package render

import (
	"encoding/xml"
	"fmt"
	"math"
	"strings"
	"time"

	"github.com/lukaszkasprzak/prognosis/internal/config"
	"github.com/lukaszkasprzak/prognosis/internal/i18n"
	"github.com/lukaszkasprzak/prognosis/internal/openmeteo"
)

// SVGFields are the hourly fields a meteogram needs, whatever columns the table
// happens to show. Requested in addition to the table's own fields.
var SVGFields = []string{
	"temperature_2m", "apparent_temperature", "precipitation",
	"precipitation_probability", "relative_humidity_2m", "wind_speed_10m",
}

// Layout constants, in user units (which are CSS pixels at 1:1).
const (
	svgMarginLeft   = 52
	svgMarginRight  = 44
	svgMarginTop    = 64
	svgMarginBottom = 34
	svgPanelGap     = 24
	svgHourWidth    = 26 // per hour, before clamping
	svgMinWidth     = 640
	svgMaxWidth     = 1800
)

// panel is one stacked chart sharing the figure's time axis.
type panel struct {
	title  string
	height int
	draw   func(b *strings.Builder, p panelBox)
}

// panelBox is a panel's rectangle on the canvas.
type panelBox struct {
	x, y, w, h int
}

// SVG renders the forecast as a standalone meteogram.
//
// Written directly rather than through a plotting library or gnuplot: SVG is
// markup, so this keeps prognosis dependency-free and works identically on a
// machine that has no plotting tools at all -- the phone, for instance.
func SVG(v View, cfg config.Config) string {
	rows := v.Rows
	if len(rows) == 0 {
		return ""
	}
	cat := i18n.For(cfg.DisplayLang)

	width := len(rows) * svgHourWidth
	if width < svgMinWidth {
		width = svgMinWidth
	}
	if width > svgMaxWidth {
		width = svgMaxWidth
	}
	plotW := width - svgMarginLeft - svgMarginRight

	series := func(field string) []float64 {
		out := make([]float64, len(rows))
		for i, r := range rows {
			out[i], _ = r.Val(field)
		}
		return out
	}
	temp := series("temperature_2m")
	feels := series("apparent_temperature")
	rain := series("precipitation")
	prob := series("precipitation_probability")
	hum := series("relative_humidity_2m")

	panels := []panel{
		{title: cat.Header("temp") + " °", height: 170, draw: func(b *strings.Builder, p panelBox) {
			plo, phi := paddedRange(append(append([]float64{}, temp...), feels...))
			lo, hi, lines := niceTicks(plo, phi, 6)
			svgGrid(b, p, lo, hi, lines, "%.0f")
			svgLine(b, p, feels, lo, hi, "#c98", 1.5, true)
			svgLine(b, p, temp, lo, hi, "#c33", 2.2, false)
			svgLegend(b, p, cat.Header("temp"), cat.Header("feels"))
		}},
		{title: cat.Header("mm") + " (" + cat.Header("rain") + " %)", height: 104, draw: func(b *strings.Builder, p panelBox) {
			hiRain := maxOf(rain)
			if hiRain < 1 {
				hiRain = 1 // an empty panel still needs a sane scale
			}
			svgGrid(b, p, 0, hiRain, 3, "%.1f")
			// Two units share this panel, so the probability gets its own axis
			// on the right. Without it the dashed line reads against millimetres.
			svgRightAxis(b, p, 0, 100, 3, "%.0f%%", "#69b")
			svgBars(b, p, rain, 0, hiRain, "#39c")
			svgLine(b, p, prob, 0, 100, "#69b", 1.2, true)
		}},
		{title: cat.Header("humidity") + " %", height: 104, draw: func(b *strings.Builder, p panelBox) {
			svgGrid(b, p, 0, 100, 3, "%.0f")
			svgLine(b, p, hum, 0, 100, "#4a7", 1.8, false)
		}},
	}

	height := svgMarginTop + svgMarginBottom
	for i, p := range panels {
		height += p.height
		if i > 0 {
			height += svgPanelGap
		}
	}

	var b strings.Builder
	fmt.Fprintf(&b, `<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="%d" `+
		`viewBox="0 0 %d %d" font-family="DejaVu Sans, Helvetica, sans-serif" font-size="11">`+"\n",
		width, height, width, height)
	fmt.Fprintf(&b, `<rect width="%d" height="%d" fill="#ffffff"/>`+"\n", width, height)

	title := fmt.Sprintf("%s   %s", v.Label, cat.Date(rows[0].When))
	fmt.Fprintf(&b, `<text x="%d" y="26" font-size="15" fill="#222">%s</text>`+"\n",
		svgMarginLeft, escape(title))
	if sun, ok := v.Sun[rows[0].When.Format("2006-01-02")]; ok {
		fmt.Fprintf(&b, `<text x="%d" y="43" fill="#777">%s %s  %s %s</text>`+"\n",
			svgMarginLeft, escape(sun[0]), escape(cat.Word("up")),
			escape(sun[1]), escape(cat.Word("down")))
	}

	y := svgMarginTop
	for i, p := range panels {
		box := panelBox{x: svgMarginLeft, y: y, w: plotW, h: p.height}
		svgNightBands(&b, box, rows, v.Sun)
		svgTimeGrid(&b, box, rows)
		p.draw(&b, box)
		fmt.Fprintf(&b, `<rect x="%d" y="%d" width="%d" height="%d" fill="none" stroke="#bbb"/>`+"\n",
			box.x, box.y, box.w, box.h)
		fmt.Fprintf(&b, `<text x="%d" y="%d" fill="#555">%s</text>`+"\n",
			box.x+4, box.y-4, escape(p.title))
		if i == len(panels)-1 {
			svgTimeAxis(&b, box, rows)
		}
		y += p.height + svgPanelGap
	}

	b.WriteString("</svg>\n")
	return b.String()
}

// svgNightBands shades the hours between sunset and sunrise, which is what makes
// a meteogram readable at a glance.
func svgNightBands(b *strings.Builder, p panelBox, rows []openmeteo.Row, sun map[string][2]string) {
	start := -1
	for i, r := range rows {
		night := isNight(r.When, sun)
		if night && start < 0 {
			start = i
		}
		if (!night || i == len(rows)-1) && start >= 0 {
			end := i
			if night {
				end = i + 1
			}
			x0 := xAt(p, start, len(rows))
			x1 := xAt(p, end, len(rows))
			fmt.Fprintf(b, `<rect x="%.1f" y="%d" width="%.1f" height="%d" fill="#eef1f6"/>`+"\n",
				x0, p.y, math.Max(x1-x0, 1), p.h)
			start = -1
		}
	}
}

// isNight reports whether an hour falls outside that date's sunrise..sunset.
// Without sun data it reports false: no shading beats wrong shading.
func isNight(t time.Time, sun map[string][2]string) bool {
	s, ok := sun[t.Format("2006-01-02")]
	if !ok {
		return false
	}
	rise, err1 := time.Parse("15:04", s[0])
	set, err2 := time.Parse("15:04", s[1])
	if err1 != nil || err2 != nil {
		return false
	}
	mins := t.Hour()*60 + t.Minute()
	return mins < rise.Hour()*60+rise.Minute() || mins >= set.Hour()*60+set.Minute()
}

// svgTimeGrid draws a faint line per labelled hour and a stronger one at each
// midnight, so a value can be traced back to a time without counting squares.
func svgTimeGrid(b *strings.Builder, p panelBox, rows []openmeteo.Row) {
	every := hourStep(len(rows))
	for i, r := range rows {
		midnight := r.When.Hour() == 0
		if !midnight && i%every != 0 {
			continue
		}
		x := xAt(p, i, len(rows)-1)
		stroke, w := "#eeeeee", 1.0
		if midnight {
			stroke, w = "#9aa3ad", 1.4
		}
		fmt.Fprintf(b, `<line x1="%.1f" y1="%d" x2="%.1f" y2="%d" stroke="%s" stroke-width="%.1f"/>`+"\n",
			x, p.y, x, p.y+p.h, stroke, w)
	}
}

// hourStep is how often the time axis is labelled, kept in one place so the
// grid and the labels cannot disagree.
func hourStep(n int) int { return 1 + n/16 }

func svgGrid(b *strings.Builder, p panelBox, lo, hi float64, lines int, format string) {
	for i := 0; i < lines; i++ {
		frac := float64(i) / float64(lines-1)
		y := float64(p.y+p.h) - frac*float64(p.h)
		value := lo + (hi-lo)*frac
		fmt.Fprintf(b, `<line x1="%d" y1="%.1f" x2="%d" y2="%.1f" stroke="#e4e4e4"/>`+"\n",
			p.x, y, p.x+p.w, y)
		fmt.Fprintf(b, `<text x="%d" y="%.1f" text-anchor="end" fill="#888">%s</text>`+"\n",
			p.x-6, y+3.5, escape(fmt.Sprintf(format, value)))
	}
}

func svgLine(b *strings.Builder, p panelBox, vals []float64, lo, hi float64, colour string, w float64, dashed bool) {
	if len(vals) == 0 {
		return
	}
	var pts []string
	for i, v := range vals {
		pts = append(pts, fmt.Sprintf("%.1f,%.1f", xAt(p, i, len(vals)-1), yAt(p, v, lo, hi)))
	}
	dash := ""
	if dashed {
		dash = ` stroke-dasharray="4 3"`
	}
	fmt.Fprintf(b, `<polyline points="%s" fill="none" stroke="%s" stroke-width="%.1f" `+
		`stroke-linejoin="round"%s/>`+"\n", strings.Join(pts, " "), colour, w, dash)
}

func svgBars(b *strings.Builder, p panelBox, vals []float64, lo, hi float64, colour string) {
	if len(vals) < 2 {
		return
	}
	bw := float64(p.w) / float64(len(vals)) * 0.7
	for i, v := range vals {
		if v <= 0 {
			continue
		}
		y := yAt(p, v, lo, hi)
		x := xAt(p, i, len(vals)-1) - bw/2
		fmt.Fprintf(b, `<rect x="%.1f" y="%.1f" width="%.1f" height="%.1f" fill="%s" opacity="0.75"/>`+"\n",
			x, y, bw, float64(p.y+p.h)-y, colour)
	}
}

// svgTimeAxis labels the hours, with dates in bold at midnight.
//
// A date label is wider than an hour, so any hour that would land under one is
// dropped: otherwise "23" and "28.08" render on top of each other as "2328.08".
func svgTimeAxis(b *strings.Builder, p panelBox, rows []openmeteo.Row) {
	const collision = 22.0 // user units either side of a date label

	var dateX []float64
	for i, r := range rows {
		if r.When.Hour() == 0 {
			dateX = append(dateX, xAt(p, i, len(rows)-1))
		}
	}
	near := func(x float64) bool {
		for _, dx := range dateX {
			if math.Abs(x-dx) < collision {
				return true
			}
		}
		return false
	}

	every := hourStep(len(rows))
	for i, r := range rows {
		x := xAt(p, i, len(rows)-1)
		switch {
		case r.When.Hour() == 0:
			fmt.Fprintf(b, `<text x="%.1f" y="%d" text-anchor="middle" font-weight="bold" fill="#222">%s</text>`+"\n",
				x, p.y+p.h+16, escape(r.When.Format("02.01")))
		case i%every == 0 && !near(x):
			fmt.Fprintf(b, `<text x="%.1f" y="%d" text-anchor="middle" fill="#666">%s</text>`+"\n",
				x, p.y+p.h+16, escape(r.When.Format("15")))
		}
	}
}

// svgLegend names the two temperature series, since a dashed line is not
// self-explanatory.
func svgLegend(b *strings.Builder, p panelBox, solid, dashed string) {
	x := float64(p.x+p.w) - 150
	y := float64(p.y) + 14
	fmt.Fprintf(b, `<rect x="%.1f" y="%.1f" width="146" height="18" fill="#ffffff" opacity="0.82"/>`+"\n",
		x-6, y-12)
	fmt.Fprintf(b, `<line x1="%.1f" y1="%.1f" x2="%.1f" y2="%.1f" stroke="#c33" stroke-width="2.2"/>`+"\n",
		x, y-4, x+18, y-4)
	fmt.Fprintf(b, `<text x="%.1f" y="%.1f" fill="#555">%s</text>`+"\n", x+23, y, escape(solid))
	x2 := x + 23 + float64(len(solid))*6 + 12
	fmt.Fprintf(b, `<line x1="%.1f" y1="%.1f" x2="%.1f" y2="%.1f" stroke="#c98" stroke-width="1.5" stroke-dasharray="4 3"/>`+"\n",
		x2, y-4, x2+18, y-4)
	fmt.Fprintf(b, `<text x="%.1f" y="%.1f" fill="#555">%s</text>`+"\n", x2+23, y, escape(dashed))
}

func xAt(p panelBox, i, n int) float64 {
	if n <= 0 {
		return float64(p.x)
	}
	return float64(p.x) + float64(i)/float64(n)*float64(p.w)
}

func yAt(p panelBox, v, lo, hi float64) float64 {
	if hi-lo < 1e-9 {
		return float64(p.y + p.h/2)
	}
	frac := (v - lo) / (hi - lo)
	frac = math.Max(0, math.Min(1, frac))
	return float64(p.y+p.h) - frac*float64(p.h)
}

// svgRightAxis labels the right-hand edge, for a panel carrying a second unit.
func svgRightAxis(b *strings.Builder, p panelBox, lo, hi float64, lines int, format, colour string) {
	for i := 0; i < lines; i++ {
		frac := float64(i) / float64(lines-1)
		y := float64(p.y+p.h) - frac*float64(p.h)
		fmt.Fprintf(b, `<text x="%d" y="%.1f" fill="%s">%s</text>`+"\n",
			p.x+p.w+6, y+3.5, colour, escape(fmt.Sprintf(format, lo+(hi-lo)*frac)))
	}
}

// niceTicks snaps a range to round numbers and returns how many gridlines that
// implies, so every label lands on a multiple of the step. Snapping the ends
// alone is not enough: with a fixed number of lines the values between them
// still come out as 12.5 and 27.5.
func niceTicks(lo, hi float64, maxLines int) (float64, float64, int) {
	span := hi - lo
	if span <= 0 {
		return lo, lo + 1, 2
	}
	step := math.Pow(10, math.Floor(math.Log10(span/float64(maxLines-1))))
	for _, m := range []float64{1, 2, 2.5, 5, 10} {
		if span/(step*m) <= float64(maxLines-1) {
			step *= m
			break
		}
	}
	lo = math.Floor(lo/step) * step
	hi = math.Ceil(hi/step) * step
	return lo, hi, int(math.Round((hi-lo)/step)) + 1
}

// paddedRange leaves a margin above and below so a curve never touches the frame.
func paddedRange(vals []float64) (float64, float64) {
	if len(vals) == 0 {
		return 0, 1
	}
	lo, hi := vals[0], vals[0]
	for _, v := range vals {
		lo, hi = math.Min(lo, v), math.Max(hi, v)
	}
	pad := math.Max((hi-lo)*0.15, 0.5)
	return lo - pad, hi + pad
}

func maxOf(vals []float64) float64 {
	m := 0.0
	for _, v := range vals {
		m = math.Max(m, v)
	}
	return m
}

// escape makes text safe for XML. A place name is user input and can contain &.
func escape(s string) string {
	var b strings.Builder
	xml.EscapeText(&b, []byte(s))
	return b.String()
}