From 7389290d80a2a3cfa860b3a29a715a50af805331 Mon Sep 17 00:00:00 2001
From: Dmitry <b4tm4n@mail.ru>
Date: Tue, 4 Oct 2022 22:58:57 +0300
Subject: [PATCH] SourceQuestionsZipReader: Iterator

---
 src/main.rs | 153 +++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 123 insertions(+), 30 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 73d206d..bc1e6b4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -267,17 +267,104 @@ impl From<SourceQuestionsBatch> for Vec<Question> {
     }
 }
 
-// measure and return time elapsed in `func` in seconds
-pub fn measure<F: FnOnce()>(func: F) -> f64 {
-    let start = Instant::now();
-    func();
-    let elapsed = start.elapsed();
-    (elapsed.as_secs() as f64) + (elapsed.subsec_nanos() as f64 / 1_000_000_000.0)
+struct SourceQuestionsZipReader<R>
+where
+    R: std::io::Read + std::io::Seek,
+{
+    zipfile: zip::ZipArchive<R>,
+    index: Option<usize>,
 }
 
-pub fn measure_and_print<F: FnOnce()>(func: F) {
-    let m = measure(func);
-    eprintln!("{}", m);
+impl<R> SourceQuestionsZipReader<R>
+where
+    R: std::io::Read + std::io::Seek,
+{
+    fn new(zipfile: zip::ZipArchive<R>) -> Self {
+        SourceQuestionsZipReader {
+            zipfile,
+            index: None,
+        }
+    }
+}
+
+impl<R> Iterator for SourceQuestionsZipReader<R>
+where
+    R: std::io::Read + std::io::Seek,
+{
+    type Item = (String, Result<SourceQuestionsBatch, serde_json::Error>);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.index.is_none() && !self.zipfile.is_empty() {
+            self.index = Some(0);
+        }
+
+        match self.index {
+            Some(i) if i < self.zipfile.len() => {
+                self.index = Some(i + 1);
+
+                self.nth(i)
+            }
+            _ => None,
+        }
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        if self.zipfile.len() <= n {
+            return None;
+        }
+        self.index = Some(n + 1);
+
+        let file = self.zipfile.by_index(n).unwrap();
+        let name = file.mangled_name();
+        let name_str = name.to_str().unwrap();
+
+        let data: Result<SourceQuestionsBatch, _> = serde_json::from_reader(file);
+
+        Some((String::from(name_str), data))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.zipfile.len();
+        let index = self.index.unwrap_or(0);
+        let rem = if len > index + 1 {
+            len - (index + 1)
+        } else {
+            0
+        };
+        (rem, Some(rem))
+    }
+
+    fn count(self) -> usize
+    where
+        Self: Sized,
+    {
+        self.zipfile.len()
+    }
+}
+
+impl<R> ExactSizeIterator for SourceQuestionsZipReader<R>
+where
+    R: std::io::Read + std::io::Seek,
+{
+    fn len(&self) -> usize {
+        self.zipfile.len()
+    }
+}
+
+trait ReadSourceQuestionsBatches<R>
+where
+    R: std::io::Read + std::io::Seek,
+{
+    fn source_questions(self) -> SourceQuestionsZipReader<R>;
+}
+
+impl<R> ReadSourceQuestionsBatches<R> for zip::ZipArchive<R>
+where
+    R: std::io::Read + std::io::Seek,
+{
+    fn source_questions(self) -> SourceQuestionsZipReader<R> {
+        SourceQuestionsZipReader::new(self)
+    }
 }
 
 fn write_db() {
@@ -292,7 +379,7 @@ fn write_db() {
 
     let zip_file = fs::File::open(ZIP_FILENAME).unwrap();
     let zip_reader = io::BufReader::new(zip_file);
-    let mut archive = zip::ZipArchive::new(zip_reader).unwrap();
+    let archive = zip::ZipArchive::new(zip_reader).unwrap();
 
     let options: Options = serde_json::from_value(json!({
         "map_size": 900 * 1024 * 1024, // 900mb
@@ -311,16 +398,8 @@ fn write_db() {
 
     let mut count: usize = 0;
     let count = &mut count;
-    (0..archive.len())
-        .map(|i| {
-            let file = archive.by_index(i).unwrap();
-            let name = file.mangled_name();
-            let name_str = name.to_str().unwrap();
-
-            let data: Result<SourceQuestionsBatch, _> = serde_json::from_reader(file);
-
-            (String::from(name_str), data)
-        })
+    archive
+        .source_questions()
         .filter(|(_, data)| data.is_ok())
         .flat_map(|(filename, data)| {
             let mut data = data.unwrap();
@@ -354,19 +433,20 @@ where
     println!("{:#?}", q)
 }
 
-fn read_from_zip(mut file_num: usize, mut num: usize) -> Option<Question> {
+fn read_from_zip(file_num: usize, mut num: usize) -> Option<Question> {
+    let mut rng = rand::thread_rng();
     let zip_file = fs::File::open(ZIP_FILENAME).unwrap();
     let zip_reader = io::BufReader::new(zip_file);
-    let mut archive = zip::ZipArchive::new(zip_reader).unwrap();
+    let archive = zip::ZipArchive::new(zip_reader).unwrap();
 
-    let mut rng = rand::thread_rng();
-    if file_num == 0 {
-        file_num = (1..=archive.len()).choose(&mut rng).unwrap();
-    }
-    let file = archive.by_index(file_num - 1).unwrap();
-    let data: Result<SourceQuestionsBatch, _> = serde_json::from_reader(file);
-    let data = data.unwrap();
-    let questions: Vec<Question> = data.into();
+    let mut source_questions = archive.source_questions();
+    let (_, batch) = if file_num == 0 {
+        source_questions.choose(&mut rng).unwrap()
+    } else {
+        source_questions.nth(file_num - 1).unwrap()
+    };
+    let batch = batch.unwrap();
+    let questions: Vec<Question> = batch.into();
 
     if num == 0 {
         num = (1..=questions.len()).choose(&mut rng).unwrap();
@@ -413,6 +493,19 @@ fn read_from_db(mut id: u32) -> Option<Question> {
     collection.get::<Question>(id).unwrap()
 }
 
+// measure and return time elapsed in `func` in seconds
+pub fn measure<F: FnOnce()>(func: F) -> f64 {
+    let start = Instant::now();
+    func();
+    let elapsed = start.elapsed();
+    (elapsed.as_secs() as f64) + (elapsed.subsec_nanos() as f64 / 1_000_000_000.0)
+}
+
+pub fn measure_and_print<F: FnOnce()>(func: F) {
+    let m = measure(func);
+    eprintln!("{}", m);
+}
+
 fn main() {
     let args = Cli::parse();