package domain

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base32"
	"encoding/binary"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"
)

var ErrConflict = errors.New("task version conflict")
var ErrNotFound = errors.New("task not found")
var ErrInvalid = errors.New("invalid event")

type TaskState string

const (
	StateQueued    TaskState = "queued"
	StateLeased    TaskState = "leased"
	StateCompleted TaskState = "completed"
	StateFailed    TaskState = "failed"
	StateBlocked   TaskState = "blocked"
)

type Estimate struct {
	Value      float64 `json:"value"`
	Who        string  `json:"who"`
	Confidence float64 `json:"confidence"`
}
type Lease struct {
	HarnessID string    `json:"harness_id"`
	Until     time.Time `json:"until"`
}
type Task struct {
	ID               string     `json:"id"`
	Source           string     `json:"source"`
	ExternalID       string     `json:"external_id"`
	Project          string     `json:"project"`
	Capability       []string   `json:"capability"`
	Parent           string     `json:"parent,omitempty"`
	InherentPriority int        `json:"inherent_priority"`
	Due              *time.Time `json:"due,omitempty"`
	Estimate         *Estimate  `json:"estimate,omitempty"`
	State            TaskState  `json:"state"`
	Lease            *Lease     `json:"lease,omitempty"`
	Version          int        `json:"version"`
	Title            string     `json:"title,omitempty"`
}

type Event struct {
	Seq     uint64          `json:"seq"`
	ID      string          `json:"id"`
	Type    string          `json:"type"`
	TaskID  string          `json:"task_id"`
	Version int             `json:"version"`
	At      time.Time       `json:"at"`
	Payload json.RawMessage `json:"payload"`
}

func Hash(v []byte) string { h := sha256.Sum256(v); return hex.EncodeToString(h[:]) }

// NewID returns a sortable, 128-bit ULID-like identifier using the canonical
// 48-bit millisecond timestamp plus 80 bits of cryptographic randomness.

var ulidEncoding = base32.NewEncoding("0123456789ABCDEFGHJKMNPQRSTVWXYZ").WithPadding(base32.NoPadding)

func NewID() string {
	b := make([]byte, 16)
	binary.BigEndian.PutUint64(b[:8], uint64(time.Now().UnixMilli())<<16)
	_, _ = rand.Read(b[6:])
	return ulidEncoding.EncodeToString(b)
}
func ValidateEvent(e Event) error {
	if e.Type == "" || e.TaskID == "" || len(e.Payload) == 0 || len(e.Payload) > 64*1024 {
		return ErrInvalid
	}
	allowed := map[string]bool{"TaskCreated": true, "TaskLeased": true, "TaskReleased": true, "TaskCompleted": true, "TaskFailed": true, "TaskBlocked": true, "ApprovalRequested": true, "ApprovalGranted": true, "ApprovalDenied": true, "TaskAmended": true, "QuotaReported": true, "StandupAdvisory": true}
	if !allowed[e.Type] {
		return fmt.Errorf("%w: unknown type %q", ErrInvalid, e.Type)
	}
	var p map[string]any
	if err := json.Unmarshal(e.Payload, &p); err != nil {
		return fmt.Errorf("%w: payload is not JSON", ErrInvalid)
	}
	return ValidatePayload(e.Type, p)
}
func ValidateCreated(p map[string]any) error {
	for _, k := range []string{"source", "external_id", "project"} {
		if s, ok := p[k].(string); !ok || strings.TrimSpace(s) == "" {
			return fmt.Errorf("%w: %s required", ErrInvalid, k)
		}
	}
	return nil
}

func ValidatePayload(typ string, p map[string]any) error {
	requiredString := func(key string) error {
		v, ok := p[key].(string)
		if !ok || strings.TrimSpace(v) == "" {
			return fmt.Errorf("%w: %s required", ErrInvalid, key)
		}
		return nil
	}
	switch typ {
	case "TaskCreated":
		return ValidateCreated(p)
	case "TaskLeased":
		if err := requiredString("harness_id"); err != nil {
			return err
		}
		if _, ok := p["until_ns"].(float64); !ok {
			return fmt.Errorf("%w: until_ns required", ErrInvalid)
		}
	case "TaskReleased":
		if err := requiredString("handoff_ref"); err != nil && p["reason"] == nil {
			return err
		}
	case "TaskCompleted":
		if err := requiredString("report_ref"); err != nil {
			return err
		}
	case "TaskFailed":
		if err := requiredString("reason"); err != nil {
			return err
		}
	case "TaskBlocked":
		if err := requiredString("blocker"); err != nil {
			return err
		}
	case "TaskAmended":
		if len(p) == 0 {
			return fmt.Errorf("%w: amendment cannot be empty", ErrInvalid)
		}
	case "ApprovalRequested":
		for _, k := range []string{"subject_ref", "options"} {
			if _, ok := p[k]; !ok {
				return fmt.Errorf("%w: %s required", ErrInvalid, k)
			}
		}
	case "ApprovalGranted", "ApprovalDenied":
		if err := requiredString("subject_ref"); err != nil {
			return err
		}
	}
	return nil
}