// Copyright 2022 Princess B33f Heavy Industries / Dave Shanley
// SPDX-License-Identifier: MIT

package base

import (
	"github.com/pb33f/libopenapi/datamodel/low"
	"github.com/pb33f/libopenapi/datamodel/low/base"
)

// SchemaProxy exists as a stub that will create a Schema once (and only once) the Schema() method is called. An
// underlying low-level SchemaProxy backs this high-level one.
//
// Why use a Proxy design?
//
// There are three reasons.
//
// 1. Circular References and Endless Loops.
//
// JSON Schema allows for references to be used. This means references can loop around and create infinite recursive
// structures, These 'Circular references' technically mean a schema can NEVER be resolved, not without breaking the
// loop somewhere along the chain.
//
// Polymorphism in the form of 'oneOf' and 'anyOf' in version 3+ only exacerbates the problem.
//
// These circular traps can be discovered using the resolver, however it's still not enough to stop endless loops and
// endless goroutine spawning. A proxy design means that resolving occurs on demand and runs down a single level only.
// preventing any run-away loops.
//
// 2. Performance
//
// Even without circular references, Polymorphism creates large additional resolving chains that take a long time
// and slow things down when building. By preventing recursion through every polymorphic item, building models is kept
// fast and snappy, which is desired for realtime processing of specs.
//
//  - Q: Yeah, but, why not just use state to avoiding re-visiting seen polymorphic nodes?
//  - A: It's slow, takes up memory and still has runaway potential in very, very long chains.
//
// 3. Short Circuit Errors.
//
// Schemas are where things can get messy, mainly because the Schema standard changes between versions, and
// it's not actually JSONSchema until 3.1, so lots of times a bad schema will break parsing. Errors are only found
// when a schema is needed, so the rest of the document is parsed and ready to use.
type SchemaProxy struct {
	schema     *low.NodeReference[*base.SchemaProxy]
	buildError error
}

// NewSchemaProxy creates a new high-level SchemaProxy from a low-level one.
func NewSchemaProxy(schema *low.NodeReference[*base.SchemaProxy]) *SchemaProxy {
	return &SchemaProxy{schema: schema}
}

// Schema will create a new Schema instance using NewSchema from the low-level SchemaProxy backing this high-level one.
// If there is a problem building the Schema, then this method will return nil. Use GetBuildError to gain access
// to that building error.
func (sp *SchemaProxy) Schema() *Schema {
	s := sp.schema.Value.Schema()
	if s == nil {
		sp.buildError = sp.schema.Value.GetBuildError()
		return nil
	}
	return NewSchema(s)
}

// GetBuildError returns any error that was thrown when calling Schema()
func (sp *SchemaProxy) GetBuildError() error {
	return sp.buildError
}

func (sp *SchemaProxy) GoLow() *base.SchemaProxy {
	if sp.schema == nil {
		return nil
	}
	return sp.schema.Value
}