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///
/// Represents a difference between two trees
///
#[derive(Clone, PartialEq, Serialize)]
pub struct Diff<TNode: Clone> {
/// The address of this difference
///
/// This is the empty list to indicate the root node, otherwise it's a list
/// of node indices forming a path through the original tree.
address: Vec<u32>,
/// The new node that should replace the original node at this address
replacement: TNode
}
impl<TNode: Clone> Diff<TNode> {
///
/// Creates a new diff item
///
pub fn new(address: &Vec<u32>, replacement: &TNode) -> Diff<TNode> {
Diff { address: address.clone(), replacement: replacement.clone() }
}
pub fn address(&self) -> &Vec<u32> {
&self.address
}
pub fn replacement(&self) -> &TNode {
&self.replacement
}
}
///
/// Trait implemented by tree structures that can describe how they
/// differ from another structure.
///
pub trait DiffableTree where Self: Clone {
///
/// Retrieves the child nodes of this item
///
fn child_nodes<'a>(&'a self) -> Vec<&'a Self>;
///
/// Returns true if this node is different from the specified node
/// (excluding child nodes)
///
fn is_different(&self, compare_to: &Self) -> bool;
}
///
/// Computes the difference between two trees
///
pub fn diff_tree<TNode: DiffableTree>(source: &TNode, target: &TNode) -> Vec<Diff<TNode>> {
diff_tree_run(&vec![], source, target)
}
///
/// Computes the difference between two trees (where we know the address)
///
fn diff_tree_run<TNode: DiffableTree>(address: &Vec<u32>, source: &TNode, target: &TNode) -> Vec<Diff<TNode>> {
let is_different = source.is_different(target);
if is_different {
// Different nodes replace the source with the target
vec![Diff::new(address, target)]
} else {
// If the nodes are not different, then check the child nodes
let source_children = source.child_nodes();
let target_children = target.child_nodes();
if source_children.len() != target_children.len() {
// If the child node counts are different, the nodes are different
vec![Diff::new(address, target)]
} else if source_children.len() == 0 {
// No point generating all the iteration structures if there's nothing to iterate
vec![]
} else {
// Check for differences in the child nodes
let mut differences = vec![];
let mut node_address = address.clone();
for node_index in 0..source_children.len() {
// Generate the address for the next node
node_address.push(node_index as u32);
// Push any differences it might have
let child_differences = diff_tree_run(&node_address, source_children[node_index], target_children[node_index]);
differences.extend(child_differences);
// Reset the node address vector so we can re-use it in the next pass
node_address.pop();
}
differences
}
}
}
#[cfg(test)]
mod test {
use super::*;
#[derive(Clone, PartialEq, Serialize, Deserialize)]
struct TestTree {
id: u32,
child_nodes: Vec<TestTree>
}
impl DiffableTree for TestTree {
fn child_nodes<'a>(&'a self) -> Vec<&'a TestTree> {
self.child_nodes.iter().collect()
}
fn is_different(&self, compare_to: &Self) -> bool {
self.id != compare_to.id
}
}
fn simple_tree() -> TestTree {
TestTree {
id: 0,
child_nodes: vec![
TestTree {
id: 1,
child_nodes: vec![]
},
TestTree {
id: 2,
child_nodes: vec![
TestTree {
id: 3,
child_nodes: vec![]
},
TestTree {
id: 4,
child_nodes: vec![]
}
]
}
]
}
}
fn tree_with_single_id_diff() -> TestTree {
TestTree {
id: 0,
child_nodes: vec![
TestTree {
id: 1,
child_nodes: vec![]
},
TestTree {
id: 3,
child_nodes: vec![
TestTree {
id: 3,
child_nodes: vec![]
},
TestTree {
id: 4,
child_nodes: vec![]
}
]
}
]
}
}
fn tree_with_multiple_differences() -> TestTree {
TestTree {
id: 0,
child_nodes: vec![
TestTree {
id: 1,
child_nodes: vec![]
},
TestTree {
id: 2,
child_nodes: vec![
TestTree {
id: 4,
child_nodes: vec![]
},
TestTree {
id: 5,
child_nodes: vec![]
}
]
}
]
}
}
fn tree_with_extra_child_nodes() -> TestTree {
TestTree {
id: 0,
child_nodes: vec![
TestTree {
id: 1,
child_nodes: vec![]
},
TestTree {
id: 2,
child_nodes: vec![
TestTree {
id: 3,
child_nodes: vec![]
},
TestTree {
id: 4,
child_nodes: vec![]
},
TestTree {
id: 5,
child_nodes: vec![]
},
TestTree {
id: 6,
child_nodes: vec![]
}
]
}
]
}
}
fn tree_with_multiple_differences_in_sublevels() -> TestTree {
TestTree {
id: 0,
child_nodes: vec![
TestTree {
id: 1,
child_nodes: vec![]
},
TestTree {
id: 3,
child_nodes: vec![
TestTree {
id: 4,
child_nodes: vec![]
},
TestTree {
id: 5,
child_nodes: vec![]
}
]
}
]
}
}
#[test]
fn compare_tree_against_self_is_empty() {
let tree = simple_tree();
let differences = diff_tree(&tree, &tree);
assert!(differences.len() == 0);
}
#[test]
fn compare_tree_against_different_ids_has_single_difference() {
let tree_a = simple_tree();
let tree_b = tree_with_single_id_diff();
let differences = diff_tree(&tree_a, &tree_b);
assert!(differences.len() == 1);
assert!(differences[0].address() == &vec![1]);
}
#[test]
fn compare_tree_against_different_ids_has_multiple_difference() {
let tree_a = simple_tree();
let tree_b = tree_with_multiple_differences();
let differences = diff_tree(&tree_a, &tree_b);
assert!(differences.len() == 2);
assert!(differences[0].address() == &vec![1, 0]);
assert!(differences[1].address() == &vec![1, 1]);
}
#[test]
fn tree_with_extra_child_nodes_is_different() {
let tree_a = simple_tree();
let tree_b = tree_with_extra_child_nodes();
let differences = diff_tree(&tree_a, &tree_b);
assert!(differences.len() == 1);
assert!(differences[0].address() == &vec![1]);
}
#[test]
fn tree_with_fewer_child_nodes_is_different() {
let tree_a = tree_with_extra_child_nodes();
let tree_b = simple_tree();
let differences = diff_tree(&tree_a, &tree_b);
assert!(differences.len() == 1);
assert!(differences[0].address() == &vec![1]);
}
#[test]
fn tree_diffs_in_sublevels_not_reported() {
let tree_a = simple_tree();
let tree_b = tree_with_multiple_differences_in_sublevels();
let differences = diff_tree(&tree_a, &tree_b);
assert!(differences.len() == 1);
assert!(differences[0].address() == &vec![1]);
}
}