damus/damus/Features/Events/Models/NoteContent.swift

//
//  NoteContent.swift
//  damus
//
//  Created by Daniel D’Aquino on 2023-11-24.
//

import Foundation
import MarkdownUI
import UIKit

struct NoteArtifactsSeparated: Equatable {
    static func == (lhs: NoteArtifactsSeparated, rhs: NoteArtifactsSeparated) -> Bool {
        return lhs.content == rhs.content
    }
    
    let content: CompatibleText
    let words: Int
    let urls: [UrlType]
    let invoices: [Invoice]
    
    var media: [MediaUrl] {
        return urls.compactMap { url in url.is_media }
    }
    
    var images: [URL] {
        return urls.compactMap { url in url.is_img }
    }
    
    var links: [URL] {
        return urls.compactMap { url in url.is_link }
    }
    
    static func just_content(_ content: String) -> NoteArtifactsSeparated {
        let txt = CompatibleText(attributed: AttributedString(stringLiteral: content))
        return NoteArtifactsSeparated(content: txt, words: 0, urls: [], invoices: [])
    }
}

enum NoteArtifactState {
    case not_loaded
    case loading
    case loaded(NoteArtifacts)
    
    var artifacts: NoteArtifacts? {
        if case .loaded(let artifacts) = self {
            return artifacts
        }
        
        return nil
    }
    
    var should_preload: Bool {
        switch self {
        case .loaded:
            return false
        case .loading:
            return false
        case .not_loaded:
            return true
        }
    }
}

func note_artifact_is_separated(kind: NostrKind?) -> Bool {
    return kind != .longform
}

func render_immediately_available_note_content(ndb: Ndb, ev: NostrEvent, profiles: Profiles, keypair: Keypair) -> NoteArtifacts {
    if ev.known_kind == .longform {
        return .longform(LongformContent(ev.content))
    }
    
    do {
        return try NdbBlockGroup.borrowBlockGroup(event: ev, using: ndb, and: keypair, borrow: { blocks in
            return .separated(render_blocks(blocks: blocks, profiles: profiles, can_hide_last_previewable_refs: true))
        })
    }
    catch {
        // TODO: Improve error handling in the future, bubbling it up so that the view can decide how display errors. Keep legacy behavior for now.
        return .separated(.just_content(ev.get_content(keypair)))
    }
}

actor ContentRenderer {
    func render_note_content(ndb: Ndb, ev: NostrEvent, profiles: Profiles, keypair: Keypair) async -> NoteArtifacts {
        return render_immediately_available_note_content(ndb: ndb, ev: ev, profiles: profiles, keypair: keypair)
    }
}

// FIXME(tyiu): There are a lot of hacks to get this function to render the blocks correctly.
// However, the entire note content rendering logic just needs to be rewritten.
// Block previews should actually be rendered in the position of the note content where it was found.
// Currently, we put some previews at the bottom of the note, which is incorrect as they take things out of
// the author's intended context.
func render_blocks(blocks: borrowing NdbBlockGroup, profiles: Profiles, can_hide_last_previewable_refs: Bool = false) -> NoteArtifactsSeparated {
    var invoices: [Invoice] = []
    var urls: [UrlType] = []
    
    var end_mention_count = 0
    var end_url_count = 0
    
    let note_ref_count: Int? = try? blocks.reduce(initialResult: 0) { index, partialResult, item in
        switch item {
        case .mention(let mention):
            if let typ = mention.bech32_type,
               typ.is_notelike {
                return .loopReturn(partialResult + 1)
            }
        default:
            break
        }
        return .loopContinue
    }
    let one_note_ref = note_ref_count == 1

    // Search backwards until we find the beginning index of the chain of previewables that reach the end of the content.
    var hide_text_index: Int = 0
    if can_hide_last_previewable_refs {
        let _: ()? = blocks.withList({ blocksList in
            let endIndex = blocksList.count
            hide_text_index = endIndex
            return blocksList.forEachItemReversed({ index, block in
                if block.is_previewable {
                    switch block {
                    case .mention:
                        end_mention_count += 1
                        
                        // If there is more than one previewable mention,
                        // do not hide anything because we allow rich rendering of only one mention currently.
                        // This should be fixed in the future to show events inline instead.
                        if end_mention_count > 1 {
                            hide_text_index = endIndex
                            return .loopBreak
                        }
                    case .url(let url_block):
                        guard let url = URL(string: url_block.as_str()) else {
                            return .loopContinue    // We can't classify this, ignore and move on
                        }
                        let url_type = classify_url(url)
                        if case .link = url_type {
                            end_url_count += 1
                            
                            // If there is more than one link, do not hide anything because we allow rich rendering of only
                            // one link.
                            if end_url_count > 1 {
                                hide_text_index = endIndex
                                return .loopBreak
                            }
                        }
                    default:
                        break
                    }
                    hide_text_index = index
                }
                else {
                    switch block {
                    case .text(let txt_block):
                        if let txt = NdbBlock.convertToStringCopy(from: txt_block),
                           txt.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
                            // We should hide whitespace at the end sequence.
                            hide_text_index = index
                        }
                        else {
                            return .loopBreak
                        }
                    case .hashtag(_):
                        // SPECIAL CASE:
                        // We should keep hashtags at the end sequence but hide all the other previewables around it.
                        hide_text_index = index
                    default:
                        return .loopBreak
                    }
                }
                return .loopContinue
            })
        })
    }

    let txt: CompatibleText? = try? blocks.withList({ blocksList in
        let endIndex = blocksList.count
        return try blocksList.reduce(initialResult: CompatibleText(), { index, str, block in

            // Add the rendered previewable blocks to their type-specific lists.
            switch block {
            case .url(let url_block):
                guard let url_string = NdbBlock.convertToStringCopy(from: url_block),
                      let url = URL(string: url_string) else {
                    break    // We can't classify this, ignore and move on
                }
                let url_type = classify_url(url)
                urls.append(url_type)
            case .invoice(let invoice_block):
                guard let invoice = invoice_block.as_invoice() else { break }
                invoices.append(invoice)
            default:
                break
            }

            if can_hide_last_previewable_refs {
                // If there are previewable blocks that occur before the consecutive sequence of them at the end of the content,
                // we should not hide the text representation of any previewable block to avoid altering the format of the note.
                if index < hide_text_index && block.is_previewable {
                    hide_text_index = endIndex
                }

                // No need to show the text representation of the block if the only previewables are the sequence of them
                // found at the end of the content.
                // This is to save unnecessary use of screen space.
                // The only exception is that if there are hashtags embedded in the end sequence, which is not uncommon,
                // then we still want to show those hashtags but hide everything else that is previewable in the end sequence.
                if index >= hide_text_index {
                    switch block {
                    case .text(let txt_block):
                        if let txt = NdbBlock.convertToStringCopy(from: txt_block),
                           txt.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
                            let returnItem: CompatibleText? = blocksList.useItem(at: index + 1, { matchingBlock in
                                switch matchingBlock {
                                case .hashtag(_):
                                    return str + CompatibleText(stringLiteral: reduce_text_block(ind: index, hide_text_index: hide_text_index, txt: txt))
                                default:
                                    return nil
                                }
                            }) ?? nil
                            if let returnItem {
                                return .loopReturn(returnItem)
                            }
                        }
                    case .hashtag(let htag):
                        return .loopReturn(str + hashtag_str(htag.as_str()))
                    default:
                        return .loopContinue
                    }
                    return .loopReturn(str)
                }
            }

            switch block {
            case .mention(let m):
                if let typ = m.bech32_type, typ.is_notelike, one_note_ref {
                    return .loopContinue
                }
                guard let mention = MentionRef(block: m) else { return .loopContinue }
                return .loopReturn(str + mention_str(.any(mention), profiles: profiles))
            case .text(let txt):
                var hide_text_index_argument = hide_text_index
                blocksList.useItem(at: index+1, { block in
                    switch block {
                    case .hashtag(_):
                        // SPECIAL CASE:
                        // Do not trim whitespaces from suffix if the following block is a hashtag.
                        // This is because of the code further up (see "SPECIAL CASE").
                        hide_text_index_argument = -1
                    default:
                        break
                    }
                })
                return .loopReturn(str + CompatibleText(stringLiteral: reduce_text_block(ind: index, hide_text_index: hide_text_index_argument, txt: txt.as_str())))
            case .hashtag(let htag):
                return .loopReturn(str + hashtag_str(htag.as_str()))
            case .invoice(let invoice):
                guard let inv = invoice.as_invoice() else { return .loopContinue }
                invoices.append(inv)
            case .url(let url):
                guard let url = URL(string: url.as_str()) else { return .loopContinue }
                return .loopReturn(str + url_str(url))
            case .mention_index:
                return .loopContinue
            }
            return .loopContinue
        })
    })

    return NoteArtifactsSeparated(content: txt ?? CompatibleText(), words: blocks.words, urls: urls, invoices: invoices)
}

func reduce_text_block(ind: Int, hide_text_index: Int, txt: String) -> String {
    var trimmed = txt

    // Trim leading whitespaces.
    if ind == 0 {
        trimmed = trim_prefix(trimmed)
    }

    // Trim trailing whitespaces if the following blocks will be hidden or if this is the last block.
    if ind == hide_text_index - 1 {
        trimmed = trim_suffix(trimmed)
    }

    return trimmed
}

func invoice_str(_ invoice: Invoice) -> CompatibleText {
    var attributedString = AttributedString(stringLiteral: abbrev_identifier(invoice.string))
    attributedString.link = URL(string: "damus:lightning:\(invoice.string)")
    attributedString.foregroundColor = DamusColors.purple

    return CompatibleText(attributed: attributedString)
}

func url_str(_ url: URL) -> CompatibleText {
    var attributedString = AttributedString(stringLiteral: url.absoluteString)
    attributedString.link = url
    attributedString.foregroundColor = DamusColors.purple
    
    return CompatibleText(attributed: attributedString)
}

func classify_url(_ url: URL) -> UrlType {
    let fileExtension = url.lastPathComponent.lowercased().components(separatedBy: ".").last

    switch fileExtension {
    case "png", "jpg", "jpeg", "gif", "webp":
        return .media(.image(url))
    case "mp4", "mov", "m3u8":
        return .media(.video(url))
    default:
        return .link(url)
    }
}

func attributed_string_attach_icon(_ astr: inout AttributedString, img: UIImage) {
    let attachment = NSTextAttachment()
    attachment.image = img
    let attachmentString = NSAttributedString(attachment: attachment)
    let wrapped = AttributedString(attachmentString)
    astr.append(wrapped)
}

func getDisplayName(pk: Pubkey, profiles: Profiles) -> String {
    let profile = try? profiles.lookup(id: pk)
    return Profile.displayName(profile: profile, pubkey: pk).username.truncate(maxLength: 50)
}

func mention_str(_ m: Mention<MentionRef>, profiles: Profiles) -> CompatibleText {
    let bech32String = Bech32Object.encode(m.ref.toBech32Object())
    
    let display_str: String = {
        switch m.ref.nip19 {
        case .npub(let pk): return getDisplayName(pk: pk, profiles: profiles)
        case .note: return abbrev_identifier(bech32String)
        case .nevent: return abbrev_identifier(bech32String)
        case .nprofile(let nprofile): return getDisplayName(pk: nprofile.author, profiles: profiles)
        case .nrelay(let url): return url
        case .naddr: return abbrev_identifier(bech32String)
        case .nsec(let prv):
            guard let npub = privkey_to_pubkey(privkey: prv)?.npub else { return "nsec..." }
            return abbrev_identifier(npub)
        case .nscript(_): return bech32String
        }
    }()

    let display_str_with_at = "@\(display_str)"

    var attributedString = AttributedString(stringLiteral: display_str_with_at)
    attributedString.link = URL(string: "damus:nostr:\(bech32String)")
    attributedString.foregroundColor = DamusColors.purple
    
    return CompatibleText(attributed: attributedString)
}

// trim suffix whitespace and newlines
func trim_suffix(_ str: String) -> String {
    var result = str
    while result.last?.isWhitespace == true {
        result.removeLast()
    }
    return result
}

// trim prefix whitespace and newlines
func trim_prefix(_ str: String) -> String {
    var result = str
    while result.first?.isWhitespace == true {
        result.removeFirst()
    }
    return result
}

struct LongformContent {
    let markdown: MarkdownContent
    let words: Int

    init(_ markdown: String) {
        let blocks = [BlockNode].init(markdown: markdown)
        self.markdown = MarkdownContent(blocks: blocks)
        self.words = count_markdown_words(blocks: blocks)
    }
}

func count_markdown_words(blocks: [BlockNode]) -> Int {
    return blocks.reduce(0) { words, block in
        switch block {
        case .paragraph(let content):
            return words + count_inline_nodes_words(nodes: content)
        case .blockquote, .bulletedList, .numberedList, .taskList, .codeBlock, .htmlBlock, .heading, .table, .thematicBreak:
            return words
        }
    }
}

func count_words(_ s: String) -> Int {
    return s.components(separatedBy: .whitespacesAndNewlines).count
}

func count_inline_nodes_words(nodes: [InlineNode]) -> Int {
    return nodes.reduce(0) { words, node in
        switch node {
        case .text(let words):
            return count_words(words)
        case .emphasis(let children):
            return words + count_inline_nodes_words(nodes: children)
        case .strong(let children):
            return words + count_inline_nodes_words(nodes: children)
        case .strikethrough(let children):
            return words + count_inline_nodes_words(nodes: children)
        case .softBreak, .lineBreak, .code, .html, .image, .link:
            return words
        }
    }
}

enum NoteArtifacts {
    case separated(NoteArtifactsSeparated)
    case longform(LongformContent)

    var images: [URL] {
        switch self {
        case .separated(let arts):
            return arts.images
        case .longform:
            return []
        }
    }
}

enum UrlType {
    case media(MediaUrl)
    case link(URL)
    
    var url: URL {
        switch self {
        case .media(let media_url):
            switch media_url {
            case .image(let url):
                return url
            case .video(let url):
                return url
            }
        case .link(let url):
            return url
        }
    }
    
    var is_video: URL? {
        switch self {
        case .media(let media_url):
            switch media_url {
            case .image:
                return nil
            case .video(let url):
                return url
            }
        case .link:
            return nil
        }
    }
    
    var is_img: URL? {
        switch self {
        case .media(let media_url):
            switch media_url {
            case .image(let url):
                return url
            case .video:
                return nil
            }
        case .link:
            return nil
        }
    }
    
    var is_link: URL? {
        switch self {
        case .media:
            return nil
        case .link(let url):
            return url
        }
    }
    
    var is_media: MediaUrl? {
        switch self {
        case .media(let murl):
            return murl
        case .link:
            return nil
        }
    }
}

enum MediaUrl {
    case image(URL)
    case video(URL)
    
    var url: URL {
        switch self {
        case .image(let url):
            return url
        case .video(let url):
            return url
        }
    }
}