package cli

import (
	"fmt"
	"math"
	"strings"
	"time"

	"github.com/charmbracelet/lipgloss"
)

// Charts drawn in a terminal the way btop draws them: Braille characters,
// each cell two dots across and four down, so a chart forty cells wide holds
// eighty points and five rows twenty levels. Filled below the line, and
// coloured by height — green low, yellow, red near the top — so how hard
// something is working reads before any number does.

// Braille dot bits by column (0 left, 1 right) and row (0 top .. 3 bottom).
var brailleBit = [2][4]rune{{0x01, 0x02, 0x04, 0x40}, {0x08, 0x10, 0x20, 0x80}}

// gradient is the colour at a fraction of a chart's height, 0 bottom, 1 top.
func gradient(f float64) lipgloss.Color {
	stops := [][3]float64{{80, 200, 120}, {230, 200, 60}, {230, 80, 70}}
	f = math.Max(0, math.Min(1, f))
	seg := f * float64(len(stops)-1)
	i := int(seg)
	if i >= len(stops)-1 {
		i, seg = len(stops)-2, float64(len(stops)-1)
	}
	t := seg - float64(i)
	c := [3]float64{}
	for k := range c {
		c[k] = stops[i][k] + (stops[i+1][k]-stops[i][k])*t
	}
	return lipgloss.Color(fmt.Sprintf("#%02x%02x%02x", int(c[0]), int(c[1]), int(c[2])))
}

// lineColors are the colours of the lines of a chart with several.
var lineColors = []lipgloss.Color{"#61afef", "#e5c07b", "#c678dd", "#56b6c2", "#e06c75", "#98c379", "#d19a66", "#abb2bf"}

// chartSeries is one line: its values, oldest first, and a name for the
// legend. NaN is no sample.
type chartSeries struct {
	name   string
	values []float64
	// at is when each value was sampled, and from and to the window drawn:
	// with them points are placed by time, across the whole width. Without,
	// the values are spread evenly over it.
	at       []time.Time
	from, to time.Time
}

// fit lays a series out in n columns.
func (s chartSeries) fit(n int) []float64 {
	if len(s.at) == len(s.values) && len(s.at) > 0 && s.to.After(s.from) {
		return byTime(s.values, s.at, s.from, s.to, n)
	}
	return resample(s.values, n)
}

// byTime puts each sample in the column of its time; a column with none
// carries the last value on, unless the last is further back than a gap in
// the samples, which is drawn as one. Before the first sample is nothing.
func byTime(vals []float64, at []time.Time, from, to time.Time, n int) []float64 {
	out := make([]float64, n)
	width := to.Sub(from) / time.Duration(n)
	// The spacing the samples were taken at; twice it is a gap.
	gap := width
	if len(at) > 1 {
		gap = max(gap, 2*at[len(at)-1].Sub(at[0])/time.Duration(len(at)-1))
	}
	j := 0
	last, lastAt := math.NaN(), time.Time{}
	for c := range out {
		end := from.Add(time.Duration(c+1) * width)
		sum, k := 0.0, 0
		for ; j < len(vals) && !at[j].After(end); j++ {
			if !math.IsNaN(vals[j]) {
				sum += vals[j]
				k++
				last, lastAt = vals[j], at[j]
			}
		}
		switch {
		case k > 0:
			out[c] = sum / float64(k)
		case !lastAt.IsZero() && end.Sub(lastAt) <= gap:
			out[c] = last
		default:
			out[c] = math.NaN()
		}
	}
	return out
}

// brailleChart draws series into width×height cells. top is the value at the
// top of the chart; 0 takes the largest value. One series is filled and
// coloured by height; several are lines, each its own colour.
func brailleChart(series []chartSeries, width, height int, top float64) []string {
	width, height = max(width, 4), max(height, 1)
	if top <= 0 {
		for _, s := range series {
			for _, v := range s.values {
				if !math.IsNaN(v) && v > top {
					top = v
				}
			}
		}
	}
	if top <= 0 {
		top = 1
	}
	cols, rows := width*2, height*4
	dots := make([][]rune, height)
	owner := make([][]int, height)
	for r := range dots {
		dots[r] = make([]rune, width)
		owner[r] = make([]int, width)
		for c := range owner[r] {
			owner[r][c] = -1
		}
	}
	set := func(x, y, who int) { // y from the bottom
		if x < 0 || x >= cols || y < 0 || y >= rows {
			return
		}
		r := height - 1 - y/4
		dots[r][x/2] |= brailleBit[x%2][3-y%4]
		owner[r][x/2] = who
	}
	area := len(series) == 1
	for si, s := range series {
		vals := s.fit(cols)
		prev := -1
		for x, v := range vals {
			if math.IsNaN(v) {
				prev = -1
				continue
			}
			h := int(math.Round(v / top * float64(rows-1)))
			h = max(0, min(rows-1, h))
			if area {
				for y := 0; y <= h; y++ {
					set(x, y, si)
				}
				continue
			}
			// A line: this point, and the rise or fall from the last.
			lo, hi := h, h
			if prev >= 0 {
				lo, hi = min(prev, h), max(prev, h)
			}
			for y := lo; y <= hi; y++ {
				set(x, y, si)
			}
			prev = h
		}
	}
	out := make([]string, height)
	for r := range dots {
		var b strings.Builder
		for c, d := range dots[r] {
			if owner[r][c] < 0 {
				b.WriteString(" ")
				continue
			}
			color := lineColors[owner[r][c]%len(lineColors)]
			if area {
				color = gradient(float64(height-1-r) / float64(max(1, height-1)))
			}
			b.WriteString(lipgloss.NewStyle().Foreground(color).Render(string(0x2800 + d)))
		}
		out[r] = b.String()
	}
	return out
}

// resample fits values into n points: the most recent n, each the average of
// what falls in it, the left padded with no sample when there are fewer.
func resample(vals []float64, n int) []float64 {
	out := make([]float64, n)
	for i := range out {
		out[i] = math.NaN()
	}
	if len(vals) == 0 {
		return out
	}
	if len(vals) <= n {
		// Fewer values than columns: each held across its share of them,
		// so the series spans the chart rather than huddling at its right.
		for i := range out {
			out[i] = vals[i*len(vals)/n]
		}
		return out
	}
	per := float64(len(vals)) / float64(n)
	for i := range out {
		from, to := int(float64(i)*per), int(float64(i+1)*per)
		sum, k := 0.0, 0
		for _, v := range vals[from:max(to, from+1)] {
			if !math.IsNaN(v) {
				sum += v
				k++
			}
		}
		if k > 0 {
			out[i] = sum / float64(k)
		}
	}
	return out
}

var sparkRunes = []rune("▁▂▃▄▅▆▇█")

// sparkline is values in one row of block characters, coloured by height.
func sparkline(vals []float64, width int, top float64) string {
	return sparkSeries(chartSeries{values: vals}, width, top)
}

// sparkSeries is sparkline for a series that knows its times.
func sparkSeries(s chartSeries, width int, top float64) string {
	vals := s.fit(width)
	if top <= 0 {
		for _, v := range vals {
			if !math.IsNaN(v) && v > top {
				top = v
			}
		}
	}
	if top <= 0 {
		top = 1
	}
	var b strings.Builder
	for _, v := range vals {
		if math.IsNaN(v) {
			b.WriteString(" ")
			continue
		}
		f := math.Max(0, math.Min(1, v/top))
		r := sparkRunes[int(math.Round(f*float64(len(sparkRunes)-1)))]
		b.WriteString(lipgloss.NewStyle().Foreground(gradient(f)).Render(string(r)))
	}
	return b.String()
}

// meter is a fraction as a bar of width cells, btop's ■, coloured by level.
func meter(f float64, width int) string {
	f = math.Max(0, math.Min(1, f))
	n := int(math.Round(f * float64(width)))
	var b strings.Builder
	for i := 0; i < width; i++ {
		if i < n {
			b.WriteString(lipgloss.NewStyle().Foreground(gradient(float64(i) / float64(max(1, width-1)))).Render("■"))
		} else {
			b.WriteString(sDim.Render("■"))
		}
	}
	return b.String()
}

// chartBox is a chart with its title and current value above it, and the
// window's span below: what a panel of the monitor shows.
func chartBox(title, now string, series []chartSeries, width, height int, top float64, span string) string {
	var b strings.Builder
	head := mdBold.Render(title)
	if now != "" {
		head += "  " + now
	}
	if len(series) > 1 {
		var leg []string
		for i, s := range series {
			if i == 6 {
				leg = append(leg, sDim.Render(fmt.Sprintf("+%d", len(series)-6)))
				break
			}
			leg = append(leg, lipgloss.NewStyle().Foreground(lineColors[i%len(lineColors)]).Render("━ ")+truncate(s.name, 18))
		}
		head += "  " + strings.Join(leg, " ")
	}
	b.WriteString(truncateWidth(head, width) + "\n")
	for _, l := range brailleChart(series, width, height, top) {
		b.WriteString(l + "\n")
	}
	left, right := "-"+span, "now"
	gap := max(1, width-len(left)-len(right))
	b.WriteString(sDim.Render(left + strings.Repeat("─", gap) + right))
	return b.String()
}