// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

//! A helper module providing json patching functions.

use serde_json::Value;

/// Recursively merges two JSON objects, `a` and `b`, into a single object.
///
/// If a key exists in both objects, the value from `b` will override the value from `a` (also if
/// value in `b` is `null`).
/// If a key exists only in `b` and not in `a`, it will be added to `a`.
/// No keys will be removed from `a`.
///
/// # Arguments
///
/// * `a` - A mutable reference to the target JSON object to merge into.
/// * `b` - The JSON object to merge with `a`.
pub fn merge(a: &mut Value, b: Value) {
	match (a, b) {
		(Value::Object(a), Value::Object(b)) =>
			for (k, v) in b {
				merge(a.entry(k).or_insert(Value::Null), v);
			},
		(a, b) => *a = b,
	};
}

#[cfg(test)]
mod tests {
	use super::*;
	use serde_json::json;

	#[test]
	fn test1_simple_merge() {
		let mut j1 = json!({ "a":123 });
		merge(&mut j1, json!({ "b":256 }));
		assert_eq!(j1, json!({ "a":123, "b":256 }));
	}

	#[test]
	fn test2_patch_simple_merge_nested() {
		let mut j1 = json!({
			"a": {
				"name": "xxx",
				"value": 123
			},
			"b": { "c" : { "inner_name": "yyy" } }
		});

		let j2 = json!({
			"a": {
				"keys": ["a", "b", "c" ]
			}
		});

		merge(&mut j1, j2);
		assert_eq!(
			j1,
			json!({"a":{"keys":["a","b","c"],"name":"xxx","value":123}, "b": { "c" : { "inner_name": "yyy" } }})
		);
	}

	#[test]
	fn test3_patch_overrides_existing_keys() {
		let mut j1 = json!({
			"a": {
				"name": "xxx",
				"value": 123,
				"keys": ["d"]

			}
		});

		let j2 = json!({
			"a": {
				"keys": ["a", "b", "c" ]
			}
		});

		merge(&mut j1, j2);
		assert_eq!(j1, json!({"a":{"keys":["a","b","c"],"name":"xxx","value":123}}));
	}

	#[test]
	fn test4_patch_overrides_existing_keys() {
		let mut j1 = json!({
			"a": {
				"name": "xxx",
				"value": 123,
				"b" : {
					"inner_name": "yyy"
				}
			}
		});

		let j2 = json!({
			"a": {
				"name": "new_name",
				"b" : {
					"inner_name": "inner_new_name"
				}
			}
		});

		merge(&mut j1, j2);
		assert_eq!(
			j1,
			json!({ "a": {"name":"new_name", "value":123, "b" : { "inner_name": "inner_new_name" }} })
		);
	}

	#[test]
	fn test5_patch_overrides_existing_nested_keys() {
		let mut j1 = json!({
			"a": {
				"name": "xxx",
				"value": 123,
				"b": {
					"c": {
						"d": {
							"name": "yyy",
							"value": 256
						}
					}
				}
			},
		});

		let j2 = json!({
			"a": {
				"value": 456,
				"b": {
					"c": {
						"d": {
							"name": "new_name"
						}
					}
				}
			}
		});

		merge(&mut j1, j2);
		assert_eq!(
			j1,
			json!({ "a": {"name":"xxx", "value":456, "b": { "c": { "d": { "name": "new_name", "value": 256 }}}}})
		);
	}

	#[test]
	fn test6_patch_does_not_remove_keys_if_null() {
		let mut j1 = json!({
			"a": {
				"name": "xxx",
				"value": 123,
				"enum_variant_1": {
					"name": "yyy",
				}
			},
		});

		let j2 = json!({
			"a": {
				"value": 456,
				"enum_variant_1": null,
				"enum_variant_2": 32,
			}
		});

		merge(&mut j1, j2);
		assert_eq!(
			j1,
			json!({
				"a": {
					"name":"xxx",
					"value":456,
					"enum_variant_1": null,
					"enum_variant_2": 32
				}
			})
		);
	}
}
