hephaestus/crates/heph-tui/src/fmt.rs

//! Small display helpers (compact human dates for task rows). The UI layer may
//! read the wall clock (unlike `heph-core`, which is clock-injected).

use chrono::{DateTime, Datelike, Local, NaiveDate};
use ratatui::style::Color;

/// Format an epoch-ms do/late date relative to `today`: `today`, `tomorrow`,
/// `yesterday`, `MM-DD` within the year, else `YYYY-MM-DD`.
pub fn fmt_date(ms: i64, today: NaiveDate) -> String {
    let Some(dt) = DateTime::from_timestamp_millis(ms) else {
        return "?".into();
    };
    let date = dt.with_timezone(&Local).date_naive();
    match (date - today).num_days() {
        0 => "today".into(),
        1 => "tomorrow".into(),
        -1 => "yesterday".into(),
        _ if date.year() == today.year() => format!("{:02}-{:02}", date.month(), date.day()),
        _ => date.format("%Y-%m-%d").to_string(),
    }
}

/// Today in the local timezone (the reference for [`fmt_date`]).
pub fn today_local() -> NaiveDate {
    Local::now().date_naive()
}

/// How many days past its do-date a task is (0 if not overdue, no do-date, or
/// future-dated). The "how overdue" signal the agenda sort ranks on (§8.1).
pub fn days_overdue(do_date: Option<i64>, today: NaiveDate) -> i64 {
    match do_date.and_then(DateTime::from_timestamp_millis) {
        Some(dt) => (today - dt.with_timezone(&Local).date_naive())
            .num_days()
            .max(0),
        None => 0,
    }
}

/// A stable display color for a project, derived from its node id (§8.1) so the
/// task list's bullets read as project identity. Hashing the id (rather than a
/// position-based palette) keeps each project's color **stable as others are
/// added or removed**, trading perfect spread for occasional near-collisions —
/// acceptable per the design. `None` (no project) is a neutral gray. A future
/// per-project override stored on the model would take precedence over this.
pub fn project_color(project_id: Option<&str>) -> Color {
    let Some(id) = project_id else {
        return Color::DarkGray;
    };
    // FNV-1a over the id → a hue in [0,360); fixed saturation/lightness tuned to
    // stay legible on a dark terminal background.
    let mut h: u32 = 0x811c_9dc5;
    for b in id.bytes() {
        h ^= b as u32;
        h = h.wrapping_mul(0x0100_0193);
    }
    let hue = (h as f64 / u32::MAX as f64) * 360.0;
    let (r, g, b) = hsl_to_rgb(hue, 0.55, 0.65);
    Color::Rgb(r, g, b)
}

/// HSL (hue 0–360, saturation/lightness 0–1) → 8-bit RGB.
fn hsl_to_rgb(h: f64, s: f64, l: f64) -> (u8, u8, u8) {
    let c = (1.0 - (2.0 * l - 1.0).abs()) * s;
    let hp = h / 60.0;
    let x = c * (1.0 - (hp.rem_euclid(2.0) - 1.0).abs());
    let (r, g, b) = match hp as u32 {
        0 => (c, x, 0.0),
        1 => (x, c, 0.0),
        2 => (0.0, c, x),
        3 => (0.0, x, c),
        4 => (x, 0.0, c),
        _ => (c, 0.0, x),
    };
    let m = l - c / 2.0;
    let to = |v: f64| ((v + m) * 255.0).round().clamp(0.0, 255.0) as u8;
    (to(r), to(g), to(b))
}

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

    fn day(y: i32, m: u32, d: u32) -> NaiveDate {
        NaiveDate::from_ymd_opt(y, m, d).unwrap()
    }

    fn ms(date: NaiveDate) -> i64 {
        date.and_hms_opt(12, 0, 0)
            .unwrap()
            .and_local_timezone(Local)
            .unwrap()
            .timestamp_millis()
    }

    #[test]
    fn relative_and_absolute_dates() {
        let today = day(2026, 6, 3);
        assert_eq!(fmt_date(ms(today), today), "today");
        assert_eq!(fmt_date(ms(day(2026, 6, 4)), today), "tomorrow");
        assert_eq!(fmt_date(ms(day(2026, 6, 2)), today), "yesterday");
        assert_eq!(fmt_date(ms(day(2026, 12, 25)), today), "12-25");
        assert_eq!(fmt_date(ms(day(2027, 1, 1)), today), "2027-01-01");
    }

    #[test]
    fn project_color_is_stable_distinct_and_neutral_when_absent() {
        assert_eq!(project_color(None), Color::DarkGray);
        // Deterministic: the same id always maps to the same color.
        assert_eq!(
            project_color(Some("01J_chores")),
            project_color(Some("01J_chores"))
        );
        // Distinct ids generally differ (these two do).
        assert_ne!(
            project_color(Some("01J_chores")),
            project_color(Some("01J_garden"))
        );
        // A project id resolves to a concrete RGB (not a named palette slot).
        assert!(matches!(project_color(Some("01J_work")), Color::Rgb(..)));
    }
}