// Package operatorask is a module's asking of a person through the seat that routes asks to the operator (design 47 G
// A-101, §700, A-74): the seat's holder is found on the seat list, an ask is published under the module's own name, the
// router's record of it is read for the warrant, and the router's `decided` is heard. It is shared code, so no module
// keeps its own copy; it names no seat, verb or module: the generated contracts' names and types are its parameters.
package operatorask

import (
	"encoding/json"
	"errors"
	"fmt"

	stdio "git.novox.be/novox/mesh-sdk/go"
)

// Caller calls a seat verb or module tool as `seat:<seat>.<verb>` or `<module>.<tool>` and returns its answer
// (stdio.Ask is one; so is a process's calls).
type Caller func(key string, body any) (json.RawMessage, error)

// Contract is what the asker takes from the generated contracts: the verb that answers the seat list with its seats
// (`Lists` is its call key, `ListBody` its input) and the asking seat and its state of the router's records.
type Contract struct {
	Lists    string
	ListBody any
	Seat     string
	// StateAsks is the seat's state holding the router's record of each ask.
	StateAsks string
}

// Bucket is the bucket of the router's records: the seat's state in the bucket of the seat's holder on the seat list.
func Bucket(call Caller, c Contract) (string, error) {
	raw, err := call(c.Lists, c.ListBody)
	if err != nil {
		return "", fmt.Errorf("who holds the seat %s is not asked of %s: %w", c.Seat, c.Lists, err)
	}
	var held struct {
		Seats []struct {
			Seat    string `json:"seat"`
			Holders []struct {
				Module string `json:"module"`
			} `json:"holders"`
		} `json:"seats"`
	}
	if err := json.Unmarshal(raw, &held); err != nil {
		return "", fmt.Errorf("the answer of %s is not the seat list's: %w", c.Lists, err)
	}
	for _, s := range held.Seats {
		if s.Seat == c.Seat && len(s.Holders) > 0 {
			return s.Holders[0].Module + "_" + c.StateAsks, nil
		}
	}
	return "", fmt.Errorf("no module holds the seat %s on the seat list, so the router's record of an ask is not read", c.Seat)
}

// Asker asks as one module. W is the generated contract's warrant type.
type Asker[W any] struct {
	Module   string
	Contract Contract
	// Call reaches the seat list's verb.
	Call Caller
	// Record reads one record of a bucket under the module's own name (process.Conn.Ask).
	Record func(bucket, id string) (*stdio.StateEntry, error)
	// Publish publishes a body de-duplicated by id: the same id twice is one message (stdio.SeatPublish).
	Publish func(subject string, body any, id string) error
	// Subscribe hears an event (stdio.Subscribe).
	Subscribe func(pattern string, handle func(stdio.Envelope) error) error
	// AskSubject and DecidedSubject are the generated contract's subjects for Module.
	AskSubject, DecidedSubject func(module string) string
}

// Ask publishes the ask (the generated contract's Ask) under the module's own name, de-duplicated by its id.
func (a *Asker[W]) Ask(id string, ask any) error {
	if a.Publish == nil || a.AskSubject == nil {
		return errors.New("the asker has no way to publish")
	}
	return a.Publish(a.AskSubject(a.Module), ask, id)
}

// Where is an ask's state as the router keeps it, and its warrant once there is one; a record not yet there is an empty
// state. It is an error while the seat's holder or the record cannot be read.
func (a *Asker[W]) Where(id string) (state string, warrant *W, err error) {
	bucket, err := Bucket(a.Call, a.Contract)
	if err != nil {
		return "", nil, err
	}
	e, err := a.Record(bucket, id)
	if err != nil || e == nil {
		return "", nil, err
	}
	var rec struct {
		State   string `json:"state"`
		Warrant *W     `json:"warrant"`
	}
	if err := json.Unmarshal(e.Value, &rec); err != nil {
		return "", nil, fmt.Errorf("the router's record of %s cannot be read: %w", id, err)
	}
	return rec.State, rec.Warrant, nil
}

// Hear hands handle each warrant the router says to this module; a handler's error leaves it for the bus to give again.
func (a *Asker[W]) Hear(handle func(W) error) error {
	if a.Subscribe == nil || a.DecidedSubject == nil {
		return errors.New("the asker has no way to hear")
	}
	return a.Subscribe(a.DecidedSubject(a.Module), func(env stdio.Envelope) error {
		var w W
		if err := json.Unmarshal(env.Body, &w); err != nil {
			return fmt.Errorf("%s holds what is no warrant: %w", env.Key, err)
		}
		return handle(w)
	})
}