diff --git a/Cargo.lock b/Cargo.lock
index 335a880..2f2952c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,5 +1,91 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "autocfg"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
+
+[[package]]
+name = "chrono"
+version = "0.4.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "670ad68c9088c2a963aaa298cb369688cf3f9465ce5e2d4ca10e6e0098a1ce73"
+dependencies = [
+ "libc",
+ "num-integer",
+ "num-traits",
+ "time",
+ "winapi",
+]
+
+[[package]]
+name = "libc"
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+checksum = "8916b1f6ca17130ec6568feccee27c156ad12037880833a3b842a823236502e7"
+
 [[package]]
 name = "matsudo-gomi-hook"
 version = "0.1.0"
+dependencies = [
+ "chrono",
+]
+
+[[package]]
+name = "num-integer"
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+ "autocfg",
+ "num-traits",
+]
+
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+ "autocfg",
+]
+
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+dependencies = [
+ "libc",
+ "wasi",
+ "winapi",
+]
+
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+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
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+[[package]]
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diff --git a/Cargo.toml b/Cargo.toml
index 667352c..4b39e23 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,3 +7,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+chrono = "0.4.19"
diff --git a/src/calendar.rs b/src/calendar.rs
new file mode 100644
index 0000000..cbf84df
--- /dev/null
+++ b/src/calendar.rs
@@ -0,0 +1,9 @@
+use chrono::{DateTime, Local};
+
+use crate::gomi::Gomi;
+
+pub(crate) mod matsudo;
+
+pub(crate) trait Calendar {
+    fn gomi_at(&self, time: DateTime<Local>) -> Vec<Gomi>;
+}
diff --git a/src/calendar/matsudo.rs b/src/calendar/matsudo.rs
new file mode 100644
index 0000000..879af71
--- /dev/null
+++ b/src/calendar/matsudo.rs
@@ -0,0 +1,83 @@
+use crate::calendar::Calendar;
+use crate::gomi::Gomi;
+
+use chrono::{DateTime, Datelike, Local, Weekday, Weekday::*};
+
+// Defines the gomi rules for Matsudo using a macro.
+macro_rules! matsudo_rules {
+    (
+        $current_base: expr,
+        $current_time: expr,
+        // This repetition represents each rules based on the base day.
+        $((
+            $base: path,
+            ($burnable1: path, $burnable2: path, $burnable3: path),
+            ($glass_week_num: expr, $glass_week_day: path),  // The Nth day of X
+            $recycle_plastic: path,
+            $other_plastic: path
+        )),*
+        $(,)?
+    ) => {
+        // Matches the current base day for the location.
+        match ($current_base) {
+            $(
+                $base => (vec![
+                    match ($current_time.weekday()) {
+                        $base => Some(Gomi::new("資源ごみ")),
+                        $burnable1 | $burnable2 | $burnable3 => Some(Gomi::new("燃やせるごみ")),
+                        $recycle_plastic => Some(Gomi::new("リサイクルするプラスチック")),
+                        $other_plastic => Some(Gomi::new("その他のプラスチックなどのごみ")),
+                        _ => None,
+                    },
+                    if (week_num_by_weekday($current_time, $glass_week_day) == $glass_week_num) {
+                        Some(Gomi::new("陶磁器・ガラスなどのごみ"))
+                    } else {
+                        None
+                    }
+                ]
+                    // Converts Vec<Option<Gomi>> to Vec<Gomi>, remaining only Some elements.
+                    .into_iter()
+                    .flat_map(|x| x)
+                    .collect()
+                )
+            ),*,
+            // Ignores the unknown base day, returning an empty Vec.
+            _ => vec![],
+        }
+    }
+}
+
+pub(crate) struct Matsudo {
+    base: Weekday,
+}
+
+impl Matsudo {
+    pub(crate) fn new(base: Weekday) -> Self {
+        Self { base }
+    }
+}
+
+impl Calendar for Matsudo {
+    fn gomi_at(&self, time: DateTime<Local>) -> Vec<Gomi> {
+        // Using the defined rules, determines which Gomi's are available to take out.
+        matsudo_rules!(
+            self.base,
+            time,
+            (Mon, (Tue, Thu, Sat), (2, Thu), Wed, Fri),
+            (Tue, (Mon, Wed, Fri), (2, Wed), Thu, Sat),
+            (Wed, (Tue, Thu, Sat), (3, Thu), Fri, Mon),
+            (Thu, (Mon, Wed, Fri), (3, Wed), Sat, Tue),
+            (Fri, (Tue, Thu, Sat), (4, Thu), Mon, Wed),
+            (Sat, (Mon, Wed, Fri), (4, Wed), Tue, Thu),
+        )
+    }
+}
+
+fn week_num_by_weekday(time: DateTime<Local>, weekday: Weekday) -> u32 {
+    time.day() / 7
+        + if time.weekday().num_days_from_sunday() < weekday.num_days_from_sunday() {
+            0
+        } else {
+            1
+        }
+}
diff --git a/src/gomi.rs b/src/gomi.rs
new file mode 100644
index 0000000..1fd6655
--- /dev/null
+++ b/src/gomi.rs
@@ -0,0 +1,19 @@
+use std::fmt::{Display, Formatter, Result};
+
+pub(crate) struct Gomi {
+    name: String,
+}
+
+impl Gomi {
+    pub(crate) fn new(name: &str) -> Self {
+        Self {
+            name: name.to_string(),
+        }
+    }
+}
+
+impl Display for Gomi {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        write!(f, "{}", self.name)
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..cb69197 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,21 @@
+pub(crate) mod calendar;
+pub(crate) mod gomi;
+
+use chrono::{Local, TimeZone, Weekday};
+
+use crate::calendar::Calendar;
+
 fn main() {
-    println!("Hello, world!");
+    let calendar = calendar::matsudo::Matsudo::new(Weekday::Thu);
+    let today = Local.ymd(2021, 3, 17).and_hms(0, 0, 0);
+    let gomi = calendar.gomi_at(today);
+
+    println!(
+        "今日 {} は {} の日です",
+        today,
+        gomi.iter()
+            .map(|g| g.to_string())
+            .collect::<Vec<String>>()
+            .join(", ")
+    )
 }