// Package caption provides a caption rendering interface that prioritises ease of use.
package caption

import (
	"sync"

	"github.com/golang/freetype/truetype"
	"golang.org/x/image/font"
	"golang.org/x/image/font/gofont/goregular"
)

var (
	// package-wide default font
	defaultFont = goregular.TTF
)

// A Context is used for efficient line rendering.
// The zero value is ready to use. Do not copy a non-zero Context.
type Context struct {
	defaultFont     font.Face
	defaultFontErr  error
	defaultFontOnce sync.Once
	defaultFontData []byte
	defaultFontOpts *truetype.Options
}

/*
NewContext initialises Context with a custom default truetype font and returns its address.

Defaults baked into Context will only take effect if both Line.Font and Line.Options are zero.
*/
func NewContext(v []byte, opts *truetype.Options) *Context {
	return &Context{defaultFontData: v, defaultFontOpts: opts}
}

// parseFont is called before using Context.defaultFont.
func (ctx *Context) parseFont() error {
	ctx.defaultFontOnce.Do(func() {
		if len(ctx.defaultFontData) == 0 {
			ctx.defaultFontData = defaultFont
		}
		if f, err := truetype.Parse(ctx.defaultFontData); err != nil {
			ctx.defaultFontErr = err
			return
		} else {
			ctx.defaultFont = truetype.NewFace(f, ctx.defaultFontOpts)
		}
	})
	return ctx.defaultFontErr
}