package config

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

// 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
}