package tokenize

import (
	"unicode/utf8"
)

// RuneMode provides (UTF8) rune-driven input/output functionality for the tokenize API.
type RuneMode struct {
	api *API
}

// Peek returns the UTF8 rune at the provided byte offset, including its byte width.
//
// The byte width is useful to know what byte offset you'll have to use to peek
// the next byte or rune. Some UTF8 runes take up 4 bytes of data, so when the
// first rune starts at offset = 0, the second rune might start at offset = 4.
//
// When an invalid UTF8 rune is encountered on the input, it is replaced with
// the utf.RuneError rune. It's up to the caller to handle this as an error
// when needed.
//
// When an error occurs during reading the input, an error will be returned.
// When an offset is requested that is beyond the length of the available input
// data, then the error will be io.EOF.
func (runeMode RuneMode) Peek(offset int) (rune, int, error) {
	a := runeMode.api
	return a.reader.RuneAt(a.stackFrame.offset + offset)
}

// Skip is used to skip over a single rune that was read from the input.
// This tells the tokenizer: "I've seen this rune. It is of no interest.
// I will now continue reading after this rune."
//
// This will merely update the position of the cursor (which keeps track of what
// line and column we are on in APIthe input data). The rune is not added to
// the output.
//
// After the call, byte offset 0 for PeekByte() and PeekRune() will point at
// the first byte after the skipped rune.
func (runeMode RuneMode) Skip(r rune) {
	f := runeMode.api.stackFrame
	f.moveCursorByRune(r)
	f.offset += utf8.RuneLen(r)
}

// SkipMulti is used to skip over one or more runes that were read from the input.
// This tells the tokenizer: "I've seen these runes. They are of no interest.
// I will now continue reading after these runes."
//
// This will merely update the position of the cursor (which keeps track of what
// line and column we are on in the input data). The runes are not added to
// the output.
//
// After the call, byte offset 0 for PeekByte() and PeekRune() will point at
// the first byte after the skipped runes.
func (runeMode RuneMode) SkipMulti(runes ...rune) {
	f := runeMode.api.stackFrame
	for _, r := range runes {
		f.moveCursorByRune(r)
		f.offset += utf8.RuneLen(r)
	}
}

// Accept is used to accept a single rune that was read from the input.
// This tells the tokenizer: "I've seen this rune. I want to make use of it
// for the final output, so please remember it for me. I will now continue
// reading after this rune."
//
// This will update the position of the cursor (which keeps track of what line
// and column we are on in the input data) and add the rune to the tokenizer
// output.
//
// After the call, byte offset 0 for PeekByte() and PeekRune() will point at
// the first byte after the accepted rune.
func (runeMode RuneMode) Accept(r rune) {
	a := runeMode.api
	f := a.stackFrame
	curBytesEnd := f.bytesEnd
	maxRequiredBytes := curBytesEnd + utf8.UTFMax

	a.growOutputData(maxRequiredBytes)
	w := utf8.EncodeRune(a.outputData[curBytesEnd:], r)
	f.bytesEnd += w
	f.offset += w

	f.moveCursorByRune(r)
}

// AcceptMulti is used to accept one or more runes that were read from the input.
// This tells the tokenizer: "I've seen these runes. I want to make use of them
// for the final output, so please remember them for me. I will now continue
// reading after these runes."
//
// This will update the position of the cursor (which keeps track of what line
// and column we are on in the input data) and add the runes to the tokenizer
// output.
//
// After the call, byte offset 0 for PeekByte() and PeekRune() will point at
// the first byte after the accepted runes.
func (runeMode RuneMode) AcceptMulti(runes ...rune) {
	a := runeMode.api
	f := a.stackFrame
	runesAsString := string(runes)
	byteLen := len(runesAsString)
	curBytesEnd := f.bytesEnd
	newBytesEnd := curBytesEnd + byteLen

	a.growOutputData(newBytesEnd)
	copy(a.outputData[curBytesEnd:], runesAsString)
	f.bytesEnd = newBytesEnd
	f.offset += byteLen

	for _, r := range runes {
		f.moveCursorByRune(r)
	}
}