Fill Cell W/ Value Present In Another Row, If Columns Match

I have a slight conundrum that goes as follows:

If in a given row, the cell in column A is empty, but the cells in columns B and C have values--would it be possible to automatically fill in the empty cell with the same value of another rows column A cell, if both rows share the same value (nb: not case sensitive) in the column B and C cells.

For example:

If one row, say Row 44, contained the following:

Column A Cell =
Column B Cell = sunday
Column C Cell = dog

and another row, say Row 10023, contained:

Column A Cell = Walk
Column B Cell = Sunday
Column C Cell = Dog

How would I go about automatically filling in Row 44's column A cell with the value "Walk", as both rows columns B and C cells match up.

I should mention that I am dealing with a sheet with over 30'000 rows, so it would be incredibly time consuming to find matches and input the missing value directly.