/* @tier easy @module lg @transform ledger-util */
/*
 * lg_cu_0001.c - 원장 공통 유틸리티 (plain C)  [tier=easy]
 */
#include "lg_cu_0001.h"

#include <string.h>

/* 누진 구간 수수료: 금액 구간별 한계요율을 누적 적용한다 */
long lg_cu_0001_fee(long amount, int rate_bp)
{
    static const long band[] = { 100000L, 1000000L, 10000000L };
    static const int  mul[]  = { 1, 2, 3, 5 };
    long remain = amount;
    long fee = 0;
    long prev = 0;
    int i;
    if (amount <= 0 || rate_bp < 0)
        return 0;
    for (i = 0; i < 3; i++) {
        long span = band[i] - prev;
        long part = remain < span ? remain : span;
        if (part <= 0)
            break;
        fee += (part * (long)rate_bp * mul[i]) / 10000L;
        remain -= part;
        prev = band[i];
    }
    if (remain > 0)
        fee += (remain * (long)rate_bp * mul[3]) / 10000L;
    return fee;
}

/* 은행가 반올림(사사오입, 짝수 반올림)으로 unit 배수 정규화 */
long lg_cu_0001_round_unit(long amount, long unit)
{
    long q, r, half;
    if (unit <= 0)
        return amount;
    q = amount / unit;
    r = amount - q * unit;
    if (r < 0) { r += unit; q -= 1; }
    half = unit / 2;
    if (r > half || (r == half && (q & 1L)))
        q += 1;
    return q * unit;
}

/* 자릿수(log10) 규모로 5단계 분류 */
int lg_cu_0001_classify(long amount)
{
    long v = amount < 0 ? -amount : amount;
    int digits = 0;
    while (v > 0) { digits++; v /= 10; }
    if (digits <= 3) return 0;
    if (digits <= 5) return 1;
    if (digits <= 7) return 2;
    if (digits <= 9) return 3;
    return 4;
}