import { Parser } from 'htmlparser2'
import Long from 'long'

import type { InputText, MessageEntity, TextWithEntities, tl } from '@mtcute/client'

const MENTION_REGEX = /^tg:\/\/user\?id=(\d+)(?:&hash=(-?[0-9a-fA-F]+)(?:&|$)|&|$)/

/**
 * Escape a string to be safely used in HTML.
 *
 * > **Note**: this function is in most cases not needed, as `html` function
 * > handles all `string`s passed to it automatically as plain text.
 */
function escape(str: string, quote = false): string {
    str = str.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;')
    if (quote) str = str.replace(/"/g, '&quot;')

    return str
}

function parse(
    strings: TemplateStringsArray | string,
    ...sub: (InputText | MessageEntity | boolean | number | undefined | null)[]
): TextWithEntities {
    const stacks: Record<string, tl.Mutable<tl.TypeMessageEntity>[]> = {}
    const entities: tl.TypeMessageEntity[] = []
    let plainText = ''
    let pendingText = ''

    function processPendingText(tagEnd = false) {
        if (!pendingText.length) return

        if (!stacks.pre?.length) {
            pendingText = pendingText.replace(/[^\S\u00A0]+/gs, ' ')

            if (tagEnd) pendingText = pendingText.trimEnd()

            if (!plainText.length || plainText.match(/\s$/)) {
                pendingText = pendingText.trimStart()
            }
        }

        for (const ents of Object.values(stacks)) {
            for (const ent of ents) {
                ent.length += pendingText.length
            }
        }

        plainText += pendingText
        pendingText = ''
    }

    const parser = new Parser({
        onopentag(name, attribs) {
            name = name.toLowerCase()

            processPendingText()

            // ignore tags inside pre (except pre)
            if (name !== 'pre' && stacks.pre?.length) return

            let entity: tl.TypeMessageEntity

            switch (name) {
                case 'br':
                    plainText += '\n'

                    return
                case 'b':
                case 'strong':
                    entity = {
                        _: 'messageEntityBold',
                        offset: plainText.length,
                        length: 0,
                    }
                    break
                case 'i':
                case 'em':
                    entity = {
                        _: 'messageEntityItalic',
                        offset: plainText.length,
                        length: 0,
                    }
                    break
                case 'u':
                    entity = {
                        _: 'messageEntityUnderline',
                        offset: plainText.length,
                        length: 0,
                    }
                    break
                case 's':
                case 'del':
                case 'strike':
                    entity = {
                        _: 'messageEntityStrike',
                        offset: plainText.length,
                        length: 0,
                    }
                    break
                case 'blockquote':
                    entity = {
                        _: 'messageEntityBlockquote',
                        offset: plainText.length,
                        length: 0,
                    }
                    break
                case 'code':
                    entity = {
                        _: 'messageEntityCode',
                        offset: plainText.length,
                        length: 0,
                    }
                    break
                case 'pre':
                    entity = {
                        _: 'messageEntityPre',
                        offset: plainText.length,
                        length: 0,
                        language: attribs.language ?? '',
                    }
                    break
                case 'spoiler':
                case 'tg-spoiler':
                    entity = {
                        _: 'messageEntitySpoiler',
                        offset: plainText.length,
                        length: 0,
                    }
                    break

                case 'emoji':
                case 'tg-emoji': {
                    const id = attribs.id || attribs['emoji-id']
                    if (!id || !id.match(/^-?\d+$/)) return

                    entity = {
                        _: 'messageEntityCustomEmoji',
                        offset: plainText.length,
                        length: 0,
                        documentId: Long.fromString(id),
                    }
                    break
                }
                case 'a': {
                    let url = attribs.href
                    if (!url) return

                    const mention = MENTION_REGEX.exec(url)

                    if (mention) {
                        const id = parseInt(mention[1])
                        const accessHash = mention[2]

                        if (accessHash) {
                            entity = {
                                _: 'inputMessageEntityMentionName',
                                offset: plainText.length,
                                length: 0,
                                userId: {
                                    _: 'inputUser',
                                    userId: id,
                                    accessHash: Long.fromString(accessHash, false, 16),
                                },
                            }
                        } else {
                            entity = {
                                _: 'messageEntityMentionName',
                                offset: plainText.length,
                                length: 0,
                                userId: id,
                            }
                        }
                    } else {
                        if (url.match(/^\/\//)) url = 'http:' + url

                        entity = {
                            _: 'messageEntityTextUrl',
                            offset: plainText.length,
                            length: 0,
                            url,
                        }
                    }
                    break
                }
                default:
                    return
            }

            if (!(name in stacks)) {
                stacks[name] = []
            }
            stacks[name].push(entity)
        },
        onclosetag(name: string) {
            processPendingText(true)

            name = name.toLowerCase()

            // ignore tags inside pre (except pre)
            if (name !== 'pre' && stacks.pre?.length) return

            const entity = stacks[name]?.pop()

            if (!entity) return // unmatched close tag

            // ignore nested pre-s
            if (name !== 'pre' || !stacks.pre?.length) {
                entities.push(entity)
            }
        },
        ontext(data) {
            pendingText += data
        },
    })

    if (typeof strings === 'string') strings = [strings] as unknown as TemplateStringsArray

    sub.forEach((it, idx) => {
        parser.write(strings[idx])

        if (typeof it === 'boolean' || !it) return

        if (typeof it === 'string' || typeof it === 'number') {
            pendingText += it
        } else {
            // TextWithEntities or MessageEntity
            const text = it.text
            const innerEntities = 'raw' in it ? [it.raw] : it.entities

            processPendingText()
            const baseOffset = plainText.length
            pendingText += text

            if (innerEntities) {
                for (const ent of innerEntities) {
                    entities.push({ ...ent, offset: ent.offset + baseOffset })
                }
            }
        }
    })

    parser.write(strings[strings.length - 1])

    processPendingText(true)

    return {
        text: plainText.replace(/\u00A0/g, ' '),
        entities,
    }
}

/** Options passed to `html.unparse` */
export interface HtmlUnparseOptions {
    /**
     * Syntax highlighter to use when un-parsing `pre` tags with language
     */
    syntaxHighlighter?: (code: string, language: string) => string
}

// internal function that uses recursion to correctly process nested & overlapping entities
function _unparse(
    text: string,
    entities: ReadonlyArray<tl.TypeMessageEntity>,
    params: HtmlUnparseOptions,
    entitiesOffset = 0,
    offset = 0,
    length = text.length,
): string {
    if (!text) return text

    if (!entities.length || entities.length === entitiesOffset) {
        return escape(text)
            .replace(/\n/g, '<br>')
            .replace(/ {2,}/g, (match) => {
                return '&nbsp;'.repeat(match.length)
            })
    }

    const end = offset + length

    const html: string[] = []
    let lastOffset = 0

    for (let i = entitiesOffset; i < entities.length; i++) {
        const entity = entities[i]
        if (entity.offset >= end) break

        let entOffset = entity.offset
        let length = entity.length

        if (entOffset < 0) {
            length += entOffset
            entOffset = 0
        }

        let relativeOffset = entOffset - offset

        if (relativeOffset > lastOffset) {
            // add missing plain text
            html.push(escape(text.substring(lastOffset, relativeOffset)))
        } else if (relativeOffset < lastOffset) {
            length -= lastOffset - relativeOffset
            relativeOffset = lastOffset
        }

        if (length <= 0 || relativeOffset >= end || relativeOffset < 0) {
            continue
        }

        let skip = false

        const substr = text.substr(relativeOffset, length)
        if (!substr) continue

        const type = entity._

        let entityText

        if (type === 'messageEntityPre') {
            entityText = substr
        } else {
            entityText = _unparse(substr, entities, params, i + 1, offset + relativeOffset, length)
        }

        switch (type) {
            case 'messageEntityBold':
            case 'messageEntityItalic':
            case 'messageEntityUnderline':
            case 'messageEntityStrike':
            case 'messageEntityCode':
            case 'messageEntityBlockquote':
            case 'messageEntitySpoiler':
                {
                    const tag = (
                        {
                            messageEntityBold: 'b',
                            messageEntityItalic: 'i',
                            messageEntityUnderline: 'u',
                            messageEntityStrike: 's',
                            messageEntityCode: 'code',
                            messageEntityBlockquote: 'blockquote',
                            messageEntitySpoiler: 'spoiler',
                        } as const
                    )[type]
                    html.push(`<${tag}>${entityText}</${tag}>`)
                }
                break
            case 'messageEntityPre':
                html.push(
                    `<pre${entity.language ? ` language="${entity.language}"` : ''}>${
                        params.syntaxHighlighter && entity.language ?
                            params.syntaxHighlighter(entityText, entity.language) :
                            entityText
                    }</pre>`,
                )
                break
            case 'messageEntityEmail':
                html.push(`<a href="mailto:${entityText}">${entityText}</a>`)
                break
            case 'messageEntityUrl':
                html.push(`<a href="${entityText}">${entityText}</a>`)
                break
            case 'messageEntityTextUrl':
                html.push(`<a href="${escape(entity.url, true)}">${entityText}</a>`)
                break
            case 'messageEntityMentionName':
                html.push(`<a href="tg://user?id=${entity.userId}">${entityText}</a>`)
                break
            default:
                skip = true
                break
        }

        lastOffset = relativeOffset + (skip ? 0 : length)
    }

    html.push(escape(text.substr(lastOffset)))

    return html.join('')
}

/**
 * Add HTML formatting to the text given the plain text and entities contained in it.
 */
function unparse(input: InputText, options?: HtmlUnparseOptions): string {
    if (typeof input === 'string') {
        return _unparse(input, [], options ?? {})
    }

    return _unparse(input.text, input.entities ?? [], options ?? {})
}

// typedoc doesn't support this yet, so we'll have to do it manually
// https://github.com/TypeStrong/typedoc/issues/2436

export const html: {
    /**
     * Tagged template based HTML-to-entities parser function
     *
     * Additionally, `md` function has two static methods:
     * - `html.escape` - escape a string to be safely used in HTML
     *   (should not be needed in most cases, as `html` function itself handles all `string`s
     *   passed to it automatically as plain text)
     * - `html.unparse` - add HTML formatting to the text given the plain text and entities contained in it
     *
     * @example
     * ```typescript
     * const text = html`<b>${user.displayName}</b>`
     * ```
     */
    (
        strings: TemplateStringsArray,
        ...sub: (InputText | MessageEntity | boolean | number | undefined | null)[]
    ): TextWithEntities
    /**
     * A variant taking a plain JS string as input
     * and parsing it.
     *
     * Useful for cases when you already have a string
     * (e.g. from some server) and want to parse it.
     *
     * @example
     * ```typescript
     * const string = '<b>hello</b>'
     * const text = html(string)
     * ```
     */
    (string: string): TextWithEntities
    escape: typeof escape
    unparse: typeof unparse
} = Object.assign(parse, {
    escape,
    unparse,
})