package docs

import (
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"testing"
)

// TestDocsRelativeLinks keeps the developer docs tree internally navigable:
// every relative markdown link must point at a file that exists. The
// api-reference overview once shipped 20+ directory-style links
// (authentication/ etc.) that 404'd — this gate makes that class of rot
// fail make test. (docs/user is excluded: end-user prose has its own pass.)
//
// Rules:
//   - http(s):, mailto:, and pure #anchors are skipped
//   - every other target must end in .md and resolve (relative to the
//     linking file) to an existing file inside the tree
//   - directory-style targets ("area/") are the exact bug this test exists
//     for and always fail
var docsLinkRe = regexp.MustCompile(`\[[^\]]*\]\(([^)\s]+)\)`)

func TestDocsRelativeLinks(t *testing.T) {
	// Walk developer docs; escape-check against the whole docs tree —
	// cross-area links into docs/user are legitimate (same site).
	devRoot, err := filepath.Abs("../../docs/developer")
	if err != nil {
		t.Fatalf("abs developer root: %v", err)
	}
	treeRoot, err := filepath.Abs("../../docs")
	if err != nil {
		t.Fatalf("abs docs root: %v", err)
	}
	err = filepath.WalkDir(devRoot, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || !strings.HasSuffix(path, ".md") {
			return err
		}
		raw, err := os.ReadFile(path)
		if err != nil {
			return err
		}
		rel, _ := filepath.Rel(docsRoot, path)
		absPath, err := filepath.Abs(path)
		if err != nil {
			return err
		}
		for _, m := range docsLinkRe.FindAllStringSubmatch(string(raw), -1) {
			target := m[1]

			if strings.HasPrefix(target, "http://") ||
				strings.HasPrefix(target, "https://") ||
				strings.HasPrefix(target, "mailto:") {
				continue
			}
			if strings.HasPrefix(target, "#") {
				continue // in-page anchor
			}

			// strip a trailing fragment for file resolution
			fileTarget := target
			if i := strings.Index(fileTarget, "#"); i >= 0 {
				fileTarget = fileTarget[:i]
			}
			if fileTarget == "" {
				continue // pure-anchor form already handled; empty = odd, skip
			}

			if !strings.HasSuffix(fileTarget, ".md") {
				t.Errorf("%s: link target %q is not a .md file — directory-style links 404 on the docs site; link the file (e.g. %q)",
					rel, target, strings.TrimSuffix(fileTarget, "/")+".md")
				continue
			}

			resolved := filepath.Clean(filepath.Join(filepath.Dir(absPath), fileTarget))
			if !strings.HasPrefix(resolved, treeRoot+string(filepath.Separator)) {
				t.Errorf("%s: link target %q escapes the docs tree", rel, target)
				continue
			}
			if _, err := os.Stat(resolved); err != nil {
				t.Errorf("%s: link target %q does not resolve to an existing file (%s)", rel, target, resolved)
			}
		}
		return nil
	})
	if err != nil {
		t.Fatalf("walk docs: %v", err)
	}
}