Add file() item op and help docs

mps-interpreter/src/interpretor.rs

@@ -171,6 +171,7 @@ pub(crate) fn standard_vocab(vocabulary: &mut MpsLanguageDictionary) {
                 .add(crate::lang::vocabulary::item_ops::ConstantItemOpFactory)
                 .add(crate::lang::vocabulary::item_ops::VariableAssignItemOpFactory)
                 .add(crate::lang::vocabulary::item_ops::FieldAssignItemOpFactory)
+                .add(crate::lang::vocabulary::item_ops::FileItemOpFactory)
                 .add(crate::lang::vocabulary::item_ops::VariableDeclareItemOpFactory)
                 .add(crate::lang::vocabulary::item_ops::InterpolateStringItemOpFactory)
                 .add(crate::lang::vocabulary::item_ops::BranchItemOpFactory)

mps-interpreter/src/lang/function.rs

@@ -66,7 +66,7 @@ impl<Op: MpsOp + 'static, F: MpsFunctionFactory<Op> + 'static> BoxedMpsOpFactory
             tokens,
         )?;
         assert_token_raw(MpsToken::OpenBracket, tokens)?;
-        let end_tokens = tokens.split_off(tokens.len()-1);
+        let end_tokens = tokens.split_off(tokens.len() - 1);
         let func = self.op_factory.build_function_params(name, tokens, dict)?;
         tokens.extend(end_tokens);
         assert_token_raw(MpsToken::CloseBracket, tokens)?;

mps-interpreter/src/lang/vocabulary/item_ops/file.rs

@@ -0,0 +1,66 @@
+use core::ops::Deref;
+use std::collections::VecDeque;
+use std::fmt::{Debug, Display, Error, Formatter};
+
+use crate::lang::utility::{assert_name, assert_token_raw, check_name};
+use crate::lang::{MpsItemBlockFactory, MpsItemOp, MpsItemOpFactory};
+use crate::lang::{MpsLanguageDictionary, MpsTypePrimitive};
+use crate::lang::{RuntimeMsg, SyntaxError};
+use crate::processing::general::MpsType;
+use crate::tokens::MpsToken;
+use crate::MpsContext;
+
+#[derive(Debug)]
+pub struct FileItemOp {
+    inner: Box<dyn MpsItemOp>,
+}
+
+impl Deref for FileItemOp {
+    type Target = dyn MpsItemOp;
+    fn deref(&self) -> &Self::Target {
+        self
+    }
+}
+
+impl Display for FileItemOp {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
+        write!(f, "file({})", self.inner)
+    }
+}
+
+impl MpsItemOp for FileItemOp {
+    fn execute(&self, context: &mut MpsContext) -> Result<MpsType, RuntimeMsg> {
+        let inner_return = self.inner.execute(context)?;
+        if let MpsType::Primitive(MpsTypePrimitive::String(path)) = inner_return {
+            Ok(MpsType::Item(context.filesystem.single(&path, None)?))
+        } else {
+            Err(RuntimeMsg(format!(
+                "Cannot use {} as filepath (should be String)",
+                inner_return
+            )))
+        }
+    }
+}
+
+pub struct FileItemOpFactory;
+
+impl MpsItemOpFactory<FileItemOp> for FileItemOpFactory {
+    fn is_item_op(&self, tokens: &VecDeque<MpsToken>) -> bool {
+        !tokens.is_empty() && check_name("file", &tokens[0])
+    }
+
+    fn build_item_op(
+        &self,
+        tokens: &mut VecDeque<MpsToken>,
+        factory: &MpsItemBlockFactory,
+        dict: &MpsLanguageDictionary,
+    ) -> Result<FileItemOp, SyntaxError> {
+        assert_name("file", tokens)?;
+        assert_token_raw(MpsToken::OpenBracket, tokens)?;
+        let end_tokens = tokens.split_off(tokens.len() - 1);
+        let inner_op = factory.try_build_item_statement(tokens, dict)?;
+        tokens.extend(end_tokens);
+        assert_token_raw(MpsToken::CloseBracket, tokens)?;
+        Ok(FileItemOp { inner: inner_op })
+    }
+}

mps-interpreter/src/lang/vocabulary/item_ops/mod.rs

@@ -6,6 +6,7 @@ mod constant;
 mod constructor;
 mod empty;
 mod field_assign;
+mod file;
 mod iter_op;
 mod logical_and;
 mod logical_or;
@@ -26,6 +27,7 @@ pub use constant::{ConstantItemOp, ConstantItemOpFactory};
 pub use constructor::{ConstructorItemOp, ConstructorItemOpFactory};
 pub use empty::{EmptyItemOp, EmptyItemOpFactory};
 pub use field_assign::{FieldAssignItemOp, FieldAssignItemOpFactory};
+pub use file::{FileItemOp, FileItemOpFactory};
 pub use iter_op::{IterItemOp, IterItemOpFactory};
 pub use logical_and::{AndItemOp, AndItemOpFactory};
 pub use logical_or::{OrItemOp, OrItemOpFactory};

mps-interpreter/src/lang/vocabulary/item_ops/retrieve_variable.rs

@@ -38,10 +38,13 @@ impl MpsItemOp for VariableRetrieveItemOp {
         let var = context.variables.get(&self.variable_name)?;
         if let Some(field_name) = &self.field_name {
             if let MpsType::Item(item) = var {
-                Ok(match item.field(field_name) {
-                    Some(val) => MpsType::Primitive(val.clone()),
-                    None => MpsType::empty(),
-                })
+                match item.field(field_name) {
+                    Some(val) => Ok(MpsType::Primitive(val.clone())),
+                    None => Err(RuntimeMsg(format!(
+                        "Cannot access field `{}` on variable `{}` (field does not exist)",
+                        field_name, self.variable_name
+                    ))),
+                }
             } else {
                 Err(RuntimeMsg(format!(
                     "Cannot access field `{}` on variable `{}` ({} is not Item)",

mps-interpreter/src/lib.rs

@@ -230,6 +230,10 @@
 //!
 //!    Format a value into a string. This behaves differently depending on the value's type: When the value is an Item, the item's corresponding field will replace all `{field}` instances in the format string. When the value is a primitive type (String, Int, Bool, etc.), the value's text equivalent will replace all `{}` instances in the format string. When the value is an iterable operation (Op), the operation's script equivalent will replace all `{}` instances in the format string.
 //!
+//! ### file(filepath) -- e.g. `file("~/Music/Romantic Traffic.flac"),`
+//!
+//! Load a item from file, populating the item with the song's tags.
+//!
 
 mod context;
 mod interpretor;

mps-interpreter/src/processing/filesystem.rs

@@ -81,7 +81,7 @@ impl FileIter {
         root: Option<P>,
         pattern: Option<&str>,
         recurse: bool,
-    ) -> Result<Self, RuntimeMsg> {
+    ) -> Result<Self, String> {
         let root_path = match root {
             None => crate::lang::utility::music_folder(),
             Some(p) => p.as_ref().to_path_buf(),
@@ -91,7 +91,7 @@ impl FileIter {
             vec.push(
                 root_path
                     .read_dir()
-                    .map_err(|e| RuntimeMsg(format!("Directory read error: {}", e)))?
+                    .map_err(|e| format!("Directory read error: {}", e))?
                     .into(),
             );
             vec
@@ -99,15 +99,12 @@ impl FileIter {
             Vec::with_capacity(DEFAULT_VEC_CACHE_SIZE)
         };
         let pattern_re = if let Some(pattern) = pattern {
-            Some(
-                Regex::new(pattern)
-                    .map_err(|e| RuntimeMsg(format!("Regex compile error: {}", e)))?,
-            )
+            Some(Regex::new(pattern).map_err(|e| format!("Regex compile error: {}", e))?)
         } else {
             None
         };
-        let tags_re = Regex::new(DEFAULT_REGEX)
-            .map_err(|e| RuntimeMsg(format!("Regex compile error: {}", e)))?;
+        let tags_re =
+            Regex::new(DEFAULT_REGEX).map_err(|e| format!("Regex compile error: {}", e))?;
         Ok(Self {
             root: root_path,
             pattern: pattern_re,
@@ -235,6 +232,24 @@ impl FileIter {
         item.set_field("filename", path_str.to_string().into());
     }
 
+    fn only_once(&mut self) -> Result<MpsItem, String> {
+        if self.root.is_file() {
+            self.is_complete = true;
+            match self.build_item(&self.root) {
+                Some(item) => Ok(item),
+                None => Err(format!(
+                    "Failed to populate item from file `{}`",
+                    self.root.display()
+                )),
+            }
+        } else {
+            Err(format!(
+                "Cannot populate item from non-file `{}`",
+                self.root.display()
+            ))
+        }
+    }
+
     /*fn default_title(path: &Path) -> String {
         let extension = path.extension().and_then(|ext| ext.to_str()).unwrap_or("");
         path.file_name()
@@ -312,6 +327,8 @@ pub trait MpsFilesystemQuerier: Debug {
         recursive: bool,
     ) -> Result<FileIter, RuntimeMsg>;
 
+    fn single(&mut self, path: &str, pattern: Option<&str>) -> Result<MpsItem, RuntimeMsg>;
+
     fn expand(&self, folder: Option<&str>) -> Result<Option<String>, RuntimeMsg> {
         #[cfg(feature = "shellexpand")]
         match folder {
@@ -338,6 +355,12 @@ impl MpsFilesystemQuerier for MpsFilesystemExecutor {
         recursive: bool,
     ) -> Result<FileIter, RuntimeMsg> {
         let folder = self.expand(folder)?;
-        FileIter::new(folder, pattern, recursive)
+        FileIter::new(folder, pattern, recursive).map_err(RuntimeMsg)
+    }
+
+    fn single(&mut self, path: &str, pattern: Option<&str>) -> Result<MpsItem, RuntimeMsg> {
+        let path = self.expand(Some(path))?;
+        let mut file_iter = FileIter::new(path, pattern, false).map_err(RuntimeMsg)?;
+        file_iter.only_once().map_err(RuntimeMsg)
     }
 }

mps-interpreter/tests/single_line.rs

@@ -534,7 +534,6 @@ fn execute_retrieveitemop_line() -> Result<(), Box<dyn MpsLanguageError>> {
     execute_single_line(
         "files(`~/Music/MusicFlac/Bruno Mars/24K Magic/`).{
     item.path = item.filename,
-    item.not_a_field,
     item.new_field = 42,
     item.title = item.path,
 }",
@@ -750,3 +749,14 @@ fn execute_uniquefilter_line() -> Result<(), Box<dyn MpsLanguageError>> {
         true,
     )
 }
+
+#[test]
+fn execute_fileitemop_line() -> Result<(), Box<dyn MpsLanguageError>> {
+    execute_single_line(
+        "files(`~/Music/MusicFlac/Bruno Mars/24K Magic/`).{
+    item = file(item.filename),
+}",
+        false,
+        true,
+    )
+}

src/help.rs

@@ -146,4 +146,7 @@ Comma-separated procedure steps will be executed sequentially (like a for loop i
     Constructor for a new item. Each function parameter defines a new field and it's value.
 
  ~`string_format` something -- e.g. ~`{filename}` item
-    Format a value into a string. This behaves differently depending on the value's type: When the value is an Item, the item's corresponding field will replace all `{field}` instances in the format string. When the value is a primitive type (String, Int, Bool, etc.), the value's text equivalent will replace all `{}` instances in the format string. When the value is an iterable operation (Op), the operation's script equivalent will replace all `{}` instances in the format string.";
+    Format a value into a string. This behaves differently depending on the value's type: When the value is an Item, the item's corresponding field will replace all `{field}` instances in the format string. When the value is a primitive type (String, Int, Bool, etc.), the value's text equivalent will replace all `{}` instances in the format string. When the value is an iterable operation (Op), the operation's script equivalent will replace all `{}` instances in the format string.
+
+ file(filepath) -- e.g. file(`~/Music/Romantic Traffic.flac`)
+    Load a item from file, populating the item with the song's tags.";