package link

import (
	"bytes"
	"fmt"
	"html/template"
	"io"
	"strings"
)

type Tree struct {
	cur      rng
	children []Tree
}

func (t Tree) text(inp string) string {
	return inp[t.cur.start:t.cur.end]
}

type rng struct {
	start, end int
	typ        string
}

type Parser struct {
	markers []int
	ranges  []rng
	stack   []Tree
}

func (p *Parser) pushMarker(start int) {
	p.markers = append(p.markers, start)
	p.stack = append(p.stack, Tree{})
}

func (p *Parser) popMarker(end int, typ string) {
	start := p.markers[len(p.markers)-1]
	p.markers = p.markers[:len(p.markers)-1]
	cur := rng{start, end, typ}
	top := p.stack[len(p.stack)-1]
	top.cur = cur
	p.stack = p.stack[:len(p.stack)-1]
	p.stack[len(p.stack)-1].children = append(p.stack[len(p.stack)-1].children, top)
	p.ranges = append(p.ranges, cur)
}
func (p *Parser) output() Tree {
	return p.stack[0].children[0]
}

func ShowTree(input string, root Tree, indent int) {
	if root.cur.start != root.cur.end {
		fmt.Printf("%s + (%s, %d-%d) %q\n", strings.Repeat(" |", indent), root.cur.typ, root.cur.start, root.cur.end, input[root.cur.start:root.cur.end])
	} else {
		indent -= 1
	}
	for _, c := range root.children {
		ShowTree(input, c, indent+1)
	}
}

func formatTitle(w io.Writer, input string, root Tree, indent int) {
	typ := root.cur.typ
	text := input[root.cur.start:root.cur.end]
	if typ == "text" {
		w.Write([]byte(text))
	}
	if typ == "link" {
		w.Write([]byte(fmt.Sprintf(`<a href="%s">`, root.children[1].text(input))))
		w.Write([]byte(text))
		w.Write([]byte(`</a>`))
		return
	}

	for _, c := range root.children {
		formatTitle(w, input, c, indent+1)
	}
}

func FormatHtmlTitle(input string) template.HTML {
	p := Parser{}
	root := p.Parse(input)
	sb := &bytes.Buffer{}
	formatTitle(sb, input, root, 0)
	return template.HTML(sb.String())
}

func (p *Parser) Parse(input string) Tree {
	p.stack = append(p.stack, Tree{})

	i := 0

	p.pushMarker(i)
	for i < len(input) {
		p.pushMarker(i)
		for i < len(input) && (input[i] != '[' && input[i] != ']') {
			i++
		}
		p.popMarker(i, "text")
		if i+2 <= len(input) && input[i:i+2] == "[[" {
			p.pushMarker(i)
			p.pushMarker(i)
			i += 2
			p.popMarker(i, "start link tag")
			p.pushMarker(i)
		} else if i+2 <= len(input) && input[i:i+2] == "]]" {
			p.popMarker(i, "link text")
			p.pushMarker(i)
			i += 2
			p.popMarker(i, "end link tag")
			p.popMarker(i, "link")
		}
	}
	p.popMarker(i, "full text")

	return p.output()
}