package treerack

import (
	"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

	// NoFailPass configures the parser to handle the failure locally. This overrides automatic fail-pass,
	// e.g. in case of Alias definitions.
	NoFailPass

	// 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
)

type formatOptions struct {
	mode        formatFlags
	targetWidth int
}

// TraceEvent indicates the type of a trace entry.
type TraceEvent int

const (

	// Enter is the type of a trace entry set when entering the parser of a definition.
	Enter TraceEvent = iota

	// Success is the type of a trace entry set when the parser of a definition is returning with success.
	Success

	// Fail is the type of a trace entry set when the parser of a definition is returning with failure.
	Fail
)

// TraceEntry represents trace events set during parsing with the purpose of helping to identify problems with
// the input being parsed or to debug a parser.
type TraceEntry struct {

	// Level indicates the level of descend while parsing. The root parser has a level of 0.
	Level int

	// Parser is the name of the parser definition that set the trace event.
	Parser string

	// From is the offset in the input where the parser, that set the trace event, has started.
	From int

	// To is the offset in the input where the parser, that set the trace event, has left.
	To int

	// FromLine is the line number where the parser, that set the trace event, has started.
	FromLine int

	// FromCol is the column number where the parser, that set the trace event, has started.
	FromCol int

	// ToLine is the line number where the parser, that set the trace event, has left.
	ToLine int

	// ToCol is the column number where the parser, that set the trace event, has left.
	ToCol int

	// Event is the type of the trace event.
	Event TraceEvent

	// Reason is the reason why the parser, that set the trace event, has failed.
	Reason string
}

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

	// 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

	// Trace contains the last parsing steps leading to the parse error.
	Trace []TraceEntry

	// UnexpectedInputLine has a non-negative value, if the parse failed due to unexpected input.
	UnexpectedInputLine int

	// UnexpectedInputLine has a non-negative value, if the parse failed due to unexpected input.
	UnexpectedInputCol int
}

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")

// InputContent returns the specified slice from the consumed parse input. If to < 0, to is length of the
// available content.
func (pe *ParseError) InputContent(from, to int) []rune {
	if to < 0 {
		to = len(pe.inputContent)
	}

	if to <= from {
		return nil
	}

	c := make([]rune, to-from)
	copy(c, pe.inputContent[from:])
	return c
}

// Error returns the formatted failure message.
func (pe *ParseError) Error() string {
	if pe.UnexpectedInputLine >= 0 && pe.UnexpectedInputCol >= 0 {
		return fmt.Sprintf(
			"%s:%d:%d:parse failed, unexpected input at %d:%d",
			pe.Input,
			pe.UnexpectedInputLine+1,
			pe.UnexpectedInputCol+1,
			pe.UnexpectedInputLine+1,
			pe.UnexpectedInputCol+1,
		)
	}

	return fmt.Sprintf(
		"%s:%d:%d:parse failed, parsing: %s, at %d:%d",
		pe.Input,
		pe.Line+1,
		pe.Column+1,
		pe.Definition,
		pe.Line+1,
		pe.Column+1,
	)
}

func parseInput(r io.Reader, p parser, b builder, kw []parser, maxTraceLength int) (Node, error) {
	bb, err := io.ReadAll(r)
	if err != nil {
		return Node{}, err
	}

	c := newContext([]rune(string(bb)), kw, maxTraceLength)
	p.parse(c)
	if c.readErr != nil {
		return Node{}, c.readErr
	}

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

		return Node{}, err
	}

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