use std::str::FromStr;

use chinese_number::{
    from_u64_to_chinese_ten_thousand as u64_to_chinese, ChineseCase, ChineseVariant,
};
use comemo::Tracked;
use ecow::{eco_format, EcoString, EcoVec};

use crate::diag::SourceResult;
use crate::engine::Engine;
use crate::foundations::{cast, func, Context, Func, Str, Value};

/// Applies a numbering to a sequence of numbers.
///
/// A numbering defines how a sequence of numbers should be displayed as
/// content. It is defined either through a pattern string or an arbitrary
/// function.
///
/// A numbering pattern consists of counting symbols, for which the actual
/// number is substituted, their prefixes, and one suffix. The prefixes and the
/// suffix are repeated as-is.
///
/// # Example
/// ```example
/// #numbering("1.1)", 1, 2, 3) \
/// #numbering("1.a.i", 1, 2) \
/// #numbering("I – 1", 12, 2) \
/// #numbering(
///   (..nums) => nums
///     .pos()
///     .map(str)
///     .join(".") + ")",
///   1, 2, 3,
/// )
/// ```
///
/// # Numbering patterns and numbering functions
/// There are multiple instances where you can provide a numbering pattern or
/// function in Typst. For example, when defining how to number
/// [headings]($heading) or [figures]($figure). Every time, the expected format
/// is the same as the one described below for the
/// [`numbering`]($numbering.numbering) parameter.
///
/// The following example illustrates that a numbering function is just a
/// regular [function] that accepts numbers and returns [`content`].
/// ```example
/// #let unary(.., last) = "|" * last
/// #set heading(numbering: unary)
/// = First heading
/// = Second heading
/// = Third heading
/// ```
#[func]
pub fn numbering(
    engine: &mut Engine,
    context: Tracked<Context>,
    /// Defines how the numbering works.
    ///
    /// **Counting symbols** are `1`, `a`, `A`, `i`, `I`, `α`, `Α`, `一`, `壹`,
    /// `あ`, `い`, `ア`, `イ`, `א`, `가`, `ㄱ`, `*`, `١`, `۱`, `१`, `১`, `ক`,
    /// `①`, and `⓵`. They are replaced by the number in the sequence,
    /// preserving the original case.
    ///
    /// The `*` character means that symbols should be used to count, in the
    /// order of `*`, `†`, `‡`, `§`, `¶`, `‖`. If there are more than six
    /// items, the number is represented using repeated symbols.
    ///
    /// **Suffixes** are all characters after the last counting symbol. They are
    /// repeated as-is at the end of any rendered number.
    ///
    /// **Prefixes** are all characters that are neither counting symbols nor
    /// suffixes. They are repeated as-is at in front of their rendered
    /// equivalent of their counting symbol.
    ///
    /// This parameter can also be an arbitrary function that gets each number
    /// as an individual argument. When given a function, the `numbering`
    /// function just forwards the arguments to that function. While this is not
    /// particularly useful in itself, it means that you can just give arbitrary
    /// numberings to the `numbering` function without caring whether they are
    /// defined as a pattern or function.
    numbering: Numbering,
    /// The numbers to apply the numbering to. Must be positive.
    ///
    /// If `numbering` is a pattern and more numbers than counting symbols are
    /// given, the last counting symbol with its prefix is repeated.
    #[variadic]
    numbers: Vec<u64>,
) -> SourceResult<Value> {
    numbering.apply(engine, context, &numbers)
}

/// How to number a sequence of things.
#[derive(Debug, Clone, PartialEq, Hash)]
pub enum Numbering {
    /// A pattern with prefix, numbering, lower / upper case and suffix.
    Pattern(NumberingPattern),
    /// A closure mapping from an item's number to content.
    Func(Func),
}

impl Numbering {
    /// Apply the pattern to the given numbers.
    pub fn apply(
        &self,
        engine: &mut Engine,
        context: Tracked<Context>,
        numbers: &[u64],
    ) -> SourceResult<Value> {
        Ok(match self {
            Self::Pattern(pattern) => Value::Str(pattern.apply(numbers).into()),
            Self::Func(func) => func.call(engine, context, numbers.iter().copied())?,
        })
    }

    /// Trim the prefix suffix if this is a pattern.
    pub fn trimmed(mut self) -> Self {
        if let Self::Pattern(pattern) = &mut self {
            pattern.trimmed = true;
        }
        self
    }
}

impl From<NumberingPattern> for Numbering {
    fn from(pattern: NumberingPattern) -> Self {
        Self::Pattern(pattern)
    }
}

cast! {
    Numbering,
    self => match self {
        Self::Pattern(pattern) => pattern.into_value(),
        Self::Func(func) => func.into_value(),
    },
    v: NumberingPattern => Self::Pattern(v),
    v: Func => Self::Func(v),
}

/// How to turn a number into text.
///
/// A pattern consists of a prefix, followed by one of the counter symbols (see
/// [`numbering()`] docs), and then a suffix.
///
/// Examples of valid patterns:
/// - `1)`
/// - `a.`
/// - `(I)`
#[derive(Debug, Clone, Eq, PartialEq, Hash)]
pub struct NumberingPattern {
    pub pieces: EcoVec<(EcoString, NumberingKind)>,
    pub suffix: EcoString,
    trimmed: bool,
}

impl NumberingPattern {
    /// Apply the pattern to the given number.
    pub fn apply(&self, numbers: &[u64]) -> EcoString {
        let mut fmt = EcoString::new();
        let mut numbers = numbers.iter();

        for (i, ((prefix, kind), &n)) in self.pieces.iter().zip(&mut numbers).enumerate()
        {
            if i > 0 || !self.trimmed {
                fmt.push_str(prefix);
            }
            fmt.push_str(&kind.apply(n));
        }

        for ((prefix, kind), &n) in self.pieces.last().into_iter().cycle().zip(numbers) {
            if prefix.is_empty() {
                fmt.push_str(&self.suffix);
            } else {
                fmt.push_str(prefix);
            }
            fmt.push_str(&kind.apply(n));
        }

        if !self.trimmed {
            fmt.push_str(&self.suffix);
        }

        fmt
    }

    /// Apply only the k-th segment of the pattern to a number.
    pub fn apply_kth(&self, k: usize, number: u64) -> EcoString {
        let mut fmt = EcoString::new();
        if let Some((prefix, _)) = self.pieces.first() {
            fmt.push_str(prefix);
        }
        if let Some((_, kind)) = self
            .pieces
            .iter()
            .chain(self.pieces.last().into_iter().cycle())
            .nth(k)
        {
            fmt.push_str(&kind.apply(number));
        }
        fmt.push_str(&self.suffix);
        fmt
    }

    /// How many counting symbols this pattern has.
    pub fn pieces(&self) -> usize {
        self.pieces.len()
    }
}

impl FromStr for NumberingPattern {
    type Err = &'static str;

    fn from_str(pattern: &str) -> Result<Self, Self::Err> {
        let mut pieces = EcoVec::new();
        let mut handled = 0;

        for (i, c) in pattern.char_indices() {
            let Some(kind) = NumberingKind::from_char(c) else {
                continue;
            };

            let prefix = pattern[handled..i].into();
            pieces.push((prefix, kind));
            handled = c.len_utf8() + i;
        }

        let suffix = pattern[handled..].into();
        if pieces.is_empty() {
            return Err("invalid numbering pattern");
        }

        Ok(Self { pieces, suffix, trimmed: false })
    }
}

cast! {
    NumberingPattern,
    self => {
        let mut pat = EcoString::new();
        for (prefix, kind) in &self.pieces {
            pat.push_str(prefix);
            pat.push(kind.to_char());
        }
        pat.push_str(&self.suffix);
        pat.into_value()
    },
    v: Str => v.parse()?,
}

/// Different kinds of numberings.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum NumberingKind {
    /// Arabic numerals (1, 2, 3, etc.).
    Arabic,
    /// Lowercase Latin letters (a, b, c, etc.). Items beyond z use base-26.
    LowerLatin,
    /// Uppercase Latin letters (A, B, C, etc.). Items beyond Z use base-26.
    UpperLatin,
    /// Lowercase Roman numerals (i, ii, iii, etc.).
    LowerRoman,
    /// Uppercase Roman numerals (I, II, III, etc.).
    UpperRoman,
    /// Lowercase Greek letters (α, β, γ, etc.).
    LowerGreek,
    /// Uppercase Greek letters (Α, Β, Γ, etc.).
    UpperGreek,
    /// Paragraph/note-like symbols: *, †, ‡, §, ¶, and ‖. Further items use
    /// repeated symbols.
    Symbol,
    /// Hebrew numerals, including Geresh/Gershayim.
    Hebrew,
    /// Simplified Chinese standard numerals. This corresponds to the
    /// `ChineseCase::Lower` variant.
    LowerSimplifiedChinese,
    /// Simplified Chinese "banknote" numerals. This corresponds to the
    /// `ChineseCase::Upper` variant.
    UpperSimplifiedChinese,
    // TODO: Pick the numbering pattern based on languages choice.
    // As the first character of Simplified and Traditional Chinese numbering
    // are the same, we are unable to determine if the context requires
    // Simplified or Traditional by only looking at this character.
    #[allow(unused)]
    /// Traditional Chinese standard numerals. This corresponds to the
    /// `ChineseCase::Lower` variant.
    LowerTraditionalChinese,
    #[allow(unused)]
    /// Traditional Chinese "banknote" numerals. This corresponds to the
    /// `ChineseCase::Upper` variant.
    UpperTraditionalChinese,
    /// Hiragana in the gojūon order. Includes n but excludes wi and we.
    HiraganaAiueo,
    /// Hiragana in the iroha order. Includes wi and we but excludes n.
    HiraganaIroha,
    /// Katakana in the gojūon order. Includes n but excludes wi and we.
    KatakanaAiueo,
    /// Katakana in the iroha order. Includes wi and we but excludes n.
    KatakanaIroha,
    /// Korean jamo (ㄱ, ㄴ, ㄷ, etc.).
    KoreanJamo,
    /// Korean syllables (가, 나, 다, etc.).
    KoreanSyllable,
    /// Eastern Arabic numerals, used in some Arabic-speaking countries.
    EasternArabic,
    /// The variant of Eastern Arabic numerals used in Persian and Urdu.
    EasternArabicPersian,
    /// Devanagari numerals.
    DevanagariNumber,
    /// Bengali numerals.
    BengaliNumber,
    /// Bengali letters (ক, খ, গ, ...কক, কখ etc.).
    BengaliLetter,
    /// Circled numbers (①, ②, ③, etc.), up to 50.
    CircledNumber,
    /// Double-circled numbers (⓵, ⓶, ⓷, etc.), up to 10.
    DoubleCircledNumber,
}

impl NumberingKind {
    /// Create a numbering kind from a representative character.
    pub fn from_char(c: char) -> Option<Self> {
        Some(match c {
            '1' => NumberingKind::Arabic,
            'a' => NumberingKind::LowerLatin,
            'A' => NumberingKind::UpperLatin,
            'i' => NumberingKind::LowerRoman,
            'I' => NumberingKind::UpperRoman,
            'α' => NumberingKind::LowerGreek,
            'Α' => NumberingKind::UpperGreek,
            '*' => NumberingKind::Symbol,
            'א' => NumberingKind::Hebrew,
            '一' => NumberingKind::LowerSimplifiedChinese,
            '壹' => NumberingKind::UpperSimplifiedChinese,
            'あ' => NumberingKind::HiraganaAiueo,
            'い' => NumberingKind::HiraganaIroha,
            'ア' => NumberingKind::KatakanaAiueo,
            'イ' => NumberingKind::KatakanaIroha,
            'ㄱ' => NumberingKind::KoreanJamo,
            '가' => NumberingKind::KoreanSyllable,
            '\u{0661}' => NumberingKind::EasternArabic,
            '\u{06F1}' => NumberingKind::EasternArabicPersian,
            '\u{0967}' => NumberingKind::DevanagariNumber,
            '\u{09E7}' => NumberingKind::BengaliNumber,
            '\u{0995}' => NumberingKind::BengaliLetter,
            '①' => NumberingKind::CircledNumber,
            '⓵' => NumberingKind::DoubleCircledNumber,
            _ => return None,
        })
    }

    /// The representative character for this numbering kind.
    pub fn to_char(self) -> char {
        match self {
            Self::Arabic => '1',
            Self::LowerLatin => 'a',
            Self::UpperLatin => 'A',
            Self::LowerRoman => 'i',
            Self::UpperRoman => 'I',
            Self::LowerGreek => 'α',
            Self::UpperGreek => 'Α',
            Self::Symbol => '*',
            Self::Hebrew => 'א',
            Self::LowerSimplifiedChinese | Self::LowerTraditionalChinese => '一',
            Self::UpperSimplifiedChinese | Self::UpperTraditionalChinese => '壹',
            Self::HiraganaAiueo => 'あ',
            Self::HiraganaIroha => 'い',
            Self::KatakanaAiueo => 'ア',
            Self::KatakanaIroha => 'イ',
            Self::KoreanJamo => 'ㄱ',
            Self::KoreanSyllable => '가',
            Self::EasternArabic => '\u{0661}',
            Self::EasternArabicPersian => '\u{06F1}',
            Self::DevanagariNumber => '\u{0967}',
            Self::BengaliNumber => '\u{09E7}',
            Self::BengaliLetter => '\u{0995}',
            Self::CircledNumber => '①',
            Self::DoubleCircledNumber => '⓵',
        }
    }

    /// Apply the numbering to the given number.
    pub fn apply(self, n: u64) -> EcoString {
        match self {
            Self::Arabic => {
                numeric(&['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'], n)
            }
            Self::LowerRoman => additive(
                &[
                    ("m̅", 1000000),
                    ("d̅", 500000),
                    ("c̅", 100000),
                    ("l̅", 50000),
                    ("x̅", 10000),
                    ("v̅", 5000),
                    ("i̅v̅", 4000),
                    ("m", 1000),
                    ("cm", 900),
                    ("d", 500),
                    ("cd", 400),
                    ("c", 100),
                    ("xc", 90),
                    ("l", 50),
                    ("xl", 40),
                    ("x", 10),
                    ("ix", 9),
                    ("v", 5),
                    ("iv", 4),
                    ("i", 1),
                    ("n", 0),
                ],
                n,
            ),
            Self::UpperRoman => additive(
                &[
                    ("M̅", 1000000),
                    ("D̅", 500000),
                    ("C̅", 100000),
                    ("L̅", 50000),
                    ("X̅", 10000),
                    ("V̅", 5000),
                    ("I̅V̅", 4000),
                    ("M", 1000),
                    ("CM", 900),
                    ("D", 500),
                    ("CD", 400),
                    ("C", 100),
                    ("XC", 90),
                    ("L", 50),
                    ("XL", 40),
                    ("X", 10),
                    ("IX", 9),
                    ("V", 5),
                    ("IV", 4),
                    ("I", 1),
                    ("N", 0),
                ],
                n,
            ),
            Self::LowerGreek => additive(
                &[
                    ("͵θ", 9000),
                    ("͵η", 8000),
                    ("͵ζ", 7000),
                    ("͵ϛ", 6000),
                    ("͵ε", 5000),
                    ("͵δ", 4000),
                    ("͵γ", 3000),
                    ("͵β", 2000),
                    ("͵α", 1000),
                    ("ϡ", 900),
                    ("ω", 800),
                    ("ψ", 700),
                    ("χ", 600),
                    ("φ", 500),
                    ("υ", 400),
                    ("τ", 300),
                    ("σ", 200),
                    ("ρ", 100),
                    ("ϟ", 90),
                    ("π", 80),
                    ("ο", 70),
                    ("ξ", 60),
                    ("ν", 50),
                    ("μ", 40),
                    ("λ", 30),
                    ("κ", 20),
                    ("ι", 10),
                    ("θ", 9),
                    ("η", 8),
                    ("ζ", 7),
                    ("ϛ", 6),
                    ("ε", 5),
                    ("δ", 4),
                    ("γ", 3),
                    ("β", 2),
                    ("α", 1),
                    ("𐆊", 0),
                ],
                n,
            ),
            Self::UpperGreek => additive(
                &[
                    ("͵Θ", 9000),
                    ("͵Η", 8000),
                    ("͵Ζ", 7000),
                    ("͵Ϛ", 6000),
                    ("͵Ε", 5000),
                    ("͵Δ", 4000),
                    ("͵Γ", 3000),
                    ("͵Β", 2000),
                    ("͵Α", 1000),
                    ("Ϡ", 900),
                    ("Ω", 800),
                    ("Ψ", 700),
                    ("Χ", 600),
                    ("Φ", 500),
                    ("Υ", 400),
                    ("Τ", 300),
                    ("Σ", 200),
                    ("Ρ", 100),
                    ("Ϟ", 90),
                    ("Π", 80),
                    ("Ο", 70),
                    ("Ξ", 60),
                    ("Ν", 50),
                    ("Μ", 40),
                    ("Λ", 30),
                    ("Κ", 20),
                    ("Ι", 10),
                    ("Θ", 9),
                    ("Η", 8),
                    ("Ζ", 7),
                    ("Ϛ", 6),
                    ("Ε", 5),
                    ("Δ", 4),
                    ("Γ", 3),
                    ("Β", 2),
                    ("Α", 1),
                    ("𐆊", 0),
                ],
                n,
            ),
            Self::Hebrew => additive(
                &[
                    ("ת", 400),
                    ("ש", 300),
                    ("ר", 200),
                    ("ק", 100),
                    ("צ", 90),
                    ("פ", 80),
                    ("ע", 70),
                    ("ס", 60),
                    ("נ", 50),
                    ("מ", 40),
                    ("ל", 30),
                    ("כ", 20),
                    ("יט", 19),
                    ("יח", 18),
                    ("יז", 17),
                    ("טז", 16),
                    ("טו", 15),
                    ("י", 10),
                    ("ט", 9),
                    ("ח", 8),
                    ("ז", 7),
                    ("ו", 6),
                    ("ה", 5),
                    ("ד", 4),
                    ("ג", 3),
                    ("ב", 2),
                    ("א", 1),
                    ("-", 0),
                ],
                n,
            ),
            Self::LowerLatin => alphabetic(
                &[
                    'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
                    'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
                ],
                n,
            ),
            Self::UpperLatin => alphabetic(
                &[
                    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
                    'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
                ],
                n,
            ),
            Self::HiraganaAiueo => alphabetic(
                &[
                    'あ', 'い', 'う', 'え', 'お', 'か', 'き', 'く', 'け', 'こ', 'さ',
                    'し', 'す', 'せ', 'そ', 'た', 'ち', 'つ', 'て', 'と', 'な', 'に',
                    'ぬ', 'ね', 'の', 'は', 'ひ', 'ふ', 'へ', 'ほ', 'ま', 'み', 'む',
                    'め', 'も', 'や', 'ゆ', 'よ', 'ら', 'り', 'る', 'れ', 'ろ', 'わ',
                    'を', 'ん',
                ],
                n,
            ),
            Self::HiraganaIroha => alphabetic(
                &[
                    'い', 'ろ', 'は', 'に', 'ほ', 'へ', 'と', 'ち', 'り', 'ぬ', 'る',
                    'を', 'わ', 'か', 'よ', 'た', 'れ', 'そ', 'つ', 'ね', 'な', 'ら',
                    'む', 'う', 'ゐ', 'の', 'お', 'く', 'や', 'ま', 'け', 'ふ', 'こ',
                    'え', 'て', 'あ', 'さ', 'き', 'ゆ', 'め', 'み', 'し', 'ゑ', 'ひ',
                    'も', 'せ', 'す',
                ],
                n,
            ),
            Self::KatakanaAiueo => alphabetic(
                &[
                    'ア', 'イ', 'ウ', 'エ', 'オ', 'カ', 'キ', 'ク', 'ケ', 'コ', 'サ',
                    'シ', 'ス', 'セ', 'ソ', 'タ', 'チ', 'ツ', 'テ', 'ト', 'ナ', 'ニ',
                    'ヌ', 'ネ', 'ノ', 'ハ', 'ヒ', 'フ', 'ヘ', 'ホ', 'マ', 'ミ', 'ム',
                    'メ', 'モ', 'ヤ', 'ユ', 'ヨ', 'ラ', 'リ', 'ル', 'レ', 'ロ', 'ワ',
                    'ヲ', 'ン',
                ],
                n,
            ),
            Self::KatakanaIroha => alphabetic(
                &[
                    'イ', 'ロ', 'ハ', 'ニ', 'ホ', 'ヘ', 'ト', 'チ', 'リ', 'ヌ', 'ル',
                    'ヲ', 'ワ', 'カ', 'ヨ', 'タ', 'レ', 'ソ', 'ツ', 'ネ', 'ナ', 'ラ',
                    'ム', 'ウ', 'ヰ', 'ノ', 'オ', 'ク', 'ヤ', 'マ', 'ケ', 'フ', 'コ',
                    'エ', 'テ', 'ア', 'サ', 'キ', 'ユ', 'メ', 'ミ', 'シ', 'ヱ', 'ヒ',
                    'モ', 'セ', 'ス',
                ],
                n,
            ),
            Self::KoreanJamo => alphabetic(
                &[
                    'ㄱ', 'ㄴ', 'ㄷ', 'ㄹ', 'ㅁ', 'ㅂ', 'ㅅ', 'ㅇ', 'ㅈ', 'ㅊ', 'ㅋ',
                    'ㅌ', 'ㅍ', 'ㅎ',
                ],
                n,
            ),
            Self::KoreanSyllable => alphabetic(
                &[
                    '가', '나', '다', '라', '마', '바', '사', '아', '자', '차', '카',
                    '타', '파', '하',
                ],
                n,
            ),
            Self::BengaliLetter => alphabetic(
                &[
                    'ক', 'খ', 'গ', 'ঘ', 'ঙ', 'চ', 'ছ', 'জ', 'ঝ', 'ঞ', 'ট', 'ঠ', 'ড', 'ঢ',
                    'ণ', 'ত', 'থ', 'দ', 'ধ', 'ন', 'প', 'ফ', 'ব', 'ভ', 'ম', 'য', 'র', 'ল',
                    'শ', 'ষ', 'স', 'হ',
                ],
                n,
            ),
            Self::CircledNumber => fixed(
                &[
                    '⓪', '①', '②', '③', '④', '⑤', '⑥', '⑦', '⑧', '⑨', '⑩', '⑪', '⑫', '⑬',
                    '⑭', '⑮', '⑯', '⑰', '⑱', '⑲', '⑳', '㉑', '㉒', '㉓', '㉔', '㉕',
                    '㉖', '㉗', '㉘', '㉙', '㉚', '㉛', '㉜', '㉝', '㉞', '㉟', '㊱',
                    '㊲', '㊳', '㊴', '㊵', '㊶', '㊷', '㊸', '㊹', '㊺', '㊻', '㊼',
                    '㊽', '㊾', '㊿',
                ],
                n,
            ),
            Self::DoubleCircledNumber => {
                fixed(&['0', '⓵', '⓶', '⓷', '⓸', '⓹', '⓺', '⓻', '⓼', '⓽', '⓾'], n)
            }

            Self::LowerSimplifiedChinese => {
                u64_to_chinese(ChineseVariant::Simple, ChineseCase::Lower, n).into()
            }
            Self::UpperSimplifiedChinese => {
                u64_to_chinese(ChineseVariant::Simple, ChineseCase::Upper, n).into()
            }
            Self::LowerTraditionalChinese => {
                u64_to_chinese(ChineseVariant::Traditional, ChineseCase::Lower, n).into()
            }
            Self::UpperTraditionalChinese => {
                u64_to_chinese(ChineseVariant::Traditional, ChineseCase::Upper, n).into()
            }

            Self::EasternArabic => {
                numeric(&['٠', '١', '٢', '٣', '٤', '٥', '٦', '٧', '٨', '٩'], n)
            }
            Self::EasternArabicPersian => {
                numeric(&['۰', '۱', '۲', '۳', '۴', '۵', '۶', '۷', '۸', '۹'], n)
            }
            Self::DevanagariNumber => {
                numeric(&['०', '१', '२', '३', '४', '५', '६', '७', '८', '९'], n)
            }
            Self::BengaliNumber => {
                numeric(&['০', '১', '২', '৩', '৪', '৫', '৬', '৭', '৮', '৯'], n)
            }
            Self::Symbol => symbolic(&['*', '†', '‡', '§', '¶', '‖'], n),
        }
    }
}

/// Stringify a number using symbols representing values. The decimal
/// representation of the number is recovered by summing over the values of the
/// symbols present.
///
/// Consider the situation where ['I': 1, 'IV': 4, 'V': 5],
///
/// ```text
/// 1 => 'I'
/// 2 => 'II'
/// 3 => 'III'
/// 4 => 'IV'
/// 5 => 'V'
/// 6 => 'VI'
/// 7 => 'VII'
/// 8 => 'VIII'
/// ```
///
/// where this is the start of the familiar Roman numeral system.
fn additive(symbols: &[(&str, u64)], mut n: u64) -> EcoString {
    if n == 0 {
        if let Some(&(symbol, 0)) = symbols.last() {
            return symbol.into();
        }
        return '0'.into();
    }

    let mut s = EcoString::new();
    for (symbol, weight) in symbols {
        if *weight == 0 || *weight > n {
            continue;
        }
        let reps = n / weight;
        for _ in 0..reps {
            s.push_str(symbol);
        }

        n -= weight * reps;
        if n == 0 {
            return s;
        }
    }
    s
}

/// Stringify a number using a base-n (where n is the number of provided
/// symbols) system without a zero symbol.
///
/// Consider the situation where ['A', 'B', 'C'] are the provided symbols,
///
/// ```text
/// 1 => 'A'
/// 2 => 'B'
/// 3 => 'C'
/// 4 => 'AA
/// 5 => 'AB'
/// 6 => 'AC'
/// 7 => 'BA'
/// ...
/// ```
///
/// This system is commonly used in spreadsheet software.
fn alphabetic(symbols: &[char], mut n: u64) -> EcoString {
    let n_digits = symbols.len() as u64;
    if n == 0 {
        return '-'.into();
    }
    let mut s = EcoString::new();
    while n != 0 {
        n -= 1;
        s.push(symbols[(n % n_digits) as usize]);
        n /= n_digits;
    }
    s.chars().rev().collect()
}

/// Stringify a number using the symbols provided, defaulting to the arabic
/// representation when the number is greater than the number of symbols.
///
/// Consider the situation where ['0', 'A', 'B', 'C'] are the provided symbols,
///
/// ```text
/// 0 => '0'
/// 1 => 'A'
/// 2 => 'B'
/// 3 => 'C'
/// 4 => '4'
/// ...
/// n => 'n'
/// ```
fn fixed(symbols: &[char], n: u64) -> EcoString {
    let n_digits = symbols.len() as u64;
    if n < n_digits {
        return symbols[(n) as usize].into();
    }
    eco_format!("{n}")
}

/// Stringify a number using a base-n (where n is the number of provided
/// symbols) system with a zero symbol.
///
/// Consider the situation where ['0', '1', '2'] are the provided symbols,
///
/// ```text
/// 0 => '0'
/// 1 => '1'
/// 2 => '2'
/// 3 => '10'
/// 4 => '11'
/// 5 => '12'
/// 6 => '20'
/// ...
/// ```
///
/// which is the familiar trinary counting system.
fn numeric(symbols: &[char], mut n: u64) -> EcoString {
    let n_digits = symbols.len() as u64;
    if n == 0 {
        return symbols[0].into();
    }
    let mut s = EcoString::new();
    while n != 0 {
        s.push(symbols[(n % n_digits) as usize]);
        n /= n_digits;
    }
    s.chars().rev().collect()
}

/// Stringify a number using repeating symbols.
///
/// Consider the situation where ['A', 'B', 'C'] are the provided symbols,
///
/// ```text
/// 0 => '-'
/// 1 => 'A'
/// 2 => 'B'
/// 3 => 'C'
/// 4 => 'AA'
/// 5 => 'BB'
/// 6 => 'CC'
/// 7 => 'AAA'
/// ...
/// ```
fn symbolic(symbols: &[char], n: u64) -> EcoString {
    let n_digits = symbols.len() as u64;
    if n == 0 {
        return '-'.into();
    }
    EcoString::from(symbols[((n - 1) % n_digits) as usize])
        .repeat((n.div_ceil(n_digits)) as usize)
}