// Package service contains the shared non-mutating health and lifecycle checks for Compose services.
package service

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

	"github.com/aritmolab/thothii/tools/tht/internal/compose"
	"github.com/aritmolab/thothii/tools/tht/internal/config"
)

const healthTimeout = 5 * time.Minute

var healthPollInterval = time.Second

// HealthFailure identifies the last non-ready service after a bounded health wait.
type HealthFailure struct {
	Service string
	State   string
}

func (e HealthFailure) Error() string {
	return fmt.Sprintf("service health timed out waiting for %s (last state: %s)", e.Service, e.State)
}

type status struct {
	Service  string          `json:"Service"`
	State    string          `json:"State"`
	Health   string          `json:"Health"`
	ExitCode json.RawMessage `json:"ExitCode"`
}

// Start optionally builds the configured project, starts it in the background, then waits for
// every required service to become healthy. It does not inspect or modify host state directly.
func Start(ctx context.Context, installation config.Installation, runner compose.Runner, build bool) error {
	if runner == nil {
		return errors.New("start requires a Docker command runner")
	}
	if build {
		if err := runCompose(ctx, installation, runner, "build"); err != nil {
			return fmt.Errorf("image build: %w", err)
		}
	}
	if err := runCompose(ctx, installation, runner, "up", "--detach", "--remove-orphans"); err != nil {
		return fmt.Errorf("stack start: %w", err)
	}
	return WaitForHealthy(ctx, installation, runner)
}

// WaitForHealthy waits for the complete ThothII Compose service set.
func WaitForHealthy(ctx context.Context, installation config.Installation, runner compose.Runner) error {
	healthContext, cancel := context.WithTimeout(ctx, healthTimeout)
	defer cancel()
	lastService, lastState := "core", "unknown"
	for {
		result, err := runner.Run(healthContext, installation.ComposeArgs("ps", "--all", "--format", "json"), nil)
		if err == nil {
			statuses, parseErr := parseStatuses(result.Stdout)
			if parseErr == nil {
				if service, state, ready := healthy(statuses); ready {
					return nil
				} else {
					lastService, lastState = service, state
				}
			} else {
				lastState = "Compose returned invalid service status"
			}
		} else if result.ExitCode != 0 {
			lastState = fmt.Sprintf("Compose exited with status %d", result.ExitCode)
		} else {
			lastState = "Compose status command failed"
		}
		select {
		case <-healthContext.Done():
			return HealthFailure{Service: lastService, State: lastState}
		case <-time.After(healthPollInterval):
		}
	}
}

// CoreRunning reports whether Compose currently identifies core as a running container.
func CoreRunning(value string) (bool, error) {
	statuses, err := parseStatuses(value)
	if err != nil {
		return false, err
	}
	for _, item := range statuses {
		if item.Service == "core" {
			return strings.EqualFold(item.State, "running"), nil
		}
	}
	return false, nil
}

// CoreHealthy reports whether core is both running and certified healthy by Compose.
func CoreHealthy(value string) (bool, error) {
	statuses, err := parseStatuses(value)
	if err != nil {
		return false, err
	}
	for _, item := range statuses {
		if item.Service == "core" {
			return strings.EqualFold(item.State, "running") && strings.EqualFold(item.Health, "healthy"), nil
		}
	}
	return false, nil
}

// Healthy verifies the full expected Compose service set, including the one-shot model initializer.
func Healthy(value string) error {
	statuses, err := parseStatuses(value)
	if err != nil {
		return err
	}
	service, state, ready := healthy(statuses)
	if ready {
		return nil
	}
	return fmt.Errorf("%s is not healthy (%s)", service, state)
}

func runCompose(ctx context.Context, installation config.Installation, runner compose.Runner, command ...string) error {
	result, err := runner.Run(ctx, installation.ComposeArgs(command...), nil)
	if err == nil {
		return nil
	}
	if result.ExitCode != 0 {
		return fmt.Errorf("Docker exited with status %d", result.ExitCode)
	}
	return err
}

func parseStatuses(value string) ([]status, error) {
	var statuses []status
	if err := json.Unmarshal([]byte(value), &statuses); err == nil && len(statuses) > 0 {
		return statuses, nil
	}
	decoder := json.NewDecoder(strings.NewReader(value))
	for {
		var item status
		err := decoder.Decode(&item)
		if errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			return nil, errors.New("Compose returned invalid service status")
		}
		statuses = append(statuses, item)
	}
	if len(statuses) == 0 {
		return nil, errors.New("Compose returned invalid service status")
	}
	return statuses, nil
}

func healthy(statuses []status) (string, string, bool) {
	wanted := map[string]bool{"core": false, "frontend": false, "qdrant": false, "embedding": false, "embedding-model-init": false}
	for _, item := range statuses {
		if _, required := wanted[item.Service]; !required {
			continue
		}
		if item.Service == "embedding-model-init" {
			if strings.EqualFold(item.State, "exited") && exitCodeZero(item.ExitCode) {
				wanted[item.Service] = true
				continue
			}
			return item.Service, item.State, false
		}
		if strings.EqualFold(item.State, "running") && strings.EqualFold(item.Health, "healthy") {
			wanted[item.Service] = true
			continue
		}
		return item.Service, strings.TrimSpace(item.State + "/" + item.Health), false
	}
	for _, name := range []string{"core", "frontend", "qdrant", "embedding", "embedding-model-init"} {
		if !wanted[name] {
			return name, "not reported by Docker Compose", false
		}
	}
	return "", "", true
}

func exitCodeZero(value json.RawMessage) bool {
	if len(value) == 0 || string(value) == "null" {
		return false
	}
	var number int
	if json.Unmarshal(value, &number) == nil {
		return number == 0
	}
	var text string
	return json.Unmarshal(value, &text) == nil && strings.TrimSpace(text) == "0"
}