Add offsets file

src/offsets.zig

@@ -0,0 +1,64 @@
+const std = @import("std");
+const types = @import("types.zig");
+
+fn utf16leCharSequenceLength(first_char: u16) !u2 {
+    const c0: u21 = first_char;
+    if (first_char & ~@as(u21, 0x03ff) == 0xd800) {
+        return 2;
+    } else if (c0 & ~@as(u21, 0x03ff) == 0xdc00) {
+        return error.UnexpectedSecondSurrogateHalf;
+    }
+    return 1;
+}
+
+pub const Encoding = enum {
+    utf8,
+    utf16,
+};
+
+pub const DocumentPosition = struct {
+    line: []const u8,
+    line_index: usize,
+    absolute_index: usize,
+};
+
+pub fn documentPosition(doc: types.TextDocument, position: types.Position, encoding: Encoding) !DocumentPosition {
+    var split_iterator = std.mem.split(doc.text, "\n");
+
+    var line_idx: i64 = 0;
+    var line: []const u8 = "";
+    while (line_idx < position.line) : (line_idx += 1) {
+        line = split_iterator.next() orelse return error.InvalidParams;
+    }
+
+    const line_start_idx = split_iterator.index.?;
+    line = split_iterator.next() orelse return error.InvalidParams;
+
+    if (encoding == .utf8) {
+        const index = @intCast(i64, line_start_idx) + position.character;
+        if (index < 0 or index > @intCast(i64, doc.text.len)) {
+            return error.InvalidParams;
+        }
+        return DocumentPosition{ .line = line, .absolute_index = @intCast(usize, index), .line_index = @intCast(usize, position.character) };
+    } else {
+        const utf8 = doc.text[line_start_idx..];
+        var utf8_idx: usize = 0;
+        var utf16_idx: usize = 0;
+        while (utf16_idx < position.character) {
+            if (utf8_idx > utf8.len) {
+                return error.InvalidParams;
+            }
+
+            const n = try std.unicode.utf8ByteSequenceLength(utf8[utf8_idx]);
+            const next_utf8_idx = utf8_idx + n;
+            const codepoint = try std.unicode.utf8Decode(utf8[utf8_idx..next_utf8_idx]);
+            if (codepoint < 0x10000) {
+                utf16_idx += 1;
+            } else {
+                utf16_idx += 2;
+            }
+            utf8_idx = next_utf8_idx;
+        }
+        return DocumentPosition{ .line = line, .absolute_index = line_start_idx + utf8_idx, .line_index = utf8_idx };
+    }
+}