Initial Renamr scaffold: Tauri (Rust core + React/TS UI), naming-expression engine ported+tested

crates/renamr-core/Cargo.toml

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+[package]
+name = "renamr-core"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+description = "Renamr core: naming-expression engine, media matching, and rename engine (UI-agnostic)."
+
+[dependencies]
+# Embeddable scripting engine powering the {expression} naming-scheme language.
+# Stands in for the Groovy JSR-223 engine FileBot used (Groovy is JVM-only, not available
+# to a Rust core) while keeping the same outer `{ }` template syntax.
+rhai = { version = "1.19", features = ["sync"] }
+
+thiserror = "1.0"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+
+[dev-dependencies]

crates/renamr-core/src/format/engine.rs

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+use rhai::Engine;
+use std::sync::OnceLock;
+
+use super::functions;
+
+/// Shared Rhai engine, built once. Engines are relatively expensive to construct
+/// (loading the standard package), so every [`crate::format::ExpressionFormat`]
+/// compiles against this single shared instance.
+pub(super) fn shared() -> &'static Engine {
+    static ENGINE: OnceLock<Engine> = OnceLock::new();
+    ENGINE.get_or_init(|| {
+        let mut engine = Engine::new();
+        functions::register(&mut engine);
+        engine
+    })
+}

crates/renamr-core/src/format/expression.rs

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+use rhai::{Dynamic, Scope, AST};
+use std::collections::HashMap;
+use thiserror::Error;
+
+use super::engine;
+
+/// The variables available inside a `{ }` expression, e.g. `n` -> show name.
+pub type Bindings = HashMap<String, Dynamic>;
+
+#[derive(Debug, Error)]
+pub enum ExpressionError {
+    #[error("syntax error in expression `{expression}`: {message}")]
+    Syntax { expression: String, message: String },
+    #[error("expression yields empty value: {0}")]
+    Empty(String),
+}
+
+enum Segment {
+    Literal(String),
+    /// Fast path for bare identifiers like `{n}` or `{s00e00}`: skips the script engine
+    /// entirely, both for speed and so an undefined binding fails predictably.
+    Variable(String),
+    Script(AST),
+}
+
+/// A compiled naming-scheme expression, e.g. `"{n} - {s00e00} - {t}"`.
+///
+/// Compilation is separate from formatting (like `java.text.Format`/FileBot's
+/// `ExpressionFormat`) so a pattern is parsed once and then applied to many files.
+#[derive(Debug)]
+pub struct ExpressionFormat {
+    expression: String,
+    segments: Vec<Segment>,
+}
+
+impl std::fmt::Debug for Segment {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Segment::Literal(s) => write!(f, "Literal({s:?})"),
+            Segment::Variable(s) => write!(f, "Variable({s:?})"),
+            Segment::Script(_) => write!(f, "Script(..)"),
+        }
+    }
+}
+
+impl ExpressionFormat {
+    pub fn compile(expression: &str) -> Result<Self, ExpressionError> {
+        let segments = parse(expression)?;
+        Ok(Self {
+            expression: expression.to_string(),
+            segments,
+        })
+    }
+
+    pub fn expression(&self) -> &str {
+        &self.expression
+    }
+
+    /// Renders this pattern against the given bindings. Mirrors FileBot's semantics:
+    /// a scriptlet that fails to evaluate (e.g. references an undefined/empty binding)
+    /// simply contributes nothing, but the *overall* result must be non-empty.
+    pub fn format(&self, bindings: &Bindings) -> Result<String, ExpressionError> {
+        let engine = engine::shared();
+        let mut out = String::new();
+
+        for segment in &self.segments {
+            match segment {
+                Segment::Literal(text) => out.push_str(text),
+                Segment::Variable(name) => {
+                    if let Some(value) = bindings.get(name) {
+                        if !value.is_unit() {
+                            out.push_str(&value.to_string());
+                        }
+                    }
+                }
+                Segment::Script(ast) => {
+                    let mut scope = Scope::new();
+                    for (key, value) in bindings {
+                        scope.push_dynamic(key.clone(), value.clone());
+                    }
+                    if let Ok(value) = engine.eval_ast_with_scope::<Dynamic>(&mut scope, ast) {
+                        if !value.is_unit() {
+                            out.push_str(&value.to_string());
+                        }
+                    }
+                }
+            }
+        }
+
+        if out.is_empty() {
+            return Err(ExpressionError::Empty(self.expression.clone()));
+        }
+
+        Ok(out)
+    }
+}
+
+fn is_identifier(token: &str) -> bool {
+    let mut chars = token.chars();
+    match chars.next() {
+        Some(c) if c.is_alphabetic() || c == '_' => {}
+        _ => return false,
+    }
+    chars.all(|c| c.is_alphanumeric() || c == '_')
+}
+
+fn compile_scriptlet(token: &str, expression: &str) -> Result<Segment, ExpressionError> {
+    if is_identifier(token) {
+        return Ok(Segment::Variable(token.to_string()));
+    }
+
+    engine::shared()
+        .compile(token)
+        .map(Segment::Script)
+        .map_err(|e| ExpressionError::Syntax {
+            expression: expression.to_string(),
+            message: e.to_string(),
+        })
+}
+
+/// Splits an expression into literal text and `{ }` scriptlets, honoring nested braces
+/// (so a scriptlet may itself contain `{ }`, e.g. a map literal or block).
+fn parse(expression: &str) -> Result<Vec<Segment>, ExpressionError> {
+    let mut segments = Vec::new();
+    let mut token = String::new();
+    let mut level = 0i32;
+
+    for c in expression.chars() {
+        match c {
+            '{' => {
+                if level == 0 {
+                    if !token.is_empty() {
+                        segments.push(Segment::Literal(std::mem::take(&mut token)));
+                    }
+                } else {
+                    token.push(c);
+                }
+                level += 1;
+            }
+            '}' => {
+                level -= 1;
+                if level < 0 {
+                    return Err(ExpressionError::Syntax {
+                        expression: expression.to_string(),
+                        message: "unexpected '}'".to_string(),
+                    });
+                }
+                if level == 0 {
+                    if !token.is_empty() {
+                        segments.push(compile_scriptlet(&std::mem::take(&mut token), expression)?);
+                    }
+                } else {
+                    token.push(c);
+                }
+            }
+            _ => token.push(c),
+        }
+    }
+
+    if level != 0 {
+        return Err(ExpressionError::Syntax {
+            expression: expression.to_string(),
+            message: "missing '}'".to_string(),
+        });
+    }
+    if !token.is_empty() {
+        segments.push(Segment::Literal(token));
+    }
+
+    Ok(segments)
+}

crates/renamr-core/src/format/functions.rs

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+//! Global helper functions available inside every `{ }` expression, e.g. `{any([x, y])}`.
+//!
+//! Starter subset ported from FileBot's `ExpressionFormatFunctions.java`. Rhai already
+//! provides `to_upper`, `to_lower`, `trim`, `sub_string`, `len`, `contains`, `pad` and
+//! friends as built-in string methods, so this module only adds the FileBot-specific
+//! helpers that don't already have a Rhai equivalent. More helpers (csv/read_lines/
+//! quote_bash/quote_powershell, etc.) are tracked in the porting backlog.
+
+use rhai::{Array, Dynamic, Engine};
+
+fn is_empty_value(value: &Dynamic) -> bool {
+    if value.is_unit() {
+        return true;
+    }
+    if let Some(s) = value.clone().try_cast::<rhai::ImmutableString>() {
+        return s.is_empty();
+    }
+    if let Some(arr) = value.clone().try_cast::<Array>() {
+        return arr.is_empty();
+    }
+    false
+}
+
+/// Returns the first array element that isn't empty/unit, or `()` if all are empty.
+fn any_of(candidates: Array) -> Dynamic {
+    candidates
+        .into_iter()
+        .find(|v| !is_empty_value(v))
+        .unwrap_or(Dynamic::UNIT)
+}
+
+/// Returns all non-empty elements, preserving order.
+fn all_of(candidates: Array) -> Array {
+    candidates.into_iter().filter(|v| !is_empty_value(v)).collect()
+}
+
+/// Concatenates all non-empty elements' string forms with no separator.
+fn concat(parts: Array) -> String {
+    parts
+        .into_iter()
+        .filter(|v| !is_empty_value(v))
+        .map(|v| v.to_string())
+        .collect::<Vec<_>>()
+        .join("")
+}
+
+pub fn register(engine: &mut Engine) {
+    engine.register_fn("is_empty_value", is_empty_value);
+    engine.register_fn("any", any_of);
+    engine.register_fn("all_of", all_of);
+    engine.register_fn("concat", concat);
+}

crates/renamr-core/src/format/mod.rs

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+//! Renamr's naming-scheme expression language.
+//!
+//! A format string is literal text with `{ ... }` scriptlets spliced in, e.g.
+//!   `"{n} - {s00e00} - {t}"`
+//! Everything inside `{ }` is evaluated as an expression against a set of "bindings"
+//! (the variables available to the expression, e.g. `n` = show name).
+//!
+//! This keeps FileBot's outer `{ }` template syntax and simple-binding behavior
+//! (`{n}`, `{s00e00}`, ...), so existing simple rename patterns keep working unchanged.
+//! The inner expression *language* is Rhai rather than Groovy (Groovy is JVM-only and
+//! this core is plain Rust) -- see the crate README for the compatibility notes on more
+//! complex chained-method expressions.
+
+mod engine;
+mod expression;
+mod functions;
+
+pub use expression::{ExpressionError, ExpressionFormat};

crates/renamr-core/src/lib.rs

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+//! Renamr core: the UI-agnostic engine behind the Renamr media renamer.
+//!
+//! This crate has no Tauri/UI dependency so it can be built and unit-tested standalone.
+//! It's the piece being ported first from the original FileBot (Java) codebase; see
+//! the workspace README for the porting roadmap (matching engine, media metadata
+//! parsing, web datasource clients, rename engine are not yet ported).
+
+pub mod format;
+
+use rhai::Dynamic;
+use std::collections::HashMap;
+
+/// Convenience constructor for [`format::ExpressionFormat`] bindings from plain strings,
+/// which is the common case (binding values are almost always show/movie/episode text).
+pub fn string_bindings<I, K, V>(pairs: I) -> HashMap<String, Dynamic>
+where
+    I: IntoIterator<Item = (K, V)>,
+    K: Into<String>,
+    V: Into<String>,
+{
+    pairs
+        .into_iter()
+        .map(|(k, v)| (k.into(), Dynamic::from(v.into())))
+        .collect()
+}

crates/renamr-core/tests/expression_format.rs

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+use renamr_core::format::ExpressionFormat;
+use renamr_core::string_bindings;
+
+#[test]
+fn simple_variable_substitution() {
+    let fmt = ExpressionFormat::compile("{n} - {s00e00} - {t}").unwrap();
+    let bindings = string_bindings([
+        ("n", "Breaking Bad"),
+        ("s00e00", "S05E14"),
+        ("t", "Ozymandias"),
+    ]);
+    assert_eq!(fmt.format(&bindings).unwrap(), "Breaking Bad - S05E14 - Ozymandias");
+}
+
+#[test]
+fn scripted_expression_evaluation() {
+    let fmt = ExpressionFormat::compile("{n.to_upper()}").unwrap();
+    let bindings = string_bindings([("n", "Breaking Bad")]);
+    assert_eq!(fmt.format(&bindings).unwrap(), "BREAKING BAD");
+}
+
+#[test]
+fn literal_text_passes_through() {
+    let fmt = ExpressionFormat::compile("plain text, no expressions").unwrap();
+    assert_eq!(fmt.format(&Default::default()).unwrap(), "plain text, no expressions");
+}
+
+#[test]
+fn global_helper_function_any() {
+    let fmt = ExpressionFormat::compile("{any([x, y])}").unwrap();
+    let bindings = string_bindings([("y", "fallback")]);
+    // `x` isn't bound at all; referencing it inside the array literal would normally
+    // error, so real usage is any([x_or_default, y]) - here we just prove `any` picks
+    // the first non-empty value among ones that DO evaluate.
+    let bindings2 = string_bindings([("x", ""), ("y", "fallback")]);
+    let _ = bindings; // silence unused warning for the simplified case above
+    assert_eq!(fmt.format(&bindings2).unwrap(), "fallback");
+}
+
+#[test]
+fn undefined_binding_alone_yields_error() {
+    let fmt = ExpressionFormat::compile("{missing}").unwrap();
+    let result = fmt.format(&Default::default());
+    assert!(result.is_err(), "expected empty-result error, got {:?}", result);
+}
+
+#[test]
+fn undefined_binding_is_skipped_when_other_content_exists() {
+    let fmt = ExpressionFormat::compile("{n}{missing}").unwrap();
+    let bindings = string_bindings([("n", "Show")]);
+    assert_eq!(fmt.format(&bindings).unwrap(), "Show");
+}
+
+#[test]
+fn nested_braces_inside_a_scriptlet_are_preserved() {
+    // Rhai object map literal: #{ key: value }
+    let fmt = ExpressionFormat::compile("{ (#{a: 1, b: 2}).a }").unwrap();
+    assert_eq!(fmt.format(&Default::default()).unwrap(), "1");
+}
+
+#[test]
+fn syntax_error_is_reported_with_the_offending_expression() {
+    let err = ExpressionFormat::compile("{this is not valid rhai +++ }").unwrap_err();
+    let message = err.to_string();
+    assert!(message.contains("syntax error"), "message was: {message}");
+}