// Package dotenv loads KEY=VALUE pairs from a .env file into the process
// environment, so secrets can live in one file that is kept out of version
// control instead of on command lines.
//
// Real environment variables always win over the file, so a deployment can
// still override anything with its own environment.
package dotenv

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

// Load reads the first of paths that exists and sets any variables it defines
// that aren't already set. It returns the path used, or "" if none existed.
func Load(paths ...string) (string, error) {
	for _, p := range paths {
		if p == "" {
			continue
		}
		f, err := os.Open(p)
		if errors.Is(err, os.ErrNotExist) {
			continue
		}
		if err != nil {
			return "", err
		}
		defer f.Close()
		sc := bufio.NewScanner(f)
		sc.Buffer(make([]byte, 64*1024), 1<<20)
		for sc.Scan() {
			k, v, ok := parseLine(sc.Text())
			if !ok {
				continue
			}
			if _, set := os.LookupEnv(k); !set {
				os.Setenv(k, v)
			}
		}
		return p, sc.Err()
	}
	return "", nil
}

// ArgPath finds -env <path> / --env=<path> in args, so the file can be chosen
// before the program's own flags are parsed (flags take their defaults from the environment).
func ArgPath(args []string, def string) string {
	for i, a := range args {
		a = strings.TrimLeft(a, "-")
		switch {
		case a == "env" && i+1 < len(args):
			return args[i+1]
		case strings.HasPrefix(a, "env="):
			return a[len("env="):]
		}
	}
	return def
}

func parseLine(line string) (key, val string, ok bool) {
	line = strings.TrimSpace(line)
	if line == "" || strings.HasPrefix(line, "#") {
		return "", "", false
	}
	line = strings.TrimSpace(strings.TrimPrefix(line, "export "))
	k, v, found := strings.Cut(line, "=")
	k = strings.TrimSpace(k)
	if !found || k == "" || strings.ContainsAny(k, " \t") {
		return "", "", false
	}
	v = strings.TrimSpace(v)
	switch {
	case len(v) >= 2 && v[0] == '"':
		if end := strings.LastIndexByte(v, '"'); end > 0 {
			v = strings.NewReplacer(`\n`, "\n", `\r`, "\r", `\t`, "\t", `\"`, `"`, `\\`, `\`).Replace(v[1:end])
		}
	case len(v) >= 2 && v[0] == '\'':
		if end := strings.LastIndexByte(v, '\''); end > 0 {
			v = v[1:end]
		}
	default:
		if i := strings.Index(v, " #"); i >= 0 { // trailing comment
			v = strings.TrimSpace(v[:i])
		}
	}
	return k, v, true
}