package agent

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"strings"

	"ollie/cmd/olliesrv/internal/backend"
	"ollie/paths"
)

const (
	compactionPrompt = `You are performing a CONTEXT CHECKPOINT COMPACTION. Produce a JSON object summarizing the current task state. Output ONLY valid JSON matching this schema:

{
  "objective": "the user's overall goal",
  "plan_step": "what step you are currently on",
  "constraints": ["any constraints or user preferences"],
  "last_action": "brief: last tool/action + outcome",
  "open_questions": ["unresolved questions"],
  "next_decision": "what to do next"
}

Be concise. Capture what another LLM needs to seamlessly continue.`

	// hotTailSize is the number of most recent messages kept verbatim (hot zone).
	hotTailSize = 8

	// warmIndexSize is the number of messages preceding the hot zone
	// summarized as a brief decision index (warm zone).
	warmIndexSize = 10
)

// RestoreHistoryFromMessages reconstructs a History from just the message list.
// Used for multi-agent session restore where each agent has separate messages.
func RestoreHistoryFromMessages(messages []backend.Message) *History {
	s := &History{
		messages: messages,
	}
	for i := range s.messages {
		if s.messages[i].Role == "assistant" && s.messages[i].ID == "" {
			s.messages[i].ID = paths.NewUUID()
		}
	}
	for _, m := range messages {
		if m.Role == "user" {
			s.goal = m.Content
			break
		}
	}
	return s
}

// History is an ephemeral in-memory state backend.
type History struct {
	goal     string
	messages []backend.Message
	// Cumulative usage tracking.
	TotalInputTokens         int
	TotalCachedInputTokens   int
	TotalCacheCreationTokens int
	TotalOutputTokens        int
	TotalRequests            int
	Estimated                bool    // true if any usage was estimated rather than reported by the backend
	LastTurnCostUSD          float64 // cost of the most recently completed turn in USD
	SessionCostUSD           float64 // cumulative cost of all turns in this session in USD
	// per-turn accumulators; reset at the start of each turn
	turnInputTokens    int
	turnCachedTokens   int
	turnCreationTokens int
	turnOutputTokens   int
	turnCostUSD        float64 // >0 when backend reported cost directly (e.g. OpenRouter)
}

// newHistory creates a new empty History. The caller is responsible for
// appending the initial user message via appendUserMessage.
func newHistory(goal string) *History {
	return &History{goal: goal}
}

func (s *History) history() []backend.Message {
	return s.messages
}

func (s *History) addUsage(u backend.Usage, estimated bool) {
	s.TotalInputTokens += u.InputTokens
	s.TotalCachedInputTokens += u.CachedInputTokens
	s.TotalCacheCreationTokens += u.CacheCreationTokens
	s.TotalOutputTokens += u.OutputTokens
	s.TotalRequests++
	s.turnInputTokens += u.InputTokens
	s.turnCachedTokens += u.CachedInputTokens
	s.turnCreationTokens += u.CacheCreationTokens
	s.turnOutputTokens += u.OutputTokens
	s.turnCostUSD += u.CostUSD
	if estimated {
		s.Estimated = true
	}
}

func (s *History) resetTurnAccumulators() {
	s.turnInputTokens = 0
	s.turnCachedTokens = 0
	s.turnCreationTokens = 0
	s.turnOutputTokens = 0
	s.turnCostUSD = 0
}

// recordTurnCost computes and stores the last turn's cost, adding it to the
// session total. model is used for the pricing-table fallback when the backend
// did not report cost directly.
func (s *History) recordTurnCost(model string) {
	var cost float64
	if s.turnCostUSD > 0 {
		cost = s.turnCostUSD
	} else {
		cost = computeCostUSD(model, backend.Usage{
			InputTokens:         s.turnInputTokens,
			CachedInputTokens:   s.turnCachedTokens,
			CacheCreationTokens: s.turnCreationTokens,
			OutputTokens:        s.turnOutputTokens,
		})
	}
	s.LastTurnCostUSD = cost
	s.SessionCostUSD += cost
}

func (s *History) update(assistant backend.Message, results []toolResult) {
	s.messages = append(s.messages, assistant)
	for _, r := range results {
		s.messages = append(s.messages, backend.Message{
			Role:          "tool",
			Content:       r.Content,
			ContentBlocks: r.ContentBlocks,
			ToolCallID:    r.ToolCallID,
		})
	}
}

// removeCancelledToolResults filters out tool results that were cancelled due
// to interrupt, keeping completed work. Also removes the corresponding tool
// calls from assistant messages to maintain a valid message sequence.
func (s *History) removeCancelledToolResults() {
	// First pass: collect cancelled tool call IDs
	cancelled := make(map[string]bool)
	for _, m := range s.messages {
		if m.Role == "tool" && isCancelledToolResult(m.Content) {
			cancelled[m.ToolCallID] = true
		}
	}
	if len(cancelled) == 0 {
		return
	}

	// Second pass: filter messages and prune tool calls from assistant messages
	filtered := s.messages[:0]
	for _, m := range s.messages {
		if m.Role == "tool" && cancelled[m.ToolCallID] {
			continue
		}
		if m.Role == "assistant" && len(m.ToolCalls) > 0 {
			// Remove cancelled tool calls from this assistant message
			kept := m.ToolCalls[:0]
			for _, tc := range m.ToolCalls {
				if !cancelled[tc.ID] {
					kept = append(kept, tc)
				}
			}
			if len(kept) == 0 && m.Content == "" {
				// All tool calls cancelled and no text content - skip message
				continue
			}
			m.ToolCalls = kept
		}
		filtered = append(filtered, m)
	}
	s.messages = filtered
}

func isCancelledToolResult(content string) bool {
	return strings.Contains(content, `"status":"cancelled"`) ||
		strings.Contains(content, "tool execution interrupted by user")
}

// Compact summarizes the conversation via an LLM call, replacing the history
// with system messages + preserved user messages + a structured summary.
// Returns (n compacted, summary text, error); n==0 means nothing to compact.
func (s *History) compact(ctx context.Context, b backend.Backend) (int, string, error) {
	if len(s.messages) <= hotTailSize+warmIndexSize {
		return 0, "", nil
	}

	// Flatten tool calls into plain text so the compaction request
	// doesn't need tool schemas.
	flattened := flattenToolMessages(s.messages)
	flattened = append(flattened, backend.Message{
		Role:    "user",
		Content: compactionPrompt,
	})

	ch, err := b.ChatStream(ctx, flattened, nil, backend.GenerationParams{})
	if err != nil {
		return 0, "", fmt.Errorf("compact: %w", err)
	}

	var summary strings.Builder
	for ev := range ch {
		if ev.Content != "" {
			summary.WriteString(ev.Content)
		}
		if ev.Done {
			break
		}
	}

	summaryText := strings.TrimSpace(summary.String())
	if summaryText == "" {
		return 0, "", fmt.Errorf("compact: empty summary")
	}

	beforeCount := len(s.messages)
	s.messages = buildCompactedHistory(summaryText, s.messages)
	return beforeCount - len(s.messages), summaryText, nil
}

// buildCompactedHistory constructs a three-zone post-compaction message list:
//   - Cold: compaction summary (everything older than warm+hot)
//   - Warm: brief index of recent decisions/actions (warmIndexSize messages)
//   - Hot: last hotTailSize messages verbatim
func buildCompactedHistory(summary string, allMessages []backend.Message) []backend.Message {
	total := len(allMessages)

	// Determine zone boundaries.
	hotStart := total - hotTailSize
	if hotStart < 0 {
		hotStart = 0
	}

	// If hotStart lands on a tool message, walk backward to include the
	// preceding assistant message with tool_calls. Without this, the hot
	// zone starts with an orphaned tool result which violates the OpenAI
	// API constraint that tool messages must follow an assistant message
	// containing the corresponding tool_calls.
	for hotStart > 0 && allMessages[hotStart].Role == "tool" {
		hotStart--
	}

	warmStart := hotStart - warmIndexSize
	if warmStart < 0 {
		warmStart = 0
	}

	// Cold zone: compaction summary.
	cold := backend.Message{
		Role:    "user",
		Content: "[compacted context]\n" + summary,
	}

	var out []backend.Message
	out = append(out, cold)

	// Warm zone: one-line summaries of decisions in the warm window.
	warmSlice := allMessages[warmStart:hotStart]
	if len(warmSlice) > 0 {
		var sb strings.Builder
		sb.WriteString("[warm zone — recent decisions]\n")
		for _, m := range warmSlice {
			line := summarizeMessage(m)
			if line != "" {
				sb.WriteString("- ")
				sb.WriteString(line)
				sb.WriteByte('\n')
			}
		}
		out = append(out, backend.Message{Role: "user", Content: sb.String()})
	}

	// Hot zone: verbatim recent messages.
	out = append(out, allMessages[hotStart:]...)
	return out
}

// summarizeMessage produces a one-line summary of a message for the warm index.
func summarizeMessage(m backend.Message) string {
	switch m.Role {
	case "assistant":
		if len(m.ToolCalls) > 0 {
			names := make([]string, len(m.ToolCalls))
			for i, tc := range m.ToolCalls {
				names[i] = tc.Name
			}
			return "called: " + strings.Join(names, ", ")
		}
		text := m.Content
		if len(text) > 120 {
			text = text[:120] + "…"
		}
		return "said: " + text
	case "user":
		text := m.Content
		if len(text) > 120 {
			text = text[:120] + "…"
		}
		return "user: " + text
	case "tool":
		text := m.Content
		if len(text) > 80 {
			text = text[:80] + "…"
		}
		return "result(" + m.ToolCallID + "): " + text
	}
	return ""
}

// flattenToolMessages converts tool call/result sequences into plain text
// so the compaction request doesn't include tool-specific structures that
// the API may reject when no tools are defined.
func flattenToolMessages(messages []backend.Message) []backend.Message {
	out := make([]backend.Message, 0, len(messages))
	for _, m := range messages {
		switch {
		case m.Role == "assistant" && len(m.ToolCalls) > 0:
			var sb strings.Builder
			if m.Content != "" {
				sb.WriteString(m.Content)
				sb.WriteString("\n\n")
			}
			for _, tc := range m.ToolCalls {
				fmt.Fprintf(&sb, "[Tool call: %s(%s)]\n", tc.Name, string(tc.Arguments))
			}
			out = append(out, backend.Message{Role: "assistant", Content: sb.String()})
		case m.Role == "tool":
			text := m.Content
			if len(text) > 4000 {
				text = text[:4000] + "..."
			}
			out = append(out, backend.Message{
				Role:    "user",
				Content: fmt.Sprintf("[Tool result for %s]:\n%s", m.ToolCallID, text),
			})
		default:
			out = append(out, m)
		}
	}
	return out
}

// injectPreamble ensures the preamble system message is at history position 0.
// If a system message already exists there, its Content is replaced; otherwise
// one is prepended.
func (s *History) injectPreamble(preamble string) {
	if preamble == "" {
		return
	}
	msg := backend.Message{Role: "system", Content: preamble}
	if len(s.messages) > 0 && s.messages[0].Role == "system" {
		s.messages[0] = msg
	} else {
		s.messages = append([]backend.Message{msg}, s.messages...)
	}
}

func (s *History) appendUserMessage(content string) {
	s.messages = append(s.messages, backend.Message{Role: "user", Content: content})
}

// estimateTokens returns a rough token count (~4 chars per token).
func (s *History) estimateTokens() int {
	chars := 0
	for _, m := range s.messages {
		chars += len(m.Content)
		for _, tc := range m.ToolCalls {
			chars += len(tc.Name) + len(tc.Arguments)
		}
	}
	return chars / 4
}

// stripCold summarizes large tool-result messages outside the hot tail
// using a single batched LLM call. Messages in the last hotTailSize slots
// are left verbatim.
func (s *History) stripCold(ctx context.Context, b backend.Backend) {
	hot := len(s.messages) - hotTailSize
	if hot < 0 {
		return
	}

	// Collect cold-zone tool results exceeding 200 chars.
	type item struct {
		id   int
		idx  int // index into s.messages
		orig string
	}
	var items []item
	for i := range s.messages {
		if i >= hot {
			break
		}
		m := &s.messages[i]
		if m.Role == "tool" && len(m.Content) > 200 {
			items = append(items, item{id: len(items), idx: i, orig: m.Content})
		}
	}
	if len(items) == 0 {
		return
	}

	// Build a single prompt listing each item.
	var sb strings.Builder
	sb.WriteString("Compress each of the following tool results to 1-3 sentences preserving key facts, file paths, values, and findings.\n\nReturn a JSON object where each key is the id and the value is the summary, for example:\n{\"0\": \"summarized result 0\", \"1\": \"summarized result 1\"}\n\nOnly include keys that were in the input.\n\n")
	for _, it := range items {
		fmt.Fprintf(&sb, "---\nid=%d:\n%s\n", it.id, it.orig)
	}

	ch, err := b.ChatStream(ctx, []backend.Message{{Role: "user", Content: sb.String()}}, nil, backend.GenerationParams{})
	if err != nil {
		return
	}
	var resp strings.Builder
	for ev := range ch {
		if ev.Content != "" {
			resp.WriteString(ev.Content)
		}
		if ev.Done {
			break
		}
	}
	summaries := make(map[string]string)
	json.Unmarshal([]byte(resp.String()), &summaries)

	// Apply summaries back into history.
	for _, it := range items {
		key := fmt.Sprintf("%d", it.id)
		if summary, ok := summaries[key]; ok && summary != "" {
			s.messages[it.idx].Content = summary
		}
	}
}

// resolveCompactionModel returns the model to use for compaction.
// Priority: agent config > OLLIE_COMPACTION_MODEL > backends.conf compactionModel > backends.conf model > current model.
func resolveCompactionModel(cfgModel string, b backend.Backend) string {
	if cfgModel != "" {
		return cfgModel
	}
	if env := os.Getenv("OLLIE_COMPACTION_MODEL"); env != "" {
		return env
	}
	if b != nil {
		if model := backend.CompactionModel(b.Name()); model != "" {
			return model
		}
		return b.Model()
	}
	return ""
}