package apiapproval

import (
	"context"
	"errors"
	"fmt"
	"slices"
	"strconv"
	"sync"
	"time"

	"git.julianfamily.org/keepassgo/apitokens"
)

var (
	ErrRequestDenied   = errors.New("authorization request denied")
	ErrRequestCanceled = errors.New("authorization request canceled")
	ErrRequestTimedOut = errors.New("authorization request timed out")
	ErrRequestNotFound = errors.New("authorization request not found")
)

type Outcome string

const (
	OutcomeAllowOnce        Outcome = "allow-once"
	OutcomeDenyOnce         Outcome = "deny-once"
	OutcomeAllowPermanent   Outcome = "allow-permanent"
	OutcomeDenyPermanent    Outcome = "deny-permanent"
	OutcomeCancel           Outcome = "cancel"
)

type Request struct {
	ID         string
	TokenID    string
	TokenName  string
	ClientName string
	Operation  apitokens.Operation
	Resource   apitokens.Resource
	RequestedAt time.Time
}

type Result struct {
	Outcome Outcome
	Rule    *apitokens.PolicyRule
}

type Broker struct {
	mu      sync.Mutex
	pending map[string]*pendingRequest
	timeout time.Duration
	now     func() time.Time
	nextID  func() string
}

type pendingRequest struct {
	request Request
	done    chan Outcome
}

type idGenerator struct {
	mu      sync.Mutex
	counter int
}

func NewBroker(timeout time.Duration) *Broker {
	gen := &idGenerator{}
	return &Broker{
		pending: map[string]*pendingRequest{},
		timeout: timeout,
		now: func() time.Time {
			return time.Now().UTC()
		},
		nextID: func() string {
			return gen.Next()
		},
	}
}

func (g *idGenerator) Next() string {
	g.mu.Lock()
	defer g.mu.Unlock()
	g.counter++
	return "approval-" + strconv.Itoa(g.counter)
}

func (b *Broker) Pending() []Request {
	b.mu.Lock()
	defer b.mu.Unlock()

	requests := make([]Request, 0, len(b.pending))
	for _, pending := range b.pending {
		requests = append(requests, pending.request)
	}
	slices.SortFunc(requests, func(a, c Request) int {
		switch {
		case a.RequestedAt.Before(c.RequestedAt):
			return -1
		case a.RequestedAt.After(c.RequestedAt):
			return 1
		case a.ID < c.ID:
			return -1
		case a.ID > c.ID:
			return 1
		default:
			return 0
		}
	})
	return requests
}

func (b *Broker) Request(ctx context.Context, token apitokens.Token, op apitokens.Operation, resource apitokens.Resource) (Result, error) {
	if b == nil {
		return Result{}, ErrRequestTimedOut
	}

	pending := &pendingRequest{
		request: Request{
			ID:          b.nextID(),
			TokenID:     token.ID,
			TokenName:   token.Name,
			ClientName:  token.ClientName,
			Operation:   op,
			Resource:    resource,
			RequestedAt: b.now(),
		},
		done: make(chan Outcome, 1),
	}

	b.mu.Lock()
	b.pending[pending.request.ID] = pending
	b.mu.Unlock()

	defer func() {
		b.mu.Lock()
		delete(b.pending, pending.request.ID)
		b.mu.Unlock()
	}()

	timer := time.NewTimer(b.timeout)
	defer timer.Stop()

	select {
	case outcome := <-pending.done:
		result, err := resultForOutcome(pending.request, outcome)
		if err != nil {
			return result, err
		}
		return result, nil
	case <-timer.C:
		return Result{}, ErrRequestTimedOut
	case <-ctx.Done():
		return Result{}, ctx.Err()
	}
}

func (b *Broker) Resolve(id string, outcome Outcome) (Request, *apitokens.PolicyRule, error) {
	b.mu.Lock()
	pending, ok := b.pending[id]
	b.mu.Unlock()
	if !ok {
		return Request{}, nil, ErrRequestNotFound
	}

	rule, err := RuleFromDecision(pending.request, outcome)
	if err != nil {
		return Request{}, nil, err
	}

	select {
	case pending.done <- outcome:
	default:
	}
	return pending.request, rule, nil
}

func resultForOutcome(request Request, outcome Outcome) (Result, error) {
	rule, err := RuleFromDecision(request, outcome)
	if err != nil {
		return Result{}, err
	}
	result := Result{Outcome: outcome, Rule: rule}
	switch outcome {
	case OutcomeAllowOnce, OutcomeAllowPermanent:
		return result, nil
	case OutcomeDenyOnce, OutcomeDenyPermanent:
		return result, ErrRequestDenied
	case OutcomeCancel:
		return result, ErrRequestCanceled
	default:
		return Result{}, fmt.Errorf("unsupported approval outcome %q", outcome)
	}
}

func RuleFromDecision(request Request, outcome Outcome) (*apitokens.PolicyRule, error) {
	switch outcome {
	case OutcomeAllowPermanent:
		rule := apitokens.PolicyRule{
			Effect:    apitokens.EffectAllow,
			Operation: request.Operation,
			Resource:  request.Resource,
		}
		return &rule, nil
	case OutcomeDenyPermanent:
		rule := apitokens.PolicyRule{
			Effect:    apitokens.EffectDeny,
			Operation: request.Operation,
			Resource:  request.Resource,
		}
		return &rule, nil
	case OutcomeAllowOnce, OutcomeDenyOnce, OutcomeCancel:
		return nil, nil
	default:
		return nil, fmt.Errorf("unsupported approval outcome %q", outcome)
	}
}