Find min peak element in an array

from typing import List

def peak_finder(arr : List[int]) -> int:
    if len(arr) < 3:
        return -1
    min_peak = float("inf") # let the initial value of the min peak be +infinity
    for i in range(len(arr) - 2):
        trail, mid, ahead = arr[i], arr[i + 1], arr[i + 2]
        if trail < mid > ahead:
            min_peak = min(mid, min_peak)
    return min_peak

arr = [5, 1, 3, 2, 4, 8, 7]
print(f"The min peak element in {arr} is : {peak_finder(arr)}")