//! # TextChange
//! this represent a range in the previous state of the string and a new content which should be
//! replaced to it, allowing to represent any combination of deletions, insertions or replacements
//!
//! bulk and widespread operations will result in a TextChange effectively sending the whole new
//! buffer, but small changes are efficient and easy to create or apply 
//!
//! ### examples
//! to insert 'a' after 4th character we should send a
//!     `TextChange { span: 4..4, content: "a".into() }`
//!
//! to delete a the fourth character we should send a
//!     `TextChange { span: 3..4, content: "".into() }`
//!

/// an editor-friendly representation of a text change in a buffer
///  span refers to previous text content
#[derive(Clone, Debug, Default)]
pub struct TextChange {
	/// range of text change, as char indexes in buffer previous state
	pub span: std::ops::Range<usize>,
	/// new content of text inside span
	pub content: String,
}

impl TextChange {
	/// create a new TextChange from the difference of given strings
	pub fn from_diff(before: &str, after: &str) -> TextChange {
		let diff = similar::TextDiff::from_chars(before, after);
		let mut start = 0;
		let mut end = 0;
		let mut from_beginning = true;
		for op in diff.ops() {
			match op {
				similar::DiffOp::Equal { .. } => {
					if from_beginning {
						start += 1
					} else {
						end += 1
					}
				},
				_ => {
					end = 0;
					from_beginning = false;
				}
			}
		}
		let end_before = before.len() - end;
		let end_after = after.len() - end;

		TextChange {
			span: start..end_before,
			content: after[start..end_after].to_string(),
		}
	}
}