// Package anthropic describes the Anthropic Messages API that Claude
// Code speaks and converts it to and from Chat Completions.
package anthropic

import (
	"bytes"
	"encoding/json"
)

// MessagesRequest is the Anthropic Messages API request body.
type MessagesRequest struct {
	Model         string          `json:"model"`
	MaxTokens     int             `json:"max_tokens"`
	Messages      []Message       `json:"messages"`
	System        json.RawMessage `json:"system,omitempty"`
	Tools         []Tool          `json:"tools,omitempty"`
	ToolChoice    json.RawMessage `json:"tool_choice,omitempty"`
	Temperature   *float64        `json:"temperature,omitempty"`
	TopP          *float64        `json:"top_p,omitempty"`
	TopK          *int            `json:"top_k,omitempty"`
	StopSequences []string        `json:"stop_sequences,omitempty"`
	Stream        bool            `json:"stream,omitempty"`
}

// Message is one conversation turn. Content is either a plain string or
// an array of blocks.
type Message struct {
	Role    string          `json:"role"`
	Content json.RawMessage `json:"content"`
}

// Tool is an Anthropic tool definition.
type Tool struct {
	Name        string          `json:"name"`
	Description string          `json:"description,omitempty"`
	InputSchema json.RawMessage `json:"input_schema,omitempty"`
}

// Block is a single content block inside a message. Only the fields
// belonging to Type are populated.
type Block struct {
	Type string `json:"type"`
	// text
	Text string `json:"text,omitempty"`
	// image
	Source *ImageSource `json:"source,omitempty"`
	// tool_use
	ID    string          `json:"id,omitempty"`
	Name  string          `json:"name,omitempty"`
	Input json.RawMessage `json:"input,omitempty"`
	// tool_result
	ToolUseID string          `json:"tool_use_id,omitempty"`
	Content   json.RawMessage `json:"content,omitempty"`
	IsError   bool            `json:"is_error,omitempty"`
	// cache_control is accepted but never forwarded upstream.
	CacheControl json.RawMessage `json:"cache_control,omitempty"`
}

// ImageSource is an image referenced by a user message.
type ImageSource struct {
	Type      string `json:"type"`
	MediaType string `json:"media_type,omitempty"`
	Data      string `json:"data,omitempty"`
	URL       string `json:"url,omitempty"`
}

// MessagesResponse is the Anthropic Messages API response body.
type MessagesResponse struct {
	ID           string  `json:"id"`
	Type         string  `json:"type"`
	Role         string  `json:"role"`
	Content      []Block `json:"content"`
	Model        string  `json:"model"`
	StopReason   string  `json:"stop_reason"`
	StopSequence *string `json:"stop_sequence"`
	Usage        Usage   `json:"usage"`
}

// Usage reports token counts.
type Usage struct {
	InputTokens  int `json:"input_tokens"`
	OutputTokens int `json:"output_tokens"`
}

// ErrorResponse is the Anthropic error envelope.
type ErrorResponse struct {
	Type  string `json:"type"`
	Error Detail `json:"error"`
}

// Detail is the error payload.
type Detail struct {
	Type    string `json:"type"`
	Message string `json:"message"`
}

// CountTokensResponse is the response of /v1/messages/count_tokens.
type CountTokensResponse struct {
	InputTokens int `json:"input_tokens"`
}

// ParseContent decodes a message content field into blocks. A plain
// string becomes a single text block.
func ParseContent(raw json.RawMessage) ([]Block, error) {
	trimmed := bytes.TrimSpace(raw)
	if len(trimmed) == 0 || string(trimmed) == "null" {
		return nil, nil
	}
	if trimmed[0] == '"' {
		var s string
		if err := json.Unmarshal(trimmed, &s); err != nil {
			return nil, err
		}
		if s == "" {
			return nil, nil
		}
		return []Block{{Type: "text", Text: s}}, nil
	}
	var blocks []Block
	if err := json.Unmarshal(trimmed, &blocks); err != nil {
		return nil, err
	}
	return blocks, nil
}

// SystemText flattens a system field (string or block array) into plain
// text.
func SystemText(raw json.RawMessage) string {
	blocks, err := ParseContent(raw)
	if err != nil {
		return ""
	}
	var parts []string
	for _, b := range blocks {
		if b.Type == "text" && b.Text != "" {
			parts = append(parts, b.Text)
		}
	}
	return joinBlocks(parts)
}

// TextOf extracts plain text from a tool_result content field.
func TextOf(raw json.RawMessage) string {
	blocks, err := ParseContent(raw)
	if err != nil {
		return ""
	}
	var sb bytes.Buffer
	for _, b := range blocks {
		if b.Type == "text" {
			sb.WriteString(b.Text)
		}
	}
	return sb.String()
}

func joinBlocks(parts []string) string {
	if len(parts) == 0 {
		return ""
	}
	out := parts[0]
	for _, p := range parts[1:] {
		out += "\n\n" + p
	}
	return out
}