term_x - node_x).hold())
    d.add(elm.Dot(open=True, radius=0.105).at(a_pos).hold())

    # ===== 中间竖支路 =====
    d.add(elm.ResistorIEC().at(top_node).down(vertical_res_len).hold())
    d.add(
        elm.Line()
        .at((node_x, top_y - vertical_res_len))
        .down((top_y - vertical_res_len) - bottom_y)
        .hold()
    )

    # 下节点
    d.add(elm.Dot(radius=0.085).at(bottom_node).hold())

    # b 端
    d.add(elm.Line().at(bottom_node).right(term_x - node_x).hold())
    d.add(elm.Dot(open=True, radius=0.105).at(b_pos).hold())

    # ===== 下支路闭合 =====
    d.add(elm.Line().at((battery_x, bottom_y)).right(node_x - battery_x).hold())

    # ===== 文本标注 =====
    # 9V：竖排，放在电池右侧偏中间，更贴近教材风格
    add_text(
        d,
        (battery_x + 0.92, battery_bottom_y + battery_len / 2),
        "10V",
        rotation=0,
        fontsize=16,
    )

    # 1kΩ：水平，置于上方电阻正下方
    add_text(
        d,
        (top_res_start_x + top_res_len / 2, top_y - 0.72),
        "1kΩ",
        rotation=0,
        fontsize=16,
    )

    # 2kΩ：竖排，置于竖直电阻左侧，方向要注意
    add_text(
        d,
        (node_x - 0.82, top_y - vertical_res_len / 2),
        "2kΩ",
        rotation=0,
        fontsize=16,
    )

    # a / b 端标注
    add_text(
        d,
        (a_pos[0] + 0.42, a_pos[1] - 0.02),
        "a",
        fontsize=19,
    )
    add_text(
        d,
        (b_pos[0] + 0.42, b_pos[1] - 0.02),
        "b",
        fontsize=19,
    )

    d.save(OUTPUT_FILE, transparent=False)