1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use crate::builder::ArrayBuilder;
use crate::{ArrayRef, NullArray};
use arrow_data::ArrayData;
use arrow_schema::DataType;
use std::any::Any;
use std::sync::Arc;

/// Builder for [`NullArray`]
///
/// # Example
///
/// Create a `NullArray` from a `NullBuilder`
///
/// ```
///
/// # use arrow_array::{Array, NullArray, builder::NullBuilder};
///
/// let mut b = NullBuilder::new();
/// b.append_empty_value();
/// b.append_null();
/// b.append_nulls(3);
/// b.append_empty_values(3);
/// let arr = b.finish();
///
/// assert_eq!(8, arr.len());
/// assert_eq!(0, arr.null_count());
/// ```
#[derive(Debug)]
pub struct NullBuilder {
    len: usize,
}

impl Default for NullBuilder {
    fn default() -> Self {
        Self::new()
    }
}

impl NullBuilder {
    /// Creates a new null builder
    pub fn new() -> Self {
        Self { len: 0 }
    }

    /// Creates a new null builder with space for `capacity` elements without re-allocating
    pub fn with_capacity(capacity: usize) -> Self {
        Self { len: capacity }
    }

    /// Returns the capacity of this builder measured in slots of type `T`
    pub fn capacity(&self) -> usize {
        self.len
    }

    /// Appends a null slot into the builder
    #[inline]
    pub fn append_null(&mut self) {
        self.len += 1;
    }

    /// Appends `n` `null`s into the builder.
    #[inline]
    pub fn append_nulls(&mut self, n: usize) {
        self.len += n;
    }

    /// Appends a null slot into the builder
    #[inline]
    pub fn append_empty_value(&mut self) {
        self.append_null();
    }

    /// Appends `n` `null`s into the builder.
    #[inline]
    pub fn append_empty_values(&mut self, n: usize) {
        self.append_nulls(n);
    }

    /// Builds the [NullArray] and reset this builder.
    pub fn finish(&mut self) -> NullArray {
        let len = self.len();
        let builder = ArrayData::new_null(&DataType::Null, len).into_builder();

        let array_data = unsafe { builder.build_unchecked() };
        NullArray::from(array_data)
    }

    /// Builds the [NullArray] without resetting the builder.
    pub fn finish_cloned(&self) -> NullArray {
        let len = self.len();
        let builder = ArrayData::new_null(&DataType::Null, len).into_builder();

        let array_data = unsafe { builder.build_unchecked() };
        NullArray::from(array_data)
    }
}

impl ArrayBuilder for NullBuilder {
    /// Returns the builder as a non-mutable `Any` reference.
    fn as_any(&self) -> &dyn Any {
        self
    }

    /// Returns the builder as a mutable `Any` reference.
    fn as_any_mut(&mut self) -> &mut dyn Any {
        self
    }

    /// Returns the boxed builder as a box of `Any`.
    fn into_box_any(self: Box<Self>) -> Box<dyn Any> {
        self
    }

    /// Returns the number of array slots in the builder
    fn len(&self) -> usize {
        self.len
    }

    /// Builds the array and reset this builder.
    fn finish(&mut self) -> ArrayRef {
        Arc::new(self.finish())
    }

    /// Builds the array without resetting the builder.
    fn finish_cloned(&self) -> ArrayRef {
        Arc::new(self.finish_cloned())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::Array;

    #[test]
    fn test_null_array_builder() {
        let mut builder = NullArray::builder(10);
        builder.append_null();
        builder.append_nulls(4);
        builder.append_empty_value();
        builder.append_empty_values(4);

        let arr = builder.finish();
        assert_eq!(20, arr.len());
        assert_eq!(0, arr.offset());
        assert_eq!(0, arr.null_count());
        assert!(arr.is_nullable());
    }

    #[test]
    fn test_null_array_builder_finish_cloned() {
        let mut builder = NullArray::builder(16);
        builder.append_null();
        builder.append_empty_value();
        builder.append_empty_values(3);
        let mut array = builder.finish_cloned();
        assert_eq!(21, array.len());

        builder.append_empty_values(5);
        array = builder.finish();
        assert_eq!(26, array.len());
    }
}