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"`
}

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

// NewHistory creates an empty History.
func NewHistory() *History {
	return &History{}
}

// Add appends a message with the current time.
func (h *History) Add(role, text string) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.messages = append(h.messages, Message{Role: role, Text: text, Time: time.Now()})
}

// 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]
}