// The metrics under one alert: a line chart of the expression that fired it, and
// what that expression reads right now. The data comes from this server, which
// asked the alert's own Prometheus (see GET /api/incidents/{id}/metrics); the
// browser never talks to Prometheus.

import { h } from './ui.js';
import { when } from './format.js';

const SVG_NS = 'http://www.w3.org/2000/svg';
const MAX_SERIES = 5;

function svg(tag, attrs = {}, text) {
  const el = document.createElementNS(SVG_NS, tag);
  for (const [k, v] of Object.entries(attrs)) el.setAttribute(k, String(v));
  if (text != null) el.textContent = text;
  return el;
}

const iso = (sec) => new Date(sec * 1000).toISOString();

// Compact number for an axis or a badge: 1.2k, 0.034, 12.
export function fmtValue(v) {
  if (v == null || Number.isNaN(v)) return '–';
  const a = Math.abs(v);
  if (a >= 1e9) return `${+(v / 1e9).toPrecision(3)}G`;
  if (a >= 1e6) return `${+(v / 1e6).toPrecision(3)}M`;
  if (a >= 1e4) return `${+(v / 1e3).toPrecision(3)}k`;
  if (a === 0) return '0';
  if (a >= 100) return String(Math.round(v));
  return String(+v.toPrecision(3));
}

const keyOf = (labels) => JSON.stringify(Object.entries(labels || {}).sort());

// seriesName is the labels that tell the series apart, e.g. {instance="web-1"}.
function seriesName(labels) {
  const parts = Object.entries(labels || {}).filter(([k]) => k !== '__name__').map(([k, v]) => `${k}="${v}"`);
  return parts.length ? `{${parts.join(', ')}}` : 'value';
}

// merge combines the snapshot taken when the incident opened with the live
// window, so the chart keeps history Prometheus may since have dropped. On the
// same timestamp the later source wins.
function merge(...sources) {
  const byKey = new Map();
  for (const src of sources) {
    for (const s of src || []) {
      const k = keyOf(s.labels);
      const cur = byKey.get(k) || { labels: s.labels, points: new Map() };
      for (const [t, v] of s.points || []) cur.points.set(t, v);
      byKey.set(k, cur);
    }
  }
  return [...byKey.values()].map((s) => ({
    labels: s.labels,
    points: [...s.points.entries()].sort((a, b) => a[0] - b[0]),
  }));
}

function parseSeries(raw) {
  if (Array.isArray(raw)) return raw;
  return [];
}

// pick chooses what to draw: while the incident is open, the opened snapshot
// plus live data; once it is closed, the closed snapshot (the whole incident),
// falling back to the opened one.
function pick(entry) {
  const snaps = entry.snapshots || {};
  const live = entry.live;
  if (live && !live.error) {
    return {
      series: merge(parseSeries(snaps.opened && snaps.opened.series), live.series),
      from: Math.min(live.window_start, snaps.opened ? snaps.opened.window_start : Infinity),
      to: live.window_end,
      current: live.current || [],
      isLive: true,
    };
  }
  const snap = snaps.closed || snaps.opened;
  if (snap && !snap.error) {
    return {
      series: merge(parseSeries(snap.series)), from: snap.window_start, to: snap.window_end, current: [], isLive: false,
    };
  }
  return null;
}

// alertMetrics renders the metrics block for one alert, or null when there is
// nothing worth saying (the feature off, or no Prometheus link on the alert).
export function alertMetrics(entry, startsAtISO, resolvedISO) {
  if (!entry) return null;
  if (!entry.available) {
    return entry.reason && entry.expr
      ? h('div', { class: 'metrics-note', text: `Metrics unavailable: ${entry.reason}.` })
      : null;
  }
  const data = pick(entry);
  if (!data) {
    const err = (entry.live && entry.live.error)
      || (entry.snapshots && ((entry.snapshots.closed && entry.snapshots.closed.error) || (entry.snapshots.opened && entry.snapshots.opened.error)));
    return h('div', { class: 'metrics-note', text: err ? `Metrics could not be fetched: ${err}` : 'Metrics are being collected…' });
  }
  const startSec = startsAtISO ? Date.parse(startsAtISO) / 1000 : null;
  const endSec = resolvedISO ? Date.parse(resolvedISO) / 1000 : null;
  return h('div', { class: 'metrics' },
    currentLine(entry, data),
    data.series.length ? chart(data, startSec, endSec) : h('div', { class: 'metrics-note', text: 'No samples in this window.' }),
    legend(data.series),
    entry.expr && h('code', { class: 'metrics-expr', text: entry.expr }),
  );
}

function currentLine(entry, data) {
  if (!data.isLive) return null;
  const vals = data.current.map((s) => s.points && s.points[0] && s.points[0][1]).filter((v) => v != null);
  if (!vals.length) {
    return h('div', { class: 'metrics-now none' },
      h('span', { class: 'metrics-now-label', text: 'Now' }),
      h('span', { text: 'no data — the alert condition no longer holds' }));
  }
  return h('div', { class: 'metrics-now' },
    h('span', { class: 'metrics-now-label', text: 'Now' }),
    h('strong', { text: vals.length === 1 ? fmtValue(vals[0]) : vals.map(fmtValue).join(' · ') }));
}

function legend(series) {
  if (series.length < 2 && !(series[0] && Object.keys(series[0].labels || {}).length)) return null;
  return h('ul', { class: 'metrics-legend' }, series.slice(0, MAX_SERIES).map((s, i) =>
    h('li', {}, h('span', { class: `mc-swatch s${i}` }), h('span', { text: seriesName(s.labels) }))));
}

function chart(data, startSec, endSec) {
  const W = 480;
  const H = 130;
  const padL = 40;
  const padR = 8;
  const padT = 8;
  const padB = 18;
  const series = data.series.slice(0, MAX_SERIES);

  let t0 = Infinity; let t1 = -Infinity; let lo = Infinity; let hi = -Infinity;
  for (const s of series) {
    for (const [t, v] of s.points) {
      if (t < t0) t0 = t;
      if (t > t1) t1 = t;
      if (v < lo) lo = v;
      if (v > hi) hi = v;
    }
  }
  if (!Number.isFinite(t0)) { t0 = data.from; t1 = data.to; lo = 0; hi = 1; }
  // Show the whole window, not just where there are samples, so the shape of
  // "it only exists while firing" is visible.
  t0 = Math.min(t0, data.from);
  t1 = Math.max(t1, data.to);
  if (t1 === t0) t1 = t0 + 1;
  if (lo === hi) { lo -= 1; hi += 1; }
  if (lo > 0 && lo < (hi - lo) * 0.5) lo = 0;

  const x = (t) => padL + ((t - t0) / (t1 - t0)) * (W - padL - padR);
  const y = (v) => padT + (1 - (v - lo) / (hi - lo)) * (H - padT - padB);

  const root = svg('svg', {
    class: 'metric-chart', viewBox: `0 0 ${W} ${H}`, role: 'img',
    'aria-label': `Metric over time, ${fmtValue(lo)} to ${fmtValue(hi)}, from ${when(iso(t0))} to ${when(iso(t1))}`,
  });
  // Gridlines and y labels at the extremes and the middle.
  for (const v of [lo, (lo + hi) / 2, hi]) {
    root.appendChild(svg('line', { class: 'mc-grid', x1: padL, x2: W - padR, y1: y(v), y2: y(v) }));
    root.appendChild(svg('text', { class: 'mc-label', x: padL - 4, y: y(v) + 3, 'text-anchor': 'end' }, fmtValue(v)));
  }
  root.appendChild(svg('text', { class: 'mc-label', x: padL, y: H - 4, 'text-anchor': 'start' }, when(iso(t0))));
  root.appendChild(svg('text', { class: 'mc-label', x: W - padR, y: H - 4, 'text-anchor': 'end' }, when(iso(t1))));

  const marker = (t, cls, text) => {
    if (t == null || t < t0 || t > t1) return;
    const m = svg('line', { class: `mc-marker ${cls}`, x1: x(t), x2: x(t), y1: padT, y2: H - padB });
    m.appendChild(svg('title', {}, `${text} ${when(iso(t))}`));
    root.appendChild(m);
  };
  marker(startSec, 'start', 'Alert started');
  marker(endSec, 'end', 'Incident resolved');

  series.forEach((s, i) => {
    if (!s.points.length) return;
    const d = s.points.map(([t, v], n) => `${n ? 'L' : 'M'}${x(t).toFixed(1)},${y(v).toFixed(1)}`).join(' ');
    const line = svg('path', { class: `mc-line s${i}`, d });
    line.appendChild(svg('title', {}, `${seriesName(s.labels)}: ${fmtValue(s.points[s.points.length - 1][1])} at ${when(iso(s.points[s.points.length - 1][0]))}`));
    root.appendChild(line);
    // A single sample has no line to draw; show it as a dot.
    if (s.points.length === 1) {
      root.appendChild(svg('circle', { class: `mc-dot s${i}`, cx: x(s.points[0][0]), cy: y(s.points[0][1]), r: 3 }));
    }
  });
  return root;
}