package server

import (
	"github.com/gomarkdown/markdown/ast"
	"strings"
	"fmt"
)

type Heading struct {
	Id string
	Level int
	Text string
}

func getDocumentHeadings(doc ast.Node) []Heading {
	ret := []Heading{}
	ast.WalkFunc(doc, func(node ast.Node, entering bool) ast.WalkStatus {
		heading, ok := node.(*ast.Heading)
		if !ok {
			return ast.GoToNext
		}
		children := node.GetChildren()
		if len(children) > 0 && !entering {
			leaf := children[0].AsLeaf()
			if leaf == nil {
				return ast.GoToNext
			}
			ret = append(ret, Heading{
				Id: heading.HeadingID,
				Level: heading.Level,
				Text: string(leaf.Literal),
			})
			return ast.SkipChildren
		}

		return ast.GoToNext
	})
	return ret
}

type HeadingTree struct {
	Heading Heading
	Children HeadingTrees
}

type HeadingTrees []*HeadingTree

func makeHeadingTrees(hs []Heading) HeadingTrees {
	if len(hs) == 0 {
		return nil
	}

	if len(hs) == 1 {
		return HeadingTrees{
			&HeadingTree{
				Heading: hs[0],
			},
		}
	}

	var (
		lasti int
		found bool
	)

	first := hs[0]
	rest := hs[1:]
	for i, h := range rest {
		if first.Level >= h.Level {
			lasti = i+1
			found = true
			break
		}
	}

	if !found {
		return HeadingTrees{
			&HeadingTree{
				Heading: first,
				Children: makeHeadingTrees(rest),
			},
		}
	}

	return append(
		makeHeadingTrees(hs[:lasti]),
		makeHeadingTrees(hs[lasti:])... ,
	)
}

func RenderHeadingTrees(trees HeadingTrees, first bool) string {
	var b strings.Builder
	fmt.Fprint(&b, "<nav")
	if first {
		fmt.Fprint(&b, " class=\"document\"")
	}
	fmt.Fprint(&b, ">")

	for _, tree := range trees {
		fmt.Fprintf(
			&b, "<a href=\"#%s\">%s</a>",
			tree.Heading.Id, tree.Heading.Text,
		)
		if len(tree.Children) > 0 {
			fmt.Fprint(&b, RenderHeadingTrees(tree.Children, false))
		}
	}
	fmt.Fprint(&b, "</nav>")
	return b.String()
}