package config

import (
	"fmt"
	"sort"
	"strconv"
	"strings"
)

// Doc is the parsed representation of keyproxy.toml: nested tables are
// Doc values; leaves are string, int64 or bool. This is a deliberate
// stdlib-only TOML subset (tables with quoted keys, basic strings with
// escapes, integers, booleans, comments). Anything richer is a parse
// error so a misconfigured file fails loudly instead of silently.
type Doc map[string]any

// Table returns the nested table at the key path, or an empty doc.
func (d Doc) Table(keys ...string) Doc {
	cur := any(d)
	for _, k := range keys {
		m, ok := cur.(Doc)
		if !ok {
			return Doc{}
		}
		cur = m[k]
	}
	if m, ok := cur.(Doc); ok {
		return m
	}
	return Doc{}
}

// Str returns the string leaf at key.
func (d Doc) Str(key string) (string, bool) {
	v, ok := d[key].(string)
	return v, ok
}

// Int returns the int64 leaf at key.
func (d Doc) Int(key string) (int64, bool) {
	v, ok := d[key].(int64)
	return v, ok
}

// Bool returns the bool leaf at key.
func (d Doc) Bool(key string) (bool, bool) {
	v, ok := d[key].(bool)
	return v, ok
}

// Keys lists the doc's keys, sorted.
func (d Doc) Keys() []string {
	out := make([]string, 0, len(d))
	for k := range d {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// parseTOML parses the TOML subset into a Doc. Errors carry line
// numbers, never line contents (a config file may sit next to secrets
// someone pasted in by mistake).
func parseTOML(data []byte) (Doc, error) {
	root := Doc{}
	cur := root
	for i, raw := range strings.Split(string(data), "\n") {
		lineno := i + 1
		line := stripComment(raw)
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		if strings.HasPrefix(line, "[") {
			if !strings.HasSuffix(line, "]") {
				return nil, fmt.Errorf("line %d: malformed table header", lineno)
			}
			path, err := splitKeyPath(strings.TrimSpace(line[1 : len(line)-1]))
			if err != nil || len(path) == 0 {
				return nil, fmt.Errorf("line %d: malformed table header", lineno)
			}
			cur = root
			for _, seg := range path {
				next, ok := cur[seg].(Doc)
				if !ok {
					if _, exists := cur[seg]; exists {
						return nil, fmt.Errorf("line %d: table conflicts with value key %q", lineno, seg)
					}
					next = Doc{}
					cur[seg] = next
				}
				cur = next
			}
			continue
		}
		eq := strings.IndexByte(line, '=')
		if eq < 1 {
			return nil, fmt.Errorf("line %d: expected key = value", lineno)
		}
		key := strings.TrimSpace(line[:eq])
		key = strings.Trim(key, `"'`)
		if key == "" || strings.ContainsAny(key, `".[]`) {
			return nil, fmt.Errorf("line %d: malformed key", lineno)
		}
		value := strings.TrimSpace(line[eq+1:])
		parsed, err := parseValue(value)
		if err != nil {
			return nil, fmt.Errorf("line %d: %v", lineno, err)
		}
		if _, dup := cur[key]; dup {
			return nil, fmt.Errorf("line %d: duplicate key %q", lineno, key)
		}
		cur[key] = parsed
	}
	return root, nil
}

// splitKeyPath splits a.b."c.d" into [a b c.d]; each segment is bare or
// double-quoted.
func splitKeyPath(s string) ([]string, error) {
	var segs []string
	for i := 0; i < len(s); {
		for i < len(s) && (s[i] == ' ' || s[i] == '\t') {
			i++
		}
		if i >= len(s) {
			break
		}
		switch s[i] {
		case '"':
			j := i + 1
			for j < len(s) && s[j] != '"' {
				j++
			}
			if j >= len(s) {
				return nil, fmt.Errorf("unterminated quoted key")
			}
			segs = append(segs, s[i+1:j])
			i = j + 1
		default:
			j := i
			for j < len(s) && s[j] != '.' {
				j++
			}
			seg := strings.TrimSpace(s[i:j])
			if seg == "" {
				return nil, fmt.Errorf("empty key segment")
			}
			segs = append(segs, seg)
			i = j
		}
		for i < len(s) && (s[i] == ' ' || s[i] == '\t') {
			i++
		}
		if i < len(s) {
			if s[i] != '.' {
				return nil, fmt.Errorf("unexpected character in table header")
			}
			i++
		}
	}
	return segs, nil
}

// parseValue parses a basic string, integer or boolean.
func parseValue(v string) (any, error) {
	if v == "" {
		return nil, fmt.Errorf("missing value")
	}
	switch v[0] {
	case '"':
		s, rest, err := parseBasicString(v)
		if err != nil {
			return nil, err
		}
		if strings.TrimSpace(rest) != "" {
			return nil, fmt.Errorf("trailing characters after string value")
		}
		return s, nil
	case '\'':
		end := strings.IndexByte(v[1:], '\'')
		if end < 0 {
			return nil, fmt.Errorf("unterminated literal string")
		}
		s := v[1 : 1+end]
		if strings.TrimSpace(v[2+end:]) != "" {
			return nil, fmt.Errorf("trailing characters after string value")
		}
		return s, nil
	}
	switch v {
	case "true":
		return true, nil
	case "false":
		return false, nil
	}
	n, err := strconv.ParseInt(v, 10, 64)
	if err != nil {
		return nil, fmt.Errorf("unsupported value (expected string, int or bool)")
	}
	return n, nil
}

// parseBasicString parses one "..." basic string with \\ \" \n \t \r
// escapes; it returns the string and the unparsed remainder.
func parseBasicString(v string) (string, string, error) {
	var b strings.Builder
	for i := 1; i < len(v); i++ {
		switch v[i] {
		case '"':
			return b.String(), v[i+1:], nil
		case '\\':
			if i+1 >= len(v) {
				return "", "", fmt.Errorf("dangling escape in string")
			}
			i++
			switch v[i] {
			case '\\':
				b.WriteByte('\\')
			case '"':
				b.WriteByte('"')
			case 'n':
				b.WriteByte('\n')
			case 't':
				b.WriteByte('\t')
			case 'r':
				b.WriteByte('\r')
			default:
				return "", "", fmt.Errorf("unsupported escape in string")
			}
		default:
			b.WriteByte(v[i])
		}
	}
	return "", "", fmt.Errorf("unterminated string")
}

// stripComment removes a trailing # comment that sits outside quotes.
func stripComment(line string) string {
	var quote byte
	for i := 0; i < len(line); i++ {
		c := line[i]
		switch {
		case quote != 0:
			if c == quote {
				quote = 0
			}
		case c == '"' || c == '\'':
			quote = c
		case c == '#':
			return line[:i]
		}
	}
	return line
}