P2 slice 6: the viewer

`wanderbooks gui [BOOK]` finds the data root, reads settings from the
journal, the vault of the book, presence through ops/, Save a copy /
Open on every document, Save the W-9, the Export menu, and colour
schemes. One builder for the CPA package and the 1099 worksheet
(ledger-package), shared by the server and the viewer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-package/src/text.rs

@@ -0,0 +1,153 @@
+//! How the books' amounts, shares, dates, and CSV cells are written and
+//! read: one spelling for the server's tools, the package, and the viewer.
+//!
+//! ```text
+//! GOAL: an amount, a share, or a date reads the same in every file and
+//!       tool the books make, and a date in is checked one way.
+//! SOURCE: ledger-mcp server.rs INVARIANT 3 (amounts out are decimal
+//!         strings with at least two places, never rounded); RFC 4180
+//!         (a CSV field holding a comma, quote, or line break is quoted,
+//!         its quotes doubled); P0 review round 3, S1 (dates).
+//! INVARIANTS:
+//!   1. money pads to two places and never rounds; it never prints "-0".
+//!   2. share_text depends on a share's value, never its spelling.
+//!   3. csv_escape quotes exactly the fields that need it.
+//!   4. parse_date takes exactly YYYY-MM-DD, a day the calendar keeps.
+//! ```
+
+use chrono::NaiveDate;
+use rust_decimal::Decimal;
+
+/// A money amount as a decimal string with at least two places: "0.00",
+/// "207.68", "1000.00". Padding only, never rounding: an exact amount with
+/// more places (an FX-converted line) keeps them. Never "-0".
+pub fn money(n: Decimal) -> String {
+    let mut n = if n.is_zero() { Decimal::ZERO } else { n };
+    if n.scale() < 2 {
+        n.rescale(2);
+    }
+    n.to_string()
+}
+
+/// A member's share as the K-1 worksheet prints it: at least two places,
+/// however it was written ("50%", "0.5" and "0.500" all print "0.50"; a
+/// share of a third keeps its places). The printed text depends on the
+/// share, never on its spelling.
+pub fn share_text(n: Decimal) -> String {
+    let mut n = n.normalize();
+    if n.scale() < 2 {
+        n.rescale(2);
+    }
+    n.to_string()
+}
+
+/// A CSV field: quoted, with its quotes doubled, when it holds a comma, a
+/// quote, or a line feed; else as it is.
+pub fn csv_escape(s: &str) -> String {
+    if s.contains([',', '"', '\n']) {
+        format!("\"{}\"", s.replace('"', "\"\""))
+    } else {
+        s.to_string()
+    }
+}
+
+/// A date: exactly YYYY-MM-DD, a real day in the calendar the books keep
+/// (0001-01-01 through 9999-12-31, `ledger_core::calendar`). No sign, no
+/// space, no five-digit year: every date past here is one date arithmetic
+/// reaches (P0 review round 3, S1).
+pub fn parse_date(s: &str) -> Result<NaiveDate, String> {
+    let shaped = s.len() == 10
+        && s.bytes().enumerate().all(|(i, b)| {
+            if i == 4 || i == 7 {
+                b == b'-'
+            } else {
+                b.is_ascii_digit()
+            }
+        });
+    shaped
+        .then(|| NaiveDate::parse_from_str(s, "%Y-%m-%d").ok())
+        .flatten()
+        .filter(|d| ledger_core::calendar::in_calendar(*d))
+        .ok_or_else(|| {
+            format!("bad date {s:?}: expected YYYY-MM-DD, a real day from 0001-01-01 to 9999-12-31")
+        })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::str::FromStr;
+
+    fn d(y: i32, m: u32, day: u32) -> NaiveDate {
+        NaiveDate::from_ymd_opt(y, m, day).unwrap()
+    }
+
+    #[test]
+    fn money_always_has_cents_and_never_rounds() {
+        let m = |s: &str| money(Decimal::from_str(s).unwrap());
+        assert_eq!(money(Decimal::ZERO), "0.00");
+        assert_eq!(m("-0"), "0.00");
+        assert_eq!(m("1000"), "1000.00");
+        assert_eq!(m("5.8"), "5.80");
+        assert_eq!(m("-207.68"), "-207.68");
+        assert_eq!(m("12.3456"), "12.3456");
+    }
+
+    /// A share prints by its value, never its spelling: at least two
+    /// places, a third keeping its own.
+    #[test]
+    fn a_share_prints_the_same_however_it_was_written() {
+        let t = |s: &str| share_text(Decimal::from_str(s).unwrap());
+        for half in ["0.5", "0.50", "0.500000"] {
+            assert_eq!(t(half), "0.50", "{half}");
+        }
+        assert_eq!(t("1"), "1.00");
+        assert_eq!(t("1.0"), "1.00");
+        assert_eq!(t("0.25"), "0.25");
+        assert_eq!(t("0.3333"), "0.3333");
+        assert_eq!(t("0.125"), "0.125");
+    }
+
+    #[test]
+    fn csv_fields_are_quoted_only_when_they_must_be() {
+        assert_eq!(csv_escape("plain"), "plain");
+        assert_eq!(csv_escape("a,b"), "\"a,b\"");
+        assert_eq!(csv_escape("say \"hi\""), "\"say \"\"hi\"\"\"");
+        assert_eq!(csv_escape("two\nlines"), "\"two\nlines\"");
+        assert_eq!(csv_escape(""), "");
+    }
+
+    /// A date is exactly YYYY-MM-DD, a real day from 0001-01-01 to
+    /// 9999-12-31 (ledger_core::calendar): no sign, no space, no fifth
+    /// year digit, no year 0 (P0 review round 3, S1).
+    #[test]
+    fn dates_are_four_digit_years_and_real_days() {
+        assert_eq!(parse_date("2026-02-28"), Ok(d(2026, 2, 28)));
+        assert_eq!(parse_date("2028-02-29"), Ok(d(2028, 2, 29)));
+        assert_eq!(parse_date("0001-01-01"), Ok(d(1, 1, 1)));
+        assert_eq!(parse_date("9999-12-31"), Ok(d(9999, 12, 31)));
+        for bad in [
+            "0000-01-01",
+            "0000-00-00",
+            "2026-02-29",
+            "2026-02-30",
+            "2026-13-01",
+            "2026-1-05",
+            "2026-01-5",
+            " 2026-01-05",
+            "2026-01-05 ",
+            "+2026-01-05",
+            "-0001-01-01",
+            "+262142-12-31",
+            "-262143-01-01",
+            "99999-12-31",
+            "2026/01/05",
+            "2026-01-05T00:00",
+            "２０２６-01-05",
+            "",
+        ] {
+            let err = parse_date(bad).expect_err(bad);
+            assert!(err.contains("0001-01-01 to 9999-12-31"), "{bad:?}: {err}");
+        }
+    }
+}