package domain

import (
	"fmt"
	"strings"
)

const (
	WatchActive   = "active"
	WatchPaused   = "paused"
	WatchArchived = "archived"

	MaxWatchTerms        = 20
	MaxWatchExcludeTerms = 30
	MaxTermLen           = 60
	MinTermLen           = 2
)

/*
RadarWatch 是常駐關鍵字監控。每日排程只撈 active 的。

regions 留空代表沿用服務檔案的地區 —— 這裡刻意不把服務檔案的值複製進來，
否則之後改服務檔案，舊訂閱會繼續用舊地區判定，而使用者不會知道。
*/
type RadarWatch struct {
	ID           string   `bson:"_id" json:"id"`
	OwnerUID     int64    `bson:"owner_uid" json:"owner_uid"`
	Terms        []string `bson:"terms" json:"terms"`
	ExcludeTerms []string `bson:"exclude_terms" json:"exclude_terms"`
	Regions      []string `bson:"regions" json:"regions"`
	Status       string   `bson:"status" json:"status"`
	LastSweptAt  int64    `bson:"last_swept_at,omitempty" json:"last_swept_at,omitempty"`
	CreatedAt    int64    `bson:"created_at" json:"created_at"`
	UpdatedAt    int64    `bson:"updated_at" json:"updated_at"`
}

type WatchListFilter struct {
	Status   string
	Page     int
	PageSize int
}

func IsWatchStatus(s string) bool {
	switch s {
	case WatchActive, WatchPaused, WatchArchived:
		return true
	}
	return false
}

/*
CanTransitionWatch 實作 spec §3.1：active ↔ paused 可往返，兩者都能封存，
archived 是終態。

終態不可逆是刻意的：封存後歷史商機與統計都還留著，如果允許復活，
「這批統計是哪個訂閱在什麼期間跑出來的」就會失去單一解釋。要再監控同一組
關鍵字請建新的訂閱。
*/
func CanTransitionWatch(from, to string) bool {
	if from == to {
		return true
	}
	switch from {
	case WatchActive:
		return to == WatchPaused || to == WatchArchived
	case WatchPaused:
		return to == WatchActive || to == WatchArchived
	default:
		return false
	}
}

func (w *RadarWatch) Transition(to string) error {
	if !IsWatchStatus(to) {
		return fmt.Errorf("%w: unknown watch status %q", ErrValidation, to)
	}
	if !CanTransitionWatch(w.Status, to) {
		if w.Status == WatchArchived {
			return fmt.Errorf("%w: archived watch cannot become %s; create a new watch instead", ErrValidation, to)
		}
		return fmt.Errorf("%w: cannot change watch from %s to %s", ErrValidation, w.Status, to)
	}
	w.Status = to
	w.UpdatedAt = NowNano()
	return nil
}

/*
Normalize 正規化關鍵字並驗證。

term 一律 lower-case 存放：Threads 搜尋不分大小寫，若不正規化，「Wedding」與
「wedding」會被當成兩個 term，之後 T556 的關鍵字轉換率就會把同一個詞拆成兩列。
*/
func (w *RadarWatch) Normalize() error {
	if w.OwnerUID <= 0 {
		return fmt.Errorf("%w: owner_uid required", ErrValidation)
	}

	terms, err := normalizeTerms(w.Terms, "terms", MaxWatchTerms)
	if err != nil {
		return err
	}
	if len(terms) == 0 {
		return fmt.Errorf("%w: terms required", ErrValidation)
	}
	w.Terms = terms

	excludes, err := normalizeTerms(w.ExcludeTerms, "exclude_terms", MaxWatchExcludeTerms)
	if err != nil {
		return err
	}
	w.ExcludeTerms = excludes

	// 同一個詞同時要與不要，等於這個訂閱永遠不會命中任何東西。
	excludeSet := map[string]bool{}
	for _, e := range excludes {
		excludeSet[e] = true
	}
	for _, t := range terms {
		if excludeSet[t] {
			return fmt.Errorf("%w: %q is in both terms and exclude_terms", ErrValidation, t)
		}
	}

	regions := make([]string, 0, len(w.Regions))
	seen := map[string]bool{}
	for _, r := range w.Regions {
		code := strings.ToUpper(strings.TrimSpace(r))
		if code == "" {
			continue
		}
		if !IsServiceAreaCode(code) {
			return fmt.Errorf("%w: regions contains unknown code %q", ErrValidation, code)
		}
		if seen[code] {
			continue
		}
		seen[code] = true
		regions = append(regions, code)
	}
	w.Regions = regions

	if w.Status == "" {
		w.Status = WatchActive
	}
	if !IsWatchStatus(w.Status) {
		return fmt.Errorf("%w: unknown watch status %q", ErrValidation, w.Status)
	}
	return nil
}

func normalizeTerms(in []string, field string, max int) ([]string, error) {
	out := make([]string, 0, len(in))
	seen := map[string]bool{}
	for _, raw := range in {
		// 全形空白也要收掉：中文輸入法很容易打出來，而它不會命中任何東西。
		t := strings.TrimSpace(strings.ReplaceAll(raw, "\u3000", " "))
		t = strings.Join(strings.Fields(t), " ")
		if t == "" {
			continue
		}
		t = strings.ToLower(t)
		if len([]rune(t)) < MinTermLen {
			return nil, fmt.Errorf("%w: %s contains a term shorter than %d characters (%q)", ErrValidation, field, MinTermLen, t)
		}
		if len([]rune(t)) > MaxTermLen {
			return nil, fmt.Errorf("%w: %s contains a term longer than %d characters", ErrValidation, field, MaxTermLen)
		}
		if seen[t] {
			continue
		}
		seen[t] = true
		out = append(out, t)
	}
	if len(out) > max {
		return nil, fmt.Errorf("%w: %s exceeds %d items", ErrValidation, field, max)
	}
	return out, nil
}