codecrafters submit [skip ci]

1 files changed, 110 insertions, 0 deletions

diff --git a/src/main.zig b/src/main.zig
index 6dbb671..cccdf44 100755
--- a/src/main.zig
+++ b/src/main.zig
@@ -3,6 +3,30 @@ var stdout_buffer: [1024]u8 = undefined;
 var stdout_writer = std.fs.File.stdout().writer(&stdout_buffer);
 const stdout = &stdout_writer.interface;
 
+fn parseVarint(data: []const u8) struct { value: u64, len: usize } {
+    var result: u64 = 0;
+    var i: usize = 0;
+
+    while (i < data.len and i < 9) : (i += 1) {
+        const byte = data[i];
+        result |= @as(u64, byte & 0x7f) << @as(u6, @intCast(i * 7));
+
+        if ((byte & 0x80) == 0) {
+            return .{ .value = result, .len = i + 1 };
+        }
+    }
+
+    return .{ .value = result, .len = i };
+}
+
+fn readStringFromRecord(data: []const u8, serial_type: u64) struct { value: []const u8, len: usize } {
+    if (serial_type >= 13 and (serial_type % 2) == 1) {
+        const size = (serial_type - 13) / 2;
+        return .{ .value = data[0..size], .len = size };
+    }
+    return .{ .value = "", .len = 0 };
+}
+
 pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
     defer _ = gpa.deinit();
@@ -34,5 +58,91 @@ pub fn main() !void {
         const num_tables = std.mem.readInt(u16, &buf, .big);
         try stdout.print("number of tables: {}\n", .{num_tables});
         try stdout.flush();
+    } else if (std.mem.eql(u8, command, ".tables")) {
+        var file = try std.fs.cwd().openFile(database_file_path, .{});
+        defer file.close();
+
+        var buf: [2]u8 = undefined;
+        _ = try file.seekTo(16);
+        _ = try file.read(&buf);
+        const page_size = std.mem.readInt(u16, &buf, .big);
+
+        _ = 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);
+
+        var first_table = true;
+
+        for (0..num_cells) |i| {
+            const cell_offset = cell_pointers[i];
+            const cell_data = page_data[cell_offset..];
+
+            var parsed = parseVarint(cell_data);
+            var pos = parsed.len;
+
+            parsed = parseVarint(cell_data[pos..]);
+            pos += parsed.len;
+
+            const record_start = pos;
+            const record_data = cell_data[record_start..];
+
+            parsed = parseVarint(record_data);
+            const header_size = parsed.value;
+            var header_pos = parsed.len;
+
+            var serial_types: [5]u64 = undefined;
+            for (0..5) |col| {
+                parsed = parseVarint(record_data[header_pos..]);
+                serial_types[col] = parsed.value;
+                header_pos += parsed.len;
+            }
+
+            var body_pos: usize = header_size;
+
+            for (0..2) |col| {
+                const serial_type = serial_types[col];
+                if (serial_type >= 13 and (serial_type % 2) == 1) {
+                    const size = (serial_type - 13) / 2;
+                    body_pos += size;
+                }
+            }
+
+            const tbl_name_type = serial_types[2];
+            const tbl_name = readStringFromRecord(record_data[body_pos..], tbl_name_type);
+
+            const body_pos_type: usize = header_size;
+            const type_serial = serial_types[0];
+            const type_str = readStringFromRecord(record_data[body_pos_type..], type_serial);
+
+            if (std.mem.eql(u8, type_str.value, "table")) {
+                if (!std.mem.eql(u8, tbl_name.value, "sqlite_sequence")) {
+                    if (!first_table) {
+                        try stdout.print(" ", .{});
+                    }
+                    try stdout.print("{s}", .{tbl_name.value});
+                    first_table = false;
+                }
+            }
+        }
+
+        if (!first_table) {
+            try stdout.print("\n", .{});
+        }
+        try stdout.flush();
     }
 }