package treerack

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

// CommitType controls how the output of a named parser is handled and represented in the resulting AST.
type CommitType int

const (

	// None indicates the default behavior: parsed segments are represented as named nodes in the AST.
	// Whitespace handling inherits the syntax's global settings.
	None CommitType = 0

	// Alias treats the parser as a pass-through. Validated segments are included in the AST node of the
	// enclosing parser rather than creating a distinct node.
	Alias CommitType = 1 << iota

	// Whitespace designates a parser (typically a character sequence) to be treated as ignored whitespace
	// throughout the input.
	Whitespace

	// NoWhitespace prevents the automatic skipping of defined whitespace characters within specific sequences.
	NoWhitespace

	// Keyword marks a sequence as a reserved keyword. This allows specific sequences to be protected or
	// restricted in certain contexts via the NoKeyword flag.
	Keyword

	// NoKeyword prevents the parser from matching sequences marked as Keywords.
	NoKeyword

	// FailPass configures the parser to propagate failure up to the enclosing parser rather than handling it
	// locally.
	FailPass

	// Root explicitly marks the parser as the root of the syntax. By default, the last defined parser is
	// considered the root.
	Root

	userDefined
)

type formatFlags int

const (
	formatNone   formatFlags = 0
	formatPretty formatFlags = 1 << iota
	formatIncludeComments
)

// ParseError reports a failure to match the input text against the defined syntax.
type ParseError struct {

	// Input denotes the name of the input source (e.g., filename), or "<input>" if unavailable.
	Input string

	// Offset is the index of the right-most token where the parse failed.
	Offset int

	// Line is the zero-based line number of the failure position.
	//
	// For display purposes, increment by one.
	Line int

	// Column is the zero-based column index of the failure position.
	Column int

	// Definition identifies the name of the specific parser definition where the match failed.
	Definition string
}

type parser interface {
	nodeName() string
	nodeID() int
	commitType() CommitType
	parse(*context)
}

type builder interface {
	nodeName() string
	nodeID() int
	build(*context) ([]*Node, bool)
}

// ErrInvalidUnicodeCharacter indicates that the input content contains invalid UTF-8 sequences.
var ErrInvalidUnicodeCharacter = errors.New("invalid unicode character")

// Error returns the formatted failure message.
func (pe *ParseError) Error() string {
	return fmt.Sprintf(
		"%s:%d:%d:parse failed, parsing: %s",
		pe.Input,
		pe.Line+1,
		pe.Column+1,
		pe.Definition,
	)
}

func parseInput(r io.Reader, p parser, b builder, kw []parser) (*Node, error) {
	c := newContext(bufio.NewReader(r), kw)
	p.parse(c)
	if c.readErr != nil {
		return nil, c.readErr
	}

	if err := c.finalizeParse(p); err != nil {
		if perr, ok := err.(*ParseError); ok {
			perr.Input = "<input>"
		}

		return nil, err
	}

	c.offset = 0
	c.results.resetPending()

	n, _ := b.build(c)
	return n[0], nil
}