/**
 * Performs a binary search within a specified range.
 * @param begin The starting index of the search range.
 * @param end The ending index of the search range.
 * @param beforeHalf A list of predicates indicating conditions before the midpoint.
 * @returns A tuple containing the indices representing the binary search state: [begin, half, end].
 */
export function binSearch(begin: number, end: number, beforeHalf: boolean[]): [number, number, number] {
    const gHalf = () => { return Math.floor((end - begin) / 2) + begin; };

    for (const pred of beforeHalf) {
        const half = gHalf();
        if (pred) {
            // Happens before "half"
            end = half;
        } else {
            begin = half;
        }
    }

    const half = gHalf();
    console.log(`Checking range: [${begin}, ${end}), ${end - begin} objects, mid ${half}`);

    return [begin, half, end];
}

export async function autoBisect(
    begin: number,
    end: number,
    check: (
        begin: number,
        end: number,
        index: number
    ) => Promise<boolean>) {

    // Try to find the first index where check() predicates to true.
    // Assume check() is true at first, for range [begin, end)
    let index = 0;
    while (end - begin > 1) {
        const mid = Math.floor((end - begin) / 2) + begin;
        if (await check(begin, mid, index)) {
            // Shrink half range.
            end = mid;
        } else {
            begin = mid;
        }
        index++;
    }

    return begin;
}