// Copyright 2017-2025 @polkadot/util authors & contributors
// SPDX-License-Identifier: Apache-2.0

// Adapted from https://github.com/JulienPalard/is_utf8/blob/master/is_utf8.c

import { u8aToU8a } from '../u8a/toU8a.js';
import { isString } from './string.js';

/**
 * @name isUtf8
 * @summary Tests if the input is valid Utf8
 * @description
 * Checks to see if the input string or Uint8Array is valid Utf8
 */
export function isUtf8 (value?: number[] | Uint8Array | string | null): boolean {
  if (!value) {
    return isString(value);
  }

  const u8a = u8aToU8a(value);
  const len = u8a.length;
  let i = 0;

  while (i < len) {
    if (u8a[i] <= 0x7F) /* 00..7F */ {
      i += 1;
    } else if (u8a[i] >= 0xC2 && u8a[i] <= 0xDF) /* C2..DF 80..BF */ {
      if (i + 1 < len) /* Expect a 2nd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // *message = "After a first byte between C2 and DF, expecting a 2nd byte between 80 and BF";
          // *faulty_bytes = 2;
          return false;
        }
      } else {
        // *message = "After a first byte between C2 and DF, expecting a 2nd byte.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 2;
    } else if (u8a[i] === 0xE0) /* E0 A0..BF 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0xA0 || u8a[i + 1] > 0xBF) {
          // *message = "After a first byte of E0, expecting a 2nd byte between A0 and BF.";
          // *faulty_bytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // *message = "After a first byte of E0, expecting a 3nd byte between 80 and BF.";
          // *faulty_bytes = 3;
          return false;
        }
      } else {
        // *message = "After a first byte of E0, expecting two following bytes.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] >= 0xE1 && u8a[i] <= 0xEC) /* E1..EC 80..BF 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // *message = "After a first byte between E1 and EC, expecting the 2nd byte between 80 and BF.";
          // *faulty_bytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // *message = "After a first byte between E1 and EC, expecting the 3rd byte between 80 and BF.";
          // *faulty_bytes = 3;
          return false;
        }
      } else {
        // *message = "After a first byte between E1 and EC, expecting two following bytes.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] === 0xED) /* ED 80..9F 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0x9F) {
          // *message = "After a first byte of ED, expecting 2nd byte between 80 and 9F.";
          // *faulty_bytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // *message = "After a first byte of ED, expecting 3rd byte between 80 and BF.";
          // *faulty_bytes = 3;
          return false;
        }
      } else {
        // *message = "After a first byte of ED, expecting two following bytes.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] >= 0xEE && u8a[i] <= 0xEF) /* EE..EF 80..BF 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // *message = "After a first byte between EE and EF, expecting 2nd byte between 80 and BF.";
          // *faulty_bytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // *message = "After a first byte between EE and EF, expecting 3rd byte between 80 and BF.";
          // *faulty_bytes = 3;
          return false;
        }
      } else {
        // *message = "After a first byte between EE and EF, two following bytes.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] === 0xF0) /* F0 90..BF 80..BF 80..BF */ {
      if (i + 3 < len) /* Expect a 2nd, 3rd 3th byte */ {
        if (u8a[i + 1] < 0x90 || u8a[i + 1] > 0xBF) {
          // *message = "After a first byte of F0, expecting 2nd byte between 90 and BF.";
          // *faulty_bytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // *message = "After a first byte of F0, expecting 3rd byte between 80 and BF.";
          // *faulty_bytes = 3;
          return false;
        }

        if (u8a[i + 3] < 0x80 || u8a[i + 3] > 0xBF) {
          // *message = "After a first byte of F0, expecting 4th byte between 80 and BF.";
          // *faulty_bytes = 4;
          return false;
        }
      } else {
        // *message = "After a first byte of F0, expecting three following bytes.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 4;
    } else if (u8a[i] >= 0xF1 && u8a[i] <= 0xF3) /* F1..F3 80..BF 80..BF 80..BF */ {
      if (i + 3 < len) /* Expect a 2nd, 3rd 3th byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // *message = "After a first byte of F1, F2, or F3, expecting a 2nd byte between 80 and BF.";
          // *faulty_bytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // *message = "After a first byte of F1, F2, or F3, expecting a 3rd byte between 80 and BF.";
          // *faulty_bytes = 3;
          return false;
        }

        if (u8a[i + 3] < 0x80 || u8a[i + 3] > 0xBF) {
          // *message = "After a first byte of F1, F2, or F3, expecting a 4th byte between 80 and BF.";
          // *faulty_bytes = 4;
          return false;
        }
      } else {
        // *message = "After a first byte of F1, F2, or F3, expecting three following bytes.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 4;
    } else if (u8a[i] === 0xF4) /* F4 80..8F 80..BF 80..BF */ {
      if (i + 3 < len) /* Expect a 2nd, 3rd 3th byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0x8F) {
          // *message = "After a first byte of F4, expecting 2nd byte between 80 and 8F.";
          // *faulty_bytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // *message = "After a first byte of F4, expecting 3rd byte between 80 and BF.";
          // *faulty_bytes = 3;
          return false;
        }

        if (u8a[i + 3] < 0x80 || u8a[i + 3] > 0xBF) {
          // *message = "After a first byte of F4, expecting 4th byte between 80 and BF.";
          // *faulty_bytes = 4;
          return false;
        }
      } else {
        // *message = "After a first byte of F4, expecting three following bytes.";
        // *faulty_bytes = 1;
        return false;
      }

      i += 4;
    } else {
      // *message = "Expecting bytes in the following ranges: 00..7F C2..F4.";
      // *faulty_bytes = 1;
      return false;
    }
  }

  return true;
}
