package main

import (
	"io/ioutil"
	"os"
	"path/filepath"

	"github.com/gdamore/tcell"
	"github.com/rivo/tview"
)

func main() {
	//Define the Application
	app := tview.NewApplication()

	//Define the Grid
	grid := tview.NewGrid().
		SetRows(2, 0, 2).
		SetColumns(20, 0, 20).
		SetBorders(true).
		AddItem(newPrimitive("File Viewer"), 0, 0, 1, 2, 0, 0, false)

	//Define Content
	main := newText()

	//Define FileTree
	TreePrimitive := func() (tview.Primitive, tview.Primitive) {
		text, tree := getFileNode(main, getFileTree())
		tree.SetAlign(false).SetGraphics(true)
		return text, tree
	}
	content, tree := TreePrimitive()

	// Layout for screens narrower than 100 cells (menu and side bar are hidden).
	grid.AddItem(tree, 0, 0, 0, 0, 0, 0, false).
		AddItem(content, 1, 0, 1, 3, 0, 0, false)

	// Layout for screens wider than 100 cells.
	grid.AddItem(tree, 1, 0, 1, 1, 0, 100, false).
		AddItem(content, 1, 1, 1, 1, 0, 100, false)

	app = app.SetRoot(grid, true)
	app = app.SetFocus(tree)

	if err := app.Run(); err != nil {
		panic(err)
	}
}

func getFileNode(text *tview.TextView, tree *tview.TreeView) (*tview.TextView, *tview.TreeView) {
	// If a directory was selected, open it.
	tree.SetSelectedFunc(func(node *tview.TreeNode) {
		reference := node.GetReference()
		if reference == nil {
			return // Selecting the root node does nothing.
		}
		path := reference.(string)
		file, err := os.Open(path)
		children := node.GetChildren()
		if err != nil {
			return
		}
		info, err := file.Stat()
		if err != nil {
			return
		}
		mode := info.Mode()
		if mode.IsDir() {
			if len(children) == 0 {
				// Load and show files in this directory.
				add(node, path)
			} else {
				// Collapse if visible, expand if collapsed.
				node.SetExpanded(!node.IsExpanded())
			}
		} else {
			switch filepath.Ext(path) {
			default:
				text = text.Clear()
				b, err := ioutil.ReadAll(file)
				if err != nil {
					return
				}
				_, err = text.Write(b)
				if err != nil {
					return
				}
			}
		}
	})
	return text, tree
}

func getFileTree() *tview.TreeView {
	rootDir := "."
	root := tview.NewTreeNode(rootDir).
		SetColor(tcell.ColorRed)
	tree := tview.NewTreeView().
		SetRoot(root).
		SetCurrentNode(root)

	add(root, rootDir)
	return tree

}

func add(target *tview.TreeNode, path string) {
	files, err := ioutil.ReadDir(path)
	if err != nil {
		panic(err)
	}
	for _, file := range files {
		node := tview.NewTreeNode(file.Name()).
			SetReference(filepath.Join(path, file.Name())).
			SetSelectable(true)
		if file.IsDir() {
			node.SetColor(tcell.ColorGreen)
		}
		target.AddChild(node)
	}
}

func newPrimitive(text string) tview.Primitive {
	return tview.NewTextView().SetTextAlign(tview.AlignCenter).SetText(text)
}

func newText() *tview.TextView {
	return tview.NewTextView().SetTextAlign(tview.AlignLeft)
}