1 files changed, 84 insertions, 0 deletions
diff --git a/src/schema.zig b/src/schema.zig
new file mode 100644
index 0000000..00bf1f7
--- /dev/null
+++ b/src/schema.zig
@@ -0,0 +1,84 @@
+const std = @import("std");
+const varint = @import("varint.zig");
+const record = @import("record.zig");
+
+pub fn getRootpage(allocator: std.mem.Allocator, file: *std.fs.File, page_size: u16, table_name: []const u8) !u32 {
+    var buf: [2]u8 = undefined;
+    _ = try file.seekTo(103);
+    _ = try file.read(&buf);
+    const num_cells = std.mem.readInt(u16, &buf, .big);
+
+    var cell_pointers = try allocator.alloc(u16, num_cells);
+    defer allocator.free(cell_pointers);
+
+    for (0..num_cells) |i| {
+        _ = try file.seekTo(108 + i * 2);
+        _ = try file.read(&buf);
+        cell_pointers[i] = std.mem.readInt(u16, &buf, .big);
+    }
+
+    var page_data = try allocator.alloc(u8, page_size);
+    defer allocator.free(page_data);
+
+    _ = try file.seekTo(0);
+    _ = try file.read(page_data);
+
+    for (0..num_cells) |i| {
+        const cell_data = page_data[cell_pointers[i]..];
+
+        var parsed = varint.parse(cell_data);
+        var pos = parsed.len;
+
+        parsed = varint.parse(cell_data[pos..]);
+        pos += parsed.len;
+
+        const record_data = cell_data[pos..];
+        parsed = varint.parse(record_data);
+        const header_size = parsed.value;
+        var header_pos = parsed.len;
+
+        var serial_types: [5]u64 = undefined;
+        for (0..5) |col| {
+            parsed = varint.parse(record_data[header_pos..]);
+            serial_types[col] = parsed.value;
+            header_pos += parsed.len;
+        }
+
+        var body_pos: usize = header_size;
+
+        for (0..2) |col| {
+            const st = serial_types[col];
+            if (st >= 13 and (st % 2) == 1) {
+                body_pos += (st - 13) / 2;
+            }
+        }
+
+        const tbl_name_result = record.readString(record_data[body_pos..], serial_types[2]);
+        body_pos += tbl_name_result.len;
+
+        if (std.mem.eql(u8, tbl_name_result.value, table_name)) {
+            const rp = record.readInt(record_data[body_pos..], serial_types[3]);
+            return @as(u32, @intCast(rp.value));
+        }
+    }
+
+    return 0;
+}
+
+pub fn countRows(allocator: std.mem.Allocator, file: *std.fs.File, page_size: u16, rootpage: u32) !u64 {
+    if (rootpage == 0) return 0;
+
+    const page_offset = (rootpage - 1) * @as(u64, page_size);
+    var page_data = try allocator.alloc(u8, page_size);
+    defer allocator.free(page_data);
+
+    _ = try file.seekTo(page_offset);
+    _ = try file.read(page_data);
+
+    const page_type = page_data[0];
+    if (page_type == 0x05 or page_type == 0x0d) {
+        return std.mem.readInt(u16, page_data[3..5], .big);
+    }
+
+    return 0;
+}