From e4d7b5ff581da26b225a567adbe6109cc8f23211 Mon Sep 17 00:00:00 2001
From: Drew DeVault <sir@cmpwn.com>
Date: Fri, 20 Aug 2021 09:39:59 +0200
Subject: [PATCH] valid: new module for input validation

---
 valid/valid.go | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 valid/valid.go

diff --git a/valid/valid.go b/valid/valid.go
new file mode 100644
index 0000000000000000000000000000000000000000..e01ac07b393fa0b38a68d7cec590f46451be4eda
--- /dev/null
+++ b/valid/valid.go
@@ -0,0 +1,95 @@
+package valid
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/99designs/gqlgen/graphql"
+	"github.com/vektah/gqlparser/v2/gqlerror"
+)
+
+type Validation struct {
+	ctx   context.Context
+	input map[string]interface{}
+}
+
+type ValidationError struct {
+	valid *Validation
+	err   *gqlerror.Error
+}
+
+// Creates a new validation context.
+func New(ctx context.Context) *Validation {
+	return &Validation{
+		ctx: ctx,
+	}
+}
+
+// Adds an input map to a validation context.
+func (valid *Validation) WithInput(input map[string]interface{}) *Validation {
+	valid.input = input
+	return valid
+}
+
+// Returns true if no errors were found.
+func (valid *Validation) Ok() bool {
+	return len(graphql.GetErrors(valid.ctx)) == 0
+}
+
+// Fetches a string from the validation context, which must have an input
+// registered. If the field is not present, the callback is not run. If
+// present, but not a string, an error is recorded. Otherwise, the function is
+// called with the string for the user to conduct further validation with.
+func (valid *Validation) OptionalString(name string, fn func(s string)) {
+	if valid.input == nil {
+		panic("Attempted to validate fields without input")
+	}
+	if o, ok := valid.input[name]; ok {
+		s, ok := o.(string)
+		valid.
+			Expect(ok, fmt.Sprintf("Expected {} to be a string", name)).
+			WithField(name)
+		if ok {
+			fn(s)
+		}
+	}
+}
+
+// Asserts that a condition is true, recording a GraphQL error with the given
+// message if not.
+func (valid *Validation) Expect(cond bool, msg string) *ValidationError {
+	if cond {
+		return &ValidationError{valid: valid}
+	}
+	err := &gqlerror.Error{
+		Path:    graphql.GetPath(valid.ctx),
+		Message: msg,
+	}
+	graphql.AddError(valid.ctx, err)
+	return &ValidationError{
+		valid: valid,
+		err:   err,
+	}
+}
+
+// Associates a field name with an error.
+func (err *ValidationError) WithField(field string) *ValidationError {
+	if err.err == nil {
+		return err
+	}
+	if err.err.Extensions == nil {
+		err.err.Extensions = make(map[string]interface{})
+	}
+	err.err.Extensions["field"] = field
+	return err
+}
+
+// Composes another assertion onto the same validation context which initially
+// created an error. Short-circuiting is used, such that if the earlier
+// condition failed, the new condition is not considered.
+func (err *ValidationError) And(cond bool, msg string) *ValidationError {
+	if err.err != nil {
+		return err
+	}
+	return err.valid.Expect(cond, msg)
+}