Further flush out ability to auto-bind to functions and types, including recursion.

Fix code coverage, support additional functions.

Add bind examples

Avoid errors where value IsZero

Add type tag, nested resolvers on Bind

Extend type

Don't call .Type() on zero values

Author: Alan Colon

bind.go

@@ -0,0 +1,251 @@
+package graphql
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"reflect"
+)
+
+var ctxType = reflect.TypeOf((*context.Context)(nil)).Elem()
+var errType = reflect.TypeOf((*error)(nil)).Elem()
+
+/*
+	Bind will create a Field around a function formatted a certain way, or any value.
+
+	The input parameters can be, in any order,
+	- context.Context, or *context.Context (optional)
+	- An input struct, or pointer (optional)
+
+	The output parameters can be, in any order,
+	- A primitive, an output struct, or pointer (required for use in schema)
+	- error (optional)
+
+	Input or output types provided will be automatically bound using BindType.
+*/
+func Bind(bindTo interface{}, additionalFields ...Fields) *Field {
+	combinedAdditionalFields := MergeFields(additionalFields...)
+	val := reflect.ValueOf(bindTo)
+	tipe := reflect.TypeOf(bindTo)
+	if tipe.Kind() == reflect.Func {
+		in := tipe.NumIn()
+		out := tipe.NumOut()
+
+		var ctxIn *int
+		var inputIn *int
+
+		var errOut *int
+		var outputOut *int
+
+		queryArgs := FieldConfigArgument{}
+
+		if in > 2 {
+			panic(fmt.Sprintf("Mismatch on number of inputs. Expected 0, 1, or 2. got %d.", tipe.NumIn()))
+		}
+
+		if out > 2 {
+			panic(fmt.Sprintf("Mismatch on number of outputs. Expected 0, 1, or 2, got %d.", tipe.NumOut()))
+		}
+
+		// inTypes := make([]reflect.Type, in)
+		// outTypes := make([]reflect.Type, out)
+
+		for i := 0; i < in; i++ {
+			t := tipe.In(i)
+			if t.Kind() == reflect.Ptr {
+				t = t.Elem()
+			}
+			switch t {
+			case ctxType:
+				if ctxIn != nil {
+					panic(fmt.Sprintf("Unexpected multiple *context.Context inputs."))
+				}
+				ctxIn = intP(i)
+			default:
+				if inputIn != nil {
+					panic(fmt.Sprintf("Unexpected multiple inputs."))
+				}
+				inputType := tipe.In(i)
+				if inputType.Kind() == reflect.Ptr {
+					inputType = inputType.Elem()
+				}
+				inputFields := BindFields(reflect.New(inputType).Interface())
+				for key, inputField := range inputFields {
+					queryArgs[key] = &ArgumentConfig{
+						Type: inputField.Type,
+					}
+				}
+
+				inputIn = intP(i)
+			}
+		}
+
+		for i := 0; i < out; i++ {
+			t := tipe.Out(i)
+			switch t.String() {
+			case errType.String():
+				if errOut != nil {
+					panic(fmt.Sprintf("Unexpected multiple error outputs"))
+				}
+				errOut = intP(i)
+			default:
+				if outputOut != nil {
+					panic(fmt.Sprintf("Unexpected multiple outputs"))
+				}
+				outputOut = intP(i)
+			}
+		}
+
+		resolve := func(p ResolveParams) (output interface{}, err error) {
+			inputs := make([]reflect.Value, in)
+			if ctxIn != nil {
+				isPtr := tipe.In(*ctxIn).Kind() == reflect.Ptr
+				if isPtr {
+					if p.Context == nil {
+						inputs[*ctxIn] = reflect.New(ctxType)
+					} else {
+						inputs[*ctxIn] = reflect.ValueOf(&p.Context)
+					}
+				} else {
+					if p.Context == nil {
+						inputs[*ctxIn] = reflect.New(ctxType).Elem()
+					} else {
+						inputs[*ctxIn] = reflect.ValueOf(p.Context).Convert(ctxType).Elem()
+					}
+				}
+			}
+			if inputIn != nil {
+				var inputType, inputBaseType, sourceType, sourceBaseType reflect.Type
+				sourceVal := reflect.ValueOf(p.Source)
+				sourceExists := !sourceVal.IsZero()
+				if sourceExists {
+					sourceType = sourceVal.Type()
+					if sourceType.Kind() == reflect.Ptr {
+						sourceBaseType = sourceType.Elem()
+					} else {
+						sourceBaseType = sourceType
+					}
+				}
+				inputType = tipe.In(*inputIn)
+				isPtr := tipe.In(*inputIn).Kind() == reflect.Ptr
+				if isPtr {
+					inputBaseType = inputType.Elem()
+				} else {
+					inputBaseType = inputType
+				}
+				var input interface{}
+				if sourceExists && sourceBaseType.AssignableTo(inputBaseType) {
+					input = sourceVal.Interface()
+				} else {
+					input = reflect.New(inputBaseType).Interface()
+					j, err := json.Marshal(p.Args)
+					if err == nil {
+						err = json.Unmarshal(j, &input)
+					}
+					if err != nil {
+						return nil, err
+					}
+				}
+
+				inputs[*inputIn], err = convertValue(reflect.ValueOf(input), inputType)
+				if err != nil {
+					return nil, err
+				}
+			}
+			results := val.Call(inputs)
+			if errOut != nil {
+				val := results[*errOut].Interface()
+				if val != nil {
+					err = val.(error)
+				}
+				if err != nil {
+					return output, err
+				}
+			}
+			if outputOut != nil {
+				var val reflect.Value
+				val, err = convertValue(results[*outputOut], tipe.Out(*outputOut))
+				if err != nil {
+					return nil, err
+				}
+				if !val.IsZero() {
+					output = val.Interface()
+				}
+			}
+			return output, err
+		}
+
+		var outputType Output
+		if outputOut != nil {
+			outputType = BindType(tipe.Out(*outputOut))
+			extendType(outputType, combinedAdditionalFields)
+		}
+
+		field := &Field{
+			Type:    outputType,
+			Resolve: resolve,
+			Args:    queryArgs,
+		}
+
+		return field
+	} else if tipe.Kind() == reflect.Struct {
+		fieldType := BindType(reflect.TypeOf(bindTo))
+		extendType(fieldType, combinedAdditionalFields)
+		field := &Field{
+			Type: fieldType,
+			Resolve: func(p ResolveParams) (data interface{}, err error) {
+				return bindTo, nil
+			},
+		}
+		return field
+	} else {
+		if len(additionalFields) > 0 {
+			panic("Cannot add field resolvers to a scalar type.")
+		}
+		return &Field{
+			Type: getGraphType(tipe),
+			Resolve: func(p ResolveParams) (data interface{}, err error) {
+				return bindTo, nil
+			},
+		}
+	}
+}
+
+func extendType(t Type, fields Fields) {
+	switch t.(type) {
+	case *Object:
+		object := t.(*Object)
+		for fieldName, fieldConfig := range fields {
+			object.AddFieldConfig(fieldName, fieldConfig)
+		}
+		return
+	case *List:
+		list := t.(*List)
+		extendType(list.OfType, fields)
+		return
+	}
+}
+
+func convertValue(value reflect.Value, targetType reflect.Type) (ret reflect.Value, err error) {
+	if !value.IsValid() || value.IsZero() {
+		return reflect.Zero(targetType), nil
+	}
+	if value.Type().Kind() == reflect.Ptr {
+		if targetType.Kind() == reflect.Ptr {
+			return value, nil
+		} else {
+			return value.Elem(), nil
+		}
+	} else {
+		if targetType.Kind() == reflect.Ptr {
+			// Will throw an informative error
+			return value.Convert(targetType), nil
+		} else {
+			return value, nil
+		}
+	}
+}
+
+func intP(i int) *int {
+	return &i
+}