package contract

import (
	"encoding"
	"encoding/json"
	"errors"
	"fmt"
	"reflect"
	"strconv"
	"strings"

	"git.yuntuo.hk/k2safe/go-omni/openapi"
)

// Scalar explicitly opts one application Go type into custom wire conversion.
// Input is a | separated union of scalar wire types; Output is one wire type.
// The value must implement json.Marshaler, its pointer json.Unmarshaler, and
// Text=true additionally requires encoding.TextUnmarshaler on the pointer.
// No process-global registry or mutation of other binders is involved.
type Scalar struct {
	Type                  reflect.Type
	JSONInput, JSONOutput string
	Text                  bool
}

func ScalarOf[T any](input, output string, text bool) Scalar {
	return Scalar{Type: reflect.TypeOf((*T)(nil)).Elem(), JSONInput: input, JSONOutput: output, Text: text}
}

type compiler struct {
	scalars map[reflect.Type]Scalar
}
type scalarText string

func (s Scalar) validate(schemaOnly bool) error {
	if s.Type == nil || s.Type.Kind() == reflect.Pointer || s.Type.Kind() == reflect.Interface {
		return errors.New("contract: scalar requires a concrete non-pointer type")
	}
	seen := map[string]bool{}
	for _, kind := range strings.Split(s.JSONInput, "|") {
		kind = strings.TrimSpace(kind)
		if wireSchema(kind) == nil || seen[kind] {
			return fmt.Errorf("contract: invalid/duplicate scalar input %q", kind)
		}
		seen[kind] = true
	}
	if wireSchema(s.JSONOutput) == nil {
		return fmt.Errorf("contract: invalid scalar output %q", s.JSONOutput)
	}
	if !schemaOnly {
		if !s.Type.Implements(reflect.TypeOf((*json.Marshaler)(nil)).Elem()) || !reflect.PointerTo(s.Type).Implements(reflect.TypeOf((*json.Unmarshaler)(nil)).Elem()) {
			return fmt.Errorf("contract: %s needs value MarshalJSON and pointer UnmarshalJSON", s.Type)
		}
		if s.Text && !reflect.PointerTo(s.Type).Implements(reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()) {
			return fmt.Errorf("contract: %s needs UnmarshalText", s.Type)
		}
	}
	return nil
}
func wireSchema(kind string) *openapi.Schema {
	switch kind {
	case "string":
		return &openapi.Schema{Type: "string"}
	case "bool":
		return &openapi.Schema{Type: "boolean"}
	case "int32", "int64":
		return &openapi.Schema{Type: "integer", Format: kind}
	case "float64":
		return &openapi.Schema{Type: "number", Format: "double"}
	}
	return nil
}
func (s Scalar) inputSchema() *openapi.Schema {
	var alternatives []*openapi.Schema
	for _, kind := range strings.Split(s.JSONInput, "|") {
		alternatives = append(alternatives, wireSchema(strings.TrimSpace(kind)))
	}
	if len(alternatives) == 1 {
		return alternatives[0]
	}
	return &openapi.Schema{AnyOf: alternatives}
}
func (s Scalar) decode(dst reflect.Value, value any) (err error) {
	// User decoders may fail; do not allow their panic to escape a binder.
	defer func() {
		if r := recover(); r != nil {
			err = errors.New("custom scalar decoder panicked")
		}
	}()
	if text, ok := value.(scalarText); ok {
		decoder, ok := dst.Addr().Interface().(encoding.TextUnmarshaler)
		if !s.Text || !ok {
			return errors.New("text decoder not available")
		}
		return decoder.UnmarshalText([]byte(text))
	}
	allowed := false
	for _, kind := range strings.Split(s.JSONInput, "|") {
		if scalarAccepts(strings.TrimSpace(kind), value) {
			allowed = true
			break
		}
	}
	if !allowed {
		return errors.New("value does not match declared scalar input")
	}
	decoder, ok := dst.Addr().Interface().(json.Unmarshaler)
	if !ok {
		return errors.New("JSON decoder not available")
	}
	raw, err := json.Marshal(value) // json.Number preserves exact integer tokens.
	if err != nil {
		return err
	}
	return decoder.UnmarshalJSON(raw)
}
func scalarAccepts(kind string, value any) bool {
	switch kind {
	case "string":
		_, ok := value.(string)
		return ok
	case "bool":
		_, ok := value.(bool)
		return ok
	case "int32", "int64":
		n, ok := value.(json.Number)
		if !ok {
			return false
		}
		bits := 64
		if kind == "int32" {
			bits = 32
		}
		_, err := strconv.ParseInt(string(n), 10, bits)
		return err == nil
	case "float64":
		n, ok := value.(json.Number)
		if !ok {
			return false
		}
		_, err := strconv.ParseFloat(string(n), 64)
		return err == nil
	}
	return false
}
func responseSchema(n *node) *openapi.Schema {
	b := base(n)
	if b.scalar != nil {
		s := wireSchema(b.scalar.JSONOutput)
		if n.typ.Kind() == reflect.Pointer {
			s = nullableSchema(s)
		}
		return s
	}
	// Preserve the field's own constraints (including pointer range/enum and
	// collection length) while changing only nested custom scalar wire types.
	s := copySchema(n.schema)
	if b.typ.Kind() == reflect.Slice {
		s.Items = responseSchema(b.elem)
	}
	if b.typ.Kind() == reflect.Map {
		s.AdditionalProperties = responseSchema(b.elem)
	}
	for _, f := range b.fields {
		if f.source == "json" {
			s.Properties[f.name] = responseSchema(f.value)
		}
	}
	return s
}

// ValidateScalars checks the application's explicitly registered method contracts.
func ValidateScalars(scalars ...Scalar) error {
	seen := map[reflect.Type]bool{}
	for _, s := range scalars {
		if err := s.validate(false); err != nil {
			return err
		}
		if seen[s.Type] {
			return fmt.Errorf("contract: duplicate scalar type %s", s.Type)
		}
		seen[s.Type] = true
	}
	return nil
}

// OpenAPI 3.0 nullable only applies alongside an explicit type. A union needs
// an explicit null alternative; an unconstrained dynamic schema already accepts null.
func nullableSchema(schema *openapi.Schema) *openapi.Schema {
	s := copySchema(schema)
	if s.Type != "" {
		s.Nullable = true
		return s
	}
	if len(s.AnyOf) > 0 {
		s.AnyOf = append(s.AnyOf, &openapi.Schema{Type: "string", Nullable: true, Enum: []any{nil}})
	}
	return s
}