Field Layout: getOffset and insert

An object's binary layout is defined by an ordered list of fields. Each field has a unique name and a size in bytes. Fields are packed contiguously starting at byte offset 0, in list order: the first field starts at offset 0, and each subsequent field starts where the previous one ends.

For example, the field list (foo, 3), (bar, 6), (baz, 2) produces this layout:

Implement a class FieldLayout that supports the following operations:

• FieldLayout(fields) — initialize the layout from a list of (name, size) pairs, in order.
• getOffset(name) — return the starting byte offset of the field name.
• insert(name, size, index) — insert a new field with the given name and size at position index in the field order (0-based; this is a position in the list of fields, not a byte offset). All fields at position index and later shift toward the end, and their byte offsets increase by size.

Example

Starting from (foo, 3), (bar, 6), (baz, 2):

getOffset("bar") -> 3
insert("qux", 2, 1) -> layout becomes foo[0,3), qux[3,5), bar[5,11), baz[11,13)
getOffset("bar") -> 5
getOffset("baz") -> 11
insert("end", 4, 4) -> appended at the end: end[13,17)
getOffset("end") -> 13
getOffset("foo") -> 0

Constraints

• 1 <= initial number of fields <= 10^5
• 1 <= total number of getOffset and insert calls <= 10^5
• 1 <= size <= 10^4 for every field
• Field names are unique non-empty strings; getOffset is only called with the name of a field that exists in the layout.
• For every insert, 0 <= index <= current number of fields (inserting at index == current number of fields appends to the end).
• Offsets fit in a 64-bit integer.