# frozen_string_literal: true

module Dispatch
  module Adapter
    class Claude < Base
      # Accumulates streaming event state for an Anthropic SSE response.
      #
      # The collector is passed to each stream event handler so that state
      # builds up incrementally.  Once the stream is complete the
      # content_blocks list holds fully-built block hashes ready for
      # ResponseBuilder or direct inspection.
      #
      # State shape:
      #   {
      #     response_id:      nil | String,
      #     model:            String,          # seed from caller, updated on message_start
      #     content_blocks:   [],              # Array<Hash> in arrival order; each has :index, :kind, …
      #     finish_reason:    nil | String,
      #     usage:            { input: 0, output: 0, cache_read: 0, cache_creation: 0 },
      #     saw_message_start: false | true,
      #     saw_terminal:      false | true,   # message_stop / message_delta with stop_reason
      #   }
      #
      # Content block Hash shapes (after content_block_stop):
      #
      #   text block:
      #     { index:, kind: "text",              text: String }
      #
      #   thinking block:
      #     { index:, kind: "thinking",          thinking: String, signature: String|nil }
      #
      #   redacted_thinking block:
      #     { index:, kind: "redacted_thinking", data: String }
      #
      #   tool_use block:
      #     { index:, kind: "tool_use",          id: String, name: String,
      #       partial_json: String, arguments: Hash }
      class StreamCollector
        # SSE event types that are valid BEFORE message_start
        ALLOWED_PRE_MESSAGE_START = %w[ping].freeze

        # SSE event types that signal the stream is done
        TERMINAL_EVENT_TYPES = %w[message_stop message_delta].freeze

        attr_reader :state

        # @param model_id [String]  seed model ID; overridden by message_start
        # @param is_oauth [Boolean] when true, strip proxy_ prefix from tool names
        def initialize(model_id, is_oauth: false)
          @is_oauth = is_oauth
          @state = {
            response_id: nil,
            model: model_id.to_s,
            content_blocks: [],
            finish_reason: nil,
            usage: { input: 0, output: 0, cache_read: 0, cache_creation: 0 },
            saw_message_start: false,
            saw_terminal: false
          }
        end

        # ── Event dispatchers ─────────────────────────────────────────────────

        # Process one parsed SSE event.
        #
        # @param event_type [String, nil]
        # @param data       [Hash]
        # @yield [StreamDelta] (optional) caller block receives streaming deltas
        def handle(event_type, data, &)
          type = event_type.to_s

          # ── Pre-message_start guard ──────────────────────────────────────
          unless @state[:saw_message_start]
            if type == "ping" || type.empty?
              return # ping / unknown preamble → ignore
            end

            if type != "message_start"
              raise RequestError.new(
                "stream envelope: received #{type.inspect} before message_start",
                provider: ClaudeErrors::PROVIDER
              )
            end
          end

          case type
          when "message_start"       then handle_message_start(data)
          when "content_block_start" then handle_content_block_start(data, &)
          when "content_block_delta" then handle_content_block_delta(data, &)
          when "content_block_stop"  then handle_content_block_stop(data, &)
          when "message_delta"       then handle_message_delta(data)
          when "message_stop"        then handle_message_stop
          when "ping"                then nil # always safe to drop
          end
        end

        # ── State accessors ───────────────────────────────────────────────────

        def saw_message_start?
          @state[:saw_message_start]
        end

        def response_id
          @state[:response_id]
        end

        def model
          @state[:model]
        end

        def usage
          @state[:usage]
        end

        # Return the content_blocks list (in arrival order).
        def content_blocks
          @state[:content_blocks]
        end

        # The raw Anthropic stop_reason string captured from message_delta.
        def finish_reason
          @state[:finish_reason]
        end

        # True once message_stop (or message_delta) has been received.
        def saw_terminal?
          @state[:saw_terminal]
        end

        # True if any content-block delta (text or tool_use JSON) has been
        # yielded to the consumer block.  Used by the retry logic to determine
        # whether the stream is safe to replay from scratch.
        def consumer_output?
          @state[:content_blocks].any? do |blk|
            case blk[:kind]
            when "text"     then blk[:text].to_s.length.positive?
            when "tool_use" then blk[:partial_json].to_s.length.positive?
            else false
            end
          end
        end

        alias has_consumer_output? consumer_output?

        private

        # ── message_start ─────────────────────────────────────────────────────

        # Extract response_id, model, and initial usage from message_start.
        # No StreamDelta is yielded — this is an envelope-only event.
        def handle_message_start(data)
          message = data["message"] || {}

          @state[:saw_message_start] = true
          @state[:response_id]       = message["id"]
          @state[:model]             = message["model"] if message["model"]

          usage_data = message["usage"] || {}
          @state[:usage][:input]          = usage_data["input_tokens"].to_i
          @state[:usage][:output]         = usage_data["output_tokens"].to_i
          @state[:usage][:cache_read]     = usage_data["cache_read_input_tokens"].to_i
          @state[:usage][:cache_creation] = usage_data["cache_creation_input_tokens"].to_i
        end

        # ── message_delta ─────────────────────────────────────────────────────

        # Capture the final stop_reason and update usage with the authoritative
        # counts the API sends at the end of the stream.
        # No StreamDelta is yielded — this is an envelope-only event.
        def handle_message_delta(data)
          delta = data["delta"] || {}

          stop_reason = delta["stop_reason"]
          @state[:finish_reason] = stop_reason if stop_reason

          u = data["usage"] || {}
          @state[:usage][:input]          = u["input_tokens"]                || @state[:usage][:input]
          @state[:usage][:output]         = u["output_tokens"]               || @state[:usage][:output]
          @state[:usage][:cache_read]     = u["cache_read_input_tokens"]     || @state[:usage][:cache_read]
          @state[:usage][:cache_creation] = u["cache_creation_input_tokens"] || @state[:usage][:cache_creation]

          @state[:saw_terminal] = true
        end

        # ── message_stop ──────────────────────────────────────────────────────

        # Mark the stream as done.  No state other than saw_terminal is mutated.
        def handle_message_stop
          @state[:saw_terminal] = true
        end

        # ── content_block_start ───────────────────────────────────────────────

        # Append a new in-progress block to content_blocks and yield the
        # appropriate opening StreamDelta.
        def handle_content_block_start(data, &block)
          index = data["index"].to_i
          cb    = data["content_block"] || {}
          kind  = cb["type"].to_s

          case kind
          when "text"
            new_blk = { index: index, kind: kind, text: "" }
            @state[:content_blocks] << new_blk
            block&.call(StreamDelta.new(type: :text_start))

          when "thinking"
            new_blk = { index: index, kind: kind, thinking: "", signature: nil }
            @state[:content_blocks] << new_blk
            block&.call(StreamDelta.new(type: :thinking_start))

          when "tool_use"
            raw_name = cb["name"].to_s
            name     = @is_oauth ? Cloaking.strip_prefix(raw_name) : raw_name
            new_blk  = {
              index: index,
              kind: kind,
              id: cb["id"].to_s,
              name: name,
              partial_json: "",
              arguments: nil
            }
            @state[:content_blocks] << new_blk
            block&.call(StreamDelta.new(
              type: :tool_use_start,
              tool_call_id: new_blk[:id],
              tool_name: name
            ))

          when "redacted_thinking"
            new_blk = { index: index, kind: kind, data: cb["data"].to_s }
            @state[:content_blocks] << new_blk
            # No StreamDelta for redacted_thinking
          end
        end

        # ── content_block_delta ───────────────────────────────────────────────

        # Append text/thinking/json fragments and yield the matching StreamDelta.
        def handle_content_block_delta(data, &block)
          index      = data["index"].to_i
          delta      = data["delta"] || {}
          delta_type = delta["type"].to_s

          blk = find_block(index)
          return unless blk # unknown index → skip

          case delta_type
          when "text_delta"
            text       = delta["text"].to_s
            blk[:text] = blk[:text].to_s + text
            block&.call(StreamDelta.new(type: :text_delta, text: text))

          when "thinking_delta"
            thinking       = delta["thinking"].to_s
            blk[:thinking] = blk[:thinking].to_s + thinking
            block&.call(StreamDelta.new(type: :thinking_delta, text: thinking))

          when "signature_delta"
            # Accumulate signature; no StreamDelta emitted
            sig             = delta["signature"].to_s
            blk[:signature] = blk[:signature].to_s + sig

          when "input_json_delta"
            json_str           = delta["partial_json"].to_s
            blk[:partial_json] = blk[:partial_json].to_s + json_str
            block&.call(StreamDelta.new(type: :tool_use_delta, argument_delta: json_str))
          end
        end

        # ── content_block_stop ────────────────────────────────────────────────

        # Finalise the block and yield the closing StreamDelta.
        def handle_content_block_stop(data, &block)
          index = data["index"].to_i
          blk   = find_block(index)
          return unless blk

          case blk[:kind]
          when "text"
            block&.call(StreamDelta.new(type: :text_end))

          when "thinking"
            block&.call(StreamDelta.new(type: :thinking_end))

          when "tool_use"
            # Parse the accumulated partial JSON → arguments hash.
            # Tolerate broken/incomplete JSON by falling back to {}.
            begin
              blk[:arguments] = JSON.parse(blk[:partial_json] || "{}")
            rescue JSON::ParserError
              blk[:arguments] = {}
            end
            block&.call(StreamDelta.new(type: :tool_use_end))

          when "redacted_thinking"
            nil # No StreamDelta for redacted_thinking
          end
        end

        # ── Helpers ───────────────────────────────────────────────────────────

        # Look up an active block by its SSE index.
        def find_block(index)
          @state[:content_blocks].find { |b| b[:index] == index }
        end
      end
    end
  end
end