From df39e658cd9e155c12667e7f6591924c56424ec9 Mon Sep 17 00:00:00 2001
From: Magnus Hoff <maghoff@gmail.com>
Date: Thu, 16 Nov 2017 15:38:45 +0100
Subject: [PATCH] Start implementing merge, for #23

---
 src/lib.rs   |   1 +
 src/merge.rs | 206 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 207 insertions(+)
 create mode 100644 src/merge.rs

diff --git a/src/lib.rs b/src/lib.rs
index c973f2f..0a823a1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -29,6 +29,7 @@ use std::net::{IpAddr, SocketAddr};
 
 mod assets;
 mod db;
+mod merge;
 mod mimes;
 mod models;
 mod rendering;
diff --git a/src/merge.rs b/src/merge.rs
new file mode 100644
index 0000000..78f5067
--- /dev/null
+++ b/src/merge.rs
@@ -0,0 +1,206 @@
+use std::ops::Range;
+
+use diff;
+use diff::Result::*;
+
+#[derive(Debug, PartialEq, Eq)]
+struct Chunk(Range<usize>, Range<usize>);
+
+#[derive(Debug, PartialEq, Eq)]
+enum ChunkKind {
+    Stable,
+    Unstable,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+struct ChunkItem {
+    kind: ChunkKind,
+    chunk: Chunk,
+}
+
+impl ChunkItem {
+    fn stable(chunk: Chunk) -> ChunkItem {
+        ChunkItem {
+            kind: ChunkKind::Stable,
+            chunk: chunk,
+        }
+    }
+
+    fn unstable(chunk: Chunk) -> ChunkItem {
+        ChunkItem {
+            kind: ChunkKind::Unstable,
+            chunk: chunk,
+        }
+    }
+}
+
+struct MergeIterator<Item> {
+    left: Vec<diff::Result<Item>>,
+    right: Vec<diff::Result<Item>>,
+
+    a: usize,
+    o: usize,
+    b: usize,
+}
+
+impl<Item> MergeIterator<Item> {
+    fn new(left: Vec<diff::Result<Item>>, right: Vec<diff::Result<Item>>) -> MergeIterator<Item> {
+        MergeIterator {
+            left,
+            right,
+            a: 0,
+            o: 0,
+            b: 0,
+        }
+    }
+}
+
+impl<Item> Iterator for MergeIterator<Item>
+where
+    Item: ::std::fmt::Debug + PartialEq
+{
+    type Item = ChunkItem;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut i = 0;
+        while let (Some(&Both(..)), Some(&Both(..))) = (self.left.get(self.a+i), self.right.get(self.b+i)) {
+            i += 1;
+        }
+        if i > 0 {
+            let chunk = ChunkItem::stable(Chunk(self.a..self.a+i, self.b..self.b+i));
+            self.a += i;
+            self.o += i;
+            self.b += i;
+            return Some(chunk);
+        }
+
+        let mut a = self.a;
+        let mut o = self.o;
+        let mut b = self.b;
+        loop {
+            match (self.left.get(a), self.right.get(b)) {
+                (Some(&Right(_)), _) => {
+                    a += 1;
+                },
+                (_, Some(&Right(_))) => {
+                    b += 1;
+                },
+                (Some(&Left(_)), Some(_)) => {
+                    a += 1;
+                    o += 1;
+                    b += 1;
+                },
+                (Some(_), Some(&Left(_))) => {
+                    a += 1;
+                    o += 1;
+                    b += 1;
+                },
+                (Some(&Both(..)), Some(&Both(..))) => {
+                    let chunk = ChunkItem::unstable(Chunk(self.a..a, self.b..b));
+                    self.a = a;
+                    self.o = o;
+                    self.b = b;
+                    return Some(chunk);
+                }
+                _ => {
+                    if self.a < self.left.len() || self.b < self.right.len() {
+                        let chunk = ChunkItem::unstable(Chunk(self.a..self.left.len(), self.b..self.right.len()));
+                        self.a = self.left.len();
+                        self.b = self.right.len();
+                        return Some(chunk);
+                    }
+                    return None;
+                }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use diff;
+
+    #[test]
+    fn simple_case() {
+        let o = "aaabbbccc";
+        let a = "aaaxxxbbbccc";
+        let b = "aaabbbyyyccc";
+
+        let oa = diff::chars(o, a);
+        let ob = diff::chars(o, b);
+
+        let merge = MergeIterator::new(oa, ob).collect::<Vec<_>>();
+        assert_eq!(vec![
+            ChunkItem::stable(Chunk(0..3, 0..3)),
+            ChunkItem::unstable(Chunk(3..6, 3..3)),
+            ChunkItem::stable(Chunk(6..9, 3..6)),
+            ChunkItem::unstable(Chunk(9..9, 6..9)),
+            ChunkItem::stable(Chunk(9..12, 9..12)),
+        ], merge);
+    }
+
+    #[test]
+    fn real_conflict() {
+        let o = "aaabbbccc";
+        let a = "aaaxxxccc";
+        let b = "aaayyyccc";
+
+        let oa = diff::chars(o, a);
+        let ob = diff::chars(o, b);
+
+        let merge = MergeIterator::new(oa, ob).collect::<Vec<_>>();
+        assert_eq!(vec![
+            ChunkItem::stable(Chunk(0..3, 0..3)),
+            ChunkItem::unstable(Chunk(3..9, 3..9)),
+            ChunkItem::stable(Chunk(9..12, 9..12)),
+        ], merge);
+    }
+
+    #[test]
+    fn additional_at_end() {
+        let o = "aaabbbccc";
+        let a = "aaabbbccc";
+        let b = "aaabbbcccddd";
+
+        let oa = diff::chars(o, a);
+        let ob = diff::chars(o, b);
+
+        let merge = MergeIterator::new(oa, ob).collect::<Vec<_>>();
+        assert_eq!(vec![
+            ChunkItem::stable(Chunk(0..9, 0..9)),
+            ChunkItem::unstable(Chunk(9..9, 9..12)),
+        ], merge);
+    }
+
+    #[test]
+    fn additional_at_end_2() {
+        let o = "aaabbb";
+        let a = "aaabbbccc";
+        let b = "aaabbbcccddd";
+
+        let oa = diff::chars(o, a);
+        let ob = diff::chars(o, b);
+
+        let merge = MergeIterator::new(oa, ob).collect::<Vec<_>>();
+        assert_eq!(vec![
+            ChunkItem::stable(Chunk(0..6, 0..6)),
+            ChunkItem::unstable(Chunk(6..9, 6..12)),
+        ], merge);
+    }
+
+    #[test]
+    fn completely_unrelated() {
+        let o = "aaa";
+        let a = "bbb";
+        let b = "ccc";
+
+        let oa = diff::chars(o, a);
+        let ob = diff::chars(o, b);
+
+        let merge = MergeIterator::new(oa, ob).collect::<Vec<_>>();
+        assert_eq!(vec![
+            ChunkItem::unstable(Chunk(0..6, 0..6)),
+        ], merge);
+    }
+}