package app

import (
	"context"
	"errors"
	"fmt"
	"slices"
	"strings"

	"finance-duck/internal/banking"
	"finance-duck/internal/domain"
)

// ManageRegistry applies registry management and, for account deletions, also
// releases the account's bank bindings first: a deleted account must never be
// resurrected by the session recovery that reconstructs interrupted connects.
func (a *App) ManageRegistry(ctx context.Context, rev, entity, action, id, target string) (State, error) {
	a.mu.Lock()
	defer a.mu.Unlock()
	s, err := a.snapshot(ctx)
	if err != nil {
		return State{}, err
	}
	if rev != s.Revision {
		return State{}, errors.New("revision conflict: reload before editing")
	}
	if err = Manage(&s.Data, entity, action, id, target); err != nil {
		return State{}, err
	}
	// Prune bindings before the canonical commit: an interruption then leaves
	// an unbound local account rather than a resurrected bank connection.
	if entity == "account" {
		changed := false
		sessions := make([]banking.Session, 0, len(a.ops.Sessions))
		for _, session := range a.ops.Sessions {
			accounts := slices.DeleteFunc(slices.Clone(session.Accounts), func(account domain.Account) bool { return account.ID == id })
			changed = changed || len(accounts) != len(session.Accounts)
			session.Accounts = accounts
			if len(accounts) == 0 {
				delete(a.ops.Consents, session.ID)
				continue
			}
			sessions = append(sessions, session)
		}
		if _, tracked := a.ops.AccountSync[id]; tracked || changed {
			a.ops.Sessions = sessions
			delete(a.ops.AccountSync, id)
			if err = a.saveOps(); err != nil {
				return State{}, err
			}
		}
	}
	return a.commit(ctx, rev, s.Data)
}

func SaveAccount(d *domain.Dataset, v domain.Account) error {
	v.DisplayName = strings.TrimSpace(v.DisplayName)
	if v.ID == "" {
		v.ID = domain.NewID("acct")
	}
	for i, x := range d.Accounts {
		if x.ID == v.ID {
			d.Accounts[i] = v
			return nil
		}
	}
	d.Accounts = append(d.Accounts, v)
	return nil
}
func SaveCategory(d *domain.Dataset, v domain.Category) error {
	v.Name = strings.TrimSpace(v.Name)
	if v.ID == "" {
		v.ID = domain.NewID("cat")
	}
	for i, x := range d.Categories {
		if x.ID == v.ID {
			d.Categories[i] = v
			return nil
		}
	}
	d.Categories = append(d.Categories, v)
	return nil
}
func SaveTag(d *domain.Dataset, v domain.Tag) error {
	v.Name = strings.TrimSpace(v.Name)
	if v.ID == "" {
		v.ID = domain.NewID("tag")
	}
	for i, x := range d.Tags {
		if x.ID == v.ID {
			d.Tags[i] = v
			return nil
		}
	}
	d.Tags = append(d.Tags, v)
	return nil
}
func SaveMerchant(d *domain.Dataset, v domain.Merchant) error {
	v.Name = strings.TrimSpace(v.Name)
	if v.ID == "" {
		v.ID = domain.NewID("merchant")
	}
	for i, x := range d.Merchants {
		if x.ID == v.ID {
			d.Merchants[i] = v
			return nil
		}
	}
	d.Merchants = append(d.Merchants, v)
	return nil
}
func replaceIDs(ids []string, from, to string) []string {
	out := make([]string, 0, len(ids))
	for _, id := range ids {
		if id == from {
			id = to
		}
		if id != "" && !slices.Contains(out, id) {
			out = append(out, id)
		}
	}
	return out
}
func Manage(d *domain.Dataset, entity, action, id, target string) error {
	if id == "" || id == target {
		return errors.New("select distinct source and target")
	}
	if action != "delete" && action != "merge" {
		return errors.New("unknown management action")
	}
	if action == "merge" && target == "" {
		return errors.New("merge target required")
	}
	switch entity {
	case "account":
		if action != "delete" {
			return errors.New("account merging is not supported")
		}
		for _, t := range d.Transactions {
			if t.Facts.AccountID == id {
				return errors.New("account contains immutable financial records; deactivate it instead")
			}
		}
		n := len(d.Accounts)
		d.Accounts = slices.DeleteFunc(d.Accounts, func(v domain.Account) bool { return v.ID == id })
		if n == len(d.Accounts) {
			return errors.New("unknown account")
		}
	case "tag":
		if !slices.ContainsFunc(d.Tags, func(v domain.Tag) bool { return v.ID == id }) {
			return errors.New("unknown tag")
		}
		if target != "" && !slices.ContainsFunc(d.Tags, func(v domain.Tag) bool { return v.ID == target }) {
			return errors.New("unknown target tag")
		}
		for i := range d.Transactions {
			d.Transactions[i].Enrichment.TagIDs = replaceIDs(d.Transactions[i].Enrichment.TagIDs, id, target)
		}
		for i := range d.Merchants {
			d.Merchants[i].DefaultTagIDs = replaceIDs(d.Merchants[i].DefaultTagIDs, id, target)
		}
		d.Tags = slices.DeleteFunc(d.Tags, func(v domain.Tag) bool { return v.ID == id })
	case "merchant":
		source := -1
		dest := -1
		for i, v := range d.Merchants {
			if v.ID == id {
				source = i
			}
			if v.ID == target {
				dest = i
			}
		}
		if source < 0 {
			return errors.New("unknown merchant")
		}
		if target != "" && dest < 0 {
			return errors.New("unknown target merchant")
		}
		if dest >= 0 {
			for _, alias := range append(slices.Clone(d.Merchants[source].Aliases), d.Merchants[source].Name) {
				if !slices.Contains(d.Merchants[dest].Aliases, alias) {
					d.Merchants[dest].Aliases = append(d.Merchants[dest].Aliases, alias)
				}
			}
		}
		for i := range d.Transactions {
			if d.Transactions[i].Enrichment.MerchantID == id {
				d.Transactions[i].Enrichment.MerchantID = target
			}
		}
		d.Merchants = slices.DeleteFunc(d.Merchants, func(v domain.Merchant) bool { return v.ID == id })
	case "category":
		if id == domain.ExpenseFallback || id == domain.IncomeFallback || id == "cat_expenses" || id == "cat_income" {
			return errors.New("built-in fallback categories and roots cannot be deleted or merged")
		}
		if !slices.ContainsFunc(d.Categories, func(v domain.Category) bool { return v.ID == id }) {
			return errors.New("unknown category")
		}
		removed := map[string]bool{id: true}
		for changed := true; changed; {
			changed = false
			for _, c := range d.Categories {
				if removed[c.ParentID] && !removed[c.ID] {
					removed[c.ID] = true
					changed = true
				}
			}
		}
		if action == "delete" && len(removed) > 1 {
			return errors.New("move or delete child categories first, or merge the subtree")
		}
		if removed[target] {
			return errors.New("cannot migrate into the removed subtree")
		}
		if target != "" {
			if !slices.ContainsFunc(d.Categories, func(v domain.Category) bool { return v.ID == target }) {
				return errors.New("unknown target category")
			}
			for _, c := range d.Categories {
				if c.ParentID == target {
					return errors.New("migration target must be a leaf category")
				}
			}
		}
		for i := range d.Transactions {
			if removed[d.Transactions[i].Enrichment.CategoryID] {
				if target == "" {
					return errors.New("category is referenced; select a migration target")
				}
				d.Transactions[i].Enrichment.CategoryID = target
			}
		}
		for i := range d.Merchants {
			if removed[d.Merchants[i].DefaultCategoryID] {
				if target == "" {
					return errors.New("merchant defaults reference this category; select a migration target")
				}
				d.Merchants[i].DefaultCategoryID = target
			}
		}
		d.Categories = slices.DeleteFunc(d.Categories, func(v domain.Category) bool { return removed[v.ID] })
	default:
		return fmt.Errorf("unknown entity %q", entity)
	}
	return nil
}