Unify parsing and typesetting functions. 🗳

1 files changed, 179 insertions, 0 deletions

diff --git a/src/engine/loader.rs b/src/engine/loader.rs
new file mode 100644
index 00000000..bae5f51a
--- /dev/null
+++ b/src/engine/loader.rs
@@ -0,0 +1,179 @@
+//! Loading of fonts by queries.
+
+use std::fmt::{self, Debug, Formatter};
+use std::cell::{RefCell, Ref};
+use std::collections::HashMap;
+use crate::font::{Font, FontProvider, FontFamily, FontInfo};
+
+
+/// Serves matching fonts given a query.
+pub struct FontLoader<'p> {
+    /// The font providers.
+    providers: &'p [Box<dyn FontProvider + 'p>],
+    /// All available fonts indexed by provider.
+    provider_fonts: Vec<&'p [FontInfo]>,
+    /// The internal state.
+    state: RefCell<FontLoaderState<'p>>,
+}
+
+/// Internal state of the font loader (wrapped in a RefCell).
+struct FontLoaderState<'p> {
+    /// The loaded fonts along with their external indices.
+    fonts: Vec<(Option<usize>, Font)>,
+    /// Allows to retrieve cached results for queries.
+    query_cache: HashMap<FontQuery<'p>, usize>,
+    /// Allows to lookup fonts by their infos.
+    info_cache: HashMap<&'p FontInfo, usize>,
+    /// Indexed by outside and indices maps to internal indices.
+    inner_index: Vec<usize>,
+}
+
+impl<'p> FontLoader<'p> {
+    /// Create a new font loader.
+    pub fn new(providers: &'p [Box<dyn FontProvider + 'p>]) -> FontLoader {
+        let provider_fonts = providers.iter()
+            .map(|prov| prov.available()).collect();
+
+        FontLoader {
+            providers,
+            provider_fonts,
+            state: RefCell::new(FontLoaderState {
+                query_cache: HashMap::new(),
+                info_cache: HashMap::new(),
+                inner_index: vec![],
+                fonts: vec![],
+            }),
+        }
+    }
+
+    /// Return the best matching font and it's index (if there is any) given the query.
+    pub fn get(&self, query: FontQuery<'p>) -> Option<(usize, Ref<Font>)> {
+        // Check if we had the exact same query before.
+        let state = self.state.borrow();
+        if let Some(&index) = state.query_cache.get(&query) {
+            // That this is the query cache means it must has an index as we've served it before.
+            let extern_index = state.fonts[index].0.unwrap();
+            let font = Ref::map(state, |s| &s.fonts[index].1);
+
+            return Some((extern_index, font));
+        }
+        drop(state);
+
+        // Go over all font infos from all font providers that match the query.
+        for family in query.families {
+            for (provider, infos) in self.providers.iter().zip(&self.provider_fonts) {
+                for info in infos.iter() {
+                    // Check whether this info matches the query.
+                    if Self::matches(query, family, info) {
+                        let mut state = self.state.borrow_mut();
+
+                        // Check if we have already loaded this font before.
+                        // Otherwise we'll fetch the font from the provider.
+                        let index = if let Some(&index) = state.info_cache.get(info) {
+                            index
+                        } else if let Some(mut source) = provider.get(info) {
+                            // Read the font program into a vec.
+                            let mut program = Vec::new();
+                            source.read_to_end(&mut program).ok()?;
+
+                            // Create a font from it.
+                            let font = Font::new(program).ok()?;
+
+                            // Insert it into the storage.
+                            let index = state.fonts.len();
+                            state.info_cache.insert(info, index);
+                            state.fonts.push((None, font));
+
+                            index
+                        } else {
+                            continue;
+                        };
+
+                        // Check whether this font has the character we need.
+                        let has_char = state.fonts[index].1.mapping.contains_key(&query.character);
+                        if has_char {
+                            // We can take this font, so we store the query.
+                            state.query_cache.insert(query, index);
+
+                            // Now we have to find out the external index of it, or assign a new
+                            // one if it has not already one.
+                            let maybe_extern_index = state.fonts[index].0;
+                            let extern_index = maybe_extern_index.unwrap_or_else(|| {
+                                // We have to assign an external index before serving.
+                                let extern_index = state.inner_index.len();
+                                state.inner_index.push(index);
+                                state.fonts[index].0 =  Some(extern_index);
+                                extern_index
+                            });
+
+                            // Release the mutable borrow and borrow immutably.
+                            drop(state);
+                            let font = Ref::map(self.state.borrow(), |s| &s.fonts[index].1);
+
+                            // Finally we can return it.
+                            return Some((extern_index, font));
+                        }
+                    }
+                }
+            }
+        }
+
+        None
+    }
+
+    /// Return a loaded font at an index. Panics if the index is out of bounds.
+    pub fn get_with_index(&self, index: usize) -> Ref<Font> {
+        let state = self.state.borrow();
+        let internal = state.inner_index[index];
+        Ref::map(state, |s| &s.fonts[internal].1)
+    }
+
+    /// Return the list of fonts.
+    pub fn into_fonts(self) -> Vec<Font> {
+        // Sort the fonts by external key so that they are in the correct order.
+        let mut fonts = self.state.into_inner().fonts;
+        fonts.sort_by_key(|&(maybe_index, _)| match maybe_index {
+            Some(index) => index as isize,
+            None => -1,
+        });
+
+        // Remove the fonts that are not used from the outside
+        fonts.into_iter().filter_map(|(maybe_index, font)| {
+            maybe_index.map(|_| font)
+        }).collect()
+    }
+
+    /// Check whether the query and the current family match the info.
+    fn matches(query: FontQuery, family: &FontFamily, info: &FontInfo) -> bool {
+        info.families.contains(family)
+          && info.italic == query.italic && info.bold == query.bold
+    }
+}
+
+impl Debug for FontLoader<'_> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        let state = self.state.borrow();
+        f.debug_struct("FontLoader")
+            .field("providers", &self.providers.len())
+            .field("provider_fonts", &self.provider_fonts)
+            .field("fonts", &state.fonts)
+            .field("query_cache", &state.query_cache)
+            .field("info_cache", &state.info_cache)
+            .field("inner_index", &state.inner_index)
+            .finish()
+    }
+}
+
+/// A query for a font with specific properties.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+pub struct FontQuery<'p> {
+    /// A fallback list of font families to accept. The first family in this list, that also
+    /// satisfies the other conditions, shall be returned.
+    pub families: &'p [FontFamily],
+    /// Whether the font shall be in italics.
+    pub italic: bool,
+    /// Whether the font shall be in boldface.
+    pub bold: bool,
+    /// Which character we need.
+    pub character: char,
+}