{{/*
Copyright 2019-present Facebook Inc. All rights reserved.
This source code is licensed under the Apache 2.0 license found
in the LICENSE file in the root directory of this source tree.
*/}}

{{ define "hook" }}

{{ with extend $ "Package" "hook" }}
	{{ template "header" . }}
{{ end }}

import "{{ $.Config.Package }}"

{{ $pkg := base $.Config.Package }}

{{ range $n := $.Nodes }}
	{{ $name := print $n.Name "Func" }}
	{{ $type := printf "*%s.%s" $pkg $n.MutationName }}

	// The {{ $name }} type is an adapter to allow the use of ordinary
	// function as {{ $n.Name }} mutator.
	type {{ $name }} func(context.Context, {{ $type }}) ({{ $pkg }}.Value, error)

	// Mutate calls f(ctx, m).
	func (f {{ $name }}) Mutate(ctx context.Context, m {{ $pkg }}.Mutation) ({{ $pkg }}.Value, error) {
		mv, ok := m.({{ $type }})
		if !ok {
			return nil, fmt.Errorf("unexpected mutation type %T. expect {{ $type }}", m)
		}
		return f(ctx, mv)
	}
{{ end }}

// Condition is a hook condition function.
type Condition func(context.Context, {{ $pkg }}.Mutation) bool

// And groups conditions with the AND operator.
func And(first, second Condition, rest ...Condition) Condition {
	return func(ctx context.Context, m {{ $pkg }}.Mutation) bool {
		if !first(ctx, m) || !second(ctx, m) {
			return false
		}
		for _, cond := range rest {
			if !cond(ctx, m) {
				return false
			}
		}
		return true
	}
}

// Or groups conditions with the OR operator.
func Or(first, second Condition, rest ...Condition) Condition {
	return func(ctx context.Context, m {{ $pkg }}.Mutation) bool {
		if first(ctx, m) || second(ctx, m) {
			return true
		}
		for _, cond := range rest {
			if cond(ctx, m) {
				return true
			}
		}
		return false
	}
}

// Not negates a given condition.
func Not(cond Condition) Condition {
	return func(ctx context.Context, m {{ $pkg }}.Mutation) bool {
		return !cond(ctx, m)
	}
}

// HasOp is a condition testing mutation operation.
func HasOp(op {{ $pkg }}.Op) Condition {
	return func(_ context.Context, m {{ $pkg }}.Mutation) bool {
		return m.Op().Is(op)
	}
}

{{ $conds := dict "HasFields" "Field" "HasAddedFields" "AddedField" "HasClearedFields" "FieldCleared" -}}
{{- range $cond := keys $conds }}
	{{ $method := get $conds $cond -}}
	// {{ $cond }} is a condition validating `.{{ $method }}` on fields.
	func {{ $cond }}(field string, fields ...string) Condition {
		return func(_ context.Context, m {{ $pkg }}.Mutation) bool {
			if {{ if ne $method "FieldCleared" }}_, {{ end }}exists := m.{{ $method }}(field); !exists {
				return false
			}
			for _, field := range fields {
				if {{ if ne $method "FieldCleared" }}_, {{ end }}exists := m.{{ $method }}(field); !exists {
					return false
				}
			}
			return true
		}
	}
{{- end }}

// If executes the given hook under condition.
//
//	hook.If(ComputeAverage, And(HasFields(...), HasAddedFields(...)))
//
func If(hk {{ $pkg }}.Hook, cond Condition) {{ $pkg }}.Hook {
	return func(next {{ $pkg }}.Mutator) {{ $pkg }}.Mutator {
		return {{ $pkg }}.MutateFunc(func(ctx context.Context, m {{ $pkg }}.Mutation) ({{ $pkg }}.Value, error) {
			if cond(ctx, m) {
				return hk(next).Mutate(ctx, m)
			}
			return next.Mutate(ctx, m)
		})
	}
}

// On executes the given hook only for the given operation.
//
//	hook.On(Log, {{ $pkg }}.Delete|{{ $pkg }}.Create)
//
func On(hk {{ $pkg }}.Hook, op {{ $pkg }}.Op) {{ $pkg }}.Hook {
	return If(hk, HasOp(op))
}

// Unless skips the given hook only for the given operation.
//
//	hook.Unless(Log, {{ $pkg }}.Update|{{ $pkg }}.UpdateOne)
//
func Unless(hk {{ $pkg }}.Hook, op {{ $pkg }}.Op) {{ $pkg }}.Hook {
	return If(hk, Not(HasOp(op)))
}

// FixedError is a hook returning a fixed error.
func FixedError(err error) {{ $pkg }}.Hook {
	return func({{ $pkg }}.Mutator) {{ $pkg }}.Mutator {
		return {{ $pkg }}.MutateFunc(func(context.Context, {{ $pkg }}.Mutation) ({{ $pkg }}.Value, error) {
			return nil, err
		})
	}
}


// Reject returns a hook that rejects all operations that match op.
//
//	func (T) Hooks() []{{ $pkg }}.Hook {
//		return []{{ $pkg }}.Hook{
//			Reject({{ $pkg }}.Delete|{{ $pkg }}.Update),
//		}
//	}
//
func Reject(op {{ $pkg }}.Op) {{ $pkg }}.Hook {
	hk := FixedError(fmt.Errorf("%s operation is not allowed", op))
	return On(hk, op)
}

// Chain acts as a list of hooks and is effectively immutable.
// Once created, it will always hold the same set of hooks in the same order.
type Chain struct {
	hooks []{{ $pkg }}.Hook
}

// NewChain creates a new chain of hooks.
func NewChain(hooks ...{{ $pkg }}.Hook) Chain {
	return Chain{append([]{{ $pkg }}.Hook(nil), hooks...)}
}

// Hook chains the list of hooks and returns the final hook.
func (c Chain) Hook() {{ $pkg }}.Hook {
	return func(mutator {{ $pkg }}.Mutator) {{ $pkg }}.Mutator {
		for i := len(c.hooks) - 1; i >= 0; i-- {
			mutator = c.hooks[i](mutator)
		}
		return mutator
	}
}

// Append extends a chain, adding the specified hook
// as the last ones in the mutation flow.
func (c Chain) Append(hooks ...{{ $pkg }}.Hook) Chain {
	newHooks := make([]{{ $pkg }}.Hook, 0, len(c.hooks)+len(hooks))
	newHooks = append(newHooks, c.hooks...)
	newHooks = append(newHooks, hooks...)
	return Chain{newHooks}
}

// Extend extends a chain, adding the specified chain
// as the last ones in the mutation flow.
func (c Chain) Extend(chain Chain) Chain {
	return c.Append(chain.hooks...)
}

{{ end }}