tix-tracker 0.12.0

//! The `F7` Stats page's **Burndown** tab (mission `burndown-scope-analytics-01M3C9J1`,
//! WP06 T029–T033).
//!
//! # A tab on a page that already ships
//!
//! The `F7` **Stats** page, its `TopMode::Stats`, its [`crate::keybindings::InputContext::Stats`]
//! and its `F7` binding all ship from `project-issue-health-status-01M3C8HX`, and its tab
//! strip from `per-issue-time-tracking-01M3C9A4`. This module is the page's **third** tab,
//! joining that strip — the rule [`crate::ui::roadmap`] documents for the `F10` Portfolio
//! page. Nothing here introduces a mode: there is no `TopMode`, no `InputContext`, no
//! `[shell]` action and no nav-tree limb, so
//! `every_mode_maps_to_a_distinct_shell_action` is untouched (analysis-report H3).
//!
//! # What the tab renders
//!
//! Every figure on the tab is a field of the shared DTOs — [`ChartExport`] and its
//! [`ChartSeries`](crate::analytics::chart::ChartSeries),
//! [`ChartProjection`](crate::analytics::chart::ChartProjection) and findings nodes — read
//! out of the **one** document the CLI's verbs read
//! ([`crate::commands::export::chart_document`]). The tab computes no series, converts no
//! unit, projects no date and groups nothing: it resolves a scope through the crate's own
//! resolver, asks the shared adapter for the document, and draws it (C-008, NFR-003). An
//! unanswerable value is `-` and never a `0` (C-005), a day's coverage marker travels beside
//! the values it qualifies, and a closed snapshot's binding is named on the scope line and
//! in the `closed_snapshot` finding (C-006).
//!
//! # The chart
//!
//! The `CHART` column is a hand-drawn terminal bar, not a dependency (C-009): one `█` per
//! unit of the day's **remaining** value, truncated at [`BAR_CELLS`] with a trailing `…`,
//! `·` for a known zero and a `-` for a day whose remaining work the record cannot answer —
//! the same value the `REMAINING` column spells, drawn. It assembles no scale, computes no
//! maximum and normalises nothing, so it can disagree with no other surface about a figure.
//!
//! # Read-only
//!
//! The tab's controls select a scope, a period source, a mode, a unit and a forecast
//! origin in **session state** and re-fold through the shared seam; none of them writes.
//! There is no key here that reaches a store's write path, and the tab's own tests assert
//! the project's bytes are untouched after every control (T033).
//!
//! [`ChartSeries`]: crate::analytics::chart::ChartSeries

use ratatui::style::{Color, Modifier, Style};
use ratatui::text::{Line, Span};

use crate::analytics::chart::{ChartExport, ChartProjection};
use crate::analytics::events::{AnalyticsScope, Period};
use crate::analytics::series::{Coverage, CoverageSummary, DailyPoint, Mode};
use crate::keybindings::TuiAction;
use crate::ui::detail::dash_number;

/// How many cells the `CHART` column draws for one value before truncating it.
///
/// A cap, not a scale: past it the bar ends in `…`, and the value it stands for is
/// printed beside it in `REMAINING`. A bar that re-scaled every day against the series'
/// largest value would be a second arithmetic of the same figure.
const BAR_CELLS: usize = 20;

/// The glyph one unit of the chart's bar is drawn with.
const BAR: &str = "█";

/// The `CHART` column's own spelling for a value the record cannot answer.
const NO_BAR: &str = "-";

/// The `CHART` column's own spelling for a **known** zero: no work remains, and the record
/// says so.
///
/// Distinct from [`NO_BAR`] on purpose — a zero-length bar and an unanswerable value must not
/// render identically, or the chart would re-introduce the assumption C-005 forbids.
const ZERO_BAR: &str = "·";

/// The daily table's columns, in the data model's field order (T031).
const DAY_COLUMNS: [&str; 7] = [
    "DATE",
    "COVERAGE",
    "REMAINING",
    "SCOPE",
    "DONE",
    "+ADD",
    "-DONE",
];

/// The daily table's column widths, one per [`DAY_COLUMNS`] entry.
///
/// The two text columns (`DATE`, `COVERAGE`) are left-aligned and every numeric column
/// right-aligned, so a column of `-`s and a column of counts read as the same column — the
/// shape the page's other tables use.
const DAY_WIDTHS: [usize; 7] = [10, 16, 9, 9, 9, 9, 9];

/// Whether the column at `index` is text (left-aligned) rather than numeric.
const fn day_text_column(index: usize) -> bool {
    index < 2
}

/// The keys the Burndown tab answers to through the binding table (T029/T033).
///
/// The tab's cursor and the page's strip are the page's own actions — `j`/`k` (and the
/// arrows), `Tab`/`Shift+Tab`, `?` and `q` — exactly as the Health and Time tabs use them.
/// `Submit` is deliberately absent: `Enter` opens nothing on this tab, and an overlay that
/// advertised it would name a key that does nothing.
pub const HELP_ACTIONS: &[TuiAction] = &[
    TuiAction::MoveUp,
    TuiAction::MoveDown,
    TuiAction::Next,
    TuiAction::Previous,
    TuiAction::Help,
    TuiAction::Close,
];

/// The keys the Burndown tab answers to **raw**, with what each one does.
///
/// These are the controls T030 asks for, and they are raw for the reason the `F8` Schedule
/// page's tab keys are: none of them is bound in
/// [`crate::keybindings::InputContext::Stats`], so the binding layer would rewrite them to
/// the inert `F(12)` sentinel, and none of them is named by a [`TuiAction`] — so the tab
/// adds no action, no key-map row and no `docs/key-bindings.md` row (analysis-report H4).
pub const HELP_RAW: &[(&str, &str)] = &[
    ("[ / ]", "previous / next scope"),
    ("p", "period source (planning / observed)"),
    ("t", "mode (count / estimate)"),
    ("u", "next estimate unit"),
    ("v", "ask for the forecast"),
    ("d / D", "forecast origin (earlier / later)"),
];

/// The footer rows the `F7` Stats page draws for its **Burndown** tab.
///
/// The page's own cursor, strip and exit rows, and nothing from the Time tab: the footer
/// truncates, and a key that exists only on another tab is exactly the leak the tab scoping
/// exists to prevent. They are the overlay's own rows — one tab, one key set, so the two
/// surfaces cannot drift — and the controls themselves are spelled in [`HELP_RAW`] and in
/// the tab's own hint row.
pub const FOOTER_ACTIONS: &[TuiAction] = HELP_ACTIONS;

/// Which period the series covers (T030).
///
/// Two callers' choices, both of them the record's own: the scope's **planning** period
/// (what the CLI passes when no `--from`/`--to` is named) and the period the recorded
/// **events** themselves span (the fold resolves an absent bound to the observed extent —
/// its own documented answer, and the remedy the shared `missing_history` finding names).
/// Neither is arithmetic: no date is shifted, only a bound released.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
pub enum BurndownPeriod {
    /// The scope's own planning period — the cycle's declared dates, the milestone's target.
    #[default]
    Planning,
    /// Both bounds released, so the fold covers exactly the days the record's events span.
    Observed,
}

impl BurndownPeriod {
    /// Both sources, in cycle order.
    pub const ALL: [Self; 2] = [Self::Planning, Self::Observed];

    /// The source's name, as the tab spells it.
    pub const fn label(self) -> &'static str {
        match self {
            Self::Planning => "planning",
            Self::Observed => "observed",
        }
    }

    /// The source's one-line explanation.
    pub const fn description(self) -> &'static str {
        match self {
            Self::Planning => "the scope's own planning period",
            Self::Observed => "the days the record's own events span",
        }
    }

    /// The next source, wrapping.
    pub fn next(self) -> Self {
        match self {
            Self::Planning => Self::Observed,
            Self::Observed => Self::Planning,
        }
    }
}

/// The `F7` Stats page's **Burndown** tab session state (T029–T032).
///
/// Every selection lives here and nowhere else: the scope, the period source, the mode, the
/// unit, whether the forecast is asked for, and the forecast's origin. Nothing is persisted
/// (a session default is not a preference), nothing is a total, and the tab's one **read** —
/// the shared [`ChartExport`] — is rebuilt when the tab is opened and after every control,
/// never during a render.
///
/// The origin is held as a count of days **back from the series' last covered day**, so a
/// refresh cannot leave it pointing at a day the fold no longer holds: the projection's own
/// refusal for an uncovered day is a statement the tab should never have to make.
#[derive(Debug, Clone, PartialEq)]
pub struct BurndownState {
    /// The scopes the record offers, resolved through the crate's own scope resolver.
    pub choices: Vec<AnalyticsScope>,
    /// Which choice is selected, as an index into [`Self::choices`].
    pub choice: usize,
    /// Which period source the series is folded over.
    pub period: BurndownPeriod,
    /// How the series counts.
    pub mode: Mode,
    /// The units the project declares a conversion for ([`crate::analytics::units::declared_units`]).
    pub units: Vec<String>,
    /// Which unit is selected, as an index into [`Self::units`]. Remembered in count mode,
    /// where the fold ignores it, so switching back does not lose the reader's choice.
    pub unit: usize,
    /// Whether the forecast is asked for.
    pub forecast: bool,
    /// The forecast origin: how many covered days back from the series' last covered day.
    pub origin_back: usize,
    /// Which daily row the cursor is on, as an index into the series' points.
    pub cursor: usize,
    /// The document the tab is showing, `None` when no fold has produced one.
    pub document: Option<ChartExport>,
    /// Why the last fold produced no document — a read that failed, or a request the
    /// record cannot carry. An explicit state, never a blank pane.
    pub problem: Option<String>,
}

impl BurndownState {
    /// A fresh tab over `choices`, with the scope's own period, count mode, unit `0`, no
    /// forecast, the origin on the series' last covered day and the cursor on the first row.
    pub fn new(choices: Vec<AnalyticsScope>, units: Vec<String>) -> Self {
        Self {
            choices,
            choice: 0,
            period: BurndownPeriod::Planning,
            mode: Mode::Count,
            units,
            unit: 0,
            forecast: false,
            origin_back: 0,
            cursor: 0,
            document: None,
            problem: None,
        }
    }

    /// The selected choice, when the record offers one.
    pub fn selected(&self) -> Option<&AnalyticsScope> {
        self.choices.get(self.choice)
    }

    /// The scope the fold is asked for: the selection with [`Self::period`] applied.
    ///
    /// The closed-snapshot binding travels with the choice (the record's close evidence), so
    /// it survives the period change — a snapshot-bound scope stays bound whatever period the
    /// reader looks through, which is what C-006 requires of a historical view.
    pub fn scope(&self) -> Option<AnalyticsScope> {
        let mut scope = self.selected()?.clone();
        if self.period == BurndownPeriod::Observed {
            scope.period = Period::unbounded();
        }
        Some(scope)
    }

    /// The unit the fold is asked for: the selection, and only in estimate mode — a count is
    /// unitless, which is what the CLI's `--unit` does too.
    pub fn unit(&self) -> Option<&str> {
        if self.mode != Mode::Estimate {
            return None;
        }
        self.units.get(self.unit).map(String::as_str)
    }

    /// The covered days the current document holds.
    pub fn days(&self) -> usize {
        self.document
            .as_ref()
            .map_or(0, |document| document.series.points.len())
    }

    /// The forecast origin: the covered day [`Self::origin_back`] days back from the last one.
    pub fn origin(&self) -> Option<&DailyPoint> {
        let points = &self.document.as_ref()?.series.points;
        points.get(points.len().checked_sub(self.origin_back + 1)?)
    }

    /// The forecast to ask the document for, as `(as_of, end_date)` — the same pair the CLI
    /// passes as `--as-of` and the scope's planning end.
    ///
    /// `None` when the forecast is off, when there is no covered day to stand on, or when the
    /// effective period declares no end: the caller renders each of those states explicitly
    /// rather than asking for a forecast the record cannot bound.
    pub fn projection(&self) -> Option<(String, String)> {
        if !self.forecast {
            return None;
        }
        let origin = self.origin()?;
        let end = self.scope()?.period_end().map(str::to_string)?;
        Some((origin.date.clone(), end))
    }

    /// Switch to the scope `delta` steps away, wrapping — so one key reaches every scope from
    /// either side, exactly as the page's tab strip does.
    pub fn shift_scope(&mut self, delta: isize) {
        if self.choices.is_empty() {
            self.choice = 0;
            return;
        }
        let len = self.choices.len() as isize;
        self.choice = ((self.choice as isize + delta).rem_euclid(len)) as usize;
        // A different scope holds a different series: the other selections are the reader's
        // and stay, but the origin is a *day* of the series and starts from the scope's own
        // end again. The cursor does too — row 12 of one scope is not row 12 of another.
        self.origin_back = 0;
        self.cursor = 0;
    }

    /// The other period source (T030).
    pub fn cycle_period(&mut self) {
        self.period = self.period.next();
    }

    /// The other mode: count ↔ estimate (T030).
    pub fn cycle_mode(&mut self) {
        self.mode = match self.mode {
            Mode::Count => Mode::Estimate,
            Mode::Estimate => Mode::Count,
        };
    }

    /// The next unit the project declares, wrapping; inert when it declares none.
    pub fn cycle_unit(&mut self) {
        if !self.units.is_empty() {
            self.unit = (self.unit + 1) % self.units.len();
        }
    }

    /// Ask for the forecast, or stop asking for it.
    pub fn toggle_forecast(&mut self) {
        self.forecast = !self.forecast;
        if !self.forecast {
            self.origin_back = 0;
        }
    }

    /// Move the forecast origin one covered day earlier, to the series' first day at most.
    pub fn origin_earlier(&mut self) {
        let last = self.days().saturating_sub(1);
        self.origin_back = (self.origin_back + 1).min(last);
    }

    /// Move the forecast origin one covered day later, to the series' last day at most.
    pub fn origin_later(&mut self) {
        self.origin_back = self.origin_back.saturating_sub(1);
    }

    /// Move the daily cursor `delta` rows, clamped into the days the document holds.
    pub fn move_cursor(&mut self, delta: isize) {
        let last = self.days().saturating_sub(1);
        let next = if delta.is_negative() {
            self.cursor.saturating_sub(delta.unsigned_abs())
        } else {
            self.cursor.saturating_add(delta as usize)
        };
        self.cursor = next.min(last);
    }

    /// Keep every index inside the list it indexes (called after every read, so a control
    /// cannot leave a cursor past the end of a document the fold just shrank).
    pub fn clamp(&mut self) {
        if self.choice >= self.choices.len() {
            self.choice = 0;
        }
        if self.unit >= self.units.len() {
            self.unit = 0;
        }
        let last = self.days().saturating_sub(1);
        self.origin_back = self.origin_back.min(last);
        self.cursor = self.cursor.min(last);
    }
}

/// The tab's rendered body: the lines to draw and the line its cursor is on.
///
/// The cursor travels with the lines so the frame can scroll the body to keep the selected
/// day visible without the tab re-deriving where that day landed.
#[derive(Debug, Clone, PartialEq)]
pub struct BurndownFrame {
    /// The body, top to bottom.
    pub lines: Vec<Line<'static>>,
    /// The index in [`Self::lines`] of the selected day's row, or `0` when none is drawn.
    pub cursor_line: usize,
}

/// The Burndown tab's body (T029/T031/T032).
///
/// The scope header, then the fold's own metadata, the daily table with its chart column,
/// the forecast when one was asked for, and every finding with its reason and its remedy —
/// in the order the CLI's report prints them. An empty answer is a sentence that says so,
/// never a blank pane.
pub fn frame(state: &BurndownState) -> BurndownFrame {
    let mut lines: Vec<Line<'static>> = Vec::new();
    let mut cursor_line = 0usize;

    if state.choices.is_empty() {
        lines.extend(no_scope_lines());
        return BurndownFrame { lines, cursor_line };
    }

    lines.extend(scope_lines(state, state.document.as_ref()));
    lines.push(Line::from(""));

    let Some(document) = state.document.as_ref() else {
        lines.extend(problem_lines(state));
        return BurndownFrame { lines, cursor_line };
    };

    lines.extend(fold_lines(document));
    lines.push(Line::from(""));

    if document.is_empty() {
        lines.extend(no_day_lines(document));
    } else {
        lines.push(head_line());
        for (index, point) in document.series.points.iter().enumerate() {
            let selected = index == state.cursor;
            if selected {
                cursor_line = lines.len();
            }
            lines.push(day_line(point, selected));
        }
    }

    lines.push(Line::from(""));
    lines.extend(projection_lines(state, document));
    lines.push(Line::from(""));
    lines.extend(diagnostic_lines(document));
    BurndownFrame { lines, cursor_line }
}

fn dim() -> Style {
    Style::default().fg(Color::DarkGray)
}

fn warning() -> Style {
    Style::default()
        .fg(Color::Yellow)
        .add_modifier(Modifier::BOLD)
}

/// One `label: value` line, in the page's own field style.
fn field(label: &str, value: &str) -> Line<'static> {
    Line::from(vec![
        Span::styled(format!("{label}: "), dim()),
        Span::raw(value.to_string()),
    ])
}

/// The scope lines, in the CLI's own order and spelling (`scope`, `id`, `period`,
/// `snapshot`, `mode`, `unit`), plus the two facts only a *tabbed* surface needs to state:
/// which period source is in force, and where the selection sits in the list.
///
/// The values are the resolved scope's own fields — the same value `tix analytics burndown`
/// prints for the same scope — so the two surfaces cannot disagree about the period or the
/// snapshot binding (NFR-003).
fn scope_lines(state: &BurndownState, document: Option<&ChartExport>) -> Vec<Line<'static>> {
    let mut lines = Vec::new();
    let Some(scope) = state.scope() else {
        return lines;
    };
    let period = format!(
        "{}..{}",
        bound_text(scope.period_start()),
        bound_text(scope.period_end())
    );
    lines.push(field("scope", scope.kind.as_str()));
    lines.push(field("id", &scope.id));
    lines.push(field("period", &period));
    lines.push(field(
        "period source",
        &format!("{} ({})", state.period.label(), state.period.description()),
    ));
    lines.push(field(
        "snapshot",
        scope.snapshot_id.as_deref().unwrap_or("-"),
    ));
    lines.push(field("mode", state.mode.as_str()));
    // The document's own unit when there is one — the CLI prints the same field — and
    // the selection otherwise, so the line reads the same before and after a fold.
    let unit = document
        .and_then(|document| document.unit.as_deref())
        .or_else(|| state.unit())
        .unwrap_or("-");
    lines.push(field("unit", unit));
    lines.push(field(
        "selected",
        &format!("{} of {}", state.choice + 1, state.choices.len()),
    ));
    lines
}

/// A period bound as the CLI prints it: the date, or `open` for a bound the record does not
/// declare (which is coverage, not a guess).
fn bound_text(bound: Option<&str>) -> &str {
    bound.unwrap_or("open")
}

/// The fold's own metadata: the formula version, the day count, the covered span and the
/// coverage tally — every value a field or an accessor of the shared document. The finding
/// count is drawn once, above the findings themselves.
fn fold_lines(document: &ChartExport) -> Vec<Line<'static>> {
    let coverage: CoverageSummary = document.coverage;
    let covered = document
        .series
        .points
        .first()
        .zip(document.series.points.last())
        .map_or_else(
            || "-".to_string(),
            |(first, last)| format!("{}..{}", first.date, last.date),
        );
    vec![
        field("formula", &document.formula_version),
        Line::from(vec![
            Span::styled("days: ", dim()),
            Span::raw(document.series.points.len().to_string()),
            Span::styled("   covered: ", dim()),
            Span::raw(covered),
        ]),
        Line::from(vec![
            Span::styled("coverage: ", dim()),
            Span::raw(format!(
                "known={} unknown={} coverage_limited={}",
                coverage.known, coverage.unknown, coverage.coverage_limited
            )),
        ]),
    ]
}

/// How many findings the tab renders: the series' own, the forecast's when one is in the
/// document, then the document's — the same sum, in the same order, as the CLI's.
fn finding_count(document: &ChartExport) -> usize {
    document.series.diagnostics.len()
        + document
            .projection
            .as_ref()
            .map_or(0, |projection| projection.diagnostics.len())
        + document.diagnostics.len()
}

/// The daily table's heading row.
fn head_line() -> Line<'static> {
    let mut text = String::from("  ");
    for (index, column) in DAY_COLUMNS.iter().enumerate() {
        if index > 0 {
            text.push_str("  ");
        }
        let width = DAY_WIDTHS[index];
        if day_text_column(index) {
            text.push_str(&format!("{column:<width$}"));
        } else {
            text.push_str(&format!("{column:>width$}"));
        }
    }
    text.push_str("  CHART");
    Line::from(Span::styled(text, dim()))
}

/// One day as the table's row: the point's own fields, the shared coverage marker beside
/// them, and the chart bar (T031).
///
/// A `None` is `-` through [`dash_number`], the crate's one rendering of "no value", so an
/// unobserved day's additions read as absent rather than as a recorded zero — the `0` an
/// *observed* quiet day carries is right beside it in the same column.
fn day_line(point: &DailyPoint, selected: bool) -> Line<'static> {
    let cells = [
        point.date.clone(),
        point.coverage.as_str().to_string(),
        dash_number(point.remaining),
        dash_number(point.scope_total),
        dash_number(point.completed),
        dash_number(point.scope_added),
        dash_number(point.completions),
    ];
    let mut text = if selected {
        String::from("> ")
    } else {
        String::from("  ")
    };
    for (index, cell) in cells.iter().enumerate() {
        if index > 0 {
            text.push_str("  ");
        }
        let width = DAY_WIDTHS[index];
        if day_text_column(index) {
            text.push_str(&format!("{cell:<width$}"));
        } else {
            text.push_str(&format!("{cell:>width$}"));
        }
    }
    text.push_str("  ");
    text.push_str(&bar_text(point.remaining));
    Line::from(Span::styled(text, day_style(point.coverage, selected)))
}

/// The style one day's row is drawn in: the coverage marker is the day's own warning, and
/// the cursor is the reader's.
fn day_style(coverage: Coverage, selected: bool) -> Style {
    let base = match coverage {
        Coverage::Known => Style::default(),
        Coverage::CoverageLimited => Style::default().fg(Color::Yellow),
        Coverage::Unknown => dim(),
    };
    if selected {
        base.add_modifier(Modifier::BOLD)
    } else {
        base
    }
}

/// The chart column's text for one day: one cell per unit of remaining work, truncated with
/// `…` past [`BAR_CELLS`], `·` for a known zero, and `-` for work the day cannot answer.
fn bar_text(remaining: Option<i64>) -> String {
    let Some(remaining) = remaining else {
        return NO_BAR.to_string();
    };
    let cells = usize::try_from(remaining).unwrap_or(0);
    if cells == 0 {
        return ZERO_BAR.to_string();
    }
    let mut bar = BAR.repeat(cells.min(BAR_CELLS));
    if cells > BAR_CELLS {
        bar.push('…');
    }
    bar
}

/// The forecast block: the projection's own fields when one was drawn, and an explicit
/// statement of *which* state the tab is in when one was not (T032).
fn projection_lines(state: &BurndownState, document: &ChartExport) -> Vec<Line<'static>> {
    let mut lines = Vec::new();
    match document.projection.as_ref() {
        Some(projection) => lines.extend(forecast_lines(projection)),
        None if !state.forecast => {
            lines.push(field("projection", "off (press `v` to ask for it)"));
        }
        None => {
            lines.push(field("projection", "unavailable"));
            match state.scope().filter(|scope| scope.period_end().is_none()) {
                Some(scope) => {
                    // The shared service names this state: the scope declares no planning end,
                    // so there is no boundary to draw a forecast against. Pressing `p` cannot
                    // bound a scope that declares none, so the remedy is the record's own.
                    lines.push(Line::from(format!(
                        "  the {} scope `{}` declares no planning end date, so a forecast has \
                         no boundary to be drawn against",
                        scope.kind, scope.id
                    )));
                    lines.push(Line::from(
                        "  remedy: give the scope an end — the cycle's `due_date` or the \
                         milestone's target date",
                    ));
                }
                None => {
                    lines.push(Line::from(
                        "  the record holds no covered day to stand the forecast on",
                    ));
                    lines.push(Line::from(
                        "  remedy: widen the series' period (press `p`) so it covers a \
                         recorded day",
                    ));
                }
            }
        }
    }
    lines
}

/// The forecast's own fields, in the CLI's `projection_block` order.
///
/// The formula version is the **projection's**, not the series' — two different documents of
/// two different formulas — and every unanswerable value is `-`: a forecast that could not be
/// drawn says its `status` and its findings rather than printing a date it did not derive.
fn forecast_lines(projection: &ChartProjection) -> Vec<Line<'static>> {
    vec![
        field("projection", projection.status.as_str()),
        field("  as_of", &projection.as_of),
        field("  end_date", &projection.end_date),
        field("  remaining", &dash_number(projection.remaining)),
        field("  observed_rate", &dash_number(projection.observed_rate)),
        field(
            "  projected_completion",
            projection.projected_completion.as_deref().unwrap_or("-"),
        ),
        field("  meets_end_date", &dash_number(projection.meets_end_date)),
        field("  formula", &projection.formula_version),
    ]
}

/// Every finding the document holds, in the count's own order, each with its reason and its
/// remedy (T031/T032).
///
/// The series' findings lead (they are the fold's), then the forecast's, then the document's
/// own. Each is drawn from its fields, not from a pre-rendered string, so the tab lays out
/// what the CLI prints to stderr — the same kind, scope, day, message and remedy.
fn diagnostic_lines(document: &ChartExport) -> Vec<Line<'static>> {
    let mut lines = vec![field("diagnostics", &finding_count(document).to_string())];
    for diagnostic in &document.series.diagnostics {
        lines.extend(finding_lines(diagnostic));
    }
    if let Some(projection) = document.projection.as_ref() {
        for diagnostic in &projection.diagnostics {
            lines.extend(finding_lines(diagnostic));
        }
    }
    for diagnostic in &document.diagnostics {
        lines.push(Line::from(format!(
            "  {}  {}  {}",
            diagnostic.kind,
            diagnostic
                .scope
                .as_deref()
                .or(diagnostic.target.as_deref())
                .unwrap_or("-"),
            diagnostic.reason
        )));
        if let Some(remedy) = diagnostic.remedy.as_deref() {
            lines.push(Line::from(Span::styled(
                format!("    remedy: {remedy}"),
                dim(),
            )));
        }
    }
    if document.series.diagnostics.is_empty()
        && document.diagnostics.is_empty()
        && document
            .projection
            .as_ref()
            .is_none_or(|projection| projection.diagnostics.is_empty())
    {
        lines.push(Line::from(Span::styled(
            "  none: the fold answered every day it covers",
            dim(),
        )));
    }
    lines
}

/// One shared [`AnalyticsDiagnostic`](crate::analytics::diagnostics::AnalyticsDiagnostic) as
/// the tab draws it: the kind and the scope it is about, its day and event when it has them,
/// the message, and the remedy.
fn finding_lines(
    diagnostic: &crate::analytics::diagnostics::AnalyticsDiagnostic,
) -> Vec<Line<'static>> {
    let mut place = diagnostic.scope.clone();
    if let Some(date) = diagnostic.date.as_deref() {
        place.push_str(&format!("  {date}"));
    }
    if let Some(event_id) = diagnostic.event_id.as_deref() {
        place.push_str(&format!("  {event_id}"));
    }
    let mut lines = vec![Line::from(format!(
        "  {}  {place}  {}",
        diagnostic.kind.as_str(),
        diagnostic.message
    ))];
    if let Some(remedy) = diagnostic.remedy.as_deref() {
        lines.push(Line::from(Span::styled(
            format!("    remedy: {remedy}"),
            dim(),
        )));
    }
    lines
}

/// The tab with no scope to report: an explicit sentence naming how to give it one.
fn no_scope_lines() -> Vec<Line<'static>> {
    vec![
        Line::from(Span::styled(
            "No cycle or milestone is recorded.",
            warning(),
        )),
        Line::from("The fold reports one scope at a time, and the record names none to report."),
        Line::from("Define one with `tix cycle add <name>` or `tix milestone create <name>`,"),
        Line::from("then open this tab again."),
    ]
}

/// The fold's own answer when it covers no day: the sentence, and the findings that say why.
fn no_day_lines(document: &ChartExport) -> Vec<Line<'static>> {
    let findings = document.series.diagnostics.len();
    let mut lines = vec![
        Line::from(Span::styled(
            "The fold answered no day for this scope.",
            warning(),
        )),
        Line::from(format!(
            "It reported {findings} finding(s) — below — rather than an empty series."
        )),
    ];
    if document.series.diagnostics.is_empty() {
        lines.push(Line::from(
            "The period could not be enumerated: press `p` for the period the record's own",
        ));
        lines.push(Line::from(
            "events span, or choose a scope whose record declares its dates.",
        ));
    }
    lines
}

/// The tab when the last fold produced no document: the problem verbatim, then what the
/// reader can do about it.
fn problem_lines(state: &BurndownState) -> Vec<Line<'static>> {
    let mut lines = vec![Line::from(Span::styled(
        "The fold produced no document.",
        warning(),
    ))];
    match state.problem.as_deref() {
        Some(problem) => lines.push(Line::from(problem.to_string())),
        None => lines.push(Line::from(
            "The scope, period, mode or unit selects no series this build can fold.",
        )),
    }
    lines.push(Line::from(""));
    lines.push(Line::from(
        "press `t` for count mode, `p` for the period the record's own events span,",
    ));
    lines.push(Line::from("or `[`/`]` for another scope"));
    lines
}

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

    /// A block of lines as text, one row per line — [`text`] renders a single [`Line`].
    fn render(lines: &[Line<'static>]) -> String {
        lines
            .iter()
            .map(|line| {
                line.spans
                    .iter()
                    .map(|span| span.content.as_ref())
                    .collect::<String>()
            })
            .collect::<Vec<_>>()
            .join("\n")
    }

    fn unknown_day() -> DailyPoint {
        DailyPoint {
            date: "2026-01-05".to_string(),
            scope_total: None,
            remaining: None,
            completed: None,
            scope_added: None,
            completions: None,
            coverage: Coverage::Unknown,
            event_ids: Vec::new(),
        }
    }

    fn quiet_day() -> DailyPoint {
        DailyPoint {
            date: "2026-01-06".to_string(),
            scope_total: Some(0),
            remaining: Some(0),
            completed: Some(0),
            scope_added: Some(0),
            completions: Some(0),
            coverage: Coverage::Known,
            event_ids: Vec::new(),
        }
    }

    fn limited_day() -> DailyPoint {
        DailyPoint {
            date: "2026-01-07".to_string(),
            scope_total: Some(2),
            remaining: Some(1),
            completed: None,
            scope_added: None,
            completions: None,
            coverage: Coverage::CoverageLimited,
            event_ids: Vec::new(),
        }
    }

    fn text(line: &Line<'_>) -> String {
        line.spans
            .iter()
            .map(|span| span.content.as_ref())
            .collect::<String>()
    }

    /// A day the record cannot answer prints `-` in every numeric column, never a `0` — and
    /// the day beside it, which *was* read, prints the zero the record holds.
    #[test]
    fn an_unanswerable_day_is_a_dash_and_a_read_quiet_day_is_a_zero() {
        let unobserved = text(&day_line(&unknown_day(), false));
        assert!(unobserved.contains("unknown"), "{unobserved}");
        assert!(
            unobserved.contains("2026-01-05  unknown"),
            "the coverage marker travels beside the values it qualifies: {unobserved}"
        );
        let cells: Vec<&str> = unobserved.split_whitespace().collect();
        assert_eq!(cells[0], "2026-01-05", "{cells:?}");
        assert_eq!(cells[1], "unknown", "{cells:?}");
        assert_eq!(
            cells[2..7].to_vec(),
            vec!["-"; 5],
            "no numeric cell of an unanswerable day reads as a recorded zero: {cells:?}"
        );
        assert_eq!(
            cells[7], "-",
            "and the chart column draws the absent marker, not a zero-length bar: {cells:?}"
        );

        let observed = text(&day_line(&quiet_day(), false));
        assert!(observed.contains("known"), "{observed}");
        assert!(
            observed.contains(" 0"),
            "an observed quiet day's zero is a value: {observed}"
        );
        assert!(
            observed.trim_end().ends_with(ZERO_BAR),
            "and its chart column says a known zero, not an unknown one: {observed}"
        );
    }

    /// A scope that declares no planning end, asked for a forecast, must say *that*: the
    /// shared service names the state (`ProjectionUnknown`), and "press `p`" cannot bound a
    /// scope that declares none. A review found the tab printing "no covered day" while it
    /// was drawing covered days, with that unfollowable remedy.
    #[test]
    fn an_unbounded_scope_under_a_forecast_names_the_missing_planning_end() {
        let unbounded = AnalyticsScope {
            kind: crate::analytics::events::ScopeKind::Cycle,
            id: "Open Cycle".to_string(),
            period: crate::analytics::events::Period {
                start: Some("2026-01-05".to_string()),
                end: None,
            },
            snapshot_id: None,
        };
        let series = crate::analytics::series::BurndownSeries {
            scope: unbounded.clone(),
            mode: Mode::Count,
            unit: None,
            points: vec![quiet_day()],
            diagnostics: Vec::new(),
            formula_version: "burndown.count.v1".to_string(),
        };
        let document = ChartExport::build(&series, None, &[]);
        let mut state = BurndownState::new(vec![unbounded.clone()], Vec::new());
        state.forecast = true;

        let rendered = render(&projection_lines(&state, &document));
        assert!(
            rendered.contains("declares no planning end date"),
            "the missing planning end is named: {rendered}"
        );
        assert!(
            !rendered.contains("no covered day"),
            "the scope has a covered day, so that sentence is false here: {rendered}"
        );
        assert!(
            rendered.contains("due_date"),
            "and the remedy names the record's own field: {rendered}"
        );

        // The other cause keeps its own sentence: a scope that has an end but no covered day.
        let bounded = AnalyticsScope {
            period: crate::analytics::events::Period {
                start: Some("2026-01-05".to_string()),
                end: Some("2026-01-09".to_string()),
            },
            ..unbounded.clone()
        };
        let mut state = BurndownState::new(vec![bounded], Vec::new());
        state.forecast = true;
        let empty = ChartExport::build(
            &crate::analytics::series::BurndownSeries {
                points: Vec::new(),
                ..series
            },
            None,
            &[],
        );
        let rendered = render(&projection_lines(&state, &empty));
        assert!(rendered.contains("no covered day"), "{rendered}");
        assert!(!rendered.contains("planning end date"), "{rendered}");
    }

    /// A coverage-limited day whose level **is** known still draws the level it has, with the
    /// marker beside it: the bar never stands in for a value the day does not hold.
    #[test]
    fn a_coverage_limited_day_draws_the_level_it_holds() {
        let row = text(&day_line(&limited_day(), true));
        assert!(row.starts_with("> "), "the cursor marks the row: {row}");
        assert!(row.contains("coverage_limited"), "{row}");
        assert!(row.contains('█'), "{row}");
    }

    /// The chart column is the value drawn, not a second arithmetic: one cell per unit, a
    /// truncation marker past the cap, and a dash for a value the record does not hold.
    #[test]
    fn the_chart_bar_draws_the_value_it_stands_for() {
        assert_eq!(bar_text(None), "-", "an unanswerable value draws no bar");
        assert_eq!(
            bar_text(Some(0)),
            "·",
            "a known zero is drawn as a zero, not as the absent marker"
        );
        assert_eq!(bar_text(Some(3)), "███");
        assert_eq!(bar_text(Some(20)), "█".repeat(20));
        assert_eq!(bar_text(Some(21)), format!("{}…", "█".repeat(20)));
    }

    /// The Burndown tab lists the actions it really has, and none of the Time tab's.
    #[test]
    fn the_burndown_rows_name_only_this_tabs_keys() {
        let bindings =
            crate::keybindings::KeyBindings::resolve(&crate::keybindings::KeyBindings::default())
                .expect("the built-in bindings resolve");
        let context = crate::keybindings::InputContext::Stats;
        for action in HELP_ACTIONS {
            assert!(
                bindings.bound_actions(context).contains(action),
                "`{}` is not bound in the Stats context",
                action.as_str()
            );
        }
        for absent in [
            TuiAction::TimeAdd,
            TuiAction::TimeEdit,
            TuiAction::TimeDelete,
            TuiAction::TimeFilter,
            TuiAction::TimeBreakdown,
            TuiAction::TimeHistory,
            // `Enter` opens nothing here, so the overlay must not name it.
            TuiAction::Submit,
        ] {
            assert!(
                !HELP_ACTIONS.contains(&absent),
                "`{}` acts on nothing on the Burndown tab",
                absent.as_str()
            );
            assert!(
                !FOOTER_ACTIONS.contains(&absent),
                "`{}` acts on nothing on the Burndown tab",
                absent.as_str()
            );
        }
        let advertised: Vec<&str> = HELP_RAW.iter().map(|(key, _)| *key).collect();
        for key in ["[ / ]", "p", "t", "u", "v", "d / D"] {
            assert!(
                advertised.contains(&key),
                "the tab names `{key}`: {advertised:?}"
            );
        }
    }

    /// A tab with no scope says so rather than drawing nothing.
    #[test]
    fn a_tab_with_no_scope_says_so() {
        let state = BurndownState::new(Vec::new(), Vec::new());
        let frame = frame(&state);
        let text: Vec<String> = frame.lines.iter().map(text).collect();
        assert!(
            text.iter()
                .any(|line| line.contains("No cycle or milestone is recorded")),
            "{text:?}"
        );
        assert_eq!(frame.cursor_line, 0);
    }

    /// The state's own controls are pure session choices: the mode toggle, the unit cycle,
    /// the period source and the scope ring.
    #[test]
    fn the_controls_move_between_the_records_own_choices() {
        let mut state = BurndownState::new(
            vec![
                AnalyticsScope::cycle("Sprint 7", Period::unbounded()).unwrap(),
                AnalyticsScope::milestone("v1", Period::unbounded()).unwrap(),
            ],
            vec!["points".to_string(), "hours".to_string()],
        );
        assert_eq!(state.mode, Mode::Count);
        assert_eq!(state.unit(), None, "a count is unitless");
        state.cycle_mode();
        assert_eq!(state.mode, Mode::Estimate);
        assert_eq!(state.unit(), Some("points"));
        state.cycle_unit();
        assert_eq!(state.unit(), Some("hours"));
        state.cycle_unit();
        assert_eq!(state.unit(), Some("points"), "the unit list wraps");
        state.cycle_period();
        assert_eq!(state.period, BurndownPeriod::Observed);
        assert_eq!(
            state.scope().unwrap().period,
            Period::unbounded(),
            "the observed source releases both bounds"
        );
        state.shift_scope(1);
        assert_eq!(state.selected().unwrap().id, "v1");
        state.shift_scope(1);
        assert_eq!(state.selected().unwrap().id, "Sprint 7", "the ring wraps");
        state.shift_scope(-1);
        assert_eq!(state.selected().unwrap().id, "v1");
    }
}