// Package model defines the Rate value type and its invariants, shared by the
// HTTP layer and the storage layer. All amounts are decimal strings matching
// the "^-?[0-9]+\\.[0-9]{2}$" pattern used across ProofedMesh schemas; we
// deliberately do not reach for float.
package model

import (
	"errors"
	"fmt"
	"regexp"
	"time"
)

var (
	countryPattern  = regexp.MustCompile(`^[A-Z]{2}$`)
	currencyPattern = regexp.MustCompile(`^[A-Z]{3}$`)
	amountPattern   = regexp.MustCompile(`^[0-9]+\.[0-9]{2}$`)
	sha256Pattern   = regexp.MustCompile(`^sha256:[0-9a-f]{64}$`)
)

// Rate mirrors a row in per_diem_rates. Monetary fields are decimal strings
// e.g. "28.00". Core business fields are set at creation and are immutable
// afterwards (enforced both by the Postgres trigger and by the admin API).
type Rate struct {
	RateID                   string     `json:"rate_id"`
	Country                  string     `json:"country"`           // ISO 3166-1 alpha-2
	City                     *string    `json:"city,omitempty"`    // optional
	Currency                 string     `json:"currency"`          // ISO 4217
	FullDay                  string     `json:"full_day"`
	PartialDayMin8h          string     `json:"partial_day_min8h"`
	ArrivalDay               string     `json:"arrival_day"`
	DepartureDay             string     `json:"departure_day"`
	ValidFrom                time.Time  `json:"valid_from"`
	ValidTo                  *time.Time `json:"valid_to,omitempty"`
	SourceRegulation         string     `json:"source_regulation"`
	CreatedBy                string     `json:"created_by"`
	CreatedAt                time.Time  `json:"created_at"`
	RateChangeAttestationRef *string    `json:"rate_change_attestation_ref,omitempty"`
}

// NewRateInput carries the fields a caller may supply when creating a new rate.
// RateID, CreatedBy, CreatedAt and the attestation ref are assigned by the API,
// not the caller.
type NewRateInput struct {
	Country          string     `json:"country"`
	City             *string    `json:"city,omitempty"`
	Currency         string     `json:"currency"`
	FullDay          string     `json:"full_day"`
	PartialDayMin8h  string     `json:"partial_day_min8h"`
	ArrivalDay       string     `json:"arrival_day"`
	DepartureDay     string     `json:"departure_day"`
	ValidFrom        time.Time  `json:"valid_from"`
	ValidTo          *time.Time `json:"valid_to,omitempty"`
	SourceRegulation string     `json:"source_regulation"`
}

// Validate checks the invariants that are enforced by the schema and that we
// want to fail-fast on in the API layer so the user sees a sensible error
// before we hit Postgres.
func (in NewRateInput) Validate() error {
	if !countryPattern.MatchString(in.Country) {
		return fmt.Errorf("country %q must be ISO 3166-1 alpha-2 (two uppercase letters)", in.Country)
	}
	if in.City != nil && (*in.City == "" || len(*in.City) > 100) {
		return errors.New("city, if set, must be 1..100 characters")
	}
	if !currencyPattern.MatchString(in.Currency) {
		return fmt.Errorf("currency %q must be ISO 4217 (three uppercase letters)", in.Currency)
	}
	for _, p := range []struct {
		name  string
		value string
	}{
		{"full_day", in.FullDay},
		{"partial_day_min8h", in.PartialDayMin8h},
		{"arrival_day", in.ArrivalDay},
		{"departure_day", in.DepartureDay},
	} {
		if !amountPattern.MatchString(p.value) {
			return fmt.Errorf("%s %q must be a decimal string with two decimals (e.g. '28.00')", p.name, p.value)
		}
	}
	if in.ValidFrom.IsZero() {
		return errors.New("valid_from is required")
	}
	if in.ValidTo != nil && in.ValidTo.Before(in.ValidFrom) {
		return errors.New("valid_to must not be before valid_from")
	}
	if l := len(in.SourceRegulation); l < 1 || l > 500 {
		return errors.New("source_regulation must be 1..500 characters")
	}
	return nil
}

// IsAttestationRef returns true for a well-formed sha256: content hash.
func IsAttestationRef(ref string) bool {
	return sha256Pattern.MatchString(ref)
}