"""Versioned, compact display data calculated from full-resolution recordings."""

import math
from types import SimpleNamespace

import click

from .analytics import analyse, numeric

ANALYSIS_VERSION = 2
CHART_LIMIT = 750
ROUTE_TARGET = 1400
CHART_KEYS = (
    "distance",
    "heart_rate",
    "speed",
    "elevation",
    "grade",
    "gap",
    "pace",
    "cadence",
    "power",
    "stride_length",
    "vertical_oscillation",
    "ground_contact",
)
ROUTE_KEYS = ("distance", "speed", "heart_rate", "grade")


def evenly_spaced(length, limit):
    if length <= limit:
        return set(range(length))
    return {round(i * (length - 1) / (limit - 1)) for i in range(limit)}


def simplify_indices(rows, tolerance):
    """Iterative Douglas-Peucker in local metre coordinates; retain endpoints."""
    if len(rows) <= 2:
        return set(range(len(rows)))
    latitude = math.radians(rows[0]["point"][0])
    points = [
        (row["point"][1] * 111320 * math.cos(latitude), row["point"][0] * 111320) for row in rows
    ]
    kept = {0, len(rows) - 1}
    stack = [(0, len(rows) - 1)]
    while stack:
        start, end = stack.pop()
        ax, ay = points[start]
        bx, by = points[end]
        dx, dy = bx - ax, by - ay
        denominator = dx * dx + dy * dy
        furthest, maximum = None, tolerance * tolerance
        for index in range(start + 1, end):
            px, py = points[index]
            fraction = (
                max(0, min(1, ((px - ax) * dx + (py - ay) * dy) / denominator))
                if denominator
                else 0
            )
            squared = (px - ax - fraction * dx) ** 2 + (py - ay - fraction * dy) ** 2
            if squared > maximum:
                furthest, maximum = index, squared
        if furthest is not None:
            kept.add(furthest)
            stack.extend(((start, furthest), (furthest, end)))
    return kept


def compact_routes(samples):
    segments, segment = [], []
    for sample in samples:
        point = sample.get("point")
        if isinstance(point, list) and len(point) == 2 and all(numeric(v) for v in point):
            segment.append(sample)
        elif segment:
            segments.append(segment)
            segment = []
    if segment:
        segments.append(segment)
    total = sum(len(segment) for segment in segments)
    result = []
    for segment in segments:
        # Preserve turns plus regular measurement samples for route colours.
        budget = max(2, round(ROUTE_TARGET * len(segment) / total))
        regular = evenly_spaced(len(segment), max(2, budget // 2))
        tolerance = 3.0
        kept = simplify_indices(segment, tolerance) | regular
        while len(kept) > budget:
            tolerance *= 2
            kept = simplify_indices(segment, tolerance) | regular
        result.append(
            [
                {
                    "point": [round(v, 6) for v in segment[i]["point"]],
                    **{
                        key: round(segment[i][key], 3) if numeric(segment[i].get(key)) else None
                        for key in ROUTE_KEYS
                    },
                }
                for i in sorted(kept)
            ]
        )
    return result


def persist_analysis(activity):
    from .effort_segments import analyze

    analysis = analyse(activity)
    effort, segments = analyze(activity.samples or [])
    analysis["summary"].update(
        {key: effort[key] for key in ("pace_variability", "heart_rate_drift", "sensor_coverage")}
    )
    activity.analysis_summary = {key: analysis[key] for key in ("summary", "terrain", "laps")}
    activity.analysis_summary["segments"] = segments
    routes = compact_routes(analysis["samples"])
    activity.route_geometry = [[sample["point"] for sample in segment] for segment in routes]
    chart_indices = evenly_spaced(len(analysis["samples"]), CHART_LIMIT)
    activity.display_data = {
        "route_segments": routes,
        "chart": [
            {key: row.get(key) for key in CHART_KEYS}
            for i, row in enumerate(analysis["samples"])
            if i in chart_indices
        ],
    }
    activity.analysis_version = ANALYSIS_VERSION


def stored_analysis(activity):
    if activity.analysis_version == ANALYSIS_VERSION:
        return activity.analysis_summary
    # No on-demand full-recording fallback: pending backfills show unavailable metrics.
    empty = analyse(
        SimpleNamespace(samples=[], laps=[], sport=activity.sport, distance_m=activity.distance_m)
    )
    return {key: empty[key] for key in ("summary", "terrain", "laps")}


def register_cli(app):
    @app.cli.command("backfill-analysis")
    @click.option("--batch-size", default=25, type=click.IntRange(1, 1000), show_default=True)
    @click.option("--owner-id", type=click.IntRange(1))
    @click.option("--force", is_flag=True)
    def backfill(batch_size, owner_id, force):
        """Backfill summaries, charts and simplified routes in resumable batches."""
        from sqlalchemy.orm import undefer

        from .extensions import db
        from .models import Activity

        maximum = db.session.scalar(db.select(db.func.max(Activity.id))) or 0
        last_id, count = 0, 0
        while last_id < maximum:
            query = db.select(Activity).where(Activity.id > last_id, Activity.id <= maximum)
            if owner_id:
                query = query.where(Activity.owner_id == owner_id)
            if not force:
                query = query.where(Activity.analysis_version != ANALYSIS_VERSION)
            rows = db.session.scalars(
                query.options(undefer(Activity.samples), undefer(Activity.laps))
                .order_by(Activity.id)
                .limit(batch_size)
                .with_for_update()
            ).all()
            if not rows:
                break
            try:
                for row in rows:
                    persist_analysis(row)
                last_id = rows[-1].id
                db.session.commit()
            except Exception as error:
                db.session.rollback()
                raise click.ClickException(
                    "Backfill failed; completed batches are saved. Rerun to resume."
                ) from error
            count += len(rows)
            db.session.expunge_all()
            click.echo(f"Backfilled {count} activities (through ID {last_id}).")
        click.echo(f"Complete: {count} activities backfilled; analysis version {ANALYSIS_VERSION}.")