Next steps 5-10: resources, cash flow, QB interop, backfill, HTTP, parallel-run plan

crates/ledger-import/src/xlsx.rs

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+//! Generate XLSX reports with `rust_xlsxwriter` (MIT).
+//!
+//! Money is converted to f64 ONLY at this presentation boundary — never in
+//! a money path. All accounting math stays `Decimal`; the conversion happens
+//! when writing a cell, rounded to cents.
+
+use ledger_core::reports::{BalanceSheet, CashFlowStatement, ProfitAndLoss, TrialBalance};
+use rust_decimal::Decimal;
+use rust_xlsxwriter::{Format, Workbook};
+use thiserror::Error;
+
+/// Which report to render.
+#[derive(Clone, Debug)]
+pub enum XlsxReport<'a> {
+    /// Trial balance lines.
+    TrialBalance(&'a TrialBalance),
+    /// Profit and loss.
+    ProfitAndLoss(&'a ProfitAndLoss, String, String),
+    /// Balance sheet.
+    BalanceSheet(&'a BalanceSheet, String),
+    /// Cash flow statement.
+    CashFlow(&'a CashFlowStatement),
+}
+
+/// XLSX errors.
+#[derive(Debug, Error)]
+pub enum XlsxError {
+    /// The writer failed.
+    #[error("xlsx write failed: {0}")]
+    Write(String),
+}
+
+/// Render a report to XLSX bytes.
+pub fn report_to_xlsx(report: &XlsxReport<'_>) -> Result<Vec<u8>, XlsxError> {
+    let mut workbook = Workbook::new();
+    let sheet = workbook.add_worksheet();
+    let bold = Format::new().set_bold();
+    let money_fmt = Format::new().set_num_format("#,##0.00");
+
+    let mut row: u32 = 0;
+    match report {
+        XlsxReport::TrialBalance(tb) => {
+            sheet.write_string(row, 0, "Trial Balance").unwrap();
+            row += 1;
+            for (i, h) in ["Code", "Account", "Debit", "Credit"].iter().enumerate() {
+                sheet
+                    .write_string_with_format(row, i as u16, *h, &bold)
+                    .unwrap();
+            }
+            row += 1;
+            for line in &tb.lines {
+                sheet.write_string(row, 0, &line.code).unwrap();
+                sheet.write_string(row, 1, &line.name).unwrap();
+                sheet
+                    .write_number_with_format(row, 2, dec_to_f64(line.debit), &money_fmt)
+                    .unwrap();
+                sheet
+                    .write_number_with_format(row, 3, dec_to_f64(line.credit), &money_fmt)
+                    .unwrap();
+                row += 1;
+            }
+        }
+        XlsxReport::ProfitAndLoss(pl, start, end) => {
+            sheet
+                .write_string(row, 0, format!("Profit and Loss ({start} to {end})"))
+                .unwrap();
+            row += 2;
+            sheet.write_string(row, 0, "Revenue").unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(pl.revenue), &money_fmt)
+                .unwrap();
+            row += 1;
+            sheet.write_string(row, 0, "Expenses").unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(pl.expenses), &money_fmt)
+                .unwrap();
+            row += 1;
+            sheet
+                .write_string_with_format(row, 0, "Net income", &bold)
+                .unwrap();
+            let net = pl.revenue - pl.expenses;
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(net), &money_fmt)
+                .unwrap();
+        }
+        XlsxReport::BalanceSheet(bs, as_of) => {
+            sheet
+                .write_string(row, 0, format!("Balance Sheet (as of {as_of})"))
+                .unwrap();
+            row += 2;
+            for (label, val) in [
+                ("Assets", bs.assets),
+                ("Liabilities", bs.liabilities),
+                ("Equity", bs.equity),
+            ] {
+                sheet.write_string(row, 0, label).unwrap();
+                sheet
+                    .write_number_with_format(row, 1, dec_to_f64(val), &money_fmt)
+                    .unwrap();
+                row += 1;
+            }
+        }
+        XlsxReport::CashFlow(cf) => {
+            sheet
+                .write_string(row, 0, format!("Cash Flow ({} to {})", cf.start, cf.end))
+                .unwrap();
+            row += 2;
+            sheet
+                .write_string_with_format(row, 0, "Operating activities", &bold)
+                .unwrap();
+            row += 1;
+            sheet.write_string(row, 0, "Net income").unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(cf.net_income), &money_fmt)
+                .unwrap();
+            row += 1;
+            sheet.write_string(row, 0, "Depreciation").unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(cf.depreciation), &money_fmt)
+                .unwrap();
+            row += 1;
+            for line in &cf.working_capital {
+                sheet.write_string(row, 0, &line.label).unwrap();
+                sheet
+                    .write_number_with_format(row, 1, dec_to_f64(line.amount), &money_fmt)
+                    .unwrap();
+                row += 1;
+            }
+            sheet
+                .write_string_with_format(row, 0, "Cash from operations", &bold)
+                .unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(cf.cash_from_operations), &money_fmt)
+                .unwrap();
+            row += 2;
+            sheet
+                .write_string_with_format(row, 0, "Investing activities", &bold)
+                .unwrap();
+            row += 1;
+            for line in &cf.investing {
+                sheet.write_string(row, 0, &line.label).unwrap();
+                sheet
+                    .write_number_with_format(row, 1, dec_to_f64(line.amount), &money_fmt)
+                    .unwrap();
+                row += 1;
+            }
+            sheet
+                .write_string_with_format(row, 0, "Cash from investing", &bold)
+                .unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(cf.cash_from_investing), &money_fmt)
+                .unwrap();
+            row += 2;
+            sheet
+                .write_string_with_format(row, 0, "Financing activities", &bold)
+                .unwrap();
+            row += 1;
+            for line in &cf.financing {
+                sheet.write_string(row, 0, &line.label).unwrap();
+                sheet
+                    .write_number_with_format(row, 1, dec_to_f64(line.amount), &money_fmt)
+                    .unwrap();
+                row += 1;
+            }
+            sheet
+                .write_string_with_format(row, 0, "Cash from financing", &bold)
+                .unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(cf.cash_from_financing), &money_fmt)
+                .unwrap();
+            row += 2;
+            sheet
+                .write_string_with_format(row, 0, "Net change in cash", &bold)
+                .unwrap();
+            sheet
+                .write_number_with_format(row, 1, dec_to_f64(cf.net_change_in_cash), &money_fmt)
+                .unwrap();
+        }
+    }
+
+    workbook
+        .save_to_buffer()
+        .map_err(|e| XlsxError::Write(e.to_string()))
+}
+
+/// Decimal to f64 at the presentation boundary. Rounded to cents first.
+fn dec_to_f64(d: Decimal) -> f64 {
+    use rust_decimal::prelude::ToPrimitive;
+    d.round_dp(2).to_f64().unwrap_or(0.0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use ledger_core::reports::TrialBalanceLine;
+
+    #[test]
+    fn xlsx_is_a_zip() {
+        let tb = TrialBalance {
+            lines: vec![TrialBalanceLine {
+                code: "1000".to_string(),
+                name: "Cash".to_string(),
+                debit: Decimal::new(10000, 2),
+                credit: Decimal::ZERO,
+            }],
+            total_debits: Decimal::new(10000, 2),
+            total_credits: Decimal::new(10000, 2),
+        };
+        let bytes = report_to_xlsx(&XlsxReport::TrialBalance(&tb)).unwrap();
+        // XLSX is a ZIP: starts with PK.
+        assert_eq!(&bytes[0..2], b"PK");
+        assert!(bytes.len() > 1000);
+    }
+}