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package acp

import (
	"encoding/json"
	"strconv"
	"strings"
)

// EntryKind says what one entry of a conversation is.
type EntryKind int

// The kinds of entry a conversation holds.
const (
	// EntryUser is something you typed.
	EntryUser EntryKind = iota
	// EntryAgent is what the agent said.
	EntryAgent
	// EntryThought is the agent thinking aloud, which is worth showing and
	// worth showing differently.
	EntryThought
	// EntryTool is a tool the agent ran, with whatever it produced.
	EntryTool
	// EntryPlan is a plan the agent published.
	EntryPlan
	// EntryNotice is the editor speaking for itself: a failure to start, a
	// turn that was cancelled, output that had to be dropped.
	EntryNotice
)

// Entry is one thing in the conversation.
//
// A run of message chunks is one entry, not one per chunk: an agent sends
// text a token at a time — "I", " found", " agent", ".yaml" — and an entry per
// chunk could neither be wrapped nor told apart from a fenced code block.
type Entry struct {
	Kind EntryKind
	// Speaker is who said it, for the label above the text: your name for a
	// prompt, the agent's for a reply. It is empty on an entry whose label is
	// fixed.
	Speaker string
	// Text is what was said. It is Markdown when it came from an agent, so
	// fenced code blocks in it are real.
	Text string

	// ToolCallID identifies a tool entry, so that a later update can be folded
	// onto it rather than appended after it. It is empty on every other kind.
	ToolCallID string
	// Status is a tool call's status: pending, in_progress, completed, failed.
	Status string
	// Detail is the one-line summary of what a tool was asked to do — the
	// command, the path — taken from the tool call's raw input.
	Detail string

	// Plan is the entries of a plan, on an EntryPlan.
	Plan []PlanEntry
}

// Done reports whether a tool call has finished, either way.
func (e Entry) Done() bool { return e.Status == StatusCompleted || e.Status == StatusFailed }

// Failed reports whether a tool call ended badly.
func (e Entry) Failed() bool { return e.Status == StatusFailed }

// MaxEntryBytes caps how much text one entry keeps. An agent printing a
// megabyte of build output should not be able to make the editor unusable;
// what was dropped is said in the entry itself.
const MaxEntryBytes = 1 << 20

// Transcript is a conversation, as a value.
//
// It knows nothing about a terminal, a window or a colour: it turns the
// stream of updates an agent sends into an ordered list of entries, and hands
// that list to whoever draws. That is what lets it be tested by calling
// functions and comparing values, and what makes the window's own tests
// deterministic — a window drawn from a fixed transcript cannot race a live
// agent.
//
//	var t acp.Transcript
//	t.AddUser("You", "hello")
//	t.Apply(update)
//	for _, entry := range t.Entries() { … }
type Transcript struct {
	entries []Entry
	// agentName labels what the agent says. It is learnt from the handshake,
	// so it is the agent's own name rather than the one in the menu.
	agentName string
	// openKind is the kind of entry chunks are currently being appended to, or
	// -1 when the last thing added was not a chunk. It is what coalesces a run
	// of tokens into one entry without coalescing a reply with the thought
	// before it.
	openKind EntryKind
	open     bool
}

// SetAgentName says what to label the agent's own messages with.
func (t *Transcript) SetAgentName(name string) { t.agentName = name }

// AgentName returns the label the agent's messages carry.
func (t *Transcript) AgentName() string { return t.agentName }

// Entries returns a copy of the conversation, in order.
//
// A copy, because the list is built on the connection's reading goroutine and
// drawn on the one that owns the screen. Handing out the slice itself would be
// a data race that a terminal is slow enough to hide for a long time.
func (t *Transcript) Entries() []Entry {
	out := make([]Entry, len(t.entries))
	copy(out, t.entries)
	return out
}

// Len returns how many entries there are.
func (t *Transcript) Len() int { return len(t.entries) }

// AddUser records something you typed.
func (t *Transcript) AddUser(speaker, text string) {
	t.closeRun()
	t.entries = append(t.entries, Entry{Kind: EntryUser, Speaker: speaker, Text: text})
}

// AddNotice records the editor speaking for itself.
//
// It is a separate kind rather than an agent message so that "the agent could
// not be started" is never mistaken for something the agent said.
func (t *Transcript) AddNotice(text string) {
	t.closeRun()
	t.entries = append(t.entries, Entry{Kind: EntryNotice, Text: text})
}

// Apply folds one session/update into the conversation.
//
// An update this package does not know is ignored and reported as such by the
// return value. The protocol grows, and an editor that refused to carry on
// talking to an agent because it learnt a new kind of message would be wrong
// more often than it was right.
//
//	known := transcript.Apply(notification.Update)
func (t *Transcript) Apply(u Update) (known bool) {
	switch u.SessionUpdate {
	case UpdateAgentMessage:
		t.appendChunk(EntryAgent, t.agentName, u.Block().Text)
	case UpdateAgentThought:
		t.appendChunk(EntryThought, t.agentName, u.Block().Text)
	case UpdateUserMessage:
		t.appendChunk(EntryUser, "", u.Block().Text)
	case UpdateToolCall:
		t.addToolCall(u)
	case UpdateToolCallDone:
		t.updateToolCall(u)
	case UpdatePlan:
		t.addPlan(u)
	case UpdateCommands, UpdateUsage, UpdateCurrentMode:
		// Kept by the session rather than drawn in the conversation.
	default:
		return false
	}
	return true
}

// appendChunk adds text to the run in progress, or starts a new entry.
func (t *Transcript) appendChunk(kind EntryKind, speaker, text string) {
	if text == "" {
		return
	}

	if t.open && t.openKind == kind && len(t.entries) > 0 {
		last := &t.entries[len(t.entries)-1]
		last.Text = capped(last.Text + text)
		return
	}

	t.entries = append(t.entries, Entry{Kind: kind, Speaker: speaker, Text: text})
	t.openKind = kind
	t.open = true
}

// closeRun ends the run of chunks in progress, so that the next one starts an
// entry of its own.
func (t *Transcript) closeRun() { t.open = false }

// addToolCall starts a tool entry.
//
// A tool call whose id is already here is updated rather than repeated: an
// agent may send the tool_call *after* the permission request that named it,
// which is exactly what docker agent does.
func (t *Transcript) addToolCall(u Update) {
	t.closeRun()

	if at := t.indexOfTool(u.ToolCallID); at >= 0 {
		t.fold(at, u)
		return
	}
	t.entries = append(t.entries, Entry{
		Kind:       EntryTool,
		Speaker:    u.Title,
		ToolCallID: u.ToolCallID,
		Status:     firstNonEmpty(u.Status, StatusPending),
	})

	// The rest of the update is folded on rather than read again here, so that
	// a tool_call carrying its own output — which the protocol allows, even
	// though docker agent sends it separately — does not lose it.
	t.fold(len(t.entries)-1, u)
}

// updateToolCall folds a later update onto the call it belongs to.
//
// An update naming an id nothing here has becomes an entry of its own, rather
// than being dropped: it is still something the agent did.
func (t *Transcript) updateToolCall(u Update) {
	if at := t.indexOfTool(u.ToolCallID); at >= 0 {
		t.fold(at, u)
		return
	}
	t.addToolCall(u)
}

// fold merges an update into an existing tool entry, leaving alone whatever
// the update does not mention.
func (t *Transcript) fold(at int, u Update) {
	entry := &t.entries[at]

	if u.Status != "" {
		entry.Status = u.Status
	}
	if u.Title != "" {
		entry.Speaker = u.Title
	}
	if detail := summarise(u.RawInput); detail != "" {
		entry.Detail = detail
	}
	if output := toolOutput(u); output != "" {
		entry.Text = capped(joinNonEmpty(entry.Text, output))
	}
}

// indexOfTool returns where a tool call already sits, or -1.
//
// An empty id never matches: two calls that both failed to name themselves are
// two different calls, and folding them together would lose one.
func (t *Transcript) indexOfTool(id string) int {
	if id == "" {
		return -1
	}
	for i, entry := range t.entries {
		if entry.Kind == EntryTool && entry.ToolCallID == id {
			return i
		}
	}
	return -1
}

// addPlan records a plan, replacing the one before it.
//
// An agent republishes the whole plan every time a step changes, so appending
// would leave five copies of a four-line plan in the window.
func (t *Transcript) addPlan(u Update) {
	t.closeRun()

	if at := t.lastPlan(); at >= 0 {
		t.entries[at].Plan = u.Entries
		return
	}
	t.entries = append(t.entries, Entry{Kind: EntryPlan, Plan: u.Entries})
}

// lastPlan returns where the plan sits, or -1.
func (t *Transcript) lastPlan() int {
	for i := len(t.entries) - 1; i >= 0; i-- {
		if t.entries[i].Kind == EntryPlan {
			return i
		}
	}
	return -1
}

// toolOutput returns the text a tool call's content carries.
func toolOutput(u Update) string {
	var parts []string
	for _, block := range u.Blocks() {
		switch {
		case block.Content.Text != "":
			parts = append(parts, block.Content.Text)
		case block.Type == "diff" && block.Path != "":
			parts = append(parts, "edited "+block.Path)
		}
	}
	return strings.Join(parts, "\n")
}

// summarise turns a tool's raw input into the one line a reader wants: the
// command, or the path, or nothing.
//
// It reads a handful of well-known keys rather than pretty-printing the JSON.
// A reader wants to see `ls -1`, not `{"cmd":"ls -1","cwd":".","timeout":30}`,
// and an input with none of these keys is better summarised by silence than by
// a brace.
func summarise(raw []byte) string {
	if len(raw) == 0 {
		return ""
	}

	fields := decodeObject(raw)
	for _, key := range []string{"cmd", "command", "path", "file_path", "pattern", "query", "url"} {
		if value, ok := fields[key]; ok && value != "" {
			return oneLine(value)
		}
	}
	return ""
}

// decodeObject reads a JSON object into the string form of each of its values.
//
// A tool's raw input is whatever the agent's tool schema says, so the values
// are of every type; numbers and booleans are rendered rather than dropped so
// that a summary key holding one still says something.
func decodeObject(raw []byte) map[string]string {
	var fields map[string]any
	if err := json.Unmarshal(raw, &fields); err != nil {
		return nil
	}

	out := make(map[string]string, len(fields))
	for key, value := range fields {
		switch typed := value.(type) {
		case string:
			out[key] = typed
		case float64:
			out[key] = strconv.FormatFloat(typed, 'f', -1, 64)
		case bool:
			out[key] = strconv.FormatBool(typed)
		}
	}
	return out
}

// oneLine flattens text to a single line, so a multi-line command cannot
// break the layout of a summary.
func oneLine(text string) string {
	return strings.Join(strings.Fields(strings.ReplaceAll(text, "\n", " ")), " ")
}

// splitLines splits text into lines, keeping neither the newlines nor a
// phantom empty line after a trailing one.
func splitLines(text string) []string {
	if text == "" {
		return nil
	}
	lines := strings.Split(strings.ReplaceAll(text, "\r\n", "\n"), "\n")
	if last := len(lines) - 1; lines[last] == "" {
		lines = lines[:last]
	}
	return lines
}

// joinLines puts lines back together, with a trailing newline when there is
// anything at all — which is what a text file has.
func joinLines(lines []string) string {
	if len(lines) == 0 {
		return ""
	}
	return strings.Join(lines, "\n") + "\n"
}

// capped truncates text that has grown past the limit, saying so.
func capped(text string) string {
	if len(text) <= MaxEntryBytes {
		return text
	}
	return text[:MaxEntryBytes] + "\n… (truncated)"
}

// joinNonEmpty joins two pieces with a newline, skipping either if it is empty.
func joinNonEmpty(first, second string) string {
	switch {
	case first == "":
		return second
	case second == "":
		return first
	default:
		return first + "\n" + second
	}
}

// firstNonEmpty returns the first of its arguments that is not empty.
func firstNonEmpty(values ...string) string {
	for _, value := range values {
		if value != "" {
			return value
		}
	}
	return ""
}