// Based on http://stackoverflow.com/a/22747272/680742, the browser with
// the lowest limit is Chrome, with 0x10000 args.
// We go 1 magnitude less, for safety
const MAX_ARGUMENTS_LENGTH = 0x1000
const base64 = require('base64-js')

function blitBuffer(src, dst, offset, length) {
    let i
    for (i = 0; i < length; ++i) {
        if ((i + offset >= dst.length) || (i >= src.length)) break
        dst[i + offset] = src[i]
    }
    return i
}

export function utf8Write(string, offset, length) {
    return blitBuffer(utf8ToBytes(string, this.length - offset), this, offset, length)
}

export function base64Slice(start, end) {
    if (start === 0 && end === this.length) {
        return base64.fromByteArray(this)
    } else {
        return base64.fromByteArray(this.slice(start, end))
    }
}

function decodeCodePointsArray(codePoints) {
    const len = codePoints.length
    if (len <= MAX_ARGUMENTS_LENGTH) {
        return String.fromCharCode.apply(String, codePoints) // avoid extra slice()
    }

    // Decode in chunks to avoid "call stack size exceeded".
    let res = ''
    let i = 0
    while (i < len) {
        res += String.fromCharCode.apply(
            String,
            codePoints.slice(i, i += MAX_ARGUMENTS_LENGTH)
        )
    }
    return res
}


export function latin1Slice(start, end) {
    let ret = ''
    end = Math.min(this.length, end)

    for (var i = start; i < end; ++i) {
        ret += String.fromCharCode(this[i])
    }
    return ret
}

export function utf8Slice(this, start, end) {
    end = Math.min(this.length, end)
    const res = []

    let i = start
    while (i < end) {
        const firstByte = this[i]
        let codePoint = null
        let bytesPerSequence = (firstByte > 0xEF) ? 4 : (firstByte > 0xDF) ? 3 : (firstByte > 0xBF) ? 2 : 1

        if (i + bytesPerSequence <= end) {
            let secondByte, thirdByte, fourthByte, tempCodePoint

            switch (bytesPerSequence) {
                case 1:
                    if (firstByte < 0x80) {
                        codePoint = firstByte
                    }
                    break
                case 2:
                    secondByte = this[i + 1]
                    if ((secondByte & 0xC0) === 0x80) {
                        tempCodePoint = (firstByte & 0x1F) << 0x6 | (secondByte & 0x3F)
                        if (tempCodePoint > 0x7F) {
                            codePoint = tempCodePoint
                        }
                    }
                    break
                case 3:
                    secondByte = this[i + 1]
                    thirdByte = this[i + 2]
                    if ((secondByte & 0xC0) === 0x80 && (thirdByte & 0xC0) === 0x80) {
                        tempCodePoint = (firstByte & 0xF) << 0xC | (secondByte & 0x3F) << 0x6 | (thirdByte & 0x3F)
                        if (tempCodePoint > 0x7FF && (tempCodePoint < 0xD800 || tempCodePoint > 0xDFFF)) {
                            codePoint = tempCodePoint
                        }
                    }
                    break
                case 4:
                    secondByte = this[i + 1]
                    thirdByte = this[i + 2]
                    fourthByte = this[i + 3]
                    if ((secondByte & 0xC0) === 0x80 && (thirdByte & 0xC0) === 0x80 && (fourthByte & 0xC0) === 0x80) {
                        tempCodePoint = (firstByte & 0xF) << 0x12 | (secondByte & 0x3F) << 0xC | (thirdByte & 0x3F) << 0x6 | (fourthByte & 0x3F)
                        if (tempCodePoint > 0xFFFF && tempCodePoint < 0x110000) {
                            codePoint = tempCodePoint
                        }
                    }
            }
        }

        if (codePoint === null) {
            // we did not generate a valid codePoint so insert a
            // replacement char (U+FFFD) and advance only 1 byte
            codePoint = 0xFFFD
            bytesPerSequence = 1
        } else if (codePoint > 0xFFFF) {
            // encode to utf16 (surrogate pair dance)
            codePoint -= 0x10000
            res.push(codePoint >>> 10 & 0x3FF | 0xD800)
            codePoint = 0xDC00 | codePoint & 0x3FF
        }

        res.push(codePoint)
        i += bytesPerSequence
    }

    return decodeCodePointsArray(res)
}
function utf8ToBytes(string, units) {
    units = units || Infinity
    let codePoint
    const length = string.length
    let leadSurrogate = null
    const bytes = []

    for (let i = 0; i < length; ++i) {
        codePoint = string.charCodeAt(i)

        // is surrogate component
        if (codePoint > 0xD7FF && codePoint < 0xE000) {
            // last char was a lead
            if (!leadSurrogate) {
                // no lead yet
                if (codePoint > 0xDBFF) {
                    // unexpected trail
                    if ((units -= 3) > -1) bytes.push(0xEF, 0xBF, 0xBD)
                    continue
                } else if (i + 1 === length) {
                    // unpaired lead
                    if ((units -= 3) > -1) bytes.push(0xEF, 0xBF, 0xBD)
                    continue
                }

                // valid lead
                leadSurrogate = codePoint

                continue
            }

            // 2 leads in a row
            if (codePoint < 0xDC00) {
                if ((units -= 3) > -1) bytes.push(0xEF, 0xBF, 0xBD)
                leadSurrogate = codePoint
                continue
            }
            // valid surrogate pair
            codePoint = (leadSurrogate - 0xD800 << 10 | codePoint - 0xDC00) + 0x10000
        } else if (leadSurrogate) {
            // valid bmp char, but last char was a lead
            if ((units -= 3) > -1) bytes.push(0xEF, 0xBF, 0xBD)
        }

        leadSurrogate = null

        // encode utf8
        if (codePoint < 0x80) {
            if ((units -= 1) < 0) break
            bytes.push(codePoint)
        } else if (codePoint < 0x800) {
            if ((units -= 2) < 0) break
            bytes.push(
                codePoint >> 0x6 | 0xC0,
                codePoint & 0x3F | 0x80
            )
        } else if (codePoint < 0x10000) {
            if ((units -= 3) < 0) break
            bytes.push(
                codePoint >> 0xC | 0xE0,
                codePoint >> 0x6 & 0x3F | 0x80,
                codePoint & 0x3F | 0x80
            )
        } else if (codePoint < 0x110000) {
            if ((units -= 4) < 0) break
            bytes.push(
                codePoint >> 0x12 | 0xF0,
                codePoint >> 0xC & 0x3F | 0x80,
                codePoint >> 0x6 & 0x3F | 0x80,
                codePoint & 0x3F | 0x80
            )
        } else {
            throw new Error('Invalid code point')
        }
    }
    return bytes
}