Support Greek Numbering (#4273)

Co-authored-by: Laurenz <laurmaedje@gmail.com>

1 files changed, 160 insertions, 7 deletions

diff --git a/crates/typst-library/src/model/numbering.rs b/crates/typst-library/src/model/numbering.rs
index f0aa06e5..b7f27bb9 100644
--- a/crates/typst-library/src/model/numbering.rs
+++ b/crates/typst-library/src/model/numbering.rs
@@ -59,9 +59,9 @@ pub fn numbering(
     context: Tracked<Context>,
     /// Defines how the numbering works.
     ///
-    /// **Counting symbols** are `1`, `a`, `A`, `i`, `I`, `一`, `壹`, `あ`, `い`,
-    /// `ア`, `イ`, `א`, `가`, `ㄱ`, `*`, `①`, and `⓵`. They are replaced by the
-    /// number in the sequence, preserving the original case.
+    /// **Counting symbols** are `1`, `a`, `A`, `i`, `I`, `α`, `Α`, `一`, `壹`,
+    /// `あ`, `い`, `ア`, `イ`, `א`, `가`, `ㄱ`, `*`, `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
@@ -141,9 +141,8 @@ cast! {
 
 /// How to turn a number into text.
 ///
-/// A pattern consists of a prefix, followed by one of `1`, `a`, `A`, `i`, `I`,
-/// `一`, `壹`, `あ`, `い`, `ア`, `イ`, `א`, `가`, `ㄱ`, `*`, `①`, or `⓵`, and then a
-/// suffix.
+/// 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)`
@@ -263,7 +262,12 @@ pub enum NumberingKind {
     LowerRoman,
     /// Uppercase Roman numerals (I, II, III, etc.).
     UpperRoman,
-    /// Paragraph/note-like symbols: *, †, ‡, §, ¶, and ‖. Further items use repeated symbols.
+    /// Lowercase Greek numerals (Α, Β, Γ, etc.).
+    LowerGreek,
+    /// Uppercase Greek numerals (α, β, γ, etc.).
+    UpperGreek,
+    /// Paragraph/note-like symbols: *, †, ‡, §, ¶, and ‖. Further items use
+    /// repeated symbols.
     Symbol,
     /// Hebrew numerals, including Geresh/Gershayim.
     Hebrew,
@@ -322,6 +326,8 @@ impl NumberingKind {
             'A' => NumberingKind::UpperLatin,
             'i' => NumberingKind::LowerRoman,
             'I' => NumberingKind::UpperRoman,
+            'α' => NumberingKind::LowerGreek,
+            'Α' => NumberingKind::UpperGreek,
             '*' => NumberingKind::Symbol,
             'א' => NumberingKind::Hebrew,
             '一' => NumberingKind::LowerSimplifiedChinese,
@@ -351,6 +357,8 @@ impl NumberingKind {
             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',
@@ -377,6 +385,8 @@ impl NumberingKind {
             Self::Arabic => eco_format!("{n}"),
             Self::LowerRoman => roman_numeral(n, Case::Lower),
             Self::UpperRoman => roman_numeral(n, Case::Upper),
+            Self::LowerGreek => greek_numeral(n, Case::Lower),
+            Self::UpperGreek => greek_numeral(n, Case::Upper),
             Self::Symbol => {
                 if n == 0 {
                     return '-'.into();
@@ -502,6 +512,7 @@ impl NumberingKind {
     }
 }
 
+/// Stringify an integer to a Hebrew number.
 fn hebrew_numeral(mut n: usize) -> EcoString {
     if n == 0 {
         return '-'.into();
@@ -555,6 +566,7 @@ fn hebrew_numeral(mut n: usize) -> EcoString {
     fmt
 }
 
+/// Stringify an integer to a Roman numeral.
 fn roman_numeral(mut n: usize, case: Case) -> EcoString {
     if n == 0 {
         return match case {
@@ -602,6 +614,147 @@ fn roman_numeral(mut n: usize, case: Case) -> EcoString {
     fmt
 }
 
+/// Stringify an integer to Greek numbers.
+///
+/// Greek numbers use the Greek Alphabet to represent numbers; it is based on 10
+/// (decimal). Here we implement the single digit M power representation from
+/// [The Greek Number Converter][convert] and also described in
+/// [Greek Numbers][numbers].
+///
+/// [converter]: https://www.russellcottrell.com/greek/utilities/GreekNumberConverter.htm
+/// [numbers]: https://mathshistory.st-andrews.ac.uk/HistTopics/Greek_numbers/
+fn greek_numeral(n: usize, case: Case) -> EcoString {
+    let thousands = [
+        ["͵α", "͵Α"],
+        ["͵β", "͵Β"],
+        ["͵γ", "͵Γ"],
+        ["͵δ", "͵Δ"],
+        ["͵ε", "͵Ε"],
+        ["͵ϛ", "͵Ϛ"],
+        ["͵ζ", "͵Ζ"],
+        ["͵η", "͵Η"],
+        ["͵θ", "͵Θ"],
+    ];
+    let hundreds = [
+        ["ρ", "Ρ"],
+        ["σ", "Σ"],
+        ["τ", "Τ"],
+        ["υ", "Υ"],
+        ["φ", "Φ"],
+        ["χ", "Χ"],
+        ["ψ", "Ψ"],
+        ["ω", "Ω"],
+        ["ϡ", "Ϡ"],
+    ];
+    let tens = [
+        ["ι", "Ι"],
+        ["κ", "Κ"],
+        ["λ", "Λ"],
+        ["μ", "Μ"],
+        ["ν", "Ν"],
+        ["ξ", "Ξ"],
+        ["ο", "Ο"],
+        ["π", "Π"],
+        ["ϙ", "Ϟ"],
+    ];
+    let ones = [
+        ["α", "Α"],
+        ["β", "Β"],
+        ["γ", "Γ"],
+        ["δ", "Δ"],
+        ["ε", "Ε"],
+        ["ϛ", "Ϛ"],
+        ["ζ", "Ζ"],
+        ["η", "Η"],
+        ["θ", "Θ"],
+    ];
+
+    if n == 0 {
+        // Greek Zero Sign
+        return '𐆊'.into();
+    }
+
+    let mut fmt = EcoString::new();
+    let case = match case {
+        Case::Lower => 0,
+        Case::Upper => 1,
+    };
+
+    // Extract a list of decimal digits from the number
+    let mut decimal_digits: Vec<usize> = Vec::new();
+    let mut n = n;
+    while n > 0 {
+        decimal_digits.push(n % 10);
+        n /= 10;
+    }
+
+    // Pad the digits with leading zeros to ensure we can form groups of 4
+    while decimal_digits.len() % 4 != 0 {
+        decimal_digits.push(0);
+    }
+    decimal_digits.reverse();
+
+    let mut m_power = decimal_digits.len() / 4;
+
+    // M are used to represent 10000, M_power = 2 means 10000^2 = 10000 0000
+    // The prefix of M is also made of Greek numerals but only be single digits, so it is 9 at max. This enables us
+    // to represent up to (10000)^(9 + 1) - 1 = 10^40 -1  (9,999,999,999,999,999,999,999,999,999,999,999,999,999)
+    let get_m_prefix = |m_power: usize| {
+        if m_power == 0 {
+            None
+        } else {
+            assert!(m_power <= 9);
+            // the prefix of M is a single digit lowercase
+            Some(ones[m_power - 1][0])
+        }
+    };
+
+    let mut previous_has_number = false;
+    for chunk in decimal_digits.chunks_exact(4) {
+        // chunk must be exact 4 item
+        assert_eq!(chunk.len(), 4);
+
+        m_power = m_power.saturating_sub(1);
+
+        // `th`ousan, `h`undred, `t`en and `o`ne
+        let (th, h, t, o) = (chunk[0], chunk[1], chunk[2], chunk[3]);
+        if th + h + t + o == 0 {
+            continue;
+        }
+
+        if previous_has_number {
+            fmt.push_str(", ");
+        }
+
+        if let Some(m_prefix) = get_m_prefix(m_power) {
+            fmt.push_str(m_prefix);
+            fmt.push_str("Μ");
+        }
+        if th != 0 {
+            let thousand_digit = thousands[th - 1][case];
+            fmt.push_str(thousand_digit);
+        }
+        if h != 0 {
+            let hundred_digit = hundreds[h - 1][case];
+            fmt.push_str(hundred_digit);
+        }
+        if t != 0 {
+            let ten_digit = tens[t - 1][case];
+            fmt.push_str(ten_digit);
+        }
+        if o != 0 {
+            let one_digit = ones[o - 1][case];
+            fmt.push_str(one_digit);
+        }
+        // if we do not have thousan, we need to append 'ʹ' at the end.
+        if th == 0 {
+            fmt.push_str("ʹ");
+        }
+        previous_has_number = true;
+    }
+    fmt
+}
+
 /// Stringify a number using a base-N counting system with no zero digit.
 ///
 /// This is best explained by example. Suppose our digits are 'A', 'B', and 'C'.