import { CharCode } from './charCode';

export function compareSubstring(
  a: string,
  b: string,
  aStart: number = 0,
  aEnd: number = a.length,
  bStart: number = 0,
  bEnd: number = b.length,
): number {
  for (; aStart < aEnd && bStart < bEnd; aStart++, bStart++) {
    const codeA = a.charCodeAt(aStart);
    const codeB = b.charCodeAt(bStart);
    if (codeA < codeB) {
      return -1;
    } else if (codeA > codeB) {
      return 1;
    }
  }
  const aLen = aEnd - aStart;
  const bLen = bEnd - bStart;
  if (aLen < bLen) {
    return -1;
  } else if (aLen > bLen) {
    return 1;
  }
  return 0;
}

export function compareIgnoreCase(a: string, b: string): number {
  return compareSubstringIgnoreCase(a, b, 0, a.length, 0, b.length);
}

export function compareSubstringIgnoreCase(
  a: string,
  b: string,
  aStart: number = 0,
  aEnd: number = a.length,
  bStart: number = 0,
  bEnd: number = b.length,
): number {
  for (; aStart < aEnd && bStart < bEnd; aStart++, bStart++) {
    let codeA = a.charCodeAt(aStart);
    let codeB = b.charCodeAt(bStart);

    if (codeA === codeB) {
      // equal
      continue;
    }

    if (codeA >= 128 || codeB >= 128) {
      // not ASCII letters -> fallback to lower-casing strings
      return compareSubstring(a.toLowerCase(), b.toLowerCase(), aStart, aEnd, bStart, bEnd);
    }

    // mapper lower-case ascii letter onto upper-case varinats
    // [97-122] (lower ascii) --> [65-90] (upper ascii)
    if (isLowerAsciiLetter(codeA)) {
      codeA -= 32;
    }
    if (isLowerAsciiLetter(codeB)) {
      codeB -= 32;
    }

    // compare both code points
    const diff = codeA - codeB;
    if (diff === 0) {
      continue;
    }

    return diff;
  }

  const aLen = aEnd - aStart;
  const bLen = bEnd - bStart;

  if (aLen < bLen) {
    return -1;
  } else if (aLen > bLen) {
    return 1;
  }

  return 0;
}

export function isLowerAsciiLetter(code: number): boolean {
  return code >= CharCode.a && code <= CharCode.z;
}