package runtime

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"reflect"
	"sync"

	"github.com/novox/mesh-tools/node-tools/internal/bus"
)

// The ledger credentials (novox/hq ADR 0597 §9, design 25 § 12.4; issue 1966 T6): one per module assignment, held by
// the machine's tool runner in its own secret `ledgers`, a map of module to credential (`{}` when none), which the vault
// rewrites on each mint and retirement. **A module's ledger history is appended, and its snapshots written, only on
// that module's own ledger connection**; everything else stays on the runner's own.

// LedgersFile is where the runner reads its own secret `ledgers`: MESH_LEDGERS_FILE when set, else beside its broker
// credential, both in its directory mesh-state (node-tools' manifest: `${dir:mesh-state}/ledgers`).
const LedgersFile = "MESH_LEDGERS_FILE"

// LedgersFileOf is the path of the secret `ledgers` for a runtime whose broker credential is at broker.
func LedgersFileOf(broker string) string {
	if file := os.Getenv(LedgersFile); file != "" {
		return file
	}
	if broker == "" {
		return ""
	}
	return filepath.Join(filepath.Dir(broker), "ledgers")
}

// LedgerCredentials are the ledger connections of the modules on this machine, read from the secret `ledgers` and
// followed as it changes, with no restart.
type LedgerCredentials struct {
	file string
	dial func(bus.Credential) (*bus.Conn, error)
	logf func(string, ...any)

	mu    sync.Mutex
	creds map[string]bus.Credential
	conns map[string]*bus.Conn
	why   string // why the file could not be read, when it could not
	stop  func()
}

// FollowLedgerCredentials reads the secret `ledgers` at file and follows it (WatchFile), dialling a module's connection
// with dial the first time it is asked for.
func FollowLedgerCredentials(file string, dial func(bus.Credential) (*bus.Conn, error), logf func(string, ...any)) *LedgerCredentials {
	l := &LedgerCredentials{file: file, dial: dial, logf: logf, creds: map[string]bus.Credential{}, conns: map[string]*bus.Conn{}}
	l.read()
	stop, err := WatchFile(file, l.read, logf, "a change of the ledger credentials is taken only after a restart")
	if err != nil {
		logf("[mesh-tools] cannot follow the ledger credentials at %s: %v; a change is taken only after a restart", file, err)
	} else {
		l.stop = stop
	}
	return l
}

// read takes the file as it is now: a module whose credential changed or went has its connection closed, and is
// dialled again from the new one when next asked for.
func (l *LedgerCredentials) read() {
	creds, why := map[string]bus.Credential{}, ""
	raw, err := os.ReadFile(l.file)
	switch {
	case errors.Is(err, os.ErrNotExist):
		why = "the file " + l.file + " is not there yet"
	case err != nil:
		why = err.Error()
	case len(bytes.TrimSpace(raw)) == 0:
		why = "the file " + l.file + " is empty"
	default:
		if err := json.Unmarshal(raw, &creds); err != nil {
			why = "the file " + l.file + " is not a map of module to credential: " + err.Error()
			creds = map[string]bus.Credential{}
		}
	}
	l.mu.Lock()
	var closing []*bus.Conn
	for module, conn := range l.conns {
		if now, has := creds[module]; !has || !reflect.DeepEqual(now, l.creds[module]) {
			closing = append(closing, conn)
			delete(l.conns, module)
		}
	}
	saidBefore := l.why
	l.creds, l.why = creds, why
	l.mu.Unlock()
	for _, c := range closing {
		c.Close()
	}
	if why != "" && why != saidBefore {
		l.logf("[mesh-tools] the ledger credentials cannot be read (%s); no ledger is written until they can", why)
	}
}

// Writer is a module's ledger connection, dialled from its credential the first time it is asked for; refused, naming
// what is missing, when the secret holds none for it.
func (l *LedgerCredentials) Writer(module string) (*bus.Conn, error) {
	l.mu.Lock()
	defer l.mu.Unlock()
	if c := l.conns[module]; c != nil {
		return c, nil
	}
	cred, has := l.creds[module]
	if !has {
		why := ""
		if l.why != "" {
			why = " (" + l.why + ")"
		}
		return nil, fmt.Errorf("%s's ledger credential is missing from the tool runner's own secret ledgers%s: its history "+
			"is published only on its own ledger connection, which the grants part issues with its membership and the "+
			"vault writes there (novox/hq ADR 0597 §9)", module, why)
	}
	if cred.Module == "" {
		cred.Module = module
	}
	c, err := l.dial(cred)
	if err != nil {
		return nil, fmt.Errorf("%s's ledger connection could not be opened: %w", module, err)
	}
	c.Logf = l.logf
	l.conns[module] = c
	return c, nil
}

// Stop ends the following and closes every ledger connection.
func (l *LedgerCredentials) Stop() {
	if l.stop != nil {
		l.stop()
	}
	l.mu.Lock()
	conns := l.conns
	l.conns = map[string]*bus.Conn{}
	l.mu.Unlock()
	for _, c := range conns {
		c.Close()
	}
}