package todo

import (
	"regexp"
	"strings"

	"g.fc.run/ai/byre/internal/api"
)

const File = "TODO.md"

var (
	heading  = regexp.MustCompile(`^#{1,6}\s+(.*?)\s*#*\s*$`)
	listItem = regexp.MustCompile(`^(?:[-*+]|\d+[.)])\s+(.*)$`)
	checkbox = regexp.MustCompile(`^\[([ xX])\]\s+`)
	fence    = regexp.MustCompile("^\\s*(```|~~~)")
)

func Parse(src string) []api.TodoItem {
	items := []api.TodoItem{}
	section := ""
	var cur *api.TodoItem
	body := []string{}
	inFence := false
	blank := false

	finish := func() {
		if cur == nil {
			return
		}
		cur.Body = dedent(body)
		items = append(items, *cur)
		cur = nil
		body = []string{}
	}

	for _, line := range strings.Split(strings.ReplaceAll(src, "\r\n", "\n"), "\n") {
		if fence.MatchString(line) {
			inFence = !inFence
			if cur != nil {
				body = append(body, line)
			}
			continue
		}
		if inFence {
			if cur != nil {
				body = append(body, line)
			}
			continue
		}

		if strings.TrimSpace(line) == "" {
			blank = true
			if cur != nil {
				body = append(body, "")
			}
			continue
		}
		indented := line[0] == ' ' || line[0] == '\t'
		afterBlank := blank
		blank = false

		if m := heading.FindStringSubmatch(line); m != nil {
			finish()
			section = m[1]
			continue
		}
		if m := listItem.FindStringSubmatch(line); m != nil {
			finish()
			title := m[1]
			box := checkbox.FindStringSubmatch(title)
			if box != nil && box[1] != " " {
				continue
			}
			title = strings.TrimSpace(checkbox.ReplaceAllString(title, ""))
			cur = &api.TodoItem{Title: title, Section: section}
			continue
		}
		if cur == nil {
			continue
		}
		if !indented && afterBlank {
			finish()
			continue
		}
		body = append(body, line)
	}
	finish()

	return items
}

func Find(items []api.TodoItem, title string) (api.TodoItem, bool) {
	for _, item := range items {
		if item.Title == title {
			return item, true
		}
	}
	return api.TodoItem{}, false
}

func Markdown(item api.TodoItem) string {
	if item.Body == "" {
		return "- " + item.Title
	}
	lines := []string{"- " + item.Title}
	for _, line := range strings.Split(item.Body, "\n") {
		if line == "" {
			lines = append(lines, "")
			continue
		}
		lines = append(lines, "  "+line)
	}
	return strings.Join(lines, "\n")
}

func dedent(lines []string) string {
	for len(lines) > 0 && lines[len(lines)-1] == "" {
		lines = lines[:len(lines)-1]
	}

	indent := -1
	for _, line := range lines {
		if line == "" {
			continue
		}
		n := len(line) - len(strings.TrimLeft(line, " \t"))
		if indent < 0 || n < indent {
			indent = n
		}
	}

	out := []string{}
	for _, line := range lines {
		if line == "" {
			out = append(out, "")
			continue
		}
		out = append(out, line[indent:])
	}
	return strings.Join(out, "\n")
}