Refactor: options module

1 files changed, 111 insertions, 0 deletions

diff --git a/src/options/get.rs b/src/options/get.rs
new file mode 100644
index 00000000..caaccd09
--- /dev/null
+++ b/src/options/get.rs
@@ -0,0 +1,111 @@
+use std::collections::HashMap;
+
+use crate::cli;
+use crate::features;
+use crate::git_config::{self, GitConfigGet};
+use crate::options::option_value::{OptionValue, ProvenancedOptionValue};
+use ProvenancedOptionValue::*;
+
+/// Look up a value of type `T` associated with `option name`. The search rules are:
+///
+/// 1. If there is a value associated with `option_name` in the main [delta] git config
+///    section, then stop searching and return that value.
+///
+/// 2. For each feature in the ordered list of enabled features:
+///
+///    2.1 Look-up the value, treating `feature` as a custom feature.
+///        I.e., if there is a value associated with `option_name` in a git config section
+///        named [delta "`feature`"] then stop searching and return that value.
+///
+///    2.2 Look-up the value, treating `feature` as a builtin feature.
+///        I.e., if there is a value (not a default value) associated with `option_name` in a
+///        builtin feature named `feature`, then stop searching and return that value.
+///        Otherwise, record the default value and continue searching.
+///
+/// 3. Return the last default value that was encountered.
+pub fn get_option_value<T>(
+    option_name: &str,
+    builtin_features: &HashMap<String, features::BuiltinFeature>,
+    opt: &cli::Opt,
+    git_config: &mut Option<git_config::GitConfig>,
+) -> Option<T>
+where
+    T: GitConfigGet,
+    T: GetOptionValue,
+    T: From<OptionValue>,
+    T: Into<OptionValue>,
+{
+    T::get_option_value(option_name, builtin_features, opt, git_config)
+}
+
+pub trait GetOptionValue {
+    fn get_option_value(
+        option_name: &str,
+        builtin_features: &HashMap<String, features::BuiltinFeature>,
+        opt: &cli::Opt,
+        git_config: &mut Option<git_config::GitConfig>,
+    ) -> Option<Self>
+    where
+        Self: Sized,
+        Self: GitConfigGet,
+        Self: From<OptionValue>,
+        Self: Into<OptionValue>,
+    {
+        if let Some(git_config) = git_config {
+            if let Some(value) = git_config.get::<Self>(&format!("delta.{}", option_name)) {
+                return Some(value);
+            }
+        }
+        for feature in opt.features.to_lowercase().split_whitespace().rev() {
+            match Self::get_provenanced_value_for_feature(
+                option_name,
+                &feature,
+                &builtin_features,
+                opt,
+                git_config,
+            ) {
+                Some(GitConfigValue(value)) | Some(DefaultValue(value)) => {
+                    return Some(value.into());
+                }
+                None => {}
+            }
+        }
+        None
+    }
+
+    /// Return the value, or default value, associated with `option_name` under feature name
+    /// `feature`. This may refer to a custom feature, or a builtin feature, or both. Only builtin
+    /// features have defaults. See `GetOptionValue::get_option_value`.
+    fn get_provenanced_value_for_feature(
+        option_name: &str,
+        feature: &str,
+        builtin_features: &HashMap<String, features::BuiltinFeature>,
+        opt: &cli::Opt,
+        git_config: &mut Option<git_config::GitConfig>,
+    ) -> Option<ProvenancedOptionValue>
+    where
+        Self: Sized,
+        Self: GitConfigGet,
+        Self: Into<OptionValue>,
+    {
+        if let Some(git_config) = git_config {
+            if let Some(value) =
+                git_config.get::<Self>(&format!("delta.{}.{}", feature, option_name))
+            {
+                return Some(GitConfigValue(value.into()));
+            }
+        }
+        if let Some(builtin_feature) = builtin_features.get(feature) {
+            if let Some(value_function) = builtin_feature.get(option_name) {
+                return Some(value_function(opt, &git_config));
+            }
+        }
+        return None;
+    }
+}
+
+impl GetOptionValue for Option<String> {}
+impl GetOptionValue for String {}
+impl GetOptionValue for bool {}
+impl GetOptionValue for f64 {}
+impl GetOptionValue for usize {}