package web

import (
	"context"
	"log/slog"
	"time"

	"gitea.mynodes.xyz/ilker/llmgw/internal/promq"
)

// History reads the cluster's past out of a metrics store.
type History interface {
	RangeQuery(ctx context.Context, expr, nameBy string, window, step time.Duration) ([]promq.Series, error)
}

// FleetCharts are the operational panels: what the cluster is doing, rather
// than what it has been billed for.
//
// The usage charts already on this page come from llmgw's own store and answer
// a different question — who spent what. These answer whether the thing is
// healthy, and they need history llmgw does not keep.
type FleetCharts struct {
	Saturation TimeSeries
	Queue      TimeSeries
	KV         TimeSeries
	Ready      TimeSeries
	// GPUBusy and GPUMemory are the fleet's cards by class, for a fleet that
	// has them.
	GPUBusy, GPUMemory TimeSeries
	Window             string
	// Err is set when the metrics store could not be read. Shown as a line of
	// text where the charts would be: an empty panel reads as a healthy cluster
	// with nothing happening, which is the opposite of not knowing. The
	// error is the metrics store's own, in English.
	Err string

	// lang is the page's language, which the charts added later are drawn in.
	lang *Lang
}

// fleetPanel is one chart and the query behind it.
var fleetPanels = []struct {
	name   string
	expr   string
	nameBy string
	unit   string
	into   func(*FleetCharts, TimeSeries)
}{
	{
		"saturation", "llmgw_pool_saturation", "model", "",
		func(f *FleetCharts, t TimeSeries) { f.Saturation = t },
	},
	{
		"queue depth", "llmgw_endpoint_waiting", "replica", "",
		func(f *FleetCharts, t TimeSeries) { f.Queue = t },
	},
	{
		"kv cache", "llmgw_endpoint_kv_cache_usage", "replica", "%",
		func(f *FleetCharts, t TimeSeries) { f.KV = t },
	},
	{
		"replicas ready", "llmgw_model_replicas_ready", "model", "",
		func(f *FleetCharts, t TimeSeries) { f.Ready = t },
	},
}

// LoadFleetCharts queries each panel and renders it.
//
// One failure fails them all, deliberately: four panels where three are drawn
// and one is blank invites reading the blank one as "nothing is happening
// there". Either the metrics store answered or it did not.
func LoadFleetCharts(ctx context.Context, h History, window time.Duration,
	log *slog.Logger,
) *FleetCharts {
	return english.loadFleetCharts(ctx, h, window, log)
}

// loadFleetCharts is LoadFleetCharts drawn in this language.
func (l *Lang) loadFleetCharts(ctx context.Context, h History, window time.Duration,
	log *slog.Logger,
) *FleetCharts {
	if h == nil {
		return nil
	}
	if window <= 0 {
		window = time.Hour
	}
	// Sixty points across the window. More is detail nobody can see at this
	// size and a bigger response to parse on every page load.
	step := window / 60

	out := &FleetCharts{Window: l.windowWord(window), lang: l}
	for _, p := range fleetPanels {
		series, err := h.RangeQuery(ctx, p.expr, p.nameBy, window, step)
		if err != nil {
			if log != nil {
				log.Warn("could not read history for the dashboard",
					"panel", p.name, "err", err)
			}
			out.Err = err.Error()
			return out
		}
		p.into(out, l.LineChart(series, p.unit, 4))
	}
	return out
}

// windowWord names a chart window the way a sentence in this language
// would: "last hour", "son 6 saat". A window that is not whole minutes is
// written as Go writes it, which is rare enough not to be worth words.
func (l *Lang) windowWord(d time.Duration) string {
	switch {
	case d == time.Hour:
		return l.T("chart.window.hour")
	case d%time.Hour == 0:
		return l.N("chart.window.hours", int64(d.Hours()))
	case d%time.Minute == 0:
		return l.N("chart.window.minutes", int64(d.Minutes()))
	}
	return d.String()
}

// LoadGPU adds the fleet's GPUs, by class: how busy on average, and how full
// their memory. Asked only of a fleet with GPUs. A failure leaves these two
// empty and the rest of the page as it was; they are not what the other
// panels' all-or-nothing is about.
func (f *FleetCharts) LoadGPU(ctx context.Context, h History, window time.Duration) {
	if f == nil || h == nil || f.Err != "" {
		return
	}
	if window <= 0 {
		window = time.Hour
	}
	step := window / 60
	l := f.lang
	if l == nil {
		l = english
	}
	if s, err := h.RangeQuery(ctx, `avg by (class) (llmgw_gpu_utilization_percent) / 100`, "class", window, step); err == nil {
		f.GPUBusy = l.LineChart(s, "%", 6)
	}
	if s, err := h.RangeQuery(ctx,
		`sum by (class) (llmgw_gpu_memory_used_bytes) / sum by (class) (llmgw_gpu_memory_total_bytes)`,
		"class", window, step); err == nil {
		f.GPUMemory = l.LineChart(s, "%", 6)
	}
}