"""Positions within a bar series, rather than on a clock.

A chart spaces bars evenly no matter how much time separates them: a weekend is
forty-nine hours but one bar wide. So a line that looks straight is straight in
*index* space, and a trendline advances per bar, not per second.

Evaluating trendlines any other way makes the drawn line and the alerted price
disagree — measured at 147 points across a weekend on a real /ES chart.
"""
from bisect import bisect_right


def index_at(times: list[int], t: int) -> float:
    """Fractional index of a timestamp within an ascending bar-time series."""
    if not times:
        return 0.0
    if len(times) == 1:
        return 0.0
    # Outside the series there are no bars to measure against, so fall back to
    # the spacing at the nearest edge.
    if t <= times[0]:
        step = times[1] - times[0]
        return (t - times[0]) / step if step else 0.0
    if t >= times[-1]:
        step = times[-1] - times[-2]
        return (len(times) - 1) + ((t - times[-1]) / step if step else 0.0)

    lower = bisect_right(times, t) - 1
    span = times[lower + 1] - times[lower]
    return lower + ((t - times[lower]) / span if span else 0.0)


def price_in_bar_space(level, times: list[int], t: int) -> float:
    """A level's price at `t`, interpolated across bars rather than seconds."""
    start_index = index_at(times, level.anchor_t)
    end_index = index_at(times, level.last_t)
    if end_index == start_index:
        return level.anchor_p
    end_price = level.anchor_p + level.slope * (level.last_t - level.anchor_t)
    ratio = (index_at(times, t) - start_index) / (end_index - start_index)
    return level.anchor_p + (end_price - level.anchor_p) * ratio