package model

import (
	"fmt"
	"sort"
	"strings"
)

// SyncScope narrows one full-sync run to an explicit channel whitelist.
//
// A nil scope, or one whose channel list normalizes to empty, means "full
// sync" and must behave exactly like a run started before this field existed.
// TriggerSource is descriptive only: it is recorded on the run for operators
// and never changes scheduling or retry behaviour.
type SyncScope struct {
	Channels      []string `json:"channels,omitempty"`
	TriggerSource string   `json:"triggerSource,omitempty"`
}

const (
	// MaxScopeChannels bounds one partial-sync request. It is a guard against
	// accidental "select everything" payloads, not a capacity limit.
	MaxScopeChannels = 200
	// MaxChanKeyLength matches t_sim_channels.chan_key varchar(32).
	MaxChanKeyLength = 32
)

// Trigger source values recorded on the run.
const (
	TriggerSourceScheduled = "scheduled"
	TriggerSourceManual    = "manual"
	TriggerSourceAPI       = "api"
	TriggerSourceReplay    = "replay"
)

// NormalizeScope validates a requested scope and returns its canonical form.
//
// Canonical form is: nil for a full sync, otherwise a scope whose channel list
// is deduplicated and sorted. Sorting makes ScopeDigest stable across requests
// that select the same channels in a different order.
func NormalizeScope(scope *SyncScope) (*SyncScope, error) {
	if scope == nil {
		return nil, nil
	}
	triggerSource := strings.TrimSpace(scope.TriggerSource)
	switch triggerSource {
	case "", TriggerSourceScheduled, TriggerSourceManual, TriggerSourceAPI, TriggerSourceReplay:
	default:
		return nil, fmt.Errorf("invalid triggerSource %q", scope.TriggerSource)
	}
	if len(scope.Channels) == 0 {
		return nil, nil
	}
	if len(scope.Channels) > MaxScopeChannels {
		return nil, fmt.Errorf("scope has %d channels, maximum is %d", len(scope.Channels), MaxScopeChannels)
	}

	seen := make(map[string]struct{}, len(scope.Channels))
	channels := make([]string, 0, len(scope.Channels))
	for _, raw := range scope.Channels {
		chanKey := strings.TrimSpace(raw)
		if err := ValidateChanKey(chanKey); err != nil {
			return nil, err
		}
		if _, exists := seen[chanKey]; exists {
			continue
		}
		seen[chanKey] = struct{}{}
		channels = append(channels, chanKey)
	}
	if len(channels) == 0 {
		return nil, nil
	}
	sort.Strings(channels)

	if triggerSource == "" {
		triggerSource = TriggerSourceManual
	}
	return &SyncScope{Channels: channels, TriggerSource: triggerSource}, nil
}

// ValidateChanKey rejects values that cannot exist in t_sim_channels.chan_key.
// The whitelist character set keeps the value safe to log and to embed in a
// Redis key without escaping.
func ValidateChanKey(chanKey string) error {
	if chanKey == "" {
		return fmt.Errorf("chanKey is empty")
	}
	if len(chanKey) > MaxChanKeyLength {
		return fmt.Errorf("chanKey %q exceeds %d characters", chanKey, MaxChanKeyLength)
	}
	for _, r := range chanKey {
		switch {
		case r >= 'a' && r <= 'z':
		case r >= 'A' && r <= 'Z':
		case r >= '0' && r <= '9':
		case r == '-' || r == '_':
		default:
			return fmt.Errorf("chanKey %q contains invalid character %q", chanKey, r)
		}
	}
	return nil
}

// ChannelSet returns the scope channels as a lookup set, or nil for a full
// sync. Callers treat nil as "no filtering".
func (s *SyncScope) ChannelSet() map[string]struct{} {
	if s == nil || len(s.Channels) == 0 {
		return nil
	}
	set := make(map[string]struct{}, len(s.Channels))
	for _, chanKey := range s.Channels {
		set[chanKey] = struct{}{}
	}
	return set
}

// Allows reports whether a card on chanKey belongs to this scope. A nil scope
// allows every channel.
func (s *SyncScope) Allows(chanKey string) bool {
	if s == nil || len(s.Channels) == 0 {
		return true
	}
	for _, allowed := range s.Channels {
		if allowed == chanKey {
			return true
		}
	}
	return false
}

// ChannelCount is the number of selected channels; zero means full sync.
func (s *SyncScope) ChannelCount() int {
	if s == nil {
		return 0
	}
	return len(s.Channels)
}

// ChannelSample returns at most limit channels for logging and run metadata.
func (s *SyncScope) ChannelSample(limit int) []string {
	if s == nil || limit <= 0 {
		return nil
	}
	if len(s.Channels) <= limit {
		return s.Channels
	}
	return s.Channels[:limit]
}