// SPDX-License-Identifier: EUPL-1.2

package agentic

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"syscall"
	"time"

	coreio "forge.lthn.ai/core/go-io"
	"gopkg.in/yaml.v3"
)

// DispatchConfig controls agent dispatch behaviour.
type DispatchConfig struct {
	DefaultAgent    string `yaml:"default_agent"`
	DefaultTemplate string `yaml:"default_template"`
	WorkspaceRoot   string `yaml:"workspace_root"`
}

// RateConfig controls pacing between task dispatches.
type RateConfig struct {
	ResetUTC       string `yaml:"reset_utc"`       // Daily quota reset time (UTC), e.g. "06:00"
	DailyLimit     int    `yaml:"daily_limit"`      // Max requests per day (0 = unknown)
	MinDelay       int    `yaml:"min_delay"`        // Minimum seconds between task starts
	SustainedDelay int    `yaml:"sustained_delay"`  // Delay when pacing for full-day use
	BurstWindow    int    `yaml:"burst_window"`     // Hours before reset where burst kicks in
	BurstDelay     int    `yaml:"burst_delay"`      // Delay during burst window
}

// AgentsConfig is the root of config/agents.yaml.
type AgentsConfig struct {
	Version     int                `yaml:"version"`
	Dispatch    DispatchConfig     `yaml:"dispatch"`
	Concurrency map[string]int    `yaml:"concurrency"`
	Rates       map[string]RateConfig `yaml:"rates"`
}

// loadAgentsConfig reads config/agents.yaml from the code path.
func (s *PrepSubsystem) loadAgentsConfig() *AgentsConfig {
	paths := []string{
		filepath.Join(CoreRoot(), "agents.yaml"),
		filepath.Join(s.codePath, "core", "agent", "config", "agents.yaml"),
	}

	for _, path := range paths {
		data, err := coreio.Local.Read(path)
		if err != nil {
			continue
		}
		var cfg AgentsConfig
		if err := yaml.Unmarshal([]byte(data), &cfg); err != nil {
			continue
		}
		return &cfg
	}

	return &AgentsConfig{
		Dispatch: DispatchConfig{
			DefaultAgent:    "claude",
			DefaultTemplate: "coding",
		},
		Concurrency: map[string]int{
			"claude": 1,
			"gemini": 3,
		},
	}
}

// delayForAgent calculates how long to wait before spawning the next task
// for a given agent type, based on rate config and time of day.
func (s *PrepSubsystem) delayForAgent(agent string) time.Duration {
	cfg := s.loadAgentsConfig()
	rate, ok := cfg.Rates[agent]
	if !ok || rate.SustainedDelay == 0 {
		return 0
	}

	// Parse reset time
	resetHour, resetMin := 6, 0
	fmt.Sscanf(rate.ResetUTC, "%d:%d", &resetHour, &resetMin)

	now := time.Now().UTC()
	resetToday := time.Date(now.Year(), now.Month(), now.Day(), resetHour, resetMin, 0, 0, time.UTC)
	if now.Before(resetToday) {
		// Reset hasn't happened yet today — reset was yesterday
		resetToday = resetToday.AddDate(0, 0, -1)
	}
	nextReset := resetToday.AddDate(0, 0, 1)
	hoursUntilReset := nextReset.Sub(now).Hours()

	// Burst mode: if within burst window of reset, use burst delay
	if rate.BurstWindow > 0 && hoursUntilReset <= float64(rate.BurstWindow) {
		return time.Duration(rate.BurstDelay) * time.Second
	}

	// Sustained mode
	return time.Duration(rate.SustainedDelay) * time.Second
}

// countRunningByAgent counts running workspaces for a specific agent type.
func (s *PrepSubsystem) countRunningByAgent(agent string) int {
	wsRoot := WorkspaceRoot()

	entries, err := os.ReadDir(wsRoot)
	if err != nil {
		return 0
	}

	count := 0
	for _, entry := range entries {
		if !entry.IsDir() {
			continue
		}

		st, err := readStatus(filepath.Join(wsRoot, entry.Name()))
		if err != nil || st.Status != "running" {
			continue
		}
		// Match on base agent type (gemini:flash matches gemini)
		stBase := strings.SplitN(st.Agent, ":", 2)[0]
		if stBase != agent {
			continue
		}

		if st.PID > 0 {
			proc, err := os.FindProcess(st.PID)
			if err == nil && proc.Signal(syscall.Signal(0)) == nil {
				count++
			}
		}
	}

	return count
}

// baseAgent strips the model variant (gemini:flash → gemini).
func baseAgent(agent string) string {
	return strings.SplitN(agent, ":", 2)[0]
}

// canDispatchAgent checks if we're under the concurrency limit for a specific agent type.
func (s *PrepSubsystem) canDispatchAgent(agent string) bool {
	cfg := s.loadAgentsConfig()
	base := baseAgent(agent)
	limit, ok := cfg.Concurrency[base]
	if !ok || limit <= 0 {
		return true
	}
	return s.countRunningByAgent(base) < limit
}


// drainQueue finds the oldest queued workspace and spawns it if a slot is available.
// Applies rate-based delay between spawns.
func (s *PrepSubsystem) drainQueue() {
	wsRoot := WorkspaceRoot()

	entries, err := os.ReadDir(wsRoot)
	if err != nil {
		return
	}

	for _, entry := range entries {
		if !entry.IsDir() {
			continue
		}

		wsDir := filepath.Join(wsRoot, entry.Name())
		st, err := readStatus(wsDir)
		if err != nil || st.Status != "queued" {
			continue
		}

		if !s.canDispatchAgent(st.Agent) {
			continue
		}

		// Apply rate delay before spawning
		delay := s.delayForAgent(st.Agent)
		if delay > 0 {
			time.Sleep(delay)
		}

		// Re-check concurrency after delay (another task may have started)
		if !s.canDispatchAgent(st.Agent) {
			continue
		}

		srcDir := filepath.Join(wsDir, "src")
		prompt := "Read PROMPT.md for instructions. All context files (CLAUDE.md, TODO.md, CONTEXT.md, CONSUMERS.md, RECENT.md) are in the parent directory. Work in this directory."

		pid, _, err := s.spawnAgent(st.Agent, prompt, wsDir, srcDir)
		if err != nil {
			continue
		}

		st.Status = "running"
		st.PID = pid
		st.Runs++
		writeStatus(wsDir, st)

		return
	}
}