// Copyright 2013-2014 The Rust Project Developers.
// Copyright 2018 The Uuid Project Developers.
//
// See the COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use crate::{error::*, std::str};

/// Check if the length matches any of the given criteria lengths.
fn len_matches_any(len: usize, crits: &[usize]) -> bool {
    for crit in crits {
        if len == *crit {
            return true;
        }
    }

    false
}

// Accumulated length of each hyphenated group in hex digits.
const ACC_GROUP_LENS: [usize; 5] = [8, 12, 16, 20, 32];

// Length of each hyphenated group in hex digits.
const GROUP_LENS: [usize; 5] = [8, 4, 4, 4, 12];

pub fn parse_str(mut input: &str) -> Result<[u8; 16], Error> {
    // Ensure length is valid for any of the supported formats
    let len = input.len();

    if len == 45 && input.starts_with("urn:uuid:") {
        input = &input[9..];
    } else if !len_matches_any(
        len,
        &[36, 32],
    ) {
        return Err(ErrorKind::InvalidLength {
            expected: ExpectedLength::Any(&[
                36,
                32,
            ]),
            found: len,
        }
        .into());
    }

    // `digit` counts only hexadecimal digits, `i_char` counts all chars.
    let mut digit = 0;
    let mut group = 0;
    let mut acc = 0;
    let mut buffer = [0u8; 16];

    for (i_char, chr) in input.bytes().enumerate() {
        if digit as usize >= 32 && group != 4 {
            if group == 0 {
                return Err(ErrorKind::InvalidLength {
                    expected: ExpectedLength::Any(&[
                        36,
                        32,
                    ]),
                    found: len,
                }
                .into());
            }

            return Err(ErrorKind::InvalidGroupCount {
                expected: ExpectedLength::Any(&[1, 5]),
                found: group + 1,
            }
            .into());
        }

        if digit % 2 == 0 {
            // First digit of the byte.
            match chr {
                // Calculate upper half.
                b'0'..=b'9' => acc = chr - b'0',
                b'a'..=b'f' => acc = chr - b'a' + 10,
                b'A'..=b'F' => acc = chr - b'A' + 10,
                // Found a group delimiter
                b'-' => {
                    if ACC_GROUP_LENS[group] as u8 != digit {
                        // Calculate how many digits this group consists of
                        // in the input.
                        let found = if group > 0 {
                            digit - ACC_GROUP_LENS[group - 1] as u8
                        } else {
                            digit
                        };

                        return Err(ErrorKind::InvalidGroupLength {
                            expected: ExpectedLength::Exact(
                                GROUP_LENS[group],
                            ),
                            found: found as usize,
                            group,
                        }
                        .into());
                    }
                    // Next group, decrement digit, it is incremented again
                    // at the bottom.
                    group += 1;
                    digit -= 1;
                }
                _ => {
                    return Err(ErrorKind::InvalidCharacter {
                        expected: "0123456789abcdefABCDEF-",
                        found: input[i_char..].chars().next().unwrap(),
                        index: i_char,
                        urn: UrnPrefix::Optional,
                    }
                    .into());
                }
            }
        } else {
            // Second digit of the byte, shift the upper half.
            acc *= 16;
            match chr {
                b'0'..=b'9' => acc += chr - b'0',
                b'a'..=b'f' => acc += chr - b'a' + 10,
                b'A'..=b'F' => acc += chr - b'A' + 10,
                b'-' => {
                    // The byte isn't complete yet.
                    let found = if group > 0 {
                        digit - ACC_GROUP_LENS[group - 1] as u8
                    } else {
                        digit
                    };

                    return Err(ErrorKind::InvalidGroupLength {
                        expected: ExpectedLength::Exact(GROUP_LENS[group]),
                        found: found as usize,
                        group,
                    }
                    .into());
                }
                _ => {
                    return Err(ErrorKind::InvalidCharacter {
                        expected: "0123456789abcdefABCDEF-",
                        found: input[i_char..].chars().next().unwrap(),
                        index: i_char,
                        urn: UrnPrefix::Optional,
                    }
                    .into());
                }
            }
            buffer[(digit / 2) as usize] = acc;
        }
        digit += 1;
    }

    // Now check the last group.
    if ACC_GROUP_LENS[4] as u8 != digit {
        return Err(ErrorKind::InvalidGroupLength {
            expected: ExpectedLength::Exact(GROUP_LENS[4]),
            found: (digit as usize - ACC_GROUP_LENS[3]),
            group,
        }
        .into());
    }

    Ok(buffer)
}