From 30a4fc7365ffa4842275bc9513e3e458308b596d Mon Sep 17 00:00:00 2001
From: "Jakob L. Kreuze" <zerodaysfordays@sdf.org>
Date: Mon, 25 May 2020 18:06:08 -0400
Subject: Implement a paginated `query` method.

---
 src/database.rs | 90 ++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 61 insertions(+), 29 deletions(-)

(limited to 'src/database.rs')

diff --git a/src/database.rs b/src/database.rs
index 77397a5..d27646b 100644
--- a/src/database.rs
+++ b/src/database.rs
@@ -23,6 +23,14 @@ use std::path::Path;
 #[derive(Debug)]
 pub struct TagDatabase(Connection);
 
+/// Tag query with a sense of "state" for pagination.
+#[derive(Debug)]
+pub struct Query<'a> {
+    tags: &'a [&'a str],
+    last_id: Option<i64>,
+    limit: Option<i64>,
+}
+
 impl TagDatabase {
     /// Instantiate a new `TagDatabase` whose backing database is at `path`.
     pub fn new(path: &str) -> Result<Self> {
@@ -137,49 +145,64 @@ impl TagDatabase {
     }
 
     /// Return the intersection of the sets of images matching each of `tags`.
-    pub fn images_by_tags(&self, tags: &[&str]) -> Result<Vec<Image>> {
-        let ids: Vec<i64> = tags
+    pub fn query(&self, q: Query) -> Result<Vec<Image>> {
+        let ids: Vec<i64> = q
+            .tags
             .iter()
             .filter_map(|tag| self.tag_id(tag).ok())
             .collect();
-        let mut tags = Vec::from(tags);
+        let mut tags = Vec::from(q.tags);
         tags.dedup();
 
+        // Query contained a tag that's not in the database.
         if ids.len() != tags.len() {
             return Ok(vec![]);
         }
 
         let union = if tags.is_empty() {
-            String::from(
-                "INNER JOIN mapping
-                 ON images.id = mapping.image",
-            )
+            None
         } else {
-            (1..ids.len() + 1)
-                .zip(ids)
-                .map(|pair| {
-                    let (n, id) = pair;
-                    format!(
-                        "INNER JOIN mapping as m{n}
+            Some(
+                (1..ids.len() + 1)
+                    .zip(ids)
+                    .map(|pair| {
+                        let (n, id) = pair;
+                        format!(
+                            "INNER JOIN mapping as m{n}
                          ON images.id = m{n}.image
                          AND {id} = m{n}.tag",
-                        n = n,
-                        id = id
-                    )
-                })
-                .collect::<Vec<String>>()
-                .join("\n")
+                            n = n,
+                            id = id
+                        )
+                    })
+                    .collect::<Vec<String>>()
+                    .join("\n"),
+            )
+        };
+
+        let query = if let (Some(id), Some(n)) = (q.last_id, q.limit) {
+            format!(
+                "SELECT id, blake2, filename, orig_dir
+                 FROM images
+                 {union}
+                 WHERE id > {last_id}
+                 GROUP BY id
+                 ORDER BY id DESC
+                 LIMIT {limit}",
+                last_id = id,
+                union = union.or(Some("".into())).unwrap(),
+                limit = n
+            )
+        } else {
+            format!(
+                "SELECT id, blake2, filename, orig_dir
+                 FROM images
+                 {union}
+                 GROUP BY id
+                 ORDER BY id DESC",
+                union = union.or(Some("".into())).unwrap(),
+            )
         };
-        // WHERE id > {lastId}
-        // LIMIT 50
-        let query = format!(
-            "SELECT id, blake2, filename, orig_dir
-             FROM images
-             {union}
-             GROUP BY id
-             ORDER BY id DESC",
-            union = union
-        );
 
         Ok(self
             .0
@@ -204,6 +227,15 @@ impl TagDatabase {
             })
             .collect())
     }
+
+    /// Return the intersection of the sets of images matching each of `tags`.
+    pub fn images_by_tags(&self, tags: &[&str]) -> Result<Vec<Image>> {
+        self.query(Query {
+            tags,
+            last_id: None,
+            limit: None,
+        })
+    }
 }
 
 /// The result of an image query in бирка-тян's tag database.
-- 
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