// Package loop is the conductor: one bounded iteration per call
// (intake -> gate -> bounded turn -> REPORT writeback). Callers chain
// iterations by re-invoking; there is no daemon.
package loop

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"time"

	"git.knownelement.com/reachableceo/MOPAC/harness/internal/config"
	"git.knownelement.com/reachableceo/MOPAC/harness/internal/intake"
	"git.knownelement.com/reachableceo/MOPAC/harness/internal/llm"
	"git.knownelement.com/reachableceo/MOPAC/harness/internal/models"
	"git.knownelement.com/reachableceo/MOPAC/harness/internal/task"
	"git.knownelement.com/reachableceo/MOPAC/harness/internal/tools"
	"git.knownelement.com/reachableceo/MOPAC/harness/internal/writeback"
)

// Sentinel error classes; the CLI maps these to distinct exit codes.
var (
	ErrIntake = errors.New("intake error")
	ErrLLM    = errors.New("llm error")
)

// Conductor wires config, routing, tools, and clients into single-shot runs.
type Conductor struct {
	cfg    *config.Config
	router *models.Router
	bash   *tools.BashTool
	out    io.Writer
}

// New validates routing config and prepares the tool palette.
func New(cfg *config.Config, out io.Writer) (*Conductor, error) {
	router, err := models.NewRouter(cfg.Models.Tiers, cfg.Models.Classes, cfg.Models.DefaultTier)
	if err != nil {
		return nil, fmt.Errorf("model routing: %w", err)
	}
	var bash *tools.BashTool
	if cfg.Bash.Enabled {
		bash, err = tools.NewBashTool(tools.BashOptions{
			WorkRoot:       cfg.WorkRoot,
			Allow:          cfg.Bash.Allow,
			Deny:           cfg.Bash.Deny,
			DefaultAllow:   cfg.Bash.DefaultAllow,
			Timeout:        time.Duration(cfg.Bash.TimeoutSecs) * time.Second,
			MaxOutputBytes: cfg.Bash.MaxOutputBytes,
		})
		if err != nil {
			return nil, err
		}
	}
	return &Conductor{cfg: cfg, router: router, bash: bash, out: out}, nil
}

// OnceOpts controls a single iteration.
type OnceOpts struct {
	DryRun bool   // intake + plan only, no LLM call
	Demo   bool   // use the [demo] issue instead of Redmine intake
	TaskID string // run only the task with this id (chaining aid)
}

// OnceResult reports what one iteration did.
type OnceResult struct {
	TasksSeen  int
	Task       task.Task
	Routed     models.Decision
	ReportPath string
	Turn       *TurnResult
}

// Once runs ONE conductor iteration then returns. Zero tasks in scope is a
// success (exit 0) so chained invocations stay cheap.
func (c *Conductor) Once(ctx context.Context, opts OnceOpts) (*OnceResult, error) {
	tasks, err := c.intake(ctx, opts)
	if err != nil {
		return nil, err
	}
	res := &OnceResult{TasksSeen: len(tasks)}
	if opts.TaskID != "" {
		var kept []task.Task
		for _, t := range tasks {
			if t.ID == opts.TaskID {
				kept = append(kept, t)
			}
		}
		if len(kept) == 0 {
			return res, fmt.Errorf("%w: task id %q not in scope", ErrIntake, opts.TaskID)
		}
		tasks = kept
	}
	if len(tasks) == 0 {
		fmt.Fprintf(c.out, "harness: no tasks in scope; nothing to do\n")
		return res, nil
	}

	t := tasks[0]
	res.Task = t
	decision, err := c.router.Resolve(t.Class)
	if err != nil {
		return res, err
	}
	res.Routed = decision
	fmt.Fprintf(c.out, "harness: task %s (%s): %q class=%s -> %s -> %s\n",
		t.ID, t.Source, t.Subject, t.Class, decision.Tier, decision.Model)

	if opts.DryRun {
		c.printPlan(t, decision)
		fmt.Fprintf(c.out, "harness: dry-run complete, no LLM call made\n")
		return res, nil
	}

	client, err := c.llmClient()
	if err != nil {
		return res, err
	}
	start := time.Now()
	turn, err := c.turn(ctx, client, t, decision.Model)
	if turn != nil {
		res.Turn = turn
	}
	if err != nil {
		// Keep whatever content the turn produced before failing.
		if turn != nil && turn.Content != "" {
			_, _ = c.writeReport(t, decision, turn, start, err)
		}
		return res, fmt.Errorf("%w: %v", ErrLLM, err)
	}
	path, err := c.writeReport(t, decision, turn, start, nil)
	if err != nil {
		return res, err
	}
	res.ReportPath = path
	return res, nil
}

// TurnResult is the bounded-turn outcome recorded in the REPORT.
type TurnResult struct {
	Content          string
	Rounds           int
	ToolCalls        int
	Denied           int
	PromptTokens     int
	CompletionTokens int
	TotalTokens      int
	StopReason       string
}

// turn runs the bounded LLM loop: request, execute tool calls, repeat until
// the model replies with plain content or the round bound is hit.
func (c *Conductor) turn(ctx context.Context, client *llm.Client, t task.Task, model string) (*TurnResult, error) {
	msgs := []llm.Message{
		{Role: "system", Content: c.systemPrompt()},
		{Role: "user", Content: t.Prompt},
	}
	var palette []llm.Tool
	if c.bash != nil {
		palette = append(palette, c.bash.Definition())
	}
	res := &TurnResult{}
	for round := 1; round <= c.cfg.Loop.MaxRounds; round++ {
		resp, err := client.Chat(ctx, llm.ChatRequest{Model: model, Messages: msgs, Tools: palette})
		if err != nil {
			res.StopReason = "llm_error"
			return res, err
		}
		res.Rounds = round
		res.PromptTokens += resp.Usage.PromptTokens
		res.CompletionTokens += resp.Usage.CompletionTokens
		res.TotalTokens += resp.Usage.TotalTokens

		m := resp.Choices[0].Message
		if m.Content != "" {
			res.Content = m.Content
		}
		if len(m.ToolCalls) == 0 {
			res.StopReason = "complete"
			return res, nil
		}
		msgs = append(msgs, m)
		for _, tc := range m.ToolCalls {
			out, derr := c.execTool(ctx, tc)
			res.ToolCalls++
			if derr != nil {
				res.Denied++
			}
			msgs = append(msgs, llm.Message{Role: "tool", ToolCallID: tc.ID, Content: out})
		}
	}
	res.StopReason = "round_limit"
	return res, nil
}

// execTool dispatches one tool call; the returned string is the model-facing
// result. The returned error is non-nil only for gate denials (counted).
func (c *Conductor) execTool(ctx context.Context, call llm.ToolCall) (string, error) {
	if c.bash == nil || call.Function.Name != "bash" {
		return fmt.Sprintf("error: unknown tool %q", call.Function.Name), nil
	}
	out, err := c.bash.Run(ctx, json.RawMessage(call.Function.Arguments))
	if err != nil {
		if errors.Is(err, tools.ErrDenied) {
			return fmt.Sprintf("permission denied: %v", err), tools.ErrDenied
		}
		if out != "" {
			return fmt.Sprintf("%s\nerror: %v", out, err), nil
		}
		return fmt.Sprintf("error: %v", err), nil
	}
	if out == "" {
		out = "(no output)"
	}
	return out, nil
}

func (c *Conductor) intake(ctx context.Context, opts OnceOpts) ([]task.Task, error) {
	if opts.Demo {
		fmt.Fprintf(c.out, "harness: intake: demo issue from harness.toml [demo]\n")
		return []task.Task{intake.DemoTask(c.cfg.Demo)}, nil
	}
	rc := c.cfg.Redmine
	if rc.URL == "" {
		return nil, fmt.Errorf("%w: no [redmine] url configured (use --demo for the demo issue)", ErrIntake)
	}
	key, err := config.ResolveKeyRef(rc.KeyRef)
	if err != nil {
		return nil, fmt.Errorf("%w: redmine key: %v", ErrIntake, err)
	}
	client := intake.NewRedmineClient(rc, key)
	tasks, err := client.ListTasks(ctx)
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrIntake, err)
	}
	fmt.Fprintf(c.out, "harness: intake: %d task(s) in redmine scope\n", len(tasks))
	return tasks, nil
}

func (c *Conductor) llmClient() (*llm.Client, error) {
	key, err := config.ResolveKeyRef(c.cfg.LiteLLM.KeyRef)
	if err != nil {
		return nil, fmt.Errorf("litellm key: %w", err)
	}
	return llm.NewClient(
		c.cfg.LiteLLM.BaseURL,
		key,
		time.Duration(c.cfg.LiteLLM.TimeoutSecs)*time.Second,
		c.cfg.LiteLLM.MaxRetries,
	), nil
}

func (c *Conductor) writeReport(t task.Task, d models.Decision, turn *TurnResult, start time.Time, turnErr error) (string, error) {
	r := writeback.Report{
		Time:             time.Now().UTC(),
		Vertical:         c.cfg.Vertical,
		Task:             t,
		Class:            t.Class,
		Tier:             d.Tier,
		Model:            d.Model,
		PromptTokens:     turn.PromptTokens,
		CompletionTokens: turn.CompletionTokens,
		TotalTokens:      turn.TotalTokens,
		Rounds:           turn.Rounds,
		ToolCalls:        turn.ToolCalls,
		Denied:           turn.Denied,
		Duration:         time.Since(start),
		StopReason:       turn.StopReason,
		Content:          turn.Content,
	}
	if turnErr != nil {
		r.StopReason = "error: " + turnErr.Error()
	}
	path, err := writeback.Write(c.cfg.ReportDir, r)
	if err != nil {
		return "", err
	}
	fmt.Fprintf(c.out, "harness: REPORT %s\n", path)
	return path, nil
}

func (c *Conductor) printPlan(t task.Task, d models.Decision) {
	fmt.Fprintf(c.out, "PLAN (dry-run)\n")
	fmt.Fprintf(c.out, "  vertical: %s\n", c.cfg.Vertical)
	fmt.Fprintf(c.out, "  task: [%s] %s (source %s)\n", t.ID, t.Subject, t.Source)
	fmt.Fprintf(c.out, "  routing: class %q -> tier %s -> model %s\n", t.Class, d.Tier, d.Model)
	if c.bash != nil {
		fmt.Fprintf(c.out, "  tools: bash (allow=%d deny=%d default=%s timeout=%ds)\n",
			len(c.cfg.Bash.Allow), len(c.cfg.Bash.Deny), denyAllow(c.cfg.Bash.DefaultAllow), c.cfg.Bash.TimeoutSecs)
	} else {
		fmt.Fprintf(c.out, "  tools: none\n")
	}
	fmt.Fprintf(c.out, "  bound: max %d rounds\n", c.cfg.Loop.MaxRounds)
}

func denyAllow(defaultAllow bool) string {
	if defaultAllow {
		return "allow"
	}
	return "deny"
}

func (c *Conductor) systemPrompt() string {
	return fmt.Sprintf(`You are %s, an agent run by the MOPAC harness (headless, bounded turn).
Complete the assigned task. Your final reply is written verbatim to the turn
REPORT. Use the bash tool only when necessary; commands run in %s and must
match the configured allow-list (unmatched or denied commands fail).`,
		c.cfg.Vertical, c.cfg.WorkRoot)
}