package approvalfact

import (
	"encoding/json"
	"errors"
	"regexp"
	"strconv"
	"time"
)

var errClaim = errors.New("Approval fact does not match required claim")
var digestPattern = regexp.MustCompile(`^sha256:[0-9a-f]{64}$`)
var uuidPattern = regexp.MustCompile(`^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$`)
var timePattern = regexp.MustCompile(`^[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}(\.[0-9]{1,9})?(Z|[+-]([01][0-9]|2[0-3]):[0-5][0-9])$`)

// Expected contains independently owner-derived native act bytes and the actual
// Access approval-free digest. Marshaling an already float64-decoded Go request
// is not an authoritative reconstruction of the native act.
type Expected struct {
	ApprovalID        string
	NativeBindingJSON []byte
	PDPDigest         string
}

// Fact is validated data shape/correspondence, NOT authenticated provider origin
// or execution authority. Access must wrap it only after its own source admission.
type Fact struct {
	raw                              []byte
	stable                           string
	digest                           string
	observed, timeLimit, validatedAt time.Time
}

func (f Fact) RawJSON() []byte       { return append([]byte(nil), f.raw...) }
func (f Fact) ObservedAt() time.Time { return f.observed }
func (f Fact) Deadline() time.Time   { return f.timeLimit }
func (f Fact) NativeDigest() string  { return f.digest }

func members(m map[string]any, required, optional []string) bool {
	allowed := map[string]bool{}
	for _, k := range required {
		allowed[k] = true
		if _, ok := m[k]; !ok {
			return false
		}
	}
	for _, k := range optional {
		allowed[k] = true
	}
	for k := range m {
		if !allowed[k] {
			return false
		}
	}
	return true
}
func object(v any) (map[string]any, bool) { m, ok := v.(map[string]any); return m, ok }
func stamp(v any) (time.Time, error) {
	s, ok := v.(string)
	if !ok || !timePattern.MatchString(s) {
		return time.Time{}, errClaim
	}
	t, e := time.Parse(time.RFC3339Nano, s)
	if e != nil {
		return time.Time{}, errClaim
	}
	return t, nil
}

// ValidateClaim checks one original or fetched schema-0.1 human/PDP-path claim
// at a caller-captured instant, using the existing Approval producer semantics.
// It has no I/O, policy evaluator, credentials, cache, or consume mutation.
func ValidateClaim(raw []byte, expected Expected, now time.Time) (Fact, error) {
	if now.IsZero() || !uuidPattern.MatchString(expected.ApprovalID) || !digestPattern.MatchString(expected.PDPDigest) {
		return Fact{}, errClaim
	}
	_, want, e := CanonicalBinding(expected.NativeBindingJSON)
	if e != nil {
		return Fact{}, errClaim
	}
	v, e := DecodeJSON(raw)
	if e != nil {
		return Fact{}, errClaim
	}
	m, ok := object(v)
	if !ok || !members(m, []string{"schema_version", "kind", "issuer", "approval_id", "state", "valid_now", "consumed", "binding", "freshness", "validity", "reason_code"}, []string{"yields_to"}) {
		return Fact{}, errClaim
	}
	if y, ok := m["yields_to"]; ok {
		if _, ok = y.(string); !ok {
			return Fact{}, errClaim
		}
	}
	if m["schema_version"] != "0.1" || m["kind"] != "approval-claim" || m["issuer"] != "approval-engine" || m["approval_id"] != expected.ApprovalID || m["state"] != "valid" || m["valid_now"] != true || m["consumed"] != false || m["reason_code"] != "ok" {
		return Fact{}, errClaim
	}
	b, ok := object(m["binding"])
	if !ok || !members(b, []string{"action", "actor", "principal", "purpose", "target", "digest", "pdp_digest", "pdp_path", "human_control"}, nil) {
		return Fact{}, errClaim
	}
	if b["digest"] != want || b["pdp_digest"] != expected.PDPDigest || b["pdp_path"] != true || b["human_control"] != true {
		return Fact{}, errClaim
	}
	text, e := canonical(b)
	if e != nil {
		return Fact{}, errClaim
	}
	_, got, e := CanonicalBinding([]byte(text))
	if e != nil || got != want {
		return Fact{}, errClaim
	}
	f, ok := object(m["freshness"])
	if !ok || !members(f, []string{"observed_at", "ttl_seconds", "not_after"}, nil) {
		return Fact{}, errClaim
	}
	observed, e := stamp(f["observed_at"])
	if e != nil {
		return Fact{}, e
	}
	notAfter, e := stamp(f["not_after"])
	if e != nil {
		return Fact{}, e
	}
	ttl, ok := f["ttl_seconds"].(json.Number)
	if !ok {
		return Fact{}, errClaim
	}
	seconds, e := strconv.ParseInt(string(ttl), 10, 64)
	if e != nil || seconds < 1 {
		return Fact{}, errClaim
	}
	// Bound arithmetic to time.Duration's representable seconds, not a new
	// semantic freshness grant or configured TTL. Unsupported extremes refuse.
	if seconds > int64((1<<63-1)/int64(time.Second)) || !observed.Add(time.Duration(seconds)*time.Second).Equal(notAfter) || now.Before(observed) || !now.Before(notAfter) {
		return Fact{}, errClaim
	}
	validity, ok := object(m["validity"])
	if !ok || !members(validity, []string{"not_before", "expires_at"}, nil) {
		return Fact{}, errClaim
	}
	before, e := stamp(validity["not_before"])
	if e != nil {
		return Fact{}, e
	}
	expires, e := stamp(validity["expires_at"])
	if e != nil || now.Before(before) || !now.Before(expires) {
		return Fact{}, errClaim
	}
	limit := notAfter
	if expires.Before(limit) {
		limit = expires
	}
	delete(m, "freshness")
	delete(m, "yields_to")
	stable, e := canonical(m)
	if e != nil {
		return Fact{}, errClaim
	}
	return Fact{raw: append([]byte(nil), raw...), stable: stable, digest: want, observed: observed, timeLimit: limit, validatedAt: now}, nil
}

// MatchObserved requires independently validated original/fetched facts at the
// same captured instant and exact nonfreshness authority correspondence. It
// never rewrites the original request or extends its original deadline.
func MatchObserved(submitted, observed Fact) error {
	if submitted.stable == "" || observed.stable == "" || !submitted.validatedAt.Equal(observed.validatedAt) || submitted.stable != observed.stable {
		return errClaim
	}
	return nil
}