//! Upload validation: turns raw uploaded bytes into a manifest of
//! `(path, bytes)` files ready to be written to R2, while defending against
//! malicious archives.
//!
//! See `docs/plans/2026-07-12-pages-design.md` §2.2. The zip-bomb defense in
//! particular is deliberately paranoid: entry sizes declared in a zip's
//! central directory are **never trusted**. Every byte is counted as it
//! streams out of the decompressor, and extraction aborts the instant a
//! per-file or total limit is crossed — so a small compressed file that
//! claims (or would produce) a huge uncompressed size is rejected long
//! before that size is ever reached, let alone materialized in memory.

use std::collections::HashSet;
use std::io::{Cursor, Read};

/// Configurable limits enforced by [`build_manifest`].
///
/// Fields are public so callers (tests, and eventually `routes::api`) can
/// construct scaled-down variants for testing or future configurability;
/// [`Default`] provides the production values from design §2.2.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct UploadLimits {
    /// Maximum size of the raw uploaded bytes (compressed, for zip; as-is,
    /// for html) in bytes. Checked against the buffered body before any
    /// parsing happens.
    pub max_compressed: usize,
    /// Maximum total *uncompressed* size across all files in the archive,
    /// in bytes. Enforced while streaming decompressed bytes, not from the
    /// zip header.
    pub max_uncompressed_total: u64,
    /// Maximum *uncompressed* size of any single file, in bytes. Enforced
    /// while streaming decompressed bytes, not from the zip header.
    pub max_file: u64,
    /// Maximum number of entries (including directories) a zip archive may
    /// contain.
    pub max_entries: usize,
    /// Maximum length, in bytes, of a single entry path.
    pub max_path_len: usize,
    /// Maximum number of `/`-separated path segments (nesting depth,
    /// including the filename) a single entry path may contain.
    pub max_depth: usize,
}

impl Default for UploadLimits {
    /// Production limits from design §2.2: 10 MiB max compressed upload,
    /// 25 MiB max total uncompressed, 5 MiB max per file, 300 max entries,
    /// 180-byte max path length, depth 10.
    fn default() -> Self {
        const MIB: u64 = 1024 * 1024;
        Self {
            max_compressed: (10 * MIB) as usize,
            max_uncompressed_total: 25 * MIB,
            max_file: 5 * MIB,
            max_entries: 300,
            max_path_len: 180,
            max_depth: 10,
        }
    }
}

/// The kind of upload being validated — determines how `bytes` is
/// interpreted by [`build_manifest`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum UploadKind {
    /// A single raw HTML file, stored as the page's `index.html`.
    Html,
    /// A zip archive of static assets, extracted per design §2.2.
    Zip,
}

/// One file destined for R2 storage: `path` is the R2 object key suffix
/// (relative to `<slug>/`), `bytes` is its full content.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ManifestEntry {
    /// Path relative to the page root, e.g. `"index.html"` or
    /// `"assets/app.js"`. Always `/`-separated, never starts with `/`,
    /// never contains a `..` segment (enforced by [`build_manifest`]).
    pub path: String,
    /// The file's full (decompressed, for zip) content.
    pub bytes: Vec<u8>,
}

/// Errors returned by [`build_manifest`].
///
/// Each variant carries a precise, user-facing `Display` message suitable
/// for a `400 Bad Request` API response body.
#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
pub enum UploadError {
    /// The raw uploaded bytes exceeded `max_compressed`.
    #[error("upload exceeds the maximum allowed size of {max} bytes")]
    CompressedTooLarge {
        /// The configured limit that was exceeded.
        max: usize,
    },
    /// A zip entry name attempted to escape the page root.
    #[error("archive entry has an unsafe path: '{path}'")]
    PathTraversal {
        /// The offending raw entry name.
        path: String,
    },
    /// A zip entry name was longer than `max_path_len`.
    #[error("archive entry path '{path}' exceeds the maximum length of {max} characters")]
    PathTooLong {
        /// The offending raw entry name.
        path: String,
        /// The configured limit that was exceeded.
        max: usize,
    },
    /// A zip entry name had more `/`-separated segments than `max_depth`.
    #[error("archive entry path '{path}' exceeds the maximum nesting depth of {max}")]
    PathTooDeep {
        /// The offending raw entry name.
        path: String,
        /// The configured limit that was exceeded.
        max: usize,
    },
    /// The archive contained more entries than `max_entries`.
    #[error("archive contains too many entries (maximum {max})")]
    TooManyEntries {
        /// The configured limit that was exceeded.
        max: usize,
    },
    /// A single file's decompressed size exceeded `max_file`.
    #[error("archive entry '{path}' exceeds the maximum per-file size of {max} bytes")]
    FileTooLarge {
        /// The offending entry name.
        path: String,
        /// The configured limit that was exceeded.
        max: u64,
    },
    /// The archive's total decompressed size exceeded `max_uncompressed_total`.
    #[error("archive's total uncompressed size exceeds the maximum allowed of {max} bytes")]
    TotalTooLarge {
        /// The configured limit that was exceeded.
        max: u64,
    },
    /// The archive did not contain a root-level `index.html`.
    #[error("archive is missing a required root-level index.html")]
    MissingIndexHtml,
    /// The archive contained the same normalized path twice.
    ///
    /// With the `zip` crate version this crate currently depends on,
    /// parsed archives cannot actually expose two entries sharing a
    /// literal name (see the `seen` check in `build_zip_manifest` for
    /// details), so this variant is presently unreachable in practice —
    /// it is kept as defense-in-depth against that internal representation
    /// changing in a future crate upgrade.
    #[error("archive contains a duplicate entry: '{path}'")]
    DuplicateEntry {
        /// The duplicated path.
        path: String,
    },
    /// The bytes could not be parsed as a zip archive at all.
    #[error("upload could not be read as a valid zip archive")]
    InvalidZip,
    /// The archive (or html upload) contained no files.
    #[error("upload contains no files")]
    Empty,
}

/// Builds the file manifest for an upload, enforcing every limit in
/// `limits` and the structural rules from design §2.2.
///
/// - [`UploadKind::Html`]: `bytes` is stored verbatim as a single
///   `"index.html"` entry (still checked against `max_compressed` and
///   `max_file`/`max_uncompressed_total`).
/// - [`UploadKind::Zip`]: `bytes` is parsed as a zip archive. Directories
///   are skipped. Every file entry's name is checked for path traversal
///   (`..` segments, leading `/`, backslashes, drive letters, empty
///   segments, NUL bytes) and length/depth limits, duplicates are
///   rejected, the entry count is capped, and decompressed bytes are
///   counted as they stream out — extraction aborts the moment a per-file
///   or running total limit is crossed, never trusting the zip header's
///   declared size. The archive must contain a root-level `index.html` and
///   at least one file.
///
/// # Examples
///
/// ```
/// use pages::core::upload::{build_manifest, UploadKind, UploadLimits};
///
/// let limits = UploadLimits::default();
/// let manifest = build_manifest(
///     UploadKind::Html,
///     b"<html>hello</html>".to_vec(),
///     &limits,
/// )
/// .unwrap();
/// assert_eq!(manifest.len(), 1);
/// assert_eq!(manifest[0].path, "index.html");
/// ```
pub fn build_manifest(
    kind: UploadKind,
    bytes: Vec<u8>,
    limits: &UploadLimits,
) -> Result<Vec<ManifestEntry>, UploadError> {
    if bytes.len() > limits.max_compressed {
        return Err(UploadError::CompressedTooLarge {
            max: limits.max_compressed,
        });
    }

    match kind {
        UploadKind::Html => build_html_manifest(bytes, limits),
        UploadKind::Zip => build_zip_manifest(bytes, limits),
    }
}

/// Builds the single-entry manifest for an [`UploadKind::Html`] upload.
fn build_html_manifest(
    bytes: Vec<u8>,
    limits: &UploadLimits,
) -> Result<Vec<ManifestEntry>, UploadError> {
    if bytes.is_empty() {
        return Err(UploadError::Empty);
    }
    let len = bytes.len() as u64;
    if len > limits.max_file {
        return Err(UploadError::FileTooLarge {
            path: "index.html".to_string(),
            max: limits.max_file,
        });
    }
    if len > limits.max_uncompressed_total {
        return Err(UploadError::TotalTooLarge {
            max: limits.max_uncompressed_total,
        });
    }
    Ok(vec![ManifestEntry {
        path: "index.html".to_string(),
        bytes,
    }])
}

/// Builds the manifest for an [`UploadKind::Zip`] upload.
fn build_zip_manifest(
    bytes: Vec<u8>,
    limits: &UploadLimits,
) -> Result<Vec<ManifestEntry>, UploadError> {
    let mut archive =
        zip::ZipArchive::new(Cursor::new(bytes)).map_err(|_| UploadError::InvalidZip)?;

    if archive.is_empty() {
        return Err(UploadError::Empty);
    }
    if archive.len() > limits.max_entries {
        return Err(UploadError::TooManyEntries {
            max: limits.max_entries,
        });
    }

    let mut manifest = Vec::new();
    // Defense-in-depth against duplicate entry names (design §2.2). Note:
    // `zip::ZipArchive` stores parsed entries in a name-keyed map
    // internally, so `archive.by_index` can never actually yield two
    // entries with the same literal name against the crate version this
    // module depends on — see
    // `zip_duplicate_named_entries_are_deduplicated_by_the_zip_crate_itself`
    // in this module's tests for the full explanation. This check stays
    // as a cheap guard in case that changes.
    let mut seen: HashSet<String> = HashSet::new();
    let mut total_used: u64 = 0;

    for i in 0..archive.len() {
        let mut entry = archive.by_index(i).map_err(|_| UploadError::InvalidZip)?;

        if entry.is_dir() {
            continue;
        }

        let name = entry.name().to_string();
        check_entry_path(&name, limits)?;

        if !seen.insert(name.clone()) {
            return Err(UploadError::DuplicateEntry { path: name });
        }

        let data = read_entry_limited(&mut entry, &name, limits, &mut total_used)?;
        manifest.push(ManifestEntry {
            path: name,
            bytes: data,
        });
    }

    if manifest.is_empty() {
        return Err(UploadError::Empty);
    }
    if !manifest.iter().any(|e| e.path == "index.html") {
        return Err(UploadError::MissingIndexHtml);
    }

    Ok(manifest)
}

/// Validates a raw zip entry name against the path-traversal and
/// length/depth rules from design §2.2.
///
/// Rejects: empty names, names over `max_path_len`, names containing a
/// backslash or NUL byte, names starting with `/` (absolute), names
/// starting with a drive letter (`C:...`), and any `.` or `..` or empty
/// path segment. Also enforces `max_depth` on the segment count.
fn check_entry_path(name: &str, limits: &UploadLimits) -> Result<(), UploadError> {
    if name.is_empty() {
        return Err(UploadError::PathTraversal {
            path: name.to_string(),
        });
    }
    if name.len() > limits.max_path_len {
        return Err(UploadError::PathTooLong {
            path: name.to_string(),
            max: limits.max_path_len,
        });
    }
    if name.contains('\\') || name.contains('\0') {
        return Err(UploadError::PathTraversal {
            path: name.to_string(),
        });
    }
    if name.starts_with('/') {
        return Err(UploadError::PathTraversal {
            path: name.to_string(),
        });
    }
    // Windows drive letter, e.g. "C:foo" or "c:/foo".
    let bytes = name.as_bytes();
    if bytes.len() >= 2 && bytes[0].is_ascii_alphabetic() && bytes[1] == b':' {
        return Err(UploadError::PathTraversal {
            path: name.to_string(),
        });
    }

    let segments: Vec<&str> = name.split('/').collect();
    if segments.len() > limits.max_depth {
        return Err(UploadError::PathTooDeep {
            path: name.to_string(),
            max: limits.max_depth,
        });
    }
    for seg in &segments {
        if seg.is_empty() || *seg == "." || *seg == ".." {
            return Err(UploadError::PathTraversal {
                path: name.to_string(),
            });
        }
    }

    Ok(())
}

/// Chunk size used by [`read_entry_limited`]'s streaming read loop.
const READ_CHUNK: usize = 64 * 1024;

/// Reads a zip entry's decompressed content, enforcing `limits.max_file`
/// and `limits.max_uncompressed_total` **during** the read rather than
/// after — the read loop aborts as soon as either limit is crossed, so a
/// high-compression-ratio "zip bomb" entry is rejected after at most
/// `READ_CHUNK` extra bytes are decompressed, never after the full
/// (potentially huge) claimed uncompressed size.
fn read_entry_limited<R: Read>(
    reader: &mut R,
    path: &str,
    limits: &UploadLimits,
    total_used: &mut u64,
) -> Result<Vec<u8>, UploadError> {
    let mut buf = Vec::new();
    let mut chunk = [0u8; READ_CHUNK];
    loop {
        let n = reader
            .read(&mut chunk)
            .map_err(|_| UploadError::InvalidZip)?;
        if n == 0 {
            break;
        }
        buf.extend_from_slice(&chunk[..n]);

        if buf.len() as u64 > limits.max_file {
            return Err(UploadError::FileTooLarge {
                path: path.to_string(),
                max: limits.max_file,
            });
        }

        *total_used += n as u64;
        if *total_used > limits.max_uncompressed_total {
            return Err(UploadError::TotalTooLarge {
                max: limits.max_uncompressed_total,
            });
        }
    }
    Ok(buf)
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Write;
    use zip::write::SimpleFileOptions;
    use zip::ZipWriter;

    /// Builds a zip archive in memory from `(name, content)` pairs, using
    /// deflate compression (the only method compiled in, matching
    /// production's `Cargo.toml`).
    fn make_zip(entries: &[(&str, &[u8])]) -> Vec<u8> {
        let mut buf = Cursor::new(Vec::new());
        {
            let mut writer = ZipWriter::new(&mut buf);
            let options =
                SimpleFileOptions::default().compression_method(zip::CompressionMethod::Deflated);
            for (name, content) in entries {
                writer.start_file(*name, options).unwrap();
                writer.write_all(content).unwrap();
            }
            writer.finish().unwrap();
        }
        buf.into_inner()
    }

    /// Builds a zip archive containing a highly-compressible single file
    /// (all zero bytes) of `uncompressed_len` bytes — a small "zip bomb"
    /// fixture used to test the streaming size guard.
    fn make_bomb_zip(name: &str, uncompressed_len: usize) -> Vec<u8> {
        make_zip(&[(name, &vec![0u8; uncompressed_len])])
    }

    fn limits() -> UploadLimits {
        UploadLimits::default()
    }

    /// Minimal, hand-rolled CRC-32 (the standard zip/PNG polynomial) — used
    /// only by [`make_zip_raw`], which builds a zip archive by hand rather
    /// than through `ZipWriter`.
    fn crc32(data: &[u8]) -> u32 {
        let mut crc: u32 = 0xFFFF_FFFF;
        for &byte in data {
            crc ^= byte as u32;
            for _ in 0..8 {
                let mask = (crc & 1).wrapping_neg();
                crc = (crc >> 1) ^ (0xEDB8_8320 & mask);
            }
        }
        !crc
    }

    /// Hand-builds a raw (stored/uncompressed) zip archive from arbitrary
    /// `(name, content)` entries, assembling the zip byte format directly
    /// instead of going through `ZipWriter`.
    ///
    /// Needed because `zip::write::ZipWriter` enforces filename uniqueness
    /// itself (`start_file` returns `InvalidArchive("Duplicate filename")`
    /// for a repeated name), so it cannot be used to build a fixture with
    /// two entries sharing a name — see
    /// `zip_duplicate_named_entries_are_deduplicated_by_the_zip_crate_itself`
    /// below for why that fixture is still useful.
    fn make_zip_raw(entries: &[(&str, &[u8])]) -> Vec<u8> {
        let mut out = Vec::new();
        let mut central = Vec::new();

        for (name, content) in entries {
            let name_bytes = name.as_bytes();
            let offset = out.len() as u32;
            let crc = crc32(content);
            let len = content.len() as u32;

            // Local file header (stored, no data descriptor).
            out.extend_from_slice(&0x0403_4b50u32.to_le_bytes());
            out.extend_from_slice(&20u16.to_le_bytes()); // version needed
            out.extend_from_slice(&0u16.to_le_bytes()); // flags
            out.extend_from_slice(&0u16.to_le_bytes()); // compression: stored
            out.extend_from_slice(&0u16.to_le_bytes()); // mod time
            out.extend_from_slice(&0u16.to_le_bytes()); // mod date
            out.extend_from_slice(&crc.to_le_bytes());
            out.extend_from_slice(&len.to_le_bytes()); // compressed size
            out.extend_from_slice(&len.to_le_bytes()); // uncompressed size
            out.extend_from_slice(&(name_bytes.len() as u16).to_le_bytes());
            out.extend_from_slice(&0u16.to_le_bytes()); // extra field len
            out.extend_from_slice(name_bytes);
            out.extend_from_slice(content);

            // Matching central directory header.
            central.extend_from_slice(&0x0201_4b50u32.to_le_bytes());
            central.extend_from_slice(&20u16.to_le_bytes()); // version made by
            central.extend_from_slice(&20u16.to_le_bytes()); // version needed
            central.extend_from_slice(&0u16.to_le_bytes()); // flags
            central.extend_from_slice(&0u16.to_le_bytes()); // compression: stored
            central.extend_from_slice(&0u16.to_le_bytes()); // mod time
            central.extend_from_slice(&0u16.to_le_bytes()); // mod date
            central.extend_from_slice(&crc.to_le_bytes());
            central.extend_from_slice(&len.to_le_bytes());
            central.extend_from_slice(&len.to_le_bytes());
            central.extend_from_slice(&(name_bytes.len() as u16).to_le_bytes());
            central.extend_from_slice(&0u16.to_le_bytes()); // extra field len
            central.extend_from_slice(&0u16.to_le_bytes()); // comment len
            central.extend_from_slice(&0u16.to_le_bytes()); // disk number start
            central.extend_from_slice(&0u16.to_le_bytes()); // internal attrs
            central.extend_from_slice(&0u32.to_le_bytes()); // external attrs
            central.extend_from_slice(&offset.to_le_bytes());
            central.extend_from_slice(name_bytes);
        }

        let cd_offset = out.len() as u32;
        let cd_size = central.len() as u32;
        out.extend_from_slice(&central);

        // End of central directory record.
        out.extend_from_slice(&0x0605_4b50u32.to_le_bytes());
        out.extend_from_slice(&0u16.to_le_bytes()); // this disk
        out.extend_from_slice(&0u16.to_le_bytes()); // disk with cd start
        out.extend_from_slice(&(entries.len() as u16).to_le_bytes());
        out.extend_from_slice(&(entries.len() as u16).to_le_bytes());
        out.extend_from_slice(&cd_size.to_le_bytes());
        out.extend_from_slice(&cd_offset.to_le_bytes());
        out.extend_from_slice(&0u16.to_le_bytes()); // comment len

        out
    }

    // ── html happy path ─────────────────────────────────────────────────

    #[test]
    fn html_happy_path() {
        let manifest =
            build_manifest(UploadKind::Html, b"<html></html>".to_vec(), &limits()).unwrap();
        assert_eq!(manifest.len(), 1);
        assert_eq!(manifest[0].path, "index.html");
        assert_eq!(manifest[0].bytes, b"<html></html>");
    }

    #[test]
    fn html_empty_is_rejected() {
        let err = build_manifest(UploadKind::Html, Vec::new(), &limits()).unwrap_err();
        assert_eq!(err, UploadError::Empty);
    }

    #[test]
    fn html_over_per_file_limit_rejected() {
        let small_limits = UploadLimits {
            max_file: 10,
            ..limits()
        };
        let err = build_manifest(UploadKind::Html, vec![b'a'; 11], &small_limits).unwrap_err();
        assert!(matches!(err, UploadError::FileTooLarge { .. }));
    }

    #[test]
    fn oversize_compressed_input_rejected_for_html() {
        let small_limits = UploadLimits {
            max_compressed: 10,
            ..limits()
        };
        let err = build_manifest(UploadKind::Html, vec![b'a'; 11], &small_limits).unwrap_err();
        assert_eq!(err, UploadError::CompressedTooLarge { max: 10 });
    }

    // ── zip happy path ───────────────────────────────────────────────────

    #[test]
    fn zip_happy_path_multi_file_with_subdirs() {
        let zip = make_zip(&[
            ("index.html", b"<html></html>"),
            ("assets/app.js", b"console.log(1)"),
            ("assets/img/logo.png", b"\x89PNG"),
        ]);
        let manifest = build_manifest(UploadKind::Zip, zip, &limits()).unwrap();
        let mut paths: Vec<&str> = manifest.iter().map(|e| e.path.as_str()).collect();
        paths.sort();
        assert_eq!(
            paths,
            ["assets/app.js", "assets/img/logo.png", "index.html"]
        );
    }

    #[test]
    fn zip_directory_entries_are_skipped() {
        // ZipWriter::add_directory creates an explicit directory entry.
        let mut buf = Cursor::new(Vec::new());
        {
            let mut writer = ZipWriter::new(&mut buf);
            let options = SimpleFileOptions::default();
            writer.add_directory("assets/", options).unwrap();
            writer.start_file("index.html", options).unwrap();
            writer.write_all(b"hi").unwrap();
            writer.start_file("assets/app.js", options).unwrap();
            writer.write_all(b"x").unwrap();
            writer.finish().unwrap();
        }
        let manifest = build_manifest(UploadKind::Zip, buf.into_inner(), &limits()).unwrap();
        assert_eq!(manifest.len(), 2);
        assert!(manifest.iter().all(|e| !e.path.ends_with('/')));
    }

    // ── path traversal ──────────────────────────────────────────────────

    #[test]
    fn zip_rejects_dotdot_traversal() {
        let zip = make_zip(&[("index.html", b"hi"), ("../evil.txt", b"pwn")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTraversal { .. }));
    }

    #[test]
    fn zip_rejects_dotdot_mid_path_traversal() {
        let zip = make_zip(&[("index.html", b"hi"), ("assets/../../evil.txt", b"pwn")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTraversal { .. }));
    }

    #[test]
    fn zip_rejects_absolute_path() {
        let zip = make_zip(&[("index.html", b"hi"), ("/etc/passwd", b"pwn")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTraversal { .. }));
    }

    #[test]
    fn zip_rejects_backslash_separator() {
        let zip = make_zip(&[("index.html", b"hi"), ("assets\\evil.js", b"pwn")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTraversal { .. }));
    }

    #[test]
    fn zip_rejects_drive_letter() {
        let zip = make_zip(&[("index.html", b"hi"), ("C:evil.txt", b"pwn")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTraversal { .. }));
    }

    #[test]
    fn zip_rejects_empty_path_segment() {
        let zip = make_zip(&[("index.html", b"hi"), ("assets//evil.js", b"pwn")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTraversal { .. }));
    }

    #[test]
    fn zip_rejects_nul_byte() {
        let zip = make_zip(&[("index.html", b"hi"), ("evil\0.js", b"pwn")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTraversal { .. }));
    }

    #[test]
    fn zip_rejects_path_too_long() {
        let long_name = format!("{}.txt", "a".repeat(200));
        let zip = make_zip(&[("index.html", b"hi"), (&long_name, b"x")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTooLong { .. }));
    }

    #[test]
    fn zip_accepts_path_at_exact_max_length() {
        // A path of exactly max_path_len (180) bytes must be accepted —
        // guards against a future off-by-one tightening (`>=` vs `>`).
        let max = limits().max_path_len;
        let name = format!("{}.txt", "a".repeat(max - 4));
        assert_eq!(name.len(), max);
        let zip = make_zip(&[("index.html", b"hi"), (&name, b"x")]);
        let manifest = build_manifest(UploadKind::Zip, zip, &limits()).unwrap();
        assert!(manifest.iter().any(|e| e.path == name));
    }

    #[test]
    fn zip_rejects_path_too_deep() {
        let deep_name = format!("{}x.txt", "a/".repeat(11));
        let zip = make_zip(&[("index.html", b"hi"), (&deep_name, b"x")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert!(matches!(err, UploadError::PathTooDeep { .. }));
    }

    #[test]
    fn zip_accepts_path_at_exact_max_depth() {
        // A path with exactly max_depth (10) `/`-separated segments
        // (including the filename) must be accepted — guards against a
        // future off-by-one tightening (`>=` vs `>`).
        let max = limits().max_depth;
        let name = format!("{}x.txt", "a/".repeat(max - 1));
        assert_eq!(name.split('/').count(), max);
        let zip = make_zip(&[("index.html", b"hi"), (&name, b"x")]);
        let manifest = build_manifest(UploadKind::Zip, zip, &limits()).unwrap();
        assert!(manifest.iter().any(|e| e.path == name));
    }

    // ── duplicates / structural ─────────────────────────────────────────

    #[test]
    fn zip_duplicate_named_entries_are_deduplicated_by_the_zip_crate_itself() {
        // `zip` 2.x parses central-directory entries into an
        // `IndexMap<Box<str>, ZipFileData>` keyed by name (see
        // `zip::read::Shared` in the vendored crate source), so it is
        // structurally impossible for `ZipArchive::by_index` to expose two
        // entries with the exact same literal name — a repeated name just
        // overwrites the earlier entry's metadata (last write wins),
        // collapsing the archive to one entry per unique name.
        //
        // `build_manifest`'s own `seen`/`DuplicateEntry` check (see
        // `build_zip_manifest` and `UploadError::DuplicateEntry`) is
        // consequently dead code against this crate version: it can never
        // observe two entries sharing a name through a real `ZipArchive`.
        // It is kept anyway as free defense-in-depth in case a future
        // `zip` upgrade changes that internal representation. This test
        // pins down the crate's current dedup/last-write-wins behavior so
        // such a change doesn't silently reopen the gap without a failing
        // test to flag it — if this test starts failing, `DuplicateEntry`
        // has become reachable and deserves its own direct test.
        let zip = make_zip_raw(&[
            ("index.html", b"hi"),
            ("dup.txt", b"one"),
            ("dup.txt", b"two"),
        ]);

        let archive = zip::ZipArchive::new(Cursor::new(zip.clone())).unwrap();
        assert_eq!(
            archive.len(),
            2,
            "expected the two dup.txt entries to collapse into one"
        );

        let manifest = build_manifest(UploadKind::Zip, zip, &limits()).unwrap();
        assert_eq!(manifest.len(), 2);
        let dup = manifest.iter().find(|e| e.path == "dup.txt").unwrap();
        assert_eq!(
            dup.bytes, b"two",
            "last write should win for a deduplicated name"
        );
    }

    #[test]
    fn zip_rejects_missing_index_html() {
        let zip = make_zip(&[("assets/app.js", b"x")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert_eq!(err, UploadError::MissingIndexHtml);
    }

    #[test]
    fn zip_rejects_nested_index_html_only() {
        // A nested index.html doesn't satisfy the root-level requirement.
        let zip = make_zip(&[("sub/index.html", b"hi")]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert_eq!(err, UploadError::MissingIndexHtml);
    }

    #[test]
    fn zip_rejects_empty_archive() {
        let zip = make_zip(&[]);
        let err = build_manifest(UploadKind::Zip, zip, &limits()).unwrap_err();
        assert_eq!(err, UploadError::Empty);
    }

    #[test]
    fn zip_rejects_archive_of_only_directories() {
        let mut buf = Cursor::new(Vec::new());
        {
            let mut writer = ZipWriter::new(&mut buf);
            writer
                .add_directory("empty/", SimpleFileOptions::default())
                .unwrap();
            writer.finish().unwrap();
        }
        let err = build_manifest(UploadKind::Zip, buf.into_inner(), &limits()).unwrap_err();
        assert_eq!(err, UploadError::Empty);
    }

    #[test]
    fn invalid_zip_bytes_rejected() {
        let err =
            build_manifest(UploadKind::Zip, b"not a zip file".to_vec(), &limits()).unwrap_err();
        assert_eq!(err, UploadError::InvalidZip);
    }

    // ── limits ───────────────────────────────────────────────────────────

    #[test]
    fn zip_rejects_too_many_entries() {
        let small_limits = UploadLimits {
            max_entries: 3,
            ..limits()
        };
        let zip = make_zip(&[
            ("index.html", b"hi"),
            ("a.txt", b"1"),
            ("b.txt", b"2"),
            ("c.txt", b"3"),
        ]);
        let err = build_manifest(UploadKind::Zip, zip, &small_limits).unwrap_err();
        assert_eq!(err, UploadError::TooManyEntries { max: 3 });
    }

    #[test]
    fn zip_rejects_oversize_compressed_input() {
        let zip = make_zip(&[("index.html", b"hi")]);
        let small_limits = UploadLimits {
            max_compressed: 4,
            ..limits()
        };
        let err = build_manifest(UploadKind::Zip, zip, &small_limits).unwrap_err();
        assert_eq!(err, UploadError::CompressedTooLarge { max: 4 });
    }

    #[test]
    fn zip_rejects_file_over_per_file_limit() {
        let zip = make_zip(&[("index.html", b"hi"), ("big.bin", &[1u8; 100])]);
        let small_limits = UploadLimits {
            max_file: 50,
            ..limits()
        };
        let err = build_manifest(UploadKind::Zip, zip, &small_limits).unwrap_err();
        assert!(matches!(err, UploadError::FileTooLarge { .. }));
    }

    #[test]
    fn zip_rejects_total_over_limit_across_multiple_files() {
        let zip = make_zip(&[
            ("index.html", &[1u8; 40]),
            ("a.bin", &[1u8; 40]),
            ("b.bin", &[1u8; 40]),
        ]);
        let small_limits = UploadLimits {
            max_file: 1000,
            max_uncompressed_total: 100,
            ..limits()
        };
        let err = build_manifest(UploadKind::Zip, zip, &small_limits).unwrap_err();
        assert!(matches!(err, UploadError::TotalTooLarge { .. }));
    }

    /// The headline zip-bomb test: a single entry whose *declared*
    /// uncompressed size (10 MiB of zeros) is well within the default
    /// 25 MiB total / 5 MiB per-file limits on paper, but a much smaller
    /// per-file limit here proves the streaming guard aborts extraction
    /// before the whole entry is decompressed — deflate compresses runs of
    /// zeros to a tiny fraction of their size, so if we trusted the zip
    /// header instead of counting streamed bytes, this would sail through.
    #[test]
    fn zip_bomb_rejected_by_streaming_guard_before_full_materialization() {
        let bomb = make_bomb_zip("index.html", 10 * 1024 * 1024);
        // Compressed size should be tiny relative to the claimed uncompressed size.
        assert!(
            bomb.len() < 100 * 1024,
            "fixture not actually a high compression ratio: {} bytes",
            bomb.len()
        );

        let tight_limits = UploadLimits {
            max_file: 1024, // far smaller than the 10 MiB decompressed content
            ..limits()
        };
        let err = build_manifest(UploadKind::Zip, bomb, &tight_limits).unwrap_err();
        assert!(matches!(err, UploadError::FileTooLarge { .. }));
    }

    #[test]
    fn zip_bomb_rejected_against_default_limits() {
        // 100 MiB of zeros compresses to a few KiB with deflate, but
        // decompressing it fully would blow the default 25 MiB total /
        // 5 MiB per-file limits — the streaming guard must catch this.
        let bomb = make_bomb_zip("index.html", 100 * 1024 * 1024);
        assert!(bomb.len() < 1024 * 1024);
        let err = build_manifest(UploadKind::Zip, bomb, &limits()).unwrap_err();
        assert!(matches!(
            err,
            UploadError::FileTooLarge { .. } | UploadError::TotalTooLarge { .. }
        ));
    }
}