// Package config resolves the waitfordb runtime configuration from environment
// variables and formats a secret-free summary for logging.
package config

import (
	"fmt"
	"strings"
	"time"
)

// Defaults applied when the corresponding env var is unset.
const (
	DefaultDriver         = "postgres"
	DefaultHost           = "localhost"
	DefaultInterval       = 2 * time.Second
	DefaultConnectTimeout = 5 * time.Second
)

// defaultPort maps a driver to the port used when none is configured.
var defaultPort = map[string]string{
	"postgres": "5432",
	"mysql":    "3306",
	"valkey":   "6379",
}

// Secret formats natively understood via WAITFORDB_SECRET_FORMAT (or
// autodetection): operator-generated secrets injected wholesale with envFrom.
const (
	FormatCNPG   = "cnpg"   // CNPG <cluster>-app secret: host/port/dbname/user/password keys
	FormatValkey = "valkey" // valkey-operator user secrets: key = username, value = password
)

// Config is the resolved, validated configuration for a single run.
type Config struct {
	Driver string

	// SecretFormat records which operator secret convention supplied the
	// connection parameters ("" when none).
	SecretFormat string

	// DSN, when set, is a full driver-native connection string that overrides
	// the discrete Host/Port/User/Password/Database fields.
	DSN string

	Host     string
	Port     string
	User     string
	Password string
	Database string
	SSLMode  string

	// Timeout is the total budget to wait for readiness. Zero means wait
	// forever.
	Timeout time.Duration
	// Interval is the gap between retries.
	Interval time.Duration
	// ConnectTimeout bounds a single connect+ping attempt.
	ConnectTimeout time.Duration
}

// Error is a configuration error; main maps it to exit code 2.
type Error struct{ msg string }

func (e *Error) Error() string { return e.msg }

func errf(format string, a ...any) *Error { return &Error{msg: fmt.Sprintf(format, a...)} }

// Getenv matches os.Getenv; injected in tests.
type Getenv func(string) string

// Load resolves configuration from env. Connection-parameter precedence is
// DSN > WAITFORDB_* > PG* > operator-secret keys (the libpq fallback applies
// to the postgres driver only).
func Load(get Getenv) (Config, error) {
	c := Config{
		Driver:         strings.ToLower(strings.TrimSpace(get("WAITFORDB_DRIVER"))),
		DSN:            get("WAITFORDB_DSN"),
		ConnectTimeout: DefaultConnectTimeout,
		Interval:       DefaultInterval,
	}
	if c.Driver == "redis" {
		c.Driver = "valkey"
	}

	c.Host = get("WAITFORDB_HOST")
	c.Port = get("WAITFORDB_PORT")
	c.User = get("WAITFORDB_USER")
	c.Password = get("WAITFORDB_PASSWORD")
	c.Database = get("WAITFORDB_DATABASE")
	c.SSLMode = get("WAITFORDB_SSLMODE")

	format := strings.ToLower(strings.TrimSpace(get("WAITFORDB_SECRET_FORMAT")))
	formatExplicit := format != ""
	if formatExplicit {
		if format != FormatCNPG && format != FormatValkey {
			return Config{}, errf("unsupported WAITFORDB_SECRET_FORMAT %q (supported: %s, %s)", format, FormatCNPG, FormatValkey)
		}
	} else {
		format = detectFormat(get, c)
	}

	// An explicit driver wins; otherwise the secret format implies it, falling
	// back to the historical postgres default.
	if c.Driver == "" {
		switch format {
		case FormatValkey:
			c.Driver = "valkey"
		default:
			c.Driver = DefaultDriver
		}
	}
	if formatExplicit && !formatMatchesDriver(format, c.Driver) {
		return Config{}, errf("WAITFORDB_SECRET_FORMAT %q does not apply to driver %q", format, c.Driver)
	}
	if formatMatchesDriver(format, c.Driver) {
		c.SecretFormat = format
	}

	// The libpq PG* fallback for still-unset postgres fields.
	if c.Driver == "postgres" {
		fill(&c.Host, get("PGHOST"))
		fill(&c.Port, get("PGPORT"))
		fill(&c.User, get("PGUSER"))
		fill(&c.Password, get("PGPASSWORD"))
		fill(&c.Database, get("PGDATABASE"))
		fill(&c.SSLMode, get("PGSSLMODE"))
	}

	// Operator-secret keys fill whatever is still unset.
	switch c.SecretFormat {
	case FormatCNPG:
		fill(&c.Host, get("host"))
		fill(&c.Port, get("port"))
		fill(&c.Database, get("dbname"))
		fill(&c.User, firstNonEmpty(get("user"), get("username")))
		fill(&c.Password, get("password"))
	case FormatValkey:
		if c.User == "" && get("_operator") != "" {
			c.User = "_operator"
		}
		if c.Password == "" && c.User != "" {
			c.Password = get(c.User)
		}
	}

	if c.Host == "" {
		c.Host = DefaultHost
	}
	if c.Port == "" {
		c.Port = defaultPort[c.Driver]
	}

	var err error
	if c.Timeout, err = parseDuration(get("WAITFORDB_TIMEOUT"), 0); err != nil {
		return Config{}, errf("WAITFORDB_TIMEOUT: %v", err)
	}
	if c.Interval, err = parseDuration(get("WAITFORDB_INTERVAL"), DefaultInterval); err != nil {
		return Config{}, errf("WAITFORDB_INTERVAL: %v", err)
	}
	if c.ConnectTimeout, err = parseDuration(get("WAITFORDB_CONNECT_TIMEOUT"), DefaultConnectTimeout); err != nil {
		return Config{}, errf("WAITFORDB_CONNECT_TIMEOUT: %v", err)
	}

	if err := c.validate(); err != nil {
		return Config{}, err
	}
	return c, nil
}

// detectFormat recognises operator-generated secrets injected via envFrom.
// CNPG <cluster>-app secrets carry lowercase host/dbname/user keys; valkey
// user secrets carry one key per username (system users start with "_").
func detectFormat(get Getenv, c Config) string {
	if get("host") != "" && get("dbname") != "" && (get("user") != "" || get("username") != "") {
		return FormatCNPG
	}
	if get("_operator") != "" || get("_replication") != "" {
		return FormatValkey
	}
	// An explicit ACL user whose password key is present, with no SQL database
	// configured anywhere, is the valkey users-secret shape.
	if (c.Driver == "" || c.Driver == "valkey") && c.User != "" && c.Password == "" &&
		c.Database == "" && get("PGDATABASE") == "" && get(c.User) != "" {
		return FormatValkey
	}
	return ""
}

func formatMatchesDriver(format, driver string) bool {
	switch format {
	case FormatCNPG:
		return driver == "postgres"
	case FormatValkey:
		return driver == "valkey"
	}
	return false
}

func fill(dst *string, v string) {
	if *dst == "" {
		*dst = v
	}
}

func (c Config) validate() error {
	if _, ok := defaultPort[c.Driver]; !ok {
		return errf("unsupported WAITFORDB_DRIVER %q (supported: postgres, mysql, valkey/redis)", c.Driver)
	}
	if c.Interval <= 0 {
		return errf("WAITFORDB_INTERVAL must be > 0")
	}
	if c.ConnectTimeout <= 0 {
		return errf("WAITFORDB_CONNECT_TIMEOUT must be > 0")
	}
	if c.Timeout < 0 {
		return errf("WAITFORDB_TIMEOUT must be >= 0")
	}
	// With a DSN the discrete fields are optional (the DSN carries them).
	// Valkey needs neither a database nor a user (unauthenticated PING is valid).
	if c.DSN == "" && c.Driver != "valkey" {
		if c.Database == "" {
			return errf("no database configured: set WAITFORDB_DATABASE (or PGDATABASE for postgres) or WAITFORDB_DSN")
		}
		if c.User == "" {
			return errf("no user configured: set WAITFORDB_USER (or PGUSER for postgres) or WAITFORDB_DSN")
		}
	}
	return nil
}

// Redacted returns a single-line, password-free summary of the resolved
// configuration suitable for the startup log line.
func (c Config) Redacted() string {
	var b strings.Builder
	fmt.Fprintf(&b, "driver=%s", c.Driver)
	if c.SecretFormat != "" {
		fmt.Fprintf(&b, " secret_format=%s", c.SecretFormat)
	}
	if c.DSN != "" {
		fmt.Fprintf(&b, " dsn=%s", redactDSN(c.DSN))
	} else {
		fmt.Fprintf(&b, " addr=%s:%s", c.Host, c.Port)
		if c.Database != "" {
			fmt.Fprintf(&b, " database=%s", c.Database)
		}
		fmt.Fprintf(&b, " user=%s password=%s", c.User, redactSecret(c.Password))
		if c.SSLMode != "" {
			fmt.Fprintf(&b, " sslmode=%s", c.SSLMode)
		}
	}
	fmt.Fprintf(&b, " timeout=%s interval=%s connect_timeout=%s",
		timeoutStr(c.Timeout), c.Interval, c.ConnectTimeout)
	return b.String()
}

func redactSecret(s string) string {
	if s == "" {
		return "(unset)"
	}
	return "***"
}

func timeoutStr(d time.Duration) string {
	if d == 0 {
		return "forever"
	}
	return d.String()
}

// redactDSN masks the password in either a URL-style or keyword-style DSN so it
// never reaches a log line.
func redactDSN(dsn string) string {
	// URL form: scheme://user:password@host/...
	if i := strings.Index(dsn, "://"); i >= 0 {
		rest := dsn[i+3:]
		if at := strings.Index(rest, "@"); at >= 0 {
			creds := rest[:at]
			if colon := strings.Index(creds, ":"); colon >= 0 {
				return dsn[:i+3] + creds[:colon] + ":***@" + rest[at+1:]
			}
		}
		return dsn
	}
	// Keyword form: key=value pairs and mysql user:pass@tcp(...) form.
	out := dsn
	for _, key := range []string{"password", "passwd"} {
		out = redactKeyword(out, key)
	}
	// mysql DSN: user:pass@tcp(host)/db
	if at := strings.Index(out, "@tcp("); at >= 0 {
		if colon := strings.LastIndex(out[:at], ":"); colon >= 0 {
			out = out[:colon+1] + "***" + out[at:]
		}
	}
	return out
}

func redactKeyword(dsn, key string) string {
	lower := strings.ToLower(dsn)
	idx := strings.Index(lower, key+"=")
	if idx < 0 {
		return dsn
	}
	valStart := idx + len(key) + 1
	valEnd := valStart
	for valEnd < len(dsn) && dsn[valEnd] != ' ' {
		valEnd++
	}
	return dsn[:valStart] + "***" + dsn[valEnd:]
}

func firstNonEmpty(vals ...string) string {
	for _, v := range vals {
		if v != "" {
			return v
		}
	}
	return ""
}

func parseDuration(s string, def time.Duration) (time.Duration, error) {
	s = strings.TrimSpace(s)
	if s == "" {
		return def, nil
	}
	d, err := time.ParseDuration(s)
	if err != nil {
		return 0, fmt.Errorf("invalid duration %q", s)
	}
	return d, nil
}