package pushserver

import (
	"context"
	"encoding/json"
	"errors"
	"sync"

	"github.com/dariuszjaniak/warp/server/internal/pushrules"
	"github.com/dariuszjaniak/warp/server/internal/storage"
)

// AccountDataType is the account data push rules are kept in, and the
// type a client is refused when it tries to write them directly.
const AccountDataType = "m.push_rules"

// Push rules are the m.push_rules account data, and this is the only
// writer of it.
//
// That is where the spec has a client read them — every client takes its
// rules from the account data of its initial sync — so keeping them
// anywhere else would mean a second copy, rendered into account data on
// every change. What is stored is the whole ruleset as a client sees it.
// What is read back from it is only what the user owns: their own rules,
// and the enabled flag and actions of each default rule. The rest comes
// from pushrules.Defaults, so a server upgrade that adds a default rule
// reaches every user without rewriting anybody's account data.

// Ruleset returns a user's rules as they apply now: their own laid over
// the server defaults.
func (a *API) Ruleset(ctx context.Context, localpart, userID string) (pushrules.Ruleset, error) {
	a.rulesMu.Lock()
	cached, ok := a.rulesCache[localpart]
	a.rulesMu.Unlock()
	if ok {
		return cached.Clone(), nil
	}

	rs, err := a.loadRuleset(ctx, localpart, userID)
	if err != nil {
		return pushrules.Ruleset{}, err
	}
	a.rulesMu.Lock()
	a.rulesCache[localpart] = rs
	a.rulesMu.Unlock()
	return rs.Clone(), nil
}

func (a *API) loadRuleset(ctx context.Context, localpart, userID string) (pushrules.Ruleset, error) {
	defaults := pushrules.Defaults(userID)
	raw, err := a.accounts.AccountData(ctx, localpart, "", AccountDataType)
	switch {
	case errors.Is(err, storage.ErrNoSuchAccountData):
		return defaults, nil
	case err != nil:
		return pushrules.Ruleset{}, err
	}
	stored, err := pushrules.ParseDocument(raw)
	if err != nil {
		// Only this package writes the rules, so an unreadable copy is a
		// bug or a hand edit. The defaults are a better answer than
		// refusing every push and every sync until somebody fixes it.
		a.log.Error("stored push rules are unreadable; using the defaults",
			"user_id", userID, "error", err)
		return defaults, nil
	}
	return pushrules.Merge(stored, defaults), nil
}

// Document is a user's rules as m.push_rules content: what a sync and a
// read of the account data return.
func (a *API) Document(ctx context.Context, localpart, userID string) ([]byte, error) {
	rs, err := a.Ruleset(ctx, localpart, userID)
	if err != nil {
		return nil, err
	}
	return pushrules.MarshalDocument(rs)
}

// Rule returns one rule.
func (a *API) Rule(ctx context.Context, localpart, userID string, kind pushrules.Kind, ruleID string) (pushrules.Rule, error) {
	rs, err := a.Ruleset(ctx, localpart, userID)
	if err != nil {
		return pushrules.Rule{}, err
	}
	rule, ok := rs.Find(kind, ruleID)
	if !ok {
		return pushrules.Rule{}, ErrNoSuchRule
	}
	return rule, nil
}

// PutRule creates or replaces a user rule; see pushrules.Ruleset.Put for
// where it goes.
func (a *API) PutRule(ctx context.Context, localpart, userID string, kind pushrules.Kind, ruleID string, rule pushrules.NewRule, before, after string) error {
	built, err := rule.Build(kind, ruleID)
	if err != nil {
		return err
	}
	return a.editRules(ctx, localpart, userID, func(rs *pushrules.Ruleset) error {
		return rs.Put(kind, built, before, after)
	})
}

// DeleteRule removes a user rule.
func (a *API) DeleteRule(ctx context.Context, localpart, userID string, kind pushrules.Kind, ruleID string) error {
	return a.editRules(ctx, localpart, userID, func(rs *pushrules.Ruleset) error {
		return rs.Delete(kind, ruleID)
	})
}

// SetRuleEnabled switches a rule on or off.
func (a *API) SetRuleEnabled(ctx context.Context, localpart, userID string, kind pushrules.Kind, ruleID string, enabled bool) error {
	return a.editRules(ctx, localpart, userID, func(rs *pushrules.Ruleset) error {
		return rs.SetEnabled(kind, ruleID, enabled)
	})
}

// SetRuleActions replaces a rule's actions.
func (a *API) SetRuleActions(ctx context.Context, localpart, userID string, kind pushrules.Kind, ruleID string, actions []json.RawMessage) error {
	return a.editRules(ctx, localpart, userID, func(rs *pushrules.Ruleset) error {
		return rs.SetActions(kind, ruleID, actions)
	})
}

// editRules is the read-modify-write every change is, serialised per user
// so that two changes made at once cannot each start from the ruleset the
// other has not written yet.
func (a *API) editRules(ctx context.Context, localpart, userID string, edit func(*pushrules.Ruleset) error) error {
	mu := a.writeLock(localpart)
	mu.Lock()
	defer mu.Unlock()

	rs, err := a.Ruleset(ctx, localpart, userID)
	if err != nil {
		return err
	}
	if err := edit(&rs); err != nil {
		return err
	}
	doc, err := pushrules.MarshalDocument(rs)
	if err != nil {
		return err
	}
	if err := a.accounts.SetAccountData(ctx, localpart, "", AccountDataType, doc); err != nil {
		return err
	}

	a.rulesMu.Lock()
	a.rulesCache[localpart] = rs
	a.rulesMu.Unlock()

	// The rules travel as account data, so a change is something every
	// one of the user's syncs has to hear about now rather than at its
	// timeout.
	a.notifyUsers(userID)
	return nil
}

func (a *API) writeLock(localpart string) *sync.Mutex {
	actual, _ := a.writeLocks.LoadOrStore(localpart, &sync.Mutex{})
	mu, ok := actual.(*sync.Mutex)
	if !ok {
		panic("pushserver: write lock map holds something that is not a mutex")
	}
	return mu
}