#8539 Config preferences backend restructure

1 files changed, 282 insertions, 0 deletions

diff --git a/components/config/pref_util.rs b/components/config/pref_util.rs
new file mode 100644
index 00000000000..3083e39b9f5
--- /dev/null
+++ b/components/config/pref_util.rs
@@ -0,0 +1,282 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use serde_json::Value;
+use std::collections::HashMap;
+use std::fmt;
+use std::str::FromStr;
+use std::sync::{Arc, RwLock};
+
+#[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
+pub enum PrefValue {
+    Float(f64),
+    Int(i64),
+    Str(String),
+    Bool(bool),
+    Missing,
+}
+
+impl PrefValue {
+    pub fn as_str(&self) -> Option<&str> {
+        if let PrefValue::Str(val) = self {
+            Some(val)
+        } else {
+            None
+        }
+    }
+
+    pub fn as_i64(&self) -> Option<i64> {
+        if let PrefValue::Int(val) = self {
+            Some(*val)
+        } else {
+            None
+        }
+    }
+
+    pub fn as_f64(&self) -> Option<f64> {
+        if let PrefValue::Float(val) = self {
+            Some(*val)
+        } else {
+            None
+        }
+    }
+
+    pub fn as_bool(&self) -> Option<bool> {
+        if let PrefValue::Bool(val) = self {
+            Some(*val)
+        } else {
+            None
+        }
+    }
+
+    pub fn is_missing(&self) -> bool {
+        match self {
+            PrefValue::Missing => true,
+            _ => false,
+        }
+    }
+
+    pub fn from_json_value(value: &Value) -> Option<Self> {
+        match value {
+            Value::Bool(b) => Some(PrefValue::Bool(*b)),
+            Value::Number(n) if n.is_i64() => Some(PrefValue::Int(n.as_i64().unwrap())),
+            Value::Number(n) if n.is_f64() => Some(PrefValue::Float(n.as_f64().unwrap())),
+            Value::String(s) => Some(PrefValue::Str(s.to_owned())),
+            _ => None,
+        }
+    }
+}
+
+impl FromStr for PrefValue {
+    type Err = PrefError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if s == "false" {
+            Ok(PrefValue::Bool(false))
+        } else if s == "true" {
+            Ok(PrefValue::Bool(true))
+        } else if let Ok(float) = s.parse::<f64>() {
+            Ok(PrefValue::Float(float))
+        } else if let Ok(integer) = s.parse::<i64>() {
+            Ok(PrefValue::Int(integer))
+        } else {
+            Ok(PrefValue::from(s))
+        }
+    }
+}
+
+macro_rules! impl_pref_from {
+    ($($t: ty => $variant: path,)*) => {
+        $(
+            impl From<$t> for PrefValue {
+                fn from(other: $t) -> Self {
+                    $variant(other.into())
+                }
+            }
+        )+
+        $(
+            impl From<Option<$t>> for PrefValue {
+                fn from(other: Option<$t>) -> Self {
+                    other.map(|val| $variant(val.into())).unwrap_or(PrefValue::Missing)
+                }
+            }
+        )+
+    }
+}
+
+macro_rules! impl_from_pref {
+    ($($variant: path => $t: ty,)*) => {
+        $(
+            impl From<PrefValue> for $t {
+                #[allow(unsafe_code)]
+                fn from(other: PrefValue) -> Self {
+                    if let $variant(value) = other {
+                        value.into()
+                    } else {
+                        panic!(
+                            format!("Cannot convert {:?} to {:?}",
+                                other,
+                                unsafe { std::intrinsics::type_name::<$t>() }
+                            )
+                        );
+                    }
+                }
+            }
+        )+
+        $(
+            impl From<PrefValue> for Option<$t> {
+                fn from(other: PrefValue) -> Self {
+                    if let PrefValue::Missing = other {
+                        None
+                    } else {
+                        Some(other.into())
+                    }
+                }
+            }
+        )+
+    }
+}
+
+impl_pref_from! {
+    f64 => PrefValue::Float,
+    i64 => PrefValue::Int,
+    String => PrefValue::Str,
+    &str => PrefValue::Str,
+    bool => PrefValue::Bool,
+}
+
+impl_from_pref! {
+    PrefValue::Float => f64,
+    PrefValue::Int => i64,
+    PrefValue::Str => String,
+    PrefValue::Bool => bool,
+}
+
+#[derive(Debug)]
+pub enum PrefError {
+    NoSuchPref(String),
+    InvalidValue(String),
+    JsonParseErr(serde_json::error::Error),
+}
+
+impl fmt::Display for PrefError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            PrefError::NoSuchPref(s) | PrefError::InvalidValue(s) => f.write_str(&s),
+            PrefError::JsonParseErr(e) => e.fmt(f),
+        }
+    }
+}
+
+impl std::error::Error for PrefError {}
+
+pub struct Accessor<P, V> {
+    pub getter: Box<Fn(&P) -> V + Sync>,
+    pub setter: Box<Fn(&mut P, V) + Sync>,
+}
+
+impl<P, V> Accessor<P, V> {
+    pub fn new<G, S>(getter: G, setter: S) -> Self
+    where
+        G: Fn(&P) -> V + Sync + 'static,
+        S: Fn(&mut P, V) + Sync + 'static,
+    {
+        Accessor {
+            getter: Box::new(getter),
+            setter: Box::new(setter),
+        }
+    }
+}
+
+pub struct Preferences<'m, P> {
+    user_prefs: Arc<RwLock<P>>,
+    default_prefs: P,
+    accessors: &'m HashMap<String, Accessor<P, PrefValue>>,
+}
+
+impl<'m, P: Clone> Preferences<'m, P> {
+    /// Create a new `Preferences` object. The values provided in `default_prefs` are immutable and
+    /// can always be restored using `reset` or `reset_all`.
+    pub fn new(default_prefs: P, accessors: &'m HashMap<String, Accessor<P, PrefValue>>) -> Self {
+        Self {
+            user_prefs: Arc::new(RwLock::new(default_prefs.clone())),
+            default_prefs,
+            accessors,
+        }
+    }
+
+    /// Access to the data structure holding the preference values.
+    pub fn values(&self) -> Arc<RwLock<P>> {
+        Arc::clone(&self.user_prefs)
+    }
+
+    /// Retrieve a preference using its key
+    pub fn get(&self, key: &str) -> PrefValue {
+        if let Some(accessor) = self.accessors.get(key) {
+            let prefs = self.user_prefs.read().unwrap();
+            (accessor.getter)(&prefs)
+        } else {
+            PrefValue::Missing
+        }
+    }
+
+    /// Creates an iterator over all keys and values
+    pub fn iter<'a>(&'a self) -> impl Iterator<Item = (String, PrefValue)> + 'a {
+        let prefs = self.user_prefs.read().unwrap();
+        self.accessors
+            .iter()
+            .map(move |(k, accessor)| (k.clone(), (accessor.getter)(&prefs)))
+    }
+
+    /// Creates an iterator over all keys
+    pub fn keys<'a>(&'a self) -> impl Iterator<Item = &'a str> + 'a {
+        self.accessors.keys().map(String::as_str)
+    }
+
+    fn set_inner<V>(&self, key: &str, mut prefs: &mut P, val: V) -> Result<(), PrefError>
+    where
+        V: Into<PrefValue>,
+    {
+        if let Some(accessor) = self.accessors.get(key) {
+            Ok((accessor.setter)(&mut prefs, val.into()))
+        } else {
+            Err(PrefError::NoSuchPref(String::from(key)))
+        }
+    }
+
+    /// Set a new value for a preference, using its key.
+    pub fn set<V>(&self, key: &str, val: V) -> Result<(), PrefError>
+    where
+        V: Into<PrefValue>,
+    {
+        let mut prefs = self.user_prefs.write().unwrap();
+        self.set_inner(key, &mut prefs, val)
+    }
+
+    pub fn set_all<M>(&self, values: M) -> Result<(), PrefError>
+    where
+        M: IntoIterator<Item = (String, PrefValue)>,
+    {
+        let mut prefs = self.user_prefs.write().unwrap();
+        for (k, v) in values.into_iter() {
+            self.set_inner(&k, &mut prefs, v)?;
+        }
+        Ok(())
+    }
+
+    pub fn reset(&self, key: &str) -> Result<PrefValue, PrefError> {
+        if let Some(accessor) = self.accessors.get(key) {
+            let mut prefs = self.user_prefs.write().unwrap();
+            let old_pref = (accessor.getter)(&prefs);
+            let default_pref = (accessor.getter)(&self.default_prefs);
+            (accessor.setter)(&mut prefs, default_pref);
+            Ok(old_pref)
+        } else {
+            Err(PrefError::NoSuchPref(String::from(key)))
+        }
+    }
+
+    pub fn reset_all(&self) {
+        *self.user_prefs.write().unwrap() = self.default_prefs.clone();
+    }
+}