package check

import (
	"fmt"
	"io/fs"
	"path"
	"regexp"
	"sort"
	"strings"

	"khosra/internal/content"
)

// Finding is one thing worth an author's attention.
type Finding struct {
	// Where names the file, or the key when the finding is about identity rather than one file.
	Where string
	// What says what is wrong, in terms the author can act on.
	What string
	// Fatal marks a finding that makes the site wrong rather than merely untidy: something the engine had to
	// drop, or a link that will 404 for a reader. Only these decide the exit status.
	Fatal bool
}

// Run validates a site and returns every finding, ordered so two runs read the same.
//
// This is where content errors are meant to surface (ADR-0029): the server never fails on a bad bundle, it
// works around it and says so in the log, which is easy to miss. `check` is the place that looks on purpose.
func Run(fsys fs.FS, bundles []content.Bundle, site *content.Site, problems []content.Problem) []Finding {
	var found []Finding
	// What the engine already worked around. Fatal by definition: each is content the site is not serving.
	for _, p := range problems {
		found = append(found, Finding{p.Path, p.Detail, true})
	}
	for _, p := range site.Problems() {
		found = append(found, Finding{p.Path, p.Detail, true})
	}
	for _, b := range bundles {
		found = append(found, inspect(fsys, b, site)...)
	}
	found = append(found, mixedOrdering(bundles, site)...)
	sort.SliceStable(found, func(i, j int) bool {
		if found[i].Where != found[j].Where {
			return found[i].Where < found[j].Where
		}
		return found[i].What < found[j].What
	})
	return found
}

// Fatal reports whether any finding means the site is actually wrong.
func Fatal(found []Finding) bool {
	for _, f := range found {
		if f.Fatal {
			return true
		}
	}
	return false
}

// inspect checks one bundle.
func inspect(fsys fs.FS, b content.Bundle, site *content.Site) []Finding {
	var found []Finding
	if b.Title == "" {
		// Not fatal: the page renders with its key as a title. Still almost never what anyone wants.
		found = append(found, Finding{b.Path, "no title, so the page is titled by its key", false})
	}
	if norm := content.Normalise(b.Path); norm != b.Path {
		found = append(found, Finding{b.Path,
			"filename is not in NFC, so two visually identical names could take different keys (ADR-0015)", true})
	}
	found = append(found, checkFigures(b)...)
	found = append(found, checkLinks(fsys, b, site)...)
	return found
}

// figureCall matches a whole figure shortcode, so its arguments can be examined.
var figureCall = regexp.MustCompile(`(?m)^\s*\{\{<\s*figure\s+([^>]*)>\}\}\s*$`)

// altArg matches a non-empty alt argument.
var altArg = regexp.MustCompile(`alt="[^"]+"`)

// checkFigures looks for pictures nobody described.
//
// Not fatal — a missing alt is a page that works and excludes someone — but it is the one accessibility fault
// the engine can see, so it says so every time.
func checkFigures(b content.Bundle) []Finding {
	var found []Finding
	for _, call := range figureCall.FindAllStringSubmatch(string(b.Body), -1) {
		if !altArg.MatchString(call[1]) {
			found = append(found, Finding{b.Path, "figure with no alt text: " + strings.TrimSpace(call[0]), false})
		}
	}
	return found
}

// internalLink matches a Markdown link or image whose target is a root-relative path.
var internalLink = regexp.MustCompile(`\]\((/[^)\s"]*)`)

// checkLinks resolves every root-relative link a body contains.
//
// Fatal: a link that 404s is the site lying to a reader, and it is exactly the mistake that survives a rename
// because nothing else looks. Engine-owned paths are skipped — they are generated, not authored.
func checkLinks(fsys fs.FS, b content.Bundle, site *content.Site) []Finding {
	var found []Finding
	seen := map[string]bool{}
	for _, m := range internalLink.FindAllStringSubmatch(string(b.Body), -1) {
		target := m[1]
		if seen[target] || engineOwned(target) {
			continue
		}
		seen[target] = true
		if !resolves(fsys, target, b, site) {
			found = append(found, Finding{b.Path, "link goes nowhere: " + target, true})
		}
	}
	return found
}

// engineOwned reports whether a path is generated rather than authored, so a checker has nothing to say.
func engineOwned(target string) bool {
	for _, prefix := range []string{"/static/", content.DerivedPrefix, "/tags/"} {
		if strings.HasPrefix(target, prefix) {
			return true
		}
	}
	switch target {
	case "/", "/robots.txt", "/sitemap.xml", "/feed.xml":
		return true
	}
	return false
}

// resolves reports whether a root-relative path would be served.
//
// It asks the same questions the resolver does — a bundle at that route, an alias, a section listing, or a file
// inside a bundle — because a checker that guesses differently from the server is worse than no checker.
func resolves(fsys fs.FS, target string, from content.Bundle, site *content.Site) bool {
	trimmed := strings.Trim(target, "/")
	if trimmed == "" {
		return true
	}
	// A language prefix resolves to the same content, so drop it before asking.
	if head, rest, found := strings.Cut(trimmed, "/"); found && site.HasLang(head) {
		trimmed = rest
	}
	key, live := site.KeyFor(content.Normalise(trimmed))
	if live {
		if _, _, ok := site.Lookup(key, content.DefaultLang); ok {
			return true
		}
		// A section with anything in it has a listing; and a file inside a bundle is served under it.
		if len(site.Run(content.Query{Section: key, Lang: content.DefaultLang})) > 0 {
			return true
		}
	}
	if _, isAlias := site.Alias(content.Normalise(trimmed)); isAlias {
		return true
	}
	return asset(fsys, trimmed, site)
}

// asset reports whether the path names a file inside some bundle's own directory.
func asset(fsys fs.FS, trimmed string, site *content.Site) bool {
	dir, file := path.Split(trimmed)
	route := strings.TrimSuffix(dir, "/")
	if route == "" || file == "" {
		return false
	}
	key, live := site.KeyFor(route)
	if !live {
		return false
	}
	b, _, ok := site.Lookup(key, content.DefaultLang)
	if !ok {
		return false
	}
	assets, hasAssets := b.Assets()
	if !hasAssets {
		return false
	}
	if _, err := fs.Stat(fsys, path.Join(assets, file)); err != nil {
		return false
	}
	return true
}

// mixedOrdering finds a series where some members declare `order` and others do not.
//
// Not fatal, but the surprise this exists for: unordered members sort after every ordered one, so adding
// `order` to one chapter silently moves every chapter that lacks it to the end (ADR-0033).
func mixedOrdering(bundles []content.Bundle, site *content.Site) []Finding {
	ordered, unordered := map[string]bool{}, map[string][]string{}
	for _, b := range bundles {
		seq, inSeries := site.Sequence(b.Key, b.Lang)
		if !inSeries || seq.Index == 0 {
			continue
		}
		if b.Order == 0 {
			unordered[seq.Series.Key] = append(unordered[seq.Series.Key], b.Key)
			continue
		}
		ordered[seq.Series.Key] = true
	}
	var found []Finding
	for series := range ordered {
		if missing := unordered[series]; len(missing) > 0 {
			sort.Strings(missing)
			found = append(found, Finding{series, fmt.Sprintf(
				"some members declare order and these do not, so they sort last: %s",
				strings.Join(missing, ", ")), false})
		}
	}
	return found
}