package model

import (
	"fmt"
	"math/big"
	"regexp"
	"time"

	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/bson/primitive"

	"github.com/tech/sendico/pkg/merrors"
	"github.com/tech/sendico/pkg/mservice"
)

// ----------------------------
// Core discriminant/type
// ----------------------------

type PropertyType = string

const (
	PTDateTime  PropertyType = "date_time"
	PTInteger   PropertyType = "integer"
	PTFloat     PropertyType = "float"
	PTMonetary  PropertyType = "monetary"
	PTReference PropertyType = "reference"
	PTString    PropertyType = "string"
	PTColor     PropertyType = "color"
	PTObject    PropertyType = "object"
)

// Value keys for SettingsT maps
const (
	VKString     = "string"
	VKStrings    = "strings"
	VKColor      = "color"
	VKColors     = "colors"
	VKInteger    = "integer"
	VKIntegers   = "integers"
	VKFloat      = "float"
	VKFloats     = "floats"
	VKDateTime   = "date_time"
	VKDateTimes  = "date_times"
	VKMonetary   = "monetary"
	VKMonetaries = "monetaries"
	VKReference  = "reference"
	VKReferences = "references"
	VKObject     = "object"
	VKObjects    = "objects"
)

// Money struct field keys
const (
	MKAmount   = "amount"
	MKCurrency = "currency"
)

// ----------------------------
// Small value types (runtime values)
// ----------------------------

// ----------------------------
// Type-specific PROPS (schema/constraints)
// ----------------------------

type IntegerProps struct {
	Default *int64  `bson:"default,omitempty" json:"default,omitempty"`
	Min     *int64  `bson:"min,omitempty"     json:"min,omitempty"`
	Max     *int64  `bson:"max,omitempty"     json:"max,omitempty"`
	Allowed []int64 `bson:"allowed,omitempty" json:"allowed,omitempty"`
}

type FloatProps struct {
	Default *float64 `bson:"default,omitempty" json:"default,omitempty"`
	Min     *float64 `bson:"min,omitempty"     json:"min,omitempty"`
	Max     *float64 `bson:"max,omitempty"     json:"max,omitempty"`
}

type StringProps struct {
	Default *string  `bson:"default,omitempty"  json:"default,omitempty"`
	Allowed []string `bson:"allowed,omitempty"  json:"allowed,omitempty"`
	Pattern string   `bson:"pattern"  json:"pattern"` // Go RE2 syntax
	MinLen  *int     `bson:"minLen,omitempty"   json:"minLen,omitempty"`
	MaxLen  *int     `bson:"maxLen,omitempty"   json:"maxLen,omitempty"`
}

type DateTimeProps struct {
	Default  *time.Time `bson:"default,omitempty"  json:"default,omitempty"` // store UTC
	Earliest *time.Time `bson:"earliest,omitempty" json:"earliest,omitempty"`
	Latest   *time.Time `bson:"latest,omitempty"   json:"latest,omitempty"`
}

type ColorProps struct {
	AllowAlpha     bool     `bson:"allowAlpha,omitempty"      json:"allowAlpha,omitempty"`
	AllowedPalette []string `bson:"allowedPalette,omitempty"  json:"allowedPalette,omitempty"` // optional whitelist of hex colors
	Default        string   `bson:"default,omitempty"         json:"default,omitempty"`
}

type ObjectProps struct {
	Properties []PropertySchema `bson:"properties,omitempty" json:"properties,omitempty"`
}

// Currency policy for monetary props.
type CurrencyMode string

const (
	CurrencyFixed CurrencyMode = "fixed" // force one currency (FixedCurrency)
	CurrencyOrg   CurrencyMode = "org"   // force org default currency at runtime
	CurrencyFree  CurrencyMode = "free"  // allow any (optionally restricted by AllowedCurrencies)
)

type MonetaryProps struct {
	CurrencyMode      CurrencyMode `bson:"currencyMode"      json:"currencyMode"`
	FixedCurrency     Currency     `bson:"fixedCurrency"     json:"fixedCurrency"`     // required if fixed
	AllowedCurrencies []Currency   `bson:"allowedCurrencies" json:"allowedCurrencies"` // for free mode

	// Optional precision/rules; if nil, infer elsewhere by ISO minor units.
	Scale    *int `bson:"scale,omitempty"    json:"scale,omitempty"`    // allowed decimal places
	Rounding *int `bson:"rounding,omitempty" json:"rounding,omitempty"` // app-specific; not enforced here

	Default *Money `bson:"default,omitempty" json:"default,omitempty"`
	Min     *Money `bson:"min,omitempty"     json:"min,omitempty"`
	Max     *Money `bson:"max,omitempty"     json:"max,omitempty"`
}

type ReferenceProps struct {
	Target     mservice.Type        `bson:"target"                 json:"target"`               // e.g. "accounts"
	AllowedIDs []primitive.ObjectID `bson:"allowedIds,omitempty"   json:"allowedIds,omitempty"` // optional whitelist
	Default    *primitive.ObjectID  `bson:"default,omitempty"      json:"default,omitempty"`    // optional default VALUE
}

// ----------------------------
// UI hints (optional)
// ----------------------------

type UIHints struct {
	Placeholder  string `bson:"placeholder"  json:"placeholder"`
	Unit         string `bson:"unit"         json:"unit"` // "kg", "cm", "€", etc.
	HiddenInList bool   `bson:"hiddenInList" json:"hiddenInList"`
	Filterable   bool   `bson:"filterable"   json:"filterable"`
}

// ----------------------------
// Multiplicity (generic, applies to any type)
// ----------------------------

type Cardinality string

const (
	One  Cardinality = "one"  // single value
	Many Cardinality = "many" // array of values
)

type Multiplicity struct {
	Mode     Cardinality `bson:"mode"     json:"mode"`                         // default "one"
	MinItems *int        `bson:"minItems,omitempty" json:"minItems,omitempty"` // only when Mode=Many
	MaxItems *int        `bson:"maxItems,omitempty" json:"maxItems,omitempty"` // only when Mode=Many
	// Distinct within one entity's list value (meaningful for Mode=Many).
	Distinct bool `bson:"distinct" json:"distinct"`
}

// ----------------------------
// Property envelope
// ----------------------------

type PropertySchema struct {
	PermissionBound `bson:",inline" json:",inline"`
	Describable     `bson:",inline" json:",inline"`

	// customer permission refernece
	ValuePermissionRef *primitive.ObjectID `bson:"valuePermissionRef,omitempty" json:"valuePermissionRef,omitempty"`

	// Stable machine key; unique within (organizatoinRef, type, key)
	Key  string       `bson:"key"  json:"key"`
	Type PropertyType `bson:"type" json:"type"`

	// Lifecycle/UX
	System bool     `bson:"system"   json:"system"`
	UI     *UIHints `bson:"ui,omitempty"       json:"ui,omitempty"`

	// Multiplicity controls (cross-type).
	Multiplicity Multiplicity `bson:"multiplicity" json:"multiplicity"`

	// Discriminated payload; a BSON subdocument shaped per Type.
	Props any `bson:"props" json:"props"`
}

func (*PropertySchema) Collection() string { return mservice.PropertySchemas }

// ----------------------------
// Typed accessors for Props
// ----------------------------

func invalidType(expected, actual PropertyType) error {
	return merrors.InvalidDataType(fmt.Sprintf("expected type is %s while actual type is %s", expected, actual))
}

// asTypedProps is a generic function that handles type checking and casting for all property types
func asTypedProps[T any](p *PropertySchema, expectedType PropertyType) (T, error) {
	var out T
	if p.Type != expectedType {
		return out, invalidType(expectedType, p.Type)
	}
	// Props is stored directly as the correct type, so we can cast it
	if props, ok := p.Props.(T); ok {
		return props, nil
	}
	return out, merrors.InvalidArgument("invalid props type")
}

// Type-specific accessor functions using the generic template
func (p *PropertySchema) AsInteger() (IntegerProps, error) {
	return asTypedProps[IntegerProps](p, PTInteger)
}

func (p *PropertySchema) AsFloat() (FloatProps, error) {
	return asTypedProps[FloatProps](p, PTFloat)
}

func (p *PropertySchema) AsString() (StringProps, error) {
	return asTypedProps[StringProps](p, PTString)
}

func (p *PropertySchema) AsDateTime() (DateTimeProps, error) {
	return asTypedProps[DateTimeProps](p, PTDateTime)
}

func (p *PropertySchema) AsMonetary() (MonetaryProps, error) {
	return asTypedProps[MonetaryProps](p, PTMonetary)
}

func (p *PropertySchema) AsReference() (ReferenceProps, error) {
	return asTypedProps[ReferenceProps](p, PTReference)
}

func (p *PropertySchema) AsColor() (ColorProps, error) {
	return asTypedProps[ColorProps](p, PTColor)
}

func (p *PropertySchema) AsObject() (ObjectProps, error) {
	return asTypedProps[ObjectProps](p, PTObject)
}

// ----------------------------
// Validation helpers (generic)
// ----------------------------

func validateMultiplicity(count int, required bool, m Multiplicity) error {
	mode := m.Mode
	if mode == "" {
		mode = One
	}
	switch mode {
	case One:
		if count > 1 {
			return merrors.DataConflict("multiple values not allowed")
		}
		if required && count == 0 {
			return merrors.DataConflict("value required")
		}
	case Many:
		min := 0
		if m.MinItems != nil {
			min = *m.MinItems
		} else if required {
			min = 1
		}
		if count < min {
			return merrors.DataConflict(fmt.Sprintf("minimum %d items", min))
		}
		if m.MaxItems != nil && count > *m.MaxItems {
			return merrors.DataConflict(fmt.Sprintf("maximum %d items", *m.MaxItems))
		}
	default:
		return merrors.InvalidArgument(fmt.Sprintf("unknown cardinality: %q", mode))
	}
	return nil
}

func ensureDistinct[T comparable](vals []T, distinct bool) error {
	if !distinct || len(vals) < 2 {
		return nil
	}
	seen := make(map[T]struct{}, len(vals))
	for _, v := range vals {
		if _, ok := seen[v]; ok {
			return merrors.DataConflict("duplicate items not allowed")
		}
		seen[v] = struct{}{}
	}
	return nil
}

func ensureDistinctByKey[T any, K comparable](vals []T, key func(T) K, distinct bool) error {
	if !distinct || len(vals) < 2 {
		return nil
	}
	seen := make(map[K]struct{}, len(vals))
	for _, v := range vals {
		k := key(v)
		if _, ok := seen[k]; ok {
			return merrors.DataConflict("duplicate items not allowed")
		}
		seen[k] = struct{}{}
	}
	return nil
}

// ----------------------------
// Type validators
// ----------------------------

func (p PropertySchema) ValidateStrings(vals []string) error {
	if p.Type != PTString {
		return invalidType(PTString, p.Type)
	}
	if err := validateMultiplicity(len(vals), false, p.Multiplicity); err != nil {
		return err
	}
	if err := ensureDistinct(vals, p.Multiplicity.Distinct); err != nil {
		return err
	}

	props, err := p.AsString()
	if err != nil {
		return err
	}

	var re *regexp.Regexp
	if props.Pattern != "" {
		rx, rxErr := regexp.Compile(props.Pattern)
		if rxErr != nil {
			return merrors.InvalidArgument(fmt.Sprintf("invalid pattern: %v", rxErr))
		}
		re = rx
	}

	allow := map[string]struct{}{}
	if len(props.Allowed) > 0 {
		for _, a := range props.Allowed {
			allow[a] = struct{}{}
		}
	}

	for _, v := range vals {
		if len(allow) > 0 {
			if _, ok := allow[v]; !ok {
				return merrors.DataConflict(fmt.Sprintf("value %q not allowed", v))
			}
		}
		if props.MinLen != nil && len(v) < *props.MinLen {
			return merrors.DataConflict(fmt.Sprintf("value too short (min %d)", *props.MinLen))
		}
		if props.MaxLen != nil && len(v) > *props.MaxLen {
			return merrors.DataConflict(fmt.Sprintf("value too long (max %d)", *props.MaxLen))
		}
		if re != nil && !re.MatchString(v) {
			return merrors.DataConflict(fmt.Sprintf("value %q does not match pattern", v))
		}
	}
	return nil
}

func (p PropertySchema) ValidateColors(vals []string) error {
	if p.Type != PTColor {
		return invalidType(PTColor, p.Type)
	}
	if err := validateMultiplicity(len(vals), false, p.Multiplicity); err != nil {
		return err
	}
	if err := ensureDistinct(vals, p.Multiplicity.Distinct); err != nil {
		return err
	}

	_, err := p.AsColor()
	if err != nil {
		return err
	}

	// For now, we can use the same validation as strings
	// In the future, we might want to add color-specific validation
	return nil
}

func (p PropertySchema) ValidateIntegers(vals []int64) error {
	if p.Type != PTInteger {
		return invalidType(PTInteger, p.Type)
	}
	if err := validateMultiplicity(len(vals), false, p.Multiplicity); err != nil {
		return err
	}
	if err := ensureDistinct(vals, p.Multiplicity.Distinct); err != nil {
		return err
	}

	props, err := p.AsInteger()
	if err != nil {
		return err
	}

	allow := map[int64]struct{}{}
	if len(props.Allowed) > 0 {
		for _, a := range props.Allowed {
			allow[a] = struct{}{}
		}
	}

	for _, v := range vals {
		if len(allow) > 0 {
			if _, ok := allow[v]; !ok {
				return merrors.DataConflict(fmt.Sprintf("value %d not allowed", v))
			}
		}
		if props.Min != nil && v < *props.Min {
			return merrors.DataConflict(fmt.Sprintf("value %d below min %d", v, *props.Min))
		}
		if props.Max != nil && v > *props.Max {
			return merrors.DataConflict(fmt.Sprintf("value %d above max %d", v, *props.Max))
		}
	}
	return nil
}

func (p PropertySchema) ValidateFloats(vals []float64) error {
	if p.Type != PTFloat {
		return invalidType(PTFloat, p.Type)
	}
	if err := validateMultiplicity(len(vals), false, p.Multiplicity); err != nil {
		return err
	}
	if err := ensureDistinct(vals, p.Multiplicity.Distinct); err != nil {
		return err
	}

	props, err := p.AsFloat()
	if err != nil {
		return err
	}

	for _, v := range vals {
		if props.Min != nil && v < *props.Min {
			return merrors.DataConflict(fmt.Sprintf("value %g below min %g", v, *props.Min))
		}
		if props.Max != nil && v > *props.Max {
			return merrors.DataConflict(fmt.Sprintf("value %g above max %g", v, *props.Max))
		}
	}
	return nil
}

func (p PropertySchema) ValidateDateTimes(vals []time.Time) error {
	if p.Type != PTDateTime {
		return invalidType(PTDateTime, p.Type)
	}
	if err := validateMultiplicity(len(vals), false, p.Multiplicity); err != nil {
		return err
	}
	// Distinct datetimes rarely matter; honor it if requested.
	if err := ensureDistinctByKey(vals, func(t time.Time) int64 { return t.UTC().UnixNano() }, p.Multiplicity.Distinct); err != nil {
		return err
	}

	props, err := p.AsDateTime()
	if err != nil {
		return err
	}

	for _, v := range vals {
		vu := v.UTC()
		if props.Earliest != nil && vu.Before(props.Earliest.UTC()) {
			return merrors.DataConflict("datetime before earliest")
		}
		if props.Latest != nil && vu.After(props.Latest.UTC()) {
			return merrors.DataConflict("datetime after latest")
		}
	}
	return nil
}

// Monetary validation (handles currency policy + Min/Max + optional scale)
func (p PropertySchema) ValidateMonetaries(vals []Money, orgCurrency Currency) error {
	if p.Type != PTMonetary {
		return invalidType(PTMonetary, p.Type)
	}
	if err := validateMultiplicity(len(vals), false, p.Multiplicity); err != nil {
		return err
	}
	// Distinct by (currency, amount)
	if err := ensureDistinctByKey(vals, func(m Money) string { return string(m.Currency) + "|" + m.Amount.String() }, p.Multiplicity.Distinct); err != nil {
		return err
	}

	props, err := p.AsMonetary()
	if err != nil {
		return err
	}

	allowedCur := map[Currency]struct{}{}
	if len(props.AllowedCurrencies) > 0 {
		for _, c := range props.AllowedCurrencies {
			allowedCur[c] = struct{}{}
		}
	}

	for _, v := range vals {
		// Currency policy
		switch props.CurrencyMode {
		case CurrencyFixed:
			if props.FixedCurrency == "" {
				return merrors.InvalidArgument("fixed currency is not configured")
			}
			if v.Currency != props.FixedCurrency {
				return merrors.DataConflict(fmt.Sprintf("currency must be %s", props.FixedCurrency))
			}
		case CurrencyOrg:
			if orgCurrency == "" {
				return merrors.InvalidArgument("org currency not provided")
			}
			if v.Currency != Currency(orgCurrency) {
				return merrors.DataConflict(fmt.Sprintf("currency must be %s", orgCurrency))
			}
		case CurrencyFree, "":
			if len(allowedCur) > 0 {
				if _, ok := allowedCur[v.Currency]; !ok {
					return merrors.DataConflict(fmt.Sprintf("currency %s not allowed", v.Currency))
				}
			}
		default:
			return merrors.InvalidArgument(fmt.Sprintf("unknown currency mode: %s", props.CurrencyMode))
		}

		// Scale check (if configured)
		if props.Scale != nil {
			ok, frac := decimal128WithinScale(v.Amount, *props.Scale)
			if !ok {
				return merrors.DataConflict(fmt.Sprintf("too many decimal places: got %d, max %d", frac, *props.Scale))
			}
		}

		// Min/Max (apply only if currencies match)
		if props.Min != nil && props.Min.Currency == v.Currency {
			cmp, cmpErr := compareDecimal128(v.Amount, props.Min.Amount)
			if cmpErr == nil && cmp < 0 {
				return merrors.DataConflict("amount below min")
			}
		}
		if props.Max != nil && props.Max.Currency == v.Currency {
			cmp, cmpErr := compareDecimal128(v.Amount, props.Max.Amount)
			if cmpErr == nil && cmp > 0 {
				return merrors.DataConflict("amount above max")
			}
		}
	}
	return nil
}

// References: existence check is injected.
type ExistFn func(resource mservice.Type, id primitive.ObjectID, filter bson.M) (bool, error)

func (p PropertySchema) ValidateReferences(vals []primitive.ObjectID, exist ExistFn) error {
	if p.Type != PTReference {
		return invalidType(PTReference, p.Type)
	}
	if err := validateMultiplicity(len(vals), false, p.Multiplicity); err != nil {
		return err
	}
	props, err := p.AsReference()
	if err != nil {
		return err
	}
	// Distinct by referenced ID (and resource)
	if err := ensureDistinctByKey(vals, func(r primitive.ObjectID) string { return props.Target + ":" + r.Hex() }, p.Multiplicity.Distinct); err != nil {
		return err
	}

	allowed := map[primitive.ObjectID]struct{}{}
	if len(props.AllowedIDs) > 0 {
		for _, id := range props.AllowedIDs {
			allowed[id] = struct{}{}
		}
	}

	for _, v := range vals {
		if len(allowed) > 0 {
			if _, ok := allowed[v]; !ok {
				return merrors.DataConflict(fmt.Sprintf("id %s not allowed", v.Hex()))
			}
		}
		if exist != nil {
			ok, exErr := exist(props.Target, v, bson.M{})
			if exErr != nil {
				return exErr
			}
			if !ok {
				return merrors.DataConflict("referenced document not found or disallowed")
			}
		}
	}
	return nil
}

// ----------------------------
// Decimal128 utilities
// ----------------------------

// compareDecimal128 returns -1 if a < b, 0 if a == b, 1 if a > b.
func compareDecimal128(a, b primitive.Decimal128) (int, error) {
	as := a.String()
	bs := b.String()

	af, _, err := big.ParseFloat(as, 10, 128, big.ToNearestEven)
	if err != nil {
		return 0, merrors.InvalidArgument(err.Error())
	}
	bf, _, err := big.ParseFloat(bs, 10, 128, big.ToNearestEven)
	if err != nil {
		return 0, merrors.InvalidArgument(err.Error())
	}
	return af.Cmp(bf), nil
}

// decimal128WithinScale checks if the number of fractional digits is <= scale.
func decimal128WithinScale(d primitive.Decimal128, scale int) (ok bool, fracDigits int) {
	// Normalize via big.Float to handle exponents; then trim trailing zeros.
	s := d.String()
	f, _, err := big.ParseFloat(s, 10, 128, big.ToNearestEven)
	if err != nil {
		fd := countFractionDigits(s)
		return fd <= scale, fd
	}
	fixed := f.Text('f', 40) // enough precision
	fixed = trimTrailingZeros(fixed)
	fd := countFractionDigits(fixed)
	return fd <= scale, fd
}

func countFractionDigits(s string) int {
	dot := -1
	for i := 0; i < len(s); i++ {
		if s[i] == '.' {
			dot = i
			break
		}
	}
	if dot < 0 {
		return 0
	}
	return len(s) - dot - 1
}

func trimTrailingZeros(s string) string {
	dot := -1
	for i := 0; i < len(s); i++ {
		if s[i] == '.' {
			dot = i
			break
		}
	}
	if dot < 0 {
		return s
	}
	j := len(s) - 1
	for j > dot && s[j] == '0' {
		j--
	}
	if j == dot {
		return s[:dot]
	}
	return s[:j+1]
}