feat: add basic reflow command and keybind (alt+q)

src/buffer/Buffer.zig

@@ -13,6 +13,7 @@ const Self = @This();
 const max_imbalance = 7;
 pub const Root = *const Node;
 pub const unicode = @import("unicode.zig");
+pub const reflow = @import("reflow.zig").reflow;
 
 pub const Manager = @import("Manager.zig");
 pub const Cursor = @import("Cursor.zig");

src/buffer/reflow.zig

@@ -0,0 +1,55 @@
+pub fn reflow(allocator: std.mem.Allocator, text: []const u8, width: usize) error{ OutOfMemory, WriteFailed }![]u8 {
+    const prefix = detect_prefix(text);
+    const words = try split_words(allocator, text, prefix.len);
+    defer allocator.free(words);
+    var output: std.Io.Writer.Allocating = .init(allocator);
+    const writer = &output.writer;
+
+    var line_len: usize = 0;
+    for (words) |word| {
+        if (line_len == 0) {
+            try writer.writeAll(prefix);
+            line_len += prefix.len;
+        }
+        if (line_len > prefix.len)
+            try writer.writeByte(' ');
+        try writer.writeAll(word);
+        line_len += word.len;
+        if (line_len >= width) {
+            try writer.writeByte('\n');
+            line_len = 0;
+        }
+    }
+
+    return output.toOwnedSlice();
+}
+
+fn split_words(allocator: std.mem.Allocator, text: []const u8, prefix: usize) error{OutOfMemory}![]const []const u8 {
+    var words: std.ArrayList([]const u8) = .empty;
+    var lines = std.mem.splitScalar(u8, text, '\n');
+    while (lines.next()) |line| {
+        var it = std.mem.splitAny(u8, line[prefix..], " \t");
+        while (it.next()) |word| if (word.len > 0) {
+            (try words.addOne(allocator)).* = word;
+        };
+    }
+    return words.toOwnedSlice(allocator);
+}
+
+fn detect_prefix(text: []const u8) []const u8 {
+    var lines = std.mem.splitScalar(u8, text, '\n');
+    const line1 = lines.next() orelse return &.{};
+    var prefix: []const u8 = line1;
+    while (lines.next()) |line|
+        prefix = lcp(prefix, line);
+    return prefix;
+}
+
+fn lcp(a: []const u8, b: []const u8) []const u8 {
+    const len = @min(a.len, b.len);
+    for (0..len) |i| if (a[i] != b[i])
+        return a[0..i];
+    return a[0..len];
+}
+
+const std = @import("std");