import Foundation
import OrgSwift
import OrgSwiftUI
import SwiftUI

/// README rendering follows the file's format. Org is rendered natively by the shared
/// `OrgSwiftUI` package; everything else keeps the established Markdown renderer.
struct ReadmeView: View {
    let name: String
    let content: String
    /// Instance host and `owner/repo`, used to resolve repository-relative links and images.
    /// Empty leaves relative references unresolved.
    var host: String = ""
    var repoPath: String = ""

    @Environment(\.colorScheme) private var colorScheme
    @Environment(\.dynamicTypeSize) private var dynamicTypeSize
    @State private var allowance = MathAllowance()

    /// Format follows the file name, never a guess at the content.
    var isOrg: Bool { name.lowercased().hasSuffix(".org") }

    var body: some View {
        if isOrg {
            let _ = allowance.reset(for: content)
            // Qualified: `OrgView` here is org-mode, not the organization view.
            OrgSwiftUI.OrgView(
                Self.preferringPNGBadges(content, host: host),
                options: renderOptions,
                styler: OrgSyntaxStyler(colorScheme: colorScheme),
                // org's TODO/DONE are the same open/done distinction the forge already
                // colors, so they reuse those tokens rather than a third treatment.
                keywords: OrgKeywordStyle(todo: .gbOK, done: .gbDone),
                math: MathRenderer.org(pointSize: UIFont.pointSize(.body, dynamicTypeSize), allowance: allowance)
            )
        } else {
            MarkdownView(markdown: content, linkOptions: renderOptions)
        }
    }

    /// Point badge sources on this instance at the PNG the forge also serves.
    ///
    /// No Apple image decoder reads SVG outside an asset catalog, so the SVG badge a README
    /// names cannot render at all. Only badges on the instance being browsed are rewritten —
    /// a badge from anywhere else has no PNG to offer, and is left as authored.
    static func preferringPNGBadges(_ content: String, host: String) -> String {
        guard !host.isEmpty,
              let pattern = try? NSRegularExpression(
                  pattern: "(https://\(NSRegularExpression.escapedPattern(for: host))"
                      + "/[^/\\s\\]]+/[^/\\s\\]]+/badge/[\\w.-]+)\\.svg"
              )
        else { return content }
        return pattern.stringByReplacingMatches(
            in: content,
            range: NSRange(content.startIndex..., in: content),
            withTemplate: "$1.png"
        )
    }

    /// gitbay serves raw bytes at `/{owner}/{repo}/raw/{ref}/…` and the file page at
    /// `/blob/…`, so relative images resolve against `raw` and links against `blob`.
    ///
    /// Both formats resolve through the same options: a relative link in a Markdown README
    /// points at the same file page an org one does.
    private var renderOptions: OrgRenderOptions {
        let parts = repoPath.split(separator: "/", maxSplits: 1).map(String.init)
        guard parts.count == 2, !host.isEmpty else {
            return OrgRenderOptions()
        }
        return OrgRenderOptions(
            host: host,
            owner: parts[0],
            repositoryName: parts[1],
            ref: "HEAD",
            readmePath: name,
            imagePathSegment: "raw",
            linkPathSegment: "blob"
        )
    }
}