From 846a73188af3349cf4c087978d4df91e5f2f208a Mon Sep 17 00:00:00 2001
From: Ihor Andrianov <andrianoia@gmail.com>
Date: Tue, 28 Jan 2025 20:00:15 +0200
Subject: [PATCH] add json_patch implementation

---
 core/json/json_operations.rs | 103 +++++++++++++++++++++++++++++++++++
 core/json/mod.rs             |   2 +
 2 files changed, 105 insertions(+)
 create mode 100644 core/json/json_operations.rs

diff --git a/core/json/json_operations.rs b/core/json/json_operations.rs
new file mode 100644
index 000000000..6a91e157a
--- /dev/null
+++ b/core/json/json_operations.rs
@@ -0,0 +1,103 @@
+use std::collections::VecDeque;
+
+use crate::types::OwnedValue;
+
+use super::{convert_json_to_db_type, get_json_value, Val};
+
+/// Represents a single patch operation in the merge queue.
+///
+/// Used internally by the `merge_patch` function to track the path and value
+/// for each pending merge operation.
+#[derive(Debug, Clone)]
+struct PatchOperation {
+    path: Vec<usize>,
+    patch: Val,
+}
+
+/// The function follows RFC 7386 JSON Merge Patch semantics:
+/// * If the patch is null, the target is replaced with null
+/// * If the patch contains a scalar value, the target is replaced with that value
+/// * If both target and patch are objects, the patch is recursively applied
+/// * null values in the patch result in property removal from the target
+pub fn json_patch(target: &OwnedValue, patch: &OwnedValue) -> crate::Result<OwnedValue> {
+    match (target, patch) {
+        (OwnedValue::Blob(_), _) | (_, OwnedValue::Blob(_)) => {
+            crate::bail_constraint_error!("blob is not supported!");
+        }
+        _ => (),
+    }
+
+    let mut parsed_target = get_json_value(target)?;
+    let parsed_patch = get_json_value(patch)?;
+
+    merge_patch(&mut parsed_target, parsed_patch);
+
+    convert_json_to_db_type(&parsed_target, false)
+}
+
+/// # Implementation Notes
+///
+/// * Processes patches in breadth-first order
+/// * Maintains path information for nested updates
+/// * Handles object merging with proper null value semantics
+/// * Preserves existing values not mentioned in the patch
+///
+/// Following RFC 7386 rules:
+/// * null values remove properties
+/// * Objects are merged recursively
+/// * Non-object values replace the target completely
+fn merge_patch(target: &mut Val, patch: Val) {
+    let mut queue = VecDeque::with_capacity(8);
+
+    queue.push_back(PatchOperation {
+        path: Vec::new(),
+        patch,
+    });
+    while let Some(PatchOperation { path, patch }) = queue.pop_front() {
+        let mut current: &mut Val = target;
+
+        for (depth, key) in path.iter().enumerate() {
+            if let Val::Object(ref mut obj) = current {
+                current = &mut obj
+                    .get_mut(*key)
+                    .unwrap_or_else(|| {
+                        panic!("Invalid path at depth {}: key '{}' not found", depth, key)
+                    })
+                    .1;
+            }
+        }
+
+        match (current, patch) {
+            (curr, Val::Null) => {
+                *curr = Val::Null;
+            }
+            (Val::Object(target_map), Val::Object(patch_map)) => {
+                for (key, patch_val) in patch_map {
+                    if let Some(pos) = target_map
+                        .iter()
+                        .position(|(target_key, _)| target_key == &key)
+                    {
+                        match patch_val {
+                            Val::Null => {
+                                target_map.remove(pos);
+                            }
+                            val => {
+                                let mut new_path = path.clone();
+                                new_path.push(pos);
+                                queue.push_back(PatchOperation {
+                                    path: new_path,
+                                    patch: val,
+                                });
+                            }
+                        };
+                    } else {
+                        target_map.push((key, patch_val));
+                    };
+                }
+            }
+            (curr, patch_val) => {
+                *curr = patch_val;
+            }
+        }
+    }
+}
diff --git a/core/json/mod.rs b/core/json/mod.rs
index 8b271c8e1..65e90697f 100644
--- a/core/json/mod.rs
+++ b/core/json/mod.rs
@@ -1,5 +1,6 @@
 mod de;
 mod error;
+mod json_operations;
 mod json_path;
 mod ser;
 
@@ -8,6 +9,7 @@ use std::rc::Rc;
 pub use crate::json::de::from_str;
 use crate::json::de::ordered_object;
 use crate::json::error::Error as JsonError;
+pub use crate::json::json_operations::json_patch;
 use crate::json::json_path::{json_path, JsonPath, PathElement};
 pub use crate::json::ser::to_string;
 use crate::types::{LimboText, OwnedValue, TextSubtype};