import Foundation

enum ChatMarkdownPreprocessor {
    /// Provenance marker appended to every OpenClaw-injected inbound context header.
    /// Keep byte-identical with `src/auto-reply/reply/inbound-context-marker.ts` INBOUND_CONTEXT_MARKER.
    private static let inboundContextMarker = "\u{27E6}openclaw:ctx\u{27E7}"

    private static let contextHeader =
        "Context: \(inboundContextMarker)"
    private static let envelopeChannels = [
        "WebChat",
        "WhatsApp",
        "Telegram",
        "Signal",
        "Slack",
        "Discord",
        "Google Chat",
        "iMessage",
        "Teams",
        "Matrix",
        "Zalo",
        "Zalo Personal",
    ]

    private static let markdownImagePattern = #"!\[([^\]]*)\]\(([^)]+)\)"#
    private static let messageIdHintPattern = #"^\s*\[message_id:\s*[^\]]+\]\s*$"#

    struct InlineImage: Identifiable {
        let id = UUID()
        let label: String
        let image: OpenClawPlatformImage?
    }

    struct Result {
        let cleaned: String
        let images: [InlineImage]
    }

    static func preprocess(markdown raw: String) -> Result {
        let withoutEnvelope = self.stripEnvelope(raw)
        let withoutMessageIdHints = self.stripMessageIdHints(withoutEnvelope)
        let withoutContextBlocks = self.stripInboundContextBlocks(withoutMessageIdHints)
        let withoutTimestamps = self.stripPrefixedTimestamps(withoutContextBlocks)
        guard let re = try? NSRegularExpression(pattern: self.markdownImagePattern) else {
            return Result(cleaned: self.normalize(withoutTimestamps), images: [])
        }

        let ns = withoutTimestamps as NSString
        let matches = re.matches(
            in: withoutTimestamps,
            range: NSRange(location: 0, length: ns.length))
        if matches.isEmpty { return Result(cleaned: self.normalize(withoutTimestamps), images: []) }

        var images: [InlineImage] = []
        let cleaned = NSMutableString(string: withoutTimestamps)

        for match in matches.reversed() {
            guard match.numberOfRanges >= 3 else { continue }
            let label = ns.substring(with: match.range(at: 1))
            let source = ns.substring(with: match.range(at: 2))

            if let inlineImage = self.inlineImage(label: label, source: source) {
                images.append(inlineImage)
                cleaned.replaceCharacters(in: match.range, with: "")
            } else {
                cleaned.replaceCharacters(in: match.range, with: self.fallbackImageLabel(label))
            }
        }

        return Result(cleaned: self.normalize(cleaned as String), images: images.reversed())
    }

    private static func inlineImage(label: String, source: String) -> InlineImage? {
        let trimmed = source.trimmingCharacters(in: .whitespacesAndNewlines)
        guard let comma = trimmed.firstIndex(of: ","),
              trimmed[..<comma].range(
                  of: #"^data:image\/[^;]+;base64$"#,
                  options: [.regularExpression, .caseInsensitive]) != nil
        else {
            return nil
        }

        let b64 = String(trimmed[trimmed.index(after: comma)...])
        let image = Data(base64Encoded: b64).flatMap(OpenClawPlatformImage.init(data:))
        return InlineImage(label: label, image: image)
    }

    private static func fallbackImageLabel(_ label: String) -> String {
        let trimmed = label.trimmingCharacters(in: .whitespacesAndNewlines)
        return trimmed.isEmpty ? "image" : trimmed
    }

    private static func stripEnvelope(_ raw: String) -> String {
        guard let closeIndex = raw.firstIndex(of: "]"),
              raw.first == "["
        else {
            return raw
        }
        let header = String(raw[raw.index(after: raw.startIndex)..<closeIndex])
        guard self.looksLikeEnvelopeHeader(header) else {
            return raw
        }
        return String(raw[raw.index(after: closeIndex)...])
    }

    private static func looksLikeEnvelopeHeader(_ header: String) -> Bool {
        if header.range(of: #"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}Z\b"#, options: .regularExpression) != nil {
            return true
        }
        if header.range(of: #"\d{4}-\d{2}-\d{2} \d{2}:\d{2}\b"#, options: .regularExpression) != nil {
            return true
        }
        return self.envelopeChannels.contains(where: { header.hasPrefix("\($0) ") })
    }

    private static func stripMessageIdHints(_ raw: String) -> String {
        guard raw.contains("[message_id:") else {
            return raw
        }
        let lines = raw.replacingOccurrences(of: "\r\n", with: "\n").split(
            separator: "\n",
            omittingEmptySubsequences: false)
        let filtered = lines.filter { line in
            String(line).range(of: self.messageIdHintPattern, options: .regularExpression) == nil
        }
        guard filtered.count != lines.count else {
            return raw
        }
        return filtered.map(String.init).joined(separator: "\n")
    }

    private static func stripInboundContextBlocks(_ raw: String) -> String {
        guard raw.contains(self.inboundContextMarker) else {
            return raw
        }

        let normalized = raw.replacingOccurrences(of: "\r\n", with: "\n")
        let lines = normalized.split(separator: "\n", omittingEmptySubsequences: false).map(String.init)
        var outputLines: [String] = []
        var inMetaBlock = false
        var inFencedJson = false
        var inProseBlock = false

        for index in lines.indices {
            let currentLine = lines[index]

            // Prose context body (chat history/window): drop lines until the
            // block-terminating blank line so the visible marker never renders.
            if inProseBlock {
                if currentLine.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
                    inProseBlock = false
                }
                continue
            }

            if !inMetaBlock, self.shouldStripTrailingUntrustedContext(lines: lines, index: index) {
                break
            }

            if !inMetaBlock {
                let trimmed = currentLine.trimmingCharacters(in: .whitespacesAndNewlines)
                let isContextHeader = trimmed.count > self.inboundContextMarker.count &&
                    trimmed.hasSuffix(self.inboundContextMarker)
                if isContextHeader {
                    let nextLine = index + 1 < lines.count ? lines[index + 1] : nil
                    if nextLine?.trimmingCharacters(in: .whitespacesAndNewlines) != "```json" {
                        inProseBlock = true
                        continue
                    }
                    inMetaBlock = true
                    inFencedJson = false
                    continue
                }
            }

            if inMetaBlock {
                if !inFencedJson, currentLine.trimmingCharacters(in: .whitespacesAndNewlines) == "```json" {
                    inFencedJson = true
                    continue
                }

                if inFencedJson {
                    if currentLine.trimmingCharacters(in: .whitespacesAndNewlines) == "```" {
                        inMetaBlock = false
                        inFencedJson = false
                    }
                    continue
                }

                if currentLine.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
                    continue
                }

                inMetaBlock = false
            }

            outputLines.append(currentLine)
        }

        return outputLines
            .joined(separator: "\n")
            .replacingOccurrences(of: #"^\n+"#, with: "", options: .regularExpression)
    }

    private static func shouldStripTrailingUntrustedContext(lines: [String], index: Int) -> Bool {
        lines[index].trimmingCharacters(in: .whitespacesAndNewlines) == self.contextHeader
    }

    private static func stripPrefixedTimestamps(_ raw: String) -> String {
        let pattern = #"(?m)^\[[A-Za-z]{3}\s+\d{4}-\d{2}-\d{2}\s+\d{2}:\d{2}(?::\d{2})?\s+(?:GMT|UTC)[+-]?\d{0,2}\]\s*"#
        return raw.replacingOccurrences(of: pattern, with: "", options: .regularExpression)
    }

    private static func normalize(_ raw: String) -> String {
        var output = raw
        output = output.replacingOccurrences(of: "\r\n", with: "\n")
        output = output.replacingOccurrences(of: "\n\n\n", with: "\n\n")
        output = output.replacingOccurrences(of: "\n\n\n", with: "\n\n")
        return output.trimmingCharacters(in: .whitespacesAndNewlines)
    }
}