package parser

import (
	"fmt"
	"strings"
	"unicode/utf8"
)

// New takes an input string and a start state,
// and initializes the parser for it.
func New(input string, startState StateFn) *Parser {
	return &Parser{
		input: input,
		len:   len(input),
		state: startState,
		items: make(chan Item, 2),
	}
}

// PushState adds the state function to the state stack.
// This is used for implementing nested parsing.
func (l *Parser) PushState(state StateFn) {
	l.stack = append(l.stack, state)
}

// PopState pops the last pushed state from the state stack.
func (l *Parser) PopState() StateFn {
	last := len(l.stack) - 1
	head, tail := l.stack[:last], l.stack[last]
	l.stack = head
	return tail
}

// AtEndOfFile returns true when there is no more data available in the input.
func (l *Parser) AtEndOfFile() bool {
	return l.pos >= l.len
}

// Emit passes a Parser item to the client, including the provided string.
func (l *Parser) Emit(t ItemType, s string) {
	l.items <- Item{t, s}
	l.buffer.Reset()
}

// EmitLiteral passes a Parser item to the client, including the accumulated
// string buffer data as a literal string.
func (l *Parser) EmitLiteral(t ItemType) {
	l.Emit(t, l.buffer.AsLiteralString())
}

// EmitLiteralTrim passes a Parser item to the client, including the
// accumulated string buffer data as a literal string with whitespace
// trimmed from it.
func (l *Parser) EmitLiteralTrim(t ItemType) {
	l.Emit(t, strings.TrimSpace(l.buffer.AsLiteralString()))
}

// EmitInterpreted passes a Parser item to the client, including the
// accumulated string buffer data a Go doubled quoted interpreted string
// (handling escape codes like \n, \t, \uXXXX, etc.)
// This method might return an error, in case there is data in the
// string buffer that is not valid for string interpretation.
func (l *Parser) EmitInterpreted(t ItemType) error {
	s, err := l.buffer.AsInterpretedString()
	if err != nil {
		return err
	}
	l.Emit(t, s)
	return nil
}

// EmitError emits a Parser error item to the client.
func (l *Parser) EmitError(format string, args ...interface{}) StateFn {
	message := fmt.Sprintf(format, args...)
	l.Emit(ItemError, message)
	return nil
}

// Match checks if the upcoming runes satisfy all provided patterns.
// It returns a slice of runes that were found, their total byte width
// and a boolean indicating whether or not all provided patterns were
// satisfied by the input data.
func (l *Parser) Match(patterns ...string) ([]rune, int, bool) {
	peeked, width, ok := l.peekMulti(len(patterns))
	if ok {
		for i, r := range patterns {
			if strings.IndexRune(r, peeked[i]) < 0 {
				return peeked, width, false
			}
		}
		return peeked, width, true
	}
	return peeked, width, false
}

// Upcoming checks if the upcoming runes satisfy all provided patterns.
// Returns true if all provided patterns are satisfied.
func (l *Parser) Upcoming(patterns ...string) bool {
	_, _, ok := l.Match(patterns...)
	return ok
}

// AcceptAny adds the next rune from the input to the string buffer.
// If no rune could be read (end of file or invalid UTF8 data),
// then false is returned.
func (l *Parser) AcceptAny() bool {
	if r, ok := l.next(); ok {
		l.buffer.WriteRune(r)
		return true
	}
	return false
}

// AcceptMatching adds the next runes to the string buffer, but only
// if the upcoming runes satisfy the provided patterns.
// When runes were added then true is returned, false otherwise.
func (l *Parser) AcceptMatching(patterns ...string) bool {
	return l.progress(func(r rune) { l.buffer.WriteRune(r) }, patterns...)
}

// AcceptConsecutive adds consecutive runes from the input to the string
// buffer, as long as they exist in the pattern.
// If any runes were added then true is returned, false otherwise.
func (l *Parser) AcceptConsecutive(pattern string) bool {
	accepted := false
	for l.AcceptMatching(pattern) {
		accepted = true
	}
	return accepted
}

// SkipMatching skips runes, but only when all provided patterns are satisfied.
// Returns true when one or more runes were skipped.
func (l *Parser) SkipMatching(patterns ...string) bool {
	if runes, w, ok := l.Match(patterns...); ok {
		l.pos += w
		for _, r := range runes {
			l.advanceCursor(r)
		}
		return true
	}
	return false
}

// SkipConsecutive skips consecutive runes from the provided pattern.
// Returns true when one or more runes were skipped.
func (l *Parser) SkipConsecutive(pattern string) bool {
	didSkip := false
	for l.SkipMatching(pattern) {
		didSkip = true
	}
	return didSkip
}

// ============================================================================
// EMIT DATA AND ERRORS
// ============================================================================

// UnexpectedInputError is used by a parser implementation to emit an
// error item that tells the client that an unexpected rune was
// encountered in the input.
// The parameter 'expected' is used to provide some context to the error.
func (l *Parser) UnexpectedInputError(expected string) StateFn {
	// next() takes care of error messages for ok == false.
	if r, ok := l.next(); ok {
		return l.EmitError(fmt.Sprintf("unexpected character %q (expected %s)", r, expected))
	}
	return nil
}

// UnexpectedEndOfFile is used by a parser implementation to emit an
// error item that tells the client that more data was expected from
// the input.
// The parameter 'expected' is used to provide some context to the error.
func (l *Parser) UnexpectedEndOfFile(expected string) StateFn {
	return l.EmitError("Unexpected end of file (expected %s)", expected)
}

// ============================================================================
// LEXER : our lexer is quite low level, it only returns UTF8 runes
// ============================================================================

// peek returns but does not advance to the next rune(s) in the input.
// Returns the rune, its width and a boolean. The boolean will be false in case
// no upcoming rune can be peeked (end of data or invalid UTF8 character).
func (l *Parser) peek() (rune, int, bool) {
	peeked, width := utf8.DecodeRuneInString(l.input[l.pos:])
	return peeked, width, peeked != utf8.RuneError
}

// peekMulti takes a peek at multiple upcoming runes in the input.
// Returns a slice of runes, their total width in bytes and a boolean.
// The boolean will be false in case less runes can be peeked than
// the requested amount (end of data or invalid UTF8 character).
func (l *Parser) peekMulti(amount int) ([]rune, int, bool) {
	width := 0
	var peeked []rune
	for i := 0; i < amount; i++ {
		r, w := utf8.DecodeRuneInString(l.input[l.pos+width:])
		switch {
		case r == utf8.RuneError:
			return peeked, width, false
		default:
			width += w
			peeked = append(peeked, r)
		}
	}
	return peeked, width, true
}

// progress moves the cursor forward in the input, returning one rune
// for every specified pattern. The cursor is only moved forward when
// all patterns are satisfied.
// Returns true when all patterns were satisfied and the cursor was
// moved forward, false otherwise.
// A callback function can be provided to specify what to do with
// the runes that are encountered in the input.
func (l *Parser) progress(callback func(rune), patterns ...string) bool {
	if runes, w, ok := l.Match(patterns...); ok {
		l.pos += w
		for _, r := range runes {
			callback(r)
			l.advanceCursor(r)
		}
		return true
	}
	return false
}

// next returns the next rune from the input and a boolean indicating if
// reading the input was successful.
// When the end of input is reached, or an invalid UTF8 character is
// read, then false is returned. Both are considered error cases,
// and for that reason these automatically emit an error to the client.
func (l *Parser) next() (rune, bool) {
	r, w, ok := l.peek()
	if ok {
		l.pos += w
		l.advanceCursor(r)
		return r, true
	}
	if r == utf8.RuneError && w == 0 {
		l.EmitError("unexpected end of file")
	} else {
		l.EmitError("invalid UTF8 character")
	}
	return r, false
}

// advanceCursor advances the rune cursor one position in the
// input data. While doing so, it keeps tracks of newlines,
// so we can report on row + column positions on error.
func (l *Parser) advanceCursor(r rune) {
	if l.newline {
		l.cursorColumn = 0
		l.cursorRow++
	} else {
		l.cursorColumn++
	}
	l.newline = r == '\n'
}