Write a C$++$ program that converts datetime strings from the format $"$YYYY$-$MM$-$DD HH:MM:SS$"$ to a more detailed human$-$readable format, $"$DDth of MonthName, YYYY at HH:MM AM$/$PM$".$ This conversion should involve validating the input format, converting the time from $24-$hour to $12-$hour format with appropriate AM$/$PM suffixes, and replacing the numeric month with its corresponding name $($e$.$g$.,"04"$ to "April"$).$

Validate Input Format: Ensure the input string matches the expected $"$YYYY$-$MM$-$DD HH:MM:SS$"$ format using string length and character checks.

Convert $24-$hour to $12-$hour Format: Extract the hour component and convert it to $12-$hour format, appending $"$AM$"$ or $"$PM$"$ as appropriate.

Replace Numeric Month with Name: Convert the month from a numeric value to its corresponding name $($e$.$g$.,"01"$ to "January"$).$

Format Day Suffix: Add the correct suffix to the day $($e$.$g$.,"1"$ to $"1$st$","2"$ to $"2$nd$").$