package sessions

// A session's whole conversation, read from the agent's own file when it is
// asked for: what was said, in order, by the user, the model and its tools.
// The file is only read; magpie keeps no copy.

import (
	"bytes"
	"encoding/json"
	"errors"
	"math"
)

// Transcript is what was said in a session, in the order it was said.
type Transcript struct {
	Parts []Part `json:"parts"`
	Cut   bool   `json:"cut,omitempty"` // there was more than is kept here
}

// transcriptMax is the characters of all of a transcript's parts.
const transcriptMax = 400_000

// ErrNoTranscript is a session whose conversation magpie can't read: an
// agent that keeps it in a database, or in a form not read here.
var ErrNoTranscript = errors.New("this agent's conversations can't be shown")

// HasTranscript says whether an agent's sessions can be read as a
// transcript.
func HasTranscript(agent string) bool {
	switch agent {
	case "claude", "qoder", "qoder-cn", "codex", "pi", "omp":
		return true
	}
	return false
}

func (t *Transcript) add(_ bool, p Part) bool {
	size := 0
	for _, x := range t.Parts {
		size += len(x.Text)
	}
	if size >= transcriptMax {
		t.Cut = true
		return false
	}
	if p, ok := keep(p); ok {
		t.Parts = append(t.Parts, p)
	}
	return true
}

// TranscriptOf reads a session's conversation from its (main) file.
func TranscriptOf(s Session) (Transcript, error) {
	out := Transcript{Parts: []Part{}}
	if !HasTranscript(s.Agent) || s.Path == "" {
		return out, ErrNoTranscript
	}
	whole := Call{Agent: s.Agent, File: s.Path, To: math.MaxInt64}
	var err error
	switch s.Agent {
	case "codex":
		err = codexContent(whole, out.add)
	case "pi", "omp":
		err = piTranscript(s.Path, out.add)
	default:
		err = claudeContent(whole, out.add)
	}
	return out, err
}

// piEntry is a line of a Pi (or oh-my-pi) session: an entry of its tree.
type piEntry struct {
	Type     string `json:"type"`
	ID       string `json:"id"`
	ParentID string `json:"parentId"`
	Summary  string `json:"summary"` // compaction, branch_summary
	Message  *struct {
		Role     string          `json:"role"`
		ToolName string          `json:"toolName"`
		Content  json.RawMessage `json:"content"`
	} `json:"message"`
}

var piMessage = []byte(`"type":"message"`)

// piTranscript reads the branch the session is on: a Pi session is a tree,
// each entry naming its parent, and the last entry written is where it
// stands (an earlier branch, left by /tree or a retry, isn't said again).
func piTranscript(path string, add func(bool, Part) bool) error {
	byID := map[string]piEntry{}
	last := ""
	_, err := scanAt(path, 0, nil, func(b []byte, _, _ int64) bool {
		var e piEntry
		if json.Unmarshal(b, &e) != nil || e.ID == "" || e.Type == "session" || e.Type == "title" {
			return true
		}
		if !bytes.Contains(b, piMessage) && e.Type != "compaction" && e.Type != "branch_summary" {
			// keep the tree whole without holding what isn't shown
			e = piEntry{Type: e.Type, ID: e.ID, ParentID: e.ParentID}
		}
		byID[e.ID], last = e, e.ID
		return true
	})
	if err != nil {
		return err
	}
	var branch []piEntry
	for id, n := last, 0; id != "" && n <= len(byID); n++ {
		e, ok := byID[id]
		if !ok {
			break
		}
		branch = append(branch, e)
		id = e.ParentID
	}
	for i := len(branch) - 1; i >= 0; i-- {
		for _, p := range piParts(branch[i]) {
			if !add(p.Role != "assistant", p) {
				return nil
			}
		}
	}
	return nil
}

// piParts are what an entry said.
func piParts(e piEntry) []Part {
	switch e.Type {
	case "compaction", "branch_summary":
		return []Part{{Role: "user", Kind: "context", Text: e.Summary}}
	case "message":
	default:
		return nil
	}
	if e.Message == nil {
		return nil
	}
	m := e.Message
	var role string
	switch m.Role {
	case "user":
		role = "user"
	case "assistant":
		role = "assistant"
	case "toolResult":
		return []Part{{Role: "tool", Kind: "tool_result", Name: m.ToolName, Text: resultText(m.Content)}}
	default:
		return nil
	}
	var s string
	if json.Unmarshal(m.Content, &s) == nil {
		return []Part{textPart(role, s)}
	}
	var blocks []struct {
		Type      string          `json:"type"`
		Text      string          `json:"text"`
		Thinking  string          `json:"thinking"`
		Name      string          `json:"name"`
		Arguments json.RawMessage `json:"arguments"`
	}
	if json.Unmarshal(m.Content, &blocks) != nil {
		return nil
	}
	var parts []Part
	for _, b := range blocks {
		switch b.Type {
		case "text":
			parts = append(parts, textPart(role, b.Text))
		case "thinking":
			parts = append(parts, Part{Role: role, Kind: "thinking", Text: b.Thinking})
		case "toolCall":
			parts = append(parts, Part{Role: role, Kind: "tool_use", Name: b.Name, Text: pretty(b.Arguments)})
		case "image":
			parts = append(parts, Part{Role: role, Kind: "image", Text: "[image]"})
		}
	}
	return parts
}