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")

// ErrDuplicate is returned by Store.Append for a TaskCreated event whose
// (source, external_id) pair was already ingested. The caller already has a
// task for this content; nothing was appended.
var ErrDuplicate = errors.New("duplicate task ingestion")

// CurrentEventSchema is 2: schema 2 requires every event to declare its
// authorizing Surface (see ValidateEvent), enforced at the store append
// boundary. Schema 1 events already on disk replay unchanged — tolerant
// reader, not upcast (spec open question #2).
const CurrentEventSchema = 2

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"`
	Description      string     `json:"description,omitempty"`
}

type Event struct {
	SchemaVersion int             `json:"schema_version,omitempty"`
	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"`
	// Surface identifies the bus capability the emitter is authorized under
	// (see internal/authz). It is required on every event so authorization is
	// enforced once, at the store append boundary, regardless of whether the
	// emitter reached the store over HTTP, from the router, from a harness
	// adapter, or from a provider.
	Surface string `json:"surface"`
}

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.SchemaVersion > CurrentEventSchema || e.Type == "" || e.TaskID == "" || len(e.Payload) == 0 || len(e.Payload) > 64*1024 {
		return ErrInvalid
	}
	if e.SchemaVersion >= 2 && strings.TrimSpace(e.Surface) == "" {
		return fmt.Errorf("%w: surface required", 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, "TaskCorrected": 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)
	}
	if p == nil {
		return fmt.Errorf("%w: payload must be an object", 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
		}
		until, untilOK := p["until_ns"].(float64)
		if ttl, ok := p["ttl"].(float64); ok {
			if ttl <= 0 {
				return fmt.Errorf("%w: ttl invalid", ErrInvalid)
			}
		} else if !untilOK || until <= float64(time.Now().UnixNano()) {
			return fmt.Errorf("%w: ttl required", ErrInvalid)
		}
		if v, ok := p["expected_version"].(float64); !ok || v < 0 || v != float64(int(v)) {
			return fmt.Errorf("%w: expected_version invalid", ErrInvalid)
		}
	case "TaskReleased":
		if err := requiredString("handoff_ref"); err != nil && p["reason"] == nil {
			return err
		}
		if _, ok := p["handoff_ref"]; ok {
			if err := requiredHash(p, "handoff_ref"); err != nil {
				return err
			}
			v, ok := p["anchor_sha"].(string)
			if !ok || len(v) != 40 || strings.TrimSpace(v) != v {
				return fmt.Errorf("%w: anchor_sha invalid", ErrInvalid)
			}
		}
	case "TaskCompleted":
		if err := requiredString("report_ref"); err != nil {
			return err
		}
		if err := requiredHash(p, "report_ref"); err != nil {
			return err
		}
		if receipt, ok := p["receipt"].(map[string]any); !ok || len(receipt) == 0 {
			return fmt.Errorf("%w: receipt required", ErrInvalid)
		}
	case "TaskFailed":
		if err := requiredString("reason"); err != nil {
			return err
		}
	case "TaskBlocked":
		if err := requiredString("blocker"); err != nil {
			return err
		}
		if _, ok := p["handoff_ref"]; ok {
			if err := requiredHash(p, "handoff_ref"); err != nil {
				return err
			}
		}
	case "TaskAmended":
		if len(p) == 0 {
			return fmt.Errorf("%w: amendment cannot be empty", ErrInvalid)
		}
	case "TaskCorrected":
		// §3.1: "a wrong event is never edited; a compensating event is
		// appended and replay sees both." `corrects` names the event this one
		// reverses/repairs — existence against the log is checked in
		// Store.Append, where the log is visible; ValidatePayload only knows
		// shape.
		if err := requiredString("corrects"); err != nil {
			return err
		}
		if v, ok := p["state"]; ok {
			s, ok := v.(string)
			if !ok {
				return fmt.Errorf("%w: state must be a string", ErrInvalid)
			}
			switch TaskState(s) {
			case StateQueued, StateLeased, StateCompleted, StateFailed, StateBlocked:
			default:
				return fmt.Errorf("%w: state invalid", ErrInvalid)
			}
		}
		if len(p) < 2 {
			return fmt.Errorf("%w: correction must change at least one field", 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
		}
	case "QuotaReported":
		if err := requiredString("harness_id"); err != nil {
			return err
		}
		if v, ok := p["consumed"].(float64); !ok || v < 0 {
			return fmt.Errorf("%w: consumed required", ErrInvalid)
		}
	case "StandupAdvisory":
		if _, ok := p["items"]; !ok {
			return fmt.Errorf("%w: items required", ErrInvalid)
		}
	}
	return nil
}

func requiredHash(p map[string]any, key string) error {
	v, ok := p[key].(string)
	if !ok || len(v) != 64 {
		return fmt.Errorf("%w: %s must be sha256", ErrInvalid, key)
	}
	if _, err := hex.DecodeString(v); err != nil {
		return fmt.Errorf("%w: %s must be sha256", ErrInvalid, key)
	}
	return nil
}