package model

import (
	"fmt"
	"strings"
)

// buildAnthropicMessages splits a normalized message list into a top-level system
// string and the remaining messages in Anthropic's content-block form. All
// RoleSystem messages are concatenated into a single system prompt (Anthropic
// carries it at the request root, not in messages); messages with no content
// parts are dropped because Anthropic rejects empty content.
func buildAnthropicMessages(msgs []Message) (string, []anthropicMessage, error) {
	var sys strings.Builder
	out := make([]anthropicMessage, 0, len(msgs))
	for _, m := range msgs {
		if m.Role == RoleSystem {
			if t := messageText(m); t != "" {
				if sys.Len() > 0 {
					sys.WriteString("\n")
				}
				sys.WriteString(t)
			}
			continue
		}
		blocks, err := encodeAnthropicMessage(m)
		if err != nil {
			return "", nil, err
		}
		if len(blocks) == 0 {
			continue
		}
		out = append(out, anthropicMessage{Role: anthropicRole(m.Role), Content: blocks})
	}
	return sys.String(), out, nil
}

// messageText concatenates the text-bearing parts of a message (system prompts
// and tool-result bodies). Tool-result parts carry their body in Text, so a
// RoleTool turn's content serializes correctly for OpenAI's tool message.
func messageText(m Message) string {
	var b strings.Builder
	for _, part := range m.Content {
		if part.Type == ContentTypeText || part.Type == ContentTypeToolResult {
			b.WriteString(part.Text)
		}
	}
	return b.String()
}

// anthropicRole maps a normalized Role to the Anthropic role vocabulary. system
// messages are extracted to the top-level system field and never reach here.
func anthropicRole(r Role) string {
	switch r {
	case RoleAssistant:
		return "assistant"
	default:
		// user, tool and any future roles all land on the user turn; tool_result
		// blocks (M2) belong to the user role in Anthropic.
		return "user"
	}
}

// encodeAnthropicMessage turns a normalized message into Anthropic content
// blocks. A RoleTool turn is ALWAYS rendered as native tool_result blocks (never
// a user plain-text turn), because Anthropic requires a tool result to arrive as
// a tool_result block carrying the tool_use_id and the is_error flag.
func encodeAnthropicMessage(m Message) ([]any, error) {
	if m.Role == RoleTool {
		return encodeAnthropicToolResult(m)
	}
	return encodeAnthropicContent(m.Content)
}

// encodeAnthropicToolResult renders a RoleTool turn as tool_result blocks. Each
// ContentTypeToolResult part becomes one block; legacy text parts are wrapped as
// tool_result blocks too so the turn never degrades into a plain user message.
// The tool_use_id falls back to the message-level ToolCallID when a part does not
// carry its own.
func encodeAnthropicToolResult(m Message) ([]any, error) {
	blocks := make([]any, 0, len(m.Content))
	for _, p := range m.Content {
		switch p.Type {
		case ContentTypeToolResult, ContentTypeText:
			id := p.ToolCallID
			if id == "" {
				id = m.ToolCallID
			}
			blocks = append(blocks, AnthropicToolResult(id, p.Text, p.IsError))
		}
	}
	if len(blocks) == 0 {
		blocks = append(blocks, AnthropicToolResult(m.ToolCallID, "", false))
	}
	return blocks, nil
}

// encodeAnthropicContent turns normalized content parts into Anthropic content
// blocks. Text / image / tool_use (assistant) parts are handled here; tool_result
// parts are rendered at the message level by encodeAnthropicToolResult.
func encodeAnthropicContent(parts []Content) ([]any, error) {
	blocks := make([]any, 0, len(parts))
	for _, p := range parts {
		switch p.Type {
		case ContentTypeText:
			blocks = append(blocks, map[string]any{"type": "text", "text": p.Text})
		case ContentTypeImage:
			mediaType, data, err := parseAnthropicImageData(p.ImageURL)
			if err != nil {
				return nil, err
			}
			blocks = append(blocks, map[string]any{
				"type": "image",
				"source": map[string]any{
					"type":       "base64",
					"media_type": mediaType,
					"data":       data,
				},
			})
		case ContentTypeToolCall:
			args := p.ToolArgs
			if args == nil {
				args = map[string]any{}
			}
			blocks = append(blocks, map[string]any{
				"type":  "tool_use",
				"id":    p.ToolCallID,
				"name":  p.ToolCallName,
				"input": args,
			})
		case ContentTypeToolResult:
			blocks = append(blocks, AnthropicToolResult(p.ToolCallID, p.Text, p.IsError))
		default:
			return nil, fmt.Errorf("model: %w: unsupported content type %q", ErrBadRequest, p.Type)
		}
	}
	return blocks, nil
}

// parseAnthropicImageData extracts the media type and base64 payload from a data:
// URI. Anthropic requires a base64 image source and cannot reference a remote
// URL, so any other URI form is rejected as a bad request.
func parseAnthropicImageData(uri string) (string, string, error) {
	if !strings.HasPrefix(uri, anthropicDataPrefix) {
		return "", "", fmt.Errorf("model: %w: anthropic image requires a data: URI, got %q", ErrBadRequest, uri)
	}
	rest := strings.TrimPrefix(uri, anthropicDataPrefix)
	comma := strings.Index(rest, ",")
	if comma < 0 {
		return "", "", fmt.Errorf("model: %w: malformed data: URI %q", ErrBadRequest, uri)
	}
	meta := rest[:comma]
	data := rest[comma+1:]
	mediaType := meta
	if idx := strings.Index(meta, ";"); idx >= 0 {
		mediaType = meta[:idx]
	}
	if mediaType == "" {
		return "", "", fmt.Errorf("model: %w: data: URI missing media type in %q", ErrBadRequest, uri)
	}
	return mediaType, data, nil
}

// buildAnthropicTools converts ToolSpec schemas into Anthropic tools.
func buildAnthropicTools(tools []ToolSpec) []anthropicTool {
	if len(tools) == 0 {
		return nil
	}
	out := make([]anthropicTool, 0, len(tools))
	for _, t := range tools {
		out = append(out, anthropicTool{
			Name:        t.Name,
			Description: t.Description,
			InputSchema: t.Parameters,
		})
	}
	return out
}