# Trial - Conversion Rounding / Distance Maths
# Purpose: Test the convert_distance() logic BEFORE connecting it to the GUI.
#          This is the standalone trial of the conversion maths component.
#
# The approach: convert everything to metres first (base unit),
# then convert from metres to the target unit.
# This means only ONE formula is needed per unit, not one per unit PAIR.

# Conversion factors: how many metres is one of each unit?
TO_METERS = {
    "km": 1000,
    "m":  1,
    "cm": 0.01,
    "mm": 0.001
}


def convert_distance(value, from_unit, to_unit):
    """
    Converts a distance value from one unit to another.
    Uses metres as an intermediate base unit.
    """
    # Step 1: convert the input value to metres
    in_metres = value * TO_METERS[from_unit]

    # Step 2: convert metres to the target unit
    result = in_metres / TO_METERS[to_unit]

    # Step 3: round to 4 decimal places, strip trailing zeros
    rounded = round(result, 4)

    if rounded == int(rounded):
        return int(rounded)
    return rounded


# ===== Test runs =====

print("===== Expected value tests =====")

tests = [
    (1,    "km", "m",  1000),
    (1000, "m",  "km", 1),
    (1,    "m",  "cm", 100),
    (100,  "cm", "m",  1),
    (1,    "cm", "mm", 10),
    (10,   "mm", "cm", 1),
    (1,    "km", "cm", 100000),
    (1,    "km", "mm", 1000000),
    (2.5,  "km", "m",  2500),
    (500,  "m",  "mm", 500000),
]

all_passed = True
for value, from_unit, to_unit, expected in tests:
    result = convert_distance(value, from_unit, to_unit)
    status = "PASS" if result == expected else "FAIL"
    if status == "FAIL":
        all_passed = False
    print(f"  {status}: {value} {from_unit} -> {to_unit} = {result}  (expected {expected})")

print()
if all_passed:
    print("All tests passed!")
else:
    print("Some tests FAILED - check logic above.")

print()
print("===== Decimal / boundary tests =====")

decimal_tests = [
    (0,    "km", "m"),
    (0.001,"km", "m"),
    (1.5,  "m",  "cm"),
    (999,  "mm", "m"),
]

for value, from_unit, to_unit in decimal_tests:
    result = convert_distance(value, from_unit, to_unit)
    print(f"  {value} {from_unit} -> {to_unit} = {result}")