// Package chart renders ```chart data blocks into PNG assets using the
// permissive go-chart library (pure Go). v0 proves one chart type end to
// end: bar.
package chart

import (
	"bytes"
	"fmt"

	"github.com/wcharczuk/go-chart/v2"
	"github.com/wcharczuk/go-chart/v2/drawing"

	"ukrrs.com/mopac/pdf/internal/markdown"
)

// accent matches the shipped templates (#1f4e79).
var accent = drawing.Color{R: 31, G: 78, B: 121, A: 255}

// Bar renders a bar chart to PNG bytes. Unknown chart types are an error:
// v0 is deliberately one type, proven end to end.
func Bar(c *markdown.Chart) ([]byte, error) {
	if c == nil || len(c.Labels) == 0 {
		return nil, fmt.Errorf("chart: no data points")
	}
	if c.Type != "bar" {
		return nil, fmt.Errorf("chart: unsupported type %q (v0: bar only)", c.Type)
	}
	values := make([]chart.Value, len(c.Labels))
	for i, label := range c.Labels {
		values[i] = chart.Value{
			Value: c.Values[i],
			Label: label,
			Style: chart.Style{FillColor: accent, StrokeColor: accent, StrokeWidth: 0.5},
		}
	}
	yfmt := chart.ValueFormatter(chart.FloatValueFormatter)
	if c.Unit != "" {
		unit := c.Unit
		yfmt = func(v interface{}) string {
			return chart.FloatValueFormatter(v) + " " + unit
		}
	}
	graph := chart.BarChart{
		Title: c.Title,
		Background: chart.Style{
			Padding: chart.Box{Top: 24, Left: 12, Right: 12, Bottom: 8},
		},
		XAxis:      chart.Style{FontSize: 9, FontColor: drawing.Color{R: 60, G: 60, B: 60, A: 255}},
		YAxis:      chart.YAxis{ValueFormatter: yfmt, Style: chart.Style{FontSize: 8}},
		BarWidth:   48,
		BarSpacing: 26,
		Height:     320,
		Width:      260 + len(values)*74,
		Bars:       values,
	}
	var buf bytes.Buffer
	if err := graph.Render(chart.PNG, &buf); err != nil {
		return nil, fmt.Errorf("chart: render: %w", err)
	}
	return buf.Bytes(), nil
}