package validjsonschema

import (
	"bytes"
	"context"
	"fmt"
	"sync"

	"github.com/santhosh-tekuri/jsonschema/v6"

	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
	"gitea.maximumdirect.net/eric/notarius/internal/framework/pipeline"
)

const Key = "generic/valid_json_schema"
const ReasonCodeInvalidJSON = "invalid_json"
const ReasonCodeSchemaInvalid = "json_schema_invalid"

type Options struct{}

type schemaIdentity struct {
	id      string
	name    string
	version string
	digest  string
}

type compiledSchema struct {
	schema *jsonschema.Schema
	err    error
}

type schemaCompiler func([]byte) (*jsonschema.Schema, error)

type Validator struct {
	mu      sync.Mutex
	schemas map[schemaIdentity]compiledSchema
	compile schemaCompiler
}

var _ contracts.SerializedValidator = (*Validator)(nil)

func New(Options) *Validator {
	return &Validator{schemas: make(map[schemaIdentity]compiledSchema), compile: compileSchema}
}

func (v *Validator) Name() string { return Key }
func (v *Validator) ExecutionClass() contracts.ExecutionClass {
	return contracts.ExecutionClassDeterministic
}

func (v *Validator) Validate(_ context.Context, req contracts.SerializedValidationRequest) (contracts.ValidationResult, error) {
	if len(req.Schema.JSONSchema) == 0 {
		_, err := v.compiledSchema(req.Schema)
		return contracts.ValidationResult{}, err
	}
	instance, err := jsonschema.UnmarshalJSON(bytes.NewReader(req.Content))
	if err != nil {
		return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCodeInvalidJSON, Message: "payload is not valid JSON", CorrectionGuidance: "Return one complete replacement response encoded as valid JSON."}, nil
	}
	schema, err := v.compiledSchema(req.Schema)
	if err != nil {
		return contracts.ValidationResult{}, err
	}
	if err := schema.Validate(instance); err != nil {
		return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCodeSchemaInvalid, Message: "payload does not conform to response schema", CorrectionGuidance: "Return one complete JSON replacement that conforms exactly to the supplied response schema."}, nil
	}
	return contracts.ValidationResult{Approved: true}, nil
}

func (v *Validator) compiledSchema(schema contracts.ArtifactSchema) (*jsonschema.Schema, error) {
	identity := schemaIdentity{
		id:      schema.ID,
		name:    schema.Name,
		version: schema.Version,
		digest:  contracts.DigestArtifactSchema(schema),
	}
	v.mu.Lock()
	defer v.mu.Unlock()
	if v.schemas == nil {
		v.schemas = make(map[schemaIdentity]compiledSchema)
	}
	if cached, ok := v.schemas[identity]; ok {
		return cached.schema, cached.err
	}
	compiler := v.compile
	if compiler == nil {
		compiler = compileSchema
	}
	compiled, err := compiler(schema.JSONSchema)
	v.schemas[identity] = compiledSchema{schema: compiled, err: err}
	return compiled, err
}

func compileSchema(schemaContent []byte) (*jsonschema.Schema, error) {
	if len(schemaContent) == 0 {
		return nil, fmt.Errorf("response schema content is not available")
	}
	schemaDocument, err := jsonschema.UnmarshalJSON(bytes.NewReader(schemaContent))
	if err != nil {
		return nil, fmt.Errorf("parse response schema: %w", err)
	}
	compiler := jsonschema.NewCompiler()
	if err := compiler.AddResource("schema.json", schemaDocument); err != nil {
		return nil, fmt.Errorf("load response schema: %w", err)
	}
	schema, err := compiler.Compile("schema.json")
	if err != nil {
		return nil, fmt.Errorf("compile response schema: %w", err)
	}
	return schema, nil
}

func Spec() pipeline.ValidatorSpec {
	return pipeline.ValidatorSpec{Key: Key, ExecutionClass: contracts.ExecutionClassDeterministic}
}

func Register(registry *pipeline.ValidatorRegistry) error {
	return pipeline.RegisterSerializedValidatorBuilder(registry, pipeline.SerializedValidatorSpec{
		ValidatorSpec: Spec(), SupportsChunks: true, SupportsArtifacts: true,
	}, validateOptions, func(request pipeline.BuildRequest) (contracts.SerializedValidator, error) {
		options, err := DecodeOptions(request.Options)
		if err != nil {
			return nil, err
		}
		return New(options), nil
	})
}

func DecodeOptions(options map[string]any) (Options, error) {
	if err := pipeline.RejectUnknownOptions(options); err != nil {
		return Options{}, err
	}
	return Options{}, nil
}
func validateOptions(options map[string]any) error { _, err := DecodeOptions(options); return err }
