From a95958de6b1897a5b9a39672f66f93283b207511 Mon Sep 17 00:00:00 2001
From: Aiden McClelland <me@drbonez.dev>
Date: Thu, 8 Sep 2022 15:39:13 -0600
Subject: [PATCH] wip

---
 patch-db/src/projector.rs | 119 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 patch-db/src/projector.rs

diff --git a/patch-db/src/projector.rs b/patch-db/src/projector.rs
new file mode 100644
index 0000000..93ad86f
--- /dev/null
+++ b/patch-db/src/projector.rs
@@ -0,0 +1,119 @@
+use std::collections::BTreeMap;
+
+use json_patch::Patch;
+use json_ptr::JsonPointer;
+use serde_json::Value;
+
+use crate::patch::diff;
+use crate::DiffPatch;
+
+fn project_patch_default<P: DataProjector + ?Sized>(
+    p: &mut P,
+    persistent: &Value,
+    volatile: &Value,
+    projection: &mut Value,
+    persistent_patch: &DiffPatch,
+    volatile_patch: &DiffPatch,
+) -> Patch {
+    let new_persistent = {
+        let mut d = persistent.clone();
+        json_patch::patch(&mut d, &*persistent_patch).unwrap();
+        d
+    };
+    let new_volatile = {
+        let mut d = volatile.clone();
+        json_patch::patch(&mut d, &*volatile_patch).unwrap();
+        d
+    };
+    let new = p.project(&new_persistent, &volatile);
+    let res = diff(projection, &new).0;
+    *projection = new;
+    res
+}
+
+pub trait DataProjector {
+    fn project(&mut self, data: &Value, volatile: &Value) -> Value;
+    /// Only implement to improve performance!
+    /// it MUST produce the same results as the default implementation.
+    /// You can test this using the `test_project_patch` function defined in this module
+    fn project_patch(
+        &mut self,
+        data: &Value,
+        volatile: &Value,
+        projection: &mut Value,
+        data_patch: &DiffPatch,
+        volatile_patch: &DiffPatch,
+    ) -> Patch {
+        project_patch_default(self, data, volatile, projection, patch)
+    }
+}
+
+pub fn test_project_patch<P: DataProjector>(
+    p: &mut P,
+    data: &Value,
+    volatile: &Value,
+    patch: &DiffPatch,
+) {
+    let projected = p.project(data, volatile);
+    let (default_projected, _default_patch) = {
+        let mut d = projected.clone();
+        let patch = project_patch_default(p, data, volatile, &mut d, patch);
+        (d, patch)
+    };
+    let (opt_projected, opt_patch) = {
+        let mut d = projected.clone();
+        let patch = p.project_patch(data, volatile, &mut d, patch);
+        (d, patch)
+    };
+    assert_eq!(default_projected, opt_projected);
+    let opt_projected_patched = {
+        let mut d = projected.clone();
+        json_patch::patch(&mut d, &opt_patch).unwrap();
+        d
+    };
+    assert_eq!(default_projected, opt_projected_patched);
+}
+
+pub struct NoProjection;
+impl DataProjector for NoProjection {
+    fn project(&mut self, data: &Value, volatile: &Value) -> Value {
+        let mut res = serde_json::Map::with_capacity(2);
+        res.insert("data".to_string(), data.clone());
+        res.insert("volatile".to_string(), volatile.clone());
+    }
+    fn project_patch(
+        &mut self,
+        _data: &Value,
+        _projection: &mut Value,
+        _patch: &DiffPatch,
+    ) -> Patch {
+        Patch(Vec::new())
+    }
+}
+
+pub enum SimpleReactive {
+    Object(BTreeMap<String, SimpleReactive>),
+    Expr {
+        relevant_fields: Box<dyn Fn(&JsonPointer) -> bool + Send + Sync + 'static>,
+        computation: Box<dyn Fn(&Value) -> Result<Value, SimpleReactive> + Send + Sync + 'static>,
+    },
+}
+impl DataProjector for SimpleReactive {
+    fn project(&mut self, data: &Value) -> Value {
+        match self {
+            SimpleReactive::Object(o) => {
+                let mut res = serde_json::Map::with_capacity(o.len());
+                for (idx, value) in o {
+                    res.insert(idx.clone(), value.project(data));
+                }
+                Value::Object(res)
+            }
+            SimpleReactive::Expr {
+                relevant_fields,
+                computation,
+            } => {
+                unimplemented!()
+            }
+        }
+    }
+}