//! Opening and saving files: XLSX, legacy XLS import, XLSB and ODS data import, CSV/TSV, JSON (debug), HTML export.

use std::fmt::Write as _;

use gridcraft_core::{CellRef, RangeRef};
use gridcraft_model::{Sheet, Workbook};

use crate::{EngineError, Result};

/// File formats GridCraft reads or writes.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum FileKind {
    Xlsx,
    /// Excel 97-2003 workbook (import only).
    Xls,
    Xlsb,
    Ods,
    Csv,
    Tsv,
    Json,
    Html,
}

impl FileKind {
    pub fn from_path(path: &str) -> Option<FileKind> {
        let ext = std::path::Path::new(path).extension()?.to_str()?.to_ascii_lowercase();
        Some(match ext.as_str() {
            "xlsx" | "xlsm" | "xltx" | "xltm" => FileKind::Xlsx,
            "xls" | "xlt" => FileKind::Xls,
            "xlsb" => FileKind::Xlsb,
            "ods" => FileKind::Ods,
            "csv" => FileKind::Csv,
            "tsv" | "tab" | "txt" => FileKind::Tsv,
            "json" | "scjson" => FileKind::Json,
            "html" | "htm" => FileKind::Html,
            _ => return None,
        })
    }
}

/// The error for an encrypted workbook opened without a password contains this. The interface
/// asks for the password when it sees it; programmatic callers pass `password` instead.
pub const PASSWORD_REQUIRED: &str = "is password-protected. Enter its password to open it.";
/// The error for a wrong password contains this.
pub const WRONG_PASSWORD: &str = "The password is incorrect.";
/// The first open warning of a workbook decrypted with its password.
pub const DECRYPTED_NOTICE: &str = "This workbook was password-protected. GridCraft saves it without the password.";

/// Parses a file's bytes into a workbook. `name` picks the format by extension when the bytes
/// don't say. An encrypted workbook needs [`open_bytes_with_password`].
pub fn open_bytes(name: &str, bytes: &[u8]) -> Result<(Workbook, Vec<String>)> {
    open_bytes_with_password(name, bytes, None)
}

/// [`open_bytes`], first decrypting a password-protected workbook with `password`. Errors never
/// quote the password.
pub fn open_bytes_with_password(name: &str, bytes: &[u8], password: Option<&str>) -> Result<(Workbook, Vec<String>)> {
    open_bytes_with(name, bytes, password, false)
}

/// [`open_bytes_with_password`], and with `csv_as_text` a CSV/TSV/TXT file keeps every field as
/// the text it holds, with no number, date or boolean conversion (identifiers such as GTINs, SKUs
/// and ZIP codes survive). It does not apply to other formats.
pub fn open_bytes_with(name: &str, bytes: &[u8], password: Option<&str>, csv_as_text: bool) -> Result<(Workbook, Vec<String>)> {
    if gridcraft_xlsx::sniff(bytes) != gridcraft_xlsx::Format::Encrypted {
        let (mut wb, warnings) = open_plain(name, bytes, csv_as_text)?;
        fit_imported_rows(&mut wb);
        return Ok((wb, warnings));
    }
    // A scheme no password opens is said straight away, rather than after asking for one.
    let decrypt_error = |e: gridcraft_xlsx::DecryptError| EngineError::Other(decrypt_message(name, e));
    let Some(password) = password else {
        gridcraft_xlsx::check_encryption(bytes).map_err(decrypt_error)?;
        return Err(EngineError::Other(format!("'{name}' {PASSWORD_REQUIRED}")));
    };
    let plain = gridcraft_xlsx::decrypt(bytes, password).map_err(decrypt_error)?;
    if gridcraft_xlsx::sniff(&plain) == gridcraft_xlsx::Format::Encrypted {
        return Err(EngineError::Other(format!("We can't open '{name}': the encrypted file is damaged (it holds another encrypted file).")));
    }
    let (mut wb, mut warnings) = open_plain(name, &plain, csv_as_text)?;
    fit_imported_rows(&mut wb);
    warnings.insert(0, DECRYPTED_NOTICE.into());
    Ok((wb, warnings))
}

/// Excel auto-fits rows to their tallest font when opening a file: rows without a user-set
/// height grow to fit their content. Rows the file made taller keep their height — our
/// line-height estimate can differ from Excel's, and shrinking files that already look
/// right would be a visible regression. Custom-height rows are left alone entirely.
fn fit_imported_rows(wb: &mut Workbook) {
    for si in 0..wb.sheets.len() {
        let Some(sh) = wb.sheet(si) else { continue };
        let mut rows: Vec<u32> = sh.cells.iter().map(|(c, _)| c.row).collect();
        rows.sort_unstable();
        rows.dedup();
        for row in rows {
            let before = wb.sheet(si).and_then(|sh| sh.rows.get(&row)).and_then(|i| i.size);
            crate::cmd::auto_row_height(wb, si, row);
            let Some(before) = before else { continue };
            let after = wb.sheet(si).and_then(|sh| sh.rows.get(&row)).and_then(|i| i.size);
            if after.is_none_or(|a| before > a + 0.5)
                && let Some(sh) = wb.sheet_mut(si)
            {
                sh.rows.entry(row).or_default().size = Some(before);
            }
        }
    }
}

/// What to tell the user when an encrypted workbook can't be decrypted. Never quotes the password.
fn decrypt_message(name: &str, e: gridcraft_xlsx::DecryptError) -> String {
    match e {
        gridcraft_xlsx::DecryptError::WrongPassword => format!("{WRONG_PASSWORD} Check that Caps Lock is off and try again."),
        gridcraft_xlsx::DecryptError::Unsupported(scheme) => {
            format!("'{name}' uses {scheme} encryption, which GridCraft can't open yet. Remove the password in Excel and try again.")
        }
        gridcraft_xlsx::DecryptError::Malformed(detail) => format!("We can't open '{name}': the encrypted file is damaged ({detail})."),
    }
}

/// Parses bytes that aren't encrypted.
fn open_plain(name: &str, bytes: &[u8], csv_as_text: bool) -> Result<(Workbook, Vec<String>)> {
    let kind = FileKind::from_path(name);
    let sniffed = gridcraft_xlsx::sniff(bytes);
    if sniffed == gridcraft_xlsx::Format::Xls {
        let (wb, report) = gridcraft_xlsx::read_xls(bytes).map_err(|e| EngineError::Other(format!("We can't open '{name}': {e}")))?;
        return Ok((wb, report.warnings));
    }
    if sniffed == gridcraft_xlsx::Format::LegacyBinary {
        return Err(EngineError::Other(format!(
            "'{name}' is a legacy binary file but not an Excel workbook (no workbook stream). GridCraft can't open it."
        )));
    }
    // Content wins over the extension: an ODS or XLSB package is imported as what it is,
    // whatever it is called; the extension only decides when the bytes don't say.
    let import = match sniffed {
        gridcraft_xlsx::Format::Ods => Some(FileKind::Ods),
        gridcraft_xlsx::Format::Xlsb => Some(FileKind::Xlsb),
        // An XLSX package is never read as ODS/XLSB just because of its name.
        gridcraft_xlsx::Format::Xlsx => None,
        _ => kind.filter(|k| matches!(k, FileKind::Ods | FileKind::Xlsb)),
    };
    if let Some(import) = import {
        let read = if import == FileKind::Ods { gridcraft_xlsx::read_ods } else { gridcraft_xlsx::read_xlsb };
        let (wb, report) = read(bytes).map_err(|e| EngineError::Other(format!("We can't import '{name}': {e}")))?;
        return Ok((wb, report.warnings));
    }
    // Text named `.xlsx` is read as text.
    if sniffed == gridcraft_xlsx::Format::Xlsx || (kind == Some(FileKind::Xlsx) && sniffed != gridcraft_xlsx::Format::Csv) {
        let (wb, report) = gridcraft_xlsx::read_xlsx(bytes).map_err(|e| {
            EngineError::Other(match (&e, gridcraft_xlsx::oversized_part(bytes)) {
                (gridcraft_xlsx::IoError::TooLarge(_), Some((part, size))) => part_too_large_message(name, &part, size),
                _ => format!("We can't open '{name}': {e}"),
            })
        })?;
        return Ok((wb, report.warnings));
    }
    match kind {
        Some(FileKind::Json) => {
            let mut wb: Workbook = serde_json::from_slice(bytes).map_err(|e| EngineError::Other(format!("not a GridCraft JSON workbook: {e}")))?;
            wb.styles.rebuild_index();
            if wb.sheets.is_empty() {
                wb = Workbook::new();
            }
            // The file's band placement and cell count are derived state: rebuild them from the
            // cells themselves, dropping what is outside the sheet grid (#1008).
            let dropped: usize = wb.sheets.iter_mut().map(|sh| std::sync::Arc::make_mut(sh).cells.rebuild()).sum();
            let mut warnings = Vec::new();
            if dropped > 0 {
                warnings.push(format!("{name}: {dropped} cells outside the 1,048,576 × 16,384 grid were dropped"));
            }
            Ok((wb, warnings))
        }
        Some(FileKind::Tsv) => {
            let opts = gridcraft_xlsx::CsvOptions { delimiter: b'\t', parse_values: !csv_as_text, ..Default::default() };
            let mut wb = gridcraft_xlsx::read_csv(bytes, &opts).map_err(|e| EngineError::Other(e.to_string()))?;
            // Tab is what makes it a .tsv/.txt; saved as .csv it gets the CSV default.
            wb.csv_delimiter = None;
            rename_first_sheet(&mut wb, name);
            Ok((wb, vec![]))
        }
        _ => {
            let opts = gridcraft_xlsx::CsvOptions { delimiter: 0, parse_values: !csv_as_text, ..Default::default() };
            let mut wb = gridcraft_xlsx::read_csv(bytes, &opts).map_err(|e| EngineError::Other(e.to_string()))?;
            rename_first_sheet(&mut wb, name);
            Ok((wb, vec![]))
        }
    }
}

/// What to tell the user when one part of an XLSX package unpacks to more than the reader's
/// per-part limit: the sizes, why the limit is there, and what gets the data in. The limit is
/// per part, so smaller sheets fit; the shared strings are one part for every sheet, so only a
/// CSV, which has no parts, helps there.
fn part_too_large_message(name: &str, part: &str, size: u64) -> String {
    let limit = gridcraft_xlsx::MAX_PART >> 20;
    let mb = size >> 20;
    let size = if mb > limit { format!("{mb} MB") } else { format!("more than {limit} MB") };
    let remedy = if part.contains("worksheets/") {
        "To open it, split the data across several sheets, since the limit applies to each part, or save the sheet as CSV, which keeps only its values."
    } else {
        "To open it, save the data as CSV, which keeps only its values."
    };
    format!(
        "We can't open '{name}': its part {part} unpacks to {size}, over GridCraft's limit of {limit} MB for one part \
         (a guard against damaged or malicious files). {remedy}"
    )
}

/// A CSV opens as a sheet named after the file (like Excel).
fn rename_first_sheet(wb: &mut Workbook, path: &str) {
    let stem = std::path::Path::new(path).file_stem().and_then(std::ffi::OsStr::to_str).unwrap_or("Sheet1");
    let clean: String = stem.chars().filter(|c| !matches!(c, ':' | '\\' | '/' | '?' | '*' | '[' | ']')).take(31).collect();
    let clean = clean.trim_matches('\'').to_string();
    // "History" is reserved (see `Workbook::check_sheet_name`): keep the default name instead.
    if !clean.is_empty()
        && !clean.eq_ignore_ascii_case("History")
        && let Some(sh) = wb.sheet_mut(0)
    {
        sh.name = clean;
    }
}

/// Encodes a workbook in the format chosen by `path`'s extension.
pub fn save_bytes(wb: &Workbook, path: &str) -> Result<Vec<u8>> {
    // An unknown or missing extension is refused rather than written as an XLSX under that name:
    // a typo like `.cvs` would otherwise produce a file no other app recognises.
    let Some(kind) = FileKind::from_path(path) else {
        let name = std::path::Path::new(path).file_name().and_then(std::ffi::OsStr::to_str).unwrap_or(path);
        return Err(EngineError::Other(format!("{name}: unknown file format. Save as .xlsx, .csv, .tsv, .json or .html.")));
    };
    save_bytes_as(wb, path, kind)
}

/// Encodes a workbook as `kind`, whatever `path`'s extension says.
pub fn save_bytes_as(wb: &Workbook, path: &str, kind: FileKind) -> Result<Vec<u8>> {
    let sheet = wb.active_sheet();
    match kind {
        // The extension picks the package kind; only the macro-enabled kinds (.xlsm, .xltm) carry
        // the VBA project, so any other name saves without it, as Excel does.
        FileKind::Xlsx => {
            let book = std::path::Path::new(path).file_name().and_then(std::ffi::OsStr::to_str).unwrap_or_default();
            gridcraft_xlsx::write_xlsx_named(wb, gridcraft_xlsx::XlsxKind::from_path(path), book).map_err(|e| EngineError::Other(e.to_string()))
        }
        FileKind::Xls => {
            Err(EngineError::Other("Excel 97-2003 (.xls) is supported for import only. Save as .xlsx or another supported export format.".into()))
        }
        FileKind::Xlsb => Err(EngineError::Other("XLSB is supported for data import only. Save as .xlsx or another supported export format.".into())),
        FileKind::Ods => Err(EngineError::Other("ODS is supported for data import only. Save as .xlsx or another supported export format.".into())),
        // A workbook read from CSV keeps the separator it was read with (a `;` file stays `;`).
        FileKind::Csv => wb.sheet(sheet).map(|sh| csv(wb, sh, wb.csv_delimiter.unwrap_or(b','))).transpose().map(Option::unwrap_or_default),
        FileKind::Tsv => wb.sheet(sheet).map(|sh| csv(wb, sh, b'\t')).transpose().map(Option::unwrap_or_default),
        FileKind::Json => serde_json::to_vec_pretty(wb).map_err(|e| EngineError::Other(e.to_string())),
        FileKind::Html => to_html(wb, sheet).map(String::into_bytes),
    }
}

/// [`save_bytes`] for the file at `path`: relative paths to linked workbooks are rewritten for
/// its folder, so they still name the same files.
pub fn save_file_bytes(wb: &Workbook, path: &str) -> Result<Vec<u8>> {
    match source_dir(path).and_then(|f| gridcraft_xlsx::rebase_links(wb, &f)) {
        Some(rebased) => save_bytes(&rebased, path),
        None => save_bytes(wb, path),
    }
}

/// The folder of the file at `path`, which relative paths to linked workbooks are relative to.
pub fn source_dir(path: &str) -> Option<std::path::PathBuf> {
    std::path::absolute(path).ok()?.parent().map(std::path::Path::to_path_buf)
}

/// The file at `path` as `CELL("filename")` reports it: absolute, so the folder is the one the
/// user sees. A workbook that arrived as bytes has no path and keeps only its name.
pub fn source_path(path: &str) -> Option<std::path::PathBuf> {
    std::path::absolute(path).ok()
}

/// Save As CSV/Text writes "the text and values as they are displayed in cells" with "all
/// characters in each cell" (Microsoft Support, *Excel formatting and features that are not
/// transferred to other file formats*): number formats applied, never column-width `#####`.
fn csv(wb: &Workbook, sh: &Sheet, delimiter: u8) -> Result<Vec<u8>> {
    gridcraft_xlsx::write_csv(sh, delimiter, |c| {
        // General's grid-width formatting rounds large identifiers to scientific notation.
        // Delimited files have no column width, so preserve the whole numeric value instead.
        if wb.styles.get(sh.style_id(c)).num_fmt.as_str().eq_ignore_ascii_case("General")
            && let gridcraft_core::Value::Number(number) = sh.value(c)
            && number.is_finite()
        {
            number.to_string()
        } else {
            crate::display::value_text(wb, sh, c)
        }
    })
    .map_err(|e| EngineError::Other(e.to_string()))
}

pub(crate) fn esc(s: &str) -> String {
    s.replace('&', "&amp;").replace('<', "&lt;").replace('>', "&gt;").replace('"', "&quot;")
}

fn html_cell_css(wb: &Workbook, sh: &Sheet, c: CellRef, dir: CellDir) -> String {
    let st = wb.styles.get(sh.style_id(c));
    let mut css = String::new();
    if st.font.bold {
        css.push_str("font-weight:bold;");
    }
    if st.font.italic {
        css.push_str("font-style:italic;");
    }
    if let Some(h) = st.font.color.hex(&wb.theme) {
        let _ = write!(css, "color:{h};");
    }
    if st.fill.pattern != gridcraft_model::PatternType::None
        && let Some(h) = st.fill.fg.hex(&wb.theme)
    {
        let _ = write!(css, "background:{h};");
    }
    let v = sh.value(c);
    let align = match st.align.h {
        gridcraft_model::HAlign::Center => Some("center"),
        gridcraft_model::HAlign::Right => Some("right"),
        gridcraft_model::HAlign::Left => Some("left"),
        _ if v.is_number() => Some(if sh.right_to_left { "left" } else { "right" }),
        _ if dir == CellDir::Auto => None,
        _ => Some("left"),
    };
    if let Some(align) = align {
        let _ = write!(css, "text-align:{align};");
    }
    css
}

/// How a cell marks its direction in HTML. Text on a right-to-left sheet, or text with
/// right-to-left letters, follows its first strong character (`dir="auto"`), so General
/// alignment puts Arabic and Hebrew on the right. Numbers on a right-to-left sheet stay left to
/// right so `-5` doesn't read `5-`.
#[derive(Clone, Copy, PartialEq, Eq)]
enum CellDir {
    Inherit,
    Auto,
    Ltr,
}

impl CellDir {
    fn of(sh: &Sheet, c: CellRef, text: &str) -> CellDir {
        if sh.value(c).is_number() {
            if sh.right_to_left { CellDir::Ltr } else { CellDir::Inherit }
        } else if sh.right_to_left || text.chars().any(is_right_to_left_letter) {
            CellDir::Auto
        } else {
            CellDir::Inherit
        }
    }

    fn attr(self) -> &'static str {
        match self {
            CellDir::Inherit => "",
            CellDir::Auto => " dir=\"auto\"",
            CellDir::Ltr => " dir=\"ltr\"",
        }
    }
}

/// Hebrew, Arabic, Syriac, Thaana, N'Ko and their presentation forms.
fn is_right_to_left_letter(c: char) -> bool {
    matches!(c, '\u{0590}'..='\u{08FF}' | '\u{FB1D}'..='\u{FDFF}' | '\u{FE70}'..='\u{FEFF}')
}

fn table_dir(sh: &Sheet) -> &'static str {
    if sh.right_to_left { " dir=\"rtl\"" } else { "" }
}

const CLIPBOARD_HTML_MAX_BYTES: usize = 4 * 1024 * 1024;
const CLIPBOARD_HTML_MAX_CELLS: u64 = 10_000;

/// An HTML fragment for the same range as `plain_text`, previously produced by
/// `display::range_text`. Large copies keep plain text only; never return a partial table.
pub(crate) fn range_html(wb: &Workbook, sheet: usize, r: RangeRef, plain_text: &str) -> Option<String> {
    let r = crate::display::clipboard_range(r);
    if r.count() > CLIPBOARD_HTML_MAX_CELLS || plain_text.len() > CLIPBOARD_HTML_MAX_BYTES {
        return None;
    }
    let sh = wb.sheet(sheet)?;
    let mut out = ClipboardHtml(String::new());
    write!(out, "<table{} style=\"border-collapse:collapse;font-family:Calibri,Carlito,Arial,sans-serif;font-size:11pt\">", table_dir(sh)).ok()?;
    for row in r.start.row..=r.end.row {
        if sh.is_row_hidden(row) {
            continue;
        }
        out.write_str("<tr>").ok()?;
        for col in r.start.col..=r.end.col {
            let c = CellRef::new(row, col);
            let span = if let Some(merged) = sh.merges.iter().find(|m| m.contains(c)).and_then(|m| m.intersection(&r)) {
                let first_row = (merged.start.row..=merged.end.row).find(|&row| !sh.is_row_hidden(row))?;
                if c != CellRef::new(first_row, merged.start.col) {
                    continue;
                }
                let rows = (first_row..=merged.end.row).filter(|&row| !sh.is_row_hidden(row)).count();
                format!(" rowspan=\"{rows}\" colspan=\"{}\"", merged.width())
            } else {
                String::new()
            };
            // Use the visible selected cell, even when the merge's original anchor
            // is outside the range or hidden. This matches the plain-text copy.
            let text = crate::display::cell_text(wb, sh, c);
            let dir = CellDir::of(sh, c, &text);
            let css = html_cell_css(wb, sh, c, dir);
            write!(out, "<td style=\"border:1px solid #d4d4d4;padding:2px 4px;white-space:pre-wrap;{css}\"{}{span}>", dir.attr()).ok()?;
            let mut chars = text.chars().peekable();
            while let Some(ch) = chars.next() {
                match ch {
                    '&' => out.write_str("&amp;"),
                    '<' => out.write_str("&lt;"),
                    '>' => out.write_str("&gt;"),
                    '"' => out.write_str("&quot;"),
                    '\r' => {
                        if chars.peek() == Some(&'\n') {
                            chars.next();
                        }
                        out.write_str("<br>")
                    }
                    '\n' => out.write_str("<br>"),
                    _ => out.write_char(ch),
                }
                .ok()?;
            }
            out.write_str("</td>").ok()?;
        }
        out.write_str("</tr>").ok()?;
    }
    out.write_str("</table>").ok()?;
    Some(out.0)
}

/// Enforce the budget while escaping, before HTML expansion can allocate a large string.
struct ClipboardHtml(String);

impl std::fmt::Write for ClipboardHtml {
    fn write_str(&mut self, s: &str) -> std::fmt::Result {
        if s.len() > CLIPBOARD_HTML_MAX_BYTES.saturating_sub(self.0.len()) {
            return Err(std::fmt::Error);
        }
        self.0.push_str(s);
        Ok(())
    }
}

/// Most rows Save as Web Page writes. A sheet whose used range is taller fails instead of losing cells.
const HTML_EXPORT_MAX_ROWS: u32 = 100_001;

/// Rows × columns of one web-page table. Save as Web Page writes every kept row's full used
/// column span into one growing String, so a sparse sheet with a lone far-right cell (or a
/// tall, wide one) would otherwise be gigabytes of `<td></td>` before finishing (#2387).
const HTML_EXPORT_MAX_CELLS: u64 = 4_000_000;

/// A sheet as a standalone HTML table (Save as Web Page). A sheet with pictures gets the sheet's
/// own column widths and row heights so each picture and chart (inline SVG) can sit at its anchor.
pub fn to_html(wb: &Workbook, sheet: usize) -> Result<String> {
    let Some(sh) = wb.sheet(sheet) else { return Ok(String::new()) };
    let fixed = !(sh.images.is_empty() && sh.charts.is_empty());
    let used = sh.used_range();
    let mut out = String::new();
    let _ = write!(
        out,
        "<!doctype html><html><head><meta charset=\"utf-8\"><title>{}</title><style>table{{border-collapse:collapse;font-family:Calibri,Carlito,Arial,sans-serif;font-size:11pt{}}}td{{border:1px solid #d4d4d4;padding:{};white-space:nowrap{}}}</style></head><body>",
        esc(&sh.name),
        if fixed { ";table-layout:fixed" } else { "" },
        if fixed { "0 4px" } else { "2px 4px" },
        if fixed { ";overflow:hidden;line-height:1" } else { "" }
    );
    if fixed {
        out.push_str("<div style=\"position:relative\">");
    }
    let _ = write!(out, "<table{}", table_dir(sh));
    if let (true, Some(r)) = (fixed, used) {
        let width: f32 = (r.start.col..=r.end.col).map(|c| sh.col_width(c)).sum();
        let _ = write!(out, " style=\"width:{width}px\"");
    }
    out.push('>');
    if let Some(r) = used {
        if r.height() > HTML_EXPORT_MAX_ROWS {
            return Err(EngineError::Other(format!(
                "the sheet is too tall for a web page ({} rows, at most {HTML_EXPORT_MAX_ROWS}). Save as .xlsx or CSV instead.",
                r.height()
            )));
        }
        // The table is one growing String: every kept row writes a `<td>` for the whole used
        // column span (unless the sheet has no row that is that wide). A tall, wide sheet
        // (or a sparse one with a lone far-right cell) would be gigabytes before finishing,
        // so the rectangle itself is bounded (#2387).
        if u64::from(r.height()) * u64::from(r.width()) > HTML_EXPORT_MAX_CELLS {
            return Err(EngineError::Other(format!(
                "the sheet is too tall × wide for a web page ({} × {} cells, at most {HTML_EXPORT_MAX_CELLS}). Save as .xlsx or CSV instead.",
                r.height(),
                r.width()
            )));
        }
        if fixed {
            out.push_str("<colgroup>");
            for col in (r.start.col..=r.end.col).filter(|&c| !sh.is_col_hidden(c)) {
                let _ = write!(out, "<col style=\"width:{}px\">", sh.col_width(col));
            }
            out.push_str("</colgroup>");
        }
        for row in r.start.row..=r.end.row {
            if sh.is_row_hidden(row) {
                continue;
            }
            if fixed {
                let _ = write!(out, "<tr style=\"height:{}px\">", sh.row_height(row));
            } else {
                out.push_str("<tr>");
            }
            for col in r.start.col..=r.end.col {
                let c = CellRef::new(row, col);
                if sh.merges.iter().any(|m| m.contains(c) && m.start != c) || (fixed && sh.is_col_hidden(col)) {
                    continue;
                }
                let text = crate::display::cell_text(wb, sh, c);
                let dir = CellDir::of(sh, c, &text);
                let css = html_cell_css(wb, sh, c, dir);
                let span = sh
                    .merges
                    .iter()
                    .find(|m| m.start == c)
                    .map(|m| {
                        if fixed {
                            let rows = (m.start.row..=m.end.row).filter(|&y| !sh.is_row_hidden(y)).count();
                            let cols = (m.start.col..=m.end.col).filter(|&x| !sh.is_col_hidden(x)).count();
                            format!(" rowspan=\"{rows}\" colspan=\"{cols}\"")
                        } else {
                            format!(" rowspan=\"{}\" colspan=\"{}\"", m.height(), m.width())
                        }
                    })
                    .unwrap_or_default();
                let _ = write!(out, "<td style=\"{css}\"{}{span}>{}</td>", dir.attr(), esc(&text));
            }
            out.push_str("</tr>");
        }
    }
    out.push_str("</table>");
    if fixed {
        // Sheet units are CSS pixels; the table starts at the used range, not at A1.
        let (left, top) = used.map_or((0.0, 0.0), |r| (sh.col_left(r.start.col), sh.row_top(r.start.row)));
        let place = |a: &gridcraft_model::Anchor| {
            format!(
                "position:absolute;left:{}px;top:{}px;width:{}px;height:{}px",
                sh.col_left(a.cell.col) - left + f64::from(a.dx),
                sh.row_top(a.cell.row) - top + f64::from(a.dy),
                a.width.max(0.0),
                a.height.max(0.0)
            )
        };
        for im in &sh.images {
            let _ = write!(
                out,
                "<img src=\"data:{};base64,{}\" alt=\"{}\" style=\"{}\">",
                esc(&im.mime),
                base64_encode(&im.data),
                esc(&im.alt),
                place(&im.anchor)
            );
        }
        for ch in &sh.charts {
            if let Some(svg) = crate::chart_svg::chart_svg(wb, sheet, ch, &place(&ch.anchor)) {
                out.push_str(&svg);
            }
        }
        out.push_str("</div>");
    }
    out.push_str("</body></html>");
    Ok(out)
}

thread_local! {
    /// How many [`ScriptSandbox`]es are alive on this thread.
    static SCRIPT_SANDBOX: std::cell::Cell<u32> = const { std::cell::Cell::new(0) };
}

/// While one is alive, [`read_file`] and [`write_file`] on this thread refuse every path: a
/// stored script's steps run inside one (#2178), so no command reaches the file system from a
/// script whatever its parameters are called. Dropping it (also on unwind) lifts the refusal.
pub(crate) struct ScriptSandbox(());

impl ScriptSandbox {
    pub(crate) fn enter() -> Self {
        let _ = SCRIPT_SANDBOX.try_with(|c| c.set(c.get().saturating_add(1)));
        ScriptSandbox(())
    }
}

impl Drop for ScriptSandbox {
    fn drop(&mut self) {
        let _ = SCRIPT_SANDBOX.try_with(|c| c.set(c.get().saturating_sub(1)));
    }
}

/// Refuses file access while a [`ScriptSandbox`] is alive (and, failing closed, while the
/// thread is being torn down).
fn script_sandbox_check(path: &str) -> Result<()> {
    if SCRIPT_SANDBOX.try_with(|c| c.get() > 0).unwrap_or(true) {
        return Err(EngineError::Other(format!("{path}: scripts can't read or write files")));
    }
    Ok(())
}

/// The largest native file the reader still touches: its own cap plus one, used to stop
/// reads whose bytes arrive faster than metadata can claim (device files, growing files).
const MAX_READ_BYTES: u64 = 2 * 1024 * 1024 * 1024;

#[cfg(not(target_arch = "wasm32"))]
pub fn read_file(path: &str) -> Result<Vec<u8>> {
    use std::io::Read;
    script_sandbox_check(path)?;
    let f = std::fs::File::open(path).map_err(|e| EngineError::Other(format!("{path}: {e}")))?;
    // A symlink to an endless device reports length 0 but streams forever, so metadata
    // alone never bounds the read: require a real file and cap the bytes actually taken.
    if !f.metadata().map_err(|e| EngineError::Other(format!("{path}: {e}")))?.is_file() {
        return Err(EngineError::Other(format!("{path}: only regular files can be opened")));
    }
    let mut buf = Vec::new();
    let mut limited = (&f).take(MAX_READ_BYTES + 1);
    limited.read_to_end(&mut buf).map_err(|e| EngineError::Other(format!("{path}: {e}")))?;
    if buf.len() as u64 > MAX_READ_BYTES {
        return Err(EngineError::Other("files larger than 2 GB aren't supported".into()));
    }
    Ok(buf)
}

#[cfg(target_arch = "wasm32")]
pub fn read_file(path: &str) -> Result<Vec<u8>> {
    script_sandbox_check(path)?;
    Err(EngineError::Other(format!("{path}: no file system in the browser")))
}

#[cfg(not(target_arch = "wasm32"))]
pub fn write_file(path: &str, bytes: &[u8]) -> Result<()> {
    use std::io::Write;
    script_sandbox_check(path)?;
    // Write to a temporary file, then rename: a crash never leaves a half-written workbook.
    // The temporary file is created exclusively, so an existing file or symlink at that
    // path (planted by another local user) makes the save fail instead of truncating the
    // link's target; and it inherits the destination's access restrictions, so saving a
    // private workbook doesn't widen who can read it.
    let tmp = format!("{path}.sctmp");
    let prior = std::fs::metadata(path).ok().map(|m| m.permissions());
    let mut opts = std::fs::OpenOptions::new();
    opts.write(true).create_new(true);
    #[cfg(unix)]
    if let Some(p) = &prior {
        use std::os::unix::fs::{OpenOptionsExt, PermissionsExt};
        opts.mode(p.mode());
    }
    let mut f = opts.open(&tmp).map_err(|e| {
        let _ = std::fs::remove_file(&tmp);
        EngineError::Other(format!("{path}: {e}"))
    })?;
    #[cfg(not(unix))]
    if let Some(p) = &prior {
        let _ = f.set_permissions(p.clone());
    }
    f.write_all(bytes).and_then(|()| f.flush()).map_err(|e| {
        let _ = std::fs::remove_file(&tmp);
        EngineError::Other(format!("{path}: {e}"))
    })?;
    std::fs::rename(&tmp, path).map_err(|e| {
        // A write or rename that fails (full disk, the workbook locked by another app) leaves
        // no temporary file beside the user's workbook.
        let _ = std::fs::remove_file(&tmp);
        EngineError::Other(format!("{path}: {e}"))
    })
}

#[cfg(target_arch = "wasm32")]
pub fn write_file(path: &str, _bytes: &[u8]) -> Result<()> {
    script_sandbox_check(path)?;
    Err(EngineError::Other(format!("{path}: no file system in the browser")))
}

const B64: &[u8; 64] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

pub fn base64_encode(data: &[u8]) -> String {
    let mut out = String::with_capacity(data.len().div_ceil(3) * 4);
    for chunk in data.chunks(3) {
        let b = [chunk.first().copied().unwrap_or(0), chunk.get(1).copied().unwrap_or(0), chunk.get(2).copied().unwrap_or(0)];
        let n = ((b[0] as u32) << 16) | ((b[1] as u32) << 8) | b[2] as u32;
        for i in 0..4 {
            if i <= chunk.len() {
                out.push(B64[((n >> (18 - 6 * i)) & 63) as usize] as char);
            } else {
                out.push('=');
            }
        }
    }
    out
}

pub fn base64_decode(s: &str) -> Option<Vec<u8>> {
    let s = s.split_once(',').filter(|(h, _)| h.starts_with("data:")).map(|(_, b)| b).unwrap_or(s);
    let mut out = Vec::with_capacity(s.len() / 4 * 3);
    let mut buf = 0u32;
    let mut bits = 0;
    for c in s.bytes() {
        if c == b'=' || c.is_ascii_whitespace() {
            continue;
        }
        let v = B64.iter().position(|&x| x == c)? as u32;
        buf = (buf << 6) | v;
        bits += 6;
        if bits >= 8 {
            bits -= 8;
            out.push((buf >> bits) as u8);
            buf &= (1 << bits) - 1;
        }
    }
    Some(out)
}

/// Pixel size of a PNG or JPEG from its header.
pub fn image_size(data: &[u8]) -> Option<(u32, u32)> {
    if data.starts_with(&[0x89, b'P', b'N', b'G']) {
        let w = u32::from_be_bytes(data.get(16..20)?.try_into().ok()?);
        let h = u32::from_be_bytes(data.get(20..24)?.try_into().ok()?);
        return Some((w, h));
    }
    if data.starts_with(&[0xFF, 0xD8]) {
        let mut i = 2;
        while i + 9 < data.len() {
            if *data.get(i)? != 0xFF {
                i += 1;
                continue;
            }
            let marker = *data.get(i + 1)?;
            let len = u16::from_be_bytes([*data.get(i + 2)?, *data.get(i + 3)?]) as usize;
            if (0xC0..=0xCF).contains(&marker) && !matches!(marker, 0xC4 | 0xC8 | 0xCC) {
                let h = u16::from_be_bytes([*data.get(i + 5)?, *data.get(i + 6)?]) as u32;
                let w = u16::from_be_bytes([*data.get(i + 7)?, *data.get(i + 8)?]) as u32;
                return Some((w, h));
            }
            i += 2 + len;
        }
    }
    None
}

#[cfg(test)]
mod tests;