package rules

import (
	"go/ast"
	"reflect"
	"strings"
)

// knownEnvVars is the set of every real framework env-var name, injected once at
// server startup from the index (see rules.SetKnownEnvVars). When empty — e.g.
// in unit tests that exercise rules without an index — config.unknown-env-var is
// a no-op, so it never fires on incomplete knowledge.
var knownEnvVars map[string]struct{}

// SetKnownEnvVars installs the authoritative set of framework env-var names that
// backs config.unknown-env-var. Call once before serving; the server derives the
// set from the index so the rule can never drift from the real struct tags.
func SetKnownEnvVars(names map[string]struct{}) {
	knownEnvVars = names
}

func init() {
	registered = append(registered,
		Rule{
			ID:       "config.unknown-env-var",
			Severity: SeverityError,
			Module:   "wire",
			Check:    checkUnknownEnvVar,
		},
	)
}

// checkUnknownEnvVar flags any struct field tagged with an EINHERJAR_* env var
// that the framework does not actually declare — the exact class of drift that
// shipped EINHERJAR_PG_DATABASE (real name: _PG_NAME) and EINHERJAR_SERVER_ADDR
// (real: _SERVER_HOST/_PORT). App-owned prefixes (APP_*) are never flagged.
func checkUnknownEnvVar(c *Context) []Finding {
	if len(knownEnvVars) == 0 {
		return nil
	}
	var hits []Finding
	ast.Inspect(c.File, func(n ast.Node) bool {
		st, ok := n.(*ast.StructType)
		if !ok || st.Fields == nil {
			return true
		}
		for _, field := range st.Fields.List {
			if field.Tag == nil {
				continue
			}
			name, ok := envName(strings.Trim(field.Tag.Value, "`"))
			if !ok || !strings.HasPrefix(name, "EINHERJAR_") {
				continue
			}
			if _, real := knownEnvVars[name]; real {
				continue
			}
			hits = append(hits, Finding{
				Message: name + " is not a real Einherjar env var (invented or misspelled)",
				Hint:    "Verify the exact tag with get_config_env. The framework never invents EINHERJAR_* names; compose the component's real Config or fix the tag.",
				Line:    c.Fset.Position(field.Tag.Pos()).Line,
			})
		}
		return true
	})
	return hits
}

// envName extracts the env-var name from a raw (backtick-stripped) struct tag,
// dropping the ,required / ,unset options. ok is false when there is no env key
// or it is "-".
func envName(tag string) (string, bool) {
	raw, present := reflect.StructTag(tag).Lookup("env")
	if !present {
		return "", false
	}
	name := strings.TrimSpace(strings.Split(raw, ",")[0])
	if name == "" || name == "-" {
		return "", false
	}
	return name, true
}