package docsite

import (
	"fmt"
	"regexp"
	"slices"
	"strings"

	gast "github.com/yuin/goldmark/ast"
)

// calloutTypes are the only `> [!TYPE]` callouts the theme renders.
var calloutTypes = []string{"NOTE", "TIP", "WARNING"}

// calloutMarker matches the first line of a callout blockquote.
var calloutMarker = regexp.MustCompile(`^\s{0,3}>\s?\[!([A-Za-z]+)\]\s*$`)

// checkPolicy enforces the page content rules:
//   - every go fence in a docs/ page carries src= (module READMEs are
//     rendered as written, D-18);
//   - callouts are NOTE, TIP or WARNING;
//   - docs/ headings are plain ASCII text without links or code spans.
func (s *site) checkPolicy(docs []parsedDoc) []Problem {
	var problems []Problem
	for _, d := range docs {
		if d.page == nil {
			continue
		}
		guide := d.page.Module == ""
		lines := strings.Split(string(d.body), "\n")
		fences := scanFences(lines)
		inFence := make([]bool, len(lines))
		for _, f := range fences {
			end := f.close
			if end < 0 {
				end = len(lines) - 1
			}
			for i := f.open; i <= end; i++ {
				inFence[i] = true
			}
			fields := strings.Fields(f.info)
			if guide && len(fields) > 0 && fields[0] == "go" &&
				!slices.ContainsFunc(fields[1:], func(f string) bool { return strings.HasPrefix(f, "src=") }) {
				problems = append(problems, Problem{File: d.file, Line: d.line + f.open, Rule: "snippet",
					Message: "go code block has no src= reference"})
			}
		}
		for i, line := range lines {
			if inFence[i] {
				continue
			}
			if m := calloutMarker.FindStringSubmatch(line); m != nil && !slices.Contains(calloutTypes, m[1]) {
				problems = append(problems, Problem{File: d.file, Line: d.line + i, Rule: "callout",
					Message: fmt.Sprintf("unknown type %s (use NOTE, TIP or WARNING)", m[1])})
			}
		}
		if guide {
			problems = append(problems, headingProblems(d)...)
		}
	}
	return problems
}

const headingMessage = "headings must be plain ASCII text without links or code"

// headingProblems reports headings with a link, image, code span or raw
// HTML, or with non-ASCII text: their IDs would not be stable across the
// site, Gitea and GitHub.
func headingProblems(d parsedDoc) []Problem {
	var problems []Problem
	_ = gast.Walk(d.doc, func(n gast.Node, entering bool) (gast.WalkStatus, error) {
		h, ok := n.(*gast.Heading)
		if !entering || !ok {
			return gast.WalkContinue, nil
		}
		bad := false
		_ = gast.Walk(h, func(c gast.Node, entering bool) (gast.WalkStatus, error) {
			if !entering {
				return gast.WalkContinue, nil
			}
			switch t := c.(type) {
			case *gast.Link, *gast.Image, *gast.CodeSpan, *gast.RawHTML, *gast.AutoLink:
				bad = true
				return gast.WalkStop, nil
			case *gast.Text:
				for _, b := range t.Segment.Value(d.body) {
					if b >= 0x80 {
						bad = true
						return gast.WalkStop, nil
					}
				}
			}
			return gast.WalkContinue, nil
		})
		if bad {
			off := -1
			if h.Lines().Len() > 0 {
				off = h.Lines().At(0).Start
			}
			problems = append(problems, Problem{File: d.file, Line: lineOf(d.body, off, d.line), Rule: "heading", Message: headingMessage})
		}
		return gast.WalkSkipChildren, nil
	})
	return problems
}