package fleet

import (
	"fmt"
	"io/ioutil"
	"os"
	"path"
	"strconv"
	"strings"

	"github.com/coreos/fleet/unit"
)

// path hierarchy for finding systemd service templates
var templatePaths = []string{
	os.Getenv("DEISCTL_UNITS"),
	path.Join(os.Getenv("HOME"), ".deis", "units"),
	"/var/lib/deis/units",
}

// and the same for systemd service "decorators" for optionally isolating
// control plane, data plane, and router mesh
var decoratorPaths = []string{
	path.Join(os.Getenv("DEISCTL_UNITS"), "decorators"),
	path.Join(os.Getenv("HOME"), ".deis", "units", "decorators"),
	"/var/lib/deis/units/decorators",
}

// Units returns a list of units filtered by target
func (c *FleetClient) Units(target string) (units []string, err error) {
	allUnits, err := c.Fleet.Units()
	if err != nil {
		return
	}
	// Look for units starting with the given target name first. If the given
	// name starts with "deis-", this will easily locate platform components,
	// but we search without canonicalizing the target name FIRST so we have the
	// opportunity to locate application containers (whose containers do not
	// adhere to the same naming convention as the platform's own components).
	for _, u := range allUnits {
		if strings.HasPrefix(u.Name, target) {
			units = append(units, u.Name)
		}
	}
	// If none are found, canonicalize the target string and search again. This
	// will locate platform components that were referenced by a target string
	// NOT already beginning with "deis-".
	if len(units) == 0 {
		canonTarget := strings.ToLower(target)
		if !strings.HasPrefix(canonTarget, "deis-") {
			canonTarget = "deis-" + canonTarget
		}
		for _, u := range allUnits {
			if strings.HasPrefix(u.Name, canonTarget) {
				units = append(units, u.Name)
			}
		}
	}
	// If still nothing is found, then we have an error on our hands.
	if len(units) == 0 {
		err = fmt.Errorf("could not find unit: %s", target)
	}
	return
}

// nextUnit returns the next unit number for a given component
func (c *FleetClient) nextUnit(component string) (num int, err error) {
	units, err := c.Units(component)
	if err != nil {
		return
	}
	num, err = nextUnitNum(units)
	if err != nil {
		return
	}
	return
}

// lastUnit returns the last unit number for a given component
func (c *FleetClient) lastUnit(component string) (num int, err error) {
	units, err := c.Units(component)
	if err != nil {
		return
	}
	num, err = lastUnitNum(units)
	if err != nil {
		return
	}
	return
}

// NewUnit takes a component type and returns a Fleet unit
// that includes the relevant systemd service template
func NewUnit(component string, templatePaths []string, decorate bool) (uf *unit.UnitFile, err error) {
	template, err := readTemplate(component, templatePaths)
	if err != nil {
		return
	}
	if decorate {
		decorator, err := readDecorator(component)
		if err != nil {
			return nil, err
		}
		uf, err = unit.NewUnitFile(string(template) + "\n" + string(decorator))
	} else {
		uf, err = unit.NewUnitFile(string(template))
	}
	return
}

// formatUnitName returns a properly formatted systemd service name
// using the given component type and number
func formatUnitName(component string, num int) (unitName string, err error) {
	component = strings.TrimPrefix(component, "deis-")
	if num == 0 {
		return "deis-" + component + ".service", nil
	}
	return "deis-" + component + "@" + strconv.Itoa(num) + ".service", nil
}

// readTemplate returns the contents of a systemd template for the given component
func readTemplate(component string, templatePaths []string) (out []byte, err error) {
	templateName := "deis-" + component + ".service"
	var templateFile string

	// look in $DEISCTL_UNITS env var, then the local and global root paths
	for _, p := range templatePaths {
		if p == "" {
			continue
		}
		filename := path.Join(p, templateName)
		if _, err := os.Stat(filename); err == nil {
			templateFile = filename
			break
		}
	}

	if templateFile == "" {
		return nil, fmt.Errorf("Could not find unit template for %v", component)
	}
	out, err = ioutil.ReadFile(templateFile)
	if err != nil {
		return
	}
	return
}

// readDecorator returns the contents of a file containing a snippet that can
// optionally be grafted on to the end of a corresponding systemd unit to
// achieve isolation of the control plane, data plane, and router mesh
func readDecorator(component string) (out []byte, err error) {
	decoratorName := "deis-" + component + ".service.decorator"
	var decoratorFile string

	// look in $DEISCTL_UNITS env var, then the local and global root paths
	for _, p := range decoratorPaths {
		filename := path.Join(p, decoratorName)
		if _, err := os.Stat(filename); err == nil {
			decoratorFile = filename
			break
		}
	}

	if decoratorFile == "" {
		return
	}
	out, err = ioutil.ReadFile(decoratorFile)
	return
}