import Foundation
import TelegramCore

/// Recurses the `InstantPage` block tree to locate the anchor `name`, returning the
/// details-sibling-ordinal path of enclosing `<details>` blocks (outermost first).
///
/// - `nil`  — the anchor exists nowhere.
/// - `[]`   — the anchor exists outside any `<details>` (top level, a table cell, a quote, etc.).
/// - `[2,0]`— inside the 3rd top-level `<details>`, then that details' 1st nested `<details>`.
///
/// Ordinals (not layout indices) because the layout's details index counter is
/// expansion-dependent. Consumers map ordinals to live indices via
/// `InstantPageV2View.firstCollapsedDetails(forOrdinalPath:)`.
public func instantPageAnchorPath(in instantPage: InstantPage, name: String) -> [Int]? {
    var ordinal = 0
    return instantPageAnchorPathSearch(instantPage.blocks, name: name, detailsOrdinal: &ordinal)
}

/// Searches `blocks` at a single details-nesting level. `detailsOrdinal` is the running count of
/// `<details>` blocks already passed at this level; container blocks that flatten in the layout
/// (`.blockQuote`/`.list`/`.cover`/`.postEmbed`) recurse sharing this counter, while a `<details>`
/// recurses with a fresh counter (a new level).
private func instantPageAnchorPathSearch(
    _ blocks: [InstantPageBlock],
    name: String,
    detailsOrdinal: inout Int
) -> [Int]? {
    for block in blocks {
        switch block {
        case let .anchor(anchorName):
            if anchorName == name { return [] }
        case let .title(text), let .subtitle(text), let .header(text), let .subheader(text),
             let .paragraph(text), let .footer(text), let .kicker(text), let .thinking(text):
            if richTextContainsAnchor(text, name: name) { return [] }
        case let .heading(text, _):
            if richTextContainsAnchor(text, name: name) { return [] }
        case let .authorDate(author, _):
            if richTextContainsAnchor(author, name: name) { return [] }
        case let .preformatted(text, _):
            if richTextContainsAnchor(text, name: name) { return [] }
        case let .pullQuote(text, caption):
            if richTextContainsAnchor(text, name: name) || richTextContainsAnchor(caption, name: name) { return [] }
        case let .details(title, childBlocks, _):
            if richTextContainsAnchor(title, name: name) { return [] }   // title is always laid out
            var childOrdinal = 0
            if let sub = instantPageAnchorPathSearch(childBlocks, name: name, detailsOrdinal: &childOrdinal) {
                return [detailsOrdinal] + sub
            }
            detailsOrdinal += 1
        case let .blockQuote(quoteBlocks, caption):
            if richTextContainsAnchor(caption, name: name) { return [] }
            if let r = instantPageAnchorPathSearch(quoteBlocks, name: name, detailsOrdinal: &detailsOrdinal) { return r }
        case let .list(items, _):
            for listItem in items {
                switch listItem {
                case let .text(text, _, _):
                    if richTextContainsAnchor(text, name: name) { return [] }
                case let .blocks(itemBlocks, _, _):
                    if let r = instantPageAnchorPathSearch(itemBlocks, name: name, detailsOrdinal: &detailsOrdinal) { return r }
                case .unknown:
                    break
                }
            }
        case let .cover(inner):
            if let r = instantPageAnchorPathSearch([inner], name: name, detailsOrdinal: &detailsOrdinal) { return r }
        case let .table(title, rows, _, _):
            if richTextContainsAnchor(title, name: name) { return [] }
            for row in rows {
                for cell in row.cells {
                    if let cellText = cell.text, richTextContainsAnchor(cellText, name: name) { return [] }
                }
            }
        default:
            // .unsupported/.divider/.formula/.image/.video/.audio/.webEmbed/.channelBanner/.map —
            // leaf/media blocks with no anchor-bearing text. (.relatedArticles also lands here: the
            // V2 layout discards its title and lays out only the article media, so its title text is
            // never rendered.)
            //
            // CRITICAL — the recursion set here must match the containers the V2 layout recurses
            // through layoutBlock (and thus counts <details> in via detailsIndexCounter). Those are
            // exactly .blockQuote, .cover, and .list's .blocks items — all handled above, sharing
            // detailsOrdinal. The following carry [InstantPageBlock] children but are deliberately
            // NOT recursed because the V2 layout does NOT lay their children out as blocks, so it
            // never counts a nested <details> in them — recursing here while sharing detailsOrdinal
            // would desync our ordinals from the layout:
            //   • .collage/.slideshow — layoutCollage/layoutSlideshow lay out only .image/.video children.
            //   • .postEmbed — layoutMediaWithCaption lays out only its caption (a real .text item,
            //     so a caption anchor is found by anchorFrame directly); its `blocks` are ignored.
            // Any anchor inside a non-laid-out child is unresolvable by anchorFrame anyway, so
            // skipping it here is a no-op either way.
            break
        }
    }
    return nil
}

/// True if the `RichText` tree contains an inline `.anchor` whose name equals `name`.
private func richTextContainsAnchor(_ text: RichText, name: String) -> Bool {
    switch text {
    case .empty, .plain, .image, .formula, .textCustomEmoji:
        return false
    case let .anchor(inner, anchorName):
        if anchorName == name { return true }
        return richTextContainsAnchor(inner, name: name)
    case let .concat(parts):
        for part in parts {
            if richTextContainsAnchor(part, name: name) { return true }
        }
        return false
    case let .bold(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .italic(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .underline(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .strikethrough(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .fixed(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .marked(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .`subscript`(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .superscript(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textAutoEmail(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textAutoPhone(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textAutoUrl(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textBankCard(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textBotCommand(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textCashtag(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textHashtag(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textMention(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .textSpoiler(inner):
        return richTextContainsAnchor(inner, name: name)
    case let .url(inner, _, _):
        return richTextContainsAnchor(inner, name: name)
    case let .email(inner, _):
        return richTextContainsAnchor(inner, name: name)
    case let .phone(inner, _):
        return richTextContainsAnchor(inner, name: name)
    case let .textMentionName(inner, _):
        return richTextContainsAnchor(inner, name: name)
    case let .textDate(inner, _, _):
        return richTextContainsAnchor(inner, name: name)
    }
}