Add diffing & apply

backend/sync_lib/src/operations/operation.rs

@@ -0,0 +1,143 @@
+use std::cmp::Ordering;
+
+use ropey::Rope;
+use serde::{Deserialize, Serialize};
+use similar::{Change, ChangeTag};
+
+use crate::errors::SyncLibError;
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum Operation {
+    Insert {
+        index: u64,
+        text: String,
+    },
+    Delete {
+        index: u64,
+        deleted_character_count: u64,
+    },
+}
+
+impl Operation {
+    pub fn new(tag: ChangeTag, index: u64, text: &str) -> Self {
+        match tag {
+            ChangeTag::Insert => Operation::Insert {
+                index,
+                text: text.to_string(),
+            },
+            ChangeTag::Delete => Operation::Delete {
+                index,
+                deleted_character_count: text.chars().count() as u64,
+            },
+            _ => panic!("Only insertion and deletions are supported"),
+        }
+    }
+    pub fn apply<'a>(&self, rope_text: &'a mut Rope) -> Result<&'a mut Rope, SyncLibError> {
+        let index: usize = self.index() as usize;
+        match self {
+            Operation::Insert { text, .. } => rope_text.try_insert(index, &text).map_err(|err| {
+                SyncLibError::OperationApplicationError(format!("Failed to insert text: {}", err))
+            }),
+            Operation::Delete {
+                deleted_character_count,
+                ..
+            } => rope_text
+                .try_remove(index..index + *deleted_character_count as usize)
+                .map_err(|err| {
+                    SyncLibError::OperationApplicationError(format!(
+                        "Failed to remove text: {}",
+                        err
+                    ))
+                }),
+        }?;
+
+        Ok(rope_text)
+    }
+
+    pub fn index(&self) -> u64 {
+        match self {
+            Operation::Insert { index, .. } => *index,
+            Operation::Delete { index, .. } => *index,
+        }
+    }
+
+    pub fn with_index(&self, index: u64) -> Self {
+        match self {
+            Operation::Insert { text, .. } => Operation::Insert {
+                index,
+                text: text.clone(),
+            },
+            Operation::Delete {
+                deleted_character_count,
+                ..
+            } => Operation::Delete {
+                index,
+                deleted_character_count: *deleted_character_count,
+            },
+        }
+    }
+
+    pub fn with_shifted_index(&self, offset: i64) -> Result<Self, SyncLibError> {
+        let new_index: i64 = self.index() as i64 + offset;
+        let new_index: u64 = new_index
+            .try_into()
+            .map_err(|err| SyncLibError::OperationShiftingError(format!("{}", err)))?;
+        Ok(self.with_index(new_index))
+    }
+}
+
+impl Ord for Operation {
+    fn cmp(&self, other: &Self) -> Ordering {
+        let result = self.index().cmp(&other.index());
+        if result == Ordering::Equal {
+            match (self, other) {
+                (Operation::Insert { .. }, Operation::Delete { .. }) => Ordering::Greater,
+                (Operation::Delete { .. }, Operation::Insert { .. }) => Ordering::Less,
+                _ => Ordering::Equal,
+            }
+        } else {
+            result
+        }
+    }
+}
+
+impl PartialOrd for Operation {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(&other))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_apply_delete() -> Result<(), SyncLibError> {
+        let mut rope = Rope::from_str("hello world");
+        let operation = Operation::Delete {
+            index: 5,
+            deleted_character_count: 6,
+        };
+
+        operation.apply(&mut rope)?;
+
+        assert_eq!(rope.to_string(), "hello");
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_apply_insert() -> Result<(), SyncLibError> {
+        let mut rope = Rope::from_str("hello");
+        let operation = Operation::Insert {
+            index: 5,
+            text: " my friend".to_string(),
+        };
+
+        operation.apply(&mut rope)?;
+
+        assert_eq!(rope.to_string(), "hello my friend");
+
+        Ok(())
+    }
+}