Support dispatch on FormFactor in spoof_by (#8)

* docs(agents): fix link reference in docstring

Link reference defined in list item is not shown in rendered
docstring.

<https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#doc_nested_refdefs>

Caught by Clippy.

* refactor(agents): remove superfluous reference

`ua_instance` is borrowed but then immediately dereferenced by the
compiler.

<https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#needless_borrow>

Caught by Clippy.

* feat(agents): support dispatch on FormFactor in spoof_by

Add functions to collate static user agents into groups by form
factor, and then dispatch on them in spoof_by.

Addresses #7: [1]

[1]: #7

* perf(ua): zero copy form factor

---------

Co-authored-by: j-mendez <jeff@spider.cloud>

Author: jakewilliami

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "ua_generator"
-version = "0.5.42"
+version = "0.5.43"
 edition = "2021"
 authors = ["j-mendez <jeff@spider.cloud>"]
 description = "Random User Agent Spoofer in Rust."

ua_generator/Cargo.toml

@@ -7,7 +7,7 @@
 //!
 //!
 //! - **Generate** get a random UA to use.
-//!   - [`spoof_ua`]: ua/fn.spoof_ua.html
+//!   - [`spoof_ua`][]: ua/fn.spoof_ua.html
 //!
 //! # Basic usage
 //!

ua_generator/src/lib.rs

@@ -367,6 +367,37 @@ pub fn spoof_by(
         // Any Safari fallback → global Safari list
         (_, _, Some(Browser::Safari)) => pick_rand(rng, STATIC_SAFARI_AGENTS),
 
+        // --- FormFactor match only ---
+        (_, Some(FormFactor::Desktop), _) => pick_rand_multi(
+            rng,
+            &[
+                STATIC_CHROME_WINDOWS_AGENTS,
+                STATIC_CHROME_MAC_AGENTS,
+                STATIC_CHROME_LINUX_AGENTS,
+                STATIC_FIREFOX_WINDOWS_AGENTS,
+                STATIC_FIREFOX_MAC_AGENTS,
+                STATIC_FIREFOX_LINUX_AGENTS,
+                STATIC_SAFARI_MAC_AGENTS,
+            ],
+        ),
+        (_, Some(FormFactor::Mobile), _) => pick_rand_multi(
+            rng,
+            &[
+                STATIC_CHROME_MOBILE_AGENTS,
+                STATIC_FIREFOX_MOBILE_AGENTS,
+                STATIC_SAFARI_MOBILE_AGENTS,
+            ],
+        ),
+        (_, Some(FormFactor::Tablet), _) => pick_rand_multi(
+            rng,
+            &[
+                STATIC_CHROME_TABLET_AGENTS,
+                STATIC_FIREFOX_TABLET_AGENTS,
+                STATIC_SAFARI_TABLET_AGENTS,
+            ],
+        ),
+
+        // --- Fall Back ---
         // IE: until IE lists are generated, fall back to mixed static
         _ => pick_rand(rng, STATIC_AGENTS),
     }
@@ -520,6 +551,30 @@ fn pick_rand<'a>(rng: Option<&mut Rng>, candidates: &'a [&'a str]) -> &'a str {
     }
 }
 
+/// Pick randomly across multiple candidate slices without allocating.
+#[inline]
+fn pick_rand_multi<'a>(rng: Option<&mut Rng>, groups: &[&'a [&'a str]]) -> &'a str {
+    let total: usize = groups.iter().map(|g| g.len()).sum();
+    if total == 0 {
+        return "";
+    }
+
+    let mut idx = match rng {
+        Some(r) => r.usize(..total),
+        None => fastrand::usize(..total),
+    };
+
+    for g in groups {
+        if idx < g.len() {
+            return g[idx];
+        }
+        idx -= g.len();
+    }
+
+    // unreachable if `total` computed correctly
+    ""
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -564,7 +619,7 @@ mod tests {
         assert!(
             Rc::ptr_eq(
                 agent3_rc,
-                &ua_instance
+                ua_instance
                     .list_map
                     .iter()
                     .find_map(|(rc, _)| if **rc == "Agent3" { Some(rc) } else { None })
@@ -633,5 +688,10 @@ mod tests {
             Some(Browser::Ie),
             None,
         );
+
+        // FormFactor-only
+        let _ = spoof_by(None, Some(FormFactor::Desktop), None, None);
+        let _ = spoof_by(None, Some(FormFactor::Mobile), None, None);
+        let _ = spoof_by(None, Some(FormFactor::Tablet), None, None);
     }
 }