package config

import (
	"bufio"
	"os"
	"strings"
	"sync"
)

// EngineCredentials reads the Basic credentials the engine generated for
// itself, from the file it writes them to.
//
// The engine only invents a credential when none is configured and its API
// listens on a routable address - which is the DEFAULT configuration, so this
// is the ordinary case and not an edge one. `paths.APICredentials` has existed
// since the agent was written, with a comment saying the agent reads the file
// "rather than storing a second copy, so a regenerated credential does not
// silently break the tray". Nothing read it. On a stock install the agent's
// api_user was therefore empty and every call it makes to the engine - health,
// stats, camera sync, embeddings for a visit - came back 401: the tray red, the
// cameras never reconciled, and no error anywhere saying why.
//
// A missing or unreadable file is not an error. A PC where the operator set
// BEHAVISION_API_USER has no such file and needs none.
func EngineCredentials(path string) (user, password string) {
	f, err := os.Open(path)
	if err != nil {
		return "", ""
	}
	defer f.Close()

	sc := bufio.NewScanner(f)
	for sc.Scan() {
		// `key=value`, and `key: value` too: the file is also read by people,
		// and which separator the engine used is not worth a support call.
		line := strings.TrimSpace(sc.Text())
		k, v, ok := strings.Cut(line, "=")
		if !ok {
			k, v, ok = strings.Cut(line, ":")
		}
		if !ok {
			continue
		}
		switch strings.TrimSpace(k) {
		case "username":
			user = strings.TrimSpace(v)
		case "password":
			password = strings.TrimSpace(v)
		}
	}
	return user, password
}

// WithEngineCredentials fills in the engine's Basic credentials from the file
// when the config carries none. Configured values always win: an operator who
// set BEHAVISION_API_USER means it.
func (c Config) WithEngineCredentials(path string) Config {
	if c.APIUser != "" || c.APIPassword != "" {
		return c
	}
	c.APIUser, c.APIPassword = EngineCredentials(path)
	return c
}

// Creds resolves the engine's Basic credentials, re-reading the file when it
// has none.
//
// Reading once at startup is wrong on a fresh install, and that is the case
// that matters: the agent starts the engine, the engine generates its
// credential and writes the file a few seconds later, and an agent that read
// the file before that holds "" forever. Every call it makes - health, stats,
// camera sync, the embedding for a visit - then comes back 401 for the life of
// the process, on a brand new shop PC, with the tray showing a red engine that
// is running perfectly. Measured on a fresh state directory: three 401s and no
// camera ever reconciled.
//
// A configured credential is never re-read: an operator who set
// BEHAVISION_API_USER means it.
type Creds struct {
	path  string
	mu    sync.Mutex
	user  string
	pass  string
	fixed bool
}

// NewCreds takes whatever the config already has. Non-empty means configured,
// and is used unchanged.
func NewCreds(path, user, password string) *Creds {
	c := &Creds{path: path, user: user, pass: password}
	c.fixed = user != "" || password != ""
	return c
}

// Get returns the current pair, reading the file if it has nothing yet.
func (c *Creds) Get() (string, string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.user == "" && !c.fixed {
		c.user, c.pass = EngineCredentials(c.path)
	}
	return c.user, c.pass
}

// Refresh re-reads the file after a rejection and reports whether the pair
// changed. Callers retry once when it did - which covers both the fresh-install
// race and a credential the engine regenerated under a running agent.
func (c *Creds) Refresh() bool {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.fixed {
		return false
	}
	u, p := EngineCredentials(c.path)
	if u == c.user && p == c.pass {
		return false
	}
	c.user, c.pass = u, p
	return u != ""
}