package acp

import (
	"sync"
	"time"
)

// Message is one entry in the conversation history.
type Message struct {
	Role      string    `json:"role"`
	Text      string    `json:"text"`
	Time      time.Time `json:"time"`
	MessageID string    `json:"messageId,omitempty"`
}

// History accumulates prompt/response messages in memory for a session.
type History struct {
	mu        sync.RWMutex
	messages  []Message
	indexByID map[string]int
}

// NewHistory creates an empty History.
func NewHistory() *History {
	return &History{indexByID: make(map[string]int)}
}

// Add appends a message with the current time. It is used for messages that
// have no messageId (e.g. the user prompt path).
func (h *History) Add(role, text string) {
	h.AppendOrCreate(role, "", text)
}

// AppendOrCreate finds the existing entry with the same messageId and appends
// text to it; otherwise creates a new entry. When messageId is empty this
// behaves like Add(role, text). It returns the time of the created or existing
// entry.
func (h *History) AppendOrCreate(role, messageId, text string) time.Time {
	h.mu.Lock()
	defer h.mu.Unlock()

	if messageId == "" {
		h.messages = append(h.messages, Message{Role: role, Text: text, Time: time.Now()})
		return h.messages[len(h.messages)-1].Time
	}

	if idx, ok := h.indexByID[messageId]; ok {
		h.messages[idx].Text += text
		return h.messages[idx].Time
	}

	h.messages = append(h.messages, Message{Role: role, Text: text, Time: time.Now(), MessageID: messageId})
	h.indexByID[messageId] = len(h.messages) - 1
	return h.messages[len(h.messages)-1].Time
}

// List returns a copy of all messages, oldest first.
func (h *History) List() []Message {
	h.mu.RLock()
	defer h.mu.RUnlock()
	out := make([]Message, len(h.messages))
	copy(out, h.messages)
	return out
}

// Len returns the number of stored messages.
func (h *History) Len() int {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return len(h.messages)
}

// Since returns messages starting at index idx.
func (h *History) Since(idx int) []Message {
	h.mu.RLock()
	defer h.mu.RUnlock()
	if idx < 0 {
		idx = 0
	}
	if idx > len(h.messages) {
		idx = len(h.messages)
	}
	out := make([]Message, len(h.messages)-idx)
	copy(out, h.messages[idx:])
	return out
}

// Clear removes all stored messages.
func (h *History) Clear() {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.messages = h.messages[:0]
	h.indexByID = make(map[string]int)
}