// Package layer asserts the NetKingdom security-layer-model §11 declaration.
package layer

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"

	"gopkg.in/yaml.v3"
)

// Layer vocabulary from security-layer-model_v0.7 §3.
var validLayers = map[string]bool{
	"Staff":   true,
	"Engine":  true,
	"Tooling": true,
}

// Engine roles from §3.3. An Engine declaration must state one.
var validEngineRoles = map[string]bool{
	"PDP": true,
	"PIP": true,
}

// Tooling clients are invocations, not mentions. These match import paths and
// argv construction that would actually contact OpenBao/Vault.
var toolingPatterns = []*regexp.Regexp{
	regexp.MustCompile(`github\.com/hashicorp/vault`),
	regexp.MustCompile(`github\.com/openbao/`),
	regexp.MustCompile(`exec\.Command\([^)]*["'](?:bao|vault)["']`),
}

// Declaration is the machine-readable §11 form carried in INTENT.md frontmatter.
type Declaration struct {
	Layer           string `yaml:"layer"`
	Role            string `yaml:"role"`
	Framework       string `yaml:"framework"`
	StandardVersion string `yaml:"standard_version"`
	DeclaredBy      string `yaml:"declared_by"`
	DeclaredAt      string `yaml:"declared_at"`
	PepStance       any    `yaml:"pep_stance"`
	ToolingContacts []any  `yaml:"tooling_contacts"`
}

// Check parses INTENT.md, asserts the Engine/PDP declaration, and scans
// production Go sources for undeclared Tooling clients.
func Check(root string) error {
	decl, err := LoadDeclaration(filepath.Join(root, "INTENT.md"))
	if err != nil {
		return err
	}
	if err := ValidateDeclaration(decl); err != nil {
		return err
	}
	hits, err := ScanToolingClients(root)
	if err != nil {
		return err
	}
	if len(hits) > 0 {
		return fmt.Errorf("undeclared Tooling client(s) under §11: %s", strings.Join(hits, "; "))
	}
	return nil
}

// LoadDeclaration reads YAML frontmatter from INTENT.md.
func LoadDeclaration(path string) (Declaration, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return Declaration{}, fmt.Errorf("read layer declaration: %w", err)
	}
	frontmatter, err := splitFrontmatter(string(data))
	if err != nil {
		return Declaration{}, err
	}
	var decl Declaration
	if err := yaml.Unmarshal([]byte(frontmatter), &decl); err != nil {
		return Declaration{}, fmt.Errorf("parse layer declaration: %w", err)
	}
	return decl, nil
}

// ValidateDeclaration asserts §3 vocabulary and Engine-role presence.
func ValidateDeclaration(decl Declaration) error {
	if !validLayers[decl.Layer] {
		return fmt.Errorf("layer %q is not in the §3 vocabulary (Staff, Engine, Tooling)", decl.Layer)
	}
	if decl.Layer == "Engine" && !validEngineRoles[decl.Role] {
		return fmt.Errorf("Engine declaration must state role PDP or PIP; got %q", decl.Role)
	}
	if decl.Layer != "Engine" && strings.TrimSpace(decl.Role) != "" {
		return fmt.Errorf("layer %q must not state an Engine role", decl.Layer)
	}
	if len(decl.ToolingContacts) > 0 {
		return fmt.Errorf("Engine/PDP holds no Tooling client; tooling_contacts must be empty")
	}
	if decl.PepStance != nil {
		return fmt.Errorf("flex-auth is not PEP-shaped; pep_stance must be null")
	}
	return nil
}

// ScanToolingClients returns production Go files that invoke OpenBao/Vault.
func ScanToolingClients(root string) ([]string, error) {
	var hits []string
	for _, dir := range []string{"cmd", "internal", "pkg"} {
		err := filepath.WalkDir(filepath.Join(root, dir), func(path string, d os.DirEntry, err error) error {
			if err != nil {
				return err
			}
			if d.IsDir() || !strings.HasSuffix(path, ".go") || strings.HasSuffix(path, "_test.go") {
				return nil
			}
			body, err := os.ReadFile(path)
			if err != nil {
				return err
			}
			for _, pattern := range toolingPatterns {
				if pattern.Find(body) != nil {
					rel, _ := filepath.Rel(root, path)
					hits = append(hits, rel)
					break
				}
			}
			return nil
		})
		if err != nil && !os.IsNotExist(err) {
			return nil, err
		}
	}
	return hits, nil
}

func splitFrontmatter(document string) (string, error) {
	document = strings.TrimPrefix(document, "\ufeff")
	lines := strings.SplitAfter(document, "\n")
	if len(lines) == 0 || strings.TrimSpace(lines[0]) != "---" {
		return "", fmt.Errorf("INTENT.md must start with YAML frontmatter")
	}
	for i := 1; i < len(lines); i++ {
		if strings.TrimSpace(lines[i]) == "---" {
			return strings.Join(lines[1:i], ""), nil
		}
	}
	return "", fmt.Errorf("INTENT.md frontmatter is not closed")
}