1 files changed, 91 insertions, 0 deletions
diff --git a/src/epub.rs b/src/epub.rs
new file mode 100644
index 0000000..c984dde
--- /dev/null
+++ b/src/epub.rs
@@ -0,0 +1,91 @@
+use std::path::{Path, PathBuf};
+use unicode_normalization::UnicodeNormalization;
+
+pub struct EpubSkeleton {
+    /// Books/<book_title (book_id)>/
+    pub root: PathBuf,
+    pub meta_inf: PathBuf,
+    pub oebps: PathBuf,
+}
+
+impl EpubSkeleton {
+    pub fn plan(base_books_dir: &Path, title: &str, bookid: &str) -> Self {
+        // Maximum number of bytes in a filename.
+        const MAX_BYTES: usize = 255;
+        let clean_title = sanitize_filename(title);
+        let root_name = if !clean_title.is_empty() {
+            // Title length should take into account the bookid, space, and () characters.
+            let title_max_length = MAX_BYTES.saturating_sub(3 + bookid.len());
+            let truncated_title = truncate_utf8_by_byte(&clean_title, title_max_length);
+            format!("{} ({})", truncated_title, bookid)
+        } else {
+            format!("({})", bookid)
+        };
+        let root_dir = base_books_dir.join(root_name);
+        Self {
+            meta_inf: root_dir.join("META-INF"),
+            oebps: root_dir.join("OEBPS"),
+            root: root_dir,
+        }
+    }
+}
+
+/// Sanitize a filename component for cross‑platform compatibility.
+/// Applies sensible defaults:
+/// - Normalize to NFC
+/// - Replace illegal characters: <>:"/\\|?*
+/// - Remove control characters
+/// - Collapse whitespace
+/// - Trim whitespace
+fn sanitize_filename(input: &str) -> String {
+    // Normalize to NFC to ensure consistency - characters displayed the same are stored the same.
+    let mut s = input.nfc().collect::<String>();
+
+    // Replace illegal Windows/FAT characters + control chars
+    const ILLEGAL: &[char] = &['<', '>', ':', '"', '/', '\\', '|', '?', '*'];
+    let mut cleaned = String::with_capacity(s.len());
+
+    for ch in s.chars() {
+        if ch.is_control() || ILLEGAL.contains(&ch) {
+            cleaned.push('_');
+        } else {
+            cleaned.push(ch);
+        }
+    }
+    s = cleaned;
+
+    // Collapse whitespace
+    let mut cleaned = String::with_capacity(s.len());
+    let mut prev_was_whitespace = false;
+    for ch in s.chars() {
+        if ch.is_whitespace() {
+            if !prev_was_whitespace {
+                cleaned.push(' ');
+                prev_was_whitespace = true;
+            }
+        } else {
+            cleaned.push(ch);
+            prev_was_whitespace = false;
+        }
+    }
+    cleaned.trim().to_string()
+}
+
+/// Truncate a UTF‑8 string safely without splitting codepoints.
+fn truncate_utf8_by_byte(s: &str, max_bytes: usize) -> &str {
+    if s.len() <= max_bytes {
+        return s;
+    }
+
+    let mut end = max_bytes;
+    // Back up until we end with a non-continuation byte.
+    while end > 0 && !s.is_char_boundary(end) {
+        end -= 1;
+    }
+
+    if end == 0 {
+        return "";
+    }
+
+    &s[..end]
+}