// conf implements a very simple config parser with permissive input syntax.
//
// It parses input file or io.Reader looking for key value pairs separated by equal
// sign into conf.Map which is a map[string]conf.Value under the hood.
//
// Input syntax rules are as follows:
//
// 1. Lines starting with "#" are considered to be comments and are discarded. If a line starts with any number of whitespace characters followed by "#" it is also discarded as comment.
//
// 2. If a line is not a comment it must follow the "key = value" pattern. Any of the following is valid:
//
//	key=value
//	key= value
//	key =value
//
// Leading and trailing whitespace characters are trimmed before parsing line. Whitespaces surrounding
// key and value strings are also trimmed.
//
// 3. Keys in the input must be unique.
//
// Map object has Find, Get and GetDefault mathod used to retrieve Value from
// Map by corresponding key.
//
// Value is essentially a string which can be converted into several types using
// Value's methods:
//
//	String() returns Value as string
//	StringSlice() interprets Value as a comma-separated list (whitespace around elements is trimmed)
//	Int() converts Value to int
//	IntSlice() tries to convert Value to []int
//	Float64() converts Value to float64
//	Float64Slice() tries to convert to []float64
//	Map() tries to interpret Value as comma-separated list of key-value pairs like in "key1: value1, key2: value2, key3: value3"
//	URL() calls url.Parse to convert Value to *url.URL
//
// See documentation for description of all available methods.
//
// Example usage:
//
//	m, _ := conf.ReadFile("myfile")
//	retries, err := m.Get("retries").Int()
//	if err != nil {
//		// handle err
//	}
//	addr, err := m.Get("addr").URL()
//	if err != nil {
//		// handle err
//	}
//
// See example folder.
package conf

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"os"
	"slices"
)

var (
	ErrFormat       = errors.New("conf: line does not match \"key = value\" pattern")
	ErrDuplicateKey = errors.New("conf: duplicate key found")
)

// Map holds key value pairs.
type Map map[string]Value

// Open reads values from file.
func Open(filename string) (Map, error) {
	m := make(Map)
	if err := m.readFile(filename); err != nil {
		return nil, err
	}

	return m, nil
}

// Read reads from r and returns Conf.
func Read(r io.Reader) (Map, error) {
	m := make(Map)
	if err := m.read(r); err != nil {
		return nil, err
	}

	return m, nil
}

func (m Map) Read(r io.Reader) error {
	return m.read(r)
}

func (m Map) ReadFile(name string) error {
	return m.readFile(name)
}

// Find looks up a the key and returns Value associated with it.
// If bool is false then the returned Value would be zero.
func (m Map) Find(key string) (Value, bool) {
	return m.get(key, "")
}

// Get returns a Value. If key was not found the returned Value
// will be empty.
func (m Map) Get(key string) Value {
	v, _ := m.get(key, "")
	return v
}

// GetDefault looks up a Value for requested key.
// If lookup fails it returns Value set to def.
func (m Map) GetDefault(key, def string) Value {
	v, _ := m.get(key, def)
	return v
}

func (m Map) Keys() []string {
	list := make([]string, 0, len(m))

	for k := range m {
		list = append(list, k)
	}

	slices.Sort(list)

	return list
}

func (m Map) get(key string, def string) (Value, bool) {
	v, ok := m[key]
	if def != "" && !ok {
		v = Value(def)
	}

	return v, ok
}

func (m Map) readFile(name string) error {
	file, err := os.Open(name)
	if err != nil {
		return err
	}

	if err := m.read(file); err != nil {
		return err
	}

	return file.Close()
}

func (m Map) read(r io.Reader) error {
	scanner := bufio.NewScanner(r)

	lineN := 0
	for scanner.Scan() {
		lineN++

		line := scanner.Text()

		line = stripComment(trim(line))
		if line == "" {
			continue
		}

		key, value, ok := toKV(line, separatorKV)
		if !ok {
			return fmt.Errorf("line: %d, err: %w", lineN, ErrFormat)
		}

		if _, ok := m[key]; ok {
			return fmt.Errorf("line: %d, err: %w %s", lineN, ErrDuplicateKey, key)
		}

		m[key] = Value(value)
	}

	if err := scanner.Err(); err != nil {
		return err
	}

	return nil
}