// Copyright (c) 2026 Probo Inc <hello@probo.com>.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package llm

import (
	"encoding/json"
	"strings"
)

type (
	ChatCompletionRequest struct {
		Model             string
		Messages          []Message
		MaxTokens         *int
		Temperature       *float64
		TopP              *float64
		FrequencyPenalty  *float64
		PresencePenalty   *float64
		StopSequences     []string
		Tools             []Tool
		ToolChoice        *ToolChoice
		ParallelToolCalls *bool
		ResponseFormat    *ResponseFormat
		Thinking          *ThinkingConfig
	}

	ThinkingConfig struct {
		Enabled      bool
		BudgetTokens int
	}

	ToolChoiceType string

	ToolChoice struct {
		Type     ToolChoiceType
		Function string // required when Type is ToolChoiceFunction
	}

	ResponseFormatType string

	ResponseFormat struct {
		Type       ResponseFormatType
		JSONSchema *JSONSchema // required when Type is ResponseFormatJSONSchema
	}

	JSONSchema struct {
		Name        string
		Description string
		Schema      json.RawMessage
		Strict      bool
	}

	FinishReason string

	Usage struct {
		InputTokens  int `json:"input_tokens"`
		OutputTokens int `json:"output_tokens"`
	}

	ChatCompletionResponse struct {
		Model        string
		Message      Message
		Usage        Usage
		FinishReason FinishReason
	}

	// ChatCompletionStream is an iterator over streaming chat completion events.
	// Callers must call Close when done, even if Next returns false.
	// The typical usage pattern is:
	//
	//	stream, err := client.ChatCompletionStream(ctx, req)
	//	if err != nil { ... }
	//	defer stream.Close()
	//	for stream.Next() {
	//	    event := stream.Event()
	//	    // process event
	//	}
	//	if err := stream.Err(); err != nil { ... }
	ChatCompletionStream interface {
		Next() bool
		Event() ChatCompletionStreamEvent
		Err() error
		Close() error
	}

	ChatCompletionStreamEvent struct {
		Model        string // present on first event if provider supports it
		Delta        MessageDelta
		Usage        *Usage        // present on final event if provider supports it
		FinishReason *FinishReason // present on final event
	}

	MessageDelta struct {
		Content           string
		Thinking          string
		ThinkingSignature string
		ToolCalls         []ToolCallDelta
	}

	ToolCallDelta struct {
		Index     int
		ID        string // set on first chunk for this tool call
		Name      string // set on first chunk for this tool call
		Arguments string // incremental JSON fragment
	}
)

const (
	ToolChoiceAuto     ToolChoiceType = "auto"
	ToolChoiceNone     ToolChoiceType = "none"
	ToolChoiceRequired ToolChoiceType = "required"
	ToolChoiceFunction ToolChoiceType = "function"
)

const (
	ResponseFormatText       ResponseFormatType = "text"
	ResponseFormatJSONObject ResponseFormatType = "json_object"
	ResponseFormatJSONSchema ResponseFormatType = "json_schema"
)

const (
	FinishReasonStop          FinishReason = "stop"
	FinishReasonToolCalls     FinishReason = "tool_calls"
	FinishReasonLength        FinishReason = "length"
	FinishReasonContentFilter FinishReason = "content_filter"
)

func (u Usage) Add(other Usage) Usage {
	return Usage{
		InputTokens:  u.InputTokens + other.InputTokens,
		OutputTokens: u.OutputTokens + other.OutputTokens,
	}
}

// StreamAccumulator wraps a ChatCompletionStream and reassembles the
// streamed deltas into a full ChatCompletionResponse. It proxies
// Next/Event/Err/Close transparently so callers can still observe
// individual deltas while accumulating the final result.
//
// After the stream is exhausted (Next returns false), call Response
// to get the fully assembled ChatCompletionResponse.
type StreamAccumulator struct {
	stream            ChatCompletionStream
	current           ChatCompletionStreamEvent
	content           strings.Builder
	thinking          strings.Builder
	thinkingSignature string
	toolCalls         map[int]*ToolCall
	usage             Usage
	finishReason      FinishReason
	model             string
}

func NewStreamAccumulator(stream ChatCompletionStream) *StreamAccumulator {
	return &StreamAccumulator{
		stream:    stream,
		toolCalls: make(map[int]*ToolCall),
	}
}

func (a *StreamAccumulator) Next() bool {
	if !a.stream.Next() {
		return false
	}

	a.current = a.stream.Event()
	a.accumulate(a.current)

	return true
}

func (a *StreamAccumulator) Event() ChatCompletionStreamEvent {
	return a.current
}

func (a *StreamAccumulator) Err() error {
	return a.stream.Err()
}

func (a *StreamAccumulator) Close() error {
	return a.stream.Close()
}

// Response returns the fully assembled ChatCompletionResponse after
// the stream has been exhausted. Must only be called after Next
// returns false and Err returns nil.
func (a *StreamAccumulator) Response() *ChatCompletionResponse {
	toolCalls := make([]ToolCall, 0, len(a.toolCalls))
	for i := 0; i < len(a.toolCalls); i++ {
		if tc, ok := a.toolCalls[i]; ok {
			toolCalls = append(toolCalls, *tc)
		}
	}

	var parts []Part
	if thinking := a.thinking.String(); thinking != "" {
		parts = append(
			parts,
			ThinkingPart{
				Text:      thinking,
				Signature: a.thinkingSignature,
			},
		)
	}

	parts = append(parts, TextPart{Text: a.content.String()})

	return &ChatCompletionResponse{
		Model: a.model,
		Message: Message{
			Role:      RoleAssistant,
			Parts:     parts,
			ToolCalls: toolCalls,
		},
		Usage:        a.usage,
		FinishReason: a.finishReason,
	}
}

func (a *StreamAccumulator) accumulate(event ChatCompletionStreamEvent) {
	if a.model == "" && event.Model != "" {
		a.model = event.Model
	}

	a.content.WriteString(event.Delta.Content)
	a.thinking.WriteString(event.Delta.Thinking)

	if event.Delta.ThinkingSignature != "" {
		a.thinkingSignature = event.Delta.ThinkingSignature
	}

	for _, tcd := range event.Delta.ToolCalls {
		tc, ok := a.toolCalls[tcd.Index]
		if !ok {
			tc = &ToolCall{}
			a.toolCalls[tcd.Index] = tc
		}

		if tcd.ID != "" {
			tc.ID = tcd.ID
		}

		if tcd.Name != "" {
			tc.Function.Name = tcd.Name
		}

		tc.Function.Arguments += tcd.Arguments
	}

	if event.Usage != nil {
		a.usage = *event.Usage
	}

	if event.FinishReason != nil {
		a.finishReason = *event.FinishReason
	}
}