"""
Ex 6.9 from "A primer on..."
Modify code from ex. 3.16 (or 4.4 in the Exercises booklet)
to make the argument a dict instead of a list.

Steps:
1. Start with the function and test function from exercise 4.4 in the
exercise booklet.
2. Modify the test function to give the vertices as a dictionary
on the format given in the question text. This makes the code fail, since
the function triangle_area still expects a list
3. Modify how the argument is treated inside triangle_area, to look up a dictionary
rather than index a list.
"""


def triangle_area(v):
    # v is a dictionary with keys 1,2,3, and coordinates as values
    [x1,y1] = v[1]
    [x2,y2] = v[2]
    [x3,y3] = v[3]
    # or more verbose code:
    # x1 = v[0][0]; y1 = v[0][1] etc

    A = abs(0.5*( (x2*y3)-(x3*y2)-(x1*y3)+(x3*y1)+(x1*y2)-(x2*y1) ))
    return A


# From book
def test_triangle_area():
    """
    Verify the area of a triangle with vertex coordinates
    (0,0), (1,0), and (0,2).
    """
    v1 = (0,0);  v2 = (1,0);  v3 = (0,2)
    vertices = {1:v1,2:v2,3:v3} #[v1, v2, v3]
    expected = 1
    computed = triangle_area(vertices)
    tol = 1E-14
    success = abs(expected - computed) < tol
    msg = f"computed area={computed} != {expected}(expected)"
    assert success, msg

test_triangle_area()

"""
Terminal> python area_triangle_dict.py
"""