package ini

import (
	"bufio"
	"fmt"
	"io"
	"strings"
)

// State machine for writing to streamable INI file sources.
type Builder struct {
	writer io.Writer
}

// Singular key-value pair under the given section within an INI file.
type Entry struct {
	Key   string
	Value string
}

// Returns the last error that occured during parsing.
func (parser *Parser) Err() error {
	return parser.err
}

// Returns `true` if `parser` has reached the end of parsable tokens, either because the stream has
// ended or it has encountered an error.
func (parser *Parser) IsEnd() bool {
	return parser.isEnd
}

// Appends a new key-value pair of `key` and `value` respectively in the `builder`.
func (builder *Builder) KeyValue(key string, value string) error {
	var _, printError = fmt.Fprintf(builder.writer, "%s = %s\n", key, value)

	return printError
}

// Creates and returns a new [Builder] by reference from `writer`.
//
// Note that [NewBuilder] does not buffer write operations.
func NewBuilder(writer io.Writer) *Builder {
	return &Builder{
		writer: writer,
	}
}

// Creates and returns a new [Parser] by reference from `reader`.
func NewParser(reader io.Reader) *Parser {
	return &Parser{
		scanner: bufio.NewScanner(reader),
		isEnd:   false,
	}
}

// Attempts to parse the next key-value pair in the `parser` stream, returning the parsed [Entry],
// or an empty one if nothing was parsed, and a `bool` representing whether or not there is any
// further data available to parse.
//
// Note that the `parser` does not guarantee any parse order for key-value pairs extracted from the
// `parser` stream.
func (parser *Parser) Parse() Entry {
	for parser.scanner.Scan() {
		var line = strings.TrimSpace(parser.scanner.Text())
		var lineLen = len(line)

		if lineLen == 0 {
			// Skip empty lines.
			continue
		}

		if (line[0] == '#') || (line[0] == ';') {
			// Skip comment lines.
			continue
		}

		var lineTail = lineLen - 1

		if (line[0] == '[') && (line[lineTail] == ']') {
			// Section name.
			parser.section = line[1:lineTail]

			continue
		}

		if assignmentIndex := strings.Index(line, "="); assignmentIndex > -1 {
			// Key with value.
			return Entry{
				Key:   unquote(strings.TrimSpace(line[0:assignmentIndex])),
				Value: unquote(strings.TrimSpace(line[assignmentIndex+1:])),
			}
		}

		// Key which is its own value.
		var keyValue = unquote(line[1:lineTail])

		return Entry{
			Key:   keyValue,
			Value: keyValue,
		}
	}

	parser.err = parser.scanner.Err()
	parser.isEnd = true

	return Entry{}
}

// State machine for parsing streamable INI file sources.
type Parser struct {
	scanner *bufio.Scanner
	err     error
	section string
	isEnd   bool
}

// Returns the name of the section last parsed, which will an empty string if currently in the
// default section.
func (parser *Parser) Section() string {
	return parser.section
}

// Appends a new section titled `name` in the `builder`.
func (builder *Builder) Section(name string) error {
	var _, printError = fmt.Fprintf(builder.writer, "[%s]\n", name)

	return printError
}

// Returns a string with the the outer-most quotes surrounding `s` trimmed, should they exist.
func unquote(s string) string {
	var sLen = len(s)

	if sLen != 0 {
		var sTail = sLen - 1

		if (s[0] == '"') && (s[sTail] == '"') {
			return s[1:sTail]
		}
	}

	return s
}