core-time: shared date/time helpers (DayWindow + Instant formatting)

First module of floret-kit, the shared Material 3 Expressive design system +
plumbing for the Floret app family. core-time is a pure-Kotlin JVM library
(DayWindow local-day boundaries + locale/zone-aware Instant formatting),
extracted from Agendula. Standalone build + 2 unit tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,16 @@
+# Gradle
+.gradle/
+build/
+
+# Local configuration
+local.properties
+
+# IDE
+*.iml
+.idea/
+
+# OS
+.DS_Store
+
+# Logs
+*.log

README.md

@@ -0,0 +1,42 @@
+# floret-kit
+
+The shared **Material 3 Expressive design system + plumbing** for the Floret
+family of Android apps ([Calendula](https://gitea.jeanlucmakiola.de/makiolaj/calendula),
+[Agendula](https://gitea.jeanlucmakiola.de/makiolaj/agendula), and future siblings).
+
+"Floret" is the family's design language: a Calendula flower head is a cluster of
+many small *florets*, and each app is one of them. This repo is the bloom they
+share — so a new app doesn't reinvent a settings screen, an edit form, or a theme;
+it draws from here.
+
+## How it's consumed
+
+Each app embeds this repo as a **git submodule** and wires it in with a Gradle
+**composite build**, so the kit is always built **from source** (no published
+artifacts — keeps every app reproducible for F-Droid):
+
+```kotlin
+// app's settings.gradle.kts
+includeBuild("floret-kit")
+```
+```kotlin
+// app module's build.gradle.kts
+implementation("de.jeanlucmakiola.floret:core-time")
+```
+
+Gradle's dependency substitution maps `de.jeanlucmakiola.floret:<module>` to the
+local source module — edit the kit and the app picks it up immediately.
+
+## Modules
+
+| Module | What it holds |
+|--------|---------------|
+| `core-time` | Pure-Kotlin date/time helpers: local-day windows (`DayWindow`) for smart-list logic and locale/zone-aware display formatting (`Instant.formatDate()` / `formatTime()` / `formatDateTime()`). No Android, no deps. |
+
+_More modules (identity/theme, components, screen recipes, provider/prefs/reminders/crash plumbing) land as they're extracted from the apps._
+
+## Build
+
+```sh
+./gradlew :core-time:test
+```

build.gradle.kts

@@ -0,0 +1,12 @@
+// Top-level build for floret-kit. Plugins are declared here (apply false) and
+// applied per-module. Every module shares the family group + version so the
+// consuming apps can depend on `de.jeanlucmakiola.floret:<module>` and Gradle's
+// composite-build substitution maps it to the local source module.
+plugins {
+    alias(libs.plugins.kotlin.jvm) apply false
+}
+
+subprojects {
+    group = "de.jeanlucmakiola.floret"
+    version = "0.1.0"
+}

core-time/build.gradle.kts

@@ -0,0 +1,29 @@
+// core-time — pure-Kotlin date/time helpers shared across the family:
+// local-day windows for "smart list" logic and locale/zone-aware display
+// formatting. No Android, no third-party deps — just kotlin.time + java.time
+// (available natively on minSdk 26+), so it's a plain JVM library.
+plugins {
+    alias(libs.plugins.kotlin.jvm)
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
+    }
+}
+
+dependencies {
+    testImplementation(libs.junit.jupiter.api)
+    testRuntimeOnly(libs.junit.jupiter.engine)
+    testRuntimeOnly(libs.junit.platform.launcher)
+    testImplementation(libs.truth)
+}
+
+tasks.test {
+    useJUnitPlatform()
+}

core-time/src/main/kotlin/de/jeanlucmakiola/floret/time/DateTimeFormat.kt

@@ -0,0 +1,28 @@
+package de.jeanlucmakiola.floret.time
+
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+import java.time.format.FormatStyle
+import kotlin.time.Instant
+
+/**
+ * Locale-aware display formatting for the [kotlin.time.Instant]s the domain
+ * uses. Kept tiny and dependency-free; the data layer stores instants, the UI
+ * renders them in the device's zone and locale.
+ */
+private val dateFormatter: DateTimeFormatter = DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM)
+private val timeFormatter: DateTimeFormatter = DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT)
+
+private fun Instant.atSystemZone() =
+    java.time.Instant.ofEpochMilli(toEpochMilliseconds())
+        .atZone(ZoneId.systemDefault())
+
+/** Medium localized date, e.g. "18 Jun 2026". */
+fun Instant.formatDate(): String = atSystemZone().format(dateFormatter)
+
+/** Short localized time, e.g. "14:30". */
+fun Instant.formatTime(): String = atSystemZone().format(timeFormatter)
+
+/** Date alone for all-day items, otherwise date + time. */
+fun Instant.formatDateTime(allDay: Boolean): String =
+    if (allDay) formatDate() else "${formatDate()} · ${formatTime()}"

core-time/src/main/kotlin/de/jeanlucmakiola/floret/time/DayWindow.kt

@@ -0,0 +1,18 @@
+package de.jeanlucmakiola.floret.time
+
+import java.time.ZoneId
+import kotlin.time.Instant
+
+/** Local-day boundaries used by smart-list predicates. Pure + testable. */
+object DayWindow {
+
+    /** Returns `[startOfToday, startOfTomorrow)` in [zone] for the instant [now]. */
+    fun today(now: Instant, zone: ZoneId): Pair<Instant, Instant> {
+        val date = java.time.Instant.ofEpochMilli(now.toEpochMilliseconds())
+            .atZone(zone)
+            .toLocalDate()
+        val start = date.atStartOfDay(zone).toInstant().toEpochMilli()
+        val end = date.plusDays(1).atStartOfDay(zone).toInstant().toEpochMilli()
+        return Instant.fromEpochMilliseconds(start) to Instant.fromEpochMilliseconds(end)
+    }
+}

core-time/src/test/kotlin/de/jeanlucmakiola/floret/time/DayWindowTest.kt

@@ -0,0 +1,35 @@
+package de.jeanlucmakiola.floret.time
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+import java.time.ZoneId
+import kotlin.time.Instant
+
+class DayWindowTest {
+
+    @Test
+    fun `today spans exactly 24h in UTC and contains now`() {
+        val zone = ZoneId.of("UTC")
+        val now = Instant.fromEpochMilliseconds(1_750_000_000_000L)
+        val (start, end) = DayWindow.today(now, zone)
+
+        assertThat(end.toEpochMilliseconds() - start.toEpochMilliseconds()).isEqualTo(86_400_000L)
+        assertThat(now >= start).isTrue()
+        assertThat(now < end).isTrue()
+        // In UTC, midnight aligns to a multiple of one day since the epoch.
+        assertThat(start.toEpochMilliseconds() % 86_400_000L).isEqualTo(0L)
+    }
+
+    @Test
+    fun `start is local midnight in a non-UTC zone`() {
+        val zone = ZoneId.of("Europe/Berlin")
+        val now = Instant.fromEpochMilliseconds(1_750_000_000_000L)
+        val (start, end) = DayWindow.today(now, zone)
+
+        val startLocal = java.time.Instant.ofEpochMilli(start.toEpochMilliseconds()).atZone(zone)
+        assertThat(startLocal.hour).isEqualTo(0)
+        assertThat(startLocal.minute).isEqualTo(0)
+        assertThat(now >= start).isTrue()
+        assertThat(now < end).isTrue()
+    }
+}

gradle/libs.versions.toml

@@ -0,0 +1,16 @@
+# Version catalog for floret-kit. Kept in lockstep with the consuming apps'
+# catalogs (same Kotlin + test stack) until the catalog itself is shared.
+[versions]
+kotlin = "2.3.21"
+junit = "6.1.0"
+junitPlatform = "6.1.0"
+truth = "1.4.5"
+
+[libraries]
+junit-jupiter-api = { group = "org.junit.jupiter", name = "junit-jupiter-api", version.ref = "junit" }
+junit-jupiter-engine = { group = "org.junit.jupiter", name = "junit-jupiter-engine", version.ref = "junit" }
+junit-platform-launcher = { group = "org.junit.platform", name = "junit-platform-launcher", version.ref = "junitPlatform" }
+truth = { group = "com.google.truth", name = "truth", version.ref = "truth" }
+
+[plugins]
+kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,8 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.5.1-bin.zip
+distributionSha256Sum=bafc141b619ad6350fd975fc903156dd5c151998cc8b058e8c1044ab5f7b031f
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,251 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed 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
+#
+#      https://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.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s\n' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH="\\\"\\\""
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,94 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle.kts

@@ -0,0 +1,31 @@
+pluginManagement {
+    repositories {
+        google {
+            content {
+                includeGroupByRegex("com\\.android.*")
+                includeGroupByRegex("com\\.google.*")
+                includeGroupByRegex("androidx.*")
+            }
+        }
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
+}
+
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
+// floret-kit — the shared Material 3 Expressive design system + plumbing for the
+// Floret family of apps (Calendula, Agendula, …). Consumed by each app as a git
+// submodule wired in via Gradle `includeBuild`, built from source (F-Droid-safe).
+rootProject.name = "floret-kit"
+
+include(":core-time")