package backend

import (
	"fmt"
	"strings"
)

// parseEnvFile parses KEY=VALUE lines in pure Go. Env files are NEVER
// sourced or eval'd (house rule: no exec of env files); there is no
// shell expansion, no command substitution, no interpolation of any
// kind. Accepted syntax per line:
//
//	# comment            skipped (also inline comments after whitespace)
//	(blank line)         skipped
//	export KEY=VALUE     optional "export " prefix, skipped
//	KEY=VALUE            KEY is [A-Za-z_][A-Za-z0-9_]*; VALUE is the rest
//	                     of the line, trimmed; one matched pair of
//	                     surrounding single or double quotes is stripped
//	                     (no escape processing)
//
// A later duplicate KEY overrides an earlier one (same order semantics
// as sourcing the file). Malformed lines fail loudly: the error carries
// the line NUMBER only, never the line contents (contents may be
// material).
func parseEnvFile(data []byte) (map[string]string, error) {
	out := map[string]string{}
	for i, line := range strings.Split(string(data), "\n") {
		line = strings.TrimRight(line, "\r")
		trimmed := strings.TrimSpace(line)
		if trimmed == "" || strings.HasPrefix(trimmed, "#") {
			continue
		}
		line = trimmed
		if strings.HasPrefix(line, "export ") || strings.HasPrefix(line, "export\t") {
			line = strings.TrimSpace(line[len("export"):])
		}
		eq := strings.IndexByte(line, '=')
		if eq <= 0 {
			return nil, fmt.Errorf("line %d: malformed KEY=VALUE line", i+1)
		}
		key := strings.TrimSpace(line[:eq])
		if !validEnvKey(key) {
			return nil, fmt.Errorf("line %d: malformed KEY=VALUE line", i+1)
		}
		value := strings.TrimSpace(line[eq+1:])
		if idx := commentIndex(value); idx >= 0 {
			value = strings.TrimSpace(value[:idx])
		}
		out[key] = unquote(value)
	}
	return out, nil
}

// validEnvKey reports whether key is a legal env-file identifier.
func validEnvKey(key string) bool {
	if key == "" {
		return false
	}
	for i := 0; i < len(key); i++ {
		c := key[i]
		switch {
		case c >= 'a' && c <= 'z', c >= 'A' && c <= 'Z', c == '_':
		case c >= '0' && c <= '9':
			if i == 0 {
				return false
			}
		default:
			return false
		}
	}
	return true
}

// commentIndex finds an inline comment start (a # preceded by whitespace)
// OUTSIDE a quoted value; -1 if none.
func commentIndex(value string) int {
	var quote byte
	for i := 0; i < len(value); i++ {
		c := value[i]
		switch {
		case quote != 0:
			if c == quote {
				quote = 0
			}
		case c == '"' || c == '\'':
			quote = c
		case c == '#' && (i == 0 || value[i-1] == ' ' || value[i-1] == '\t'):
			return i
		}
	}
	return -1
}

// unquote strips one matched pair of surrounding quotes.
func unquote(v string) string {
	if len(v) >= 2 {
		if (v[0] == '"' && v[len(v)-1] == '"') || (v[0] == '\'' && v[len(v)-1] == '\'') {
			return v[1 : len(v)-1]
		}
	}
	return v
}