package main

import (
	"log"
	"time"

	"gioui.org/ui"
	"gioui.org/ui/app"
	"gioui.org/ui/input"
	"gioui.org/ui/layout"
	"gioui.org/ui/measure"
	"gioui.org/ui/text"

	"golang.org/x/image/font/gofont/goregular"
	"golang.org/x/image/font/sfnt"
)

type Context struct {
	w *app.Window
	c *app.Config
	q input.Queue
	ops *ui.Ops
	cs layout.Constraints
	dims layout.Dimens
	faces measure.Faces
	extra map[string]interface{}
}

func NewContext(w *app.Window) Context {
	return Context{
		ops: new(ui.Ops),
		q: w.Queue(),
		extra: make(map[string]interface{}),
	}
}

func (ctx *Context) Reset(e app.DrawEvent) {
	ctx.c = &e.Config
	ctx.ops.Reset()
	ctx.cs = layout.RigidConstraints(e.Size)
	ctx.faces.Reset(ctx.c)
}

func (fw fWidget) Layout(ctx Context) Context {
	return fw.l(ctx)
}

type Widget interface {
	Layout(Context) Context
}

type WidgetCombinator func(...Widget) Widget

type fWidget struct {
	l Layout
}

type Layout func(Context) Context

type LayoutCombinator func(...Layout) Layout

func LayoutWithContext(ctx Context, ls ...Layout) Context {
	for _, l := range ls {
		ctx = l(ctx)
	}
	return ctx
}

type Label struct {
	l *text.Label
}

func (l *Label) Layout(ctx Context) Context {
	ctx.dims = l.l.Layout(ctx.ops, ctx.cs)
	return ctx
}

type Editor struct {
	e *text.Editor
}

func NewEditor(face text.Face, singleline bool) *Editor {
	ret := &Editor{}
	ret.e = &text.Editor{ Face: face, SingleLine: singleline }
	return ret
}

func (e *Editor) Layout(ctx Context) Context {
	ctx.dims = e.e.Layout(ctx.c, ctx.q, ctx.ops, ctx.cs)
	return ctx
}

func main() {
	go func() {
		w := app.NewWindow(nil)
		regular, err := sfnt.Parse(goregular.TTF)
		if err != nil {
			log.Fatal("Cannot parse font.")
		}
		ctx := NewContext(w)
		t := time.NewTicker(time.Second/30)
		e1 := NewEditor(ctx.faces.For(regular, ui.Sp(24)), true)
		e1.e.SetText("hi there")
		e1.e.Focus()

		e2 := NewEditor( ctx.faces.For(regular, ui.Sp(24)), true)
		e2.e.SetText("ok bye")

		f := NewFlex(layout.Vertical, layout.Start, layout.Start)
		ins10a := NewInset(ui.Dp(10),ui.Dp(10),ui.Dp(10),ui.Dp(10))
		ins10b := NewInset(ui.Dp(10),ui.Dp(10),ui.Dp(10),ui.Dp(10))

		btn := &Label{}
		btn.l = &text.Label{
			Face: ctx.faces.For(regular, ui.Sp(24)),
			Text: "centered",
			Alignment: text.Center,
		}

		for {
			select {
			case <-t.C:
				w.Invalidate()
			case e := <-w.Events():
				switch e := e.(type) {
				case app.DestroyEvent:
					return
				case app.DrawEvent:
					ctx.Reset(e)
					LayoutWithContext(ctx,
						ins10a(f(
							e1,
							Flexible(5),
							ins10b(e2),
							Flexible(10),
							btn,
						)).Layout)
					w.Draw(ctx.ops)
				}
			}
		}
	}()
	app.Main()
}

type FlexChild struct {
	x float32
	w Widget
}

func Flexible(v float32) Widget {
	ret := fWidget{}
	ret.l = func(ctx Context) Context {
		ctx.extra["Flexible"] = v
		return ctx
	}
	return ret
}

func NewFlex(axis layout.Axis, mainAxisAlignment layout.MainAxisAlignment, crossAxisAlignment layout.CrossAxisAlignment) WidgetCombinator {
	f := layout.Flex{
		Axis: axis,
		MainAxisAlignment: mainAxisAlignment,
		CrossAxisAlignment: crossAxisAlignment,
	}
	return func(ws ...Widget) Widget {
		ret := fWidget{}
		ret.l = func(ctx Context) Context {
			f.Init(ctx.ops, ctx.cs)
			fcs := make([]layout.FlexChild,len(ws))
			for i, w := range ws {
				if v,ok := ctx.extra["Flexible"]; ok {
					switch v := v.(type) {
					case float32:
						ctx.cs = f.Flexible(v)
					default:
						log.Fatal("Type error")
					}
				} else {
					ctx.cs = f.Rigid()
				}
				ctx = w.Layout(ctx)
				fcs[i] = f.End(ctx.dims)
			}
			ctx.dims = f.Layout(fcs...)
			delete(ctx.extra, "Flexible")
			return ctx
		}
		return ret
	}
}

func NewInset(top, right, bottom, left ui.Value) WidgetCombinator {
	ins := layout.Inset{ Top: top, Right: right, Bottom: bottom, Left: left }
	return func(ws ...Widget) Widget {
		ret := fWidget{}
		ret.l = func(ctx Context) Context {
			ctx.cs = ins.Begin(ctx.c, ctx.ops, ctx.cs)
			var dims layout.Dimens
			for _, w := range ws {
				ctx = w.Layout(ctx)
			}
			ctx.dims = ins.End(dims)
			return ctx
		}
		return ret
	}
}