Add ImmutableRangeMap.toImmutableRangeMap with Key, Value, and Merge Functions (#6822)Issue 6822

[Mirrious]

Description

This PR implements a new Collector method called toImmutableRangeMap, which allows building an ImmutableRangeMap from a stream of elements. This functionality is useful when dealing with overlapping ranges, where a custom mergeFunction is used to handle overlapping cases.

Key Features:

• Key Function (keyFunction): A function to derive the range key from the input elements.
• Value Function (valueFunction): A function to extract the values from the input elements.
• Merge Function (mergeFunction): A binary operator to resolve values when ranges overlap.

Code Explanation

The method toImmutableRangeMap uses a TreeRangeMap to collect elements, while handling overlapping ranges:

• If an overlapping range is detected, the mergeFunction is applied to merge the values.
• The result is an immutable ImmutableRangeMap, constructed from the collected ranges and values.

Usage Example

Here's an example of how the new method can be used:

RangeMap<Instant, Integer> load(List<Job> jobs) {
    return jobs.stream().collect(
        ImmutableRangeMap.toImmutableRangeMap(
            Job::span,
            job -> 1,
            Integer::sum
        )
    );
}

Test Coverage

• Tested with overlapping ranges to ensure the mergeFunction correctly handles conflicts.
• Verified that the output ImmutableRangeMap is accurately constructed with non-overlapping ranges.
• Checked the immutability of the resulting ImmutableRangeMap.

Related Issues

Fixes #6822.

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